Participation of Surface Oxygen in the Stabilization of the Rh/HOPG System with Respect to NO₂

Abstract

In this work, using the method of X-ray photoelectron spectroscopy (XPS), a comparative study of the nature of the interaction of NO₂ at room temperature and a pressure of 10⁻⁵ mbar with two samples of highly oriented pyrolytic graphite (HOPG), on the surface of which rhodium was preliminarily deposited by vacuum deposition, was carried out. Before metal deposition, one of the HOPG samples was annealed in vacuum at 600°C, and the other was subjected to bombardment with argon ions, followed by exposure to air at room temperature for an hour in order to introduce strongly bound oxygen atoms into the surface composition. After deposition of rhodium on two samples of HOPG prepared, two model catalysts were obtained, designated as Rh/C and Rh/C(A)-O. It was found that the interaction of NO₂ with Rh/C led to the oxidation of graphite with the destruction of the surface layer. The Rh particles remained in the metallic state, but at the same time they were introduced into the near-surface layer of the carbon support. On the contrary, when the Rh/C(A)-O sample was treated with NO₂, the deposited rhodium was partially converted into RH₂O₃, while the graphite was oxidized to an insignificant degree and retained its original structure. The role of surface oxygen in the stabilization of graphite with respect to oxidation to NO₂ was discussed.