Promotional role of boron on Ni/SiO2 catalysts for dibenzofuran hydrodeoxygenation

Abstract

Controlling the oxygen-free product selectivity in catalytic hydrodeoxygenation is essential for producing high quality fuels from coal- and biomass-derived crude liquids. A series of boron-doped Ni/SiO₂ catalysts were prepared for the efficient hydrodeoxygenation of dibenzofuran as a model compound. Boron doping significantly promoted the transformation of 2-cyclohexylcyclohexanol, which was accumulated as the main oxygen-containing intermediate compound on the pristine Ni/SiO₂ catalyst, to the target products bicyclohexane and its isomer cyclopentylmethylcyclohexane. Characterization results show that boron doping increases Ni dispersion, modifies the electronic properties of Ni sites and in situ generates Brønsted acid sites by H₂ spillover to boron oxides. The reduced Ni particle size improves the rates of dibenzofuran hydrogenation and 2-cyclohexylcyclohexanol dehydration. Electron-deficient Ni and boron oxides as the Lewis acid sites enhance the adsorption of 2-cyclohexylcyclohexanol. Furthermore, the in situ generated Brønsted acid sites favor the dehydration of 2-cyclohexylcyclohexanol, which gives the Ni-5B/SiO₂ catalyst a better deoxygenation activity than the mechanical mixture of equal amounts of 5B/SiO₂ and Ni/SiO₂, as well as the one with a smaller Ni particle size of 3.8 nm.