Noble metal-doped perovskites for the oxidation of organic air pollutants

Ag-Pt- and Pd-doped LaMnO₃-based perovskite catalysts were prepared and their activity in the oxidation of toluene, n-heptane and ethanol was investigated. The activity of LaMnO₃-based catalyst was very high in the oxidation of each compound tested. The Ag-doped catalyst was the most active in the oxidation of each compound and it displayed the highest BET specific surface area (SSA) also. The influence of Pt or Pd doping on perovskite activity is negligibly small. Pt-doped catalysts are slightly more active while Pd-doped catalysts are slightly less active than the pure perovskite. Thermogravimetric-differential thermal analysis (TG-DTA) for the catalyst precursor indicates that above 500 °C a perovskite structure began to form. The XRD analysis reveals the presence of the LaMnO_3.15 perovskite phase and, additionally, the presence of some metal oxide phases (e.g. La₂O₂CO₃, Mn₂O₃) and carbon. BET SSA measured after the oxidation tests was found to decrease for each catalyst. There was no relation between the chemical composition of the catalyst and the loss of SSA.