Design of a catalyst through Fe doping of the boron cage B10H14 for CO2 hydrogenation and investigation of the catalytic character of iron hydride (Fe–H)

Abstract

The innovative catalyst Fe@B₁₀H₁₄ is designed through Fe doping of the boron cage B₁₀H₁₄ and is employed to catalyze CO₂ hydrogenation using a quantum mechanical method. First, the structure of the Fe@B₁₀H₁₄ complex is characterized through calculated ¹¹B NMR chemical shifts and Raman spectra, and the interactions between Fe and the four H atoms of the opening in the cage are analyzed, which show that various iron hydride (Fe–H) characteristics exist. Subsequently, the potential of Fe@B₁₀H₁₄ as a catalyst for the hydrogenative reduction of CO₂ in the gas phase is computationally evaluated. We find that an equivalent of Fe@B₁₀H₁₄ can consecutively reduce double CO₂ to obtain the double product HCOOH through a two-step reduction, and Fe@B₁₀H₁₂ and Fe@B₁₀H₁₀ are successively obtained. The Fe presents single-atom character in the reduction of CO₂, which is different from the common iron(II) catalyzed CO₂ reduction. The calculated total free energy barrier of the first CO₂ reduction is only 8.79 kcal mol⁻¹, and that of the second CO₂ reduction is 25.71 kcal mol⁻¹. Every reduction reaction undergoes two key transition states TS_C–H and TS_O–H. Moreover, the transition state of the C–H bond formation TS_C–H is the rate-determining step, where the interaction between π_CO* and the weak σ_Fe–H bond plays an important role. Furthermore, the hydrogenations of Fe@B₁₀H₁₂ and Fe@B₁₀H₁₀ are investigated, which aim at determining the ability of Fe–H circulation in the Fe doped decaborane complex. We find that the hydrogenation of Fe@B₁₀H₁₀ undergoes a one-step H₂-adsorbed transition state TS_H-adsorb with an energy barrier of 6.42 kcal mol⁻¹ from Fe@B₁₀H₁₂. Comparing with the hydrogenation of Fe@B₁₀H₁₀, it is slightly more difficult for the hydrogenation of Fe@B₁₀H₁₂, where the rate-determining step is the H₂-cleaved transition state TS2_H–H with an energy barrier of 17.38 kcal mol⁻¹.