Near ambient pressure XPS investigation of hydrous palladium oxide under water and oxygen gas environments

Pd takes various chemical forms according to the types of catalysts and even its pristine chemical state is often subject to change in operation. To understand the mechanism how Pd-based catalysts activate reactions, it is important to have a capability to identify the surface chemical state of Pd-based catalysts in contact with reactants. In this study, we conducted in situ near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) in gas conditions with water and oxygen for hydrous Pd oxide, which is also known as palladium hydroxide (Pd(OH)2) and it is the key component of the Pearlman's catalyst widely used for organic reactions. We found that hydrous Pd oxide showed different spectral features to that of anhydrous Pd oxide under gaseous water environments. We believe that this NAP-XPS study provides new information for a better identification of hydrous Pd oxide under reaction conditions, which is not available from conventional XPS in ultrahigh vacuum.