SURFACE SPECIES ON A PALLADIUM ZIRCONIA CO OXIDATION CATALYST PREPARED FROM A GLASSY METAL PRECURSOR - CHARACTERIZATION BY DIFFUSE REFLECTANCE FTIR SPECTROSCOPY

CO adsorption and oxidation on the surface of a palladium/zirconia catalyst prepared from an amorphous Pd25Zr75 precursor have been studied by diffuse reflectance FTIR (DRIFT) spectroscopy. In pure CO atmosphere, the most abundant surface species observed is bridge-bound CO. When the catalyst is exposed to a reactant feed consisting of CO and N2-O2 (purified air), the coverage of two-fold coordinated CO molecules decreases, and singly and triply bound CO species appear on the surface. Apparently the bridge-bound CO reacts with subsurface and/or gas-phase oxygen, and is subsequently desorbed from the catalyst surface as CO2. When the oxygen partial pressure is increased, the triply bound CO species also participate in the surface reaction. A simple model is proposed to account, in a qualitative way, for the changes in surface coverage observed under oxidative conditions.