Catalytic hydrogenation of levulinic acid to form γ-valerolactone was studied over Cu-ZrO2 catalysts doped with metal oxides from the first row transition metals. The Cu-ZrO2 material was prepared by oxalate gel co-precipitation and dopants were added by an incipient wetness approach. The addition of 1% Mn into Cu-ZrO2 significantly increases the yield of γ-valerolactone and the catalytic activity of Mn/Cu-ZrO2 was found to be 1.6 times higher than that of the undoped Cu-ZrO2 catalyst. Catalyst characterization suggests that the Mn dopant improves the dispersion of Cu on the surface of ZrO2. Kinetic studies show that the reaction order with respect to the substrate concentration is approximately zero. However, the order of reaction with respect to the partial pressure of H2 is different for the Mn/Cu-ZrO2 and Cu-ZrO2 catalysts. Comparison of reaction products from reactions carried out in H2O and D2O solvents using 1 H NMR and 13 C NMR show that there is a pre-equilibrium keto-enol isomerisation step under our reaction conditions. DFT calculations show that the enol isomers have a higher affinity for the Cu surface which may improve the availability of the substrate in the hydrogenation step of the reaction.
Articles you may be interested inCO2 hydrogenation to methanol over Cu/CeO2 and Cu/ZrO2 catalysts: Tuning methanol selectivity via metal-support interaction Journal of Energy Chemistry 40, 22 (2020);In situ synthesis of biomass-derived Ni/C catalyst by self-reduction for the hydrogenation of levulinic acid to γ-valerolactone a b s t r a c t A novel pH gradient methodology was used to synthesise a series of Cu-ZrO 2 catalysts containing different quantities of Cu and Zr. All of the catalysts were highly selective to the desired product, γvalerolactone, and are considerably more stable than Cu-ZrO 2 catalysts prepared by other co-precipitation methods for this reaction. Characterisation and further investigation of these catalysts by XRD, BET, SEM and XPS provided insight into the nature of the catalytic active site and the physicochemical properties that lead to catalyst stability. We consider the active site to be the interface between Cu/CuO x and ZrO x and that lattice Cu species assist with the dispersion of surface Cu through the promotion of a strong metal support interaction. This enhanced understanding of the active site and roles of lattice and surface Cu will assist with future catalyst design. As such, we conclude that the activity of Cu-ZrO 2 catalysts in this reaction is dictated by the quantity of Cu-Zr interface sites.
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