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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, N2 adsorption–desorption, Raman spectroscopy, temperature-programmed reduction and in situ diffuse reflection infrared Fourier transform spectroscopy. The catalyst–soot combustion activities were tested in O2 and NO + O2 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 T10 = 256 °C and high selectivity with S CO 2 = 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 O2 also promoted soot oxidation, which follows the NO2-assisted mechanism. Moreover, the in situ DRIFTS performed under an isothermal condition in NO + O2 confirmed the strong adsorption capacity for NOx species on the doped ceria catalyst. [ABSTRACT FROM AUTHOR]

The soot combustion on Pd-doped La2Sn2O7 pyrochlore oxides was studied. Palladium promoter was doped into the pyrochlore system via two ways: bulk substitution (La2Sn1.9Pd0.1O7) and surface impregnation (Pd/La2Sn2O7). The catalysts were characterized by XRD, BET, SEM, HRTEM, PL, XPS and H2-TPR measurements. Pd modifications increased the concentration of surface oxygen vacancy, especially Pd/La2Sn2O7. The different morphologies of palladium promoters were revealed in the two palladium-doped catalysts. Palladium was present primarily in the form of a lattice Pd2+ in the bulk-doping sample, with trace of metal palladium deposited on the surface. As for the surface-doping sample, PdO was the predominant form, accompanied with some of highly dispersed metallic palladium. Due to the adhesion of massive surface palladium species on Pd/La2Sn2O7, a strong metal oxide interaction occurred in the interface between Pd species and La2Sn2O7. The activity evaluation results show that Pd/La2Sn2O7 possesses the highest performance, exhibiting the lowest activation energy (98.83 kJ/mol) for soot combustion. Surface Pd/PdO redox couples as well as Pd-O-Sn interface species were identified to be the active phases for the superior catalytic behavior of Pd/La2Sn2O7. A possible oxidation mechanism for the reactions has been speculated. [ABSTRACT FROM AUTHOR]