Reduction of Pt/Al2O3 catalysts: Effect of hydrogen and of water and hydrochloric acid vapor on the accessibility of platinum

Abstract The direct reduction by hydrogen, without precalcination, of Pt/Al 2 O 3 activated by H 2 PtCl 6 was studied on several series of catalysts with different metal and chloride loadings. It appears that H 2 O acts as a kinetic inhibitor of the reduction reaction but can also induce platinum sintering. HCl has no kinetic effect on the reduction but is able to increase the metallic accessibility. The higher the hydrogen pressure, the lower the platinum dispersion. The extent to which the metal is accessible is considered to be resultant of two parallel reactions, namely polymerization and reduction of partly reduced Pt 2+ complexes.