The role of silver species in the H₂-assisted NH₃ selective catalytic reduction of NOx (H₂-NH₃-SCR) over Ag/Al₂O₃ catalysts was investigated by operando spectroscopy (DRIFTS-MS and DR-UV–Vis) and Density Functional Theory (DFT) calculation. UV–Vis analysis showed that several kinds of silver species were present on the Ag/Al₂O₃, including dispersed silver cations, partially oxidized silver clusters, metallic silver clusters, and silver nanoparticles. Operando DRIFTS-MS experiments showed that the reduction of NOx was dependent on the formation rate of nitrates, which was closely related to the silver content, H₂ concentration, and reaction temperature. Notably, operando DR-UV–Vis experiments unambiguously confirmed that the metallic silver clusters were the active sites for nitrates formation, and the reduction of silver nitrates was much slower than NO oxidation. DFT calculations further revealed that reducing silver nitrates required higher energy barriers than NO oxidation, while H₂ dissociation could occur on metallic silver clusters with a moderate energy barrier. In conclusion, metallic silver clusters contributed to the formation of nitrates and H₂ dissociation, and the reduction of silver nitrates was the rate-determining step in the overall H₂-NH₃-SCR reaction.

通过操作光谱法（DRIFTS-MS和DR-UV– ）研究了银物种在Ag / Al ₂ O ₃催化剂上的H ₂辅助NH ₃选择性催化还原NO x（H ₂ -NH ₃ -SCR）中的作用。Vis）和密度泛函理论（DFT）计算。UV-Vis分析表明，Ag / Al ₂ O ₃上存在几种银，包括分散的银阳离子，部分氧化的银簇，金属银簇和银纳米颗粒。Operando DRIFTS-MS实验表明，NO x的还原取决于硝酸盐的形成速率，这与银含量，H ₂浓度和反应温度密切相关。值得注意的是，DR-UV-Vis操作实验明确证实了金属银团簇是形成硝酸盐的活性位点，硝酸银的还原要比NO氧化慢得多。DFT计算进一步表明，还原硝酸银需要比NO氧化更高的能垒，而在具有中等能垒的金属银簇上可能发生H ₂离解。总之，金属银团簇有助于硝酸盐的形成和H _2的离解，而硝酸银的还原是整个H _2中决定速率的步骤-NH ₃ -SCR反应。