Comparison of phosphide catalysts prepared by temperature-programmed reduction and liquid-phase methods in the hydrodeoxygenation of 2-methylfuran

Two types of Ni₂P/SiO₂ were prepared by different methods, a conventional method involving temperature-programmed reduction (TPR) and a liquid-phase synthesis (LP). Both methods resulted in phase-pure materials with the Ni₂P hexagonal phase, but the sample prepared by TPR had lower particle size (7 nm) than the sample prepared by LP synthesis (25 nm). The samples were tested in the gas-phase hydrodeoxygenation of 2-methylfuran (2-MF) in H₂ at 0.5 MPa and 250–450 °C, and it was found that the Ni₂P/SiO₂-TPR gave higher conversions and turnover frequencies than the Ni₂P/SiO₂-LP. It was conjectured that the difference in activity was due to the higher phosphorus content of the sample prepared by TPR, and this was confirmed by measurements of the P/Ni ratio by x-ray photoelectron spectroscopy. The main products formed by the two catalysts were 2-pentanone and n-pentane and small amounts of 1-pentanol and 2-pentanol. Contact time measurements on the Ni₂P/SiO₂-TPR sample indicated that 2-pentanone was a primary product, the pentanols were intermediary compounds, and the n-pentane was a final product. Kinetic measurements on the Ni₂P/SiO₂-LP revealed orders of 0.6 for the 2-MF and 0.5 for H₂, consistent with adsorption of both reactants on the catalyst and a surface reaction between the adsorbed species. TPR was also employed to prepare a Cu₃P/SiO₂ sample. Although a phase-pure material was formed, the substance showed very low activity for the HDO of 2-MF.