SBA-15-supported molybdenum oxides as efficient catalysts for selective oxidation of ethane to formaldehyde and acetaldehyde by oxygen

The selective oxidation of ethane was investigated over SBA-15-supported molybdenum oxide catalysts. Our characterizations suggest that the MoOx species were dispersed mostly in mesoporous channels of SBA-15 at Mo content <9.5 wt%. At higher Mo content (15.4 and 20.1 wt%), MoOx nanoparticles together with small amount of MoO3 crystallites were found. The growth of MoOx species in mesoporous channels to MoOx nanoparticles causes the collapse of the silica wall of SBA-15. The rate of ethane conversion per Mo atom over the catalyst with Mo content of 9.5–20.1 wt% was significantly higher than that over the catalyst with lower Mo content, suggesting that polymeric MoOx clusters and MoOx nanoparticles are more active toward ethane activation. The catalysts with highly dispersed MoOx species favor the selectivity of acetaldehyde, whereas those containing polymeric MoOx clusters or MoOx nanoparticles show higher formaldehyde formation rates. Formaldehyde is likely produced through the consecutive oxidation of ethylene.