Low temperature DPF regeneration by delafossite catalysts

Several Li–Cr delafossite catalysts (LiCrO2, LiCr0.9O2, LiCr0.8O2, LiCr0.7O2, Li0.9CrO2, Li0.8CrO2 and Li0.7CrO2) were prepared via a highly exothermic and self-sustaining reaction, the so-called “solution combustion synthesis (SCS)” method, and characterized by means of XRD, BET, FESEM-EDS, H2-temperature programmed reduction (TPR) and XPS analyses, as catalysts for the combustion of soot, a major pollutant emitted by diesel engines. These catalysts already showed appreciable activity at 350 °C towards the catalytic combustion of soot even under loose contact conditions. The best prepared catalyst (LiCr0.9O2) could ignite soot combustion well below 350 °C, which is inside the range of temperatures reached at the exhaust line of a diesel engine. The correlation between the activity order and the capability to provide surface adsorbed oxygen (O−) by the prepared delafossite catalysts, enabled by a shift of the chromium from a high valence to a low valence state, is pointed out as a peculiar feature of these catalysts. An in situ SCS method was tailored to the preparation of a LiCr0.9O2-catalyzed trap based on a SiC wall-flow monolith. Engine bench tests on these catalytic traps (trap loading and regeneration by induced temperature increase) showed that the presence of the catalyst enabled both a more complete regeneration and a one-third fold reduction of the regeneration time compared to the case of a bare, non-catalytic trap. The catalyzed trap was finally characterized in terms of soot emissions during both the loading and the regeneration phase.