Methanol To Aromatics Research Articles

Aromatics Production via Methanol-Mediated Transformation Routes

The methanol-to-aromatics (MTA) process is regarded as a promising route to produce aromatic commodities through non-petroleum carbon resources, such as biomass, waste, coal, natural gas, and CO2. In contrast with the industrially implemented methanol-to-olefin (MTO) process, most MTA studies are still in the laboratory-scale stage. Recently, a few demonstration plants of MTA have been successfully launched, indicating the importance and the gradual industrial maturity of this technology. However, there are still many fundamental questions and technological challenges that must be addressed. In this Review, we summarize the recent advances in mechanistic understanding on the reaction and catalyst deactivation during MTA, elaborate the available strategies to improve the catalytic performance, and correlate MTA studies with other important catalytic aromatization processes. With this knowledge in hand, we share our views on future research directions in this field.

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.

High-Efficiency Conversion of Methanol to BTX Aromatics Over a Zn-Modified Nanosheet-HZSM-5 Zeolite

A Zn-modified nanosheet-HZSM-5 zeolite (Zn-SH-HZSM-5) was prepared and tested as a catalyst in the methanol-to-aromatics (MTA) reaction. First, both an effective suppression of C9+ aromatics formation and a significantly enhanced yield of benzene, toluene, and xylene (BTX) aromatics were achieved by reasonably controlling the reactive pathways in this catalytic reaction system. Further alkylation of BTX aromatics to form C9+ byproducts was effectively limited by the significantly reduced retention time of BTX molecules in the micropore system, with a significantly shortened diffusion-reaction path. Furthermore, the conversion of methanol to BTX was significantly improved by introducing new surface Zn-Lewis acid sites, achieving a synergistic catalysis with Brönsted acid sites. Second, this catalyst also exhibited strong capabilities both to limit the formation and deposition of large-size coke molecules, thanks to its shortened diffusion-reaction path, and to accommodate carbon, due to the high external surface area and considerable stacking mesopores. As a result, our Zn-SH-HZSM-5 catalyst demonstrated good stability in a 100 h on-stream reaction, providing a BTX yield higher than 54.5%, with a C9+ aromatic byproduct formation lower than 5.1%. The present work may provide a promising way for developing an elegant catalyst for a more sustainable MTA process.

The effect of introducing Ga on the ZSM-5-catalyzed methanol to aromatics reaction: taking methylcyclopentane to benzene as an example.

Naphthenes are key intermediates in the formation of aromatic compounds during the methanol to aromatics (MTA) reaction, and the dehydrogenation process is more important than the hydrogen transfer process. Theoretical studies were performed to investigate the methylcyclopentane, which represents a naphthene, to benzene MTA process catalyzed by ZSM-5 before and after introducing Ga, showing that Ga-ZSM-5 was more favorable for carrying out the reaction than two H-type ZSM-5 (H-Z1 and H-Z2) models. H-Z1 and H-Z2 are favorable for the transfer of H during ring expansion reactions and the reformation of Brønsted acids, but the dehydrogenation reactions involving H-Z1 and H-Z2 require high free-energy barriers to be overcome. Although introducing Ga to ZSM-5 is not conducive to the transfer of H after dehydrogenation, it can reduce the extremely high dehydrogenation free-energy barrier compared with H-Z1 and H-Z2; this is mainly because Ga at dehydrogenation active centers, [GaH]2+, can accept electrons and donate them to the H atoms of [GaH]2+, giving H negative charge and making it easy to combine with positive B-acid H atoms that come from methylcyclopentane, cyclohexene, and cyclohexadiene to produce H2. Also, analysis of the transition state structures of all DH processes shows that Ga-ZSM-5 is more favorable for promoting the combination of H to produce H2 than H-Z1 and H-Z2.

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).

Stable Zn@ZSM-5 catalyst via a dry gel conversion process for methanol-to-aromatics reaction

Abstract A unique synthesis route to stabilize zinc species in ZSM-5 zeolite crystals was developed. Firstly, extensive mesoporosity in ZSM-5 was obtained through alkali treatment, after which Zn nanoparticles were introduced into the hierarchical ZSM-5 by impregnation. Then the sample was mixed with SiO2-sol and shaped. Finally, the Zn-fixed ZSM-5 zeolites was obtained by dry gel conversion. By this method, zinc species can be effectively stabilized in zeolite, which can not only improve the aromatic hydrocarbons selectivity, but also increase the stability of the catalyst in the reaction of methanol to aromatics (MTA). The acidity properties and the state of zinc species were studied. It was found that the catalyst possessed more Lewis acid sites and the ratio of Zn(OH)+/ZnO was increased after dry gel conversion.

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.

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Abstract Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics (MTA) reaction, which is often attributed to the metal promoting the aromatization of intermediate olefins. However, the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied. Here, we report that HCHO, which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation, can participate in the synthesis of aromatics. Methanol conversion can produce more aromatics than olefins (propylene or ethylene) conversion over Zn/H-ZSM-5, indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete. Moreover, an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.

Controlled synthesis of ZSM-5 zeolite with an unusual Al distribution in framework from natural aluminosilicate mineral

Abstract Precisely tuning the location of Al atoms in zeolite framework that plays a critical role in determining the catalytic performance of zeolite based catalysts has attracted considerable attention. In this article, we present an organotemplate-free approach for the controllable synthesis of ZSM-5 zeolite with a high content of Al pairs selectively located at the channel intersections, which is achieved by using a submolten salt (SMS) depolymerized rectorite as both the Al source and heteropical crystalline seeds. The quasi in-situ characterizations tracking the zeolite crystallization process reveal that the depolymerized rectorite with abundant oligomeric aluminosilicate species and Al–O-(Si–O)1,2-Al sequences plays dual roles in the synthesis of ZSM-5 zeolite. These oligomeric aluminosilicate species like 5- and 6-membered ring structures serve as the crystalline seeds to promote the zeolite nucleation; simultaneously, the Al–O-(Si–O)1,2-Al sequences are in-situ transformed into the final zeolite framework leading to the generation of numerous Al pairs selectively located at the channel intersections. Such an unusual Al distribution endows the synthesized ZSM-5 zeolite with excellent catalytic performance in methanol to aromatics (MTA) reaction. Our strategy provides a sustainable and efficient way to design and synthesize high-performance zeolites with special framework Al distributions for catalytic applications.

High-Impact Promotional Effect of Mo Impregnation on Aluminum-Rich and Alkali-Treated Hierarchical Zeolite Catalysts on Methanol Aromatization.

A systematic change of HZSM-5 (HZ5) as a catalyst of the methanol to aromatics (MTA) reaction was undertaken by employing a fixed-bed tubular-type reactor under ambient pressure, applying a weight hourly space velocity (WHSV) of 2 h–1 at 375 °C, as the first report on the application of low-Si/Al-ratio alkaline-[Mo,Na]-HZSM-5 in the MTA process. To characterize the surface and textural properties of the catalysts, powder X-ray diffraction (PXRD), nitrogen adsorption/desorption, temperature-programmed desorption of ammonia (NH3-TPD), pyridine-infrared spectroscopy (Py-IR), thermogravimetric analysis (TGA), and energy-dispersive X-ray (EDX) methods were employed. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) measurements demonstrated a selectivity of up to 86 wt % (65.7 wt % for benzene, toluene, and xylene (BTX)) over 2[Mo]HZ5. NH3-TPD and Py-IR results indicated a sensible decrease of strong acid sites on the impregnated samples, while the surface analyses revealed the highest Lewis acid sites (LAS) together with the largest mesopore surface area for 2[Mo]alk-HZ5, supporting the migration of Mo species to the bulk of the catalysts. Mo impregnation had a minor effect on the observed coke formation in the promoted catalyst.

Synthesis of 10 and 12 Ring Zeolites (MCM-22, TNU-9 and MCM-68) Modified with Zn and Its Potential Application in the Reaction of Methanol to Light Aromatics and Olefins

The effect on the incorporation of zinc of three zeolites TNU-9, MCM-22, and MCM-68 was investigated. The physico-chemical properties of zeolites were studied by X‐ray diffraction, N2-adsorption, temperature‐programmed desorption of NH3 (TPD), nuclear magnetic resonance of 27Al and 29Si (MAS NMR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Then all the samples were characterized and evaluated in the reaction of methanol to aromatics (MTA). The correlation of zinc incorporation method and acidic properties of zeolites with catalytic performance was investigated. The form of zinc incorporation, the acidity, the type of zeolitic structure and the reaction temperature had a great influence on the catalytic activity. Regarding the type of structure, the total aromatics selectivity in this work increased in the followed order for zeolites modified with Zn: MCM-68 > TNU-15 > MCM-22. The medium pore zeolite T9-15 (TNU-9 zeolite and Si/Al 15 ratio) catalysts with the ratio ZnO/ZnO + Al2O3 equal to 0.34 (T9-15 0.5 Zn) showed better stability with conversion of methanol completes during 9 h of reaction and 17% to BTX selectivity and 32% to total aromatics compounds at 450 °C and WHSV of 4.24 h−1. In methanol conversion, the selectivity to aromatics over the T9-15 modified-Zn materials (TNU-9 zeolite and Si/Al 15 ratio) under study, increased in the followed order: T9-15 0.5 Zn > ZT9-15 > T9-15 > T9-15 0.2 Zn. The reaction temperature is an important variable in the MTA process. At 450 °C a better activation of acid sites is achieved in zeolite with Zn and therefore a high percentage of BTX selectivity is obtained for TNU-9 zeolite.

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.

Molecular Dynamics Simulation of the Implantation of b-Oriented ZSM-5 Film Modified α-Quartz Substrate Surface With Different Modifiers.

In this study, we investigated the structure–absorption relationship of common surface modifiers of chitosan (CTS), polyvinyl acetate (PVA), and titanium dioxide (TiO2) with α-quartz surface using molecular dynamics simulation. And the orientations and combinations derived from structures between modified α-quartz and ZSM-5 crystallites were also investigated. The results show that PVA is a non-linear organic macromolecule with a large amount of hydroxyl groups on its surface, which easily adhere to the surface of the substrate and agglomerate. CTS is a straight-chain structure containing a large number of hydroxyl and amino groups, which easily accumulate and spread on the surface of the substrate. TiO2 not only forms hydrogen bonds and complexes with the substrate but also interacts with each other to form a dense modifier layer. We observed that a large number of stable Ti–O–Si chemical bonds formed between the modified layer of inorganic small-molecule TiO2 and the surface of α-quartz, which compacted and stabilized the attached ZSM-5 film. Moreover, the orientation angle of the ZSM-5 nanocrystalline nucleus on the modified α-quartz was computed, which confirmed that the b-axis orientation of the ZSM-5 nanocrystalline nucleus was the highest on the surface of the substrate modified by TiO2. We discussed the influence of the modified temperature of modifiers in the constructed materials, and we have observed the adsorption state differences of TiO2 at different modified temperatures. We also discussed the catalytic properties of the materials prepared by the corresponding methods in conversion of methanol-to-aromatics (MTA) reaction. These results agree with our previous experimental data. By employing molecular dynamics simulation, we have obtained more precise conclusive information of the b-oriented growth of ZSM-5 crystallites, which highly depends on the surface modifiers.

Insight into the Formation of COX By‐Products in Methanol‐to‐Aromatics Reaction over Zn/HZSM‐5: Significantly Affected by the Chemical State of Surface Zn Species

AbstractSeveral Zn‐modified HZSM‐5 catalysts prepared by impregnation or ion exchange were characterized, and tested in methanol‐to‐aromatics (MTA) reaction. The obviously enhanced output of COX by‐products (CO & CO2) was observed over these modified catalysts, although they showed the significantly improved selectivity of aromatics. It was found COX formation is actually determined by the chemical state of surface Zn species. Concretely, both surface ZnO and surface metal‐zinc are the reactive sites for the conversion of methanol to COX and H2. At the initial period of reaction, surface ZnO (no reduction) causes COX (mainly CO2) formation may almost‐exclusively through methanol steam‐reforming. With the extending of reaction‐time, while it′s partially reduced to metal‐zinc which more violently catalyzes the conversion of methanol to COX (both CO and CO2) may through the pathway of first dehydrogenation‐decomposition and subsequent Water‐Gas‐Shift reaction. However, the surface ZnOH+ species as Lewis acid hardly results in COX formation, but significantly promotes aromatization due to its interaction‐dehydrogenation effect. As high as possible ratio of the ZnOH+ in surface Zn species is conducive to both suppressing the side‐reaction which produces COX and incubating the high aromatic selectivity even in the time‐on‐stream reaction. Our work may provide a theoretical guidance for developing the elegant catalyst for the MTA process with high carbon atom utilization.

Heterogeneous catalysis in multi‐stage fluidized bed reactors: From fundamental study to industrial application

AbstractThe multi‐stage fluidized bed (MSFB) reactor with several stages connected in series prevents gas and solids back‐mixing effectively and obtains the plug‐flow reactor performance. Besides, different process steps can be accomplished in a single reactor by establishing different temperatures and/or concentrations in each stage. Therefore, multi‐stage fluidized bed reactors are acknowledged as novel and flexible multi‐phase flow reactors for heterogeneous catalytic processes, especially with the intermediates as the desired products. Typical process developments in the industry involve the methanol to aromatics (MTA), regeneration in fluid catalytic cracking (FCC), and hydrogenation of nitrobenzene to aniline. The purpose of this article is to provide a comprehensive review of the fundamental research as well as particular industrial applications on multi‐stage fluidized bed reactors in the Fluidization Laboratory of Tsinghua University (FLOTU).

A Mechanistic Study of Methanol-to-Aromatics Reaction over Ga-Modified ZSM-5 Zeolites: Understanding the Dehydrogenation Process

The methanol-to-aromatics (MTA) reaction was investigated on Ga-modified ZSM-5 zeolites (Ga/ZSM-5). As revealed by 71Ga and 1H solid-state NMR and FT-IR of pyridine adsorption measurements, cationi...

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.

Deactivation kinetics with activity coefficient of the methanol to aromatics process over modified ZSM-5

A lumped kinetic model for methanol to aromatics (MTA) process was investigated using modified ZSM-5 industrialized catalyst. The deactivation kinetic behavior of MTA was studied by developing a 5-lump kinetic model to describe the product distributions. The feedstock and products are divided into five lumps by simplifying reaction network, including oxygenates (methanol and dimethyl ether), C1 (CO, CO2, CH4 and H2), aliphatic hydrocarbons, light aromatics (C6-C8) and heavy aromatics (C9+). The catalytic activity was reflected by activity coefficient a. The deactivation model kinetic parameters were estimated using simplex and nonlinear least squares methods. This model can be used to predict key products and their compositions of MTA industrial process.

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.