The research on CO oxidation over Ce–Mn oxides: The preparation method effects and oxidation mechanism

A series of CeO2-MnOx for highly efficient catalytical oxidation of carbon monoxide were prepared by citrate sol-gel (C), hydrothermal (H) and hydrothermal-citrate complexation (CH) methods. The outcome indicates that the catalyst generated using the CH technique (CH-1:8) demonstrated the greatest catalytic performance for CO oxidation with a T50 of 98 °C, and also good stability in 1400 min. Compared to the catalysts prepared by C and H method, CH-1:8 has the highest specific surface of 156.1 m2 g-1, and the better reducibility of CH-1:8 was also observed in CO-TPR. It is also observed the high ratio of adsorbed oxygen/lattice oxygen (1.5) in the XPS result. Moreover, characterizations by the TOF-SIMS method indicated that obtained catalyst CH-Ce/Mn = 1:8 had stronger interactions between Ce and Mn oxides, and the redox cycle of Mn3++Ce4+ ↔ Mn4++Ce3+ was a key process for CO adsorption and oxidation process. According to in-situ FTIR, the possible reaction pathway for CO was deduced in three ways. CO directly oxidize with O2 to CO2, CO adsorbed on Mn4+ and Ce3+ reacts with O to form intermediates (COO-) (T > 50 °C) and carbonates (T > 90 °C), which are further oxidized into CO2.