Essential elucidation for preparation of supported nickel phosphide upon nickel phosphate precursor

摘要

Preparation of supported nickel phosphide (Ni_2P) depends on nickel phosphate precursor, generally related to its chemical composition and supports. Study of this dependence is essential and meaningful for the preparation of supported Ni_2P with excellent catalytic activity. The chemical nature of nickel phosphate precursor is revealed by Raman and UV-vis spectra. It is found that initial P/Ni mole ratio ≥ 0.8 prohibits the Ni-O-Ni bridge bonding (i.e., nickel oxide). This chemical bonding will not result in Ni_2P structure, verified by XRD characterization results. The alumina (namely, γ-Al_2O_3, θ-Al_2O_3, or α-Al_2O_3) with distinct physiochemical properties also results in diverse chemical nature of nickel phosphate, and then different nickel phosphides. The influence of alumina support on producing Ni_2P was explained by the theory of surface energy heterogeneity, calculated by the NLDFT method based on N2-sorption isotherm. The uniform surface energy of α-Al_2O_3 results only in the nickel phosphosate precursor and thus the Ni_2P phase.