Heterogeneous Ni and MoOx co-loaded CeO2 catalyst for the hydrogenation of fatty acids to fatty alcohols under mild reaction conditions

Abstract

To develop an efficient Ni-based catalyst for converting renewable fatty acids into high value-added fatty alcohols under mild reaction conditions, the scope of metal oxide modified nickel catalysts was scrutinized. The results show that MoOx modified Ni/CeO2 catalyst exhibits the excellent catalytic performance in the conversion of fatty acids to form corresponding alcohols at mild reaction conditions (235 °C, 3.0 MPa H2). Using stearic acid as a model substrate, Ni-MoOx/CeO2 catalyst shows the 98.0% conversion and 96.2% selectivity to stearyl alcohol, which is significantly higher than that of Ni/CeO2 catalyst and of a physical mixture of both Ni/CeO2 and MoOx/CeO2. Detailed characterization (XRD, Raman, XPS, in situ CO-FTIR, HRTEM, and EPR) indicates that NiMoO4 is the mainly active phase in the pre-reduced bimetallic catalysts. After reduction at 500 °C in a H2 flow, the surface of Ni metal is decorated by the MoOx species, the phenomenon is similar to the strong metal-support interaction (SMSI) previously observed on reducible oxides. The presence of MoOx species in the bimetallic Ni-MoOx/CeO2 catalyst not only improves the dispersion of metallic Ni, but also promotes the charge transfer from Ni to Mo. The electronic interaction at the interface of Ni and MoOx provides synergistic catalysis sites of electron-deficient Ni and MoOx species, which is primarily responsible for the excellent catalytic performance of the bimetallic Ni-MoOx catalyst. Additionally, the introduction of Mo species provides much oxygen vacancy sites for the adsorption of fatty acids, which results in high activity for the conversion of fatty acids. The insights into the synergistic catalysis between Ni and MoOx will provide new possibilities in the design of efficient Ni-based catalysts for selective hydrogenation of other biomass-derived compounds containing carboxylic group.