Competition between acidic sites and hydrogenation sites in Cu/ZrO2 catalysts with different crystal phases for conversion of biomass-derived organics

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Oxides with different crystal phases can have important effects on the configuration of surface atoms, which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of these varied types of catalytic sites. This could be potentially used to tailor the distribution of the products. In this study, zirconium oxides with different crystal phases supported copper catalysts were prepared for the hydrogenation of the biomass-derived furfural, vanillin, etc. The results showed that both calcination temperature and Cu species affected the shift of zirconia from tetragonal phase to the monoclinic phase. Monoclinic zirconia supported copper catalyst can effectively catalyze the hydrogenation of furfural to furfuryl alcohol via hydrogenation route due to its low amount of Brønsted acidic sites, although the surface area and the exposed metallic Cu surface area were much lower than the tetragonal zirconia supported copper catalyst. Zirconia with tetragonal or tetragonal/monoclinic phases supported copper catalysts contain abundant acidic sites and especially the Brønsted acidic sites, which catalyzed mainly the conversion of furfural via the acid-catalyzed routes such as the acetalization, rather than the hydrogenation. The acidic sites over the Cu/ZrO2 catalyst played more predominant roles than the hydrogenation sites in determining the conversion of the organics like furfural and vanillin.