NH3-SCR反应过程中NH3和NOx在Cu/SAPO-34分子筛催化剂上的吸附特性和作用

摘要

To investigate the adsorption properties and roles of different feed gases in the selective catalytic reduction by ammonia (NH3-SCR),the adsorption sites,strength,and amount as well as reaction rates of NH3 and NOx (a mixture of NO and NO2) on exchanged Cu/SAPO-34 (chabazite zeolite) catalyst were studied.Transient response,temperature programmed desorption (TPD),and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to characterize the catalyst.Transient response experiments showed that NH3 was adsorbed by the catalyst.TPD and DRIFTS indicated that NH3 can be adsorbed at both Brφnsted and Lewis acid sites to form various NH3 adsorption species that show different SCR activities.The adsorption rate of NH3 by Cu2+ cations was the fastest and the adsorption bond strength of NH3-Cu2+ was the strongest between NH3 and the Cu/SAPO-34 catalyst.NOx can be oxidized and stored as nitrates and nitrites on the Cu catalyst.The intermediate species formed at Cu active sites during the NH3-SCR reaction are discussed,allowing SCR reaction mechanisms to be inferred.%通过离子交换法制得Cu/SAPO-34菱沸石分子筛催化剂,同时研究了NH3和NOx(NO和NO2)在该催化剂上的吸附位、吸附强度、吸附量和吸附速率,得到了不同反应气氛在Cu/SAPO-34上的吸附性能及其在NH3选择性催化还原(NH3-SCR)反应中的作用.研究采用瞬态实验、程序升温脱附(TPD)和漫反射傅里叶变换红外光谱(DRIFTS)等方法进行表征实验.瞬态实验结果表明NH3是吸附性气体.程序升温脱附实验和红外漫反射实验结果表明NH3可以吸附在布朗斯特和路易斯酸性位上形成不同的NH3物种,它们显示不同的SCR活性.NH3在Cu2+上的吸附速率最快,且键强最强.NOx可以氧化并以硝酸盐/亚硝酸盐的形式吸附在CU物种上.最后,本文讨论了NH3选择性催化还原反应过程中在Cu物种上的中间物种并推测反应机理.