Methanol To Aromatics Reaction Research Articles

Self-assembly of hierarchical ZSM-5 particles on rice husk template as hybrid catalysts for boosting methanol aromatization

Herein, natural rice husks with hierarchically porous structures were used as a platform to assemble ZSM-5 particles (denoted as hierarchical ZSM-5) to improve diffusion properties in the methanol-to-aromatics (MTA) reactions. Rice husk could work as the platform to immobilize zeolite grains and provide additional silicon sources for the growth of zeolite particles. Sodium hydroxide amount and SiO2/Al2O3 ratio strongly determined the acid properties, and the rotational crystallization condition favored the zeolite formation. Improved diffusion properties of hierarchical ZSM-5 particles were confirmed by comprehensive pore analysis and benzene diffusion experiments, showing an excellent diffusion property towards aromatic molecules. Compared with commercial microporous zeolite in the catalytic MTA reaction, hierarchical ZSM-5 exhibited superior aromatics selectivity (40.8 vs. 35.8 %), higher liquid hydrocarbon yield (22.3 vs. 14.7 wt%), and longer lifetime (60 vs. 40 h). These results offer new insights into the controllable synthesis of Hier-ZSM-5 with a hierarchically porous structure using biomass as templates.

Simultaneously enhanced aromatics selectivity and catalyst lifetime in methanol aromatization over [Zn, Al]-ZSM-5 via isomorphous substitution with optimized acidic properties and pore structure

Zinc-modified HZSM-5 zeolites as efficient catalysts have been widely applied in methanol to aromatics (MTA) reactions, however, the relationship between aromatics selectivity and catalytic stability in traditionally loaded catalysts seems to be a stubborn trade-off. To improve both catalytic indicators simultaneously and reveal the relation of the states of introduced Zn species to the consequential influence in physiochemical properties, a series of [Zn, Al]-Z5 zeolites with different Zn contents were prepared via isomorphous substitution under a fixed Si/Me (Me = Al or Al and Zn) ratio. Results revealed that there were three possible states of the introduced Zn species, namely the highly-dispersed ZnO phase, the Zn(OH)+ occupying the ion-exchange sites, and the tetra-coordinated ZnO42- integrated into the zeolite framework. A portion of Zn was successfully integrated into the five-membered rings of zeolite in the form of Si-O(H)-Zn, which played the role of strong Brönsted acid sites and led to the formation of hierarchical structures aside from the intrinsic micropores. Besides, extra-framework Zn(OH)+ was formed by the interaction between dissociate Zn species and the Si-O(H)-Al structure, giving rise to larger proportions of Lewis acid sites. Benefitting from the optimized acidic properties and pore structure, 0.5[Zn, Al]-Z5 exhibited higher aromatics selectivity and longer catalyst lifetime (26.0% and 132 h) than [Al]-Z5 without Zn addition (19.6% and 52 h) in methanol aromatization. Overall, our findings opened a new way to improve the efficiency of MTA reaction and broadened the method to obtain metal-modified zeolite catalysts.

Facilely adjusting acidity features of zeolites by steaming treatment for enhanced methanol conversion to aromatics: A mechanism study

In this contribution, the effects of the steaming treatment on the acidity and aluminum structure of ZSM-5 were systematically investigated by using different types of zeolite catalysts. The relationships between the acid properties and the catalytic performance of the methanol-to-aromatics (MTA) reaction were also elucidated. The results revealed that different kinds of acid sites showed varied stability during the steaming treatment. Especially for Brønsted acid sites (BAS), the reduction of the acid site was highly related to the stability of different distributed framework Al sites (Alsingle > Alpairs) and the existence of non-framework species (“neutralization” by the EFAL and ZnO). Additionally, the presence of the extra-framework aluminum (EFAl) and metal compensation ions could enhance the stability of the zeolite framework Si-O(H)-Al. Besides, it was found that the reduction degree in the content of the Zn-LAS (LAS = Lewis acid sites) was less than the Al-LAS. The effects of steaming treatment on acid properties over zeolites with different particle sizes were also explored. Furthermore, the catalytic performance for the MTA reaction showed that the stability of the ZSM-5 catalyst was significantly enhanced after the steaming treatment. Moreover, the reduction in the proportion of the Alpairs sites may inhibit the hydrogen-transfer aromatization process of alkenes, while the increase of the Alsingle species enhanced the cracking process of higher olefins, leading to the reduction of aromatics selectivity and the increase of light olefins selectivity, respectively.

Enhancement of catalytic and anti-carbon deposition performance of SAPO-34/ZSM-5/quartz films in MTA reaction by Si/Al ratio regulation

In order to further improve the catalytic performance of zeolite catalyst for methanol to aromatics (MTA) technology, the double-tier SAPO-34/ZSM-5/quartz composite zeolite films were successfully synthesized via hydrothermal crystallization. The Si/Al ratio of SAPO-34 film was used as the only variable to study this material. The composite zeolite material with 0.6 Si/Al ratio of SAPO-34 has the largest mesoporous specific surface area and the most suitable acid distribution. The catalytic performance for the MTA process showed that 0.6-SAPO-34/ZSM-5/quartz film has as high as 50.3% BTX selectivity and 670 min lifetime. The MTA reaction is carried out through the path we designed to effectively avoid the hydrocarbon pool circulation of ZSM-5 zeolite, so as to improve the aromatics selectivity and inhibit the occurrence of deep side reactions to a great extent. The coke deposition behavior was monitored by TG and GC-MS, it is found that with the increase of Si/Al ratio, the active intermediates changed from low-substituted methylbenzene to high-substituted methylbenzene, which led to the rapid deactivation of the catalyst. This work provides a possibility to employ the synergy effect of composite zeolite film synthesizing anti-carbon deposition catalyst in MTA reaction.

Correlation of Brønsted acid strengths and species substituted Si in ZSM-5 and their effects on propylene polymerization in MTA reaction

Methanol to aromatics (MTA) is regarded as an efficient process to generate benzene, toluene, xylene (BTX), and other important chemical raw materials, and the polymerization of alkenes is an important reaction in MTA. In this work, the effect of different Brønsted acid strengths over ZSM-5 on propylene polymerization was studied by using the density functional theory (DFT) method. H-M-ZSM5 with different Brønsted acid strengths are formed by substituting Si atoms in ZSM-5 by Al, Ga, In, Fe, and B atoms, respectively. And three steps including the formation of propoxide, propylene dimerization, and the deprotonation of C6 hydrocarbon are investigated. The i-propoxide is most easily generated by the protonation of propylene. And the polymerization of i-propoxide with propylene is easier compared to n-propoxide in the dimerization step. Subsequently, hexoxy primary carbon dehydrogenation to generate C6 olefins is prone in the C6 hydrocarbon deprotonation step. Therefore, the optimal path is the protonation of propylene to produce i-propoxide, which in turn polymerizes with propylene to produce hexoxy (IM5), followed by a deprotonation step to produce the most favorable product 2-Methyl-pentene. Meanwhile, the enhanced strength of the Brønsted acid significantly promotes the activity of propylene protonation and C6 hydrocarbons deprotonation, while it has little effect on the propylene dimerization. Therefore, the Brønsted acid strength is proposed as an appropriate descriptor to reflect the catalytic activity of H-M-ZSM5 to the propylene protonation and C6 hydrocarbons deprotonation. And H–Al-ZSM5 and H-Ga-ZSM5 with high acid strength are found to have the best performance for the propylene polymerization to C6 olefins.

Synthesis of hollow HZSM-5 zeolite-based catalysts and catalytic performance in MTA reaction

Although HZSM-5 zeolite is more and more widely used in petrochemical industry and other fields, its single narrow micropore system often leads to mass transfer issues during some types of catalytic reactions. In addition, dealumination in the presence of steam and coking due to the presence of strong acids sites are issues of aluminosilicate catalysts in general. In this work, a simple post-treatment method based on the traditional prepared HZSM-5 catalyst was proposed and an outlayer SiO2 encapsulated Gd/HZSM-5 catalyst with hollow and hierarchical porous systems ([email protected]/Z5-T) was obtained. This catalyst can overcome those defects for the traditional HZSM-5 mentioned above, such as, the outermost SiO2 layer can protect the aluminum species in the framework of Gd/HZSM-5 and cover part of strong acid sites, and the hollow and hierarchical porous systems can minimize the mass transfer resistance, etc. The [email protected]/Z5-T catalyst exhibited high selectivity of BTX (65.7%), especially xylene (39.7%), in the methanol to aromatics reaction (MTA) owing to the suitable acidity and optimized porous system. In addition, the [email protected]/Z5-T catalyst possessed much better hydrothermal stability and the excellent anticoking ability in the MTA reaction as expected. Thus, this should be a general method for the modification of silica alumina molecular sieve catalysts to obtain the novel catalyst with hollow and hierarchical porous systems, adjustable acidity and high hydrothermal stability.

Methanol aromatization over Zn-modified HZSM-5 catalysts derived from ZIF-8

Methanol to aromatics (MTA) is an effective way to produce aromatics by non-petroleum route. The acidity and structure of zeolite catalysts are the key to aromatics yield and stability of catalysts in MTA reaction. Here, Zn-modified HZSM-5 catalysts were prepared by physical mixing method (PM), in-situ hydrothermal synthesis method (SH) and steam-assisted crystallization method (SAC) using ZIF-8 as sacrificial template and Zn source. XRD, SEM, TEM, N2 adsorption-desorption, ICP-OES, NH3-TPD, Py-IR, XPS, H2-TPR, TG characterization methods were used to investigate the physical and chemical properties of the catalysts. The influence of preparation methods of catalysts, the addition amount of ZIF-8, different Zn sources and reaction conditions on the products distribution in MTA reaction were investigated. The results showed that the crystallinity of ZnZ8(SAC)/Z5 catalyst was improved and the hierarchical pore structure was obtained successfully after introduced ZIF-8 by steam-assisted crystallization method. Among them, ZnZ8 mainly exists as ZnOH+ species, which improved the utilization rate of Zn atoms and more L acid sites and moderate acid concentration were formed. The addition amount of ZIF-8 can affect the crystalline size, pore structure and the concentration of ZnOH+ species of ZnZ8(SAC)/Z5. An appropriate ratio of B/L acid concentration was formed when adding an appropriate amount of ZIF-8. Compared with the traditional Z5 catalyst modified with Zn(NO3)2 as Zn source (1% ZnZN(SAC)/Z5), there are smaller particle size, larger specific surface area and mesopore volume as well as suitable acid distribution in 1% ZnZ8(SAC)/Z5 catalyst. The preparation method of catalyst, the addition amount of ZIF-8, different Zn sources and reaction conditions have a significant effect on the selectivity of BTX.

Regulating hierarchical structure and acidity of HZSM-5 for methanol to aromatics via protective desiliconization and external surface modification

HZSM-5 is a widely used catalyst for the conversion of methanol to aromatics (MTA), but its single micropore system often results in severe diffusion limitations, leading to the decrease of reaction rate and the change of selectivity to aromatics, as well as affecting the carbon deposition and catalyst deactivation. Thus, an ingenious protective desiliconization method with a mixed solution of sodium hydroxide and tetrapropylammonium hydroxide as a desiliconization agent was developed to create hierarchical porous systems without destruction of the main structure of the molecular sieve. Such modification leads to the greatly increased mesoporous volume from 0.12 to 0.38 cm3 g−1, and only slightly decreased microporous volume from 0.12 to 0.09 cm3 g−1. However, the desiliconization sharply increases the acidity of the catalyst (from 0.248 to 0.341 mmol g−1 for the strong acid sites), which may significantly affect the distribution of aromatics and accelerate the carbon deposition rate. Thus, the deposition of inert SiO2 on the catalyst surface is subsequently carried out to passivate the surface acidity and adjust the orifice of the catalyst. Accordingly, a hierarchical porous HZSM-5 molecular sieve catalyst ([email protected] + TP) with suitable acidity is precisely prepared, which exhibits the high selectivity to benzene, toluene and xylenes (BTX) with the excellent anticoking ability in the MTA reaction. The selectivity to BTX in aromatics (63.32%) and the carbon deposition rate (0.91 mg gcat−1 h−1) over the [email protected] + TP catalyst are both much more superior than those over the parent HZSM-5 catalyst (47.5% and 2.23 mg gcat−1 h−1, respectively).

Decentralized methanol feed in a two-stage fluidized bed for process intensification of methanol to aromatics

Methanol to aromatics (MTA) process not only involves the dehydrogenation-aromatization reactions but also the undesirable side reactions (e.g., hydrogen transfer, dealkylation, disproportionation, isomerization). As-produced aromatics composition was not favorable for the subsequent para-xylene (PX) manufacturing process in the MTA plant. In this study, we proposed the decentralized methonal feed strategy for process intensification of MTA and compared the effects of the centralized feed and decentralized feed on MTA reaction. It was found that the decentralized feed could weaken the occurrence of side reactions and affect the product distribution, the aromatics yield produced no change though. By inhibiting the dealkylation and disproportionation and isomerization reactions, the decentralized feed decreased the yields of benzene (B) and toluene (T) while increased the xylene (X) yield and PX selectivity in X beyond thermodynamic equilibrium, which is highly expected in industry. With the decentralized feed, the restricted hydrogen transfer reaction increased olefins and C5+ non-aromatics, which could be further converted into aromatics, and reduced unwanted alkanes. Our methodology of process intensification provided insight into product distribution optimization to match large materials flow in terms of PX production in the MTA plant.

Temperature-dependent secondary conversion of primary products from methanol aromatization in a two-stage fluidized bed

Methanol to aromatics (MTA) following dual cycles concept unavoidably produced considerable amounts of olefinic intermediates and paraffinic by-products. Their formation and further conversion were vitalto improving aromatics production. In this study, a two-stage fluid bed packed with fluid Zn/ZSM-5 catalyst in each stage was used to investigate the MTA reaction at 470 °C in the first stage and the secondary conversion of MTA primary products at temperatures from 270 °C to 550 °C in the second stage with time on stream. During the MTA reaction, the decrease of catalyst acidity was beneficial to controlling hydrogen transfer, thus blocking propane formation. During the secondary conversion of MTA products, at temperatures below 390 °C, the alkylation and hydrogen transfer reactions dominated and thus olefins were converted into more alkylbenzene as well as the undesired propane and butane. As the temperature increased from 430 °C to 550 °C, the aromatization of light hydrocarbon and the dealkylation of alkylbenzene were facilitated, producing more benzene and toluene but increasing methane and ethane yields. Meanwhile, the dehydrogenation and cracking of propane and butane were favored by high temperature and strong acidity so that the yields of ethene and propene increased. It was clarified that the characteristics of secondary conversion of MTA products varied and depended on reaction temperature and catalyst acidity. Based on these findings, the concept of regional functionalization of fluidized bed reactor was proposed for intensification of MTA process based on the reconfiguration of the temperature and acidity of catalyst stream during the fluidized bed reaction-regeneration cycle.

Effect of framework Al siting on catalytic performance in methanol to aromatics over ZSM-5 zeolites

ZSM-5 zeolites with different framework Al (AlF) siting were hydrothermally synthesized by adding mineralizer, urea, or by changing the silicon source. The morphology, textural properties, AlF siting, and acidity of different ZSM-5 zeolites were characterized using SEM, XRD, BET, XRF, MAS NMR, NH3-TPD, and Py-FTIR. Furthermore, methanol to aromatics (MTA) was used to investigate the catalytic performance of different catalysts. The results suggested that different ZSM-5 zeolites were highly crystalline with a uniform morphology, but there were large differences in AlF siting and acidity. The AlF in the ellipsoidal ZSM-5 sample was mainly distributed in straight or sinusoidal channels and displayed more acidic sites. AlF of bulk ZSM-5 was mainly located at the intersection of channels, and it showed the lowest amount of strong acid sites. The ellipsoidal ZSM-5 catalyst in which AlF was mainly located in straight or sinusoidal channels exhibited more acidic sites and higher stability and aromatic selectivity during the MTA reaction.

Enhanced Stability of Mo-Promoted Zn/HZSM-5 Catalyst for Methanol to Aromatics

A Mo-promoted Zn/HZSM-5 catalyst was prepared by isometric impregnation method (IM). The physicochemical properties of catalysts were characterized by X-ray diffraction, registration of N2 adsorption-desorption isotherms, transmission electron microscopy, NH3 temperature-programmed desorption and IR spectroscopic study of pyridine adsorption. The results show that by doping zeolite with Mo species it is possible to tune the microstructures, acidity and crystallinity of the catalyst. Additionally, it was found that the 1%Mo(IM)–5%Zn(IE)/HZSM-5 catalyst had a high catalytic activity and stability for methanol to aromatics (MTA) reaction. The yield of aromatics reached 77.3% at 450°C and TOS = 3 h. When the TOS = 98 h, the yield of total aromatics remains at a 60.4% level. The lifetime of catalysts was influenced by the synergetic effect of Bronsted and Lewis acid sites, so the modification with Mo may bring an opportunity to prolong the lifetime of Zn/HZSM-5 catalyst in the MTA reaction. The metal components are sintered and lost in continuous reaction-regeneration cycles. Accordingly, the activity of deactivated catalyst cannot be completely restored to the initial level.

Efficient and selective conversion of methanol to para-xylene over stable H[Zn,Al]ZSM-5/SiO2 composite catalyst

A highly shape-selective H[Zn,Al]ZSM-5/SiO2 composite catalyst was prepared by direct incorporating Zn species via isomorphous substitution into the zeolite framework and subsequent SiO2 deposition on zeolite surface. Its catalytic performance in methanol to aromatics (MTA) was compared with Zn/HZSM-5/SiO2 prepared by impregnation of Zn species and subsequent SiO2 deposition. The textural properties and acidic properties as well as the subsequent catalytic performances of the resultant catalysts in MTA reaction were obviously influenced by the introduction method of Zn species. H[Zn,Al]ZSM-5/SiO2 prepared by isomorphous substitution contained more inter-crystalline voids, which provided much space to resist deposition of coke and avoided quick blockage of micropore entrances. In contrast, Zn/HZSM-5/SiO2 prepared by impregnation contained sub-nanometric ZnO clusters at the pore entrances, which might restrict large molecule products diffusion and deteriorated the catalyst deactivation. Moreover, the sum of strong and medium acid sites in H[Zn,Al]ZSM-5/SiO2 was more than that in Zn/HZSM-5/SiO2, which meant there were more active sites for cyclization and aromatization steps in MTA reaction in the former. As a result, the lifetime of H[Zn,Al]ZSM-5/SiO2 was almost twice that of Zn/HZSM-5/SiO2. In addition, the enhancement in catalytic activity by Zn introduction and the improvement in para-selectivity in xylene by SiO2 deposition were also studied. Finally, nearly 100% methanol conversion, 95.6% para-selectivity in xylene and 18.2% para-xylene yield were simultaneously obtained over the stable H[Zn,Al]ZSM-5/SiO2 (with 24 h lifetime) in MTA reaction.

Brønsted/Lewis Acid Synergy in Methanol-to-Aromatics Conversion on Ga-Modified ZSM-5 Zeolites, As Studied by Solid-State NMR Spectroscopy

1H–71Ga internuclear spatial proximity/interaction between Bronsted acid site (BAS) and cationic Ga species (Lewis acid sites) in Ga-modified ZSM-5 zeolites, which leads to a synergic effect in the methanol-to-aromatics (MTA) conversion, was identified with solid-state NMR spectroscopy. The internuclear distance between BAS and Ga species was measured, which is similar to that of a neighboring BAS pair located in the six-membered rings of ZSM-5. The Bronsted acidity of the Ga-modified zeolite was considerably enhanced due to the synergic effect, and the synergic active sites were quantified by 1H–71Ga double-resonance solid-state NMR, which shows a correlation with the aromatics selectivity in the MTA reaction.

Product distribution and catalytic performance of nano-sized H-ZSM-5 zeolites in the methanol-to-aromatics (MTA) reaction

ABSTRACTA study of the effect of SiO2/Al2O3 molar ratio on the activity and selectivity of H-ZSM-5 catalyst in the reaction of methanol to aromatics (MTA) has been carried out in this work. Aluminosilicate zeolite (ZSM-5) zeolites with different SiO2/Al2O3 molar ratios were successfully synthesized by the hydrothermal method. The SiO2/Al2O3 molar ratio of the prepared ZSM-5 zeolite particles could be easily controlled by changing the ratio of tetraethylorthosilicate to aluminum nitrate nonahydrate. The effect of SiO2/Al2O3 molar ratio on the activity of nano-sized H-ZSM-5 zeolites in the MTA reaction was studied. The H-ZSM-5 zeolite catalyst with low SiO2/Al2O3 molar ratios shows remarkable selectivity toward aromatics and benzene, toluene, and xylene (BTX) in the MTA reaction.

Correlation between H-ZSM-5 crystal size and catalytic performance in the methanol-to-aromatics reaction

The porosity of H-ZSM-5 zeolite is known to facilitate the diffusion of molecules in the methanol-to-aromatics (MTA) reaction. The activity and selectivity of the H-ZSM-5 catalyst in the MTA reaction has been studied as a function of crystal size. ZSM-5 zeolites with different crystal sizes were successfully synthesized by conventional hydrothermal methods. Tailoring ZSM-5 particle size was easily controlled by changes to the sol-gel composition, and in particular, the deionized water to tetrapropylammonium hydroxide ratio, and crystallization time. The structure of the H-ZSM-5 zeolites were characterized by X-ray diffraction and the morphology of the zeolite particles was determined by scanning electron microscopy. N2 adsorption-desorption measurements established changes to the textural properties, and compositional properties were characterized by X-ray fluorescence spectroscopy. Acidity measurements of the catalysts were measured by pyridine-adsorbed Fourier transform infrared spectroscopy and the temperature-programmed desorption of ammonia. After subjecting the catalysts to the MTA reaction, the total amount of coke formed on the spent deactivated catalysts was determined by thermal gravimetric analysis. The results show that the SiO2/Al2O3 molar ratios and acidic properties of the H-ZSM-5 samples are similar, however, the nano-sized hierarchical ZSM-5 zeolite with an additional level of auxiliary pores possesses a higher surface area, larger mesopore volume and larger macropore volume, resulting in more effective mass transportation properties. The H-ZSM-5 zeolite catalysts were evaluated for their activity towards the MTA reaction as a function of crystal size. The nano-sized H-ZSM-5 catalyst having shorter diffusion path lengths, substantial mesoporosity and a high external surface area showed excellent selectivity toward aromatics (average > 42%) and benzene, toluene and xylenes (37% at 180 min). Furthermore, lower coking levels were observed on the nano-sized H-ZSM-5 catalyst when compared with the H-ZSM-5 catalysts possessing larger particle sizes and is attributed to a reduction in polyaromatic hydrocarbons being deposited within the internal surface area.

The comparison of mesoporous HZSM-5 zeolite catalysts prepared by different mesoporous templates and their catalytic performance in the methanol to aromatics reaction

Three kinds of mesoporous HZSM-5 were synthesized successfully by using a hydrothermal methodology with different mesoporous templates, namely, hexadecyl trimethyl ammonium bromide (CTAB), dimethyl distearylammonium chloride (DDAC) and carbon nanotube (CNT). The differences in crystallinity, textural property and acidity among these micro-mesoporous composite molecular sieves were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy techniques, transmission electron microscopy, nitrogen adsorption and NH3 temperature programmed desorption. The catalytic performances of these mesoporous HZSM-5 zeolites were evaluated by methanol to aromatics (MTA) reaction, and the conventional microporous HZSM-5 was also tested in this reaction for comparison. The results show that mesoporous HZSM-5 zeolite synthesized with CNT mesoporous templates exhibited the highest BTX yields and lowest rate of carbon deposition in MTA reaction among all catalysts. This improved catalytic performance is mainly attributed to not only the well-preserved strong acid sites, which would provide enough active sites for methanol aromatization, but also the generated intra-crystalline mesopores, which would facilitate the access of reactant to the active sites and improve the mass transfer of products. However, mesoporous HZSM-5 synthesized with CTAB and DDAC mesoporous templates did not present improved catalytic performances due to their disconnected micro-mesopores and inadequate strong acidic sites.

Stable and efficient aromatic yield from methanol over alkali treated hierarchical Zn-containing HZSM-5 zeolites

Fast deactivation of catalyst is the main problem in methanol-to-aromatics (MTA) process. Herein, Zn-containing HZSM-5 zeolites with hierarchical pores (H-Zn/HZSM-5) were prepared by treating directly synthesized Zn/HZSM-5 with NaOH solution. The changes in crystallinity, acidity and textural properties of Zn/HZSM-5 before and after alkali treatment were characterized by X-ray diffraction, NH3-TPD, 27Al MAS-NMR, N2 physisorption, X-ray fluorescence and TEM techniques. MTA reaction under the operating conditions of T = 400 °C and WHSV = 2.5 h−1 showed that the aromatic yield was improved from 41.4% for HZSM-5 to 55.3%. Furthermore, H-Zn/HZSM-5 exhibited a high initial space time yield of 0.62 g gcat−1 h−1 and a long lifetime up to 120 h. These results could be ascribed to the hierarchical pores and the providential acidity, which enhanced the adsorption and diffusion of intermediates/products during the reaction.

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined in air shows much higher activity and selectivity for the MTA conversion compared with AgZSM-5 zeolite calcined in vacuum or HZSM-5 zeolite. A possible reaction mechanism is proposed for the MTA conversion on the AgZSM-5 zeolite.