Facile Preparation of Noble Metal–Free Cu-Doped CeO2 Oxidation Catalyst Suitable for Engine Exhaust Gas Treatment

Abstract

Carbon monoxide oxidation reaction was carried out over Cu-doped CeO2, prepared by a simple and cost-effective route without the aid of any stabilizing agents or solvents. A low-percentage incorporation of Cu of 2% by weight with Ce was sufficient for 100% conversion of CO at a reaction temperature of 300°C. The efficiency of the catalyst remained as such for a sustained period of 5 h. The activity was also tested in the treatment of diesel engine exhaust gas at a very high flow rate of 3,600 mL/min. Complete oxidation of CO and high conversion of hydrocarbons (90%) were achieved at the reasonably moderate temperature of 300°C. In the catalysts, CeO2 is found to exist in its fluorite structure as revealed from X-ray diffraction (XRD) patterns. Raman spectral analysis indicated lattice expansion and oxygen vacancies upon incorporation of Cu, whereas X-ray photoelectron spectroscopic analysis pointed out the existence of Cu in the forms of CuO and Cu2O as well as the presence of Ce in its +4 oxidation state, all of which could facilitate oxidation reactions. The CeO2 nanoparticles were found to be irregular in shape, with size varying from 10 to 20 nm, as evident from the transmission electron microscopic images and crystallite size determination from XRD patterns, confirming the efficiency of present preparation method in the formation of CeO2 nanoparticles. Catalyst characterization studies and catalytic oxidation results indicated the formation of lattice-expanded CeO2 solid solution as well as highly dispersed copper oxides as the active centers of the catalyst.