The catalytic performance of Mo-impregnated HZSM-5 zeolite in CH4 aromatization: Strong influence of Mo loading and pretreatment conditions

Enhancement of Molybdenum/ZSM‐5 Catalysts in Methane Aromatization by the Addition of Iron Promoters and by Reduction/Carburization Pretreatment

“…Amongst the different techniques, the addition of promoters, such as Fe, [22][23][24][25][26][27][28][29] and the use of different pretreatment methods have been studied extensively. [31,32,43,44] The resultso btained with Fe as an additive are not conclusive as different groups obtained differ-ent results based on the synthesism ethod and on the Mo and Fe loadings employed. However, plenty of work shows that Fe could improvethe catalytic behavior of the Mo-based catalysts, and it is,t herefore, worth exploring at ad eeper level.…”

“…Previous work has demonstrated that the pretreatment of Mo/ZSM-5 catalysts in amixture of CH 4 + +H 2 results in enhanced catalytic behavior, which renderedh igher yields to benzene and ab etter catalytic stability. [31,32] As it is agreed that molybdenum carbides are the active speciesr esponsible for the activation of CH 4 ,i ti sr easonable to assume that the precarburization of the supported molybdenum oxides must result in improvedc atalytic behavior. Recently, [45] we discovered that the ex situ preparation of HZSM-5-supported molybdenumc arbides and then their application in methane aromatization improvest he catalytic behavior drastically compared to supported molybdenumo xides, in which the active carbides pecies are formed in situ during the reaction induction period.F urthermore, the use of higher loadings of molybdenum carbides (up to 12 wt %M o) results in highera nd more stable benzene yields over long periodso ft ime compared to oxidesw ith the same Mo loadings.…”

“…Pretreatmenti sa lso known to play ak ey role to improve the catalytic performance. Tempelman and Hensen [31] and Ta n [32] have reported that the precarburizationo ft he catalysts seems to improve their performance in comparison to He pretreatment, as precarburization resultsi nt he conversion of the molybdenumo xidest om olybdenum carbides, which are believed to be the actives sites that convert methane to C 2 species. However,t ot he best of our knowledge,t he precarburization of Mo catalysts modified with as econd metal has not been investigated.…”

Polyoxometalates as alternative Mo precursors for methane dehydroaromatization on Mo/ZSM-5 and Mo/MCM-22 catalysts

“…11 a) Overview of the highest transient aromatics yields reported in the literature for methane dehydroaromatization performed at 700°C using Mo-based catalysts supported on different zeotypes. 5,7,8,[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] Red triangles represent experimental values reported in this work. Code: "% wt Mo -Mo precursor -Zeotype (Time on stream)", e.g.…”

“…Code: "% wt Mo -Mo precursor -Zeotype (Time on stream)", e.g. "56M" corresponds to 5% Mo 6 /MCM-22; b) methane conversion and aromatics selectivity evolution after 18 hours on stream for the catalysts with the highest reported transient aromatics productivity 15,56,57 and the two best catalysts of this work, i.e. 5% Mo 6 /MCM-22 and 8% Mo 6 /MCM-22.…”