Selective Catalytic Reduction of CO<sub>2</sub> to CO by a Single-Site Heterobimetallic Iron–Potassium Complex Supported on Alumina
A Isah, Oluwatosin Ohiro, Li Li, Y. Nasiru, Kaï C. Szeto, Pierre‐Yves Dugas, Anass Benayad, Aimery De Mallmann, Susannah L. Scott, Bryan R. Goldsmith, Mostafa Taoufik
Abstract
CO 2 has attracted much attention as a C 1 feedstock for synthetic fuels via its selective catalytic hydrogenation to liquid hydrocarbons. One strategy is the catalytic reduction of CO 2 to CO through the reverse water–gas shift (RWGS) reaction, followed by the hydrogenation of CO. In this work, potassium tris( tert -butoxy)ferrate, [{(THF) 2 KFe(O t Bu) 3 } 2 ], was supported on alumina that had been partially dehydroxylated at 500 °C (Al 2 O 3–500 ), and the resulting catalyst was investigated in the selective reduction of CO 2 to CO. The active site precursor was identified as [(THF)K(Al s O)Fe(O t Bu) 2 (OHAl)] (i.e., [(THF)KFe(O t Bu) 2 ]/Al 2 O 3–500 ), denoted 2-K, based on elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (high-resolution transmission electron microscopy (HRTEM) and EDS), X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Under the reaction conditions, the precursor becomes an active, stable, and selective RWGS catalyst (100% selectivity to CO at 22.5% CO 2 conversion). The reaction mechanism was studied by operando DRIFT spectroscopy and density functional theory (DFT) modeling. The results are consistent with a mechanism involving H 2 activation by K[(Al s O) 2 FeOH], leading to K[(Al s O) 2 FeH]. CO 2 insertion gives hydroxycarbonyl intermediate K[(Al s O) 2 FeCOOH], followed by liberation of CO to regenerate K[(Al s O) 2 FeOH].