The Influence of Cerium to Manganese Ratio and Preparation Method on the Activity of Ceria-Manganese Mixed Metal Oxide Catalysts for VOC Total Oxidation

Abstract

A set of ceria-manganese mixed metal oxide catalysts with varying Ce:Mn ratios were prepared by coprecipitation using sodium carbonate and were evaluated for the total oxidation of propane and naphthalene. Manganese-rich samples were the most active, with Ce0.25Mn0.75Ox having the highest activity. Catalysts were characterised using X-ray diffraction, Brunauer–Emmett–Teller (BET) surface area, Raman spectroscopy, temperature programmed reduction (TPR), electron microscopy, and X-ray photoelectron spectroscopy (XPS), establishing that the high activity of Ce0.25Mn0.75Ox was due to the formation of phase-separated Mn-substituted ceria and Mn2O3 phases that were not simultaneously present in the other catalysts. The catalyst preparation technique for the most active ratio was investigated using co-precipitation by urea, oxalic acid and citric acid, and mechanochemical grinding. For propane, the mechanochemical and urea catalysts were more active than the carbonate coprecipitated catalyst, due to greater surface area and increased phase separation. This work demonstrates that ceria-manganese mixed metal oxides are more active than the parent oxide, but that preparation technique is also important for controlling activity.