Non-oxidative dehydrogenation of methanol to formaldehyde over supported GaOx-based catalysts

Abstract

The non-oxidative dehydrogenation of methanol to formaldehyde is a potential alternative to the established industrial oxidative dehydrogenation. Advantages are the production of anhydrous formaldehyde and of hydrogen as a coupled valuable by-product. The catalytic performance of supported GaOx catalysts prepared by wet impregnation of SiO2 and γ-Al2O3 was compared with bulk β-Ga2O3. Fumed SiO2 was identified as the more suitable support, and already at a loading of 4 wt% Ga on SiO2, a high formaldehyde production rate was observed at 550 °C. Significant by-products were dimethyl ether over low-loaded catalysts characterized by the presence of well-dispersed GaOx species, and CH4, CO, and CO2 over the Ga2O3-like phase present at high Ga loadings. Deactivation by coke deposition was faster for increasing Ga loadings, but the catalysts were completely regenerated by an O2 treatment. A two-path mechanism for CH2O formation is proposed comprising a stepwise and a concerted pathway.