Galloza-Lorenzo, Darlene Z.

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    Bifunctional catalysts with improved hydrothermal stability for the hydrolytic hydrogenation of cellulose into polyols
    (2014) Galloza-Lorenzo, Darlene Z.; Cardona-Martínez, Nelson; College of Engineering; Curet, María; Martínez, María; Hernández, Arturo; Department of Chemical Engineering; Cortés, José
    The increase in the world’s energy needs has caused a renewed interest in finding green ways to produce fuels. In this work, we present a study of the hydrolytic hydrogenation of cellulose on bifunctional catalysts for the production of glucose and/or sorbitol. These molecules offer the potential to be used as renewable feedstock in a biorefinery for the production of fuels and value added chemicals. We report results for the study of the effects of: cellulose crystallinity, cellulose/catalyst ratio, the acid functionality, the hydrothermal stability, reaction temperature and reaction time on the catalytic performance for the conversion of cellulose into sorbitol. A series of single, binary and ternary metal oxide supports with a range of surface acidity, transition metal (V) phosphate and zeolites, were studied. Ruthenium was supported using evaporative deposition on the supports. Our results show that the hydrolysis catalytic activity for the single metal oxide supports correlate with the Sanderson electronegativity of the metal oxide, passing through a maximum for Nb2O5 (HY 340). The Lewis acidity of the metal oxide also correlates well with the Sanderson electronegativity of the sample. However, when ruthenium is supported on the metal oxides they all displayed comparable catalytic performance that was similar to the performance observed in a reaction without catalyst. This result suggests that the change in product distribution causes a leveling effect on the hydrolysis activity. The absence of carboxylic acids when the bifunctional catalysts are used explains the decrease in apparent catalytic activity. Under these reaction conditions the rate determining step, i.e., the initial hydrolysis of cellulose is not promoted by the bifunctional catalyst but rather by the hydronium ions present in water at the reaction conditions. The addition of Brønsted acidity by phosphating niobium or tantalum oxide significantly enhances the hydrolysis of cellulose. Of all catalytic materials tested, ruthenium supported on NbOPO4 displayed the best catalytic performance with hexitols yields of about 45% at 100% cellulose conversion. All materials suffer changes in their properties after treatment in hot water. However, treating the catalysts based on transition metal (V) phosphate in water at 503 K 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.