Abstract
The study investigated the mechanism of CO oxidation at atmospheric pressure and low temperature over copper catalysts supported on the oxygen –ion- conducting materials, especially the light-off mechanism occurred at this kind of catalysts. We staged it in two parts: First, only the three oxidated states of copper, Cu, Cu2O, CuO, was chosen to discuss the roles of copper oxides in the oxidation reaction. Second, we added the oxygen –ion -conducting materials (SDC) as supports to catalyze the reaction. Results were showed that the activities of copper catalysts were proportional to the reduction ratios of copper oxides on the catalysts by the technique of carbon monoxide temperature –programmed -reduction technique (CO-TPR). These also suggest that valence changing of copper clusters was the key to the activity, and the copper cluster in the intermediate oxidation state was the most active one. By heat transfer analysis, the cause of light-off effect was clarified and the formation of the new active sites with high turnover frequency (TOF) was the most probable of it. After participating oxygen-ion-conducting materials, the reduction of CuO/SDC speeded up and the whole reaction mechanism was converted to a complex one similar to Langmuir-Hinshwood mechanism but involved with the redox cycle. Finally, a mechanism is proposed to and confirmed by the results of our studies.The effect of the catalyst activity in CO oxidation was studied over different heat treatments in the preparation of SDC supports. The study was divided into two parts：changing the calcination temperature and the cooling methods. The variation in the material properties of the SDC supports and the activity of CuO/SDC were analyzed over various calcination temperature (500℃-1100℃) and different cooling methods—quenching the support or not. By the techniques of XRD, N2 physisoption, N2O chemisorption, EDX and CO-TPR, the information about the material properties of SDC, the number of co-shared oxygen ions formed on the catalyst surface, and the activity of the catalyst could be obtained. When the calcination temperature of SDC was lower, more co-shared oxygen ions were formed. Quenching step was beneficial to increase the surface area of SDC and make CuO supported on SDC became more dispersed, but it would make the phase change on SDC. Similar to our previous study, the results in this study also revealed that as more more co-shared oxygen ions were formed, the better activity of CuO/SDC would be.