INVESTIGATION OF THE STATE OF PALLADIUM IN THE PD SO4/ZRO2 SYSTEM BY DIFFUSE-REFLECTANCE IR SPECTROSCOPY/

The Pd/ZrO2 and Pd/SO4/ZrO2 systems were investigated by diffuse-refle ctance IR spectroscopy using CO as the probe molecule. For the Pd/ZrO2 system, the behavior of the metal is characteristic of the weak metal -support interaction. Intense bands attributed to the bridging CO spec ies indicate the formation of large metal particles in the reduced sys tems. Modification of the ZrO2 support with SO42- anions leads to an i ncrease in the metal-support interaction and makes the metal more resi stant to reduction. On the surface promoted by SO42- anions, metal par ticles with a positive charge (Pd+ and Pddelta+) were observed. The sm aller the size of the metal clusters and the higher degree of oxidatio n of sulfur, the stronger the influence of acidic protons and surface sulfur compounds on the metal.