Adsorption-Oxidation Reaction Mechanism of NO on Na-ZSM-5 Molecular Sieves with a High Si/Al Ratio at Ambient Temperature

The oxidation reaction mechanism of NO by O(2) over Na-ZSM-5 molecular sieves with a high SiO(2)/Al(2)O(3) ratio was studied at ambient temperature by temperature-programmed surface reaction (TPSR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the NO catalytic oxidation process is accompanied by a significant adsorption of NO(2) and it exhibits a dynamic equilibrium between NO(2) adsorption and the reaction of NO. TPSR and in situ DRIFTS characterization of the adsorbed NO species revealed that adsorbed NO(3) formed on the surface of the Na-ZSM-5 molecular sieve as a result of the reaction between adsorbed NO and gaseous O(2). The oxidation of NO(3) with NO produced weakly-adsorbing NO(2) and N(2)O(4) which were released once the adsorption reached saturation. Therefore, the strongly-adsorbing NO(3) was an intermediate of the NO oxidation reaction and its presence promoted NO adsorption.