In-situ deoxygenation of methyl palmitate to hydrocarbons on highly dispersed Ni–Re/TiO2 catalyst in aqueous phase using methanol as a hydrogen donor

Abstract

Herein, TiO2 supported Ni–Re alloy catalysts (i.e., NiRe(x:y)/TiO2, x:y denotes the Ni/Re atomic ratio) were prepared and tested for in situ deoxygenation of methyl palmitate to hydrocarbons in aqueous phase using methanol as hydrogen donor. Raman spectra indicates that there is interaction between NiO and ReO4− species via forming Ni–O-Re(=O)3 species in the calcined catalysts, which contributes to the formation of Ni–Re alloy and promotes the Ni dispersion during the reduction with H2. Particularly, the Ni–Re alloy particles with average size of ∼1.4 nm highly disperse on spherical TiO2 particles (∼14 nm in diameter) in NiRe(3:4)/TiO2 (the nominal Ni content of 3 wt%). XPS reveals a charge transfer from metallic Ni to Re in the Ni–Re alloy. In in situ deoxygenation of methyl palmitate, compared with Ni/TiO2, NiRe(x:y)/TiO2 give remarkably higher deoxygenation activity and lower activity for the C–C bond hydrogenolysis, ascribed to the synergistic effect between Ni and Re species and the geometrical effect of Re, respectively, which are further verified by propanoic acid-TPD and TPSR. The yield of C6∼C16 liquid hydrocarbons can achieve as high as 98.0% on NiRe(3:4)/TiO2 at 330 °C. There is no obvious sintering of Ni–Re alloy and support TiO2 particles during the recycling of NiRe(3:4)/TiO2, while the carbon deposition and the leaching of Re species slightly reduce the catalyst activity.