Mechanisms of reactions of methoxy species with benzene and cyclohexane over H-ZSM-5 zeolites

Abstract

The first-step reaction mechanisms of d₃-methoxy (OCD₃) species on H-ZSM-5 zeolite with benzene and cyclohexane were directly observed by infrared (IR) spectroscopy. Only toluene was produced in the gas phase at the beginning, simultaneous with the consumption of methoxy species on the surface at 473 K. Acidic OH groups were formed in place of d₃-methoxy groups for the reaction with benzene, while OD groups were recovered for the reaction with cyclohexane, similar to the case of light olefins. Thus, the presence of different methylation mechanisms of methoxy species is confirmed; the CD₃ unit reacted with benzene as in the cases of amines and dimethyl ether, but the CD₂ unit reacted with cyclohexane and light olefins, leaving one of the deuterium atoms on the zeolite. The difference of these mechanisms in activation energy is also estimated and used for further discussion on the mechanisms.