FTIR Spectroscopic Study of Thiophene, SO2, and CO Adsorption on Cu/Al2O3 Catalysts

Abstract

Infrared spectra are reported of copper/alumina catalysts in various states of oxidation or reduction and exposed to carbon monoxide, thiophene, sulphur dioxide, co-adsorbed carbon monoxide and thiophene, and co-adsorbed carbon monoxide and sulphur dioxide. Available adsorption sites could be broadly divided into four groups: Cu2+, Cu+ in a matrix of Cu2+, Cu+ in a matrix of Cu+, and Cu0. Both site-blocking and electronic effects of thiophene on CO adsorption have been identified and are discussed in terms of the nature of the surface-adsorbate interactions, the oxidation state of the adsorption sites, and the specific effects of thiophene on the adsorption sites for CO. Sulphur dioxide blocked CO adsorption on Cu2+ sites. Adsorption of CO on Cu+ sites was not inhibited by adsorption of sulphur dioxide, the latter having an electronic effect on CO molecules at adjacent sites. Adsorption of sulphur dioxide on a reduced Cu0 surface caused surface oxidation giving Cu+ sites which were available for the subsequent adsorption of CO. The pre-adsorption of CO impeded but did not prevent the oxidative effects of sulphur dioxide chemisorption.