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CeO2–K catalysts supported on porous alumina substrate have been prepared by using a novel water-immiscible solvent. The advantage of this method is to load the catalyst onto the filter surface by one-time coating and prevent depositing the catalyst into the porous structure of support materials. The catalytic activities of the supported catalysts were evaluated by TPR system and the results showed that the pure CeO2 displayed a poor catalytic activity for soot oxidation, while the addition of K element into CeO2 would result in the formation of CeO2–K solid solution and significant enhancement of catalytic activity. Nevertheless, the variation of K content had a limited effect on soot ignition temperature. The catalyst with a Ce:K molar ratio of 1:2 exhibited an ignition temperature of about 330 °C and the oxidation rates of about 0.16 and 0.28 mg min−1 cm−2 at temperatures of 370 and 390 °C, respectively.

The alkali carbonates displayed a good catalytic activity for soot oxidation and their catalytic performances follow the order K 2 CO 3 > Na 2 CO 3 > Li 2 CO 3 with soot ignition onset temperatures (IOTs) of 310 °C, 320 °C and 320 °C respectively. Na/K and Li/Na/K carbonate catalysts produced by combinations of the three alkali carbonates displayed the lowest IOT of about 320 °C that was higher than that of pure K 2 CO 3 . It was found that the variation of Li:Na:K molar ratios has very limited effect on the catalytic activity, but considerable effect on the thermal stability of the catalysts.Thermal treatment at 700 °C caused a limited change of IOT, but the deterioration of catalytic performance. In the Li/Na/K catalyst system, the formation of crystalline phases with low melting temperature was observed.

The CeO 2 –K catalysts loaded on porous alumina substrate have been produced by a new route. The potassium halides played an important role on the catalytic activity enhancement of CeO 2 catalyst for soot oxidation. This improvement could partially originate from the catalytic production of CO by the potassium halides. Their effects on the catalytic activity promotion followed the order KF ∼ KCl > KBr > KI and their addition into CeO 2 resulted in the CeO 2 –K catalysts with the lowest soot ignition temperatures of about 334, 335, 345 and 362 °C, respectively, at a loose soot/catalyst contact mode. Nevertheless, the CeO 2 with addition of KCl behaved a better catalytic performance. It was also found that the catalysts have a CO 2 absorption capability.

The CO 2 absorption characteristics and catalytic oxidation activities of V/K and V/Ce/K-based catalysts were studied by temperature-programmed reactions. It was found that the V/K and V/Ce/K catalysts displayed a strong CO 2 absorption characteristic that was believed to be attributable to the formation of potassium bicarbonate species and physical CO 2 absorption. The experimental procedure used could precisely identify the soot ignition onset temperature (IOT) of the prepared catalysts. The V/K catalyst prepared at a V:K molar ratio of 1:2 showed the lowest IOT, but behaved a poor catalytic oxidation performance. The addition of CeO 2 into the V/K catalyst with a V:K molar ratio of 1:6 could reduce the IOT from about 320 to 303 °C at a loose soot/catalyst contact mode.