Enhanced catalytic performance of cobalt and iron co-doped ceria catalysts for soot combustion

摘要

A series of promising Ce-Co-Fe catalysts were successfully synthesized using a cetyl-trimethylammonium-bromide-assisted co-precipitation method and investigated for diesel soot combustion. The surface morphological and structural properties were systematically examined using various techniques: X-ray diffraction, scanning electron microscope, N-2 adsorption-desorption, Raman spectroscopy, temperature-programmed reduction and in situ diffuse reflection infrared Fourier transform spectroscopy. The catalyst-soot combustion activities were tested in O-2 and NO + O-2 using a temperature-programmed technique. Nanometer crystalline solid solutions were formed with high surface areas when the Fe and Co cations were co-doped in the ceria lattice. Transition metals doping played a key role in increasing oxygen vacancies and promoting the redox performance of Ce-Co-Fe catalysts. Co-Fe co-doping accelerated the oxidation of soot under both "tight" and "loose" contact conditions. Among all the ceria-based catalysts, Ce80Co15Fe5 showed superior activity with T-10 = 256 degrees C and high selectivity with S-CO2 = 100% under tight a contact mode. The observed high catalytic activity following co-doping was proved to have occurred because of various reasons such as improved redox properties, increased oxygen vacancies and high surface area. The presence of NO in O-2 also promoted soot oxidation, which follows the NO2-assisted mechanism. Moreover, the in situ DRIFTS performed under an isothermal condition in NO + O-2 confirmed the strong adsorption capacity for NOx species on the doped ceria catalyst.