ZSM-5 Framework Research Articles

Upcycling rice husk ash and coal-fired fly ash as si/al sources into hierarchical ZSM-5 for efficient mercury capture from industrial flue gas

Limiting gaseous Hg0 emission is pressing due to the high toxicity in the ecosystem. Zeolites can be regarded as a promising alternative to carbon-based Hg0 adsorbents. However, the mass transfer limitations of conventional singe-sized zeolites constrain the industrial application of zeolites. This study explores the synthesis of hierarchical ZSM-5 zeolites using rice husk ash (RHA) and coal-fired fly ash (FA) as sustainable sources of silicon and aluminum, aimed at enhancing Hg0 removal from industrial flue gases. By adopting a one-step hydrothermal method, we introduced hierarchical porosity into the ZSM-5 framework, enhancing mass transfer and adsorption efficiencies. Iron (III) chloride (FeCl3) was utilized as an active species for modifying the hierarchical ZSM-5, significantly boosting its Hg0 adsorption capabilities. Fe/6RF-hZ demonstrating more than 92% mercury removal efficiency in 60 min under mixed flue gas condition. The structural and chemical attributes of the synthesized ZSM-5 were detailedly characterized, revealing notable differences in surface chemistry and porosity that correlate with varying calcination temperatures of RHA. TEA analysis reveals that hierarchical ZSM-5 zeolites outperform traditional sorbents in demercuration (DeHg) applications, with exceptional DeHg efficiency, energy efficiency (12 kWh), synthesis cost (860 $/ton), and carbon content (non-carbon). This study not only sheds light on the upcycling of solid wastes in synthesizing novel adsorbents but also contributes to the broader application of zeolitic materials in environmental remediation.

Synthesis of hierarchical Fe-incorporated ZSM-5 molecular sieves with an Fe-based metal-organic framework as a mesoporogen and iron source for catalytic pyrolysis of alkanes

To increase the yield of light olefins during the catalytic pyrolysis of alkanes, a novel hierarchical Fe-incorporated ZSM-5 molecular sieve (FeM-Z5) was synthesized using an Fe-based metal-organic framework (Fe-MOF) as a mesoporogen and iron source through the dry gel conversion (DGC) method. In contrast to the conventional method of incorporating Fe species into ZSM-5 via impregnation, the DGC method incorporates Fe species into the framework of ZSM-5, decreasing the amount of Brønsted (B) acid sites and thereby inhibiting the side reactions of hydrogen transfer during the catalytic pyrolysis of alkanes. Compared with the FeN-Z5 catalyst prepared by the DGC method with Fe(NO3)3 as an iron source, FeM-Z5 had a larger amount of strong B acid sites and more mesopores with a size range of 10–40 nm originating from the decomposition of Fe-MOF; these aspects improved n-pentane pyrolysis and ethylene and propylene diffusion. As a result, the optimal FeM-Z5 catalyst exhibited the highest yield of ethylene and propylene (33.4 wt%) and the lowest deactivation rate (0.07 %/h) among the prepared catalysts during the catalytic pyrolysis of n-pentane.

Trace ethylene adsorbents Ag/F-Z5(X) for improved preservation of fruits and vegetables: Enhanced adsorption and water resistance

During the storage/transportation of fruits and vegetables, ethylene-induced over-maturation and spoilage is a serious problem. Currently developed ethylene adsorbents exhibit great potentials due to their low cost and high efficiency, but always lack of water resistance. Herein, we developed Ag/F-Z5(X) adsorbents via the modification of ZSM-5 with different amounts of NH4F followed by silver loading, which exhibits enhanced ethylene adsorption and water resistance. Among the samples, Ag/F-Z5(25) featured with the largest capacity (6.44 mg·g−1) and the best water resistance, achieving near-complete removal of trace ethylene (100 ppm) at room temperature. Based on the characterizations, NH4F modification induced a hierarchical structure within the ZSM-5 framework, concurrently enhancing surface acidity, increasing the proportion of Ag+, and improving the dispersion of metals in the adsorbents. These enhancements collectively contribute to enhanced adsorption and water resistance. Further, banana storage experiments confirmed the actual preservation ability of Ag/F-Z5(25) thanks to the better adsorption and water resistance than unmodified Ag/Z5. These findings offer meaningful insights for developing high-efficient and water-resistant adsorbents to remove trace ethylene, consequently mitigating food aste and enlarging the commercial value of agricultural products.

Hierarchically porous ZSM-5/SBA-15 composite: Tuning pore structure and acidity for hydrodesulfurization of dibenzothiophene

Series ZSM-5/SBA-15 (ZS15-x) composites with different pore structure and acidity were synthesized, and the corresponding NiMo/ZS15-x catalysts were prepared for dibenzothiophene (DBT) hydrodesulfurization (HDS). The controlled introduction of ZSM-5 nanocrystal imparts more acid sites to the NiMo/ZS15 catalyst without altering its fundamental morphology. Furthermore, the increased presence of acid sites enhances the HDS effect of NiMo/ZS15-x catalysts. Simultaneously, the introduction of ZSM-5 nanocrystal modulates the interactions between metal and support (MSI), thereby promoting the dispersion of the active sites. The optimized NiMo/ZS15-50 exhibited superior HDS activities of 98.9 % for DBT, with the optimal reaction rate constant of 3.0 × 10−7 mol/g s−1 and turnover frequency of 2.0 × 10−4 s−1. This can be attributed to its two-dimensional open channels, suitable acidic sites and highly dispersed MoS2. The increased proportion of the ZSM-5 framework and enhanced acidity are advantageous for DBT HDS.

Imaging of Single Molecular Behaviors Under Bifurcated Three-Centered Hydrogen Bonding.

The mechanism for interaction and bonding of single guest molecules with active sites fundamentally determines the sorption and subsequent catalytic processes occurring in host zeolitic frameworks. However, no real-space studies on these significant issues have been reported thus far, since atomically visualizing guest molecules and recognizing single Al T-sites in zeolites remain challenging. Here, we atomically resolved single thiophene probes interacting with acid T-sites in the ZSM-5 framework to study the bonding behaviors between them. The synergy of bifurcated three-centered hydrogen bonds and van der Waals interactions can "freeze" the near-horizontal thiophene and make it stable enough to be imaged. By combining the imaging results with simulations, direct atomic observations enabled us to precisely locate the single Al T-sites in individual straight channels. Then, we statistically found that the thiophene bonding probability of the T11 site is 15 times higher than that of the T6 site. For different acid T-sites, the variation in the interaction synergy changes the inner angle of the host-guest O-H···S hydrogen bond, thereby affecting the stability of the near-horizontal thiophene and leading to considerable bonding inhomogeneities.

Optimization of hierarchical ZSM-5 structure from kaolin as catalysts for biofuel production.

Optimization of hierarchical ZSM-5 structure by variation of the first hydrothermal step at different times provides insight into the evolution of micro/mesopores and its effect as a catalyst for deoxygenation reaction. The degree of tetrapropylammonium hydroxide (TPAOH) incorporation as an MFI structure directing agent and N-cetyl-N,N,N-trimethylammonium bromide (CTAB) as a mesoporogen was monitored to understand the effect towards pore formation. Amorphous aluminosilicate without the framework-bound TPAOH achieved within 1.5 h of hydrothermal treatment provides flexibility to incorporate CTAB for forming well-defined mesoporous structures. Further incorporation of TPAOH within the restrained ZSM-5 framework reduces the flexibility of aluminosilicate gel to interact with CTAB to form mesopores. The optimized hierarchical ZSM-5 was obtained by allowing hydrothermal condensation at 3 h, in which the synergy between the readily formed ZSM-5 crystallites and the amorphous aluminosilicate generates the proximity between micropores and mesopores. A high acidity and micro/mesoporous synergy obtained after 3 h exhibit 71.6% diesel hydrocarbon selectivity because of the improved diffusion of reactant within the hierarchical structures.

Nickel nano-particles confined in ZSM-5 framework as an efficient catalyst for selective hydrodeoxygenation of lignin-derived monomers

The present study offers an efficient, economical, non-noble metal based catalytic process for the selective HDO of lignin-derived compounds. HDO of major lignin constituting monomers like vanillin, syringaldehyde, guaiacol, and cresol were studied over Ni(2.5)@ZSM-5 catalysts. Complete conversion of vanillin and syringaldehyde was achieved with >99% selectivity towards creosol and 4-methylsyringol respectively, while the reactions with guaiacol and cresol did not show any conversion. The catalyst is highly selective towards the conversion of the aldehydic group to methyl group. Potential of the catalyst to be used at more realistic conditions was ascertained by evaluating the catalyst with simulated feed prepared by mixing lignin monomers and impurities like S, Na, and K. The catalyst showed excellent results with simulated feed similar to the pure model compounds. Various characterization techniques like XRD, FTIR, NH3-TPD, H2-TPR, UV-DRS, TEM, TGA, etc. were employed to understand the physico-chemical properties of the catalytic material. The nature and location of Ni species in the catalyst were determined as well as the most plausible active center for the HDO reaction was identified. The study revealed that active metal and acid site in close proximity exhibits a synergistic effect which leads to superior catalytic activity. Effect of support acidity was studied in more detail by evaluating the catalysts with variable acidity. The meritorious properties of the catalyst like exceptionally high selectivity, good stability, tolerance for impurities, excellent recyclability as well as economical catalyst formulation make it suitable to be used for the processing of real feeds at realistic conditions.

Coupling CO2 reduction with ethane aromatization for enhancing catalytic stability of iron-modified ZSM-5

The shale gas revolution and the carbon-neutrality goal are motivating the landscape toward the synthesis of value-added chemicals or fuels from underutilized ethane with the assistance of greenhouse gas CO2. Combining ethane aromatization with CO2 reduction offers an opportunity to directly produce liquid products for facile separation, storage, and transportation. In the present work, Fe/ZSM-5 catalysts showed promise in the simultaneous CO2 reduction and ethane aromatization at atmospheric pressure and 873 K. The catalysts were further investigated using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements under in-situ conditions, indicating that most of Fe species existed in the form of Fe oxides and a portion of Fe was incorporated into the ZSM-5 framework generating Lewis acid sites. Both types of Fe species remained almost unchanged under reaction conditions, contributing to an enhanced aromatization activity of Fe/ZSM-5. The effects of CO2 and steam on the acid sites and in turn aromatization activity were also investigated by transient studies, which exhibited a reversible modification behavior. Moreover, CO2 was identified to be critical to enhance coke resistance and in turn catalyst stability. This work highlights the feasibility of using CO2 to assist the upgrading of abundant ethane from shale gas to aromatics over non-precious Fe-based zeolite catalysts.

Preparation of Titanium to Zirconium ZSM-5: Structure Elucidation And Photocatalytic Behaviour

In this study, a series of Titanium to Zirconium ZSM-5 framework was prepared. Elucidations of the structure were performed using XRD, IR, DR, and SEM images. The results showed that Ti and/or Zr could exist in either tetrahedral or octahedral sites. Simultaneous dye photodegradation with the removal of heavy metal was performed and completely studied with four-dimensional curves. The analysis of the data showed that the metal ions could play an important role in the photodegradation mechanism of organic dye. Photodegradation mechanism is elucidated and kinetic studies showed that the degradation followed up pseudo-first-order kinetics. For the first time deconvolution of IR spectra could be assigned for the elucidation of the structure of prepared materials. The prepared materials are found to be efficient in multiple removals of organic/inorganic pollutants which raise its economic impact.

The effect of structure directing agents on micro/mesopore structures of aluminosilicates from Indonesian kaolin as deoxygenation catalysts

Abstract Indonesian kaolin was successfully transformed into aluminosilicates (ALS) via two-step hydrothermal synthesis using different structure directing agents (SDA). The effects of structure, porosity and catalytic activity of ALS were determined for deoxygenation of bio-oil into green diesel. The first hydrothermal step used silicalite and tetrapropyl ammonium hydroxide (TPAOH) as SDA, followed by the addition of cetyltrimethyl ammonium bromide (CTAB) in the second hydrothermal step to induce mesopores. Silicalite formed ZSM-5 with hierarchical structures meanwhile TPAOH produced ZSM-5 mainly with microporosity. ZSM-5 framework was rapidly formed when using TPAOH preventing the formation of mesostructure in the second crystallization processes. In the absence of SDA, the aluminosilicate was characterized as mesoporous Al-MCM-41. At similar Si/Al ratios, Al-MCM-41 exhibited high surface area, mesopore volume and surface acidities than ZSM-5, consequently enhancing the conversion and selectivity of deoxygenation reaction towards long-chain (C11-C18) green diesel hydrocarbon.

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene.

The effect of two different modification methods for introducing Ni into the ZSM-5 framework was investigated under high-temperature synthesis conditions. The nickel was successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM- 5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BETBJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPD-NH3) were applied to investigate the physicochemical properties. Although all the catalysts showed pure silica MFI-type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced the more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3/gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.

Research on propene oligomerization reaction over the Fenton's reagent modified ZSM-5

ZSM-5 zeolite was modified by Fenton's reagent, FeSO4 and H2O2 aqueous solutions using impregnation method, respectively. All these catalysts were characterized by XRD, ICP-OES, N2 adsorption-desorption, NH3-TPD, Py-FTIR and evaluated in propene oligomerization process. The results demonstrated that the framework of the parent ZSM-5 was well preserved after modification with Fenton's reagent, FeSO4 or H2O2 solutions. However, the SiO2/Al2O3 ratios for all the modified ZSM-5 samples increased due to the dealumination. Furthermore, Fe was detected in Fenton-ZSM-5 while no Fe was observed for FeSO4-ZSM-5 catalyst. The BET surface areas and total pore volumes of three modified catalysts significantly increased compared with the original ZSM-5 sample. Among them, the BET surface area of the Fenton-ZSM-5 increased by 17.86%. The increase of mesopores was probably caused by the removal of the residual organic template in the catalysts due to the generation of ·OH radicals by Fenton's reagent and H2O2. The Fenton-ZSM-5 catalyst formed new acid sites of Brønsted (B) and Lewis (L) with little change in the total calculated amount, which significantly changed the B/L ratio. Compared with the parent ZSM-5, the Fenton-ZSM-5 catalyst exhibited the best activity and stability for propene oligomerization reaction. The initial propene conversion and diesel selectivity were as high as 98.3% and 92.4%, respectively, and kept at >80% and >82% for about 24 h, respectively.

Synthesis of HZSM-5 Rich in Paired Al and Its Catalytic Performance for Propane Aromatization

A series of HZSM-5 catalysts with similar Si/AlF mole ratio, textual properties and morphology, but different contents of AlF pairs, were synthesized by controlling the Na/Al molar ratios in the precursor gel and used for propane aromatization. It is shown that the catalyst with a Na/Al molar ratio of 0.8 in the synthetic gel possesses the highest paired AlF concentration (64.4%) and shows higher propane conversion (38.2%) and aromatics selectivity (19.7 wt.%). Propane pulse experiments, micro reactor activity estimation, Operando diffuse reflectance ultraviolet-visible (DR UV-vis) spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) analysis of coke species deposited on the catalysts provide evidence that AlF pairs in the ZSM-5 framework promote oligomerization and cyclization reactions of olefins, and then produce more aromatics. Density Functional Theory (DFT) calculations demonstrate that the cyclization of olefins and hydride transfer reaction occurring on AlF pairs in HZSM-5 zeolite show a lower free energy barrier and a higher rate constant than those on single AlF, indicating that the structure of AlF pairs in the HZSM-5 zeolite has a stronger electrostatic stabilization effect on the transition states than that of single AlF.

High promoting of selective oxidation of ethylbenzene by Mn-ZSM-5 synthesized without organic template and calcination

Acetophenone is a valuable and widely applied intermediate in chemical industry, but limited by the synthesis with low-cost and efficient heterogeneous catalyst. Herein, we report tetrahedral coordination manganese-incorporated ZSM-5 zeolite (Mn-ZSM-5) by three steps involving acid hydrolysis of Mn(NO3)2 with tetraethylorthosilicate, basic aging and hydrothermal crystallization without organic template and calcination. Mn-ZSM-5 was identified by characterizations such as X-ray diffraction, Fourier transform infrared spectra (FTIR), field emission scanning electron microscopy, inductively coupling plasma spectrometer, N2-adsorption/desorption and FTIR, X-ray photoelectron spectroscopy (XPS), electron spin-resonance spectroscopy (ESR), NH3-TPD and H2-TPR. Moreover, tetrahedral coordination Mn atoms successfully incorporate into the framework of ZSM-5 demonstrated by ESR and XPS spectra. Furthermore, Mn-ZSM-5 with high crystallinity performs high and stable catalytic activity in the oxidation of ethylbenzene owing to tetrahedral Mn3+ in the framework of ZSM-5 as catalytic active sites. Tetrahedral coordination manganese-incorporated ZSM-5 zeolites synthesized without organic template and calcination performed high and stable catalytic activity on the oxidation of ethylbenzene owing to tetrahedral Mn3+ as catalytic active sites.

Framework Fe-Doped Mobil Five (MFI) Zeolites as Highly Active and Stable Fenton-Like Catalysts for Basic Dyes Degradation.

Highly active and stable framework Fe-doped ZSM-5 (f-Fe-ZSM-5) zeolites with different Fe contents, which were synthesized using a facile one-pot hydrothermal method, could effectively resolve the loss of iron element during the catalytic degradation of basic dyes. The successful introduction of Fe species into the framework of ZSM-5 was confirmed by elemental mappings, Fourier transform infrared (FT-IR) spectroscopy and Ultraviolet-visible spectroscopy (UV-vis spectra). The operational parameters, such as Fe content, H₂O₂ concentration, reaction temperature, types of dyes as well as the stability of the synthesized samples were extensively evaluated. It was demonstrated that the f-Fe(0.10)-ZSM-5 exhibited an efficient catalytic ability and excellent stability even after seven consecutive runs. The degradation efficiency of f-Fe-ZSM-5 for basic dyes was higher than that for acid dye. Therefore, f-Fe-ZSM-5 zeolites may present major potential for the treatment of basic dyes waste water without adjusting the initial pH value.

Effect of Hydrothermal Aging Treatment on Decomposition of NO by Cu-ZSM-5 and Modified Mechanism of Doping Ce against This Influence.

Cu-ZSM-5 and Ce-doped Cu-Ce-ZSM-5 samples were prepared by liquid-phase ion exchange method. The two catalysts were subjected to hydrothermal aging treatment in the simulated flue gas of a coal-fired power station at an ageing temperature of 650–850 °C. The denitration experiment found that the activity of the aged Cu-ZSM-5 was 19.6% to 41% lower than that of the fresh Cu-ZSM-5 at the optimal decomposition temperature of NO at 550 °C, while the aged Cu-Ce-ZSM-5 had only a 14.8% to 31.5% reduction in activity than the fresh Cu-Ce-ZSM-5. The samples were characterized by XRD, BET, H2-TPR, XPS, NO-TPD, etc. The results showed that hydrothermal aging treatment leads to the dealumination of the ZSM-5 framework and reduces the specific surface area and pore volume of the micropore in the sample. It also exacerbates the isolated Cu2+, and the active center {Cu2+-O2−-Cu2+}2+ dimers migrate towards the sample surface and form inactive CuO. Doping with Ce can promote the dispersion of Cu(OH)+, which was the precursor of {Cu2+-O2−-Cu2+}2+. Ce3+ can preferentially occupy the less active bridged hydroxyl exchange sites, so that copper ions occupy the more active aluminum hydroxyl sites, thereby inhibiting the migration of active centers.

Direct Imaging of Atomically Dispersed Molybdenum that Enables Location of Aluminum in the Framework of Zeolite ZSM-5.

Integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM) is capable of directly probing guest molecules in zeolites, owing to its sufficient and interpretable image contrast for both heavy and light elements under low-dose conditions. This unique ability is demonstrated by imaging volatile organic compounds adsorbed in zeolite Silicalite-1; iDPC-STEM was then used to investigate molybdenum supported on various zeolites including Silicalite-1, ZSM-5, and mordenite. Isolated single-Mo clusters were observed in the micropores of ZSM-5, demonstrating the crucial role of framework Al in driving Mo atomically dispersed into the micropores. Importantly, the specific one-to-one Mo-Al interaction makes it possible to locate Al atoms, that is, catalytic active sites, in the ZSM-5 framework from the images, according to the positions of Mo atoms in the micropores.

Hierarchically pure and M (Cu, Ni)-impregnated ZSM-5 zeolites for the isomerization catalysis of n-hexane and 1-hexene

Conversion of bio-waste into high value catalytic materials is an option in the quest of maintaining sustainable environment. Here, we report an elaborated analysis of the catalytic activity of synthesized hierarchical pure and M (Cu, Ni)-impregnated ZSM-5 zeolite structures from the rice hull ash (RHuA), which is an abundant bio-waste material in most rice producing regions. To achieve the desired characteristics of ZSM-5 framework for metal (i.e., Cu and Ni) impregnation, an organic template-free method synthesis was designed. Further, the catalytic performance of the metal impregnated ZSM-5 in the isomerization of n-hexane and 1-hexene were carried out in a continuous flow stainless steel fixed bed reactor. Three (3) metal impregnation percentages, namely 1, 3 and 5% of Cu/Ni were investigated and compared in respect to the metals. The isomerization of higher alkanes/alkenes is crucial in petroleum industries to increase the octane number of gasoline. Reaction parameters of interest were catalyst amount, reaction temperature, weight hourly space velocity (WHSV), and reaction time were optimized and the obtained results are elaborately discussed. The Ni-ZSM-5 have superior catalytic activity compared Cu-ZSM-5, although the catalytic activity of ZSM-5 zeolite increases with the loading percentage for both Cu and Ni. To explain the metal loading effects on catalytic activity of the ZSM-5, density functional theory calculations were done through adsorption-desorption mechanistic approach. This combined experimental and theoretical investigation strongly validated the reliability of the results.

Facile moderate-temperature hydrothermal design of nanocrystalline coffin-shaped ZSM-5 catalyst for transformation of CH3OH to C2H4/C3H6

Different crystallization times were studied during hydrothermally synthesis of ZSM-5 framework at moderate temperature to investigate the physicochemical properties and MTO catalytic behavior. The ZSM-5 samples were synthesized at moderate temperature (250 °C) and different crystallization times (24, 18, 12, 6, and 3 h). The synthesized samples were analyzed by XRD, FESEM, EDX, BET-BJH, FTIR, and TPD-NH3 experimental approaches. The results revealed that the purity of crystalline phase, nucleation rate, crystallinity, morphology, porosity, and acidic properties of catalysts depended on the condition of moderate temperature synthesis with strong dependence on crystallization time. This was indicative of the ZSM-5 zeolite prepared at short crystallization time (3 h) facilitated facile design of coffin-shaped ZSM-5 particles which were capable of producing improved properties could provide some useful indication for MTO reaction. So, the MTO catalytic process was carried out using the specific MTO reaction condition of T = 460 °C, CH3OH: H2O = 1:1 (vol:vol) and the feed gas hourly space velocity (GHSV) = 10500 cm3/gcat.h). The ZSM-5(250-3) catalyst showed an enhanced selectivity toward desired olefins, whereas it presented 65% selectivity to propylene and 9% selectivity to ethylene after 35 h on stream. The possible reaction pathway for facile design synthesis of ZSM-5 catalyst via moderate temperature was proposed.

Bimetallic Mo-Co/ZSM-5 and Mo-Ni/ZSM-5 catalysts for methane dehydroaromatization: A study of the effect of pretreatment and metal loadings on the catalytic behavior

Methane dehydroaromatization is studied using different loadings (0.2 wt%, 0.6 and 1 wt%) of Co and Ni additives on a 6 wt% Mo/ZSM-5 catalyst to evaluate the promoting effect of Ni and Co on reactivity and stability of the catalysts. A synergy between Mo and the additives is observed when combining a reduction/carburization pretreatment with an optimum additive loading: benzene yield and catalytic stability are both improved. The fresh and spent samples were characterized by X-Ray Diffraction, 27Al Magic-Angle Spinning Solid State Nuclear Magnetic Resonance Spectroscopy, Temperature-Programmed Reduction and Thermogravimetric Analysis. The results suggest that catalytic enhancement in precarburized Mo-Co and Mo-Ni samples is due to a combination of effects: extraction of Al from the ZSM-5 framework to form inactive Al2(MoO4)3 is reduced, interaction of Mo with the additives enhances the retention of Mo species within the zeolite channels, prevents Mo aggregation in reaction and modifies the reducibility of the Mo sites.