Ru-based catalysts for glycerol hydrogenolysis—Effect of support and metal precursor

Hydrogenolysis of biomass-derived glycerol is an alternative route for the production of value-added chemicals, such as 1,2-propanediol. Ru-based (γ-Al2O3, SiO2, ZrO2) catalysts were prepared by the wet impregnation method and evaluated in glycerol hydrogenolysis at 240 °C and 8 MPa H2. The effect of the refractory oxide and metal precursor (RuCl3·xH2O, RuNO(NO3)3) used for catalyst preparation was examined. The nature of the oxidic support was found to influence the ability of the catalyst to both activate the glycerol substrate and selectively convert it to propanediol. Among the tested catalysts, Ru/Al2O3 prepared with the chloride precursor exhibited the highest activity (69%) and the lowest selectivity to 1,2-propanediol due to excessive hydrogenolysis of 1,2-propanediol to 1-propanol. Ru/SiO2 prepared with the nitrate precursor yielded to the highest selectivity to 1,2-propanediol (65%) at 20% conversion level. The characterization of the catalytic materials revealed a correlation between catalytic activity for the hydrogenolysis reaction and total acidity, as the yield to hydrogenolysis products increased with the concentration of the acid sites. The use of different metal precursors affected the catalytic activity and product selectivity mainly in the case of γ-Al2O3 used as support, but with SiO2 support as well. The supported Ru samples prepared using the chloride precursor showed higher activity compared to the corresponding materials prepared with nitrate, but selectivity to 1,2-propanediol was lower due to the promotion of excessive hydrogenolysis to propanols. These effects were attributed to the retention of Cl− ions on the support surface, as evidenced by TEM-EDS.