Preparation and Characterization of the Multicomponent Mesoporous Mixed Oxide Catalysts La-Mn-Ce-O

Abstract

A series of mesoporous multicomponent mixed oxide catalysts La-Mn-Ce-O with various ratios of (n La+n Mn)/(n La+n Mn+n Ce) were prepared by citric acid complexation-organic template decomposition (CAC-OTD) method. For comparison, the sample with the same composition was also prepared by conventional coprecipitation method. The results of N 2 adsorption/desorption showed that the samples prepared by using CAC-OTD method possessed relatively large specific surface area and uniform pore diameter distribution (3.4.4.4 nm). The results of X-ray diffraction (XRD) identified the formation of La-Ce and Mn-Ce solid solution. Mn species were not detected by XRD. The results of X-ray photoelectron spectroscopy (XPS) showed that there was a strong electronic state interaction between Mn and Ce species, resulting in the formation of Mn 2p shake-up peak. Such interaction enhanced the transfer of oxygen species from Ce to Mn oxide and therefore increased the redox activity of the samples. The sample with the strongest shake-up peak showed the highest oxidation activity. The results of temperature programmed reduction (TPR) showed that the manganese species in the samples prepared by using CAC-OTD method were easier to be reduced, which was relevant to the oxidation activity of the catalysts. The results of activity evaluation showed that the light-off temperature of the LMC(0.5)-500 sample was about 50°C lower than that of the sample prepared by using coprecipitation method. The samples prepared by using CAC-OTD method showed good thermal stability.