Elucidation of quantitative effects of zeolitic pores in Mo-impregnated MWW type zeolites on catalytic activities and stabilities of methane dehydroaromatization reaction

The quantitative effects of the pores in Mo-impregnated zeolites on their catalytic activity and stability during methane dehydroaromatization (MDA) were investigated. For this, MCM-22 (Mobil Composition of Matter-22) and its derivatives (MCM-36, ITQ-2, and delaminated MCM-22 in this study), having MWW type zeolite topologies but different zeolite structures, were applied. Although Mo-impregnated catalysts exhibited different catalytic activities and stabilities, interestingly, all Mo-impregnated catalysts showed similar intrinsic benzene-toluene formation rates per zeolitic pore at the initial time-on-stream regardless of the different structures. Moreover, investigation of spent Mo-impregnated catalysts revealed that the coke deposited inside the zeolitic channels (viz., internal coke) was the cause of catalyst deactivation. In particular, the preferential deposition of internal coke in the 12-membered-ring supercage can retard zeolite channel blocking and, consequently, catalyst deactivation. Thus, the amount of zeolitic pore volumes in the catalyst structure is a crucial factor that determines the catalytic activity and stability during MDA.