Key Takeaways & Executive Findings
- •• • Ag loading on MgO(100) enhances C2H4 adsorption to -1.46 eV, but O2 adsorption remains weak at -0.45 eV, limiting complete oxidation; Cu addition improves O2 adsorption to -0.76 eV, enabling synergistic co-activation. • • Among 17 AgCu-MgO DAC configurations, those with Ag and Cu at Mg sites exhibit binding energies below -10 eV, ensuring thermodynamic stability under reaction conditions, critical for long-term catalyst durability. • • Configuration 6 of AgCu-MgO shows the lowest rate-limiting energy barrier of 0.32 eV for C2H4 oxidation to *CH3 and CO2, outperforming other configurations and indicating superior catalytic activity at low temperatures. • • C2H4 oxidation over AgCu-MgO preferentially proceeds via C=C bond cleavage to *CH3 and CO2, with energy barriers consistently lower than the *HCO and CH2O pathway, guiding catalyst design for selective total oxidation.
Abstract
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.
1. Introduction
Ethylene (C2H4) in automotive exhaust is a highly reactive VOC that contributes to photochemical smog and PM2.5 formation. Conventional noble metal-based oxidation catalysts (e.g., DOC, CDPF) achieve only ~65% C2H4 removal efficiency, limited by high cost and insufficient low-temperature activity. Platinum group metals (PGMs) like Pt and Pd show promise but are constrained by scarcity and expense, necessitating alternative catalyst designs that balance activity, stability, and cost.
This study addresses the bottleneck by employing density functional theory (DFT) to design a MgO-supported Ag-Cu bimetallic catalyst. Ag enhances C2H4 adsorption, while Cu improves O2 activation, creating a synergistic effect that lowers reaction barriers. The systematic investigation of 17 dual-atom configurations identifies optimal structures for catalytic oxidation, providing a rational basis for developing efficient, non-PGM catalysts for olefinic pollutant removal.
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ZHANG Wei, ZHAO Genrui, LI Zehong, CHEN Guisheng, CHEN Zhaohui (2026). Oxidation Mechanism of Ethylene over MgO-Supported Ag-Cu Bimetallic Synergistic Catalysts: A DFT Study. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60640-8
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Frequently Asked Questions
What is the rate-limiting step in C2H4 oxidation over the optimal AgCu-MgO configuration, and what is its energy barrier?
For Configuration 6, the rate-limiting step in the pathway to *CH3 and CO2 has an energy barrier of 0.32 eV, which is the lowest among the studied configurations, indicating superior catalytic activity.
How does the adsorption strength of C2H4 and O2 vary between Ag-MgO, Cu-MgO, and AgCu-MgO, and why is this important?
Ag-MgO shows strong C2H4 adsorption (-1.46 eV) but weak O2 adsorption (-0.45 eV), while Cu-MgO shows moderate C2H4 (-0.87 eV) and stronger O2 (-0.76 eV). AgCu-MgO combines these properties, enabling co-adsorption and activation of both reactants, which is critical for efficient oxidation.
What is the thermodynamic stability of the AgCu-MgO configurations, and how does it affect catalyst durability?
Configurations with Ag and Cu at Mg sites have binding energies below -10 eV, indicating high thermodynamic stability. This suggests resistance to sintering or metal leaching under reaction conditions, which is essential for long-term catalyst performance.
How does the reaction pathway selectivity differ between the *CH3/CO2 and *HCO/CH2O routes, and what are the implications?
The *CH3/CO2 pathway (C=C cleavage) has consistently lower energy barriers than the *HCO/CH2O pathway across configurations. This selectivity toward complete oxidation to CO2 is desirable for minimizing partial oxidation products and achieving high conversion efficiency.
What are the limitations of this DFT study in predicting real-world catalytic performance?
DFT calculations assume ideal surfaces and do not account for temperature, pressure, or the presence of other exhaust components (e.g., water, SO2). Experimental validation is needed to confirm activity and stability under realistic conditions.
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