Rational Design of Aluminium-containing Zeolites with Typological Structure of HZSM-5 and Catalytic Properties

Rational Design of Aluminium-containing Zeolites with Typological Structure of HZSM-5 and Catalytic Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Rational Design of Aluminium-containing Zeolites with Typological Structure of HZSM-5 and Catalytic Properties Elena Domoroshchina, Galina Kuz’micheva, Аlexander Vasiliev, Ivan Pavlov, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3796442/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In this work, the analysis and generalization of data on the elemental, phase and surface composition, crystal structure and microstructure of MFI-type HZSM-5 with Si/Al = 12, 25, 40, 300 were presented. Relationships between HZSM-5 silicate modulus (Si/Al) and pore volume, specific surface, the area of framework voids were established. Data obtained by electron microscopy and energy dispersive X-ray microanalysis explained the discrepancy between HZSM-5 real composition and the initial one. Samples with the maximum content of Brønsted (HZSM-5 with Si/Al = 25) and Lewis (HZSM-5 with Si/Al = 12) acid sites responsible for the catalytic activity were identified using diffuse reflectance Fourier transform infrared spectroscopy. N 2 O decomposition reaction rate was found to decrease in the row HZSM-5(25) > HZSM-5(12) > HZSM-5(40) > HZSM-5(40)С>>HZSM-5(300). The high N 2 O decomposition rate demonstrated by HZSM-5(25) makes it promising catalyst. The second phase of iron oxides and the presence of faceted particles {001} oriented in HZSM-5(25) were shown to contribute to its maximum catalytic activity in N 2 O decomposition. The applied methodology for studying aluminosilicalites with different silicate modules and the revealed correlations can provide a fundamental perspective in studying other zeolites or modifying data. HZSM-5 composition and structure transmission electron microscopy nitrous oxide catalytic decomposition Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction HZSM-5 aluminosilicalites (MFI type, general composition (H 1 + x )[Al 3 + x Si 4 + 12-x O 24 ]× wA , Si/Al from 8 to ∞), space group Pnma or P2 1 /n (z = 8) with close unit cell parameters (which makes it difficult to separate them in a structural experiment), belong to the large class of zeolites which structural feature is vertex-jointed (Si/Al)O 4 tetrahedra forming a framework of 5- (two types), 6- and 10-membered rings. They form a three-dimensional system of intersecting rectilinear and sinusoidal channels, which can contain atoms, groups of atoms, molecules, including water ( A ). The channels are located along (rectilinear) and (sinusoidal) directions and are interconnected by 10-membered rings of tetrahedra (Fig. 1 ). Based only on this structural description of zeolites, one can expect them primarily to have catalytic and sorption properties as the first stage of the catalytic process. Indeed, HZSM-5 aluminosilicates are indispensable for use in many petrochemical processes, where they exhibit greater catalytic activity than currently used conventional catalytic systems [1]. HZSM-5 catalytic activity (in the general case, without specifying a particular catalytic process) depends on all levels of structure and composition organization, which we refer to as composition and structure parameters: - the atomic structure and composition of HZSM-5 main phase: symmetry, Si/Al silicate modulus [2–4], Al 3+ ions distribution over the crystallographic sites (not excluded in [4]), Al 3+ ions content in each crystallographic site of the structure (no data), the content of “zeolite water” with OH groups or other atomic formations in the zeolite framework [3] or extra-framework ones [5]; dimensions of voids and channels [6]; - elemental composition of samples [3]; - phase composition of samples [3]; - surface composition: the content of Si, Al, Si(Al)-O bonds, OH groups, water [3], and acid sites [3, 6, 7] which include Lewis acid sites (LAS) ([AlO 4-x [] x ] σ‎+ ) [8] and Brønsted ones – BAS (bridging hydroxyls [Si-OH-Al]) [8]; - local structure, or local environment of Al 3+ ions (no data); - microstructure: specific surface area, meso- and micropores volume [3], pore size [9]; average sizes of crystallites and particles [3, 10, 11]. These components of HZSM-5 composition and structure depend or may depend on the method and/or conditions of their fabrication [12, 13], which allows their directed variation to optimize structure-dependent catalytic characteristics, subject to found or known correlations. Note that each catalytic process may have its own set of optimal catalyst parameters, in particular, surface or volume ones. The rate of heterogeneous catalytic processes can be regulated by changing the composition and structure of HZSM-5 active sites (ensembles of {AlO 4 ×SiO 4 } tetrahedra in which the Al 3+ ion contains free 3d 0 atomic orbitals exhibiting strongly pronounced electron-acceptor properties), texture (specific surface area, pore volume, pore size distribution, particle shape, surface composition), etc. [14]. Knowledge of all levels of the hierarchy of HZSM-5 composition and structure, the role of preparation conditions for their variation will help to find the relationship between the composition and structural parameters and functional characteristics, in particular, the catalytic characteristics of a specific catalytic process with the identification of active centers on the surface and/or in the volume. This was the motivation for our study, the purpose of which is to establish the role of each component of HZSM-5 composition and structure in the manifestation of catalytic activity using the example of nitrous oxide decomposition reaction. Some characteristics of HZSM-5 zeolites have been studied in our previous works [3, 4, 15] using the powder X-ray diffraction (XRPD; high-precision synchrotron measurements of HZSM-5(12, 40, 300): symmetry, phase composition, water molecules content in the framework cavities), neutron diffraction (Rietveld refinement of HZSM-5(12, 25, 40) composition, Al 3+ ions distribution over the crystallographic sites), X-ray photoelectron spectroscopy (XPS; HZSM-5(12, 25, 40) surface investigation), FT-IR and Differential Scanning Calorimetry (DSC) (the content of “zeolite water” with OH groups in the HZSM-5(12, 25, 40) framework), temperature programmed desorption of ammonia (TPD; HZSM-5(12, 25, 40) total acidity). In this work, the methods of scanning/transmission electron microscopy (S/TEM) with energy-dispersive X-ray microanalysis (EDX), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma atomic emission spectrometry (ICP AES), low-temperature nitrogen adsorption as well as XRPD (to obtain missing data for HZSM-5(25, 40C and 300)) were applied to get the most complete understanding of the composition, microstructure, morphology and elemental composition of HZSM-5(12, 25, 40, 40C, 300). Previously obtained results together with new data were used to build new correlations between composition, structure and functional (catalytic) properties, that was necessary for a deep understanding of the role of each of the comprehensive characteristics in the manifestation of functional properties and the achievability of their maximum values. A direct catalytic decomposition of nitrous oxide, which is an ozone-depleting gas, into oxygen and nitrogen is considered to be the most efficient neutralization approach. In the literature there is a wide diversity of possible catalytic systems in the form of both supported nanoparticles [16–21], including noble metals [22–25] and bulk materials (mostly mixed metal oxides [26–28]). Among the most efficient catalysts used for N 2 O decomposition, HZSM-5 zeolites with low Si/Al included modified ones (Cu, Co, Fe- or Zn-containing HZSM-5) were shown to demonstrate the best performance [29]. Experimental Section Synthesis of HZSM-5 aluminosilicalites ZSM-5 zeolites (sodium form) were synthesized by the hydrothermal method [4, 15] (the main synthesis conditions are presented in Table 1 ) followed by calcination at T ≥ 500°C to remove the organic components and ion exchange in ammonia buffer to obtain HZSM-5. The powder X-ray diffraction (XRPD) patterns of the obtained zeolites are presented in Fig. 2 , which clearly exhibit a series of diffraction peaks assigning to typical MFI structure. MOR zeolite impurity. Table 1 HZSM-5 synthesis conditions Synthesis conditions HZSM-5(12)* HZSM-5(25)** HZSM-5(40)** HZSM-5(40)C** HZSM-5(300)** Template Commercial, Zeolite International, USA C 12 H 29 NO (TPAOH) С 4 H 10 O (n-butanol) C 8 H 20 BrN (TEAB) C 4 H 13 NO (TMAOH) Silicon source Ludox HS-30 сolloidal silica Ludox HS-30 сolloidal silica Silicic acid (nSiO 2 ·mH 2 O) Silicic acid (nSiO 2 ·mH 2 O) Aluminum source Al 2 (SO 4 ) 3 ·18H 2 O Al 2 (SO 4 ) 3 ·18H 2 O Al 2 (SO 4 ) 3 ·18H 2 O sodium aluminate (NaAlO 2 ) solution Temperature, o C 438 443 443 443 Duration, hours 50 20 20 40 Si/Al (Initial/Refined [4]) 12/14 25/22 30/39 40/42 300/*** *Contains an impurity of MOR zeolite in addition to the main phase (~ 7%) (X-ray diffraction data, Fig. 2 ) **Single-phase sample (X-ray diffraction data, Fig. 2 ) *** No data The pH > 7 was for HZSM-5(25, 40C, 300) samples and pH ~ 6 was for HZSM-5(40). As can be seen from Table 1 , HZSM-5(12, 25, 40, 40C, 300) samples differed both in the initial reagents (template, silicon, and aluminum sources), and in the temperature and duration of synthesis, which is due to different crystallization rates of samples of different compositions. In addition to different templates and silicon sources, the synthesis of the HZSM-5(40) and HZSM-5(40)C was distinguished by the absence of the use of seed polycrystals in the case of HZSM-5(40)C, which were used for the synthesis of the remaining samples [4]. Microstructure. Morphology. Elemental Composition Textural characteristics (specific surface area, micropore volume, total pore volume, cumulative desorption surface area of pores) were studied by low-temperature nitrogen adsorption at -196°C on the ASAP 2010 facility (Micromeritics Corp., USA). Prior to nitrogen adsorption, the samples were vacuum treated at 250°C for 10 hours. The measurement errors of textural characteristics were no more than ± 10%. Electron microscopy was used to study the morphology and microstructure of zeolite samples. Scanning electron microscopy (SEM) was carried out using a JSM 7500F high-resolution scanning electron microscope. Scanning/transmission electron microscopy (S/TEM) was performed using an Osiris scanning/transmission electron microscope (ThermoFisher Scientific, USA) equipped with a high-angle annular dark-field (HAADF) detector. The Digital Micrograph and TIA software were used to carry out image processing. The samples in their initial form were deposited on the carbon-coated copper electron microscopic grids. The content of Al, Fe, and Na in the obtained zeolite samples was determined by inductively coupled plasma atomic emission spectrometry (ICP AES) using an OPTIMA 4300 DV ICP spectrometer (Perkin Elmer, USA). The absolute error limits of the element mass fraction ± Δ were 0.005%. EDX microanalysis of the obtained zeolite samples using Bruker energy-dispersive X-ray microanalysis (EDX) system (Bruker, USA) [30] was applied for the qualitative analysis of single-phase samples with specific standard deviations for each element and its content. To detect the presence of a certain element by the EDX microanalysis, its content must be at least 0.1 at. %. The error in determining the concentrations of elements in powders by the EDX microanalysis is up to 3–5 at. %. Moreover, the efficiency of characteristic X-ray radiation detecting by EDX decreases with a decrease in atomic number [30]. Quantitative analysis of even single-phase samples, considering all atoms in the sample composition (for example, impurity atoms from the initial components), cannot be correctly applied to defect structures with vacancies, since the balance of elements in this case cannot be reduced to 100%. In HZSM-5 crystal structures vacancies are possible in the silicon and oxygen sites, as well as the presence of hydroxyl groups replacing oxygen ions [31]. Moreover, in the HZSM-5 framework voids, there may be water and other atomic formations with a high hydrogen content, which may not be detected by microanalysis. However, the EDX microanalysis application for the qualitative analysis of the samples’ composition and the ratio of individual elements content, especially for single-phase regions, can be very successful [30]. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the zeolite surface composition and the content of acid sites (LAS and BAS). Diffuse reflectance IR spectra were recorded at room temperature on a NICOLET Protege 460 spectrometer equipped with a diffuse reflection prefix [32], in the wavenumber range of 6000 − 400 cm − 1 with a step of 4 cm − 1 . Prior measuring, the samples were dehydroxylated by calcination at 700°C and subjected to thermal vacuum treatment at 400°C and a pressure of 10 − 3 mmHg for 2 hours (heating rate was 5 o C/min). Deuterated acetonitrile (CD 3 CN) was used as acidity test molecules. The spectra were recorded and processed using the OMNIC software. Catalytic experiment Catalytic decomposition of nitrous oxide (N 2 O) was carried out in a flow-type quartz reactor with internal diameter of 4 mm (atmospheric pressure, temperature range of 400–700°C) according to the procedure described in [33]. Catalytic tests were performed in a 100% N 2 O flow with gas hourly space velocity of 30,000 ml/(h –1 ×g –1 ). The gas mixture composition was analyzed on a Crystall 5000 gas chromatograph (Chromatech, Russia) equipped with a HayeSep-Q column for measuring N 2 O concentration and NaX molecular sieves for separating N 2 and O 2 . Before loading into the reactor, the samples were calcined in a muffle furnace at 700 o C for 5 hours. Result and Discussion Composition and сrystal structure According to elemental analysis (ICP AES) of all studied samples, Al content in HZSM-5 zeolites logically decreases with an increase in Si/Al: from 3.2 wt.% for HZSM-5(12), to 0.14–0.16 wt.% for HZSM-5(300). HZSM-5(25) is characterized by the maximum content of Fe – 0.07 wt.% (the most common impurity introduced at the stage of zeolite synthesis [34]), and the minimum content of the residual Na – 0.01 wt.% (the initial zeolites were synthesized in the Na form, Table 1 ). Maximum Na content is in HZSM-5(300) – 0.06 wt.%. HZSM-5 with the same initial Si/Al, but different fabrication conditions differ in aluminum content:1.9 wt.% and 1.1 wt.% for HZSM-5(40) and HZSM-5(40)C, respectively. On the DRIFT-OH spectra of HZSM-5(12, 25, 40, 40C, 300) zeolites preliminarily dehydroxylated by calcination at 700°C and evacuated (to remove the gas phase) at 400°C, three bands are observed in the OH groups’ region: ~3740–3745 cm -1 (refers to linear isolated silanol (Si-OH) groups [35–37]), ~ 3662 and ~ 3610–3612 cm -1 (characterize bridging OH-groups [35–37]) (Fig. 3 a, b, c, d, f, g). HZSM-5(300) spectrum has only one weak band at ~ 3745 cm -1 (Fig. 3 e). The intensity of the bands at ~ 3610 and ~ 3740–3745 cm -1 indicates that the maximum content of bridging hydroxyls is in HZSM-5(25) (Fig. 3 f), and isolated silanols - in HZSM-5(40)C (Fig. 3 g). According to the X-ray diffraction data all the samples under study are single-phase except for HZSM-5(12) with MOR zeolite impurity phase (Table 1 ). HZSM-5 zeolites have selectivity for the reacting molecules’ size, which is due to the size of the pores through which molecules of only certain sizes and shapes can pass. This applies to both initial materials and reaction products. The sizes of voids (cavities) (5, 6 and 10-membered) in the HZSM-5 structures (Fig. 1 ) depend on the composition (Si/Al) and symmetry which is due to a larger number of sites occupied by silicon atoms in the monoclinic structure (24 T sites) compared to the orthorhombic one (12 T sites) [38]. The area of rings and voids on a two-dimensional projection of tetrahedra in HZSM-5 structures (Fig. 1 ), calculated using ELLIPSE software [39], decreases with an increase in Si/Al (Fig. 4 a, b). The most pronounced change is observed for 10-membered rings of tetrahedra, mainly when going from Si/Al = 25 to Si/Al = 40 (Fig. 4 a). This means higher channel accessibility in HZSM-5(12 and 25) compared to HZSM-5(40). Channel sizes, which are characterized by sizes of rings of tetrahedra, specify limitations to the size and shape of molecules capable to “penetrate” into the zeolite crystalline structure. Microstructure. Morphology Analysis of BET and BJH data showed that the values of HZSM-5 textural characteristics (Table 2 ) increase in the row HZSM-5(12) < HZSM-5(25) < HZSM-5(40) , and then get smaller for HZSM-5(300) ( sequence 1 ). Тhere is a break at Si/Al = 40 in the relationship of HZSM-5 specific surface value and silicate modulus (Fig. 5 ). Similar break was observed in [15] in the dependences of Si/Al on the unit cell volume (V, Å 3 ) and unit cell volume on water molecules content in the framework cavities, which is caused by the change in the HZSM-5 symmetry (from Pnma to P2 1 /n ). Due to the different fabrication conditions, HZSM-5(40)C with a slightly higher silicate modulus (Si/Al = 42) compared to HZSM-5(40) (Si/Al = 39) (Rietveld refinement) has the same value of the total pore volume, a larger value of micropore volume ( V µ , cm 3 /g), but smaller values of the specific surface area (Fig. 5 ) and the outer surface compared to HZSM-5(40) (Table 2 ). Table 2 Textural characteristics of HZSM-5(12, 25, 40, 40C, 300) catalysts. Catalyst V µ (cm 3 /g) V ∑ (cm 3 /g) S BET (m 2 /g) S ext (m 2 /g) HZSM-5(12) 0.14 0.21 336 20–33 HZSM-5(25) 0.15 0.25 354 29 HZSM-5(40) 0.16 0.26 429 68 HZSM-5(40)C 0.18 0.26 421 16–24 HZSM-5(300) 0.17 0.22 414 24 V µ , cm 3 /g – zeolite micropore volume; V Σ , cm 3 /g - single point total pore volume of pores with diameter less than 1727.4939 Å at P/Po = 0.9887; S BET , m 2 /g – BET surface area; S ext , m 2 /g – BJH cumulative desorption surface area of pores with diameter between 17.0000 and 3000.0000 Å SEM data obtained at three sample points (representative photos are given in Fig. 6 ) indicate that HZSM-5(12, 25, 40, 300) differ in morphology and particle sizes (maximum sizes are given for elongated particles): elongated prisms (probably with {100} or/and {010} faces oriented to the surface) with a small content of spheres < 200 nm in size (Si/Al = 12); approximately equal content of almost homogeneous spheres (~ 120 nm) and faceted particles (with {001} faces oriented to the surface) (Si/Al = 25); spheres (Si/Al = 40); approximately equal content of elongated and shortened prisms (probably with {100}, {010}, {001} faces oriented to the surface) and small spheres < 250 nm in size (Si/Al = 300). The specific surface area (S BET , m 2 /g) is inversely proportional to the particle size ( N , nm): N = K p /(ρ×S)×10 9 (Eq. 1), where S, m 2 /g is the specific surface area, K p is the particle shape factor: 6 for spheres and cubes, 4 for cylinders and rods, 2 for flat plates [40]; ρ, g/cm 3 is the X-ray density of the zeolite: ρ, g/cm 3 = M z /V (Eq. 2), where M is the molecular mass in carbon units, z is the number of formula units in the cell, V (Å 3 ) is the unit cell volume. It follows from the equations 1 and 2 that S=(K p ×V)/( N ×Mz)×10 9 . That is, the specific surface area of the sample directly depends not only on the unit cell volume, but on the sample morphology (particle shape factor). It should be noted that the specific surface area obtained using the BET method for microporous materials, to which HZSM-5 belongs, are formal, which is associated with the effects of volume filling of micropores. It is known that the method of adsorption data analysis using Eq. 1 does not provide for the presence of micropores, since the energy homogeneity of the adsorbent surface is postulated. This leads to a directly proportional relationship between the specific surface area and the content of small pores in the samples and the absence of a relationship with the particle size (Eq. 1). The largest specific surface area is for HZSM-5(40) (Table 2 ) consisting of spherical particles with predominant sizes of ~ 100 nm and ~ 500 nm (Fig. 6 c). The difference in the morphology and particle sizes of HZSM-5 is due to their different fabrication conditions (Table 1 ), which is the reason of the lack of relationship between the morphology of studied samples and their silicate modules. Figure 7 . HAADF STEM image (Figs. I ) and element distribution maps (EDX method) (Figs. II-IV ) of HZSM-5(12) zeolite (a) and an enlarged images of areas with a high (Area 1 , yellow square on Fig. a- I ) (b) and a low (Area 2 , green square on Fig. a- I ) (c) content of Al; HRTEM image of HZSM-5(12) irregular particle with a low Al content (marked with the red circle on Fig. c- I ) (d). Faceted particle marked with the blue circle in Fig. c- I Тhe enlarged image of the Area 2 of HZSM-5(12) (Fig. 7 c-I) indicates that the zeolite particles can be either faceted (size ≤ 500 nm) (blue circle on Fig. 7 c-I) or irregular (≤ 200 nm) (red circle on Fig. 7 c-I). Particles in the area with a high Al content (Area 1, Fig. 7 b) are irregular. Figure 7 d represents HRTEM image of Area 2 of HZSM-5(12) with a lower Al content and particles without pronounced faceting (red circle on Fig. 7 c-I). In the inset the two-dimensional Fourier spectrum of the ~ 100 nm region (marked with a red square in Fig. 7 d) is depicted, which is consistent with the MFI type structure [41] observed along the [123] crystallographic direction. HRTEM images of faceted particles (Area 2, blue circle on Fig. 7 c-I) and particles of Area 1 with a high Al content could not be obtained due to the material decomposition under the electron beam. Table 3 Results of qualitative and quantitative EDX of HZSM-5(12, 25, 40) samples areas (area average values) Element at. % at. % HZSM-5(12) Area 1 (Fig. 7 a, b) Area 2 (Fig. 7 a, c) Oxygen 71.50 55.90 Aluminium 14.36 3.76 Silicon 14.12 40.33 HZSM-5(25) Area 1 (Fig. 8 b) Area 2 (Fig. 8 b) Oxygen 58.82 66.40 Aluminium 2.43 0.66 Silicon 38.74 32.93 HZSM-5(40) Area 1 (Fig. 9 b) the sample composition is homogeneous Oxygen 62.82 Aluminium 1.40 Silicon 35.77 HAADF STEM images of HZSM-5(25) (Fig. 8 a) display large faceted particles (≤ 5 µm) and numerous irregular particles ≤ 100 nm in size. EDX maps (Fig. 8 b) demonstrate that the irregular particles (Area 2 in Fig. 8 b) of HZSM-5(25) contain almost no Al, in contrast to the faceted particles (Area 1), which is confirmed by the EDX results (Table 3 ). HRTEM image of a HZSM-5(25) faceted particle (size > 1 µm) is presented in Fig. 8 c. This particle is layered. The two-dimensional Fourier spectrum in the inset (Fig. 8 c-I) corresponds to the MFI type structure [41] observed along the [ \(\stackrel{-}{1}\stackrel{-}{4}\) 3] zone axis. The two-dimensional Fourier spectrum of irregular particles 10–20 nm in size (Fig. 8 c– II ) does not show large interplanar distances, which are present in MFI type structure [41]. Moreover, observed interplanar distances and the angles between the crystallographic planes are not consistent with any high index zone axis. Figure 8 c- III demonstrates a faceted particle with irregular particles on its surface, and the Fourier spectrum of one of them is shown in the inset. The structure of the phase in irregular particles, which does not correspond to MFI type phases [41], could not be determined. HZSM-5(40) consists of irregular particles close to spherical in shape (Fig. 9 a and 9 b). HRTEM image of HZSM-5(40) particles is depicted in Fig. 9 c. The correspondent Fourier spectrum (inset to Fig. 9 c) fits to the [111] direction of the MFI type structure [41]. So, according to SEM and HAADF STEM data, together with EDX: - HZSM-5(12) consists of faceted particles ({100} or/and {010} faces; ≤ 500 nm in size, predominant size ~ 400 nm) and irregular (≤ 200 nm; predominantly ~ 75 nm) ones with the MFI type structure and higher Al content (consistent with ICP AES results); - HZSM-5(25) contains separate iron oxides inclusions and consists of large faceted particles ({001} faces; ≤ 5 µm in size, predominant size ~ 800–1000 nm) with the MFI type structure and irregular ones (≤ 100 nm) containing no Al and not related to the MFI structure (consistent with ICP AES results - maximum Fe content in this sample). The heterophase nature of HZSM-5(25) (which was not determined by X-ray diffraction) should affect its functional characteristics, in particular catalytic activity, which will be discussed further. - HZSM-5(40) consists of irregular, nearly spherical particles (predominant sizes of ~ 100 nm and ~ 500 nm) with the MFI type structure and uniform Al content; - HZSM-5(300) consists of faceted particles ({100}, {010}, {001} faces), predominant size ~ 1200 nm) and irregular (< 250 nm, predominantly ~ 75 nm) ones. The different morphology and particle size of HZSM-5 samples are due to their synthesis conditions (Table 1 ): different composition of the aluminosilicate gel (templates, sources of silicon and aluminum and their ratios, pH) as well as various temperatures and duration of synthesis due to the changes in the crystallization rates of samples of different compositions (Si/Al). Catalytic activity of HZSM-5 in the reaction of nitrous oxide conversion The activity and selectivity of MFI type catalysts are closely related to the strength and concentration of acid sites on their surface. The acidity of a solid is a general name referring to the strength of acid sites and their number on the surface of a solid (surface composition), as well as the nature of the acid sites: BAS (Brønsted acid sites – bridging hydroxyls [Si-OH-Al] or LAS (Lewis acid sites - [Al 3+ O 4 − x [] x ] σ‎+ ). After the deuterated acetonitrile (CD 3 CN) adsorption on HZSM-5(12, 25, 40, 40C, 300) OH-bands disappear from the spectra and a broad intense band appears with a maximum at ~ 2761–2776 cm -1 (refers to O-D band) (Fig. 3 a, b, c, d) except for HZSM-5(300) zeolite spectrum in which this band is absent (Fig. 3 e). The difference between the wavenumbers (cm -1 ) of the absorption bands before (~ 3610–3612 cm -1 ) and after (~ 2761–2776 cm -1 ) adsorption gives shift values (Δ cm -1 ) that decrease in the row HZSM-5(25) (Δ 849 cm -1 ) > HZSM-5(40) (Δ 847 cm -1 ) > HZSM-5(40)C (Δ 844 cm -1 ) > HZSM-5(12) (Δ 834 cm -1 ) ( sequence 2 ) (Fig. 3 h). This indicates the presence of strong BASs [35–37] on the surface of these zeolites, maximum for HZSM-5(25). There are no BASs on the HZSM-5(300) surface (Fig. 3 e, f). The ~ 2315–2321 cm − 1 band on the DRIFT-CD 3 CN spectra of HZSM-5(12, 25, 40, 40C) (Fig. 10 ) corresponds to the coordination of acetonitrile molecules by LASs [42–44]. The maximum intensity of the ~ 2315–2321 cm − 1 band is for HZSM-5(12) (Fig. 10 a, f), which indicates the maximum LASs content in this zeolite: HZSM-5(12) > HZSM-5(40)C > HZSM-5(40) > HZSM-5(25) ( sequence 3 ). The blue shift of the frequency of C ≡ N stretching vibrations during CD 3 CN adsorption on LASs compared to the frequency in the gas phase (2253 cm –1 ) [45] is 62–68 cm –1 for all samples, which indicates approximately the same LASs strength in the studied HZSM-5 (taking into account the step of ± 4 cm − 1 ). The evacuation of the samples leads to the disappearance of the ~ 2264–2266 cm − 1 band (refers to the physical adsorption of acetonitrile molecules [37, 42–44]) in the spectra of all HZSM-5 (Fig. 10 ). The ~ 2299 − 2298 cm − 1 band in the DRIFT-CD 3 CN spectra of evacuated HZSM-5(12, 25, 40, 40C) is responsible for the coordination of acetonitrile molecules by BASs [37, 42–44]. The blue shift of the frequency of C ≡ N stretching vibrations during CD 3 CN adsorption on BASs is approximately the same for HZSM-5(12, 25, 40, 40C) and is 45–46 cm − 1 (Fig. 10 a-d). There are no ~ 2315–2321 cm –1 and ~ 2299–2298 cm –1 bands (which are responsible for the coordination of acetonitrile molecules by LASs and BASs, respectively) in the DRIFT-CD 3 CN spectra of HZSM-5(300) (Fig. 10 e), which means the absence of LASs and BASs on the HZSM-5(300) surface. The absorption band at ~ 2111–2115 cm − 1 in the DRIFT-CD 3 CN spectra of HZSM-5 refers to bending vibrations of C-D bonds in the CD 3 group (Fig. 10 ). The direct catalytic decomposition of N 2 O over the zeolite samples was performed in the temperature range of 400–650°C. The samples were annealed at 700°C before the catalytic process but were not ground. Figure 11 a shows conversion curves for each sample. Nitrous oxide decomposition starts simultaneously at 500°C, however, a furcation of the curves takes place with the increase in temperature. The conversion of nitrous oxide decreases in the row HZSM-5(25) > HZSM-5(12) > HZSM-5(40) > HZSM-5(40)С >> HZSM-5(300) ( sequence 4 ). An increase in the catalytic activity of HZSM-5(25) is facilitated by iron oxides present in the sample (ICP AES and HAADF STEM), which were not detected by X-ray diffraction. In [46] iron oxides introduction into the framework voids and/or on the HZSM-5 surface were shown to contribute to the enhancement of the catalytic properties in the reactions involving Lewis bases, such as N 2 O decomposition [47]. Metal oxide catalysts are known [48] to have excellent redox performance and high N 2 O catalytic decomposition activity, making them very promising catalysts. It was shown in [49] that iron and its oxides had a strong catalytic effect on N 2 O: the increase in iron content improved the decomposition rate of N 2 O and promoted the overall N 2 O transformation. In this case, it can be assumed that, without taking into account the effect of iron ions, the conversion of nitrous oxide should decrease in the row HZSM-5(12) > HZSM-5(25) > HZSM-5(40) > HZSM-5(40)С >> HZSM-5(300) ( sequence 4а ) with a decrease in aluminum content (with an increase in Si/Al). This should indicate the decisive role in N 2 O catalytic conversion of Lewis acid sites ([AlO 4 − x [] x ] σ‎+ ), which are present in HZSM-5 along with Brønsted ones ([Si-OH-Al]) [8]. The content of BASs and LASs decreases respectively in the rows HZSM-5(25) > HZSM-5(40) > HZSM-5(40)C > HZSM-5(12) ( sequence 2 ) and HZSM-5(12) > HZSM-5(40)C > HZSM-5(40) > HZSM-5(25) ( sequence 3 ). It is possible that MOR zeolite impurity in HZSM-5(12) contributes to the reduction of BASs strength [50]. Note that maximum content of BASs in HZSM-5(25) is accompanied by minimum content of LASs (DRIFT). Comparing with each other the changes in the characteristics of HZSM-5 identified by different methods ( sequences 1–4 ), one can see that they describe the change in characteristics of both bulk properties ( sequence 4) and surface ones ( sequences 1, 2, 3 ). Moreover, the sequence 1 (the change in textural characteristics depending on Si/Al) is logically consistent with the content of OH groups in the same zeolites. It is possible that the N 2 O decomposition reaction occurs both on the particles’ surface and in the samples’ volume. It should be noted that no relationship between Al 3+ ions content in each crystallographic site of HZSM-5 structure and their catalytic activity was revealed [4], possibly due to the lack of a sufficient number of HZSM-5 samples with different silicate moduli obtained under the same controlled conditions. The possibility of the Lewis acid sites participation in the N 2 O decomposition was demonstrated in [51] where the complexation of N 2 O with BASs and LASs in high-silica HZSM-5 zeolites was studied by the IRS (Intelligent Reflecting Surfaces) method in diffuse-scattered light. It was shown that the strength of adsorption of the N 2 O-LAS complex is significantly superior to the N 2 O complex with a proton acid site (BAS). The difference in the strength of adsorption, according to the authors, is due to the different geometry of the N 2 O adsorption on acid sites. According to quantum-chemical calculations, the N 2 O molecule is adsorbed on the aprotic acid site (LAS) by a two-point mechanism with the participation of a three-coordinated aluminum atom and an adjacent basic oxygen atom. This adsorption complex is characterized by a higher interaction energy (261 kJ/mol) as compared to a single-point complex formed upon interaction with a proton center (BAS) (70 kJ/mol). Such a strong activation of the N 2 O molecule promotes its further decomposition. N 2 O-LAS complexes decompose at 200–350°C, and it was found that the only product released into the gas phase is nitrogen, and oxygen is chemisorbed on the zeolite [51]. However, an increased content of LASs is not a determining factor in the increase in the HZSM-5 catalytic activity, which can be seen in the example of HZSM-5(40) and HZSM-5(40)C zeolites with different fabrication conditions: the catalytic reaction rate is higher for HZSM-5(40) (refined composition Si/Al = 39) compared to HZSM-5(40)C (refined composition Si/Al = 42) (Fig. 11 ), which has a lower intensity of the absorption band corresponding to LASs (~ 2315–2321 cm − 1 , Fig. 10 c, d). It should be noted that the increase in the catalytic activity of HZSM-5(40) compared to HZSM-5(40)C is accompanied by an increase in the specific surface area (S BET , m 2 /g) and outer surface area (S ext , m 2 /g) (Table 2 ), i.e., of two competing factors - the active surface size and LASs content - the first one prevails. For the remaining zeolites, there is no direct relationship between these characteristics and the N 2 O decomposition reaction rate (Table 2 , Fig. 11 a). It is important to note that the studied HZSM-5 samples have different morphologies (Figs. 6 – 9 ) depending on synthesis condition. It is not excluded that HZSM-5(25) catalytic activity, determined from the N 2 O decomposition rate, is related precisely with the {001} faces, which does not contradict the data of [14]. Conclusions This work presents systematized data on the study of HZSM-5 aluminosilicalites with different silicate modules (Si/Al = 12, 25, 40, 300) and synthesis conditions (different templates, silicon and aluminum sources and their ratio, aluminosilicate gel pH, temperature and duration of synthesis) by a complex of diffraction and complementary methods. Data obtained by EDX microanalysis, STEM and HRTEM on the phase composition of samples combined with the analysis of our previously obtained results made it possible to identify an impurity phase of iron oxide in HZSM-5(25), which was not determined by X-ray methods, but allowed to establish its role in this sample’s catalytic activity manifestation in N 2 O decomposition reaction. HZSM-5(25) demonstrates a significantly higher rate of N 2 O decomposition reaction compared to previously studied samples of titanosilicalites [33] as well as Fe/Beta and Fe/SSZ-13 [52]. HZSM-5(25) turned out to be the most preferred catalyst in the N 2 O decomposition reaction among aluminosilicalites under study. It differs not only in the maximum content of iron oxides, but also in morphology and composition, and contains the maximum amount of Brønsted acid sites, which apparently enhances HZSM-5(25) catalytic activity. This makes it promising for use in the direct catalytic decomposition of N 2 O, both alone and as a matrix for nanocomposites. The presented methodology for studying HZSM-5 aluminosilicalites with different silicate modules and the results of their detailed characterization (phase and elemental composition of the samples, composition of the main phase of the zeolite and the surface composition; crystal structure; microstructure with textural parameters, sizes and shapes of particles) with revealed correlations or explanations for their absence can be useful in studying other zeolites or modifying data. Declarations Author Contributions E.N. Domoroshchina: Experimental and theoretical analysis, Data curation, Writing – review & editing; G . M . Kuz ’ micheva : Metodology, Conceptualization, XRPD measurements and their evaluation, Writing; A.L. Vasiliev: HAADF STEM, EDX and HRTEM mesurements; I.S. Pavlov: HAADF STEM, EDX and HRTEM measurements, Writing; L.V. Pirutko: HZSM-5 synthesis, ICP AES and BET measurements and evaluation; O.P. Tkachenko: DRIFTS measurements; A.L. Kustov: Catalytic tests, Writing. Conflicts of interest There are no conflicts to declare. Acknowledgements This research was funded by Ministry of Science and Higher Education of the Russian Federation, grant number 0706-2020-0026. Zeolite synthesis was partially supported by the Ministry of Science and Higher Education of the Russian Federation within the governmental order for Boreskov Institute of Catalysis. References S.M.Al-Jubouri, S.I.Al-Batty, S.M. 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Circles (ellipses) marked with a solid line are rings of tetrahedra (5-membered – blue, two types of 6-membered – green and red, 10-membered – black), and marked with a dotted line are corresponding voids in HZSM-5 framework (sp. gr. Pnma)\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/e96e279d1518e17ae9b1fc04.png"},{"id":49072208,"identity":"0ccbf90e-5854-4630-af8e-aa221869380e","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":492042,"visible":true,"origin":"","legend":"\u003cp\u003eXRPD patterns of HZSM-5 (λ= 1.54051 Å). Red arrow indicates\u003c/p\u003e\n\u003cp\u003eMOR zeolite impurity.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/101d860576228ccc31f725ac.png"},{"id":49072202,"identity":"eb277d2f-cbef-4cdf-ade6-8b4640d286b1","added_by":"auto","created_at":"2024-01-02 17:16:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":458490,"visible":true,"origin":"","legend":"\u003cp\u003eDRIFT-OH spectra of dehydroxylated HZSM-5 aluminosilicalites with Si/Al=12 (a), 25 (b), 40 (c) 40C (d), 300 (e). 1 - after vacuum treatment at 400 °C; 2 - after deuterated acetonitrile (CD\u003csub\u003e3\u003c/sub\u003eCN) adsorption. Relationship between silicate modulus (Si/Al) and the maximum intensities of bands ~3610 cm\u003csup\u003e-1\u003c/sup\u003e (f), ~3740-3745 cm\u003csup\u003e-1\u003c/sup\u003e (g) and the difference between the wavenumbers of the absorption bands (cm\u003csup\u003e-1\u003c/sup\u003e) before and after deuterated acetonitrile (CD\u003csub\u003e3\u003c/sub\u003eCN) adsorption (Δ cm\u003csup\u003e-1\u003c/sup\u003e) (h)\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/9bfb841f0044a7cbc8ab5399.png"},{"id":49072204,"identity":"03ea8fca-6888-4735-969a-f6bc3b0123fc","added_by":"auto","created_at":"2024-01-02 17:16:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":339544,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationships between HZSM-5 silicate modulus (Si/Al) and areas of rings (a) and voids (b) in HZSM-5 framework calculated by ELLIPSE software [39]\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/8be9131de59642689078c55f.png"},{"id":49073079,"identity":"924fb0fe-5f33-4c6d-bb4e-c2dc773558c4","added_by":"auto","created_at":"2024-01-02 17:24:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":53609,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between HZSM-5 silicate modulus (Si/Al) and their specific surface value (S\u003csub\u003eBET\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/9bf82cd1c36517c881c10918.png"},{"id":49072211,"identity":"0c022833-2216-48f3-a7b0-ec2628a3f182","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3591630,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (a) HZSM-5(12), (b) HZSM-5(25), (c) HZSM-5(40) and (d) HZSM-5(300). Diagrams show particles’ size distribution\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/a680dfd169c2cd3326bb5f57.png"},{"id":49072210,"identity":"f480f320-9485-4206-a2fb-2cab25e0a574","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":6152492,"visible":true,"origin":"","legend":"\u003cp\u003eHAADF STEM image (Figs. \u003cem\u003eI\u003c/em\u003e)\u003cem\u003e \u003c/em\u003eand element distribution maps (EDX method) (Figs. \u003cem\u003eII-IV\u003c/em\u003e) of HZSM-5(12) zeolite (a) and an enlarged images of areas with a high (Area \u003cem\u003e1\u003c/em\u003e, yellow square on Fig. a-\u003cem\u003eI\u003c/em\u003e) (b) and a low (Area\u003cem\u003e 2\u003c/em\u003e, green square on Fig. a-\u003cem\u003eI\u003c/em\u003e) (c) content of Al; HRTEM image of HZSM-5(12) irregular particle with a low Al content (marked with the red circle on Fig. c-\u003cem\u003eI\u003c/em\u003e) (d). Faceted particle marked with the blue circle in Fig. c-\u003cem\u003eI\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/81036aa05b6f3a7b843c4f3f.png"},{"id":49072209,"identity":"4d39dc86-bcf1-45dc-9cc5-8ecb493ddfb2","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":4990278,"visible":true,"origin":"","legend":"\u003cp\u003eHAADF STEM image (Figs. \u003cem\u003eI\u003c/em\u003e)\u003cem\u003e \u003c/em\u003eand element distribution maps (EDX method) (Figs. \u003cem\u003eII-V\u003c/em\u003e) of HZSM-5(25) zeolite (a) and an enlarged images (yellow square - Area \u003cem\u003e1\u003c/em\u003ewith faceted and irregular particles; green square – Area 2 with only irregular particles) (b); HRTEM image of faceted HZSM-5(25) particle (c-\u003cem\u003eI\u003c/em\u003e), irregular HZSM-5(25) particle (c-\u003cem\u003eII\u003c/em\u003e), irregular HZSM-5(25) particle located on the surface of faceted particle (c-\u003cem\u003eIII\u003c/em\u003e)\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/b48e61146eeaaf4aa9194afa.png"},{"id":49072212,"identity":"1bc3a961-71ba-4465-bcd8-2dd040e071be","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":5009777,"visible":true,"origin":"","legend":"\u003cp\u003eHAADF STEM image (Figs. \u003cem\u003eI\u003c/em\u003e)\u003cem\u003e \u003c/em\u003eand element distribution maps (EDX method) (Figs. \u003cem\u003eII-IV\u003c/em\u003e) of HZSM-5(40) zeolite (a) and an enlarged images of Area 1 (yellow square on Fig. a-\u003cem\u003eI\u003c/em\u003e) (b); HRTEM image of HZSM-5(40) irregular particles (c)\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/09bd9a731e9930feb2d29fa4.png"},{"id":49072205,"identity":"5277d410-b59f-4f54-937e-5b0903788942","added_by":"auto","created_at":"2024-01-02 17:16:48","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1321692,"visible":true,"origin":"","legend":"\u003cp\u003eDRIFT-CD\u003csub\u003e3\u003c/sub\u003eCN spectra of HZSM-5 with Si/Al=12 (a), 25 (b), 40 (c), 40C (d), 300 (e). (f) Relationship between silicate modulus (Si/Al) and maximum intensity of band ~2315-2321 cm\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/ba17d74c72198c1683493fb2.png"},{"id":49073080,"identity":"3949a66c-356e-4778-bfb8-35d7d22cfdb6","added_by":"auto","created_at":"2024-01-02 17:24:48","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":782903,"visible":true,"origin":"","legend":"\u003cp\u003eConversion curves for catalytic N\u003csub\u003e2\u003c/sub\u003eO decomposition process over HZSM-5(12), HZSM-5(25), HZSM-5(40), HZSM-5(40)C and HZSM-5(300) samples (a); relationship between HZSM-5 catalytic activity and silicate modulus (Si/Al) (b), the content of framework water (XRPD, Rietveld method, synchrotron emission ESRF [15]) (c), heat capacity (H, J/g) with the content of “zeolite water” with OH groups (DSC [3]) (d)\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/a51458ac76be6dcdcea60e65.png"},{"id":51599245,"identity":"2729ee52-5ab7-4879-a45e-00f942280d5e","added_by":"auto","created_at":"2024-02-25 08:54:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5190490,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3796442/v1/7e367897-ec64-4de5-8981-30ddf3dfa72a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Rational Design of Aluminium-containing Zeolites with Typological Structure of HZSM-5 and Catalytic Properties","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHZSM-5 aluminosilicalites (MFI type, general composition (H\u003csup\u003e1\u0026thinsp;+\u003c/sup\u003e\u0026thinsp;\u003csub\u003ex\u003c/sub\u003e)[Al\u003csup\u003e3\u0026thinsp;+\u003c/sup\u003e\u0026thinsp;\u003csub\u003ex\u003c/sub\u003eSi\u003csup\u003e4\u0026thinsp;+\u003c/sup\u003e\u0026thinsp;\u003csub\u003e12-x\u003c/sub\u003eO\u003csub\u003e24\u003c/sub\u003e]\u0026times;\u003cem\u003ewA\u003c/em\u003e, Si/Al from 8 to \u0026infin;), space group Pnma or P2\u003csub\u003e1\u003c/sub\u003e/n (z\u0026thinsp;=\u0026thinsp;8) with close unit cell parameters (which makes it difficult to separate them in a structural experiment), belong to the large class of zeolites which structural feature is vertex-jointed (Si/Al)O\u003csub\u003e4\u003c/sub\u003e tetrahedra forming a framework of 5- (two types), 6- and 10-membered rings. They form a three-dimensional system of intersecting rectilinear and sinusoidal channels, which can contain atoms, groups of atoms, molecules, including water (\u003cem\u003eA\u003c/em\u003e). The channels are located along \u0026lt;\u0026thinsp;010\u0026gt; (rectilinear) and \u0026lt;\u0026thinsp;100\u0026gt; (sinusoidal) directions and are interconnected by 10-membered rings of tetrahedra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased only on this structural description of zeolites, one can expect them primarily to have catalytic and sorption properties as the first stage of the catalytic process. Indeed, HZSM-5 aluminosilicates are indispensable for use in many petrochemical processes, where they exhibit greater catalytic activity than currently used conventional catalytic systems [1]. HZSM-5 catalytic activity (in the general case, without specifying a particular catalytic process) depends on all levels of structure and composition organization, which we refer to as composition and structure parameters:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e- the atomic structure and composition of HZSM-5 main phase: symmetry, Si/Al silicate modulus [2\u0026ndash;4], Al\u003csup\u003e3+\u003c/sup\u003e ions distribution over the crystallographic sites (not excluded in [4]), Al\u003csup\u003e3+\u003c/sup\u003e ions content in each crystallographic site of the structure (no data), the content of \u0026ldquo;zeolite water\u0026rdquo; with OH groups or other atomic formations in the zeolite framework [3] or extra-framework ones [5]; dimensions of voids and channels [6];\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- elemental composition of samples [3];\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- phase composition of samples [3];\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- surface composition: the content of Si, Al, Si(Al)-O bonds, OH groups, water [3], and acid sites [3, 6, 7] which include Lewis acid sites (LAS) ([AlO\u003csub\u003e4-x\u003c/sub\u003e[]\u003csub\u003ex\u003c/sub\u003e]\u003csup\u003eσ\u0026lrm;+\u003c/sup\u003e) [8] and Br\u0026oslash;nsted ones \u0026ndash; BAS (bridging hydroxyls [Si-OH-Al]) [8];\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- local structure, or local environment of Al\u003csup\u003e3+\u003c/sup\u003e ions (no data);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- microstructure: specific surface area, meso- and micropores volume [3], pore size [9]; average sizes of crystallites and particles [3, 10, 11].\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThese components of HZSM-5 composition and structure depend or may depend on the method and/or conditions of their fabrication [12, 13], which allows their directed variation to optimize structure-dependent catalytic characteristics, subject to found or known correlations.\u003c/p\u003e \u003cp\u003eNote that each catalytic process may have its own set of optimal catalyst parameters, in particular, surface or volume ones. The rate of heterogeneous catalytic processes can be regulated by changing the composition and structure of HZSM-5 active sites (ensembles of {AlO\u003csub\u003e4\u003c/sub\u003e\u0026times;SiO\u003csub\u003e4\u003c/sub\u003e} tetrahedra in which the Al\u003csup\u003e3+\u003c/sup\u003e ion contains free 3d\u003csup\u003e0\u003c/sup\u003e atomic orbitals exhibiting strongly pronounced electron-acceptor properties), texture (specific surface area, pore volume, pore size distribution, particle shape, surface composition), etc. [14]. Knowledge of all levels of the hierarchy of HZSM-5 composition and structure, the role of preparation conditions for their variation will help to find the relationship between the composition and structural parameters and functional characteristics, in particular, the catalytic characteristics of a specific catalytic process with the identification of active centers on the surface and/or in the volume. This was the motivation for our study, \u003cb\u003ethe purpose of which is\u003c/b\u003e to establish the role of each component of HZSM-5 composition and structure in the manifestation of catalytic activity using the example of nitrous oxide decomposition reaction.\u003c/p\u003e \u003cp\u003eSome characteristics of HZSM-5 zeolites have been studied in our previous works [3, 4, 15] using the powder X-ray diffraction (XRPD; high-precision synchrotron measurements of HZSM-5(12, 40, 300): symmetry, phase composition, water molecules content in the framework cavities), neutron diffraction (Rietveld refinement of HZSM-5(12, 25, 40) composition, Al\u003csup\u003e3+\u003c/sup\u003e ions distribution over the crystallographic sites), X-ray photoelectron spectroscopy (XPS; HZSM-5(12, 25, 40) surface investigation), FT-IR and Differential Scanning Calorimetry (DSC) (the content of \u0026ldquo;zeolite water\u0026rdquo; with OH groups in the HZSM-5(12, 25, 40) framework), temperature programmed desorption of ammonia (TPD; HZSM-5(12, 25, 40) total acidity).\u003c/p\u003e \u003cp\u003eIn this work, the methods of scanning/transmission electron microscopy (S/TEM) with energy-dispersive X-ray microanalysis (EDX), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma atomic emission spectrometry (ICP AES), low-temperature nitrogen adsorption as well as XRPD (to obtain missing data for HZSM-5(25, 40C and 300)) were applied to get the most complete understanding of the composition, microstructure, morphology and elemental composition of HZSM-5(12, 25, 40, 40C, 300). Previously obtained results together with new data were used to build new correlations between composition, structure and functional (catalytic) properties, that was necessary for a deep understanding of the role of each of the comprehensive characteristics in the manifestation of functional properties and the achievability of their maximum values.\u003c/p\u003e \u003cp\u003eA direct catalytic decomposition of nitrous oxide, which is an ozone-depleting gas, into oxygen and nitrogen is considered to be the most efficient neutralization approach. In the literature there is a wide diversity of possible catalytic systems in the form of both supported nanoparticles [16\u0026ndash;21], including noble metals [22\u0026ndash;25] and bulk materials (mostly mixed metal oxides [26\u0026ndash;28]). Among the most efficient catalysts used for N\u003csub\u003e2\u003c/sub\u003eO decomposition, HZSM-5 zeolites with low Si/Al included modified ones (Cu, Co, Fe- or Zn-containing HZSM-5) were shown to demonstrate the best performance [29].\u003c/p\u003e"},{"header":"Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of HZSM-5 aluminosilicalites\u003c/h2\u003e \u003cp\u003eZSM-5 zeolites (sodium form) were synthesized by the hydrothermal method [4, 15] (the main synthesis conditions are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) followed by calcination at T\u0026thinsp;\u0026ge;\u0026thinsp;500\u0026deg;C to remove the organic components and ion exchange in ammonia buffer to obtain HZSM-5.\u003c/p\u003e \u003cp\u003eThe powder X-ray diffraction (XRPD) patterns of the obtained zeolites are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, which clearly exhibit a series of diffraction peaks assigning to typical MFI structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMOR zeolite impurity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHZSM-5 synthesis conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSynthesis conditions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHZSM-5(12)*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHZSM-5(25)**\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHZSM-5(40)**\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHZSM-5(40)C**\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHZSM-5(300)**\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemplate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eCommercial, Zeolite International, USA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eC\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e29\u003c/sub\u003eNO\u003c/p\u003e \u003cp\u003e(TPAOH)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eС\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003e(n-butanol)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC\u003csub\u003e8\u003c/sub\u003eH\u003csub\u003e20\u003c/sub\u003eBrN (TEAB)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eC\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e13\u003c/sub\u003eNO (TMAOH)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilicon source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLudox HS-30 сolloidal \u003cem\u003esilica\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLudox HS-30 сolloidal \u003cem\u003esilica\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSilicic acid (nSiO\u003csub\u003e2\u003c/sub\u003e\u0026middot;mH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSilicic acid (nSiO\u003csub\u003e2\u003c/sub\u003e\u0026middot;mH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAluminum source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;18H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;18H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;18H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003esodium aluminate (NaAlO\u003csub\u003e2\u003c/sub\u003e) solution\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature, \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e438\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e443\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e443\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e443\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDuration, hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSi/Al (Initial/Refined [4])\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12/14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25/22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30/39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40/42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e300/***\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e*Contains an impurity of MOR zeolite in addition to the main phase (~\u0026thinsp;7%) (X-ray diffraction data, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e**Single-phase sample (X-ray diffraction data, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e*** No data\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe pH\u0026thinsp;\u0026gt;\u0026thinsp;7 was for HZSM-5(25, 40C, 300) samples and pH\u0026thinsp;~\u0026thinsp;6 was for HZSM-5(40). As can be seen from Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, HZSM-5(12, 25, 40, 40C, 300) samples differed both in the initial reagents (template, silicon, and aluminum sources), and in the temperature and duration of synthesis, which is due to different crystallization rates of samples of different compositions. In addition to different templates and silicon sources, the synthesis of the HZSM-5(40) and HZSM-5(40)C was distinguished by the absence of the use of seed polycrystals in the case of HZSM-5(40)C, which were used for the synthesis of the remaining samples [4].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eMicrostructure. Morphology. Elemental Composition\u003c/h2\u003e \u003cp\u003eTextural characteristics (specific surface area, micropore volume, total pore volume, cumulative desorption surface area of pores) were studied by low-temperature nitrogen adsorption at -196\u0026deg;C on the ASAP 2010 facility (Micromeritics Corp., USA). Prior to nitrogen adsorption, the samples were vacuum treated at 250\u0026deg;C for 10 hours. The measurement errors of textural characteristics were no more than \u0026plusmn;\u0026thinsp;10%.\u003c/p\u003e \u003cp\u003eElectron microscopy was used to study the morphology and microstructure of zeolite samples. Scanning electron microscopy (SEM) was carried out using a JSM 7500F high-resolution scanning electron microscope. Scanning/transmission electron microscopy (S/TEM) was performed using an Osiris scanning/transmission electron microscope (ThermoFisher Scientific, USA) equipped with a high-angle annular dark-field (HAADF) detector. The Digital Micrograph and TIA software were used to carry out image processing. The samples in their initial form were deposited on the carbon-coated copper electron microscopic grids.\u003c/p\u003e \u003cp\u003eThe content of Al, Fe, and Na in the obtained zeolite samples was determined by inductively coupled plasma atomic emission spectrometry (ICP AES) using an OPTIMA 4300 DV ICP spectrometer (Perkin Elmer, USA). The absolute error limits of the element mass fraction\u0026thinsp;\u0026plusmn;\u0026thinsp;Δ were 0.005%.\u003c/p\u003e \u003cp\u003eEDX microanalysis of the obtained zeolite samples using Bruker energy-dispersive X-ray microanalysis (EDX) system (Bruker, USA) [30] was applied for the qualitative analysis of single-phase samples with specific standard deviations for each element and its content. To detect the presence of a certain element by the EDX microanalysis, its content must be at least 0.1 at. %. The error in determining the concentrations of elements in powders by the EDX microanalysis is up to 3\u0026ndash;5 at. %. Moreover, the efficiency of characteristic X-ray radiation detecting by EDX decreases with a decrease in atomic number [30]. Quantitative analysis of even single-phase samples, considering all atoms in the sample composition (for example, impurity atoms from the initial components), cannot be correctly applied to defect structures with vacancies, since the balance of elements in this case cannot be reduced to 100%. In HZSM-5 crystal structures vacancies are possible in the silicon and oxygen sites, as well as the presence of hydroxyl groups replacing oxygen ions [31]. Moreover, in the HZSM-5 framework voids, there may be water and other atomic formations with a high hydrogen content, which may not be detected by microanalysis. However, the EDX microanalysis application for the qualitative analysis of the samples\u0026rsquo; composition and the ratio of individual elements content, especially for single-phase regions, can be very successful [30].\u003c/p\u003e \u003cp\u003eDiffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the zeolite surface composition and the content of acid sites (LAS and BAS). Diffuse reflectance IR spectra were recorded at room temperature on a NICOLET Protege 460 spectrometer equipped with a diffuse reflection prefix [32], in the wavenumber range of 6000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a step of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Prior measuring, the samples were dehydroxylated by calcination at 700\u0026deg;C and subjected to thermal vacuum treatment at 400\u0026deg;C and a pressure of 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mmHg for 2 hours (heating rate was 5 \u003csup\u003eo\u003c/sup\u003eC/min). Deuterated acetonitrile (CD\u003csub\u003e3\u003c/sub\u003eCN) was used as acidity test molecules. The spectra were recorded and processed using the OMNIC software.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eCatalytic experiment\u003c/h2\u003e \u003cp\u003eCatalytic decomposition of nitrous oxide (N\u003csub\u003e2\u003c/sub\u003eO) was carried out in a flow-type quartz reactor with internal diameter of 4 mm (atmospheric pressure, temperature range of 400\u0026ndash;700\u0026deg;C) according to the procedure described in [33]. Catalytic tests were performed in a 100% N\u003csub\u003e2\u003c/sub\u003eO flow with gas hourly space velocity of 30,000 ml/(h\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u0026times;g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e). The gas mixture composition was analyzed on a Crystall 5000 gas chromatograph (Chromatech, Russia) equipped with a HayeSep-Q column for measuring N\u003csub\u003e2\u003c/sub\u003eO concentration and NaX molecular sieves for separating N\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e. Before loading into the reactor, the samples were calcined in a muffle furnace at 700 \u003csup\u003eo\u003c/sup\u003eC for 5 hours.\u003c/p\u003e \u003c/div\u003e"},{"header":"Result and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003eComposition and сrystal structure\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eAccording to elemental analysis (ICP AES) of all studied samples, Al content in HZSM-5 zeolites logically decreases with an increase in Si/Al: from 3.2 wt.% for HZSM-5(12), to 0.14\u0026ndash;0.16 wt.% for HZSM-5(300). HZSM-5(25) is characterized by the maximum content of Fe \u0026ndash; 0.07 wt.% (the most common impurity introduced at the stage of zeolite synthesis [34]), and the minimum content of the residual Na \u0026ndash; 0.01 wt.% (the initial zeolites were synthesized in the Na form, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Maximum Na content is in HZSM-5(300) \u0026ndash; 0.06 wt.%. HZSM-5 with the same initial Si/Al, but different fabrication conditions differ in aluminum content:1.9 wt.% and 1.1 wt.% for HZSM-5(40) and HZSM-5(40)C, respectively.\u003c/p\u003e \u003cp\u003eOn the DRIFT-OH spectra of HZSM-5(12, 25, 40, 40C, 300) zeolites preliminarily dehydroxylated by calcination at 700\u0026deg;C and evacuated (to remove the gas phase) at 400\u0026deg;C, three bands are observed in the OH groups\u0026rsquo; region: ~3740\u0026ndash;3745 cm\u003csup\u003e-1\u003c/sup\u003e (refers to linear isolated silanol (Si-OH) groups [35\u0026ndash;37]), ~\u0026thinsp;3662 and ~\u0026thinsp;3610\u0026ndash;3612 cm\u003csup\u003e-1\u003c/sup\u003e (characterize bridging OH-groups [35\u0026ndash;37]) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b, c, d, f, g). HZSM-5(300) spectrum has only one weak band at ~\u0026thinsp;3745 cm\u003csup\u003e-1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). The intensity of the bands at ~\u0026thinsp;3610 and ~\u0026thinsp;3740\u0026ndash;3745 cm\u003csup\u003e-1\u003c/sup\u003e indicates that the maximum content of bridging hydroxyls is in HZSM-5(25) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef), and isolated silanols - in HZSM-5(40)C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to the X-ray diffraction data all the samples under study are single-phase except for HZSM-5(12) with MOR zeolite impurity phase (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHZSM-5 zeolites have selectivity for the reacting molecules\u0026rsquo; size, which is due to the size of the pores through which molecules of only certain sizes and shapes can pass. This applies to both initial materials and reaction products. The sizes of voids (cavities) (5, 6 and 10-membered) in the HZSM-5 structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) depend on the composition (Si/Al) and symmetry which is due to a larger number of sites occupied by silicon atoms in the monoclinic structure (24 \u003cem\u003eT\u003c/em\u003e sites) compared to the orthorhombic one (12 \u003cem\u003eT\u003c/em\u003e sites) [38].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe area of rings and voids on a two-dimensional projection of tetrahedra in HZSM-5 structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), calculated using ELLIPSE software [39], decreases with an increase in Si/Al (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, b). The most pronounced change is observed for 10-membered rings of tetrahedra, mainly when going from Si/Al\u0026thinsp;=\u0026thinsp;25 to Si/Al\u0026thinsp;=\u0026thinsp;40 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). This means higher channel accessibility in HZSM-5(12 and 25) compared to HZSM-5(40). Channel sizes, which are characterized by sizes of rings of tetrahedra, specify limitations to the size and shape of molecules capable to \u0026ldquo;penetrate\u0026rdquo; into the zeolite crystalline structure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMicrostructure. Morphology\u003c/h2\u003e \u003cp\u003eAnalysis of BET and BJH data showed that the values of HZSM-5 textural characteristics (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) increase in the row HZSM-5(12)\u0026thinsp;\u0026lt;\u0026thinsp;HZSM-5(25)\u0026thinsp;\u0026lt;\u0026thinsp;\u003cb\u003eHZSM-5(40)\u003c/b\u003e, and then get smaller for HZSM-5(300) (\u003cem\u003esequence 1\u003c/em\u003e). Тhere is a break at Si/Al\u0026thinsp;=\u0026thinsp;40 in the relationship of HZSM-5 specific surface value and silicate modulus (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Similar break was observed in [15] in the dependences of Si/Al on the unit cell volume (V, \u0026Aring;\u003csup\u003e3\u003c/sup\u003e) and unit cell volume on water molecules content in the framework cavities, which is caused by the change in the HZSM-5 symmetry (from \u003cem\u003ePnma\u003c/em\u003e to \u003cem\u003eP2\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/n\u003c/em\u003e). Due to the different fabrication conditions, HZSM-5(40)C with a slightly higher silicate modulus (Si/Al\u0026thinsp;=\u0026thinsp;42) compared to HZSM-5(40) (Si/Al\u0026thinsp;=\u0026thinsp;39) (Rietveld refinement) has the same value of the total pore volume, a larger value of micropore volume (\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u0026micro;\u003c/sub\u003e, cm\u003csup\u003e3\u003c/sup\u003e/g), but smaller values of the specific surface area (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) and the outer surface compared to HZSM-5(40) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTextural characteristics of HZSM-5(12, 25, 40, 40C, 300) catalysts.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003e\u0026micro;\u003c/sub\u003e (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003e\u0026sum;\u003c/sub\u003e (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eS\u003csub\u003eBET\u003c/sub\u003e (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eS\u003csub\u003eext\u003c/sub\u003e (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHZSM-5(12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e336\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u0026ndash;33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHZSM-5(25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e354\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHZSM-5(40)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.26\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e429\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e68\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHZSM-5(40)C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e0.18\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.26\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e421\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16\u0026ndash;24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHZSM-5(300)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e414\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eV\u003csub\u003e\u0026micro;\u003c/sub\u003e, cm\u003csup\u003e3\u003c/sup\u003e/g \u0026ndash; zeolite micropore volume; V\u003csub\u003eΣ\u003c/sub\u003e, cm\u003csup\u003e3\u003c/sup\u003e/g - single point total pore volume of pores with diameter less than 1727.4939 \u0026Aring; at P/Po\u0026thinsp;=\u0026thinsp;0.9887; S\u003csub\u003eBET\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g \u0026ndash; BET surface area; S\u003csub\u003eext\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g \u0026ndash; BJH cumulative desorption surface area of pores with diameter between 17.0000 and 3000.0000 \u0026Aring;\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSEM data obtained at three sample points (representative photos are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) indicate that HZSM-5(12, 25, 40, 300) differ in morphology and particle sizes (maximum sizes are given for elongated particles): elongated prisms (probably with {100} or/and {010} faces oriented to the surface) with a small content of spheres\u0026thinsp;\u0026lt;\u0026thinsp;200 nm in size (Si/Al\u0026thinsp;=\u0026thinsp;12); approximately equal content of almost homogeneous spheres (~\u0026thinsp;120 nm) and faceted particles (with {001} faces oriented to the surface) (Si/Al\u0026thinsp;=\u0026thinsp;25); spheres (Si/Al\u0026thinsp;=\u0026thinsp;40); approximately equal content of elongated and shortened prisms (probably with {100}, {010}, {001} faces oriented to the surface) and small spheres\u0026thinsp;\u0026lt;\u0026thinsp;250 nm in size (Si/Al\u0026thinsp;=\u0026thinsp;300).\u003c/p\u003e \u003cp\u003eThe specific surface area (S\u003csub\u003eBET\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g) is inversely proportional to the particle size (\u003cem\u003eN\u003c/em\u003e, nm): \u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;K\u003csub\u003ep\u003c/sub\u003e/(ρ\u0026times;S)\u0026times;10\u003csup\u003e9\u003c/sup\u003e (Eq.\u0026nbsp;1), where S, m\u003csup\u003e2\u003c/sup\u003e/g is the specific surface area, K\u003csub\u003ep\u003c/sub\u003e is the particle shape factor: 6 for spheres and cubes, 4 for cylinders and rods, 2 for flat plates [40]; ρ, g/cm\u003csup\u003e3\u003c/sup\u003e is the X-ray density of the zeolite: ρ, g/cm\u003csup\u003e3\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;M\u003cem\u003ez\u003c/em\u003e/V (Eq.\u0026nbsp;2), where M is the molecular mass in carbon units, z is the number of formula units in the cell, V (\u0026Aring;\u003csup\u003e3\u003c/sup\u003e) is the unit cell volume. It follows from the \u003cem\u003eequations 1\u003c/em\u003e and \u003cem\u003e2\u003c/em\u003e that S=(K\u003csub\u003ep\u003c/sub\u003e \u0026times;V)/(\u003cem\u003eN\u003c/em\u003e\u0026times;Mz)\u0026times;10\u003csup\u003e9\u003c/sup\u003e. That is, the specific surface area of the sample directly depends not only on the unit cell volume, but on the sample morphology (particle shape factor).\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eIt should be noted that the specific surface area obtained using the BET method for microporous materials, to which HZSM-5 belongs, are formal, which is associated with the effects of volume filling of micropores. It is known that the method of adsorption data analysis using \u003cem\u003eEq.\u0026nbsp;1\u003c/em\u003e does not provide for the presence of micropores, since the energy homogeneity of the adsorbent surface is postulated. This leads to a directly proportional relationship between the specific surface area and the content of small pores in the samples and the absence of a relationship with the particle size (Eq.\u0026nbsp;1). The largest specific surface area is for HZSM-5(40) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) consisting of spherical particles with predominant sizes of ~\u0026thinsp;100 nm and ~\u0026thinsp;500 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The difference in the morphology and particle sizes of HZSM-5 is due to their different fabrication conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which is the reason of the lack of relationship between the morphology of studied samples and their silicate modules.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. HAADF STEM image (Figs. \u003cem\u003eI\u003c/em\u003e) and element distribution maps (EDX method) (Figs. \u003cem\u003eII-IV\u003c/em\u003e) of HZSM-5(12) zeolite (a) and an enlarged images of areas with a high (Area \u003cem\u003e1\u003c/em\u003e, yellow square on Fig. a-\u003cem\u003eI\u003c/em\u003e) (b) and a low (Area \u003cem\u003e2\u003c/em\u003e, green square on Fig. a-\u003cem\u003eI\u003c/em\u003e) (c) content of Al; HRTEM image of HZSM-5(12) irregular particle with a low Al content (marked with the red circle on Fig. c-\u003cem\u003eI\u003c/em\u003e) (d). Faceted particle marked with the blue circle in Fig. c-\u003cem\u003eI\u003c/em\u003e\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eТhe enlarged image of the Area 2 of HZSM-5(12) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec-I) indicates that the zeolite particles can be either faceted (size\u0026thinsp;\u0026le;\u0026thinsp;500 nm) (blue circle on Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec-I) or irregular (\u0026le;\u0026thinsp;200 nm) (red circle on Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec-I). Particles in the area with a high Al content (Area 1, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb) are irregular.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed represents HRTEM image of Area 2 of HZSM-5(12) with a lower Al content and particles without pronounced faceting (red circle on Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec-I). In the inset the two-dimensional Fourier spectrum of the ~\u0026thinsp;100 nm region (marked with a red square in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed) is depicted, which is consistent with the MFI type structure [41] observed along the [123] crystallographic direction. HRTEM images of faceted particles (Area 2, blue circle on Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec-I) and particles of Area 1 with a high Al content could not be obtained due to the material decomposition under the electron beam.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResults of qualitative and quantitative EDX of HZSM-5(12, 25, 40) samples areas (area average values)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eat. %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eat. %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eHZSM-5(12)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArea 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArea 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, c)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOxygen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e71.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAluminium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilicon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e\u003cb\u003eHZSM-5(25)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArea 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArea 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOxygen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAluminium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilicon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e\u003cb\u003eHZSM-5(40)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArea 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb) the sample composition is homogeneous\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOxygen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAluminium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilicon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eHAADF STEM images of \u003cb\u003eHZSM-5(25)\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea) display large faceted particles (\u0026le;\u0026thinsp;5 \u0026micro;m) and numerous irregular particles\u0026thinsp;\u0026le;\u0026thinsp;100 nm in size. EDX maps (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb) demonstrate that the irregular particles (Area 2 in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb) of HZSM-5(25) contain almost no Al, in contrast to the faceted particles (Area 1), which is confirmed by the EDX results (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). HRTEM image of a HZSM-5(25) faceted particle (size\u0026thinsp;\u0026gt;\u0026thinsp;1 \u0026micro;m) is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec. This particle is layered. The two-dimensional Fourier spectrum in the inset (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec-I) corresponds to the MFI type structure [41] observed along the [\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\stackrel{-}{1}\\stackrel{-}{4}\\)\u003c/span\u003e\u003c/span\u003e3] zone axis. The two-dimensional Fourier spectrum of irregular particles 10\u0026ndash;20 nm in size (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec\u0026ndash;\u003cem\u003eII\u003c/em\u003e) does not show large interplanar distances, which are present in MFI type structure [41]. Moreover, observed interplanar distances and the angles between the crystallographic planes are not consistent with any high index zone axis. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec-\u003cem\u003eIII\u003c/em\u003e demonstrates a faceted particle with irregular particles on its surface, and the Fourier spectrum of one of them is shown in the inset. The structure of the phase in irregular particles, which does not correspond to MFI type phases [41], could not be determined.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eHZSM-5(40)\u003c/b\u003e consists of irregular particles close to spherical in shape (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb). HRTEM image of HZSM-5(40) particles is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec. The correspondent Fourier spectrum (inset to Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec) fits to the [111] direction of the MFI type structure [41].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSo, according to SEM and HAADF STEM data, together with EDX:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e- HZSM-5(12) consists of faceted particles ({100} or/and {010} faces; \u0026le; 500 nm in size, predominant size\u0026thinsp;~\u0026thinsp;400 nm) and irregular (\u0026le;\u0026thinsp;200 nm; predominantly\u0026thinsp;~\u0026thinsp;75 nm) ones with the MFI type structure and higher Al content (consistent with ICP AES results);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- HZSM-5(25) contains separate iron oxides inclusions and consists of large faceted particles ({001} faces; \u0026le; 5 \u0026micro;m in size, predominant size\u0026thinsp;~\u0026thinsp;800\u0026ndash;1000 nm) with the MFI type structure and irregular ones (\u0026le;\u0026thinsp;100 nm) containing no Al and not related to the MFI structure (consistent with ICP AES results - maximum Fe content in this sample). The heterophase nature of HZSM-5(25) (which was not determined by X-ray diffraction) should affect its functional characteristics, in particular catalytic activity, which will be discussed further.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- HZSM-5(40) consists of irregular, nearly spherical particles (predominant sizes of ~\u0026thinsp;100 nm and ~\u0026thinsp;500 nm) with the MFI type structure and uniform Al content;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e- HZSM-5(300) consists of faceted particles ({100}, {010}, {001} faces), predominant size\u0026thinsp;~\u0026thinsp;1200 nm) and irregular (\u0026lt;\u0026thinsp;250 nm, predominantly\u0026thinsp;~\u0026thinsp;75 nm) ones.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe different morphology and particle size of HZSM-5 samples are due to their synthesis conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): different composition of the aluminosilicate gel (templates, sources of silicon and aluminum and their ratios, pH) as well as various temperatures and duration of synthesis due to the changes in the crystallization rates of samples of different compositions (Si/Al).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eCatalytic activity of HZSM-5 in the reaction of nitrous oxide conversion\u003c/h2\u003e \u003cp\u003eThe activity and selectivity of MFI type catalysts are closely related to the strength and concentration of acid sites on their surface. The acidity of a solid is a general name referring to the strength of acid sites and their number on the surface of a solid (surface composition), as well as the nature of the acid sites: BAS (Br\u0026oslash;nsted acid sites \u0026ndash; bridging hydroxyls [Si-OH-Al] or LAS (Lewis acid sites - [Al\u003csup\u003e3+\u003c/sup\u003e O\u003csub\u003e4\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003e[]\u003csub\u003ex\u003c/sub\u003e]\u003csup\u003eσ\u0026lrm;+\u003c/sup\u003e).\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eAfter the deuterated acetonitrile (CD\u003csub\u003e3\u003c/sub\u003eCN) adsorption on HZSM-5(12, 25, 40, 40C, 300) OH-bands disappear from the spectra and a broad intense band appears with a maximum at ~\u0026thinsp;2761\u0026ndash;2776 cm\u003csup\u003e-1\u003c/sup\u003e (refers to O-D band) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b, c, d) except for HZSM-5(300) zeolite spectrum in which this band is absent (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). The difference between the wavenumbers (cm\u003csup\u003e-1\u003c/sup\u003e) of the absorption bands before (~\u0026thinsp;3610\u0026ndash;3612 cm\u003csup\u003e-1\u003c/sup\u003e) and after (~\u0026thinsp;2761\u0026ndash;2776 cm\u003csup\u003e-1\u003c/sup\u003e) adsorption gives shift values (Δ cm\u003csup\u003e-1\u003c/sup\u003e) that decrease in the row \u003cb\u003eHZSM-5(25)\u003c/b\u003e (Δ 849 cm\u003csup\u003e-1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40) (Δ 847 cm\u003csup\u003e-1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)C (Δ 844 cm\u003csup\u003e-1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(12) (Δ 834 cm\u003csup\u003e-1\u003c/sup\u003e) (\u003cem\u003esequence 2\u003c/em\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). This indicates the presence of strong \u003cb\u003eBASs\u003c/b\u003e [35\u0026ndash;37] on the surface of these zeolites, maximum for HZSM-5(25). There are no \u003cb\u003eBASs\u003c/b\u003e on the HZSM-5(300) surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, f).\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe ~\u0026thinsp;2315\u0026ndash;2321 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band on the DRIFT-CD\u003csub\u003e3\u003c/sub\u003eCN spectra of HZSM-5(12, 25, 40, 40C) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e) corresponds to the coordination of acetonitrile molecules by LASs [42\u0026ndash;44]. The maximum intensity of the ~\u0026thinsp;2315\u0026ndash;2321 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band is for \u003cb\u003eHZSM-5(12)\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea, f), which indicates the maximum LASs content in this zeolite: \u003cb\u003eHZSM-5(12)\u003c/b\u003e\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)C\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(25) (\u003cem\u003esequence 3\u003c/em\u003e).\u003c/p\u003e \u003cp\u003eThe blue shift of the frequency of C\u0026thinsp;\u0026equiv;\u0026thinsp;N stretching vibrations during CD\u003csub\u003e3\u003c/sub\u003eCN adsorption on LASs compared to the frequency in the gas phase (2253 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) [45] is 62\u0026ndash;68 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e for all samples, which indicates approximately the same LASs strength in the studied HZSM-5 (taking into account the step of \u0026plusmn;\u0026thinsp;4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eThe evacuation of the samples leads to the disappearance of the ~\u0026thinsp;2264\u0026ndash;2266 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band (refers to the physical adsorption of acetonitrile molecules [37, 42\u0026ndash;44]) in the spectra of all HZSM-5 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). The ~\u0026thinsp;2299\u0026thinsp;\u0026minus;\u0026thinsp;2298 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band in the DRIFT-CD\u003csub\u003e3\u003c/sub\u003eCN spectra of evacuated HZSM-5(12, 25, 40, 40C) is responsible for the coordination of acetonitrile molecules by BASs [37, 42\u0026ndash;44]. The blue shift of the frequency of C\u0026thinsp;\u0026equiv;\u0026thinsp;N stretching vibrations during CD\u003csub\u003e3\u003c/sub\u003eCN adsorption on BASs is approximately the same for HZSM-5(12, 25, 40, 40C) and is 45\u0026ndash;46 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea-d).\u003c/p\u003e \u003cp\u003eThere are no\u0026thinsp;~\u0026thinsp;2315\u0026ndash;2321 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and ~\u0026thinsp;2299\u0026ndash;2298 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e bands (which are responsible for the coordination of acetonitrile molecules by LASs and BASs, respectively) in the DRIFT-CD\u003csub\u003e3\u003c/sub\u003eCN spectra of HZSM-5(300) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ee), which means the absence of LASs and BASs on the HZSM-5(300) surface. The absorption band at ~\u0026thinsp;2111\u0026ndash;2115 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the DRIFT-CD\u003csub\u003e3\u003c/sub\u003eCN spectra of HZSM-5 refers to bending vibrations of C-D bonds in the CD\u003csub\u003e3\u003c/sub\u003e group (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe direct catalytic decomposition of N\u003csub\u003e2\u003c/sub\u003eO over the zeolite samples was performed in the temperature range of 400\u0026ndash;650\u0026deg;C. The samples were annealed at 700\u0026deg;C before the catalytic process but were not ground. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea shows conversion curves for each sample.\u003c/p\u003e \u003cp\u003eNitrous oxide decomposition starts simultaneously at 500\u0026deg;C, however, a furcation of the curves takes place with the increase in temperature. The conversion of nitrous oxide decreases in the row \u003cb\u003eHZSM-5(25)\u003c/b\u003e\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(12)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)С \u0026gt;\u0026gt; HZSM-5(300) (\u003cem\u003esequence 4\u003c/em\u003e). An increase in the catalytic activity of HZSM-5(25) is facilitated by iron oxides present in the sample (ICP AES and HAADF STEM), which were not detected by X-ray diffraction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn [46] iron oxides introduction into the framework voids and/or on the HZSM-5 surface were shown to contribute to the enhancement of the catalytic properties in the reactions involving Lewis bases, such as N\u003csub\u003e2\u003c/sub\u003eO decomposition [47]. Metal oxide catalysts are known [48] to have excellent redox performance and high N\u003csub\u003e2\u003c/sub\u003eO catalytic decomposition activity, making them very promising catalysts. It was shown in [49] that iron and its oxides had a strong catalytic effect on N\u003csub\u003e2\u003c/sub\u003eO: the increase in iron content improved the decomposition rate of N\u003csub\u003e2\u003c/sub\u003eO and promoted the overall N\u003csub\u003e2\u003c/sub\u003eO transformation.\u003c/p\u003e \u003cp\u003eIn this case, it can be assumed that, without taking into account the effect of iron ions, the conversion of nitrous oxide should decrease in the row \u003cb\u003eHZSM-5(12)\u003c/b\u003e\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(25)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)С \u0026gt;\u0026gt; HZSM-5(300) (\u003cem\u003esequence 4а\u003c/em\u003e) with a decrease in aluminum content (with an increase in Si/Al). This should indicate the decisive role in N\u003csub\u003e2\u003c/sub\u003eO catalytic conversion of Lewis acid sites ([AlO\u003csub\u003e4\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003e[]\u003csub\u003ex\u003c/sub\u003e]\u003csup\u003eσ\u0026lrm;+\u003c/sup\u003e), which are present in HZSM-5 along with Br\u0026oslash;nsted ones ([Si-OH-Al]) [8]. The content of BASs and LASs decreases respectively in the rows \u003cb\u003eHZSM-5(25)\u003c/b\u003e\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)C\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(12) (\u003cem\u003esequence 2\u003c/em\u003e) and \u003cb\u003eHZSM-5(12)\u003c/b\u003e\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)C\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(25) (\u003cem\u003esequence 3\u003c/em\u003e). It is possible that MOR zeolite impurity in HZSM-5(12) contributes to the reduction of BASs strength [50]. Note that maximum content of BASs in HZSM-5(25) is accompanied by minimum content of LASs (DRIFT). Comparing with each other the changes in the characteristics of HZSM-5 identified by different methods (\u003cem\u003esequences 1\u0026ndash;4\u003c/em\u003e), one can see that they describe the change in characteristics of both bulk properties (\u003cem\u003esequence 4)\u003c/em\u003e and surface ones (\u003cem\u003esequences 1, 2, 3\u003c/em\u003e). Moreover, the \u003cem\u003esequence 1\u003c/em\u003e (the change in textural characteristics depending on Si/Al) is logically consistent with the content of OH groups in the same zeolites. It is possible that the N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction occurs both on the particles\u0026rsquo; surface and in the samples\u0026rsquo; volume.\u003c/p\u003e \u003cp\u003eIt should be noted that no relationship between Al\u003csup\u003e3+\u003c/sup\u003e ions content in each crystallographic site of HZSM-5 structure and their catalytic activity was revealed [4], possibly due to the lack of a sufficient number of HZSM-5 samples with different silicate moduli obtained under the same controlled conditions.\u003c/p\u003e \u003cp\u003eThe possibility of the Lewis acid sites participation in the N\u003csub\u003e2\u003c/sub\u003eO decomposition was demonstrated in [51] where the complexation of N\u003csub\u003e2\u003c/sub\u003eO with BASs and LASs in high-silica HZSM-5 zeolites was studied by the IRS (Intelligent Reflecting Surfaces) method in diffuse-scattered light. It was shown that the strength of adsorption of the N\u003csub\u003e2\u003c/sub\u003eO-LAS complex is significantly superior to the N\u003csub\u003e2\u003c/sub\u003eO complex with a proton acid site (BAS). The difference in the strength of adsorption, according to the authors, is due to the different geometry of the N\u003csub\u003e2\u003c/sub\u003eO adsorption on acid sites. According to quantum-chemical calculations, the N\u003csub\u003e2\u003c/sub\u003eO molecule is adsorbed on the aprotic acid site (LAS) by a two-point mechanism with the participation of a three-coordinated aluminum atom and an adjacent basic oxygen atom. This adsorption complex is characterized by a higher interaction energy (261 kJ/mol) as compared to a single-point complex formed upon interaction with a proton center (BAS) (70 kJ/mol). Such a strong activation of the N\u003csub\u003e2\u003c/sub\u003eO molecule promotes its further decomposition. N\u003csub\u003e2\u003c/sub\u003eO-LAS complexes decompose at 200\u0026ndash;350\u0026deg;C, and it was found that the only product released into the gas phase is nitrogen, and oxygen is chemisorbed on the zeolite [51].\u003c/p\u003e \u003cp\u003eHowever, an increased content of LASs is not a determining factor in the increase in the HZSM-5 catalytic activity, which can be seen in the example of HZSM-5(40) and HZSM-5(40)C zeolites with different fabrication conditions: the catalytic reaction rate is higher for HZSM-5(40) (refined composition Si/Al\u0026thinsp;=\u0026thinsp;39) compared to HZSM-5(40)C (refined composition Si/Al\u0026thinsp;=\u0026thinsp;42) (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e), which has a lower intensity of the absorption band corresponding to LASs (~\u0026thinsp;2315\u0026ndash;2321 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec, d). It should be noted that the increase in the catalytic activity of HZSM-5(40) compared to HZSM-5(40)C is accompanied by an increase in the specific surface area (S\u003csub\u003eBET\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g) and outer surface area (S\u003csub\u003eext\u003c/sub\u003e, m\u003csup\u003e2\u003c/sup\u003e/g) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), i.e., of two competing factors - the active surface size and LASs content - the first one prevails. For the remaining zeolites, there is no direct relationship between these characteristics and the N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction rate (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eIt is important to note that the studied HZSM-5 samples have different morphologies (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) depending on synthesis condition. It is not excluded that HZSM-5(25) catalytic activity, determined from the N\u003csub\u003e2\u003c/sub\u003eO decomposition rate, is related precisely with the {001} faces, which does not contradict the data of [14].\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis work presents systematized data on the study of HZSM-5 aluminosilicalites with different silicate modules (Si/Al\u0026thinsp;=\u0026thinsp;12, 25, 40, 300) and synthesis conditions (different templates, silicon and aluminum sources and their ratio, aluminosilicate gel pH, temperature and duration of synthesis) by a complex of diffraction and complementary methods. Data obtained by EDX microanalysis, STEM and HRTEM on the phase composition of samples combined with the analysis of our previously obtained results made it possible to identify an impurity phase of iron oxide in HZSM-5(25), which was not determined by X-ray methods, but allowed to establish its role in this sample\u0026rsquo;s catalytic activity manifestation in N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction.\u003c/p\u003e \u003cp\u003eHZSM-5(25) demonstrates a significantly higher rate of N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction compared to previously studied samples of titanosilicalites [33] as well as Fe/Beta and Fe/SSZ-13 [52]. HZSM-5(25) turned out to be the most preferred catalyst in the N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction among aluminosilicalites under study. It differs not only in the maximum content of iron oxides, but also in morphology and composition, and contains the maximum amount of Br\u0026oslash;nsted acid sites, which apparently enhances HZSM-5(25) catalytic activity. This makes it promising for use in the direct catalytic decomposition of N\u003csub\u003e2\u003c/sub\u003eO, both alone and as a matrix for nanocomposites.\u003c/p\u003e \u003cp\u003eThe presented methodology for studying HZSM-5 aluminosilicalites with different silicate modules and the results of their detailed characterization (phase and elemental composition of the samples, composition of the main phase of the zeolite and the surface composition; crystal structure; microstructure with textural parameters, sizes and shapes of particles) with revealed correlations or explanations for their absence can be useful in studying other zeolites or modifying data.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eE.N. Domoroshchina:\u0026nbsp;\u003c/strong\u003eExperimental and theoretical analysis, Data curation, Writing \u0026ndash; review \u0026amp; editing;\u0026nbsp;\u003cstrong\u003eG\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003cstrong\u003eM\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eKuz\u003c/strong\u003e\u003cstrong\u003e\u0026rsquo;\u003c/strong\u003e\u003cstrong\u003emicheva\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Metodology, Conceptualization, XRPD measurements and their evaluation, Writing; \u003cstrong\u003eA.L. Vasiliev:\u003c/strong\u003e HAADF STEM,\u0026nbsp;EDX and HRTEM mesurements; \u003cstrong\u003eI.S. Pavlov:\u003c/strong\u003e HAADF STEM,\u0026nbsp;EDX and HRTEM measurements, Writing; \u003cstrong\u003eL.V. Pirutko:\u003c/strong\u003e HZSM-5 synthesis,\u0026nbsp;ICP AES\u0026nbsp;and BET measurements and evaluation; \u003cstrong\u003eO.P. Tkachenko:\u003c/strong\u003e DRIFTS measurements; \u003cstrong\u003eA.L. Kustov:\u003c/strong\u003e Catalytic tests, Writing.\u003c/p\u003e\n\u003cp\u003eConflicts\u0026nbsp;of\u0026nbsp;interest\u003c/p\u003e\n\u003cp\u003eThere are no conflicts to declare.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThis research was funded by Ministry of Science and Higher Education of the Russian Federation, grant number 0706-2020-0026.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eZeolite synthesis was partially supported by the Ministry of Science and Higher Education of the Russian Federation within the governmental order for Boreskov Institute of Catalysis.\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS.M.Al-Jubouri,\u0026nbsp;S.I.Al-Batty,\u0026nbsp;S.M.\u0026nbsp;Holmes, \u003cem\u003eMicroporous and Mesoporous Materials\u003c/em\u003e, 2021, 316, 110953, https://doi.org/10.1016/j.micromeso.2021.110953\u003c/li\u003e\n\u003cli\u003eA. Janda, A.T. 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Relationships between HZSM-5 silicate modulus (Si/Al) and pore volume, specific surface, the area of framework voids were established. Data obtained by electron microscopy and energy dispersive X-ray microanalysis explained the discrepancy between HZSM-5 real composition and the initial one. Samples with the maximum content of Br\u0026oslash;nsted (HZSM-5 with Si/Al\u0026thinsp;=\u0026thinsp;25) and Lewis (HZSM-5 with Si/Al\u0026thinsp;=\u0026thinsp;12) acid sites responsible for the catalytic activity were identified using diffuse reflectance Fourier transform infrared spectroscopy. N\u003csub\u003e2\u003c/sub\u003eO decomposition reaction rate was found to decrease in the row HZSM-5(25)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(12)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)\u0026thinsp;\u0026gt;\u0026thinsp;HZSM-5(40)С\u0026gt;\u0026gt;HZSM-5(300). The high N\u003csub\u003e2\u003c/sub\u003eO decomposition rate demonstrated by HZSM-5(25) makes it promising catalyst. The second phase of iron oxides and the presence of faceted particles {001} oriented in HZSM-5(25) were shown to contribute to its maximum catalytic activity in N\u003csub\u003e2\u003c/sub\u003eO decomposition. The applied methodology for studying aluminosilicalites with different silicate modules and the revealed correlations can provide a fundamental perspective in studying other zeolites or modifying data.\u003c/p\u003e","manuscriptTitle":"Rational Design of Aluminium-containing Zeolites with Typological Structure of HZSM-5 and Catalytic Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-02 17:16:43","doi":"10.21203/rs.3.rs-3796442/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c46590fd-5781-4446-bdc5-2ad9a3bf82fe","owner":[],"postedDate":"January 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-02-25T08:46:13+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-02 17:16:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3796442","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3796442","identity":"rs-3796442","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}