Bifunctional Catalysts With Improved Hydrothermal Stability for the Hydrolytic Hydrogenation of Cellulose

The production of glucose and/or sorbitol from the hydrolytic hydrogenation of cellulose, offers the potential to be used as a renewable feedstock in a biorefinery for the production of fuels and value added chemicals. Here we report the results of the study of the effect of cellulose crystallinity, cellulose/catalyst ratio, reaction temperature and reaction time on the catalytic performance for the conversion of cellulose into sorbitol.  We studied a series of single, binary and ternary metal oxide supports with a range of surface acidity and phosphated niobic acid.  Ru was supported using evaporative deposition on the supports.  The catalytic materials were characterized using nitrogen adsorption, X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR).  Ruthenium supported on NbOPO₄ displayed the best catalytic performance with hexitols yields of about 45% at 100% cellulose conversion.  All materials suffer a decrease in their surface areas after treatment in hot water.  However, treating Ru/NbOPO₄ in water at 210°C and 230 °C and 35 bar H₂ for 24 h or 48 h caused a slight decrease in cellulose conversion, but a significant increase in hexitol and hydrogenolysis products yield.  Ru/Nb₂O₅ (HY 340) and the equivalent amount of phosphoric acid present in Ru/NbOPO₄ give essentially the same conversion as Ru/NbOPO₄ but a lower yield to sugar alcohols and a higher yield to hydrogenolysis products.  Decreasing cellulose crystallinity and cellulose/catalyst ratio, increases the cellulose conversion and hexitols yield for Ru/NbOPO₄.