Hydrogenolysis of glycerol over supported bimetallic Ni/Cu catalysts with and without external hydrogen addition in a fixed-bed flow reactor

The role of high hydrogen pressure in the hydrogenolysis of glycerol to 1,2-propanediol has been studied extensively. Given the peculiar properties of hydrogen such as its inflammability and explosibility, the hydrogenolysis of glycerol without external hydrogen addition seems a more advantageous option. This study focuses on the conversion of glycerol to 1,2-propanediol over different supported bimetallic Ni/Cu catalysts in a fixed bed flow reactor, using in situ hydrogen production and external hydrogen. Among the catalysts prepared, Ni/Cu/TiO2 catalyst was observed to efficiently catalyze the hydrogenolysis of glycerol to 1,2-propanediol under N-2 pressure using 2-propanol as hydrogen source. This was due to the high Cu dispersion and Ni/Cu atomic ratio on the catalyst surface. However, the experimental results indicated that the effect of catalyst acid sites on glycerol hydrogenolysis was more noticeable when the reaction was performed under H-2 pressure. The metal active sites of the catalyst played a significant role in the hydrogen production and also affected the glycerol hydrogenolysis with hydrogen produced from 2-propanol catalytic transfer hydrogenation (CTH) and glycerol aqueous phase reforming (APR). The stability study revealed that the Ni/Cu/TiO2 catalyst underwent serious deactivation during the hydrogenolysis of glycerol. The characterization results showed that the metal leaching and metal particles sintering were responsible for the catalyst deactivation when the glycerol hydrogenolysis was conducted using water as a solvent. However, the activity loss for reactions performed using 2-propanol as a solvent was mainly related to the metal particles sintering and the presence of adsorbed species on the catalyst surface.