Oxygen-removal of dibenzofuran as a model compound in biomass derived bio-oil on nickel phosphide catalysts: Role of phosphorus

Abstract

The hydrodeoxygenation (HDO) of dibenzofuran (DBF) was investigated over silica-supported nickel phosphide catalysts with low metallic loadings (2.5–10wt.%) and with different initial P/Ni atomic ratios. The formation of the nickel phosphide phase as well as the textural, structural and acidic properties of the catalysts were evaluated by X-ray fluorescence (XRFS), H2-temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), CO chemisorption at 35°C, N2 adsorption–desorption isotherms at −196°C, NH3-temperature programmed desorption (NH3-TPD) and elemental analysis (CNHS). The effect of metallic loading, the initial P/Ni molar ratio as well as the feed O-concentration on the catalytic activity were studied. Characterization results reveal that smaller particle sizes are formed at lower metallic loadings and high P/Ni atomic ratios, and that the acidity increases linearly with the metallic loading pointing to nickel and phosphorous species as the acidic centers in reduced catalysts. Nickel phosphide catalysts display good activity and stability in the HDO of DBF, reaching high DBF conversion values at moderate temperatures (300°C) and with high selectivity to bicyclohexane (BCH), the main deoxygenated product which was obtained by hydrogenation of both aromatic rings (HYD pathway). Catalyst deactivation due to coke was minimal due to the low strength of the acid sites, while the formation of water did not present an inhibiting effect even under high O-concentration. This behavior might occur because water interacts preferentially with the excess phosphorous present on the catalyst surface and thus nickel phosphide particles do not undergo oxidation.