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

Abstract

Preparation of supported nickel phosphide (Ni2P) 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 Ni2P 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 NiONi bridge bonding (i.e., nickel oxide). This chemical bonding will not result in Ni2P structure, verified by XRD characterization results. The alumina (namely, γ-Al2O3, θ-Al2O3, or α-Al2O3) 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 Ni2P 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-Al2O3 results only in the nickel phosphosate precursor and thus the Ni2P phase.