Lowering the synthesis temperature of Ni₂P/SiO₂ by palladium addition

Abstract

The addition of small amounts of palladium (0.1%, 0.5% and 1.0% w/w) to a NixPyOz/SiO₂ sample led to a decrease of ∼200 K in the synthesis temperature of Ni₂P/SiO₂, allowing synthesis to proceed at 723 K. In situ X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) experiments demonstrated that the phosphate → phosphide transformation started at approximately 673 K, and the total time to reduce the phosphate phase was decreased by the presence of palladium. Based on the in situ P K-edge XANES experiments and CO chemisorption uptakes, it was proposed that, depending on the amount of palladium incorporated, the final catalysts present different degrees of reduction, thereby impacting catalytic activity. An increase in activity was observed for the palladium-containing samples during time on stream, which might be associated with the formation of a phosphosulfide active species. The extent of the phosphosulfide species formation was dependent on the degree of reduction.