Kinetics of ethane aromatization over a gallium-doped H-ZSM-5 catalyst

Abstract

The kinetics of the catalytic ethane aromatization over Ga-(3 wt.-%) H-ZSM-5 ( Si/Al=15) were investigated in a catalytic fixed-bed micro reactor under atmospheric pressure. Reaction temperatures were 873, 898, and 923 K; inlet partial pressures ranged from 0.1 to 0.8 bar for ethane and from 0.1 to 0.7 bar for hydrogen. The aromatization reaction was described by a 4-step reaction scheme, comprising the formation of aromatic hydrocarbons via the subsequent formation of ethylene and higher alkenes, and the formation of methane as a side product of cracking. The kinetic model takes into account the bifunctionality of the catalyst by assuming gallium sites for the dehydrogenation of ethane and acid sites for alkene interconversion and aromatics formation. The latter proceeds with the formation of surface hydrogen on the zeolite, which can only desorb after a back-spillover step to the gallium sites.