High Specific Surface Area Of ​​cuo-ceo <sub> 2 </ Sub> Catalyst And Its Activity For Co Oxidation

Nanostructured CuO-CeO₂ catalysts with high surface area were prepared bymodified citrate sol-gel method (the precursor was firstly pretreated under N₂ to formcarbon powers at high temperature and then the carbon powers was burned up). Thesamples were characterized by TG-DSC, BET nitrogen adsorption, XRD, TEM,Raman spectroscopy and TPR technologies. Results show that using the modifiedcitrate sol-gel method, the incorporation of thermal treatment at high temperatureunder N₂ atmosphere can prevent small crystallite size from sintering and affordCuO-CeO₂ catalysts with high surface area (more than 90 m²/g) and ultrafine, crystallite size (less than 10 ran). Furthermore, due to the high temperature calcination,Ce_xCu_1-xO_2-δ solid solutions and oxygen vacancies are formed in these CuO-CeO₂catalysts. Due to the decrease in the crystalline size, the increase of the surface areaand the formation of the solid solutions, the catalyst shows high catalytic activity forlow temperature CO oxidation. XRD and TPR results show that there are three CuOspecies in the CuO-CeO2 catalyst, namely the finely dispersed CuO, the bulk CuO andthe Cu²⁺ in the CeO₂ lattice.The three CuO species in the CuO-CeO₂ catalysts were identified by the fact of that the finely dispersed CuO and the bulk CuO can be dissolved in nitric acid. According to the conversion of the CO oxidation, the specific rate of the individual CuO species at 100℃was obtained. It is clear that the finely dispersed CuO has the largest contribution of the activity for CO oxidation (18.21 mol_COg_Cu^-1 h^-1), bulk CuO has medium one (9.98 mol_COg_Cu^-1 h^-1) while the Cu²⁺ in the CeO₂ lattice has the least (2.13 mol_COg_Cu^-1 h^-1). Moreover, based on the CO oxidation activities of the acid treated sample calcined at different temperatures and the CO-TPR profiles of these samples, combined the change of surface composition of the the acid treated sample by the XPS measurement and the CO cyclic oxidation of the sample, shift between the three CuO species in the catalyst was illustrated. The finely dispersed CuO could be translated to the bulk CuO at high temperature of 800°C; while part of the Cu²⁺ in the CeO₂ lattice could migrate from lattice to surface to form finely dispersed CuO particles calcined at high temperature of 600°C or under CO oxidation.