Oxidation Mechanism of Ethylene over MgO-Supported Ag-Cu Bimetallic Synergistic Catalysts: A DFT Study
Ethylene (C2H4) in vehicle exhaust is a highly reactive volatile organic compound (VOC) whose photo-oxidation with NOx contributes to the formation of O3 and secondary organic aerosols (SOA), a key precursor of PM2.5. This study designs a novel MgO-supported Ag-Cu bimetallic catalyst and investigates its performance using density functional theory (DFT). The effects of Ag and Cu loading on geometric structure, stability, and reactant adsorption are analyzed, and the catalytic oxidation pathways of C2H4 over AgCu-MgO are elucidated. Results indicate that loading Ag significantly enhances C2H4 adsorption, with a maximum adsorption energy of -1.46 eV, while O2 adsorption remains weak (-0.45 eV). Cu-MgO shows moderate C2H4 adsorption (-0.87 eV at bridge site) but higher O2 adsorption (-0.76 eV). Among 17 AgCu-MgO dual-atom catalyst (DAC) configurations, those with Ag and Cu co-adsorbed at Mg sites are thermodynamically more stable (binding energies below -10 eV). Configurations with Ag and Cu in close proximity enhance co-adsorption of C2H4 and O2. C2H4 oxidation preferentially proceeds via C=C bond cleavage to form *CH3 and CO2. For three representative configurations (1, 3, 6), free energy barriers for rate-limiting steps in the *HCO and CH2O pathway are consistently higher than those for *CH3 and CO2 pathway. Configuration 6 exhibits the lowest energy barrier (0.32 eV) for its rate-limiting step, indicating the highest catalytic performance. This study provides atomic-scale insights for rational design of efficient catalysts targeting olefinic pollutants in automotive emissions.