(188d) Selective Catalytic Reduction of CO2 to CO By a Single-Site Heterobimetallic Iron–Potassium Complex Supported on Alumina

The hydrogenation of CO₂ to CO via the reverse water-gas shift (RWGS) reaction is considered a viable approach for recycling CO₂ emissions from point sources. However, the selectivity of this reaction is hindered by the competing and favorable endothermic methanation reaction at low temperatures. Metal size ensemble effects have been shown to influence the selectivity of CO₂ hydrogenation, with the RWGS reaction being the majority product on well-dispersed catalysts, while undesired methanation is favored on metal nanoparticle catalysts.¹ Alkali metal promoters have also been demonstrated to increase the stability of well-dispersed transition metal catalysts, thereby enhancing CO selectivity.

In this work, we achieved a well-defined supported single-site Fe catalyst on alumina with an alkali (Li, Na, K) promoter using surface organometallic chemistry by grafting monomeric and dimeric molecular complexes onto partially dehydroxylated alumina. These materials were characterized using various techniques, including inductively coupled plasma (ICP), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and X-ray absorption fine structure (XAFS). The supported Fe complexes were activated by thermolysis in flowing Ar in a packed-bed reactor and then used directly to catalyze the hydrogenation of CO₂ to CO, with particular interest in effect of the alkali metal promoter on the catalyst selectivity and activity. Density functional theory (DFT) and mean-field microkinetic modeling were performed to clarify the active site, surface intermediates as well as the RWGS mechanism of the best-performing K+-promoted Fe-complex catalyst.²

References:

(1) Doherty, F.; Goldsmith, B. R. ChemCatChem 2021, 13 (13), 3155–3164. https://doi.org/10.1002/cctc.202100292.

(2) Isah, A. A.; Ohiro, O.; Li, L.; Nasiru, Y.; Szeto, K. C.; Dugas, P.-Y.; Benayad, A.; De Mallmann, A.; Scott, S. L.; Goldsmith, B. R.; Taoufik, M. ACS Catal. 2024, 2418–2428. https://doi.org/10.1021/acscatal.3c04989.