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 O2 over Na-ZSM-5 molecular sieves with a high SiO2/Al2O3 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 NO2 and it exhibits a dynamic equilibrium between NO2 adsorption and the reaction of NO. TPSR and in situ DRIFTS characterization of the adsorbed NOx species revealed that adsorbed NO3 formed on the surface of the Na-ZSM-5 molecular sieve as a result of the reaction between adsorbed NO and gaseous O2. The oxidation of NO3 with NO produced weakly-adsorbing NO2 and N2O4 which were released once the adsorption reached saturation. Therefore, the strongly-adsorbing NO3 was an intermediate of the NO oxidation reaction and its presence promoted NO adsorption.

摘 要：采用程序升温表面反应 (TPSR) 和原位漫反射红外光谱 (DRIFTS) 等手段研究了常温下 NO 和 O2 在高硅 Na-ZSM-5 分子筛上吸附-氧化反应机理. 结果表明, Na-ZSM-5 分子筛上 NO 的催化氧化过程中伴随着显著的 NO2 物理吸附, 表现为 NO 氧化和 NO2 吸附间的动态平衡. Na-ZSM-5 分子筛表面 NOx 吸附物种的 TPSR 和原位 DRIFTS 表征表明, 化学吸附的 NO 和气相中的 O2 在 Na-ZSM-5 表面反应生成吸附态的 NO3, 并继续与 NO 作用生成弱吸附的 NO2 和 N2O4, 它们吸附饱和后释放出来; 其中, 强吸附的 NO3 在 NO 氧化过程中起到了反应中间体的作用, 同时也促进了 NO 的吸附.

A dynamic equilibrium exists for the physical adsorption of NO2 and for NO oxidation on Na-ZSM-5. Strongly adsorbed NO3 (ONOO) is formed by adsorbed NO and gaseous O2, is an intermediate for NO oxidation, and accelerates the reaction.Figure optionsDownload as PowerPoint slide