A low-temperature IR spectroscopic study of selective adsorption of NO and CO on CuO/γ-Al 2O 3

Abstract

The composition of the crystal phase and the valence state of surface copper ions was measured by XRD and XPS methods on a CuO/γ-Al 2O 3 catalyst. It was concluded that the bulk phase was composed of CuO and CuAl 2O 4, and Cu 2+ and Cu + ions coexisted on the surface, although the sample was oxidized in oxygen atmosphere. The infrared spectra of CO, NO, and (CO + NO) adsorbed on this catalyst were recorded from 123 to 173 K. All infrared bands were assigned. The adsorption experiment of CO and NO also demonstrated that Cu 2+ (CuO and CuAl 2O 4) and Cu + ions coexisted on the surface. CO or NO could be adsorbed on Cu 2+ and Cu + sites below 173 K, but CO was only adsorbed on Cu + sites and NO only on CU 2+ sites over 173 K. The alternate adsorption and coadsorption of NO and CO found that CO was selectively adsorbed on the Cu + sites (2120 cm −1 band) and NO was selectively adsorbed on the Cu 2+ sites (1888 cm −1 on CuO and 1862 cm −1 on CuAl 2O 4), when CO and NO coexisted in the gas phase.