Hydrodeoxygenation of guaiacol over physically mixed Co/TiO2 and WO3/TiO2 catalysts

Abstract

To replace the noble metals used in hydrodeoxygenation (HDO) catalysts, guaiacol HDO was conducted using various transition metal-loaded catalysts. Co/TiO₂ was highly active for guaiacol HDO, enabling a more economic removal of the methoxy groups compared to the Ru/TiO₂ catalyst, resulting in superior cyclohexanol selectivity. When a WO₃ promoter was added to the Co catalyst to enhance its oxygen removal ability, the conversion of guaiacol was severely reduced because the co-impregnated WO_x species decreased the number of exposed Co sites. To avoid this phenomenon, Co and WO₃ were isolated by physically mixing Co/TiO₂ and WO₃/TiO₂, where 100% conversion and oxygen removal could be achieved under 10 bar H₂ at 250 °C. The cause of the catalyst deactivation was systematically investigated by magnetic separation of the physical mixture of the catalysts after the reaction, followed by a series of characterization studies. Temperature-programmed-oxidation mass spectroscopy and Raman spectroscopy revealed that the deposition of carbonaceous species was the main contributor to the deactivation of WO₃/TiO₂, and the catalytic activity could be successfully recovered by simple calcination at 400 °C. This study provides insights into the development of economical and efficient physically mixed HDO catalysts using transition metals, and contributes to the understanding of the deactivation and regeneration of physically mixed HDO catalysts.