Progresses on Soot Combustion Perovskite Catalysts

Soot particles are emitted by diesel engines together with NO, CO, and unburned hydrocarbons (HCs) in gas streams with high O2, CO2, and H2O concentrations and temperatures typically below 500-550 °C Under these conditions, CO and HC oxidation can be easily accomplished with a diesel oxidation catalyst (DOC), but both NO and soot require complex abatement strategies. 

DPF filters must be regenerated by soot combustion in order to avoid pressure drop in the exhaust and several commercially available technologies have been designed for this purpose [5]. 

The PSA system consists of using metal-fuel additives to obtain soot particles with catalytically active metak well embedded in the structure. A DPF k used to collect the metal catalyst-containing soot particles and, once filter regeneration is required, extra fuel is injected and its exothermic combustion initiates the catalytic combustion of soot. 

The continuously regenerating trap (CRT) system (by Johnson Matthey) con-skts of a DPF filter located downstream of a Pt-containing DOC catalyst. CO and HC are oxidized in the DOC, which ako oxidizes NO to NO2. NO2 k much more active in its oxidizing reactions than NO and O2 and reacts rapidly with the soot and initiates its ignition. 

Some other filter regeneration strategies are under investigation, such as modifications of the CRT systems that incorporate active phases in the filter instead of, or in addition to, that in the previous oxidation catalyst or the Toyota Motors DPNR (diesel particulate NO reduction) system for the simultaneous removal of NO and soot. 

---