Selective oxidation of methane to formaldehyde by oxygen over SBA-15-supported molybdenum oxides

The selective oxidation of CH₄ to formaldehyde by oxygen and its kinetics studies were investigated over MoO_x/SBA-15 under atmospheric pressure. The comparative studies on catalytic reaction showed that the activity of polymeric MoO_x species was significantly higher than that of isolated MoO_x. The maximum HCHO yield was achieved over 20 wt% MoO_x/SBA-15 catalyst at 873 K. Although the studies on contact time effect indicated that HCHO was the primary product over both isolated and polymeric Mo species, the CH₄ conversion followed different mechanisms: the reaction over isolated MoO_x species was a first-order reaction, whereas the other was a higher-order reaction. The catalytic activity of SBA-15-supported Mo-V-O mixed oxide was also investigated in this study. Hydrogen temperature-programmed reduction (H₂-TPR), UV-visible (UV-vis) spectroscopy and X-ray photoelectron spectra (XPS) studies were performed to characterize the supported MoO_x species, results showed that the nature of MoO_x species remained unchanged during the reaction.