Catalytic oxidation of benzene over alumina-supported Cu-Mn-Ce mixed oxide catalysts

Based on the response surface methodology (RSM), Cu-Mn-Ce catalysts were prepared via the vacuum impregnation method. Also, Their performance in the oxidation of a tar model compound (Benzene, 5,000 ppm) was evaluated. Results show that the optimum condition is CuO-MnO content of 30% and CeO2 content of 4.4% at a calcination temperature of 620 degrees C for 4.1 h. In this condition, the confirmatory experiment indicates the average carbon conversion rate within half an hour (Xc-05h) and four hours (Xc-4h) are 99.5% and 97.1% at 300 degrees C, respectively, which is in good agreement with the model prediction. XRD, H-2-TPR, SEM, and XPS were employed in catalyst characterization. CuO is the primary active metal in the catalysts, which is affected easily by the calcination temperature. A lower calcination temperature tends to cause a weak structure strength, but a higher temperature results in impairing the reducibility. The major roles of CeO2 are displayed in two aspects that CeO2 increases the dispersion of the active metal, enhances the catalyst stability, and increases the oxygen vacancies and improves the oxygen transfer ability. For Cu-Mn-Ce composite catalyst, the catalytic oxidization of benzene complies with the Mars-van Krevelen mechanism (MVK). The content of CuO-MnO determines the number of active sites on the catalyst, which promotes the reduction of catalyst. CeO2 plays an important role in enhancing the oxidization of the catalyst. Therefore, the ratio of CuO-MnO to CeO2 in the catalyst will cause a change of the control step of the redox reaction.