Mo LIII-edge XANES study of catalytically active Mo species on silica-alumina supports for methane dehydroaromatization

L-edge XANES spectroscopy is applied to characterize the active Mo species for methane dehydroaromatization over MoO3/VSiO2-Al2O3 and MoO3/H-MFI. For highly active MoO3(7.5 wt%)/H-MFI in Si/Al-2 = 90, dispersed molybdenum(II) carbide species are formed with oxy-carbide species after the reaction. Partially reduced species (Mo4+) are formed on amorphous SiO2-Al2O3 support, as well as MoO3/H-MFI in high Si/Al-2 ratio. In contrast, formation of deeply reduced ions such as metallic ones on H-MFI with low Si/Al-2 ratio also gives low activity. It is suggested that stable molybdenum(11) carbide can be formed dispersively on H-MFI (Si/Al-2 = 90) even in coexistence of oxo-species.