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

摘要

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-methyl-furan (2-MF) in H-2 at 0.5 MPa and 250-450 degrees 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.