A Kinetic Study of Oxygen Adsorption/Desorption and NO Oxidation over Pt/Al₂O₃ Catalysts

Abstract

Laboratory tests and kinetic modeling were carried out in order to provide kinetic input data to a systematic investigation of the mechanism of nitrogen oxides (NO x ) storage in catalysts used for lean-burn engines. In particular, we present a kinetic model of the NO oxidation to NO 2 over a Pt/Al 2 O 3 model catalyst for the temperature range 250−450 °C. Since the oxygen behavior at atmospheric pressure is critical for such a model, we have also studied the adsorption/desorption of oxygen by temperature-programmed desorption (TPD) experiments. The experiments show that oxygen starts to desorb at about 300 °C. Furthermore, the NO oxidation was studied in a temperature ramp with NO and oxygen in the gas feed. The data from this experiment and the above-determined values for the oxygen adsorption/desorption were used to construct a kinetic model for the NO oxidation. Finally, the model was validated with some transient experiments with either NO or NO 2 and different oxygen concentrations in the gas feed. We found a good agreement between these experiments and the model.