利用理論計算探討電催化還原二氧化碳的反應機制

Abstract

RuII(bpy)(trpy)(CO), bpy = 2,2'-Bipyridine, trpy = 2,2':6',2”-terpyridine, 這個錯合物是少數能夠將二氧化碳直接還原成甲醇的有機錯金屬錯合物，這個錯合物曾經被報導可以在通入-1.5V的電壓環境下，生成甲醇和碳碳鍵生成的產物，利用此催化劑還原二氧化碳的產物包括了CO、HCOOH、CH3OH、HC(O)H、H(O)CCOOH以及HOCH2COOH，而第一個推測這個催化反應的反應機制是Tanaka，但是這個催化反應的各種中間產物的詳細資訊，不管是在實驗或是理論計算中都還是不清楚的。 在目前的研究利用理論計算的方法來分析這個反應機制，包括利用還原電位，pKa以及自由能來更完善Tanaka所預測的反應機制，並探討其反應的可行性。

關鍵字: 二氧化碳，理論計算，電催化，反應機構RuII(bpy)(trpy)(CO), bpy = 2,2'-Bipyridine, trpy = 2,2':6',2”-terpyridine, complex is one of the few organometallic complexes to be able to generate methanol directly from carbon dioxide. This complex was reported to produce methanol and C2-product with applying -1.5V vs. NHE. The products generated by this reductive catalysis include CO, HCOOH, CH3OH, HC(O)H, H(O)CCOOH, and HOCH2COOH. The catalytic mechanism was postulated first by Tanaka and coworker. However, the details regarding the various intermediates along the catalytic reaction coordinate are still not clearly understood from experimental and theoretical perspectives. In the present study, we have carried out a comprehensive first-principle theoretical analysis on the detailed mechanism. Each potential electrochemical step is calculated by thermodynamic cycle method coupled with continuum solvation model. The predicted electronic assignment, redox potential, pKa, as well as the electronic structure for each intermediate will be provided.

Key point : CO2, computational, electrocatalysis and mechanism