Oxidation state of platinum clusters during the reduction of NOx with propene and propane

The oxidation state of platinum supported on mesoporous SiO2 and Al2O3 with MCM-41 type structure during the reduction of NOx with propene or propane was investigated using in situ X-ray absorption spectroscopy. Platinum supported on MCM-41 (SiO2) was reduced at low and oxidized at high reaction temperatures when propene was used as reducing agent, while it was found to be always oxidized in Pt/MCM-41 (Al2O3). When propane was used as reducing agent significant NO conversion was not observed over Pt/MCM-41 (SiO2) and on both supports platinum was in an oxidized state. At the successive adsorption of the reactants, the prereduced catalysts were oxidized after NO adsorption and reduced after addition of the hydrocarbons. Addition of oxygen re-oxidized the catalysts, while the presence of water vapor did not influence the oxidation state.