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-reflectance 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 attibuted to the bridging CO species indicate the formation of large metal particles in the reduced systems. Modification of the ZrO₂ support with SO₄ ^2? anions leads to an increase in the metal—support interaction and makes the metal more resistant to reduction. On the surface promoted by SO₄ ^2? anions, metal particles with a positive charge (Pd⁺ and Pd^δ+) were observed. The smaller the size of the metal clusters and the higher degree of oxidation of sulfur, the stronger the influence of acidic protons and surface sulfur compounds on the metal.