Cesium (Cs) is a key promoter to improve the selectivity of Ag catalyst for ethylene epoxidation. However, there is still no consensus in the literature about the origin of enhanced ethylene oxide (EO) electivity by Cs-promoted Ag catalysts. In this paper, the role of Cs as a promoter for ethylene epoxidation on Ag catalyst is studied by both experiments conducted under industrially relevant conditions as well as density functional theory (DFT) calculations. Ag/α-Al₂O₃ and Ag-Cs/α-Al₂O₃ catalyst are prepared by excessive impregnation and evaluated for ethylene epoxidation to determine the mechanism of selectivity enhancement for Ag catalysts that contain Cs. With the optimal loading of Cs, Ag particles of uniform size are evenly distributed on the support and EO selectivity increases from approximately 72.5%–82.0% compared with the Ag/α-Al₂O₃. O₂-TPD results indicate that Cs decreases the adsorption strength of oxygen on Ag and XPS analyses show that Cs shifts the Ag 3d_5/2 binding energy to facilitate the desorption of the EO precursor to form gas EO. DFT calculations demonstrate that Cs-promotor can weaken the adsorption of atomic oxygen. Electron density of atom oxygen absorbed on silver decreases with the addition of Cs on Ag(111) thereby enhancing the electrophilic attack by atomic oxygen at the electron-rich CC bond of C₂H₄. Therefore, Cs lowers the activation energy for the formation of the oxometallacycle (OMC) and EO, while increasing the barrier for acetaldehyde (AA) formation, thereby leading to higher EO selectivity.

铯（Cs）是提高Ag催化剂对乙烯环氧化的选择性的关键促进剂。但是，关于由Cs促进的Ag催化剂提高环氧乙烷（EO）选择性的起源的文献仍未达成共识。在本文中，通过在工业上相关条件下进行的实验以及密度泛函理论（DFT）计算，研究了Cs作为在Ag催化剂上乙烯环氧化的促进剂的作用。的Ag /α-Al系₂ ö ₃和Ag-CS /α-Al系₂ ö ₃催化剂通过过量浸渍制备，并进行乙烯环氧化评估，以确定含Cs的Ag催化剂选择性提高的机理。随着Cs的最佳负载，均匀尺寸的Ag粒子均匀地分布在载体上和EO选择性增加约72.5％-82.0％与银/α-Al系相比₂ ö ₃。O ₂ -TPD结果表明Cs降低了氧在Ag上的吸附强度，XPS分析表明Cs改变了Ag 3d _5/2结合能量以促进EO前体的解吸以形成气体EO。DFT计算表明，Cs-促进剂可以削弱原子氧的吸附。随着银在Ag（111）上的添加，吸附在银上的原子氧的电子密度降低，从而增强了原子氧在C ₂ H ₄的富电子C C键上的亲电子攻击力。因此，Cs降低了形成氧金属环（OMC）和EO的活化能，同时增加了乙醛（AA）形成的势垒，从而导致更高的EO选择性。