Advanced in situ IR spectroscopy study of anisole hydrodeoxygenation over Ni/SiO2 catalysts

Hydrodeoxygenation (HDO) of anisole was investigated over Ni/SiO2 catalysts prepared by incipient wetness impregnation (IWI) and deposition–precipitation (DP). The in situ FTIR, temperature-programmed surface reaction (TPSR-MS), as well as high pressure flow reactions were carried out to relate catalyst properties and reaction mechanism. The small-size Ni0-Ni+ species (2.0 nm) in Ni/SiO2-DP catalyst exhibits a strong hydrogenolysis activity for anisole, favouring the formation of phenol and benzene. The demethylation of anisole to phenol is a rapid step compared to the deoxygenation of phenol to benzene as indicated by in situ FTIR studies. The intensity of C–C stretching vibration in the two rings was enhanced with increasing temperature, suggesting the formation of condensed-ring products was promoted by high reaction temperature. The Ni/SiO2-IWI catalyst, which exhibits a larger Ni0 particle size (14.1 nm) and higher amount of desorbed H2 per surface Ni compared to Ni/SiO2-DP, shows a high hydrogenation but low hydrogenolysis activity, towards the formation of methoxycyclohexane under 40 bar H2 pressure flow reaction.