Ag promoted Cu-SAPO-34 has been developed to improve the low-temperature hydrothermal stability of Cu-SAPO-34 for the NH₃-SCR reaction. Kinetic tests show that the addition of Ag into Cu-SAPO-34 doesn’t change the reaction mechanism. The ion-exchanged Ag species, which decrease the Brønsted acid density and provide more Lewis acid sites with moderate acidity, have a protective effect on the SAPO framework against low-temperature steaming treatment (LTST). Higher surface Cu content is observed for CuAg_2.25-SAPO-34, although CuAg_2.25-SAPO-34 and Cu-SAPO-34 have similar content of isolated Cu ions. In situ DRIFTS studies demonstrate, for the first time, the NH₃ molecules adsorbed on the weak/moderate acid sites (independent of the acid types such as Brønsted acid or Lewis acid) are more active than on the strong acid sites for the low-temperature SCR reaction. Compared with the original catalyst Cu-SAPO-34, the enhanced SCR activity of CuAg_2.25-SAPO-34 after LTST is ascribed to the better preservation of total acid sites, higher moderate acid density (Lewis acid sites) and larger amount of surface Cu species on the CuAg_2.25-SAPO-34 catalyst.

已经开发了Ag促进的Cu-SAPO-34，以改善用于NH ₃ -SCR反应的Cu-SAPO-34的低温水热稳定性。动力学测试表明，向Cu-SAPO-34中添加Ag不会改变反应机理。离子交换的Ag种类降低了布朗斯台德酸密度，并提供了更多具有中等酸度的路易斯酸位点，从而对SAPO骨架具有保护作用，使其免受低温蒸煮处理（LTST）的影响。尽管CuAg _2.25 -SAPO-34和Cu-SAPO-34具有相似含量的分离的Cu离子，但对于CuAg _2.25 -SAPO-34观察到较高的表面Cu含量。原位DRIFTS研究首次证明了NH ₃对于低温SCR反应，吸附在弱酸/中等酸位点上的分子（与布朗斯台德酸或路易斯酸等酸类型无关）比强酸位点上的分子更具活性。与原始催化剂Cu-SAPO-34相比，LTST后CuAg _2.25 -SAPO-34的SCR活性增强归因于总酸位更好的保存，较高的中等酸密度（路易斯酸位）和大量的表面Cu CuAg _2.25 -SAPO-34催化剂上的所有物种。