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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

“…The strong effect of adding a small amount of H 2 into the CH 4 feed on suppression of coke accumulation in Mo/HZSM-5 catalyst and improvement of its stability has been well demonstrated by other groups. 18,[60][61][62] In this connection, the opposite cases have been reported as well where removal of part of the formed H 2 out of the reaction system with the assistance of a hydrogen permeable-membrane enhances coke accumulation and catalyst deactivation. [64][65][66] Finally, two sets of coke-removing tests were performed to further confirm that much longer than 5 min H 2 exposure is truly needed to remove most of the carbon nanotubes formed during a 5 min CH 4 exposure or accumulated over cyclic exposures, and consequently make the Fe nanoparticles attached to them available again in the succeeding CH 4 exposure.…”

“…Then to prove this speculative statement, the following additional tests were especially designed and performed. 18,[60][61][62] In this connection, the opposite cases have been reported as well where removal of part of the formed H 2 out of the reaction system with the assistance of hydrogen permeablemembrane enhances reversely coke accumulation and catalyst deactivation. As specified in Fig.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] However, industrialization of this reaction encounters a serious bottleneck caused by rapid deactivation of the catalyst due to coking. [14][15][16] A large number of approaches have been attempted to deal with the coking problem and improve the catalyst stability, which include addition of a small amount of oxygen-containing gas into the CH 4 feed, [17][18][19][20][21] doping of a metal promoter to the Mo/HZSM-5 catalyst, [22][23][24][25][26] modification of the surface or bulk Si/Al atomic ratio of HZSM-5 zeolite, [27][28][29][30][31] and use of HZSM-5 zeolite with hierarchical porosity or mesopores. [32][33][34][35] Nevertheless, no catalyst has been found to have a sufficiently long lifetime to meet the requirement of long-term operation at the industrially required conditions.…”

The distribution of coke formed over a multilayer Mo/HZSM-5 fixed bed in H2 co-fed methane aromatization at 1073 K: Exploration of the coking pathway

“…In fact, adding H 2 into CH 4 feed has been experimentally demonstrated to be very effective in suppressing overall coke formation over Mo/HZSM-5 catalysts, and consequently stabilizing their activity [21][22][23][24]. Thus, the nascent hydrogen formed in the inlet layer of an integral catalyst bed is expected to function to suppress coke formation in the rest of the bed [27][28][29], particularly in its outlet layer, where the H 2 concentration in the gas phase always reaches its highest level. As a result, a nonuniform coke distribution could form in any integral catalyst bed.…”

Understanding the Impact of Hydrogen Activation by SrCe0.8Zr0.2O3−δ Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion

“…Hydrogen is the co-product of dehydrogenation of alkane, whose presence impacts both the reaction kinetics and thermodynamics of DNMC. Studies for DNMC in the fix-bed reactors have shown that addition of a significant amount of hydrogen co-feed would reduce methane conversion, while a small amount would have favorable effect in terms of catalyst stability and lighter hydrocarbon production ( Liu et al, 2002c ; Ma et al, 2003 ; Osawa et al, 2003 ; Ma et al, 2005 ; Kojima et al, 2006 ; Aritani et al, 2009 ). For example, it was proposed that 3–6% of H 2 suppressed coke deposition on a 6 wt% Mo/HZSM-5 catalyst in a DNMC reaction ( Ma et al, 2003 ; Ma et al, 2005 ; Kojima et al, 2006 ).…”