Effect of the preparation method on the performance of CuO-MnO_x-CeO_2 catalysts for selective oxidation of CO in H_2-rich streams

摘要

Selective oxidation of CO in H2-rich streams is performed over a series of CuO-MnO_x-CeO_2 catalysts prepared by hydrothermal (CuMC-HY), co-precipitation (CuMC-CP), impregnation (CuMC-IM) and citrate sol-gel (CuMC-SG) methods. The catalysts are characterized by N_2 adsorption/desorption, XRD, SEM, HR-TEM, TPR and XPS techniques. The results show that the catalyst prepared by a hydrothermal method exhibits the best catalytic activity, especially at low temperatures. The temperature of 50% CO conversion (T_50) is only 74 C and the temperature window of CO conversions up to 99.0% is about 40 C wide, from 110 to 140 C. Moreover, the temperature window is still maintained 20 C wide even at lower temperatures when there are 15% CO_2 and 7.5% H_2O in the reaction gas. The superior catalytic performance of CuMC-HY is attributed to the formation of Mn-Cu-Ce-0 solid solution, the unique pore structure and the existence of more Cu~+ and Mn~(4+) species as well as oxygen vacancies. The sequence of catalytic activity is as follows: CuMC-HY>CuMC-SG>CuMC-IM>CuMC-CP. The worst catalytic activity, obtained from the catalyst prepared by the co-precipitation method, is possibly related to the existence of independent CuO_x and MnO-x oxides, which weakly interact with ceria in the catalyst.