透過您的圖書館登入
IP:3.87.209.162
  • 期刊

利用密度泛函理論計算探討二氧化碳還原反應在金銅合金之催化效果

Mechanism Study of CO_2 Reduction Reactions on CuAu Bimetallic Catalysts by Density Functional Theory Calculation

摘要


溫室效應一直是全球關注的重要問題。將二氧化碳(CO_2)轉化為有用的生物質能可以有效解決該問題,也在最近被廣泛的研究,而二氧化碳還原為一氧化碳(CO)的還原反應是這轉化過程中的關鍵步驟。在當前的工作中,我們利用密度泛函理論計算有系統地研究了此還原反應在銅、金與它們的合金的催化劑上。我們的機理研究表明最佳催化劑可以與羧酸根(COOH)牢固的吸附,形成較低的吉布士自由能(Gibbs free energy),以協助二氧化碳的初始還原步驟;此外,催化劑也需與一氧化碳產生弱吸附,形成較高的吉布士自由能,從而輕易的從表面去除產物一氧化碳。計算結果顯示純銅和純金分別能對羧酸根與一氧化碳的吸附有較好的能量;但是,它們兩個金屬都對另一個物種都有不利的吸附。因此,考慮利用銅金雙金屬合金來優化催化劑。合金的計算結果發現關鍵中間產物的吸附能受電子(electronic),結構(structural)和集體(ensemble)整體效應的控制。受這些效應的影響,從表面16個銅中置換6個為金的銅核金殼合金(CuAu_6)與將表面16金均置換為銅的金核銅殼合金(AuCu_(16))對二氧化碳還原反應有最佳的催化活性,其原因為這兩個合金具有最適當的羧酸根與一氧化碳吸附能以及吉布斯自由能。我們的研究發現清楚的闡明了二氧化碳還原反應的反應機理,並為合理設計最優化的催化劑提供了有用的信息。

並列摘要


The greenhouse effect has always been an important issue of global concern. Converting CO_2 into the useful biomass energy can effectively resolve the problematic issue and has been widely studied recently. In the present work, we systematically investigate the reduction reaction of CO_2 to CO, the key step in the converting process, on Cu, Au and their alloys by density functional theory (DFT) calculation. Our mechanistic study indicates that the optimal catalysts can strongly bond with COOH*, with the related lower Gibbs free energy for its formation, to assist the initial reduction of CO_2 and weakly adsorb with CO*, with the related higher Gibbs free energy, to easily remove the product of CO from the surface. The computational results find that pure Cu and Au have better energetics for the COOH* and CO* formation, respectively; however, both of them have the disfavor energetics for the other adspecies. Thus, the ideal of CuAu bimetallic alloys has been considered to optimize the catalysts. Our results for the alloys show that the adsorption energies of the key adspecies is controlled by electronic, structural and ensemble effects. Accordingly, the Cu-core/Au-shell alloy of CuAu_6, in which 6 of 16 surface Cu are replaced with Au, and the Au-core/Cu-shell alloy of AuCu_(16), in which all the 16 surface Au are replaced with Cu, demonstrated the best catalytic activity for CO_2 reduction reaction due mainly to their proper COOH* and CO* adsorption energies and Gibbs free energies. Our findings thoroughly clarify the reaction mechanism and provide useful information to rationally design the optimized catalysts for the important CO_2 reduction reaction.

延伸閱讀