Effects of sulphur on a palladium surface on the adsorption of carbon monoxide and the adsorption and decomposition of nitric oxide

Abstract

The effects of sulphur on a Pd( > 99.9 %) surface on the adsorption of CO and the adsorption and decomposition of NO were studied by combined use of Auger electron spectroscopy, ultraviolet photoelectron spectroscopy and mass spectrometry. CO and NO were molecularly adsorbed on Pd at 298 K and the amount of adsorbed CO or NO decreased linearly as the amount of sulphur on the Pd surface increased. NO decomposed at 573 K to form nitrogen gas and adsorbed atomic oxygen was observed by u.p.s. with a binding energy of 6 eV. The decomposition of NO is inhibited by surface sulphur more sharply than the adsorption of CO and NO and is stopped when the surface sulphur reaches a coverage of 0.3. The poisoning effects of sulphur are discussed in terms of the electronic interaction between Pd and NO, CO or S.