Interaction of Hydrogen with Palladium Supported onto an Oxidized Graphite Surface

Abstract

The interaction of palladium deposited by vacuum evaporation onto the surface of highly oriented pyrolytic graphite (HOPG) with hydrogen was studied using X-ray photoelectron spectroscopy (XPS). Graphite was preliminarily subjected to oxidative treatment including the stages of etching by Ar⁺ ions and exposure to air at room temperature. Before contact with hydrogen, the spectrum of the Pd/O-HOPG sample contained two O 1s lines with binding energies E_b ∼ 530.5 and ∼532.5 eV belonging to two types of oxygen atoms in the functional groups on the surface of the carbon support. After interaction with H₂ at a temperature of 150°C and a pressure of 20 mbar, the line with E_b ≈ 530.5 eV disappeared, probably, due to the reduction of the corresponding functional groups. Under these conditions, the surface oxygen was retained in the oxidized graphite sample without deposited palladium (O-HOPG), which indicated the participation of palladium particles in the reduction of oxygen-containing groups. Apparently, dissociation of hydrogen molecules occurred on the palladium surface, followed by spillover of the resulting H atoms onto the carbon support.