Non-PGM Iron Perovskite Three-Way Gasoline Emissions Control Catalysts: Kinetics, Reaction Mechanism and Catalyst Sizing Study

An A-site deficient perovskite material, namely La 0.8 FeO 3 , has been tested as a catalyst for the reduction of nitrogen oxide with carbon monoxide. The activity of the La 0.8 FeO 3 has been compared with that of a low loaded supported Rh catalyst. Kinetic parameter fitting was performed on a range of model types to select the most suitable description of the two catalysts. The CO–NO reaction over the La 0.8 FeO 3 is described by a Mars–van Krevelen mechanism, with active vacancy sites formed by reduction of the surface by carbon monoxide, and then reduction of nitrogen oxide at these vacancy sites. The Rh catalyst is best described by a Langmuir–Hinshelwood model. Once the best model was selected, kinetic parameters were derived that successfully describe the light-off behavior of the catalysts. Finally, the kinetic parameters were applied to a monolith reactor model, and sizing studies were carried out: under these simple reactor feeds, without the presence of other exhaust gas components, equivalent catalyst performance was achieved with double the volume of the La 0.8 FeO 3 compared to the supported Rh catalyst. However, atomistic modelling studies show that other species typically present in an exhaust gas will strongly compete for the active vacancy surface sites, and this has also been seen in catalyst testing. Therefore, under real conditions the volume of catalyst required is likely to be much larger than that predicted for the simple system.