ABSTRACT Water-assisted proton hopping (WAPH) plays an important role in the aqueous-phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). In this study, based on a strategy of spontaneously polarized ceramic (SPCE)-reinforced WAPH, a Ni–Co/SPCE–C catalyst was constructed by high-temperature calcination of a dual mechanical activation-treated precursor. Ni–Co/SPCE–C with favorable structural characteristics, intimate interfacial compatibility, and unique spontaneous polarization effect enhanced the migration efficiency of active hydrogen and activated water to form small water clusters, contributing to outstanding catalytic activity for aqueous-phase hydrogenation of LA to produce GVL at relatively low reaction temperature and H 2 pressure. A LA conversion of 99.9% and a GVL yield of 92.3% were achieved at 160°C and 1.5 MPa H 2 over the Ni–Co/SPCE–C catalyst, which were significantly higher than those catalyzed by contrastive catalysts. A variety of tests and theoretical calculations reveal that SPCE with far-infrared emission and surface electric field was conducive to the reduction in the hydrogen spillover energy barrier, the stabilization of the transition state, and the facile exchange of H 2 and water for accelerating WAPH. Moreover, a reasonable SPCE-reinforced WAPH mechanism was proposed to explain the enhanced aqueous hydrogenation of LA. This research can provide valuable insights into the design and development of high-performance non-noble metal catalysts for aqueous hydrogenation applications.
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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