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首页> 外文期刊>ACS catalysis >Selectivity for HCO2- over H-2 in the Electrochemical Catalytic Reduction of CO2 by (POCOP)IrH2
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Selectivity for HCO2- over H-2 in the Electrochemical Catalytic Reduction of CO2 by (POCOP)IrH2

机译：（POCOP）IrH2电化学催化还原CO2中HCO2-对H-2的选择性

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It has been demonstrated experimentally that electrochemical CO2 reduction catalyzed by (POCOP)IrH2 ([C6H3-2,6[OP(tBu)(2)](2)]IrH2) produces formate without significant H-2. We use first-principles density functional theory (M06) including Poisson-Boltzmann solvation to determine the detailed atomistic mechanism and illuminate strategies for designing formate-selective catalysts. A mechanism involving hydride transfer from Ir-III dihydride explains the selectivity for formate over H-2 and is corroborated by reduction potential (irreversible reduction of (POCOP)Ir(H)(NCMe)(2)(+) at ca.-1.3 V vs NHE, in comparison to -1.31 V vs NHE calculated for one-electron reduction of Ir-III(H)(NCMe)(2)(+)) and turnover frequency. We find that several thermodynamically favorable pathways exist for the hydrogen evolution reaction (HER) from both Ir-III(H)(2) and Ir-I-H- but are kinetically hindered, posing computed activation barriers above 25 kcal/mol at pH 7. However, with formate or bicarbonate acting as cocatalyst, the barriers are lowered to 18.8 kcal/mol. The preference of (POCOP)Ir to form a dihydride instead of a dihydrogen adduct also disfavors the HER and facilitates catalyst regeneration. In contrast, substituting cobalt for iridium raises the barrier for hydride transfer to CO2 by 12.0 kcal/mol and lowers the required reduction potential to -1.65 V vs NHE. Calculated driving forces for hydride transfer from Ir-I and Ir-III intermediates illustrate different strategies for positioning the hydricity relative to the thermodynamic hydricities of H-2/H+ and HCOO-/CO2. The data support an approach of selecting a hydricity that is just thermodynamically able to reduce CO2. The effect of solvation on calculated driving forces for hydride transfer is also discussed.
机译：实验证明，（POCOP）IrH2（[C6H3-2,6 [OP（tBu）（2）]（2）] IrH2）催化的电化学CO2还原反应生成的甲酸酯没有明显的H-2。我们使用包括泊松玻尔兹曼溶剂化在内的第一原理密度泛函理论（M06）确定详细的原子机理并阐明设计甲酸酯选择性催化剂的策略。涉及从Ir-III二氢化物转移氢化物的机理解释了甲酸对H-2的选择性，并通过还原电位得到证实（（POCOP）Ir（H）（NCMe）（2）（+）的不可逆还原约为-1.3 V vs NHE，与为Ir-III（H）（NCMe）（2）（+））的单电子还原和转换频率计算的-1.31 V vs NHE相比。我们发现从Ir-III（H）（2）和Ir-IH-都存在氢发生反应（HER）的几个热力学上有利的途径，但在动力学上受阻，在pH 7时，计算出的激活壁垒高于25 kcal / mol。但是，在甲酸或碳酸氢盐作为助催化剂的情况下，势垒降低到18.8 kcal / mol。 （POCOP）Ir优选形成二氢化物而不是二氢加合物也不利于HER并且促进催化剂再生。相反，用钴代替铱会使氢化物向CO2的转移势垒提高12.0 kcal / mol，并将所需的还原电势降低到-1.65 V vs. NHE。计算得出的从Ir-1和Ir-III中间体转移氢化物的驱动力说明了相对于H-2 / H +和HCOO- / CO2的热力学水力来确定水力的不同策略。数据支持选择一种在热力学上能够减少二氧化碳的水力的方法。还讨论了溶剂化对计算得出的氢化物转移驱动力的影响。

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