Stable Mo/HZSM-5 methane dehydroaromatization catalysts optimized for high-temperature calcination-regeneration

Kosinov, Nikolay; Coumans, Ferdy J. A. G.; Li, Guanna; Uslamin, Evgeny A.; Mezari, Brahim; Wijpkema, Alexandra S. G.; Pidko, Evgeny A.; Hensen, Emiel J. M.

doi:10.1016/j.jcat.2016.12.006

Cited by 150 publications

(140 citation statements)

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“…[8] 2) Adsorptive or oxidative scavenging of hydrogen for the same purpose. [12] Finally,the influence of such parameters as temperature and space velocity of methane [13] and continuous co-feeding of hydrogen, [14] oxygen, [15] and oxygenates [16] has been studied in great detail. [10] 4) Use of oxygenpermeable membranes for ac ontrolled supply of as mall amount of oxygen for removal of coke species.…”

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confidence: 99%

“…After the reaction the spent catalysts were collected and characterized by 13 CNMR spectroscopy and TPO-MS to determine the surface 13 Cc ontent before and after exchange with 12 CH 4 .F igure 3c,d demonstrate that it is possible to observe the interaction of surface and gaseous carbon atoms by analyzing the ratio between m/z = 78 and 79 MS signals,c orresponding to benzene molecules with 0a nd 1 13 Cl abels,r espectively.I nitially,i nt he 12 CH 4 flow the m/z 78/79 ratio of 16 is consistent with the natural abundance of 13 C( 1.1 %). Thet ransient increase corresponds to the exchange of gas-phase 12 Ca toms with surface 13 Ca toms. Thet ransient increase corresponds to the exchange of gas-phase 12 Ca toms with surface 13 Ca toms.…”

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Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

et al. 2019

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Non‐oxidative dehydroaromatization of methane over Mo/ZSM‐5 zeolite catalysts is a promising reaction for the direct conversion of abundant natural gas into liquid aromatics. Rapid coking deactivation hinders the practical implementation of this technology. Herein, we show that catalyst productivity can be improved by nearly an order of magnitude by raising the reaction pressure to 15 bar. The beneficial effect of pressure was found for different Mo/ZSM‐5 catalysts and a wide range of reaction temperatures and space velocities. High‐pressure operando X‐ray absorption spectroscopy demonstrated that the structure of the active Mo‐phase was not affected by operation at elevated pressure. Isotope labeling experiments, supported by mass‐spectrometry and 13 C nuclear magnetic resonance spectroscopy, indicated the reversible nature of coke formation. The improved performance can be attributed to faster coke hydrogenation at increased pressure, overall resulting in a lower coke selectivity and better utilization of the zeolite micropore space.

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Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

et al. 2019

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“…As Figure 1a demonstrates, we chose these catalysts to distinguish between the larger Mo clusters,w hich are abundant on the surface of 5%Mo,a nd dispersed Mo complexes located inside the zeolite pores, which are exclusively present in 1%Mo. [10] This discrimination is important as the Mo centers confined inside the pores catalyze the reaction, and larger,c atalytically irrelevant, and generally more easily detectable species on the external surface often dominate during spectroscopy characterization.…”

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Confined Carbon Mediating Dehydroaromatization of Methane over Mo/ZSM‐5

et al. 2017

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Non-oxidative dehydroaromatization of methane (MDA) is apromising catalytic process for direct valorization of natural gas to liquid hydrocarbons.T he application of this reaction in practical technology is hindered by al acko f understanding about the mechanism and nature of the active sites in benchmark zeolite-based Mo/ZSM-5 catalysts,w hich precludes the solution of problems such as rapid catalyst deactivation. By applying spectroscopya nd microscopy, it is shown that the active centers in Mo/ZSM-5 are partially reduced single-atom Mo sites stabilized by the zeolite framework. By combining ap ulse reaction techniquew ith isotope labeling of methane,M DA is shown to be governed by ah ydrocarbon pool mechanism in whichb enzenei sd erived from secondary reactions of confined polyaromatic carbon species with the initial products of methane activation.The abundance of natural gas reserves calls for the development of an efficient conversion technology to upgrade its principal component, methane,i nto easily transportable chemicals.[1] Several catalytic technologies,w hich could replace the current indirect route involving an expensive synthesis gas generation step,a re being considered. Broadly, we can distinguish between oxidative and non-oxidative direct routes.[2] Among the non-oxidative approaches,c atalytic methane dehydroaromatization (MDA) is one of the most promising methods.A fter the initial reports on MDA almost three decades ago, [3] as ubstantial body of literature has appeared.[4] Thei ndustrial implementation of the MDA process is mainly hindered by rapid catalyst deactivation caused by the deposition of ac arbonaceous material that blocks the catalytically active sites. [5] Although there have been remarkable achievements in regeneration procedures, [6] developing astable MDAcatalyst is still required to arrive at acommercial process.Aprogress in this direction is seriously hampered by limited understanding of the active sites in the benchmark Mo/ZSM-5 catalyst and the mechanism of methane conversion to benzene and hydrogen. Despite considerable debate on the nature of the active phase,t here is ag rowing consensus that the active sites are confined as highly dispersed Mo species by the zeolite pores in working Mo/ZSM-5 catalysts and that Mo 2 Cn anoparticles on the external surface are inactive. [7] Concerning the reaction mechanism, most reports support ab ifunctional pathway in which methane is activated and coupled to ethylene over Mocarbide species,followed by ethylene aromatization over the zeolite Brønsted acid sites. [8] Important challenges in gaining insight into these aspects are the high reaction temperature at which the MDAreaction takes place and its transient nature,w hich involves rapid activation and deactivation stages when the fresh Mo/ZSM-5 catalyst is exposed to am ethane feed. These factors complicate operando spectroscopy and kinetic investigations.A valuable approach in this regard is to increase the temporal resolution by pulsing the reactant over the catalyst an...

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“…10 % single pass conversion) on carbidic forms of Mo encapsulated in zeolites at temperatures of about 950 K. [3][4][5] Oxidic precursors of Mo deposited in H-ZSM-5 zeolitic channels via vapor-phase solid-state ion exchange result in formulations that catalyze CH 4 DHA at 950-973 K. [6] Formation of MoC x clusters of 0.6-1.5 nm size after carburization of Mooxidic precursors in Mo/H-ZSM-5 catalyst and their involvement in catalytic CÀHb ond activation during CH 4 DHA reactions has been evidenced using spectroscopic studies. [3][4][5][6][7][8][9] Although the stoichiometry and coordination of MoC x clusters is still atopic of debate,the proficiency and reduced nature of active Mo-centers is no longer debated. [8,[10][11][12][13][14] Four noteworthy recent publications examine evolution and speciation of MoC x species in CH 4 DHA, [10,12,15,16] however, we make no effort to probe identity of MoC x species in this study and instead report in situ absorptive-hydrogen removal as as trategy to overcome thermodynamic limitations that limit single-pass conversion in CH 4 DHA to about 10 %.…”

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“…[3][4][5][6][7][8][9] Although the stoichiometry and coordination of MoC x clusters is still atopic of debate,the proficiency and reduced nature of active Mo-centers is no longer debated. [8,[10][11][12][13][14] Four noteworthy recent publications examine evolution and speciation of MoC x species in CH 4 DHA, [10,12,15,16] however, we make no effort to probe identity of MoC x species in this study and instead report in situ absorptive-hydrogen removal as as trategy to overcome thermodynamic limitations that limit single-pass conversion in CH 4 DHA to about 10 %. Arecent report proposes that addition of Zr metal as ah ydrogen absorber to MoO x /H-ZSM-5 formulations leads to increased CH 4 conversion and aromatic yields.…”

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Absorptive Hydrogen Scavenging for Enhanced Aromatics Yield During Non‐oxidative Methane Dehydroaromatization on Mo/H‐ZSM‐5 Catalysts

et al. 2018

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Addition of Zr metal particles to MoC x /ZSM-5 in interpellet mixtures (2:1 weight ratio) resulted in maximum single-pass methane conversion of 27 %f or dehydroaromatization at 973 K( in significant excess of the equilibrium prescribed circa 10 %c onversion at these conditions) and ac oncurrent 1.4-5.6-fold increase in aromatic product yields due to circumvention of thermodynamic equilibrium limitations by absorptive H 2 removal by Zr while retaining cumulative aromatic product selectivity.T he absorptive function of the polyfunctional catalyst formulation can be regenerated by thermal treatment in He flowa t9 73 K, yielding above-equilibrium methane conversion in successive regeneration cycles.H 2 uptake experiments demonstrate formation of bulk ZrH 1.75 on hydrogen absorption by Zr at 973 K. Cooperation between absorption and catalytic centers distinct in location and function enables circumvention of persistent thermodynamic challenges in non-oxidative methane dehydrogenation.

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Stable Mo/HZSM-5 methane dehydroaromatization catalysts optimized for high-temperature calcination-regeneration

Cited by 150 publications

References 61 publications

Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

Confined Carbon Mediating Dehydroaromatization of Methane over Mo/ZSM‐5

Absorptive Hydrogen Scavenging for Enhanced Aromatics Yield During Non‐oxidative Methane Dehydroaromatization on Mo/H‐ZSM‐5 Catalysts

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