On the dynamic nature of Mo sites for methane dehydroaromatization

Vollmer, Ina; Linden, Bart van der; Ould‐Chikh, Samy; Aguilar‐Tapia, Antonio; Yarulina, Irina; Abou-Hamad, Edy; Sneider, Yuri G; Suarez, Alma I. Olivos; Hazemann, Jean‐Louis; Kapteijn, Freek; Gascón, Jorge

doi:10.1039/c8sc01263f

Cited by 77 publications

(108 citation statements)

References 53 publications

(56 reference statements)

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“…In contrast to that, we recently found that the carbon that is present at the active site itself plays an important role in activating methane equivalent to oxygen in the Mars‐van‐Krevelen mechanism . This is indicated by the fact that the carbon from the active site was found to be incorporated into the final products . In the iron catalyzed Fischer‐Tropsch synthesis, iron carbide initiates the hydrocarbon chain growth, and a similar mechanism can be envisaged for MDA.…”

Section: C−h Bond Activationmentioning

confidence: 97%

“…The chemical shift of 13 C MAS NMR and its anisotropy can yield information about carbidic Mo species forming at reaction conditions, but often the signal is dominated by a big contribution from carbonaceous deposits . We recently demonstrated that CO pretreatment results in an active site equivalent to the one formed at reaction conditions, but without the presence of any carbonaceous deposits . High resolution 13 C MAS NMR then revealed three different carbidic resonances: a sharp one stemming from Mo 2 C nanoparticles on the outer surface of the zeolite and two broad resonances corresponding to smaller species inside the pores of the zeolite.…”

Section: Understanding the Structure Of The Metal Sitementioning

confidence: 99%

“…We recently found that the formation of carbonaceous deposits during activation can be avoided using a treatment in CO to reduce Mo to its active phase. This treatment creates an active site equivalent to the one forming during regular MDA operation . This technique has potential for studying the metal support interaction at reaction conditions without interference from aromatics.…”

Section: Understanding the Structure Of The Metal Sitementioning

confidence: 99%

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Progress in Developing a Structure‐Activity Relationship for the Direct Aromatization of Methane

et al. 2018

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To secure future supply of aromatics, methane is a commercially interesting alternative feedstock. Direct conversion of methane into aromatics combines the challenge of activating one of the strongest C−H bonds in all hydrocarbons with the selective aromatization over zeolites. To address these challenges, smart catalyst and process design are a must. And for that, understanding the most important factors leading to successful methane C−H bond activation and selective aromatization is needed. In this review, we summarize mechanistic insight that has been gained so far not only for this reaction, but also for other similar processes involving aromatization reactions over zeolites. With that, we highlight what can be learnt from similar processes. In addition, we provide an overview of characterization tools and strategies, which are useful to gain structural information about this particular metal‐zeolite system at reaction conditions. Here we also aim to inspire future characterization work, by giving an outlook on characterization strategies that have not yet been applied for the methane dehydroaromatization catalyst, but are promising for this system.

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Section: C−h Bond Activationmentioning

confidence: 97%

Section: Understanding the Structure Of The Metal Sitementioning

confidence: 99%

Section: Understanding the Structure Of The Metal Sitementioning

confidence: 99%

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Progress in Developing a Structure‐Activity Relationship for the Direct Aromatization of Methane

et al. 2018

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“…The majority of research on direct nonoxidative catalytic methane conversion deals with methane dehydroaromatization (MDA), and the most extensively studied catalyst for this purpose is Mo/HZSM‐5. Typically, 1 to 6 wt% of molybdenum loading is used . The number of studies focusing on nonoxidative conversion of methane to light hydrocarbons and olefins is relatively scarce compared with the number of studies on MDA.…”

Section: Introductionmentioning

confidence: 99%

Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

et al. 2019

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Summary A high abundance of methane and its relatively low price make it an attractive raw feedstock for the production of ethylene, which is in the consumer demand in recent years. Direct catalytic nonoxidative conversion is interesting, because it could be utilized on natural gas well sites. Monometallic and bimetallic Fe and Mo catalysts were prepared for the purpose of the coupling to ethane and ethene. Three supported materials were synthesized with the following loading of metal: 2.5‐wt% Fe, 5.0‐wt% Fe, and 2.5‐wt% Mo on HZSM‐5. Process' chemical reactions were also catalyzed with a constant 2.5‐wt% Mo/HZSM‐5, which had different amounts of Fe, namely, 0.5, 1.0, and 2.5 wt%. Fourier transform infrared (FTIR), N2 adsorption/desorption, NH3 temperature‐programmed desorption (TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were applied for characterization. Coke, accumulated on spent solids, was determined by thermogravimetric analysis (TGA). Activity was evaluated in quartz‐packed bed reactor. All surfaces suffered from deactivation due to carbon formation. The addition of Fe to Mo increased CH4 reacted. The highest selectivity for alkenes was achieved over 1.0‐wt% Fe to 2.5‐wt% Mo/HZSM‐5. At the peak of performance, the C‐based reactivity was 52% for olefins and 2% for alkanes. Stability was accomplished over 2.5‐wt% Fe/HZSM‐5, where the rate of C2 synthesis was comparatively stable for 20 hours of the time on stream. The selective C‐basis yield for C2H4 and C2H6 was 36% and 23%, respectively. The lowest measured quantity of (carbonaceous) by‐products was deposited on 2.5‐wt% Fe/HZSM‐5 after 26 hours. Propylene was detected very limitedly.

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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.…”

mentioning

confidence: 99%

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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On the dynamic nature of Mo sites for methane dehydroaromatization

Abstract: The dynamic catalytic site on Mo/HZSM-5 for methane dehydroaromatization is formed during the initial phases of the reaction. Labelling experiments show that carbon from the carbidic active site is incorporated into the final products.

Cited by 77 publications

References 53 publications

Progress in Developing a Structure‐Activity Relationship for the Direct Aromatization of Methane

Progress in Developing a Structure‐Activity Relationship for the Direct Aromatization of Methane

Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

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

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