Reaction mechanism of dichloromethane oxidation on LaMnO3 perovskite

• Published in: Chemosphere (Oxford) Vol. 277; p. 130194
• Main Authors: Ding, Junyan, Liu, Jing, Yang, Yingju, Wang, Zhen, Yu, Yingni
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2021
• Subjects: Density functional theory; Dichloromethane; LaMnO3 catalyst; Oxidation mechanism; Dichloromethane; Density functional theory; LaMnO3 catalyst; Oxidation mechanism
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.130194

The reaction mechanism of dichloromethane (CH2Cl2) oxidation on LaMnO3 catalyst was investigated using density functional theory calculations. The results showed that CH2Cl2 dechlorination proceeds via CH2Cl2 → CH2ClO → HCHO. The adsorbed Cl∗ and formaldehyde (HCHO) are identified as the important intermediates of CH2Cl2 dechlorination process. The dissociated Cl atoms prefer to adsorb on the surface Mn sites. Surface hydroxyl groups are not directly involved in the CH2Cl2 dechlorination process, but react with the adsorbed Cl∗ to form HCl. The energy barrier of HCl formation is lower than that of Cl2 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 → H2O desorption → CO/CO2 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 CH2Cl2 oxidation on LaMnO3 catalyst. The catalytic cycle includes CH2Cl2 dechlorination, HCl formation and HCHO oxidation. The microkinetic analysis indicates that there are four steps controlling the reaction cycle: CH2Cl2∗ + ∗ → CH2Cl∗ + Cl∗, CH2OCl∗ + Cl∗ → CH2O∗ + Cl∗, O2∗ + ∗ → 2O∗, and CHO2∗ + OH∗ → CO2 + H2O∗. [Display omitted] •The reaction mechanism of CH2Cl2 oxidation on LaMnO3 was studied using DFT method.•CH2Cl2 oxidation contains CH2Cl2 dechlorination, HCl formation and HCHO oxidation.•CH2Cl2 dechlorination proceeds through CH2Cl2.→ CH2ClO → HCHO.•The surface activated O atoms are favorable for HCHO deep oxidation.•OH groups promote the removal of adsorbed Cl atoms in the form of HCl.