Effects of Pr-and La-doped CeO 2 on desorption of active lattice oxygen to soot oxidation were studied. Thermogravimetric analysis under N 2 flow indicated that, despite the decrease in reducible Ce content, the amount of oxygen deficiency increases with increasing La content (x) to 15 mol % in Ce 0.80−x Pr 0.20 La x O 2 . In inert atmosphere, the introduction of oxygen vacancies by doping La increased the available lattice oxygen for desorption. In the oxygen isotopic exchange, under 18 O 2 flow, desorption of oxygen molecules containing lattice oxygen atom ( 16 O) was favored because of Pr and La doping in CeO 2 . These dopants increase the exchange rate constant between gas-phase and lattice oxygen atoms. The apparent activation energy, derived from an Arrhenius plot, for CeO 2 , Ce 0.80 Pr 0.20 O 2 , and Ce 0.65 Pr 0.20 La 0.15 O 2 were 311, 230, and 135 kJ/mol, respectively. The values indicated that Pr and La doping causes facile oxygen exchange between the gas phase and the solid. The comparison of the rate constants for 16 O 18 O formation under 18 O 2 flow and 18 O 2 / 16 O 2 mixture flow showed that lattice oxygen predominantly contributes to the exchange reaction. Surface exchange coefficient (k) and diffusion coefficient (D) were obtained by secondary ion mass spectrometry (SIMS) depth analysis of the oxides after diffusion annealing in 18 O 2 . The values of both k and D increase by doping Pr and La, and the surface exchange coefficient value, k, especially increases significantly. Hence, Pr and La doping enhances the oxygen exchange with lattice oxygen, and so high soot oxidation activity at low temperature could be related to the increased contribution of lattice oxygen.

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Catalytic particulate matter oxidation and its promotion by high oxide ion conductors, Zr–Y–O and Zr–Nd–O, has been studied. Zr-Based oxides show higher particulate matter oxidation activity by O2 compared to a Ce-based conventional catalyst using Pt-loaded oxide coated on a DPF substrate. Isotopic tracer methods involving 18O indicate Zr-based oxides release a large amount of lattice oxygen during carbon oxidation. Also, unique to the Zr-based oxides is an electron and electromotive force generation between carbon-deposited sites and carbon-free sites during carbon oxidation. Zr-Based oxides appear to have the capability to effectively generate oxide ions well suited for carbon oxidation.

Catalyst-loaded wall-flow type honeycomb is effective for reducing the level of carbon particle emissions from diesel engines. Pt-supported oxides were investigated for the oxidation and reduction of carbon particles accumulated in the wall-flow type honeycomb. The initiation temperature of combustion of carbon particles was the same for all samples. After the initiation, Pt-supported Ce composite oxides, such as Pt/Ce0.7Zr0.3O2 and Pt/Ce0.9Pr0.1O2, combusted carbon particles at lower temperatures than Pt-supported CeO2, Pt/CeO2. In particular, combustion occurred at the lowest temperature over Pt/Ce0.9Pr0.1O2 after air aging treatment at 1073 K. Pt/Ce0.9Pr0.1O2 released the highest amount of O2 from the oxide at low temperatures and the Pt surface readily oxidized adsorbed CO by O2 in the gaseous phase. Presumably these properties improved the combustion properties of carbon particles.

Effects of rare earth or transition metal doping on the activity of CeO2 to particulate matter oxidation were investigated, and it was found that a Ce–Pr–La–O mixed oxide demonstrates the lowest ignition temperature of carbon, as low as 550 K. Oxygen-temperature-programmed desorption measurements suggested that the amount of O2 desorbed from CeO2 increases with the substitution of Pr, and furthermore, La doping reduces the desorption temperature of the lattice oxygen. Even in the absence of oxygen, carbon oxidation occurs on Ce–Pr–La–O, and the ignition temperature of carbon is almost the same as the desorption temperature of the lattice oxygen. Doping of La and Pr into CeO2 has a positive impact on carbon oxidation because of this decreased desorption temperature of the lattice oxygen.