Role of the Cu-ZrO2 interface in the hydrogenation of levulinic acid to γ-valerolactone
Here we exquisitely fabricated Cu/ZrO 2 -dp catalysts with plentiful Cu-ZrO 2 interfaces by depositing amorphous ZrO 2 onto Cu nanoparticles for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). With the created plentiful Cu-ZrO 2 interfaces, the optimal catalyst 3Cu/ZrO 2 -dp exhibited exceptional catalytic performance under mild reaction conditions, and achieved the highest GVL mass productivity of 266.0 mmol GVL·h −1 ·g −1 Cu, which was 12.5 and 2.3 times of Cu/ZrO 2 catalysts with equivalent Cu loadings prepared by traditional impregnation (3Cu/ZrO 2 -im) or co-precipitation (3Cu/ZrO 2 -cp). As far as we know, this GVL mass productivity stood at the highest level compared with those obtained using non-noble metal catalysts under similar reaction conditions. By systematic investigation with multiple characterizations, density functional theory (DFT) calculations, and kinetic studies, it was found that interfacial active centers were created at Cu-ZrO 2 interfaces, which contained oxygen vacancies (O v ), negatively charged Cu δ− and partially reduced Zr 3+ . The O v favored the adsorption and activation of LA via its ketone group, while negatively charged Cu δ− was able to enhance heterolysis of H 2 , which resulted in the formation of H + -Cu δ− and Zr 3+ -H − active species via hydrogen spillover. Also, plentiful acid sites, which derived from coordinatively unsaturated and defective Zr species, generated at Cu-ZrO 2 interfaces. With the cooperation of interfacial active centers (Cu δ− -O v -Zr 3+ ) and acid sites, the fabricated 3Cu/ZrO 2 -dp with plentiful Cu-ZrO 2 interfaces achieved excellent catalytic performance for the hydrogenation of LA to GVL. Hence, the synergistic catalysis of Cu-ZrO 2 interfaces provided an effective strategy for designing catalysts with a satisfactory performance for the hydrogenation of LA, which also can be expanded to other hydrodeoxygenation reactions.
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