State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China.
State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China.
Chemosphere. 2021 Aug;277:130194. doi: 10.1016/j.chemosphere.2021.130194. Epub 2021 Mar 12.
The reaction mechanism of dichloromethane (CHCl) oxidation on LaMnO catalyst was investigated using density functional theory calculations. The results showed that CHCl dechlorination proceeds via CHCl → CHClO → HCHO. The adsorbed Cl∗ and formaldehyde (HCHO) are identified as the important intermediates of CHCl dechlorination process. The dissociated Cl atoms prefer to adsorb on the surface Mn sites. Surface hydroxyl groups are not directly involved in the CHCl dechlorination process, but react with the adsorbed Cl∗ to form HCl. The energy barrier of HCl formation is lower than that of Cl formation, indicating that hydroxyl groups facilitate the removal of adsorbed Cl∗ species. Three possible pathways of HCHO oxidation with the assist of lattice oxygen, active oxygen atom and hydroxyl groups were investigated. HCHO catalytic oxidation contains four steps: HCHO → CHO → CO → HO desorption → CO/CO desorption. Compared with the HCHO oxidation by lattice oxygen and hydroxyl groups, HCHO oxidation assisted with activated oxygen atom is more thermodynamically favorable. A complete catalytic cycle was proposed to understand the preferable reaction pathway for CHCl oxidation on LaMnO catalyst. The catalytic cycle includes CHCl dechlorination, HCl formation and HCHO oxidation. The microkinetic analysis indicates that there are four steps controlling the reaction cycle: CHCl∗ + ∗ → CHCl∗ + Cl∗, CHOCl∗ + Cl∗ → CHO∗ + Cl∗, O∗ + ∗ → 2O∗, and CHO∗ + OH∗ → CO + HO∗.
采用密度泛函理论计算研究了二氯甲烷（CHCl）在 LaMnO 催化剂上氧化的反应机理。结果表明，CHCl 脱氯通过 CHCl → CHClO → HCHO 进行。吸附的 Cl和甲醛（HCHO）被鉴定为 CHCl 脱氯过程的重要中间体。解离的 Cl 原子倾向于吸附在表面 Mn 位上。表面羟基基团不直接参与 CHCl 脱氯过程，但与吸附的 Cl反应形成 HCl。HCl 形成的能垒低于 Cl 形成的能垒，表明羟基基团有利于去除吸附的 Cl物种。考察了晶格氧、活性氧原子和羟基基团辅助下 HCHO 氧化的三种可能途径。HCHO 催化氧化包含四个步骤：HCHO → CHO → CO → HO 脱附 → CO/CO 脱附。与晶格氧和羟基基团辅助的 HCHO 氧化相比，活性氧原子辅助的 HCHO 氧化在热力学上更为有利。提出了一个完整的催化循环来理解 LaMnO 催化剂上 CHCl 氧化的优选反应途径。催化循环包括 CHCl 脱氯、HCl 形成和 HCHO 氧化。微观动力学分析表明，反应循环有四个步骤控制：CHCl + * → CHCl* + Cl*，CHOCl* + Cl* → CHO* + Cl*，O* + * → 2O*，和 CHO* + OH* → CO + HO*。
