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

Abstract

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 °C for 4.1 h. In this condition, the confirmatory experiment indicates the average carbon conversion rate within half an hour (X_c-0.5h) and four hours (X_c-4h) are 99.5% and 97.1% at 300 °C, respectively, which is in good agreement with the model prediction. XRD, H₂-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.