利用理論計算方法探討O2及C2H4在 Cu32- Au6及Au32- Cu6奈米團簇上的吸附及反應機制

Adsorption and reaction mechanisms of O2 and C2H4 on Cu32-Au6 and Au32-Cu6 nanoclusters: A computational study

曾若怡(Jo-Yi Tseng)

指導教授 ： 陳欣聰

中原大學/理學院/化學研究所/碩士(2017年)

https://doi.org/10.6840/cycu201700325

摘要

我們利用週期性之密度泛函理論 (Density functional theory, DFT) 的方法來探討乙烯及氧氣在Cu32-Au6 和Au32-Cu6奈米團簇上的吸附及反應機制。對C2H4/M32-M、6、O2/ M32-M、6以及C2H4-O2/ M32-M、6進行吸附結構預測 (M和 M、為Cu , Au) 。計算結果發現吸附的位置有正上方 (top, T) 、橋接 (bridge, B) 、三角形面中心 (hexagonal, h) 、四面形中心 (hollow, H) ，在Cu32-Au6奈米團簇上，O2和C2H4最穩定的吸附能分別為 -2.09和 -0.65 eV，Au32-Cu6奈米團簇為 -0.81和 -1.24 eV。乙烯在Cu32-Au6和Au32-Cu6奈米團簇上的環氧化反應機制的位能曲面圖是使用nudged elastic band (NEB) 方法建構。氧化反應的進行是以Langmuir-Hinshelwood (LH) 機制產生環氧乙烷 (ethylene oxide, EO) 以及乙醛 (acetaldehyde, AA) 。整體反應分成兩個部分： (1) C2H4 + O2 + M32-M、6→環氧乙烷 (ethylene oxide, EO) + O/ M32-M、6，此反應M32-M、6為Cu32-Au6會放熱約 3.31 ~ 3.34 eV，若為Au32-Cu6則會放熱約 2.17 ~ 2.26 eV； (2) C2H4 + O2 + M32-M、6 → 乙醛 (acetaldehyde, AA) + O/ M32- M、6，反應中M32-M、6為Cu32-Au6放熱約為3.76 ~ 4.24 eV，為Au32-Cu6時，放熱約2.19 ~ 2.73 eV。

關鍵字

乙烯的環氧化反應；Cu32-Au6奈米團簇；Au32-Cu6奈米團簇；DFT計算法；吸附反應

並列摘要

We have investigated the adsorption and reaction mechanisms of C2H4 and O2 catalyzed by a Cu32-Au6 and Au32-Cu6 nanoclusters based on periodic density-functional theory (DFT) calculations. The configurations of the adsorption of C2H4/ M32-M、6, and O2/ M32-M、6, as well as the coadsorption of C2H4-O2/ M32-M、6 were predicted. (M/ M、=Au or Cu) The calculation results show that O2 and C2H4 can be bound at top (T) , bridge (B) , hexagonal (h) , and hollow (H) sites with the most stable adsorption energies of -2.09, and -0.65 eV, respectively on Cu32-Au6 nanoclusters, and -0.81 and -1.24 eV on Au32-Cu6 nanoclusters. The detailed reaction mechanisms for ethylene epoxidation on Cu32-Au6 and Au32-Cu6 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 and aldehyde. The overall reaction of C2H4 + O2 + M32-M、6 → ethylene oxide + O/ M32-M、6 is exothermic by 2.17 ~ 2.26 eV for Cu32-Au6 ,and 2.17 ~ 2.26 eV for Au32-Cu6, while those are 3.76 ~ 4.24 eV and 2.19 ~ 2.73 eV for the production of acetaldehyde .

並列關鍵字

Ethylene epoxidation； Cu32-Au6 nanocluster；Au32-Cu6 nanocluster；DFT calculations；adsorption

參考文獻

[1] B. Hodnett, Heterogeneous Catalytic Oxidation, John Wiley and Sons Ltd., Chichester, UK, 2000.

[2] Sinha, A. K.; Seelan, S.; Tsubota, S.; Haruta, M. Angew. Chem., Int. Ed. 2004,43, 1546.

[3] Nijhuis, T. A. R.; Visser, T.; Weckhuysen, B. M. Angew. Chem., Int. Ed. 2005, 44, 1115.

[4] Chang, F. W.; Yu, H. Y.; Roselin, L. S.; Yang, H. C.; Ou, T. C. Appl. Catal. A 2006, 302, 157.

[5] M.O. Ozbek, I. Onal(2009): Ethylene Epoxidation Catalized by Silver Oxide