Understanding the Preparation and Reactivity of Mo/ZSM-5 Methane Dehydroaromatization Catalysts.

Methane dehydroaromatization is a promising reaction for the direct conversion of methane to liquid hydrocarbons. The active sites and the mechanism of this reaction remain controversial. This work is focused on the operando X-ray absorption near edge structure spectroscopy analysis of conventional Mo/ZSM-5 catalyst during its whole lifetime. Complemented by other characterization techniques, we derived spectroscopic descriptors of molybdenum precursor decomposition and its exchange with zeolite Bronsted acid sites. We found that the reduction of Mo-species proceeds in two steps and the active sites are of siminar nature, regardless of the Mo content. Furthermore, the ZSM-5 unit cell contracts at the beginning of the reaction, which coincided with benzene formation and it is likely related to the formation of hydrocarbon pool intermediates. Finally, although reductive regeneration of used catalysts via methanation is less effective as compared to combustion of coke, it does not affect the structure of the catalyst.