Lowering the synthesis temperature of Ni2P/SiO2 by palladium addition

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 similar to 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. (C) 2011 Elsevier Inc. All rights reserved.