Methane dehydro-aromatization over Mo/MCM-22 catalysts: a highly selective catalyst for the formation of benzene

A molybdenum-modified MCM-22 catalyst has been used for methane dehydro-aromatization. The catalytic performance on this Mo/MCM-22 catalyst is featured by a higher yield of benzene and a lesser yield of naphthalene in comparison with that on a Mo/HZSM-5 catalyst under the same experimental conditions. Methane conversion of 10.0% and benzene selectivity of 80% over a 6Mo/MCM-22 catalyst at 973 K was obtained. Based on the effect of contact time, it is suggested that the reaction is severely inhibited by the products, probably due to their strong adsorption and slow desorption. The Mo/MCM-22 catalysts were characterized by XRD, NH3-TPD and TPSR techniques. XRD patterns of the Mo/MCM-22 catalysts confirmed that Mo species are highly dispersed on/in the MCM-22 zeolite if the Mo loading is less than 10%. NH3-TPD experiment shows that the MCM-22 zeolite contains strong and exchangeable Bronsted acid sites. TPSR of methane revealed that there is an induction period during which the Mo species are reduced by methane and transformed probably into Mo2C or Mo2OxCy. It is concluded that the nature of the methane dehydro-aromatization reaction over the Mo/MCM-22 catalysts is similar to that on the Mo/HZSM-5 catalysts. The unique pore systems, the proper acid strength of the MCM-22 zeolite and the Mo species are factors important for methane dehydro-aromatization over Mo/MCM-22 catalysts