Effects of CuO/CeO2 and CuO/γ-Al2O3 catalysts on NO + CO reaction

Abstract

Reducibility and characteristics of CeO2, γ-Al2O3, CuO/CeO2, CuO/γ-Al2O3 and ceria-modified CuO/γ-Al2O3 catalysts were examined using a microreactor-GC NO+CO reaction system and the methods of BET, XRD, TPR, XPS and NO-TPD. The results showed that the catalytic activities of CuO/CeO2 and CuO/γ-Al2O3 were increased compared to that of CeO2 or γ-Al2O3 alone, probably due to the presence of the copper oxide species with low valence and surface dispersion. There were two TPR peaks of CuO/CeO2, a low-temperature peak due to the reduction of highly dispersed copper oxide species and a high-temperature peak due to the reduction of bulk CuO. CuO/γ-Al2O3 had one TPR peak, while the CeO2-modified CuO/γ-Al2O3 had three reduction peaks with one low-temperature peak and two high-temperature peaks. The Cu 2p3/2 (eV) binding energy of 5.0 wt.% CuO/CeO2 was 932.79 to 934.11 eV, compared to that of CuO/γ-Al2O3 equal to 935.0 eV. After added with CeO2, the Cu 2p3/2 (eV) binding energy was 934.1 eV, slightly lower than the Cu 2p3/2 (eV) binding energy. During the thermal desorption of NO, five desorption species (NO, N2O, N2, O2 and NO2) were adsorbed on CeO2 and γ-Al2O3 but only four desorption species (NO, N2O, N2 and NO2) adsorbed on CuO/CeO2 and CuO/γ-Al2O3. Two adsorbing states of NO were observed on the catalyst’s surface, the weak one at low temperatures and the strong one at high temperatures. The NO-TPD profile also showed that peak temperatures of NO desorption by the catalysts were lower than that by the supports, indicating that the NO decomposition activity of the catalysts was higher than that of the supports.