Zhang Lin, Pu Min, Lei Ming
State Key Laboratory of Chemical Resource Engineering, Institute of Computational Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing, 100029, China.
Dalton Trans. 2021 Jun 1;50(21):7348-7355. doi: 10.1039/d1dt01243f.
Herein, density functional theory (DFT) calculations were employed to explore the reaction mechanism of three cascade cycles for the hydrogenation of carbon dioxide to methanol (CO2 + 3H2 → CH3OH + H2O) catalyzed by a manganese pincer complex [Mn(Ph2PCH2SiMe2)2N(CO)2]. The three cascade cycles involve: the hydrogenation of CO2 to formic acid, the hydrogenation of formic acid to methanediol and the decomposition of methanediol to formaldehyde and water, and the hydrogenation of formaldehyde to methanol. The calculated results demonstrate that hydrogen activation is the rate-determining step of each catalytic cycle under solvent-free conditions, and the energy span of the whole reaction is 27.1 kcal mol-1. Furthermore, the solvent was found to be of importance in this reaction. In three different solvents, the rate-determining steps of this reaction are all the hydrogen transfer step of the formic acid hydrogenation stage, and the corresponding energy spans in water, toluene and THF solvents are 21.3, 20.8 and 20.4 kcal mol-1, respectively. Such a low energy span implies that this manganese complex could be a promising catalyst for the efficient conversion of CO2 and H2 to methanol at temperatures below 100-150 °C.
在此，采用密度泛函理论（DFT）计算来探究由锰钳形配合物[Mn(Ph2PCH2SiMe2)2N(CO)2]催化的二氧化碳加氢制甲醇（CO2 + 3H2 → CH3OH + H2O）的三个级联循环的反应机理。这三个级联循环包括：二氧化碳加氢生成甲酸、甲酸加氢生成甲二醇以及甲二醇分解生成甲醛和水，以及甲醛加氢生成甲醇。计算结果表明，在无溶剂条件下，氢活化是每个催化循环的速率决定步骤，整个反应的能量跨度为27.1 kcal mol-1。此外，发现溶剂在该反应中很重要。在三种不同溶剂中，该反应的速率决定步骤均为甲酸加氢阶段的氢转移步骤，在水、甲苯和四氢呋喃溶剂中的相应能量跨度分别为21.3、20.8和20.4 kcal mol-1。如此低的能量跨度意味着这种锰配合物可能是一种有前景的催化剂，可在100 - 150 °C以下的温度下将CO2和H2高效转化为甲醇。
