Pd-Pt/Al

Pd-Pt/Al2O3 catalysts are prepared by controlled surface redox reactions, the refilling or the direct redox reaction. By the refilling method, the reduction of platinum salt is made by hydrogen preadsorbed on the palladium parent catalyst. By the direct redox reaction, the metallic palladium of the parent catalyst acts directly as reducer. The characterization of bimetallic catalysts by different techniques (metal accessibility, IR, EXAFS) points out a platinum selective deposit over palladium according to the preparation method under consideration. By using preadsorbed hydrogen, platinum is deposited on low coordination sites of palladium, whereas by direct redox reaction, the deposit occurs preferentially on the palladium faces. The knowledge of the bimetallic species structure allows to explain the catalytic results for the 18O/16O isotopic exchange