Revisiting the absolute green synthesis of MFI zeolite and derived metal-acid bifunctional catalysts

Revisiting the absolute green synthesis of MFI zeolite and derived metal-acid bifunctional catalysts | 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 Revisiting the absolute green synthesis of MFI zeolite and derived metal-acid bifunctional catalysts Wenqi Xu, Hongqing Li, Mengxuan Zhu, Rui Wang, Heng Jiang, Changzi Jin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3930274/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Developing sustainable synthesis method of versatile zeolites to overcome the shortcoming of traditional process is of significant for development of green chemistry and environmentally friendly techniques. In this work, MFI zeolite (ZSM-5) was synthesized through organotemplate-, solvent- and seed-free quasi-solid state transformation with commercial silica gel or Stöber colloidal SiO 2 as silica source. The key influencing factors to this absolute green synthesis process, such as starting material composition, crystallization temperature and time, had been unambiguously investigated by combining a series of characterization techniques and the optimized synthesis conditions had been obtained. In addition, this green synthesis method can be extended into the fabrication of encapsulated metal-zeolite bifunctional catalyst, which is effective in hydroisomerization of n -heptane. These results are instructive for development of green synthesis of aluminosilicate zeolites and derived heterogeneous catalysts. ZSM-5 zeolite Green synthesis Bifunctional catalyst Colloidal SiO2 Quasi-solid state transformation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Zeolites of crystalline aluminosilicate have attracted tremendous attentions for their prominent characters of large surface areas, uniform and abundant porosities, tunable acidity and excellent thermal/hydrothermal stability, which endow them wide application in the field of catalysis, adsorption and separation, ion exchange, energy transformation and so on.[ 1 – 8 ] Among those hundreds of reported zeolites, the MFI-type ZSM-5 zeolite is undoubtedly one of the most popular members because of its special three-dimensional channel system with 10-rings channel window, which can be used as catalysts and catalyst supports in oil refining, petrochemical and fine chemicals processing and exhibit outstanding performance.[ 9 – 17 ] Heavy use of zeolite materials has led to creased demand of reasonable zeolite preparation. However, the conventional preparation method of ZSM-5, as well as some other important zeolites, is hydrothermal process that consuming organic structural directing agents (OSDA) and plenty of water as solvent, usually existing the cost and environment problems.[ 18 – 23 ] For example, the consumption of expensive organic templates will result in high cost of synthesis process. Both the template and the decomposition products of template (NO x , CO 2 ) are almost noxious. In addition, large amount of water in hydrothermal system not only produce lots of waste liquid, but the dissolution of Si- and Al- nutrients in solvent lead to the loss of zeolite product yield. Therefore, the development of sustainable economic and green synthesis routes without organic template and solvent for important zeolites is of significance and much-anticipated.[ 24 , 25 ] In general, the functions of templates in the zeolite synthesis involve structure-directing, channel-filling and charge-balance.[ 26 ] So, other alternatives with similar roles are necessary in OSDA-free zeolite synthesis system. Fortunately, the ZSM-5 zeolite can be synthesized by various templating routes. Except the most commonly used tetrapropyl ammonium templates (TPAOH and TPABr), other organic amines such as n-butylamine and ethanediamine, alcohols and alkali metal ions can also act as templates for successful preparation of ZSM-5 zeolite.[ 21 – 23 , 27 – 31 ] To pursue the goal of OSDA-free synthesis, the utilization of alkali metal ions and alcohols are seemed to be more promising. The most typical is sodium ions, which can induce the synthesis of ZSM-5 in template-free hydrothermal system and the obtained products possessing open channel even without calcination treatment. But the drawback of low yield still exists for the use of large amount of water solvent in synthetic system.[ 32 – 35 ] Until Xiao and coworkers pronounced sustainable synthesis strategy for ZSM-5 and some other zeolites by conflating organotemplate-free and solvent-free routes, the green synthesis of zeolites had made further substantial progress.[ 25 , 35 – 40 ] The solid raw materials are first mixed and ground well and then suffered crystallization treatment, the crystalline zeolite can be prepared. Because there is no use water solvent, the crystal water in raw materials plays a crucial role in formation of zeolite products. The raw materials of this green OSDA-free synthesis process can be expanded from conventional commercial reagent to natural mineral, such as kaolin and illite, which further reduce the synthesis cost.[ 41 – 43 ] However, the metal impurities in natural materials have significant effect on synthesis of zeolites, hampering the clarification of key synthetic conditions in synthesis process. In addition, it worth noting that most aforementioned green synthesis process are assisted by pre-synthesized target zeolites as seed. As Wu et al had stated, same synthetic system will generate amorphous product without seed.[ 38 ] Therefore, it is obvious that the sustainable synthesis strategy for ZSM-5 zeolite can be further optimized. Herein, a green OSDA-, solvent- and seed-free synthesis for ZSM-5 with commercial silica gel or prepared Stöber-derived silica spheres as raw materials is presented. The influences of system composition and crystallization parameters on product are investigated to clarify the crucial synthetic conditions of this green synthesis process. The synthesized ZSM-5 zeolites are characterized and as catalyst for catalytic reactions. 2 Experimental 2.1 Chemicals Silica gel (specific surface area: 350–460 m 2 /g, pore size: 8–12 nm, SiO 2 : 99%.) was purchased from Qingdao Xinchanglai Silica Gel Ltd. Tetraethylorthosilicate (TEOS), polyvinylpyrrolidone (PVP K30, M.W.=38000) and dihydrogen hexachloroplatinate (H 2 PtCl 6 ·6H 2 O) were purchased from Shanghai Aladdin Biochemical Technology Co. Sodium aluminate (NaAlO 2 ), aluminium sulphate (Al 2 (SO 4 ) 3 ·18H 2 O), sodium hydroxide, sodium carbonate, ethanol, ammonium chloride and ammonia hydroxide (NH 3 ·H 2 O, 25–28 wt %) were purchased from Tianjin Damao Chemical Co. The distilled water was homemade. All the reagents were used without further purification. 2.2 Synthesis of Pt nanoparticles The Pt nanoparticles was synthesized by alcohol reduction process.[ 44 ] Firstly, 85.7 mg PVP and 1.08 mL H 2 PtCl 6 aqueous solution (38.6 mM) were dissolved in 45 mL ethanol and 5 mL water. Then, the synthetic mixture was refluxed at 80 o C under stirring for 2 h. Finally, the generated black Pt nanoparticles were collected by centrifugation and were redispersed in ethanol for further use. 2.3 Synthesis of SiO 2 spheres and Pt@SiO 2 The SiO 2 colloidal spheres were synthesized by a well-known Stӧber method with slight modification. In typical, 70 mL ethanol, 15 mL water and 4 mL NH 3 ·H 2 O were mixed together, followed by the addition of 3.5 g TEOS. After stirring constantly at room temperature for 24 h, the SiO 2 colloidal spheres were obtained by centrifugation and dried at 100 o C. The synthesis process of Pt@SiO 2 is similar to SiO 2 spheres except for the additional introduction of recommended amount of Pt nanoparticles (0.025 mmol) preceding the addition of TEOS. 2.4 Green synthesis of ZSM-5 and derived catalysts The synthesis of ZSM-5 zeolite was performed by reported solid-state conversion. In a typical run, 1.5 g of silica source (silica gel or Stӧber SiO 2 sphere), 0.10 g of NaAlO 2 , 0.09 g of NaOH and 0.90 g of water were mixed by grinding for 10 min. Then the mixture was transferred into 25 mL Teflon-lined autoclave and heated at 170 o C for 24 h and the crystalline product can be obtained. For the synthesis of Pt@ZSM-5 catalyst, Pt@SiO 2 was used as silica source and other conditions remained unchanged. The H-form zeolites were obtained by ion-exchange of as-synthesized Na-form products in 1 M NH 4 Cl aqueous solution at 80 o C for 8 h, followed by calcination process (550 o C, 4 h). This ion-exchange process needs to be repeated once. For comparison, supported Pt/ZSM-5 catalyst was prepared with H-form ZSM-5 from Stӧber SiO 2 sphere as carrier via incipient-wetness impregnation method. 2.5 Characterization Powder X-ray diffraction (XRD) pattern was recorded in a Bruck D8 Advance powder X-ray diffractometer using Cu Kα radiation in 2 θ range of 4-50 o . Scanning electronic microscopy (SEM) images were taken on SU8010 field-emission scanning electronic microscope operating at 5 kV. Transmission electronic microscopy (TEM) images were taken on a JEM-2100 electronic microscope with an accelerating voltage of 200 kV. Nitrogen physical adsorption/desorption isotherms were measured on Quantachrome Autosorb-IQ2-MP physical adsorption apparatus. The specific surface areas were calculated using the BET method. Ammonia temperature programmed desorption (NH 3 -TPD) measurements were performed on Quantachrome TPD/TDR-Pulsar chemisorption analyzer in the range of 150–600°C at a ramp rate of 20°C min − 1 . The SiO 2 /Al 2 O 3 ratio in the samples was analyzed on Bruker D8 Tiger X-ray fluorescence (XRF) spectrometer. 2.6 Catalytic tests Catalytic performance of the prepared catalysts for hydroisomerization of n -heptane were operated on a fixed-bed stainless steel reactor at atmospheric pressure. Before reaction, the catalyst (0.5 g) was reduced by H 2 flow at 400°C for 2h, and then was cooled to reaction temperature. The n -heptane was fed into reactor with HPLC pump at a weight hourly space velocity (WHSV) of 2.0 h − 1 and the H 2 / n -heptane molar ratio was fixed at 10. The reaction products were detected on Techcomp GC7890 equipped with a TM-PONA capillary column (50m×0.2mm×0.5µm) and FID detector. 3 Results and discussion 3.1 Sustainable synthesis for ZSM-5 zeolite The absolute green synthesis for ZSM-5 zeolite without using organotemplate, solvent and zeolite seed is described in Fig. 1 . The starting materials are mixed by grinding in the absence of adequate solvent and further crystallize into zeolite. Figure 2 shows the XRD patterns of prepared zeolites with various SiO 2 /Al 2 O 3 molar ratio from commercial silica gel and sodium aluminate. It can be observed that the SiO 2 /Al 2 O 3 ratio of starting materials has significant influence on the synthesis. Only suitable SiO 2 /Al 2 O 3 ratio (30–40) can produce the MFI-type zeolite with highly crystallinity and the lower Al content of starting materials (SiO 2 /Al 2 O 3 = 50–60) have generated the zeolite product accompanied by amorphous phase (Table S1 ), which confirmed by the broad reflection of XRD pattern in 2 θ of 20-25 o . Further decreasing the Al content of starting materials (SiO 2 /Al 2 O 3 = 100) has led to the formation of tetragonal SiO 2 impurity, which is dominant in the product from Al-free synthesis system (Figure S1 ). Therefore, well crystalline ZSM-5 zeolite can be formed in narrow SiO 2 /Al 2 O 3 ratio region and the SiO 2 /Al 2 O 3 = 40 was used in follow-up research. The SEM images of products with different SiO 2 /Al 2 O 3 ratio are showed in Fig. 2 . It can be found that the synthesized ZSM-5 zeolite possesses uneven morphology with micrometer size. Except the hexagonal crystal main body, most samples contain some needle-like particles that might be the associated impurity. It is well known that the sodium ions not only work as charge balancing in aluminosilicate zeolites, but also play a role of templating in OSDA-free synthesis process.[ 39 , 42 , 43 ] So, the Na 2 O/SiO 2 ratio is another important factor affecting our OSDA-free synthesis of ZSM-5. Figure 4 shows the XRD patterns of samples synthesized with different Na 2 O/SiO 2 ratio. Compared to the well crystalline product synthesized with Na 2 O/SiO 2 ratio at 0.072 (Fig. 2 ), whether increasing or decreasing the sodium amount are unfavorable to the crystallization of product. At the Na 2 O/SiO 2 ratio of 0.108, the product also exhibits well-defined MFI-type diffraction peaks with lower relative crystallinity (54%, Table S1 ), which will be further decreased by increasing the sodium amount. When the Na 2 O/SiO 2 ratio was decreased to 0.036, no appreciable diffraction peaks can be found in the product. So, the Na 2 O/SiO 2 ratio of 0.072–0.108 is suitable for this sustainable synthesis of ZSM-5. It should be noted that the sodium in our synthesis system is provided by NaOH and alumina source (NaAlO 2 ). If the NaOH is replaced by NaHCO 3 or the NaAlO 2 is replaced by aluminum sulfate while remaining the total Na 2 O/SiO 2 ratio at 0.072, no MFI zeolite can be formed (Figure S2), which may be due to the variation of the basicity of synthesis system. It follows that under premise of suitable Na 2 O/SiO 2 ratio, adequate basicity is necessary to successful synthesis of MFI zeolite. Even in the so-called solvent-free synthesis of zeolites, the water is significant and necessary. In previous reports, the crystal water of raw materials usually plays a crucial role in solvent-free synthesis of zeolites without consuming additional water, which lead to the ambiguity of the lowest level of water content for successful synthesis of zeolite.[ 25 , 39 ] Herein, the green synthesis protocol uses raw materials containing little water and needs assistance of additional water with specific dosage so that the dose threshold of water for successful synthesis of zeolite might be ascertained. Figure 5 indicates the effect of water amount on the synthesis of ZSM-5. As expected, MFI zeolite cannot be prepared in the water-free system. When a small amount of water was added into the synthesis system (H 2 O/SiO 2 = 1.0), MFI crystal appeared in the product, but the relative crystallinity is lower (48%) and the amorphous phase also exists. By comparison, the H 2 O/SiO 2 ratio at 2.0 generated highly crystalline ZSM-5 zeolite (Fig. 2 ) and the products remain well MFI structure with further increasement of water. These results confirmed the importance of water for zeolite crystallization. However, it seems that the crucial role of water is not irreplaceable. When water is replaced with an equal amount of ethanol, ZSM-5 zeolite with well crystallinity can also be synthesized (Figure S3), which confirms the availability of organic solvent in this OSDA and solvent-free zeolite synthesis process. Similar to the conventional hydrothermal synthesis, this sustainable synthesis process uses the common crystallization temperature at 170 o C for more than 18h (Fig. 6 ). When the crystallization time is less than 12h, or the crystallization temperature is lower (150 o C), only amorphous products can be obtained. After crystallized at 170 o C for 18h, the product displays typical MFI structure with relative crystallinity of 61%. Further increasing the crystallization time to 24h, the XRD of product shows the strongest peaks in intensity (Fig. 2 , Table S1 ). When the crystallization time reaches to 48h, the relative crystallinity of sample slightly decreased (88%), indicating that long crystallization time is not necessary for synthesis of zeolite. In addition, as the SEM images have shown (Fig. 7 ), the sample that crystallized for 48h contain some needle-like impurity, which can not be found in the sample crystallized for 18h. The above experiments were performed with solid silica gel as silica source. In fact, the SiO 2 spheres prepared by Stöber method are also available in this sustainable synthesis for ZSM-5. As Fig. 8 has shown, XRD pattern of the sample synthesized from Stöber SiO 2 spheres displays highly crystalline MFI structure. The SEM image exhibits irregular crystals with micrometer size regardless of the starting raw materials with uniform diameter (Figure S3), which indicates that the Stöber SiO 2 spheres aggregate and crystallize into micro-size zeolite particles at the expense of losing original morphology. Figure 9 presents the N 2 physical adsorption-desorption isotherms of the prepared ZSM-5 zeolites and corresponding textural properties are listed in Table 1 . Owing to the template-free synthesis route, the as-synthesized samples without any thermal treatment possess open porous structure. It can be found that both the zeolites from solid silica gel and Stöber SiO 2 sphere exhibit adsorption at low P/P 0 (< 0.01), confirming the presence of open micropores in the samples. Compared to the type-I isotherm of silica gel-derived sample, the zeolite from Stöber SiO 2 sphere shows a hysteresis loop at high relative pressure (0.5–0.9), which indicates that the sample contains some larger pores and leading to higher total pore volume (Table 1 ). In addition, the total surface areas of green-synthesized zeolites herein are less than that of sample from conventional hydrothermal synthesis (Table 1 and Figure S6), which is in accordance with previous report.[ 43 ] Table 1 Textural properties of prepared samples. No. Silica source SiO 2 /Al 2 O 3 a (mol/mol) S T b (m 2 /g) S M c (m 2 /g) V M d (cm 3 /g) V T e (cm 3 /g) 1 Silica gel 53 237 196 0.08 0.14 2 Stöber SiO 2 62 227 136 0.06 0.26 a SiO 2 /Al 2 O 3 molar ratio in H-type zeolites analyzed by XRF. b Total surface area from BET analysis. c Micropore surface area from t-plot analysis. d Micropore volume from t-plot analysis. e Total pore volume calculated from the adsorption at P/P 0 of 0.99. The as-synthesized Na-type zeolites had been converted into H-type ones through NH 4 + - exchanging process to obtain acid properties. Figure 10 shows the NH 3 -TPD profiles of the obtained H-type zeolites synthesized from solid silica gel and Stöber SiO 2 sphere. Regardless of the slight difference on actual Al 2 O 3 content in two samples (Table 1 ), which might be due to different purity of corresponding silica sources, they display similar profiles with two intensive desorption peaks at temperature of 190–320 o C and 420–450 o C, indicating the weak and strong acid sites in the samples, respectively. 3.2 Fabrication of Pt-ZSM-5 catalysts and catalytic performance The availability of Stöber SiO 2 spheres has expanded this sustainable synthesis route into fabrication of metal-zeolite composites, which benefit from the universality of Stöber process in constructing metal@SiO 2 hybrids.[ 45 , 46 ] Herein, PVP-stabilized Pt nanoparticles with size of 2 ~ 3 nm (Figure S4) from alcohol reduction process were incorporated into Stöber system, and then Pt@SiO 2 core-shell hybrid had been obtained (Fig. 11 a). By utilizing this Pt@SiO 2 as silica source, the Pt@ZSM-5 composite can be synthesized through aforementioned green synthesis route. The TEM image of the prepared Pt@ZSM-5 (H-form) showed in Fig. 11 b exhibits that the metallic nanoparticles are embedded in ZSM-5 matrix. Compared to original Pt nanoparticles and Pt@SiO 2 hybrid, the size of metal particles in composite slightly increased (~ 5nm), which can be attributed to the thermal treatment during ion-exchange procedure. After all, serious aggregation of metal particles was avoided for the zeolite confinement effect. By contrast, the supported Pt/ZSM-5 with same Pt content (0.5%) prepared via incipient-wetness impregnation displays uneven sized metal particle with some individuals exceed 10 nm (Fig. 11 c), which indicates the agglomeration of Pt nanoparticles. Even so, the XRD pattern of both Pt@ZSM-5 and Pt/ZSM-5 only displays MFI diffraction peaks with high crystallinity and no characteristic peaks associated with Pt or PtO x phase are visible (Fig. 11 d), which indicates the absence of bulky metallic particles in the samples. It was evident that Pt nanoparticles embedded in colloid SiO 2 spheres did not hamper the formation of zeolite. When the Pt nanoparticles were directly mixed with SiO 2 spheres and other raw materials, nevertheless, a poor crystalline product had been obtained (Figure S6). This result indicates that the OSDA and solvent-free synthesis process is susceptible to other external factors. The catalytic performance of prepared Pt-ZSM-5 composites had been investigated in hydroisomerization of n -heptane, which is a typical reaction catalyzed by bifunctional metal-acid catalysts.[ 47 – 49 ] As Fig. 12 a has shown, both Pt@ZSM-5 and Pt/ZSM-5 show low n -heptane conversion (6% and 11.4%) at lower reaction temperature of 220 o C. With the reaction temperature increasing, the n -heptane conversion over two catalysts also increases. Especially the Pt@ZSM-5, giving the n -heptane conversion as high as 92% at 280 o C, more than twice that of Pt/ZSM-5 (37.4%). However, the selectivity to isomers for both catalysts decline with the increase of temperature (Fig. 12 b). Compared to the Pt/ZSM-5 catalyst that generating serious cracking side reactions at investigated temperature range, Pt@ZSM-5 exhibits dominant isomers selectivity at lower reaction temperature (220–240 o C). Abundant Bronsted acid sites of Al-rich zeolite should be responsible for cracking side reactions at high temperature.[ 50 ] Detailed products distribution listed in Table S2 indicate that mono-branched 2-/3-methylhexanes and propane/iso-butane dominate isomerization and cracking products, respectively, which are accordance with previous report.[ 51 ] Considering the physical properties of Pt@ZSM-5 and Pt/ZSM-5, the different structure may be one of critical factor for different catalytic performance. The encapsulation structure of Pt@ZSM-5 may provide better metal-acid sites intimacy, which is favorable to isomerization of n -heptane.[ 48 ] Conclusion In summary, the absolute green synthesis for ZSM-5 zeolites without organotemplates, solvents or seeds have been further developed. By using highly purity of silica sources (commercial silica gel and Stӧber colloidal silica), the crucial influencing factors to the successful synthesis have been obtained unambiguously. In addition, this green synthesis can also be extended to the construction of encapsulated metal-zeolite composites, which act as bifunctional catalysts for hydroisomerization of alkanes. Despite the problems of limited Al content, lower surface areas and sensitive synthetic conditions, the merits on cost and environment of green synthesis determine its good prospect of application in heterogeneous catalysis. 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Teranishi T, Hosoe M, Tanaka T, Miyake M (1999) Size control of monodispersed Pt nanoparticles and their 2D organization by electrophoretic deposition. J Phys Chem B 103: 3818-3827. Liu SH, Han MY (2010) Silica-coated metal nanoparticles. Chem-Asian J 5: 36-45. Lu Y, Yin YD, Li ZY, Xia YN (2002) Synthesis and self-assembly of Au@SiO 2 core-shell colloids. Nano Letters 2: 785-788. Noh G, Shi ZC, Zones SI, Iglesia E (2018) Isomerization and β-scission reactions of alkanes on bifunctional metal acid catalysts: Consequences of confinement and diffusional constraints on reactivity and selectivity. J Catal 368: 389-410. Chen HM, Yi FJ, Ma CP, Gao X, Liu SY, Tao ZC, Wu BS, Xiang HW, Yang Y, Li YW (2020) Hydroisomerization of n -heptane on a new kind of bifunctional catalysts with palladium nanoparticles encapsulating inside zeolites. Fuel 268: 117241. Oenema J, Harmel J, Vélez RP, Meijerink MJ, Eijsvogel W, Poursaeidesfahani A, Vlugt TJH, Zecevic J, De Jong KP (2020) Influence of nanoscale intimacy and zeolite micropore size on the performance of bifunctional catalysts for n -heptane hydroisomerization. Acs Catal 10: 14245-14257. Bhan A, Gounder R, Macht J, Iglesia E (2008) Entropy considerations in monomolecular cracking of alkanes on acidic zeolites. J Catal 253: 221-224. Kim J, Kim W, Seo Y, Kim JC, Ryoo R (2013) n -Heptane hydroisomerization over Pt/MFI zeolite nanosheets: Effects of zeolite crystal thickness and platinum location. J Catal 301: 187-197. Additional Declarations No competing interests reported. Supplementary Files Supportinginformation.docx Cite Share Download PDF Status: Posted Version 1 posted 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-3930274","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":272160223,"identity":"b922dbb6-cdb4-4594-94c4-5e41cf2dcb47","order_by":0,"name":"Wenqi Xu","email":"","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":false,"prefix":"","firstName":"Wenqi","middleName":"","lastName":"Xu","suffix":""},{"id":272160224,"identity":"78f2c043-e4df-4c91-9e67-5a7599d0f43f","order_by":1,"name":"Hongqing Li","email":"","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":false,"prefix":"","firstName":"Hongqing","middleName":"","lastName":"Li","suffix":""},{"id":272160225,"identity":"8ca9b45e-e9d3-4914-9df7-0bd7808ccb26","order_by":2,"name":"Mengxuan Zhu","email":"","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":false,"prefix":"","firstName":"Mengxuan","middleName":"","lastName":"Zhu","suffix":""},{"id":272160226,"identity":"cb77c3b9-e8b6-4f38-b2ed-fa4adc107aa4","order_by":3,"name":"Rui Wang","email":"","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":false,"prefix":"","firstName":"Rui","middleName":"","lastName":"Wang","suffix":""},{"id":272160227,"identity":"06bad8c1-4450-4675-a042-bd74074e4ef1","order_by":4,"name":"Heng Jiang","email":"","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":false,"prefix":"","firstName":"Heng","middleName":"","lastName":"Jiang","suffix":""},{"id":272160228,"identity":"237f8370-bbcc-4e79-b26d-dbffb8051d36","order_by":5,"name":"Changzi Jin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAApklEQVRIiWNgGAWjYBACxmYQ0cAgx8befoA0LcZ8PGcSSLGqgSFxnoSDAXGqmdt5DzD83FGX3ibBkMDwo2IbMQ7jS2DsPcOW2ybdeICx58xtYrTwGDAztvHktskcSAAyiNcikc4mkWBAkhaDBNK0MPa2JRi2AQP5IFF+Mew/Y8Dws61OXr69/eCDHxXEaGlgYP8B4xwgrB4I5IlSNQpGwSgYBSMbAAAG2jQuBwZMUQAAAABJRU5ErkJggg==","orcid":"","institution":"Liaoning Petrochemical University","correspondingAuthor":true,"prefix":"","firstName":"Changzi","middleName":"","lastName":"Jin","suffix":""}],"badges":[],"createdAt":"2024-02-05 07:14:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3930274/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3930274/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":50999314,"identity":"14ed05b7-fee7-40cd-83c1-062da8ebc414","added_by":"auto","created_at":"2024-02-12 12:58:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":79234,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation for the green synthesis of ZSM-5\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/81dc0a747f64bf3769a2dac3.png"},{"id":50999317,"identity":"7a1d51a1-fe91-426e-bcfa-5998d021d589","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":15736,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of as-synthesized products prepared from the starting materials with SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio at (a) 30, (b) 40, (c) 50, (d) 60 and (e) 100. Synthesis condition: Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u0026nbsp;\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/5b3bc2312e47c6f27f654b45.png"},{"id":50999315,"identity":"ce2ba59e-b9a1-4921-b4fb-c0d81f27239b","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":312055,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of as-synthesized products prepared from the starting materials with SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio at (a) 30, (b) 40, (c) 50 and (d) 60. Synthesis condition: Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/c3211ea09ef99c9648c05743.png"},{"id":50999324,"identity":"ba5cb946-88b4-4386-af29-1558815cdd69","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":13870,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of as-synthesized products prepared from the starting materials with Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio at (a) 0.036, (b) 0.108 and (c) 0.144. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/e2ab350caee005747dac26de.png"},{"id":50999973,"identity":"a2deb3ac-99a1-42c2-8d13-c99f1952353a","added_by":"auto","created_at":"2024-02-12 13:06:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":13975,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of as-synthesized products prepared from the starting materials with H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio at (a) 0, (b) 1.0, (c) 3.0 and (d) 4.0. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/66383a0ae832b4ef4ac68e4a.png"},{"id":50999974,"identity":"b3a5ca8e-fd4e-4f94-89eb-861eef6076d3","added_by":"auto","created_at":"2024-02-12 13:06:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":15951,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of crystallization temperature and time-depending synthesized samples. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/b97252d8ac7e1fa0fad07d81.png"},{"id":50999323,"identity":"c9f7b251-5bfc-4199-90fa-0f4ee9eb9841","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":225906,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of as-synthesized samples with crystallization time of (a) 18h and (b) 48h. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/1597ba90b57ccbdc6530d6c2.png"},{"id":50999975,"identity":"fc6e3162-a2e6-4343-b86f-ed909d163c32","added_by":"auto","created_at":"2024-02-12 13:06:59","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":177787,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern (a) and SEM image of as-synthesized samples from Stöber SiO\u003csub\u003e2\u003c/sub\u003e spheres. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/1e632cf50a7320026639e4de.png"},{"id":50999325,"identity":"07e93f3e-abc9-4629-900c-adf553919b1d","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":12550,"visible":true,"origin":"","legend":"\u003cp\u003eN\u003csub\u003e2\u003c/sub\u003e physical adsorption-desorption isotherms of as-synthesized samples from (a) solid silica gel and (b) Stöber SiO\u003csub\u003e2\u003c/sub\u003e sphere. Synthesis condition: SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e =40, Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=0.072, H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e=2.0, 170 \u003csup\u003eo\u003c/sup\u003eC, 24h.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/ae0da14363276948e4cc3ab3.png"},{"id":50999326,"identity":"8431a14a-6e84-4127-941d-aa881f8efad4","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":14886,"visible":true,"origin":"","legend":"\u003cp\u003eNH\u003csub\u003e3\u003c/sub\u003e-TPD profiles of H-type zeolites synthesized from (a) Solid silica gel and (b) Stöber SiO\u003csub\u003e2\u003c/sub\u003e sphere.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/1e331189a4350502f5fbb1d5.png"},{"id":50999321,"identity":"45cd6c84-fab8-42fb-b769-e4fd26ad5cdf","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":413168,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image of (a) Pt@SiO\u003csub\u003e2\u003c/sub\u003e, (b) Pt@ZSM-5 and (c) Pt/ZSM-5, (d) XRD pattern of Pt@ZSM-5 and Pt@ZSM-5.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/c79680e6101377dff83bc2f3.png"},{"id":50999327,"identity":"1f43491c-b321-4463-ab5c-bd538db301b0","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":41895,"visible":true,"origin":"","legend":"\u003cp\u003eConversion (a) and products selectivity (b) of prepared Pt-ZSM-5 catalysts in hydroisomerization of \u003cem\u003en\u003c/em\u003e-heptane.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/e70ed8cebf78c518a99a1e9b.png"},{"id":53207992,"identity":"e301045f-0510-41cb-af24-9b3b0471cebf","added_by":"auto","created_at":"2024-03-21 23:52:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1487098,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/43a2f024-8af5-4249-878b-a7c3414e469d.pdf"},{"id":50999319,"identity":"4a080552-c268-446b-a38a-6ee3a62b84cc","added_by":"auto","created_at":"2024-02-12 12:58:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":486999,"visible":true,"origin":"","legend":"","description":"","filename":"Supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3930274/v1/4cf50f83cbb6908050c17bd9.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Revisiting the absolute green synthesis of MFI zeolite and derived metal-acid bifunctional catalysts","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eZeolites of crystalline aluminosilicate have attracted tremendous attentions for their prominent characters of large surface areas, uniform and abundant porosities, tunable acidity and excellent thermal/hydrothermal stability, which endow them wide application in the field of catalysis, adsorption and separation, ion exchange, energy transformation and so on.[\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] Among those hundreds of reported zeolites, the MFI-type ZSM-5 zeolite is undoubtedly one of the most popular members because of its special three-dimensional channel system with 10-rings channel window, which can be used as catalysts and catalyst supports in oil refining, petrochemical and fine chemicals processing and exhibit outstanding performance.[\u003cspan additionalcitationids=\"CR10 CR11 CR12 CR13 CR14 CR15 CR16\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] Heavy use of zeolite materials has led to creased demand of reasonable zeolite preparation. However, the conventional preparation method of ZSM-5, as well as some other important zeolites, is hydrothermal process that consuming organic structural directing agents (OSDA) and plenty of water as solvent, usually existing the cost and environment problems.[\u003cspan additionalcitationids=\"CR19 CR20 CR21 CR22\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] For example, the consumption of expensive organic templates will result in high cost of synthesis process. Both the template and the decomposition products of template (NO\u003csub\u003ex\u003c/sub\u003e, CO\u003csub\u003e2\u003c/sub\u003e) are almost noxious. In addition, large amount of water in hydrothermal system not only produce lots of waste liquid, but the dissolution of Si- and Al- nutrients in solvent lead to the loss of zeolite product yield. Therefore, the development of sustainable economic and green synthesis routes without organic template and solvent for important zeolites is of significance and much-anticipated.[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eIn general, the functions of templates in the zeolite synthesis involve structure-directing, channel-filling and charge-balance.[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] So, other alternatives with similar roles are necessary in OSDA-free zeolite synthesis system. Fortunately, the ZSM-5 zeolite can be synthesized by various templating routes. Except the most commonly used tetrapropyl ammonium templates (TPAOH and TPABr), other organic amines such as n-butylamine and ethanediamine, alcohols and alkali metal ions can also act as templates for successful preparation of ZSM-5 zeolite.[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28 CR29 CR30\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] To pursue the goal of OSDA-free synthesis, the utilization of alkali metal ions and alcohols are seemed to be more promising. The most typical is sodium ions, which can induce the synthesis of ZSM-5 in template-free hydrothermal system and the obtained products possessing open channel even without calcination treatment. But the drawback of low yield still exists for the use of large amount of water solvent in synthetic system.[\u003cspan additionalcitationids=\"CR33 CR34\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eUntil Xiao and coworkers pronounced sustainable synthesis strategy for ZSM-5 and some other zeolites by conflating organotemplate-free and solvent-free routes, the green synthesis of zeolites had made further substantial progress.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36 CR37 CR38 CR39\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] The solid raw materials are first mixed and ground well and then suffered crystallization treatment, the crystalline zeolite can be prepared. Because there is no use water solvent, the crystal water in raw materials plays a crucial role in formation of zeolite products. The raw materials of this green OSDA-free synthesis process can be expanded from conventional commercial reagent to natural mineral, such as kaolin and illite, which further reduce the synthesis cost.[\u003cspan additionalcitationids=\"CR42\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] However, the metal impurities in natural materials have significant effect on synthesis of zeolites, hampering the clarification of key synthetic conditions in synthesis process. In addition, it worth noting that most aforementioned green synthesis process are assisted by pre-synthesized target zeolites as seed. As Wu et al had stated, same synthetic system will generate amorphous product without seed.[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] Therefore, it is obvious that the sustainable synthesis strategy for ZSM-5 zeolite can be further optimized.\u003c/p\u003e \u003cp\u003eHerein, a green OSDA-, solvent- and seed-free synthesis for ZSM-5 with commercial silica gel or prepared St\u0026ouml;ber-derived silica spheres as raw materials is presented. The influences of system composition and crystallization parameters on product are investigated to clarify the crucial synthetic conditions of this green synthesis process. The synthesized ZSM-5 zeolites are characterized and as catalyst for catalytic reactions.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals\u003c/h2\u003e \u003cp\u003eSilica gel (specific surface area: 350\u0026ndash;460 m\u003csup\u003e2\u003c/sup\u003e/g, pore size: 8\u0026ndash;12 nm, SiO\u003csub\u003e2\u003c/sub\u003e: 99%.) was purchased from Qingdao Xinchanglai Silica Gel Ltd. Tetraethylorthosilicate (TEOS), polyvinylpyrrolidone (PVP K30, M.W.=38000) and dihydrogen hexachloroplatinate (H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO) were purchased from Shanghai Aladdin Biochemical Technology Co. Sodium aluminate (NaAlO\u003csub\u003e2\u003c/sub\u003e), aluminium sulphate (Al\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;18H\u003csub\u003e2\u003c/sub\u003eO), sodium hydroxide, sodium carbonate, ethanol, ammonium chloride and ammonia hydroxide (NH\u003csub\u003e3\u003c/sub\u003e\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO, 25\u0026ndash;28 wt %) were purchased from Tianjin Damao Chemical Co. The distilled water was homemade. All the reagents were used without further purification.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of Pt nanoparticles\u003c/h2\u003e \u003cp\u003eThe Pt nanoparticles was synthesized by alcohol reduction process.[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] Firstly, 85.7 mg PVP and 1.08 mL H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e aqueous solution (38.6 mM) were dissolved in 45 mL ethanol and 5 mL water. Then, the synthetic mixture was refluxed at 80 \u003csup\u003eo\u003c/sup\u003eC under stirring for 2 h. Finally, the generated black Pt nanoparticles were collected by centrifugation and were redispersed in ethanol for further use.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Synthesis of SiO\u003csub\u003e2\u003c/sub\u003e spheres and Pt@SiO\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eThe SiO\u003csub\u003e2\u003c/sub\u003e colloidal spheres were synthesized by a well-known Stӧber method with slight modification. In typical, 70 mL ethanol, 15 mL water and 4 mL NH\u003csub\u003e3\u003c/sub\u003e\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO were mixed together, followed by the addition of 3.5 g TEOS. After stirring constantly at room temperature for 24 h, the SiO\u003csub\u003e2\u003c/sub\u003e colloidal spheres were obtained by centrifugation and dried at 100 \u003csup\u003eo\u003c/sup\u003eC. The synthesis process of Pt@SiO\u003csub\u003e2\u003c/sub\u003e is similar to SiO\u003csub\u003e2\u003c/sub\u003e spheres except for the additional introduction of recommended amount of Pt nanoparticles (0.025 mmol) preceding the addition of TEOS.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Green synthesis of ZSM-5 and derived catalysts\u003c/h2\u003e \u003cp\u003eThe synthesis of ZSM-5 zeolite was performed by reported solid-state conversion. In a typical run, 1.5 g of silica source (silica gel or Stӧber SiO\u003csub\u003e2\u003c/sub\u003e sphere), 0.10 g of NaAlO\u003csub\u003e2\u003c/sub\u003e, 0.09 g of NaOH and 0.90 g of water were mixed by grinding for 10 min. Then the mixture was transferred into 25 mL Teflon-lined autoclave and heated at 170 \u003csup\u003eo\u003c/sup\u003eC for 24 h and the crystalline product can be obtained. For the synthesis of Pt@ZSM-5 catalyst, Pt@SiO\u003csub\u003e2\u003c/sub\u003e was used as silica source and other conditions remained unchanged. The H-form zeolites were obtained by ion-exchange of as-synthesized Na-form products in 1 M NH\u003csub\u003e4\u003c/sub\u003eCl aqueous solution at 80 \u003csup\u003eo\u003c/sup\u003eC for 8 h, followed by calcination process (550 \u003csup\u003eo\u003c/sup\u003eC, 4 h). This ion-exchange process needs to be repeated once.\u003c/p\u003e \u003cp\u003eFor comparison, supported Pt/ZSM-5 catalyst was prepared with H-form ZSM-5 from Stӧber SiO\u003csub\u003e2\u003c/sub\u003e sphere as carrier via incipient-wetness impregnation method.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Characterization\u003c/h2\u003e \u003cp\u003ePowder X-ray diffraction (XRD) pattern was recorded in a Bruck D8 Advance powder X-ray diffractometer using Cu Kα radiation in 2\u003cem\u003eθ\u003c/em\u003e range of 4-50\u003csup\u003eo\u003c/sup\u003e. Scanning electronic microscopy (SEM) images were taken on SU8010 field-emission scanning electronic microscope operating at 5 kV. Transmission electronic microscopy (TEM) images were taken on a JEM-2100 electronic microscope with an accelerating voltage of 200 kV. Nitrogen physical adsorption/desorption isotherms were measured on Quantachrome Autosorb-IQ2-MP physical adsorption apparatus. The specific surface areas were calculated using the BET method. Ammonia temperature programmed desorption (NH\u003csub\u003e3\u003c/sub\u003e-TPD) measurements were performed on Quantachrome TPD/TDR-Pulsar chemisorption analyzer in the range of 150\u0026ndash;600\u0026deg;C at a ramp rate of 20\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio in the samples was analyzed on Bruker D8 Tiger X-ray fluorescence (XRF) spectrometer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Catalytic tests\u003c/h2\u003e \u003cp\u003eCatalytic performance of the prepared catalysts for hydroisomerization of \u003cem\u003en\u003c/em\u003e-heptane were operated on a fixed-bed stainless steel reactor at atmospheric pressure. Before reaction, the catalyst (0.5 g) was reduced by H\u003csub\u003e2\u003c/sub\u003e flow at 400\u0026deg;C for 2h, and then was cooled to reaction temperature. The \u003cem\u003en\u003c/em\u003e-heptane was fed into reactor with HPLC pump at a weight hourly space velocity (WHSV) of 2.0 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the H\u003csub\u003e2\u003c/sub\u003e/\u003cem\u003en\u003c/em\u003e-heptane molar ratio was fixed at 10. The reaction products were detected on Techcomp GC7890 equipped with a TM-PONA capillary column (50m\u0026times;0.2mm\u0026times;0.5\u0026micro;m) and FID detector.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Sustainable synthesis for ZSM-5 zeolite\u003c/h2\u003e \u003cp\u003eThe absolute green synthesis for ZSM-5 zeolite without using organotemplate, solvent and zeolite seed is described in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The starting materials are mixed by grinding in the absence of adequate solvent and further crystallize into zeolite. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the XRD patterns of prepared zeolites with various SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e molar ratio from commercial silica gel and sodium aluminate. It can be observed that the SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio of starting materials has significant influence on the synthesis. Only suitable SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio (30–40) can produce the MFI-type zeolite with highly crystallinity and the lower Al content of starting materials (SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e = 50–60) have generated the zeolite product accompanied by amorphous phase (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), which confirmed by the broad reflection of XRD pattern in 2\u003cem\u003eθ\u003c/em\u003e of 20-25\u003csup\u003eo\u003c/sup\u003e. Further decreasing the Al content of starting materials (SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e = 100) has led to the formation of tetragonal SiO\u003csub\u003e2\u003c/sub\u003e impurity, which is dominant in the product from Al-free synthesis system (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Therefore, well crystalline ZSM-5 zeolite can be formed in narrow SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio region and the SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e = 40 was used in follow-up research. The SEM images of products with different SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio are showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. It can be found that the synthesized ZSM-5 zeolite possesses uneven morphology with micrometer size. Except the hexagonal crystal main body, most samples contain some needle-like particles that might be the associated impurity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is well known that the sodium ions not only work as charge balancing in aluminosilicate zeolites, but also play a role of templating in OSDA-free synthesis process.[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] So, the Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio is another important factor affecting our OSDA-free synthesis of ZSM-5. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the XRD patterns of samples synthesized with different Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio. Compared to the well crystalline product synthesized with Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio at 0.072 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), whether increasing or decreasing the sodium amount are unfavorable to the crystallization of product. At the Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio of 0.108, the product also exhibits well-defined MFI-type diffraction peaks with lower relative crystallinity (54%, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), which will be further decreased by increasing the sodium amount. When the Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio was decreased to 0.036, no appreciable diffraction peaks can be found in the product. So, the Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio of 0.072–0.108 is suitable for this sustainable synthesis of ZSM-5. It should be noted that the sodium in our synthesis system is provided by NaOH and alumina source (NaAlO\u003csub\u003e2\u003c/sub\u003e). If the NaOH is replaced by NaHCO\u003csub\u003e3\u003c/sub\u003e or the NaAlO\u003csub\u003e2\u003c/sub\u003e is replaced by aluminum sulfate while remaining the total Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio at 0.072, no MFI zeolite can be formed (Figure S2), which may be due to the variation of the basicity of synthesis system. It follows that under premise of suitable Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio, adequate basicity is necessary to successful synthesis of MFI zeolite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEven in the so-called solvent-free synthesis of zeolites, the water is significant and necessary. In previous reports, the crystal water of raw materials usually plays a crucial role in solvent-free synthesis of zeolites without consuming additional water, which lead to the ambiguity of the lowest level of water content for successful synthesis of zeolite.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] Herein, the green synthesis protocol uses raw materials containing little water and needs assistance of additional water with specific dosage so that the dose threshold of water for successful synthesis of zeolite might be ascertained. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e indicates the effect of water amount on the synthesis of ZSM-5. As expected, MFI zeolite cannot be prepared in the water-free system. When a small amount of water was added into the synthesis system (H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e = 1.0), MFI crystal appeared in the product, but the relative crystallinity is lower (48%) and the amorphous phase also exists. By comparison, the H\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio at 2.0 generated highly crystalline ZSM-5 zeolite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and the products remain well MFI structure with further increasement of water. These results confirmed the importance of water for zeolite crystallization. However, it seems that the crucial role of water is not irreplaceable. When water is replaced with an equal amount of ethanol, ZSM-5 zeolite with well crystallinity can also be synthesized (Figure S3), which confirms the availability of organic solvent in this OSDA and solvent-free zeolite synthesis process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilar to the conventional hydrothermal synthesis, this sustainable synthesis process uses the common crystallization temperature at 170 \u003csup\u003eo\u003c/sup\u003eC for more than 18h (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). When the crystallization time is less than 12h, or the crystallization temperature is lower (150 \u003csup\u003eo\u003c/sup\u003eC), only amorphous products can be obtained. After crystallized at 170 \u003csup\u003eo\u003c/sup\u003eC for 18h, the product displays typical MFI structure with relative crystallinity of 61%. Further increasing the crystallization time to 24h, the XRD of product shows the strongest peaks in intensity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). When the crystallization time reaches to 48h, the relative crystallinity of sample slightly decreased (88%), indicating that long crystallization time is not necessary for synthesis of zeolite. In addition, as the SEM images have shown (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), the sample that crystallized for 48h contain some needle-like impurity, which can not be found in the sample crystallized for 18h.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe above experiments were performed with solid silica gel as silica source. In fact, the SiO\u003csub\u003e2\u003c/sub\u003e spheres prepared by Stöber method are also available in this sustainable synthesis for ZSM-5. As Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e has shown, XRD pattern of the sample synthesized from Stöber SiO\u003csub\u003e2\u003c/sub\u003e spheres displays highly crystalline MFI structure. The SEM image exhibits irregular crystals with micrometer size regardless of the starting raw materials with uniform diameter (Figure S3), which indicates that the Stöber SiO\u003csub\u003e2\u003c/sub\u003e spheres aggregate and crystallize into micro-size zeolite particles at the expense of losing original morphology.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e presents the N\u003csub\u003e2\u003c/sub\u003e physical adsorption-desorption isotherms of the prepared ZSM-5 zeolites and corresponding textural properties are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Owing to the template-free synthesis route, the as-synthesized samples without any thermal treatment possess open porous structure. It can be found that both the zeolites from solid silica gel and Stöber SiO\u003csub\u003e2\u003c/sub\u003e sphere exhibit adsorption at low P/P\u003csub\u003e0\u003c/sub\u003e (\u0026lt; 0.01), confirming the presence of open micropores in the samples. Compared to the type-I isotherm of silica gel-derived sample, the zeolite from Stöber SiO\u003csub\u003e2\u003c/sub\u003e sphere shows a hysteresis loop at high relative pressure (0.5–0.9), which indicates that the sample contains some larger pores and leading to higher total pore volume (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In addition, the total surface areas of green-synthesized zeolites herein are less than that of sample from conventional hydrothermal synthesis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Figure S6), which is in accordance with previous report.[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTextural properties of prepared samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSilica source\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(mol/mol)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eS\u003csub\u003eT\u003c/sub\u003e \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eS\u003csub\u003eM\u003c/sub\u003e \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eV\u003csub\u003eM\u003c/sub\u003e \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eV\u003csub\u003eT\u003c/sub\u003e \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSilica gel\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e237\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e196\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStöber SiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e62\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e227\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e136\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003eSiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e molar ratio in H-type zeolites analyzed by XRF. \u003csup\u003eb\u003c/sup\u003eTotal surface area from BET analysis. \u003csup\u003ec\u003c/sup\u003eMicropore surface area from t-plot analysis. \u003csup\u003ed\u003c/sup\u003eMicropore volume from t-plot analysis. \u003csup\u003ee\u003c/sup\u003eTotal pore volume calculated from the adsorption at P/P\u003csub\u003e0\u003c/sub\u003e of 0.99.\u003c/p\u003e \u003cp\u003eThe as-synthesized Na-type zeolites had been converted into H-type ones through NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e- exchanging process to obtain acid properties. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the NH\u003csub\u003e3\u003c/sub\u003e-TPD profiles of the obtained H-type zeolites synthesized from solid silica gel and Stöber SiO\u003csub\u003e2\u003c/sub\u003e sphere. Regardless of the slight difference on actual Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e content in two samples (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which might be due to different purity of corresponding silica sources, they display similar profiles with two intensive desorption peaks at temperature of 190–320 \u003csup\u003eo\u003c/sup\u003eC and 420–450 \u003csup\u003eo\u003c/sup\u003eC, indicating the weak and strong acid sites in the samples, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Fabrication of Pt-ZSM-5 catalysts and catalytic performance\u003c/h2\u003e \u003cp\u003eThe availability of Stöber SiO\u003csub\u003e2\u003c/sub\u003e spheres has expanded this sustainable synthesis route into fabrication of metal-zeolite composites, which benefit from the universality of Stöber process in constructing metal@SiO\u003csub\u003e2\u003c/sub\u003e hybrids.[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] Herein, PVP-stabilized Pt nanoparticles with size of 2 ~ 3 nm (Figure S4) from alcohol reduction process were incorporated into Stöber system, and then Pt@SiO\u003csub\u003e2\u003c/sub\u003e core-shell hybrid had been obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea). By utilizing this Pt@SiO\u003csub\u003e2\u003c/sub\u003e as silica source, the Pt@ZSM-5 composite can be synthesized through aforementioned green synthesis route. The TEM image of the prepared Pt@ZSM-5 (H-form) showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb exhibits that the metallic nanoparticles are embedded in ZSM-5 matrix. Compared to original Pt nanoparticles and Pt@SiO\u003csub\u003e2\u003c/sub\u003e hybrid, the size of metal particles in composite slightly increased (~ 5nm), which can be attributed to the thermal treatment during ion-exchange procedure. After all, serious aggregation of metal particles was avoided for the zeolite confinement effect. By contrast, the supported Pt/ZSM-5 with same Pt content (0.5%) prepared via incipient-wetness impregnation displays uneven sized metal particle with some individuals exceed 10 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ec), which indicates the agglomeration of Pt nanoparticles. Even so, the XRD pattern of both Pt@ZSM-5 and Pt/ZSM-5 only displays MFI diffraction peaks with high crystallinity and no characteristic peaks associated with Pt or PtO\u003csub\u003ex\u003c/sub\u003e phase are visible (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ed), which indicates the absence of bulky metallic particles in the samples. It was evident that Pt nanoparticles embedded in colloid SiO\u003csub\u003e2\u003c/sub\u003e spheres did not hamper the formation of zeolite. When the Pt nanoparticles were directly mixed with SiO\u003csub\u003e2\u003c/sub\u003e spheres and other raw materials, nevertheless, a poor crystalline product had been obtained (Figure S6). This result indicates that the OSDA and solvent-free synthesis process is susceptible to other external factors.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe catalytic performance of prepared Pt-ZSM-5 composites had been investigated in hydroisomerization of \u003cem\u003en\u003c/em\u003e-heptane, which is a typical reaction catalyzed by bifunctional metal-acid catalysts.[\u003cspan additionalcitationids=\"CR48\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e–\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] As Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea has shown, both Pt@ZSM-5 and Pt/ZSM-5 show low \u003cem\u003en\u003c/em\u003e-heptane conversion (6% and 11.4%) at lower reaction temperature of 220 \u003csup\u003eo\u003c/sup\u003eC. With the reaction temperature increasing, the \u003cem\u003en\u003c/em\u003e-heptane conversion over two catalysts also increases. Especially the Pt@ZSM-5, giving the \u003cem\u003en\u003c/em\u003e-heptane conversion as high as 92% at 280 \u003csup\u003eo\u003c/sup\u003eC, more than twice that of Pt/ZSM-5 (37.4%). However, the selectivity to isomers for both catalysts decline with the increase of temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb). Compared to the Pt/ZSM-5 catalyst that generating serious cracking side reactions at investigated temperature range, Pt@ZSM-5 exhibits dominant isomers selectivity at lower reaction temperature (220–240 \u003csup\u003eo\u003c/sup\u003eC). Abundant Bronsted acid sites of Al-rich zeolite should be responsible for cracking side reactions at high temperature.[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] Detailed products distribution listed in Table S2 indicate that mono-branched 2-/3-methylhexanes and propane/iso-butane dominate isomerization and cracking products, respectively, which are accordance with previous report.[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] Considering the physical properties of Pt@ZSM-5 and Pt/ZSM-5, the different structure may be one of critical factor for different catalytic performance. The encapsulation structure of Pt@ZSM-5 may provide better metal-acid sites intimacy, which is favorable to isomerization of \u003cem\u003en\u003c/em\u003e-heptane.[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, the absolute green synthesis for ZSM-5 zeolites without organotemplates, solvents or seeds have been further developed. By using highly purity of silica sources (commercial silica gel and Stӧber colloidal silica), the crucial influencing factors to the successful synthesis have been obtained unambiguously. In addition, this green synthesis can also be extended to the construction of encapsulated metal-zeolite composites, which act as bifunctional catalysts for hydroisomerization of alkanes. Despite the problems of limited Al content, lower surface areas and sensitive synthetic conditions, the merits on cost and environment of green synthesis determine its good prospect of application in heterogeneous catalysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the financial supports from the Talent Scientific Research Fund of LNPU (2020XJJL-016), the Liaoning Provincial Natural Science Foundation of China (2019-MS-323).\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLi Y, Li L, Yu JH (2017) Applications of zeolites in sustainable chemistry. Chem-Us 3: 928-949.\u003c/li\u003e\n\u003cli\u003eCorma A (1995) Inorganic solid acids and their use in acid-catalyzed hydrocarbon reactions. 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J Catal 301: 187-197.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"ZSM-5 zeolite, Green synthesis, Bifunctional catalyst, Colloidal SiO2, Quasi-solid state transformation","lastPublishedDoi":"10.21203/rs.3.rs-3930274/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3930274/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDeveloping sustainable synthesis method of versatile zeolites to overcome the shortcoming of traditional process is of significant for development of green chemistry and environmentally friendly techniques. In this work, MFI zeolite (ZSM-5) was synthesized through organotemplate-, solvent- and seed-free quasi-solid state transformation with commercial silica gel or St\u0026ouml;ber colloidal SiO\u003csub\u003e2\u003c/sub\u003e as silica source. The key influencing factors to this absolute green synthesis process, such as starting material composition, crystallization temperature and time, had been unambiguously investigated by combining a series of characterization techniques and the optimized synthesis conditions had been obtained. In addition, this green synthesis method can be extended into the fabrication of encapsulated metal-zeolite bifunctional catalyst, which is effective in hydroisomerization of \u003cem\u003en\u003c/em\u003e-heptane. These results are instructive for development of green synthesis of aluminosilicate zeolites and derived heterogeneous catalysts.\u003c/p\u003e","manuscriptTitle":"Revisiting the absolute green synthesis of MFI zeolite and derived metal-acid bifunctional catalysts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-12 12:58:54","doi":"10.21203/rs.3.rs-3930274/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6aa97383-79ea-4926-b458-56934578370f","owner":[],"postedDate":"February 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-21T23:44:34+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-12 12:58:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3930274","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3930274","identity":"rs-3930274","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}