| Summary: | 碩士 === 中原大學 === 化學研究所 === 103 === We have investigated the adsorption and reaction mechanisms of C2H4 and O2 catalyzed by a Au38 and Cu38 nanoclusters based on periodic density-functional theory (DFT) calculations. The configurations of the adsorption of C2H4/M38, and O2/M38, as well as the coadsorption of C2H4-O2/M38 (M=Au, Cu) were predicted. We considered four different positions: top (T), bridge (B), hexagonal (h), and hollow (H) sites. The calculation results show that C2H4 and O2 are preferably adsorbed at top (T) and bridge (B) with adsorption energies of -0.66, and -0.99 eV, respectively for Au38 nanoclusters, and -0.51 and -2.19 eV for Cu38 nanoclusters. The detailed reaction mechanisms for ethylene epoxidation on Au38 and Cu38 nanoclusters has been illustrated using the nudged elastic band (NEB) method. The oxidation process takes place via the Langmuir-Hinshelwood (LH) mechanism to generate ethylene oxide andacetaldehyde. The overall reaction of C2H4 + O2 + M38 → ethylene oxide + O/M38, exothermic by 2.20 ~ 2.40 eV or 3.20 ~ 3.56 eV for M is Au or Cu respectively, while those are 3.03 ~ 3.08 eV or 3.83 ~ 4.31 eV for the production of acetaldehyde and O/M38.The nature of interaction between adsorbate and gold or copper nanoclusters has been analyzed by the detailed electronic local density of states (LDOS) to understand high catalytic activity of the gold or copper nanoclusters.
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