Critical step in the HCl oxidation reaction over single-crystalline CeO2−x(111): Peroxo-induced site change of strongly adsorbed surface chlorine

The catalytic oxidation of HCl by molecular oxygen (Deacon process) over ceria allows the recovery of molecular chlorine from omnipresent HCl waste produced in various industrial processes. In previous density functional theory (DFT) model calculations by Amrute et al. [J. Catal. 2012, 286, 287–297.], it was proposed that the most critical reaction step in this process is the displacement of tightly bound chlorine at a vacant oxygen position on the CeO2(111) surface (Clvac) toward a less strongly bound cerium on-top (Cltop) position. This step is highly endothermic by more than 2 eV. On the basis of a dedicated model study, namely the re-oxidation of a chlorinated single crystalline Clvac-CeO2−x(111)-(√3 × √3)R30° surface structure, we provide in-situ synchrotron-based spectroscopic data (high-resolution core level spectroscopy (HRCLS) and X-ray adsorption near edge structure (XANES)) for this oxygen-induced de-chlorination process. Combined with theoretical evidence from DFT calculations, the Clvac → Cltop displacement reaction is predicted to be induced by an adsorbed peroxo species (O22-), making the displacement step concerted and exothermic by only 0.6 eV with an activation barrier of only 1.04 eV. The peroxo species is shown to be important for the re-oxidation of Clvac-CeO2−x(111) and is considered essential for understanding the function of ceria in oxidation catalysis.

在二氧化铈载体上通过分子氧催化氧化盐酸（Deacon过程）能够从工业生产过程中广泛产生的无处不在的盐酸废料中回收分子氯。在Amrute等人[《J. Catal. 2012, 286, 287–297》]先前基于密度泛函理论（DFT）的模型计算中，提出该过程中最关键的反应步骤是在CeO2(111)表面空氧位点上紧密结合的氯离子（Clvac）向结合较弱的上层铈离子（Cltop）位置的迁移。此步骤的吸热效应超过2电子伏特。基于一个专门的模型研究，即对氯化单晶Clvac-CeO2−x(111)-(√3 × √3)R30°表面结构的再氧化，我们提供了该氧诱导脱氯过程的原位同步辐射光谱数据（高分辨率核心能级光谱（HRCLS）和X射线吸收近边结构（XANES））。结合DFT计算的理论证据，预测Clvac → Cltop的迁移反应是由吸附的过氧物种（O22-）诱导的，使得迁移步骤协同并放热，仅增加0.6电子伏特的能量，且活化能仅为1.04电子伏特。过氧物种被证明对于Clvac-CeO2−x(111)的再氧化至关重要，并被认为是理解二氧化铈在氧化催化作用中功能的关键。