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

Sridhar, Apoorva; Rahman, Mustafizur; Infantes‐Molina, Antonia; Wylie, Benjamin J.; Borcik, Collin G.; Khatib, Sheima J.

doi:10.1016/j.apcata.2019.117247

Cited by 64 publications

(51 citation statements)

References 66 publications

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“…The decrease in Lewis acid site due to the loading of both Co and Mo was also reported by Sadiq et al [32]. They suggested that the loading of both Co and Mo could decrease the Lewis acid site due to the formation of a CoMoO 4 metal cluster [32] and/or the formation of inactive Al 2 (MoO 4 ) 3 [33].…”

Section: Catalysts Characterizationssupporting

confidence: 63%

Improved Brønsted to Lewis (B/L) Ratio of Co- and Mo-Impregnated ZSM-5 Catalysts for Palm Oil Conversion to Hydrocarbon-Rich Biofuels

et al. 2021

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The purposes of this study are to investigate the effect of metal (Co and Mo) impregnation to ZSM-5 catalysts on the Brønsted to Lewis (B/L) ratio as the active sites of cracking reaction, and the catalysts’ performance testing for palm oil cracking to produce hydrocarbon-rich biofuels. Both metals were impregnated on the ZSM-5 catalyst using a wet-impregnation method. The catalysts were characterized using X-ray diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), and Pyridine-probed Fourier-Transform Infrared (Py-FTIR) spectroscopy methods. The catalysts were tested on the cracking process of palm oil to biofuels in a continuous fixed-bed catalytic reactor. In order to determine the composition of the organic liquid product (OLP, biofuels), the product was analyzed using a gas chromatography-mass spectrometry (GC-MS) method. The results showed that the co-impregnation of Co and Mo to ZSM-5 highly increased the Brønsted to Lewis acid site (B/L) ratio, although the total number of acid sites decreased. However, the impregnation of Co and Mo on the ZSM-5 decreased the surface area of catalysts due to pore blocking by metals, while the B/L ratio of the catalysts increased. It was obtained that by utilizing Co- and Mo-impregnated ZSM-5 catalysts, the hydrocarbons product selectivity increased from 84.32% to 95.26%; however, the yield of biofuels decreased from 67.57% to 41.35%. The increase in hydrocarbons product selectivity was caused by the improvement of the Brønsted to Lewis (B/L) acid sites ratio.

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Section: Catalysts Characterizationssupporting

confidence: 63%

Improved Brønsted to Lewis (B/L) Ratio of Co- and Mo-Impregnated ZSM-5 Catalysts for Palm Oil Conversion to Hydrocarbon-Rich Biofuels

et al. 2021

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“…[124][125][126] Significant improvements in stability, activity, and selectivity of Mo/ZSM-5 catalysts were observed with Fe, Co, and Ni. [127][128][129] As these metals demonstrate high methane conversion activity (for instance for the decomposition of methane to carbon materials and hydrogen gas), it is likely that their promotional role is related to increasing the rate of C-H bond activation. Another explanation for the observed improved performance can be the exchange of remaining Brønsted acid sites with metal (oxo) cations, effectively decreasing coking propensity.…”

Section: Catalyst Engineeringmentioning

confidence: 99%

Reactivity, Selectivity, and Stability of Zeolite‐Based Catalysts for Methane Dehydroaromatization

2020

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strong C-H bonds complicates the selective conversion of methane to higher hydrocarbons and oxygenates. Currently, the main industrial method to use methane as a material feedstock involves the transformation to syngas by steam reforming, followed by processes such as methanol synthesis and Fischer-Tropsch synthesis to obtain liquid fuels and other useful chemicals. A disadvantage of this indirect technology is the high capital cost of reforming plants, making it only economically attractive at a very large scale. An efficient direct process for the conversion of methane to higher hydrocarbons or oxygenates remains one of the "holy grails" of chemistry. [6,7] The approaches to directly convert methane can be categorized into oxidative and non-oxidative methods. Oxidative processes are often met with low product selectivity because of the higher reactivity of targeted products as compared to methane itself, resulting in overoxidation to CO 2. Non-oxidative methods are generally more atom-efficient, because, in addition to valuable hydrocarbon products, pure CO xfree hydrogen gas (H 2) is obtained, which can be used for instance in fuel cells. [8] Among several alternatives, including non-oxidative coupling of methane to ethylene and deep methane dehydrogenation to solid carbon and hydrogen, [9-12] methane dehydroaromatization (MDA) remains one of the most promising non-oxidative reactions for the direct valorization of natural gas. MDA involves the selective conversion of methane to a mixture of easily transportable aromatics, that is, benzene (predominantly), naphthalene, and toluene. As all other non-oxidative methane conversion reactions, MDA is a highly endothermic process: 6CH C H 9H 532 kJ mol Non-oxidative dehydroaromatization is arguably the most promising process for the direct upgrading of cheap and abundant methane to liquid hydrocarbons. This reaction has not been commercialized yet because of the suboptimal activity and swift deactivation of benchmark Mo-zeolite catalysts. This progress report represents an elaboration on the recent developments in understanding of zeolite-based catalytic materials for high-temperature non-oxidative dehydroaromatization of methane. It is specifically focused on recent studies, relevant to the materials chemistry and elucidating i) the structure of active species in working catalysts; ii) the complex molecular pathways underlying the mechanism of selective conversion of methane to benzene; iii) structure, evolution and role of coke species; and iv) process intensification strategies to improve the deactivation resistance and overall performance of the catalysts. Finally, unsolved challenges in this field of research are outlined and an outlook is provided on promising directions toward improving the activity, stability, and selectivity of methane dehydroaromatization catalysts.

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“…Thus, heating the fresh catalyst, i.e., with molybdenum in oxidized form, above 550 °C under inert (N 2 , He) or oxidative (O 2 ) atmosphere may lead to material damage through molybdenum sintering and migration at the external surface. Moreover, mobile molybdenum species can extract aluminum from the zeolite framework and form extra-framework Al 2 (MoO 4 ) 3 species. ,, Molybdenum carbides clusters resulting from external molybdenum oxide reduction and Al 2 (MoO 4 ) 3 species promote coke formation during MDA reaction. ,,, On the other hand, the heating of the Mo/HZSM-5 catalyst under a reductive atmosphere such as pure flow of CH 4 , H 2 , CO, or a CH 4 /H 2 mixture showed improvement of the catalyst stability and an increase of the benzene yield. − ,,, In these conditions, the reduction of Mo sites occurred at lower temperatures, preventing the Mo migration . Recently, Rahman et al reported the effect of different pretreatment atmospheres including He, CH 4 , H 2 , and a mixture of CH 4 /H 2 on the structural properties and performance of MDA catalysts.…”

Section: Methane Dehydroaromatization (Mda)mentioning

confidence: 99%

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

et al. 2022

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Natural gas, the cleanest fossil fuel, is an abundant source of methane and expected to play an increasingly important role in powering the world’s economic growth over the energy transition of the coming decades. Methane has the potential to be a CO2-free feedstock to cogenerate hydrogen (H2) and added value “building-blocks” chemicals (e.g., olefins and aromatics) for petrochemistry. In this review, the two processes (i) the oxidative coupling of methane (OCM) for production of ethylene and (ii) the nonoxidative methane dehydroaromatization (MDA) producing hydrogen and benzene are discussed. Both routes convert methane directly into valuable products, an advantage over the several-steps syngas route. The performances of various a variety of catalysts reported during the last 25 years for OCM (MnNaW, La2O3, Li-MgO, etc.) and MDA (M/HZSM-5, M/TNU-9, M/IM-5, M/ITQ-2, M@SiO2, M@CeO2, TaH/SiO2, GaN/SBA15, single-site M@HZSM-5, bimetallic M-M′/HZSM-5, core–shell structures, M/Zr(SO4)2 with M = Mo, Fe, Pt) under similar reaction conditions are compared. The major drawbacks and the strategies used to mitigate the main challenges related with the performance of the catalysts in both OCM and MDA reactions are critically revealed. For instance, the overoxidation in the OCM is mitigated by optimizing of the operating conditions, using alternative oxidants, and the application of membrane reactor technology are discussed. In the MDA reaction, the major issue is the catalyst deactivation by coke formation and migration and sintering of metallic active phases. Strategies for robust catalysts, methods for mild coke removal, pretreatment under reductive atmosphere are presented. Approaches to improve aromatics yields over coke production by addition of promoters or co-feed reactants to the MDA catalysts are also discussed.

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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

Cited by 64 publications

References 66 publications

Improved Brønsted to Lewis (B/L) Ratio of Co- and Mo-Impregnated ZSM-5 Catalysts for Palm Oil Conversion to Hydrocarbon-Rich Biofuels

Improved Brønsted to Lewis (B/L) Ratio of Co- and Mo-Impregnated ZSM-5 Catalysts for Palm Oil Conversion to Hydrocarbon-Rich Biofuels

Reactivity, Selectivity, and Stability of Zeolite‐Based Catalysts for Methane Dehydroaromatization

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

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