Methane aromatisation based upon elementary steps: Kinetic and catalyst descriptors

Wong, Kae Shin; Thybaut, Joris W.; Tangstad, Elisabeth; Stöcker, Michael; Marin, Guy

doi:10.1016/j.micromeso.2012.07.002

Cited by 60 publications

(40 citation statements)

References 60 publications

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“…The effect of HZSM‐5 acidity was evaluated and with higher acidity of support, ie, lower SiO 2 /Al 2 O 3 ratio, selectivity to aromatics increased. This is in agreement with the presumed mechanism of aromatization over Mo/HZSM‐5, which suggests that ethylene forms on Mo active sites and undergoes a sequence of reactions on zeolite acid sites to form aromatics, mainly benzene, because of shape selectivity of the zeolite . Even though Mo/HZSM‐5 is well studied, the mechanism of methane aromatization is still under debate, mostly because it is not clear if zeolite Brønsted acid sites are actually responsible for aromatization .…”

Section: Introductionsupporting

confidence: 79%

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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Section: Introductionsupporting

confidence: 79%

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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“…It has been traditionally accepted that MDA over Mo/zeolites occurs via a bifunctional mechanism involving two different active sites . According to this mechanism, molybdenum species constitute the sites responsible for methane activation, forming H 2 as well as C 2 H x and C 3 H x intermediates, which subsequently transform into aromatic products over the zeolite Brønsted acid sites (BAS) associated to framework Al 3+ .…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6] It has been traditionally accepted that MDA over Mo/ zeolites occurs via a bifunctional mechanism involving two different active sites. [2,3,[7][8][9][10] According to this mechanism, molybdenum species constitute the sites responsible for methane activation, forming H 2 as well as C 2 H x and C 3 H x intermediates, which subsequently transform into aromatic products over the zeolite Brønsted acid sites (BAS) associated to framework Al 3 + . This mechanism was proposed on the basis of several activity studies carried out on Mo-based catalysts prepared using either non zeolitic supports -such as SiO 2 and TiO 2 [11] -or Cs, Ca or Na-exchanged zeolites, with no remaining BAS.…”

Section: Introductionmentioning

confidence: 99%

Implications of the Molybdenum Coordination Environment in MFI Zeolites on Methane Dehydroaromatisation Performance

et al. 2019

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The structure and activity of Mo/Silicalite‐1 (MFI, Si/Al=∞) were compared to Mo/H‐ZSM‐5 (MFI, Si/Al=15), a widely studied catalyst for methane dehydroaromatisation (MDA). The anchoring mode of Mo was evaluated by in situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT). The results showed that in Mo/Silicalite‐1, calcination leads to dispersion of MoO3 precursor into tetrahedral Mo‐oxo species in close proximity to the microporous framework. A weaker interaction of the Mo‐oxo species with the Silicalite‐1 was determined by XAS and DFT. While both catalysts are active for MDA, Mo/Silicalite‐1 undergoes rapid deactivation which was attributed to a faster sintering of Mo species leading to the accumulation of carbon deposits on the zeolite outer surface. The results shed light onto the nature of the Mo structure(s) while evidencing the importance of framework Al in stabilising active Mo species under MDA conditions.

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“…[1][2][3][4][5][6][7][8][9][10][11][12] However, industrialization of this reaction encounters a serious bottleneck of rapid deactivation of the catalyst due to coking. [1][2][3][4][5][6][7][8][9][10][11][12] However, industrialization of this reaction encounters a serious bottleneck of rapid deactivation of the catalyst due to coking.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH₄–H₂switching modes

Song

Suzuki

et al. 2014

Catal. Sci. Technol.

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ARTICLE This journal isThe catalytic stabilities of Fe-modified and -unmodified 5%Mo/HZSM-5 catalysts in the non-oxidative methane dehydroaromatization were compared at 1073 K and three reaction/H 2 -regeneration cycle periods: 5 min CH 4 -5 min H 2 , 5 min CH 4 -10 min H 2 , and 5 min CH 4 -20 min H 2 . Fe addition proved capable of remarkably increasing the catalyst stability over the cycles of 5 min CH 4 -20 min H 2 but hardly effective over the cycles of 5 min CH 4 -5 min H 2 . On the other hand, SEM observation of all spent samples revealed that Fe addition causes a massive accumulation of carbon nanotubes under the latter cyclic condition but little at the former. Thus several sets of comparative tests were specially designed and performed to get insight into the rule of Fe-catalyzed cyclic formation of carbon nanotubes in stabilizing the activity at the cyclic condition of 5 min CH 4 -20 min H 2 . The results further confirmed that at this condition cyclic formation of carbon nanotubes enhances cyclic evolution of H 2 and makes the H 2 concentration of the system higher, which is thermodynamically beneficial for suppression of formation of the activity-deactivating surface coke. Finally, it was further confirmed that at least a 20 min H 2 exposure is required to remove most of the carbon nanotubes and surface coke formed during a 5 min CH 4 exposure and make most of Fe nanoparticles reactivated and available again for catalytic carbon nanotubes formation with an enhanced H 2 evolution, i.e., with a controlled formation of the surface coke in the next CH 4 exposure.

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Methane aromatisation based upon elementary steps: Kinetic and catalyst descriptors

Cited by 60 publications

References 60 publications

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

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

Implications of the Molybdenum Coordination Environment in MFI Zeolites on Methane Dehydroaromatisation Performance

Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH₄–H₂switching modes

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Methane aromatisation based upon elementary steps: Kinetic and catalyst descriptors

Cited by 60 publications

References 60 publications

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

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

Implications of the Molybdenum Coordination Environment in MFI Zeolites on Methane Dehydroaromatisation Performance

Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH4–H2switching modes

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Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH₄–H₂switching modes