Aromatization of methanol and methylation of benzene over Mo 2C/ZSM-5 catalysts

Abstract

The adsorption and reaction pathways of methanol were investigated on various Mo 2C-containing catalysts characterized by XPS and surface acidity measurements. FTIR spectroscopy indicated the formation of a strongly bonded methoxy species on Mo 2C/ZSM-5(80) at 300 K that which was converted into adsorbed dimethyl ether at 373–473 K. TPD experiments following the adsorption of methanol on both ZSM-5 and Mo 2C/ZSM-5 at 300 K showed desorption profiles corresponding to unreacted methanol and decomposition products (H 2, CH 2O, CH 3CHO, CH 3 O CH 3, and C 2H 4). Unsupported Mo 2C catalyzes only the decomposition of methanol. The same feature was observed for silica-supported Mo 2C. But a completely different picture was obtained when ZSM-5 was used as a support, which is known to be an active material in converting methanol into ethylene. The aromatization of methanol also occurred on this zeolite, but to only a limited extent. The deposition of Mo 2C on ZSM-5 markedly enhanced the formation of aromatics (benzene, toluene, xylene and C 9+), however. The highest yield of the formation of aromatics was measured for 5% Mo 2C/ZSM-5 (SiO 2/Al 2O 3 = 80) at 773 K. It is assumed that Mo 2C opens a new route for the activation of methanol and also for the reactions of ethylene thus formed. Further experiments showed that Mo 2C/ZSM-5(80) was able to catalyze the methylation of benzene with methanol, which explains the formation of toluene, xylenes, and C 9+ aromatics in the reaction of methanol alone.