Imapct of the Al sites of ZSM-5 Zeolite on product distribution in methanol to aromatics reaction

Imapct of the Al sites of ZSM-5 Zeolite on product distribution in methanol to aromatics reaction | 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 Imapct of the Al sites of ZSM-5 Zeolite on product distribution in methanol to aromatics reaction Juanjuan Liu, Xiaohua Shen, Lixia Lin, Jianjun Lu, Yu Zhou This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5430628/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Feb, 2025 Read the published version in Journal of Porous Materials → Version 1 posted 13 You are reading this latest preprint version Abstract Great progress has been made in the methanol to aromatics (MTA) reaction over ZSM-5 zeolite, the location of Al atoms in ZSM-5 framework is very important for understanding the relationship among structure and activity of catalytic reaction system. In this paper, a series of ZSM-5 zeolites with different Al sites were prepared by changing the tetrapropyl ammonium hydroxide (TPAOH) content in the synthetic gel. The results showed that the quantity of Al sites at the channel intersections reach a maximum when the ratio of TPA + /Si increased to 0.4, and the selectivity of BTX increased from 16.15% to 24%, simultaneously. When the ratio of TPA + /Si continues to increase to 0.5, the catalytic performance decreases and the BTX selectivity decreases to 15%. Therefore, the Al loctaion effects the performance of ZSM-5 zeolite catalyst, and the zeolite with a higher proportion of Al in the intersection channels shows higher BTX selectivity in the methanol to aromatics reaction. This study elucidates the relationship between the distribution of MTA reaction products and Al sites, establishing the synthesis-structure-performance relationship of zeolite, and providing the experimental basis for rational design of catalysts. MTA reaction Al sites Acid BTX selectivity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Aromatics, especially light aromatics (benzene, toluene and p-xylene, BTX) are important raw materials in China. At present, BTX mainly produced from petrochemical processes. But China’s energy resources characteristic is abundant in coal and deficient in oil.. The methanol to aromatics (MTA) process is a new route for the preparation of light aromatics by coal-based methanol at present[ 1 – 4 ]. It is an efficient way for development of clean coal technology. ZSM-5 is a conventional solid acid catalysts for MTA process due to suitable acidity and shape selectivity[ 5 ]. The acid sites at different framework sites might be different in their catalytic behavior. The sites of Al atoms in the ZSM-5 zeolites determine the acid properties. Regulating the framework of Al siting should be effective to alter the reaction pathway. The distribution of Al affects the acidity of ZSM-5, determining the adsorption of reactants in zeolite pores and the desorption and diffusion of products. Thus,the Al sites play an vital role in the reaction pathway and distribution of reaction products of catalysts[ 6 – 9 ]. There are three types of pores and 12 diffience Al sites in ZSM-5. T8 and T11 are located in linear pore channels of the zeolite. T4 and T10 are located in sinusoidal pore channels. T1, T2, T3, T5, T6, T7, T9 and T12 are located at the intersection of linear and sinusoidal pore channels[ 11 ]. In addition, the [Al-O-(Si-O)n-Al] (n ≥ 3) structure of the zeolite is named "isolated Al" when the Al atoms are far apart in the framework. Adjacent "Al pairs" will form the [Al-O-(Si-O)n-Al] (n = 1,2) structure[ 10 – 12 ]. There are three kinds of Al pairs can be exchanged by three kinds of different bivalent cations, known as α, β and γ. The α sites are situated on the 10-member-ring straight channel. The β sites are at the intersections of the straight channel and the sinusoidal channel and the γ is located at the sinusoidal channel [ 13 ]. The content of tetrapropyl ammonium hydroxide (TPAOH) plays an important role in the crystallization process of ZSM-5 zeolite, which ditermines micro-morphology, pore structure, acid site, and the locations of framework aluminium. Tang[ 14 ] and Claireet [ 15 ] simulated the relationship between the distribution of framework aluminum in ZSM-5 zeolite and the organic structure guiding agent (OSDA) through density functional theory (DFT). The results showed that tetrapropyl ammonium (TPA + ) cations will make the distribution of Al atoms mainly at the intersection, and further effectively affect the catalytic performance.The experiment and theoretical simulations illustrate that the Al species at the intersection channels could lower the energy barrier of key aromatization step during CO 2 hydrogenation into value-added chemicals over Fe-ZSM-5[ 16 ]. The location of Al atoms in ZSM-5 zeolite can be modulated by changing different synthesis conditions.It remains challenging to properly design synthesis parameters to selectively place Al atoms in the disired sites [ 17 – 20 ].The understanding relationship among structure, composition and catalytic activity is helpful to develop new efficient catalyst. In this work, the framework Al (Al F ) siting in H-ZSM-5 was regulated through changing the ratio of TPA + /Si in the synthetic gel. With a varitey of characterization methods, the relation between the catalytic performance of H-ZSM-5 in MTA and Al sites of freamwork was clarified. 2. Experiment 2.1 Preparation of Z5-X samples ZSM-5 zeolite was prepared by traditional hydrothermal crystallization method, using sodium aluminate (NaAlO 2 ) as Al source, ethyl orthosilicate (TEOS; 98 wt%) as a Si source, and tetrapropyl ammonium hydroxide (TPAOH; 25 wt%) as the template agent, the initial sol ratio is SiO 2 :0.01Al 2 O 3 :0.02Na 2 O:xTPAOH:25H 2 O (x=0.2,0.3,0.4,0.5). Typically, the TPAOH was added into an aqueous mixture of NaAlO 2 and NaOH under vigorous stirring at room temperature for 1 h until a clear solution formed. Then, TEOS were dropped into the above solution and continued to stir for 4 h at room temperature. After stirring for 4 hours, the clear solution was transferred into a Teflon-lined autoclave and hydrothermally treated at 170 ℃ for 72 h. The products were centrifuged and washed with water until neutral pH. After dring for 12 h at 120 ℃ , the organic template was removed by calcination at 550 ℃ for 6 h in air. The as-calcined zeolites were ion-exchanged for three times with 1 mol L − 1 NH 4 Cl solution at 80 ℃ for 8 h to obtain H-ZSM-5. Then the prodcts were dried overnight and calcined at 550 ℃ for 6 h. The obtained samples were named Z5-0.2, Z5-0.3, Z5-0.4 and Z5-0.5, respectively. The most commonly used template is TPAOH, which has the best crystallization effect. The content of different TPAOH will have a great influence on the framework Al location, so we synthesized zeolite with different TPAOH content to explore its effects on the catalytic performance of MTA. 2.2. Characterization Powder X-ray diffraction (XRD) measurements were conducted by a LabX XRD-600 diffractometer using Cu-Kα (k = 1.5406 Å) radiation with a scanning size of 0.02° from 5° to 50°. TEM images were taken on a field transmission electron microscopy (JEM-2100F,JEOL,Japan). The sample was finely ground before the test, dispersed in anhydrous ethanol and ultrasonic for 8min, and then added to the copper mesh with an eyedropper. Nitrogen adsorption/desorption isotherms were measured at -196 ℃ on a TriStar II 3020 gas adsorption analyzer. Prior to the measurement, the zeolite sample was degassed under at 250 ℃, 10 -2 Pa vacuum for 4 h. The total surface area was calculated from the adsorption branch in the range of relative pressure from 0.05 to 0.25 by Brunauer−Emmett−Teller (BET) method; the micropore volume and external surface area were calculated from the isotherms by t-Plot method. Total pore volume was estimated at a nitrogen relative pressure of 0.99. Temperature-programmed desorption of NH 3 (NH 3 -TPD) was performed on a TP-5076 chemisorption analyzer. Approximately 100 mg of zeolite sample was first pretreated at 600 °C for 1.5 h in an nitrogen stream (30 mL·min −1 ) and then cooled to 120 °C. Saturated adsorption of NH 3 on the zeolite sample was achieved by introducing gaseous NH 3 into the sample tube for 30 min. After that, the physically adsorbed NH 3 was removed by flushing the sample tube with the nitrogen flow (30 mL·min −1 ) at 120 °C for 5 min, the zeolite sample was then heated up from 120 to 600 °C at a ramp of 10 °C min −1 . The quantities of weak and strong acid sites were determined by the amounts of ammonia desorbed at 120-250 °C and 250-550 °C. X-ray photoelectron spectrometer was characterized by EscaLab 250 Xi. The instrument uses the monochromatic Al Kα as the X-ray source (hv=1486.6 eV), the line source voltage and current are 16 kV and 14.9 mA, respectively. The C 1s peak (284.7 eV) is used as the binding energy of the calibration sample for charge correction. The diffuse reflectance (DR) UV-vis spectra of samples were tested on an Agilent Cary 5000 UV-vis spectrophotometer. Before measurement, the H-type samples were ion-exchanged to Na-type with 1.0 M NaCl solution for two times at 80 °C for 8 h, then the samples were ion-exchanged with 0.05 M Co(NO 3 ) 2 solution for three times at 80 °C for 2 h. After ion exchange, the Co ion exchange ZSM-5 sample was washed five times in deionized water and dried overnight in an air oven at 120 ℃. The samples were dehydrated at 500 ℃ and vacuum (<10 -1 Pa) for 5 h and cooled to room temperature. Solid state MAS NMR experiments were performed on a 600 MHz Bruker Avance III nuclear magnetic resonance spectrometer. Among them, the 27 Al MAS NMR adopts single pulse sequence with 4 mm probe, 1M Al(NO 3 ) 3 ·6H 2 O as the standard sample, and the corresponding rotating speed is 12 kHz. 2.3 Catalytic Activity Tests. The catalytic performance was tested in a continuously fixed bed reactor equipped with a cold trap (-5 ℃). For each test, 800 mg of catalyst with a sieving size of 40-60 mesh was loaded in the middle of the reactor and preheated with N 2 at 450 ℃ for 1 h. After the temperature was declined to 440 ℃, methanol was pumped into the reactor with a weight hourly space velocity (WHSV) of 1 h − 1 . N 2 was used as the balance gas and the flow rate was 35 mL·min −1 . The reaction products are separated into gas phase, liquid hydrocarbons and water using cold hydrazine separation. The chromatography was performed on a DM-5 capillary column (30 m×0.32 mm×0.5 μm) equiped with a hydrogen flame ion (FID) detector. The selectivity of C 5 -C 10 hydrocarbons and the main products were benzene, toluene and xylene. The aqueous phase products mainly include unreacted methanol, dimethyl ether and water, which are mainly used to calculate methanol conversion. The conversion of methanol (X n0 ), yield of aromatics (Y aro. ), selectivity of the BTX (S BTX ) calculated as below. Methanol conversion： 3. Results and discussion 3.1 Physicochemical property of ZSM-5 zeolites Figure 1 shows the X-ray diffraction spectra of ZSM-5 zeolites with different TPAOH content. All samples shows the strong diffraction peaks at 7.7°, 8.8°, 23.5° and 24°, which is consistent with the traditional MFI structure. There were few changes in the XRD patterns, all the samples were well-crystallized with high crystallinity. The relative crystallinity was calculated from the intensities of five characteristic peaks of 7.8, 8.8, 23.0, 23.9 and 24.4°[ 21 ]. With the increase of the TPAOH content, the relative crystallinity of ZSM-5 zeolite first increases then decreases. The amount of TPAOH has little effect on the formation of MFI framework. However, excessive amount of TPAOH change the aggregate state of SiO 4 4− during crystalization process. Therefore, the relative crystallinity decreased slightly when the ratio of TPAOH/SiO 2 increase to 0.5. TEM was carried out to further confirm the morphology of zeolite and the images are shown in Fig. 2 . It can be seen from Fig. 2 that the amount of TPAOH has a significant effect on the grain size of ZSM-5 zeolites. By changing the ratio of TPA + /SiO 2 , the samples Z5-0.2, Z5-0.3 and Z5-0.4 exhibit a typical hexagonal shaped by the accumulation of small nanocrystals. The particle size is mostly 300–400 nm and the surface of the zeolite has irregular holes. The morphology of Z5-0.5 changed obviously after TPAOH increase continuousiy. It is estimated that when the amount of TPAOH is small, TPAOH is not enough for Al species and Si species to form tetrahedron structure. Excessive TPAOH shortenes the nucleation time, accelerates the crystallization rate, which result in changing crystal size to affect morphology[ 22 ]. Figure 3 and Table 1 shows the N 2 adsorption/desorption isotherm curves and textural properties of the samples. As shown in Fig. 3 (a), all samples showed the typical characteristics of type Ⅳ isothermal curve. When p/p 0 is less than 0.1, Langmuir monolayer begins to adsorb, and the hysteresis in the middle segment is caused by capillary condensation during mesoporous adsorption, which is consistent with Fig. 3 (b). According to the Table 1 , Z5-0.4 has the largest micropore surface area and pore volume, more complete pore structure formation, and fewer defect sites. The results are in coincidence with those of XRD results. The crystallinity decreases when the ratio of TPAOH/SiO 2 increased to 0.5, and the pore surface area and volume decrease. All samples had mesopore volumes in the range of 0.1–0.15 cm 3 /g. The formation of mesopore can be attributed to the intercrystalline void space caused by the agglomeration of nanosized particles. Table 1 N 2 adsorption data of ZSM-5 zeolites with different TPAOH contents Z5-x (TPAOH/Si) specific surface area(m 2 /g) pore volume(cm 3 /g) S micro a S ext S BET a V micro b V meso V total c 0.2 260.18 73.34 333.52 0.099 0.108 0.207 0.3 289.64 79.84 369.48 0.097 0.127 0.224 0.4 293.55 86,08 379.63 0.106 0.145 0.375 0.5 252.89 70.12 323.01 0.075 0.106 0.181 a BET method b t-plot method c Volume adsorbed at p/p 0 = 0.99 Figure 4 shows the spectrum of NH 3 -TPD of ZSM-5 zeolite samples prepared by different TPAOH/Si ratios. It can be seen that all samples have two desorption peaks at 210 ~ 260 ℃ and 430 ~ 480 ℃ respectively, which are corresponding to weak and strong acid sites [ 5 , 27 – 30 ]. The amount of TPAOH has a great influence on the acidity and acid distribution of samples. According to Fig. 4 , the total acid content of ZSM-5 zeolite first increased and then decreased, all samples have almost the same desorption temperature.This result indicates that the synthesized ZSM-5 samples have similar acid strength under different TPAOH/Si ratios in the range of 0.2 ~ 0.5. According to Table 2 the proportion of weak acids reaches a maximum when the TPAOH/SiO 2 ratio is 0.4. Table 2 Acid scales of ZSM-5 zeolites with different TPAOH contents Z5-x (TPAOH/SiO 2 ) The amount of acidity Strong/Weak Weak acid site (℃) Weak Acidity (area) Strong acid site (℃) Strong Acidity (area) Middle Acid site (℃) Middle Acidity (area) 0.2 248.6 556.7 460.8 542.1 299.0 596.8 0.9756 0.3 246.6 734.5 458.2 780.3 296.4 689.8 0.9399 0.4 234.0 796.5 452.3 485.2 347.5 213.8 0.6091 0.5 234.7 334.5 431.0 312.8 291.0 164.9 0.9351 The reaction of methanol to hydrocarbons is a typical acid-catalyzed reaction, and the Al site of the zeolite framework is an important source of acidity [ 12 – 13 ]. Combining with the above results, it can be conclude that the Z5-X share similar physicochemical properties for Z5-0.2, Z5-0.3 and Z5-0.4. However, Z5-0.4 shows a better performance than others which may be determined by different Al location. 3.2 Framework Al location of ZSM-5 zeolite ZSM-5 zeolite contains a large number of Al, Si, O species. The distribution of Al sites of ZSM-5 zeolite can be estimated by XPS, NMR and Co-UV-vis characterization technology[ 7 , 30 ]. Figure 5 shows the XPS spectrum of ZSM-5 zeolite with the different ratio of TPAOH/SiO 2 . By charge correction of Al 2p and Si 2p, it can be seen that the chemical environment in all the ZSM-5 zeolite framework is similar [ 12 , 23 ]. Figure 5 (b)(c) is semi-quantitative analysis and fitting of Al and Si. Due to the content of TEOS in the synthesis gel remains constant, the spectrum of Si 2p almost remains unchanged.When the content of TPAOH increased, the Al content on the surface of ZSM-5 first climb up and then decline. The Al content on the surface of Z5-0.3 reached to 3.16% while the weak acid amount increased simultaneously. Al species are more easily dissolved than Si species in strong alkaline solution, therefore, the content of Al atoms on the surface decreased with the increase of pH values in the synthetic solution [ 31 ]. The Si/Al ratio on the surface of Z5-0.5 zeolite reached 58, which was approach the Si/Al ratio in the gel(according to the Table 3 ).The results indicated that Al is enriched on the surface of the synthesized ZSM-5 zeolite. The spatial distribution of Al pairs in the ZSM-5 framework was identified in detail through the individual types of the Co 2+ ions determined by UV-vis-DRS spectra, as seen in Table 3 . There are several bands between 14,000 to 23,000 cm − 1 , corresponding to d-d transitions of Co(II) ions exchanged by different framework Al sites[ 13 , 33 ].The broad absorption bands of Co(II) ions were deconvoluted into seven bands by Gaussian function, and are shown in Fig. 6 . The band at 15100 cm − 1 belongs to Co(II) ion (α) located in straight channels of the ten-member ring. The bands at 16000, 17150, 18600, and 21,200 cm − 1 are ascribed to Co(II) ions (β) occupied channel intersections, and the bands at 20100 and 22000 cm − 1 correspond to Co(II) ions in the sinusoidal channels (γ). Most of framework Al (Al F ) atoms, except for Z5-0.5, are located in channel intersections.As shown in the Table 3 , the proportion of Al F in channel intersections was about 87% for Z5-0.4 zeolite, and decreased to about 40% for Z5-0.5. TPA + first occupy the channel intersections of MFI-type zeolite due to large size, while AlO 4 − tetrahedrons with negative charge are also located in channel intersections for the charge effect. With the increase of TPAOH in the gel, it may block the channel intersections so that Al atoms will occupy the straight and sinusoidal channels for Z5-0.5[ 21 ]. However, the UV-vis-DRS spectrum of Co-ZSM-5 zeolite can only reflect the states of "Al pairs", while "Al pairs" in the zeolite account for about 60–70% of Al F content, and Co(II) ions cannot characterize all Al F distributions[ 33 ]. Therefore, Al F distributions with different TPAOH contents would be further analyzed by 27 Al MAS NMR. Table 3 Elements and distribution of ZSM-5 zeolites with different TPAOH contents Z5-x (TPAOH/Si) Al (wt%) a Si (wt%) a Extra-framework Si/Al (area) a Distributed of Al sites and relative peak areas(%) α (%) b β(%) b γ(%) b Z5-0.2 2.67 67.70 25.4 16.85 66.63 16.72 Z5-0.3 3.16 66.12 20.9 7.66 75.05 17.29 Z5-0.4 1.94 68.75 35.4 2.72 87.52 12.38 Z5-0.5 1.15 67.7 58.4 51.93 41.08 6.99 a detected by XPS b detected by Co-UV-vis DRS The 27 Al MAS NMR spectra revealed all Al F distributions, including those that cannot be coordinated by Co(II) cations[ 23 , 34 – 38 ]. Al states in ZSM-5 are revealed by solid-state NMR spectroscopy shown in Fig. 7 . Two peaks at 0 ppm and 55 ppm were observered in all the samples. The assignment of fomer peaks at 0 ppm were related to extra-framework Al (FEAL) species while the latter peaks at 55 pm were concern with tetrahedrally coordinated Al species in the ZSM-5 framework[ 25 ]. The peaks at 55 ppm are stronger than those at 0 ppm, confirming that the majority of Al species were four-coordinated framework Al in all Z5-x samples. The peak area at 0 ppm decreased wth the increse of TPAOH content for Z5-0.2 and Z5-0.3, which means that the extra-framework Al species decreased. It can be concluded that most of Al species incorporated into the framework of ZSM-5. The results explained the reason that the relative crystallinity increased with the increase of TPAOH content accroding to XRD patterns. Moreover, the 27 Al NMR peak at 55 ppm can be deconvoluted into five peaks at 52, 53, 54, 56, and 58 ppm, respectively[ 34 ]. Typically, the peak at 54 ppm corresponded to the framework Al species located at the intersection channels, while the peak at 56 ppm was relevant to the framework Al species located at either the straight or sinusoidal channels. Al sites at insection channel increased with the increase of TPAOH/Si ratio. Z5-0.4 shows the highest peak area at 54 ppm, accounting for 57.46%, which means that The Al species are mainly distributed in intersection channel. Non-framework Al species increases for Z5-0.5 a decrease in crystallinity which were consistent with the results of XRD. It can be seen that the Al 54 /Al 56 ratio gradually increased then decreased with the increase of the TPAOH/Si ratio from the Table 3 , which means that Al F in channel intersections increasing first and then decreased. Al 54 /Al 56 from the 27 Al MAS NMR spectra shows the same variation trend to the β/(α + γ) ratio from UV-vis-DRS of Co 2+ for all samples. The result indicted that the Al 54 /Al 56 ratio was in direct correlation to the value of β/(α + γ) for all samples. Table 4 Al site distribution of H-ZSM-5 zeolites synthesized with different TPAOH contents Samples Chemical shift (ppm) assignment of Al sites and relative peak areas(%) 56+54 (%) 54/56 52 53 Channel interaction Straight/ Sinusoidal 58 54 56 Z5-0.2 26.40 15.88 36.74 11.97 9.02 48.71 3.07 Z5-0.3 26.17 11.92 42.73 13.37 5.81 56.10 3.20 Z5-0.4 19.81 4.48 57.46 12.18 6.06 69.64 4.72 Z5-0.5 37.50 12.81 28.14 15.81 5.74 43.95 1.78 3.4 Catalytic performance in MTA reaction. The aromatization process of methanol with zeolite catalyst is a typical acid catalytic reaction. MTA reaction involves various reaction steps, such as dehydrogenation, isomerization, oligomerization, pyrolysis, aromatization, cyclization, etc. All processes play a crucial role in the product distribution. Figure 9 shows the methanol conversion and aromatics yield as a function of time on stream for MTA reaction over H-ZSM-5 with different TPAOH/Si ratios. The methanol conversion over all the ZSM-5 samples is close to 100%. The life of catalyst is within about 7 hours due to the micropore structure. The highest aromatics yield is 45% when TPAOH/SiO 2 ratio is 0.4 and TOS was 1h − 1 . When the TPAOH/Si ratios is increased to 0.5, the yield of aromatics significantly decreased to 24.53%, mainly due to the decrease of selectivity of toluene and xylene. According to the Fig. 10 and Table 5 , the selectivity of BTX increased from 16.15 wt% to 24.18 wt% with the increase of TPAOH/Si ratios.When the TPAOH/Si ratios is increased to 0.5, BTX selectivity is decreased to 15.15 wt%. Z5-0.4 showed the better catalytic performance than other samples. From the microstructure point of view in considering catalytic performance, the Al distribution played an important role in MTA reaction. The framework Al species at insection channel reached the maximum for Z4-0.4 and showed the highest aromatics yield. Different Al location is a key role in determing catalytic performance. The results of MTA reaction showed that framework Al located at the intersection channel is conducive to improving yield of aromatic. However, catalyst is easy to deposite carbon and deactivate. Figure 11 shows a linear correlation between the selectivity of BTX and framework Al distribution. Z5-0.4 shows a higher selectivity of aromatics because the Al pairs are more beneficial to hydrogen transfer reactions to form the aromatics[ 39 ]. Martínez et al.[ 40 ]demonstrated that the Al pairs in the channel intersections enhance the aromatic-based cycle. High densities of Al sites favour the hydrogen transfer reactions and alkane formation whereas in samples with low Al contents[ 42 ]. According to the double cycle mechanism, aromatics are mainly formed by dehydroaromatization of higher olefins, and accompanied by the formation of low carbon alkanes. One possible explanation is that part of the "retained alkenes" are converted to C 5 -C 9 non-aromatics [ 21 , 29 , 42 ]. It is the Al species located at intersection channel that led to increse aromatics yield and improve catalytic performance, but how to prevent carbon accumulation and improve the catalyst life needs further research [ 42 – 45 ]. Table 5 Main product distribution of methanol conversion on ZSM-5 with different TPAOH contents Samples B T X BTX C 8 C 9 C 9 + X-Xylene P-Xylene 124 135 Z5-0.2 0.35 1.46 1.48 12.86 16.15 8.80 6.09 5.59 13.67 Z5-0.3 0.64 2.65 1.22 13.67 18.18 9.31 6.40 3.53 10.49 Z5-0.4 1.02 4.75 1.98 16.43 24.18 9.37 5.35 3.29 15.06 Z5-0.5 1.00 1.66 1.29 11.24 15.15 7.94 5.96 4.50 9.38 4. Conclusion In summary, we systematically investigated the influence of Al siting in zeolite channels on the product BTX selectivity in MTA reaction. Since Al pairs in the channel intersections occupy a large space, whcih means a small resistance to transitional states of aromatic hydrocarbons in aromatic-based cycle, thus displaying high BTX selectivity. In addition, the well balance between the quantities of weak and strong acid sites is favor of aromatics selectivity in the methanol to aromatics reaction. Weak acid ammount was closely related to the Al locations in ZSM-5 zeolite framework. The zeolite with a high proportion of Al in the channel intersections showed higher catalytic performance in the methanol to aromatics reaction. This study reveals that the product distribution in the methanol to aromatics reaction is controlled by the Al location of ZSM-5 zeolite by different TPAOH contents. Declarations Author Contributions Juanjuan Liu: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Data Curation, Writing - Original Draft, Writing - Review & Editing. Xiaohua Shen: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Review & Editing, Supervision, Project administration, Funding acquisition. Lixia Lin: Supervision, Funding acquisition. Jianjun Lu: Validation, Supervision, Project administration, Funding acquisition. Yu Zhou: performed catalyst characterizations. Acknowledgements We gratefully acknowledge financial support from the National Natural Science Foundation of China (No.22278296). Availability of Data and Materials All data generated or analyzed during this study are included in this published article. Conflicts of Interest The authors declare no conflicts of interest. References Yang L, Liu Z, Liu Z, et al. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 05 Feb, 2025 Read the published version in Journal of Porous Materials → Version 1 posted Editorial decision: Revision requested 24 Nov, 2024 Reviews received at journal 23 Nov, 2024 Reviews received at journal 21 Nov, 2024 Reviewers agreed at journal 15 Nov, 2024 Reviewers agreed at journal 14 Nov, 2024 Reviews received at journal 13 Nov, 2024 Reviewers agreed at journal 13 Nov, 2024 Reviewers agreed at journal 12 Nov, 2024 Reviewers agreed at journal 12 Nov, 2024 Reviewers invited by journal 12 Nov, 2024 Editor assigned by journal 11 Nov, 2024 Submission checks completed at journal 11 Nov, 2024 First submitted to journal 11 Nov, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5430628","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":381927149,"identity":"350c726f-b6dd-4c35-8d3b-02c17798de84","order_by":0,"name":"Juanjuan Liu","email":"","orcid":"","institution":"College of Chemistry and Chemical Engineering , Taiyuan University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Juanjuan","middleName":"","lastName":"Liu","suffix":""},{"id":381927151,"identity":"8205be44-1af0-41c8-8453-ab036b36a305","order_by":1,"name":"Xiaohua Shen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7UlEQVRIiWNgGAWjYDACCRBhAEaMD6BiBkRrYTY4AOETowWijE2CKC3ys5uPPeYpsJMzl0h+Vv2x7XAdA3vzNgmGmjs4tRjcOZZuOMMg2dhyRprZjYNthyUYeI6VSTAce4Zbi0SOmcQHA+bEDTcSoFpAIowNh3E7bEb+N4kEg3qglvRvBWAt8m/wa2G4kcMGtOUwUEuOGQPEFh78WgxupJlJzjA4bmxw5k2xxJlz6ZJtPGnFFgnH8Dks+Zk0z59qOYPj6Rs/VJRZ8/OzH95440MNHoehAEY2YOyAGAlEagCCP8QrHQWjYBSMgpEDANCsU7iZrq3RAAAAAElFTkSuQmCC","orcid":"","institution":"College of Chemistry and Chemical Engineering , Taiyuan University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Xiaohua","middleName":"","lastName":"Shen","suffix":""},{"id":381927154,"identity":"3f04f02b-f4b4-49f5-ac4e-dd670e3afe6b","order_by":2,"name":"Lixia Lin","email":"","orcid":"","institution":"College of Chemistry and Chemical Engineering , Taiyuan University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Lixia","middleName":"","lastName":"Lin","suffix":""},{"id":381927157,"identity":"5164f6be-378d-4a95-9ac1-3f9ae3ea01a3","order_by":3,"name":"Jianjun Lu","email":"","orcid":"","institution":"College of Textile Engineering, Taiyuan University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Jianjun","middleName":"","lastName":"Lu","suffix":""},{"id":381927158,"identity":"55dab9f1-0bac-4a8e-a8dc-63e85d9c1a9e","order_by":4,"name":"Yu Zhou","email":"","orcid":"","institution":"College of Chemistry and Chemical Engineering , Taiyuan University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Zhou","suffix":""}],"badges":[],"createdAt":"2024-11-11 09:23:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5430628/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5430628/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10934-025-01765-2","type":"published","date":"2025-02-05T15:57:56+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":70119798,"identity":"df9425b7-b895-49eb-b9fc-d138059d4345","added_by":"auto","created_at":"2024-11-28 13:58:21","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":989357,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of ZSM-5 zeolite under different TPAOH contents\u003c/p\u003e","description":"","filename":"Fig.1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/ddaf6aad47a41042d9d1beef.jpg"},{"id":70119805,"identity":"f8d40c00-1810-48c9-9c5f-63b3307732f0","added_by":"auto","created_at":"2024-11-28 13:58:21","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":416255,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e","description":"","filename":"Fig.2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/17a49ca2488f37431e210181.jpg"},{"id":70119801,"identity":"352eed96-dc7e-4430-8fc3-eacaf75613aa","added_by":"auto","created_at":"2024-11-28 13:58:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":212043,"visible":true,"origin":"","legend":"\u003cp\u003eNitrogen adsorption and desorption curves (a) and pore size distribution curves (b) of ZSM-5 zeolite with different TPAOH content\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/10d97a53efa764eccb9f9102.png"},{"id":70120081,"identity":"570ad936-a5e9-44c6-8bed-215f55586ace","added_by":"auto","created_at":"2024-11-28 14:06:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":235257,"visible":true,"origin":"","legend":"\u003cp\u003eNH3-TPD amount of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/02e435c5e5e3a914449c708a.png"},{"id":70120085,"identity":"e6a15e02-de70-49c3-b184-7bbfd0e18468","added_by":"auto","created_at":"2024-11-28 14:06:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":270108,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Full XPS spectrum of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e\n\u003cp\u003e(b) Al 2p fitting spectrum (c) Si 2p Spectrum\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/343366ad258efbc6195d2da6.png"},{"id":70120986,"identity":"ddbd6926-151c-43e3-811d-62709ccd16c7","added_by":"auto","created_at":"2024-11-28 14:14:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":269088,"visible":true,"origin":"","legend":"\u003cp\u003eUV-vis-DRS spectra of Co-ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/b304483432ecfaca7a9fff17.png"},{"id":70119799,"identity":"f2893d6e-dbd8-4e2a-a628-68fb0d9d63c8","added_by":"auto","created_at":"2024-11-28 13:58:21","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":786132,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e27\u003c/sup\u003eAl MAS NMR of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e","description":"","filename":"Fig.7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/d7f8bc85d2a9cf783a2ea9df.jpg"},{"id":70120084,"identity":"1e34390e-7601-48ec-82c2-0ce99796667d","added_by":"auto","created_at":"2024-11-28 14:06:21","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":125329,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e27\u003c/sup\u003eAl MAS NMR sub-peak fitting of ZSM-5 with different TPAOH contents\u003c/p\u003e","description":"","filename":"Fig.8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/068dc076240c7ecd981da46c.jpg"},{"id":70120985,"identity":"e2c93d60-338d-4874-95a9-bc8df8df794a","added_by":"auto","created_at":"2024-11-28 14:14:21","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1178830,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram of methanol conversion and aromatics yield of methanol to aromatics catalyzed by ZSM-5 with different TPAOH contents\u0026nbsp; (reaction conditions: T=440 ℃, P=0.1MPa, WHSV=1h\u003csup\u003e-1\u003c/sup\u003e)\u0026nbsp;\u003c/p\u003e","description":"","filename":"Fig.9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/60d6968b7c4b2d89b5ad9131.jpg"},{"id":70119808,"identity":"fc8707ba-048e-4717-bf0f-535a40bd8e31","added_by":"auto","created_at":"2024-11-28 13:58:21","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":876911,"visible":true,"origin":"","legend":"\u003cp\u003eMTA liquid phase product distribution of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e\n\u003cp\u003e(Reaction conditions: TOS=4 h，T=440 ℃, P=0.1 MPa, WHSV=1h\u003csup\u003e-1\u003c/sup\u003e)\u0026nbsp;\u003c/p\u003e","description":"","filename":"Fig.10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/0afd8c12ec8806928a975ecd.jpg"},{"id":70120082,"identity":"4d08df09-9dc8-4875-abc8-64062cc2c322","added_by":"auto","created_at":"2024-11-28 14:06:21","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":29713,"visible":true,"origin":"","legend":"\u003cp\u003eLinear dependency relation-ships obtained by linear fitting using the data of MTA catalytic reactions and frame-work Al distributions: \u003csup\u003e27\u003c/sup\u003eAl NMR MAS Al in channel intersections versus BTX selectivity\u003c/p\u003e","description":"","filename":"Fig.11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/423e5aaf47c5776c2916af56.jpg"},{"id":75930483,"identity":"1b2ef55a-8b52-440f-8588-ba4e523c0492","added_by":"auto","created_at":"2025-02-10 16:12:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6096721,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5430628/v1/80846f05-8f32-485a-ae7c-8bf3908caee3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Imapct of the Al sites of ZSM-5 Zeolite on product distribution in methanol to aromatics reaction","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAromatics, especially light aromatics (benzene, toluene and p-xylene, BTX) are important raw materials in China. At present, BTX mainly produced from petrochemical processes. But China\u0026rsquo;s energy resources characteristic is abundant in coal and deficient in oil.. The methanol to aromatics (MTA) process is a new route for the preparation of light aromatics by coal-based methanol at present[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. It is an efficient way for development of clean coal technology. ZSM-5 is a conventional solid acid catalysts for MTA process due to suitable acidity and shape selectivity[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The acid sites at different framework sites might be different in their catalytic behavior. The sites of Al atoms in the ZSM-5 zeolites determine the acid properties. Regulating the framework of Al siting should be effective to alter the reaction pathway. The distribution of Al affects the acidity of ZSM-5, determining the adsorption of reactants in zeolite pores and the desorption and diffusion of products. Thus,the Al sites play an vital role in the reaction pathway and distribution of reaction products of catalysts[\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThere are three types of pores and 12 diffience Al sites in ZSM-5. T8 and T11 are located in linear pore channels of the zeolite. T4 and T10 are located in sinusoidal pore channels. T1, T2, T3, T5, T6, T7, T9 and T12 are located at the intersection of linear and sinusoidal pore channels[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. In addition, the [Al-O-(Si-O)n-Al] (n\u0026thinsp;\u0026ge;\u0026thinsp;3) structure of the zeolite is named \"isolated Al\" when the Al atoms are far apart in the framework. Adjacent \"Al pairs\" will form the [Al-O-(Si-O)n-Al] (n\u0026thinsp;=\u0026thinsp;1,2) structure[\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. There are three kinds of Al pairs can be exchanged by three kinds of different bivalent cations, known as α, β and γ. The α sites are situated on the 10-member-ring straight channel. The β sites are at the intersections of the straight channel and the sinusoidal channel and the γ is located at the sinusoidal channel [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The content of tetrapropyl ammonium hydroxide (TPAOH) plays an important role in the crystallization process of ZSM-5 zeolite, which ditermines micro-morphology, pore structure, acid site, and the locations of framework aluminium. Tang[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] and Claireet [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] simulated the relationship between the distribution of framework aluminum in ZSM-5 zeolite and the organic structure guiding agent (OSDA) through density functional theory (DFT). The results showed that tetrapropyl ammonium (TPA\u003csup\u003e+\u003c/sup\u003e) cations will make the distribution of Al atoms mainly at the intersection, and further effectively affect the catalytic performance.The experiment and theoretical simulations illustrate that the Al species at the intersection channels could lower the energy barrier of key aromatization step during CO\u003csub\u003e2\u003c/sub\u003e hydrogenation into value-added chemicals over Fe-ZSM-5[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe location of Al atoms in ZSM-5 zeolite can be modulated by changing different synthesis conditions.It remains challenging to properly design synthesis parameters to selectively place Al atoms in the disired sites [\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].The understanding relationship among structure, composition and catalytic activity is helpful to develop new efficient catalyst. In this work, the framework Al (Al\u003csub\u003eF\u003c/sub\u003e) siting in H-ZSM-5 was regulated through changing the ratio of TPA\u003csup\u003e+\u003c/sup\u003e/Si in the synthetic gel. With a varitey of characterization methods, the relation between the catalytic performance of H-ZSM-5 in MTA and Al sites of freamwork was clarified.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cp\u003e\u003cstrong\u003e2.1 Preparation of Z5-X samples\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZSM-5 zeolite was prepared by traditional hydrothermal crystallization method, using sodium aluminate (NaAlO\u003csub\u003e2\u003c/sub\u003e) as Al source, ethyl orthosilicate (TEOS; 98 wt%) as a Si source, and tetrapropyl ammonium hydroxide (TPAOH; 25 wt%) as the template agent, the initial sol ratio is SiO\u003csub\u003e2\u003c/sub\u003e:0.01Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:0.02Na\u003csub\u003e2\u003c/sub\u003eO:xTPAOH:25H\u003csub\u003e2\u003c/sub\u003eO (x=0.2,0.3,0.4,0.5).\u0026nbsp;Typically, the TPAOH was added into an aqueous mixture of NaAlO\u003csub\u003e2\u003c/sub\u003e and NaOH under vigorous stirring at room temperature for 1 h until a clear solution formed. Then, TEOS were dropped into the above solution and continued to stir for 4 h at room temperature. After stirring for 4 hours, the clear solution was transferred into a Teflon-lined autoclave and hydrothermally treated at 170 ℃ for 72 h. The products were centrifuged and washed with water until neutral pH. After dring for 12 h at 120 ℃ , the organic template was removed by calcination at 550 ℃ for 6 h in air. The as-calcined zeolites were ion-exchanged for three times with 1 mol L\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e1\u0026nbsp;\u003c/sup\u003eNH\u003csub\u003e4\u003c/sub\u003eCl solution at 80 ℃ for 8 h to obtain H-ZSM-5. Then the prodcts were dried overnight and calcined at 550 ℃ for 6 h. The obtained samples were named Z5-0.2, Z5-0.3, Z5-0.4 and Z5-0.5, respectively.\u003c/p\u003e\n\u003cp\u003eThe most commonly used template is TPAOH, which has the best crystallization effect. The content of different TPAOH will have a great influence on the framework Al location, so we synthesized zeolite with different TPAOH content to explore its effects on the catalytic performance of MTA.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003e2.2. Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePowder X-ray diffraction (XRD) measurements were conducted by a LabX XRD-600 diffractometer using Cu-K\u0026alpha; (k = 1.5406 \u0026Aring;) radiation with a scanning size of 0.02\u0026deg; from 5\u0026deg; to 50\u0026deg;. TEM images were taken on a field transmission electron microscopy (JEM-2100F,JEOL,Japan). The sample was finely ground before the test, dispersed in anhydrous ethanol and ultrasonic for 8min, and then added to the copper mesh with an eyedropper.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNitrogen adsorption/desorption isotherms were measured at -196 ℃ on a TriStar II 3020 gas adsorption analyzer. Prior to the measurement, the zeolite sample was degassed under at 250 ℃, 10\u003csup\u003e-2\u003c/sup\u003e Pa vacuum for 4 h. The total surface area was calculated from the adsorption branch in the range of relative pressure from 0.05 to 0.25 by Brunauer\u0026minus;Emmett\u0026minus;Teller (BET) method; the micropore volume and external surface area were calculated from the isotherms by t-Plot method. Total pore volume was estimated at a nitrogen relative pressure of 0.99.\u003c/p\u003e\n\u003cp\u003eTemperature-programmed desorption of NH\u003csub\u003e3\u003c/sub\u003e (NH\u003csub\u003e3\u003c/sub\u003e-TPD) was performed on a TP-5076 chemisorption analyzer. Approximately 100 mg of zeolite sample was first pretreated at 600 \u0026deg;C for 1.5 h in an nitrogen stream (30 mL\u0026middot;min\u003csup\u003e\u0026minus;1\u003c/sup\u003e) and then cooled to 120 \u0026deg;C. Saturated adsorption of NH\u003csub\u003e3\u0026nbsp;\u003c/sub\u003eon the zeolite sample was achieved by introducing gaseous NH\u003csub\u003e3\u003c/sub\u003e into the sample tube for 30 min. After that, the physically adsorbed NH\u003csub\u003e3\u003c/sub\u003e was removed by flushing the sample tube with the nitrogen flow (30 mL\u0026middot;min\u003csup\u003e\u0026minus;1\u003c/sup\u003e) at 120 \u0026deg;C for 5 min, the zeolite sample was then heated up from 120 to 600 \u0026deg;C at a ramp of 10 \u0026deg;C min\u003csup\u003e\u0026minus;1\u003c/sup\u003e. The quantities of weak and strong acid sites were determined by the amounts of ammonia desorbed at 120-250 \u0026deg;C and 250-550 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eX-ray photoelectron spectrometer was characterized by EscaLab 250 Xi. The instrument uses the monochromatic Al K\u0026alpha; as the X-ray source (hv=1486.6 eV), the line source voltage and current are 16 kV and 14.9 mA, respectively. The C\u003csub\u003e1s\u003c/sub\u003e peak (284.7 eV) is used as the binding energy of the calibration sample for charge correction.\u003c/p\u003e\n\u003cp\u003eThe diffuse reflectance (DR) UV-vis spectra of samples were tested on an Agilent Cary 5000 UV-vis spectrophotometer.\u0026nbsp;Before measurement, the H-type samples were ion-exchanged to Na-type with 1.0 M NaCl solution for two times at 80 \u0026deg;C for 8 h, then the samples were ion-exchanged with 0.05 M Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e solution for three times at 80 \u0026deg;C for 2 h. After ion exchange, the Co ion exchange ZSM-5 sample was washed five times in deionized water and dried overnight in an air oven at 120 ℃. The samples were dehydrated at 500 ℃ and vacuum (\u0026lt;10\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003ePa) for 5 h and cooled to room temperature.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSolid state MAS NMR experiments were performed on a 600 MHz Bruker Avance III nuclear magnetic resonance spectrometer. Among them, the \u003csup\u003e27\u003c/sup\u003eAl MAS NMR adopts single pulse sequence with 4 mm probe, 1M Al(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO as the standard sample, and the corresponding rotating speed is 12 kHz.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Catalytic Activity Tests.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe catalytic performance was tested in a continuously fixed bed reactor equipped with a cold trap (-5 ℃). For each test, 800 mg of catalyst with a sieving size of 40-60 mesh was loaded in the middle of the reactor and preheated with N\u003csub\u003e2\u003c/sub\u003e at 450 ℃ for 1 h.\u003c/p\u003e\n\u003cp\u003eAfter the temperature was declined to 440 ℃, methanol was pumped into the reactor with a weight hourly space velocity (WHSV) of 1 h\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e. N\u003csub\u003e2\u003c/sub\u003e was used as the balance gas and the flow rate was 35 mL\u0026middot;min\u003csup\u003e\u0026minus;1\u003c/sup\u003e. The reaction products are separated into gas phase, liquid hydrocarbons and water using cold hydrazine separation.\u003c/p\u003e\n\u003cp\u003eThe chromatography was performed on a DM-5 capillary column (30 m\u0026times;0.32 mm\u0026times;0.5 \u0026mu;m) equiped with a hydrogen flame ion (FID) detector. The selectivity of C\u003csub\u003e5\u003c/sub\u003e-C\u003csub\u003e10\u003c/sub\u003e hydrocarbons and the main products were benzene, toluene and xylene. The aqueous phase products mainly include unreacted methanol, dimethyl ether and water, which are mainly used to calculate methanol conversion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe conversion of methanol (X\u003csub\u003en0\u003c/sub\u003e), yield of aromatics (Y\u003csub\u003earo.\u003c/sub\u003e), selectivity of the BTX (S\u003csub\u003eBTX\u003c/sub\u003e) calculated as below.\u003c/p\u003e\n\u003cp\u003eMethanol conversion：\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Physicochemical property of ZSM-5 zeolites\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the X-ray diffraction spectra of ZSM-5 zeolites with different TPAOH content. All samples shows the strong diffraction peaks at 7.7\u0026deg;, 8.8\u0026deg;, 23.5\u0026deg; and 24\u0026deg;, which is consistent with the traditional MFI structure. There were few changes in the XRD patterns, all the samples were well-crystallized with high crystallinity. The relative crystallinity was calculated from the intensities of five characteristic peaks of 7.8, 8.8, 23.0, 23.9 and 24.4\u0026deg;[\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. With the increase of the TPAOH content, the relative crystallinity of ZSM-5 zeolite first increases then decreases. The amount of TPAOH has little effect on the formation of MFI framework. However, excessive amount of TPAOH change the aggregate state of SiO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e during crystalization process. Therefore, the relative crystallinity decreased slightly when the ratio of TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e increase to 0.5.\u003c/p\u003e\n \u003cp\u003eTEM was carried out to further confirm the morphology of zeolite and the images are shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. It can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e that the amount of TPAOH has a significant effect on the grain size of ZSM-5 zeolites. By changing the ratio of TPA\u003csup\u003e+\u003c/sup\u003e/SiO\u003csub\u003e2\u003c/sub\u003e, the samples Z5-0.2, Z5-0.3 and Z5-0.4 exhibit a typical hexagonal shaped by the accumulation of small nanocrystals. The particle size is mostly 300\u0026ndash;400 nm and the surface of the zeolite has irregular holes. The morphology of Z5-0.5 changed obviously after TPAOH increase continuousiy. It is estimated that when the amount of TPAOH is small, TPAOH is not enough for Al species and Si species to form tetrahedron structure. Excessive TPAOH shortenes the nucleation time, accelerates the crystallization rate, which result in changing crystal size to affect morphology[\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption isotherm curves and textural properties of the samples. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(a), all samples showed the typical characteristics of type Ⅳ isothermal curve. When p/p\u003csub\u003e0\u003c/sub\u003e is less than 0.1, Langmuir monolayer begins to adsorb, and the hysteresis in the middle segment is caused by capillary condensation during mesoporous adsorption, which is consistent with Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b). According to the Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, Z5-0.4 has the largest micropore surface area and pore volume, more complete pore structure formation, and fewer defect sites. The results are in coincidence with those of XRD results. The crystallinity decreases when the ratio of TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e increased to 0.5, and the pore surface area and volume decrease. All samples had mesopore volumes in the range of 0.1\u0026ndash;0.15 cm\u003csup\u003e3\u003c/sup\u003e/g. The formation of mesopore can be attributed to the intercrystalline void space caused by the agglomeration of nanosized particles.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eN\u003csub\u003e2\u003c/sub\u003e adsorption data of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eZ5-x\u003c/p\u003e\n \u003cp\u003e(TPAOH/Si)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003especific surface area(m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003epore volume(cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003csub\u003emicro\u003c/sub\u003e\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003csub\u003eext\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003csub\u003eBET\u003c/sub\u003e\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eV\u003csub\u003emicro\u003c/sub\u003e\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eV\u003csub\u003emeso\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eV\u003csub\u003etotal\u003c/sub\u003e\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e260.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e333.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.099\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.207\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e289.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e369.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.097\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.127\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.224\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e293.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e86,08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e379.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.106\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.375\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e252.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e323.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.075\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.106\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.181\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003ea\u003c/sup\u003eBET method\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003eb\u003c/sup\u003et-plot method\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003ec\u003c/sup\u003eVolume adsorbed at p/p\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.99\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows the spectrum of NH\u003csub\u003e3\u003c/sub\u003e-TPD of ZSM-5 zeolite samples prepared by different TPAOH/Si ratios. It can be seen that all samples have two desorption peaks at 210\u0026thinsp;~\u0026thinsp;260 ℃ and 430\u0026thinsp;~\u0026thinsp;480 ℃ respectively, which are corresponding to weak and strong acid sites [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The amount of TPAOH has a great influence on the acidity and acid distribution of samples. According to Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the total acid content of ZSM-5 zeolite first increased and then decreased, all samples have almost the same desorption temperature.This result indicates that the synthesized ZSM-5 samples have similar acid strength under different TPAOH/Si ratios in the range of 0.2\u0026thinsp;~\u0026thinsp;0.5. According to Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e the proportion of weak acids reaches a maximum when the TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e ratio is 0.4.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAcid scales of ZSM-5 zeolites with different TPAOH contents\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eZ5-x\u003c/p\u003e\n \u003cp\u003e(TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"6\"\u003e\n \u003cp\u003eThe amount of acidity\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eStrong/Weak\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWeak acid site (℃)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWeak Acidity\u003c/p\u003e\n \u003cp\u003e(area)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStrong acid site (℃)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStrong Acidity\u003c/p\u003e\n \u003cp\u003e(area)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMiddle\u003c/p\u003e\n \u003cp\u003eAcid site\u003c/p\u003e\n \u003cp\u003e(℃)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMiddle\u003c/p\u003e\n \u003cp\u003eAcidity\u003c/p\u003e\n \u003cp\u003e(area)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e248.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e556.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e460.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e542.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e299.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e596.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9756\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e246.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e734.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e458.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e780.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e296.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e689.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9399\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e234.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e796.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e452.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e485.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e347.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e213.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6091\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e234.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e334.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e431.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e312.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e291.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e164.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9351\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe reaction of methanol to hydrocarbons is a typical acid-catalyzed reaction, and the Al site of the zeolite framework is an important source of acidity [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Combining with the above results, it can be conclude that the Z5-X share similar physicochemical properties for Z5-0.2, Z5-0.3 and Z5-0.4. However, Z5-0.4 shows a better performance than others which may be determined by different Al location.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Framework Al location of ZSM-5 zeolite\u003c/h2\u003e\n \u003cp\u003eZSM-5 zeolite contains a large number of Al, Si, O species. The distribution of Al sites of ZSM-5 zeolite can be estimated by XPS, NMR and Co-UV-vis characterization technology[\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the XPS spectrum of ZSM-5 zeolite with the different ratio of TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e. By charge correction of Al 2p and Si 2p, it can be seen that the chemical environment in all the ZSM-5 zeolite framework is similar [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(b)(c) is semi-quantitative analysis and fitting of Al and Si. Due to the content of TEOS in the synthesis gel remains constant, the spectrum of Si 2p almost remains unchanged.When the content of TPAOH increased, the Al content on the surface of ZSM-5 first climb up and then decline. The Al content on the surface of Z5-0.3 reached to 3.16% while the weak acid amount increased simultaneously. Al species are more easily dissolved than Si species in strong alkaline solution, therefore, the content of Al atoms on the surface decreased with the increase of pH values in the synthetic solution [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. The Si/Al ratio on the surface of Z5-0.5 zeolite reached 58, which was approach the Si/Al ratio in the gel(according to the Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).The results indicated that Al is enriched on the surface of the synthesized ZSM-5 zeolite.\u003c/p\u003e\n \u003cp\u003eThe spatial distribution of Al pairs in the ZSM-5 framework was identified in detail through the individual types of the Co\u003csup\u003e2+\u003c/sup\u003e ions determined by UV-vis-DRS spectra, as seen in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. There are several bands between 14,000 to 23,000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to d-d transitions of Co(II) ions exchanged by different framework Al sites[\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].The broad absorption bands of Co(II) ions were deconvoluted into seven bands by Gaussian function, and are shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The band at 15100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e belongs to Co(II) ion (\u0026alpha;) located in straight channels of the ten-member ring. The bands at 16000, 17150, 18600, and 21,200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are ascribed to Co(II) ions (\u0026beta;) occupied channel intersections, and the bands at 20100 and 22000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to Co(II) ions in the sinusoidal channels (\u0026gamma;). Most of framework Al (Al\u003csub\u003eF\u003c/sub\u003e) atoms, except for Z5-0.5, are located in channel intersections.As shown in the Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, the proportion of Al\u003csub\u003eF\u003c/sub\u003e in channel intersections was about 87% for Z5-0.4 zeolite, and decreased to about 40% for Z5-0.5. TPA\u003csup\u003e+\u003c/sup\u003e first occupy the channel intersections of MFI-type zeolite due to large size, while AlO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e tetrahedrons with negative charge are also located in channel intersections for the charge effect. With the increase of TPAOH in the gel, it may block the channel intersections so that Al atoms will occupy the straight and sinusoidal channels for Z5-0.5[\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. However, the UV-vis-DRS spectrum of Co-ZSM-5 zeolite can only reflect the states of \u0026quot;Al pairs\u0026quot;, while \u0026quot;Al pairs\u0026quot; in the zeolite account for about 60\u0026ndash;70% of Al\u003csub\u003eF\u003c/sub\u003e content, and Co(II) ions cannot characterize all Al\u003csub\u003eF\u003c/sub\u003e distributions[\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. Therefore, Al\u003csub\u003eF\u003c/sub\u003e distributions with different TPAOH contents would be further analyzed by \u003csup\u003e27\u003c/sup\u003eAl MAS NMR.\u003c/p\u003e\n \u003cp\u003eTable 3 Elements and distribution of ZSM-5 zeolites with different TPAOH contents\u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eZ5-x\u003c/p\u003e\n \u003cp\u003e(TPAOH/Si)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003cp\u003e(wt%)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003cp\u003e(wt%)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eExtra-framework Si/Al\u003c/p\u003e\n \u003cp\u003e(area)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eDistributed of Al sites and relative peak areas(%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026alpha; (%)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026beta;(%)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026gamma;(%)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e66.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e66.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e87.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e58.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e41.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.99\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003ea\u003c/sup\u003edetected by XPS\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003eb\u003c/sup\u003edetected by Co-UV-vis DRS\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003eThe \u003csup\u003e27\u003c/sup\u003eAl MAS NMR spectra revealed all Al\u003csub\u003eF\u003c/sub\u003e distributions, including those that cannot be coordinated by Co(II) cations[\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. Al states in ZSM-5 are revealed by solid-state NMR spectroscopy shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. Two peaks at 0 ppm and 55 ppm were observered in all the samples. The assignment of fomer peaks at 0 ppm were related to extra-framework Al (FEAL) species while the latter peaks at 55 pm were concern with tetrahedrally coordinated Al species in the ZSM-5 framework[\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]. The peaks at 55 ppm are stronger than those at 0 ppm, confirming that the majority of Al species were four-coordinated framework Al in all Z5-x samples. The peak area at 0 ppm decreased wth the increse of TPAOH content for Z5-0.2 and Z5-0.3, which means that the extra-framework Al species decreased. It can be concluded that most of Al species incorporated into the framework of ZSM-5. The results explained the reason that the relative crystallinity increased with the increase of TPAOH content accroding to XRD patterns. Moreover, the \u003csup\u003e27\u003c/sup\u003eAl NMR peak at 55 ppm can be deconvoluted into five peaks at 52, 53, 54, 56, and 58 ppm, respectively[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. Typically, the peak at 54 ppm corresponded to the framework Al species located at the intersection channels, while the peak at 56 ppm was relevant to the framework Al species located at either the straight or sinusoidal channels. Al sites at insection channel increased with the increase of TPAOH/Si ratio. Z5-0.4 shows the highest peak area at 54 ppm, accounting for 57.46%, which means that The Al species are mainly distributed in intersection channel. Non-framework Al species increases for Z5-0.5 a decrease in crystallinity which were consistent with the results of XRD. It can be seen that the Al\u003csub\u003e54\u003c/sub\u003e/Al\u003csub\u003e56\u003c/sub\u003e ratio gradually increased then decreased with the increase of the TPAOH/Si ratio from the Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, which means that Al\u003csub\u003eF\u003c/sub\u003e in channel intersections increasing first and then decreased. Al\u003csub\u003e54\u003c/sub\u003e/Al\u003csub\u003e56\u003c/sub\u003e from the \u003csup\u003e27\u003c/sup\u003eAl MAS NMR spectra shows the same variation trend to the \u0026beta;/(\u0026alpha;\u0026thinsp;+\u0026thinsp;\u0026gamma;) ratio from UV-vis-DRS of Co\u003csup\u003e2+\u003c/sup\u003e for all samples. The result indicted that the Al\u003csub\u003e54\u003c/sub\u003e/Al\u003csub\u003e56\u003c/sub\u003e ratio was in direct correlation to the value of \u0026beta;/(\u0026alpha;\u0026thinsp;+\u0026thinsp;\u0026gamma;) for all samples.\u003c/p\u003e\n \u003cp\u003eTable 4 Al site distribution of H-ZSM-5 zeolites synthesized with different TPAOH contents\u003c/p\u003e\n \u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\" width=\"600\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 128px;\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" style=\"width: 353px;\"\u003e\n \u003cp\u003eChemical shift (ppm) assignment of Al sites and relative peak areas(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"3\" style=\"width: 59px;\"\u003e\n \u003cp\u003e56+54\u003c/p\u003e\n \u003cp\u003e(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"3\" style=\"width: 59px;\"\u003e\n \u003cp\u003e54/56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e52\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 62px;\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003eChannel interaction\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003eStraight/\u003c/p\u003e\n \u003cp\u003eSinusoidal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 57px;\"\u003e\n \u003cp\u003e58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003eZ5-0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e26.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e15.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e36.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e11.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e9.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e48.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e3.07\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003eZ5-0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e26.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e11.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e42.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e13.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e5.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e56.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e3.20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003eZ5-0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e19.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e4.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e57.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e12.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e6.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e69.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e4.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003eZ5-0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e37.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e12.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e28.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e15.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e5.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e43.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e1.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Catalytic performance in MTA reaction.\u003c/h2\u003e\n \u003cp\u003eThe aromatization process of methanol with zeolite catalyst is a typical acid catalytic reaction. MTA reaction involves various reaction steps, such as dehydrogenation, isomerization, oligomerization, pyrolysis, aromatization, cyclization, etc. All processes play a crucial role in the product distribution. Figure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e shows the methanol conversion and aromatics yield as a function of time on stream for MTA reaction over H-ZSM-5 with different TPAOH/Si ratios. The methanol conversion over all the ZSM-5 samples is close to 100%. The life of catalyst is within about 7 hours due to the micropore structure. The highest aromatics yield is 45% when TPAOH/SiO\u003csub\u003e2\u003c/sub\u003e ratio is 0.4 and TOS was 1h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. When the TPAOH/Si ratios is increased to 0.5, the yield of aromatics significantly decreased to 24.53%, mainly due to the decrease of selectivity of toluene and xylene. According to the Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, the selectivity of BTX increased from 16.15 wt% to 24.18 wt% with the increase of TPAOH/Si ratios.When the TPAOH/Si ratios is increased to 0.5, BTX selectivity is decreased to 15.15 wt%. Z5-0.4 showed the better catalytic performance than other samples.\u003c/p\u003e\n \u003cp\u003eFrom the microstructure point of view in considering catalytic performance, the Al distribution played an important role in MTA reaction. The framework Al species at insection channel reached the maximum for Z4-0.4 and showed the highest aromatics yield. Different Al location is a key role in determing catalytic performance. The results of MTA reaction showed that framework Al located at the intersection channel is conducive to improving yield of aromatic. However, catalyst is easy to deposite carbon and deactivate.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e shows a linear correlation between the selectivity of BTX and framework Al distribution. Z5-0.4 shows a higher selectivity of aromatics because the Al pairs are more beneficial to hydrogen transfer reactions to form the aromatics[\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eMart\u0026iacute;nez et al.[\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]demonstrated that the Al pairs in the channel intersections enhance the aromatic-based cycle. High densities of Al sites favour the hydrogen transfer reactions and alkane formation whereas in samples with low Al contents[\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. According to the double cycle mechanism, aromatics are mainly formed by dehydroaromatization of higher olefins, and accompanied by the formation of low carbon alkanes. One possible explanation is that part of the \u0026quot;retained alkenes\u0026quot; are converted to C\u003csub\u003e5\u003c/sub\u003e-C\u003csub\u003e9\u003c/sub\u003e non-aromatics [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. It is the Al species located at intersection channel that led to increse aromatics yield and improve catalytic performance, but how to prevent carbon accumulation and improve the catalyst life needs further research [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMain product distribution of methanol conversion on ZSM-5 with different TPAOH contents\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eT\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eX\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eBTX\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eC\u003csub\u003e8\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eC\u003csub\u003e9\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eC\u003csub\u003e9\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eX-Xylene\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP-Xylene\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e124\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e135\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ5-0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, we systematically investigated the influence of Al siting in zeolite channels on the product BTX selectivity in MTA reaction. Since Al pairs in the channel intersections occupy a large space, whcih means a small resistance to transitional states of aromatic hydrocarbons in aromatic-based cycle, thus displaying high BTX selectivity. In addition, the well balance between the quantities of weak and strong acid sites is favor of aromatics selectivity in the methanol to aromatics reaction. Weak acid ammount was closely related to the Al locations in ZSM-5 zeolite framework. The zeolite with a high proportion of Al in the channel intersections showed higher catalytic performance in the methanol to aromatics reaction. This study reveals that the product distribution in the methanol to aromatics reaction is controlled by the Al location of ZSM-5 zeolite by different TPAOH contents.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJuanjuan Liu: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Data Curation, Writing - Original Draft, Writing - Review \u0026amp; Editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eXiaohua Shen: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Review \u0026amp; Editing, Supervision, Project administration, Funding acquisition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLixia Lin: Supervision, Funding acquisition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eJianjun Lu: Validation, Supervision, Project administration, Funding acquisition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eYu Zhou: performed catalyst characterizations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe gratefully acknowledge financial support from the National Natural Science Foundation of China (No.22278296).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eYang L, Liu Z, Liu Z, et al. 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Angewandte Chemie International Edition, 2022, 61(10): e202114786.\u003c/li\u003e\n\u003c/ol\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-porous-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopo","sideBox":"Learn more about [Journal of Porous Materials](http://link.springer.com/journal/10934)","snPcode":"10934","submissionUrl":"https://submission.nature.com/new-submission/10934/3","title":"Journal of Porous Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"MTA reaction, Al sites, Acid, BTX selectivity","lastPublishedDoi":"10.21203/rs.3.rs-5430628/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5430628/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGreat progress has been made in the methanol to aromatics (MTA) reaction over ZSM-5 zeolite, the location of Al atoms in ZSM-5 framework is very important for understanding the relationship among structure and activity of catalytic reaction system. In this paper, a series of ZSM-5 zeolites with different Al sites were prepared by changing the tetrapropyl ammonium hydroxide (TPAOH) content in the synthetic gel. The results showed that the quantity of Al sites at the channel intersections reach a maximum when the ratio of TPA\u003csup\u003e+\u003c/sup\u003e/Si increased to 0.4, and the selectivity of BTX increased from 16.15% to 24%, simultaneously. When the ratio of TPA\u003csup\u003e+\u003c/sup\u003e/Si continues to increase to 0.5, the catalytic performance decreases and the BTX selectivity decreases to 15%. Therefore, the Al loctaion effects the performance of ZSM-5 zeolite catalyst, and the zeolite with a higher proportion of Al in the intersection channels shows higher BTX selectivity in the methanol to aromatics reaction. This study elucidates the relationship between the distribution of MTA reaction products and Al sites, establishing the synthesis-structure-performance relationship of zeolite, and providing the experimental basis for rational design of catalysts.\u003c/p\u003e","manuscriptTitle":"Imapct of the Al sites of ZSM-5 Zeolite on product distribution in methanol to aromatics reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-28 13:58:15","doi":"10.21203/rs.3.rs-5430628/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-11-24T14:29:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-23T07:29:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-21T05:48:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"172200744929810302479378714740651945653","date":"2024-11-15T06:08:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"306761849393727224312447878760356460041","date":"2024-11-15T02:15:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-13T09:02:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"217082341656800145521440423038070744759","date":"2024-11-13T08:28:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"167935613989625759585006701554633989908","date":"2024-11-13T01:08:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"305924118921512563596008056087257268438","date":"2024-11-12T23:46:24+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-12T23:09:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-11-11T12:19:11+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-11-11T12:15:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Porous Materials","date":"2024-11-11T09:14:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-porous-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopo","sideBox":"Learn more about [Journal of Porous Materials](http://link.springer.com/journal/10934)","snPcode":"10934","submissionUrl":"https://submission.nature.com/new-submission/10934/3","title":"Journal of Porous Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0d07809c-b5f5-4079-98ef-f2a3d24b508e","owner":[],"postedDate":"November 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-02-10T16:03:45+00:00","versionOfRecord":{"articleIdentity":"rs-5430628","link":"https://doi.org/10.1007/s10934-025-01765-2","journal":{"identity":"journal-of-porous-materials","isVorOnly":false,"title":"Journal of Porous Materials"},"publishedOn":"2025-02-05 15:57:56","publishedOnDateReadable":"February 5th, 2025"},"versionCreatedAt":"2024-11-28 13:58:15","video":"","vorDoi":"10.1007/s10934-025-01765-2","vorDoiUrl":"https://doi.org/10.1007/s10934-025-01765-2","workflowStages":[]},"version":"v1","identity":"rs-5430628","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5430628","identity":"rs-5430628","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}