Interaction of ethylene and hydrogen with a commercial Pd black: carbon accumulation and possible adsorbate-induced rearrangement

Abstract

The interaction of hydrogen, ethylene and their mixtures with a commercial Pd black was studied. Hydrogen treatment at 300 K created a rather clean Pd surface with some residual carbon. Ethylene introduced in high hydrogen excess exerted hardly any influence on the metallic properties of Pd, as shown by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The carbon content did not change. Contacting Pd with ethylene in low excess of H₂ or without any hydrogen changed the Pd 3d line, indicating its chemical interaction with C. Simultaneously, a new component appeared in the C 1s region at BE∽283.5 eV. It indicated the formation of Pd–C bonds, responsible for changes in the Pd valence state. Intensity drop at the near-Fermi edge region in UPS corroborated this interaction. Pd also underwent considerable structural rearrangement, as shown by the appearance of a large peak in the UP spectra at ∽8 eV, corresponding to the enrichment of the sodium carbonate impurity on the surface. This component proved to be a good indicator of surface flexibility.