以理論計算探討以金屬為基材的單原子催化劑上進行二氧化碳電化學還原成乙醇的反應機制

Abstract

使用過渡金屬可以改善二氧化碳還原反應的效率，及能將二氧化碳轉換成更有價值的產物，因為唯獨銅元素具有產生多碳產物的優點，所以被廣泛運用在二氧化碳還原反應上，2011年，Zheng教授的團隊成功合成出單金屬原子催化劑(Pt1/FeOx)，並在一氧化碳的氧化反應中展現不錯的催化效果，最近，有實驗團隊使用此合成策略於二氧化碳還原反應中，發現在”以部分氧化的鈀金屬為基材的單顆銅金屬原子催化劑”上對於乙醇有高度的選擇性，所以我們將透過模擬該系統在進行二氧化碳還原的反應產生乙醇的反應路徑。 鈀金屬在二氧化碳還原的反應上對於探討產生CO具有選擇性，因此二氧化碳會先經過鈀基材還原成一氧化碳，隨後轉移至銅原子周圍進行 “氫化”及“碳-碳耦合”的動作。而最終的實驗結果顯示，在（100）系統中碳碳耦合的速率決定步驟是， COH與CHO在Pd與Cu的交界處進行耦合；而（111）系統中碳碳耦合的速率決定步驟是，CO及CHO直接在銅原子上方進行耦合的步驟。It has been reported that the usage of the transition metals can improve the efficiency of CO2 electrochemical reduction reaction (CO2RR), and convert CO2 to more valuable products. Because of the advantage of producing multi-carbon products, copper is widely applied in CO2RR. In 2011, Zheng and coworkers carried out CO oxidation reaction on Pt1 / FeOx, and first observed the presence of single metal atom with HAADF-STEM. Recently, our collaborator used similar strategy to design a single-atom catalyst for CO2RR, and found that placing a single Cu atom on a metal substrate with partial palladium oxide has a high selectivity for CO2 electrochemical reduction to ethanol. Consequently, we simulate the possible reaction mechanism to rationalize ethanol in such a system of CO2RR. Palladium can selectively produce CO during CO2RR. On a single-atom Cu catalyst on Pd, CO2 could be reduced to CO by Pd support, subsequently transferred to Cu site for "carbon-carbon coupling" and "hydrogenation" processes. We propose that the rate-determining step could be the step of "CHO coupling with COH on the Cu-Pd(100) junction ” and "CHO coupling with CO on Cu-Pd(111) junction”.