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

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NO_x (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. NO_x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.

Properties and Roles of Adsorbed NH3 and NOx over Cu/SAPO-34 Zeolite Catalyst in NH3-SCR Process

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 NO_x (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 Br?nsted 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. NO_x 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.