Insights into the Role of Dual-Interfacial Sites in Cu/ZrO2 Catalysts in 5-HMF Hydrogenolysis with Isopropanol

Abstract

In this work, we synthesized a series of Cu/ZrO₂ catalysts with tunable V_o-Cu⁰ (oxygen vacancy adjacent to Cu metal) and V_Zr-Cu^δ+ (zirconium vacancy adjacent to electron-deficient Cu species) dual-interface sites and investigated the role of the dual-interface sites in the 5-hydroxymethylfurfural (5-HMF) hydrogenolysis reaction with isopropanol as the hydrogen source. By combining a series of in situ infrared characterization and catalytic performance analysis, it is identified that V_o-Cu⁰ interface sites were responsible for activating isopropanol dehydrogenation and C═O dissociation of 5-HMF, while the V_Zr-Cu^δ+ interface sites were responsible for the dehydroxylation of an intermediate product 5-methyl-2-furfuryl alcohol (5-MFA). Specifically, C-OH was first deprotonated on the V_Zr at the V_Zr-Cu^δ+ interface site to reduce the activation energy of 5-MFA dehydroxylation and then adjacent Cu^δ+ promoted the dissociation of the C-O bond by enhancing the adsorption energy while elongating the C-O bond, as confirmed by the density functional theory calculations. Because the dual-interface sites provided separate sites for activating intermediate products and reactants, the coupling reaction caused by competitive adsorption is thus well avoided. Therefore, the optimized Cu/ZrO₂ catalyst with the most V_Zr-Cu^δ+ and moderate V_o-Cu⁰ sites exhibited 98.4% of 2,5-dimethylfuran yield under the conditions of 180 °C and self-vapor pressure.

Keywords: 5-MFA dehydroxylation; Cu-based catalyst; catalytic transfer hydrogenation (CTH) process; dual-interface sites; synergistic mechanism.