利用密度泛函理論計算機理性探討二氧化碳還原反應在金銅合金與金銀合金之催化效果

Abstract

隨著人類文明快速發展，溫室問題已成為全球關注的重要問題。將二氧化碳轉化為可再生能源，可以緩和溫室效應加劇的速度。在本研究中，我們通過密度泛函理論（DFT）的計算，機理性探討轉化過程的基本反應：二氧化碳還原為一氧化碳。分析機制後發現，中間體COOH*和CO*的吸附以及其對應的吉布斯自由能是控制還原反應的關鍵：COOH*的吸附力更高，吉布斯自由能越低，有利於啟動CO2還原反應； CO*的吸附力越弱，吉布斯自由能越高，代表CO越容易被脫除，以完成整體的還原反應。銅具有前者的優勢，而金和銀具有後者的優勢。因此，期望金銅和金銀合金可以結合兩種金屬的特性，形成有利於COOH *吸附且擁有最佳還原活性的催化劑。合金上的吸附受電子結構和整體效應的影響，我們找出在銅核金殼/金核銅殼/銅核銀殼中的最佳合金比例為：CuAu6，AuCu16和CuAg7其中又以AuCu16最好。

With the rapid development of human civilization, greenhouse problem become an important issue of global concern. Converting carbon dioxide into renewable energy resources is an effective way to resolve the detrimental problem. In the present study, we mechanistically examine the reduction reaction of carbon dioxide to carbon monoxide, the fundamental reaction for the converting process, by density functional theory (DFT) calculation. The resolved mechanism indicates that adsorption and the related Gibbs free energy of the two key intermediates COOH* and CO* control the reduction reaction: stronger adsorption of COOH* with lower Gibbs free energy to initiate the CO2 reduction and weaker adsorption of CO* with higher Gibbs free energy to remove the product of CO can essentially promote the reduction reaction. Copper has the advantage for the former adsorption, while gold and silver have those for the later one. Thus, the alloys of CuAu and CuAg are expected to benefit both adsorptions and achieve the best activity for the reduction reaction. The adsorptions on the alloys are affected by the electronic structural and ensemble effects. Accordingly, the best alloy ratios have been rationally determined: CuAu6, AuCu16 and CuAg7 are the optimal Cu-core/Au-shell, Au-core/Cu-shell and Cu-core/Ag-shell catalysts, respectively; among them AuCu16 is the best one.