A platinum complex catalyst of silica-supported poly- r -diphenylphosphinopropylsiloxa-ne has been investigated by XPS. The exprimental results suggest that (1) the complex is formed by coodination of lone pair electrons on two phosphorus atoms in poly- r -diphenyl-phosphinopropylsiloxane to a platinum atom in chloroplatinic acid

(2) the catalytic activity of the complex in the hydrogena-tion of aromatics is greatly affected by the P/Pt atomic ratio in the complex and the amount of hydrochloric acid in the reactant

and it also closely relates to the strenght ratio ratio of two Cl2p photoelectron peaks in the complex.