Mesoporous Zeolites In Methane Aromatization Class Mesoporous Zeolites

1579 words - 7 pages

Tremendous progress in methane dearomatization reaction has been made since the past decade. Till now, Mo modified HZSM-5 and MCM-22 have been considered as the most suitable catalysts for this reaction. Recently, it was reported that IM-5 is an excellent support for this reaction[endnoteRef:1],[endnoteRef:2]. As far as these catalysts are concerned, their catalytic activity seems to decrease because of extensive coke formation. To facilitate improved selectivity to aromatics and simultaneously suppress the carbonaceous deposits, is a problem that is still faced by many researchers who are interested in MDA. [1: Liu, H., Wu, S., Guo, Y., Shang, F., Yu, X., Ma, Y., Xu, C., Guan, J. and Kan, Q. (2011). Synthesis of Mo/IM-5 catalyst and its catalytic behavior in methane non-oxidative aromatization. Fuel, 90(4), pp.1515-1521.] [2: Liu, H., Hu, J., Li, Z., Wu, S., Liu, L., Guan, J. and Kan, Q. (2013). Synthesis of Zeolite IM-5 under Rotating and Static Conditions and the Catalytic Performance of Mo/H-IM-5 Catalyst in Methane Non-Oxidative Aromatization. Кинетика и катализ, 54(4), pp.466-473.]
Performance of a catalyst depends on many factors: the zeolite pore structure, catalyst composition, distribution and number of acid sites, and other physiochemical properties[endnoteRef:3],[endnoteRef:4],[endnoteRef:5]. Nevertheless, various strategies have been implemented to enhance the catalytic performance. Examples include addition of proper promoters, changing reactor designs, addition of co reactants, and acidity adjustments[endnoteRef:6]. Preparing zeolite catalysts with hierarchical pores can reduce the diffusion limitations, thereby, facilitating the aromatic molecules to gain access into the pores during the reaction. There has been a growing interest in the field of hierarchical zeolites and it has found applications in other reactions like isomerization, catalytic cracking, and methanol to hydrocarbons. Various ways to synthesize hierarchical zeolites have been invented and they are mainly classified into two groups: “top-down” approach and “bottom-down” approach. In the “bottom-up” approach, the secondary pores are introduced during the synthesis of zeolite while “top-down” approach involves secondary pores being introduced post zeolite synthesis. Examples for “bottom-up” approach include “hard templating” methods, “soft-templating” methods[endnoteRef:7], and desilication, dealumination, irradiation, recrystallization[endnoteRef:8] for “top-down” approach. Some of the most common techniques employed to synthesize hierarchical zeolites are, desilication, dealumination and template assisted synthesis which are explained below: [3: Bibby, D. (1986). Coke formation in zeolite ZSM-5. Journal of Catalysis, 97(2), pp.493-502.] [4: Guisnet, M. and Magnoux, P. (1989). Coking and deactivation of zeolites. Applied Catalysis, 54(1), pp.1-27.] [5: Guisnet, M. and Magnoux P. (2010). ChemInform Abstract: Fundamental Description of Deactivation and...

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