Abstract 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.