Position and Lewis acidic property of active cobalt species on MFI zeolite for catalytic methylation of benzene with methane

Abstract

Crystallographic position and acidic properties of the Co species in MFI zeolite which was catalytically active for methylation of benzene with methane (CH4 + C6H6 → H3C–C6H5 + H2) were investigated with UV–vis spectroscopy and an ammonia IRMS-TPD method. Among the divalent cation sites in MFI classified into α, β and γ, loading of Co2+ at the α site on the wall of straight channel proceeded mainly in the relatively high Co concentration region (Cozeo/Alzeo > 0.25) without additive or in the low Co concentration region in the co-presence of Mg and Pb. On the other hand, Co2+ on MFI were classified from the view of Lewis acidity into four types (L1S, L1W, L2S and L2W). The L1S type possessing strong base-stabilizing and electron-withdrawing nature showed similar dependency on the Co content to the Co2+ at the α site as well as the catalytic activity for direct methylation of benzene with methane. These observations indicate that the Co2+ at the α site with L1S nature was active for the methylation of benzene with methane, a reaction promising to open a way of utilization of methane as a feedstock of valued chemicals.