COMBINATIONS OF PLATINUM AND PALLADIUM ON ALUMINA SUPPORTS AS OXIDATION CATALYSTS

The effects of the total content of Pd + Pt, the mol-% ratio of Pd to Pt, hydrothermal treatment of the catalyst wash-coat, and the oxygen concentration on the light-off temperature, T50, for the complete oxidation of xylene isomers, propene, and carbon monoxide were studied. The alumina wash-coats were thermally treated at 500-degrees-C for 2 h in air or after the thermal treatment, hydrothermally treated at 814-degrees-C for 2 h in 100-% steam. The catalysts were impregnated with 5, 10, and 20-mu-mol of Pd + Pt per gram of catalyst. The mol-% ratio of Pd to Pt was varied in the range from 0:100 to 100:0. The light-off temperatures had a minimum at a Pd:Pt mol-% ratio of 80:20, and decreased with increasing total metals concentration, increasing oxygen concentration and hydrothermal treatment of the alumina wash-coat.