Influence of phosphorus concentration on the state of the surface layer of Pd-P hydrogenation catalysts

Phase composition and surface layer state of the Pd-P hydrogenation catalyst formed at various P/Pd ratios from Pd(acac)(2) and white phosphorus in a hydrogen atmosphere were determined. Palladium on the catalyst surface is mainly in two chemical states: as Pd(0) clusters and as palladium phosphides. As the P/Pd ratio increases, the fraction and size of palladium clusters decrease, and also the phase composition of formed palladium phosphides changes: Pd3P0.8 -> Pd5P2 -> PdP2. The causes of the modifying action of phosphorus on the properties of palladium catalysts for hydrogenation of unsaturated compounds were considered.