First-principle calculations on CO oxidation catalyzed by a gold nanoparticle

We have elucidated the mechanism of CO oxidation catalyzed by gold nanoparticles through first-principle density-functional theory (DFT) calculations. Calculations on selected model show that the low-coordinated Au atoms of the Au(29) nanoparticle carry slightly negative charges, which enhance the O(2) binding energy compared with the corresponding bulk surfaces. Two reaction pathways of the CO oxidation were considered: the Eley-Rideal (ER) and Langmuir-Hinshelwood (LH). The overall LH reaction O(2(ads)) + CO((gas)) --> O(2(ads)) + CO((ads)) --> OOCO((ads)) --> O((ads)) + CO(2(gas)) is calculated to be exothermic by 3.72 eV; the potential energies of the two transition states (TS(LH1) and TS(LH2)) are smaller than the reactants, indicating that no net activation energy is required for this process. The CO oxidation via ER reaction Au(29) + O(2(gas)) + CO((gas)) --> Au(29)-O(2(ads)) + CO((gas)) --> Au(29)-CO(3(ads)) --> Au(29)-O((ads)) + CO(2(gas)) requires an overall activation barrier of 0.19 eV, and the formation of Au(29)-CO(3(ads)) intermediate possesses high exothermicity of 4.33 eV, indicating that this process may compete with the LH mechanism. Thereafter, a second CO molecule can react with the remaining O atom via the ER mechanism with a very small barrier (0.03 eV). Our calculations suggest that the CO oxidation catalyzed by the Au(29) nanoparticle is likely to occur at or even below room temperature. To gain insights into high-catalytic activity of the gold nanoparticles, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis.