Abstract
As a promising material for heterogeneous catalytic applications, layered iron (II) monosulfide (FeS) contains active edges and an inert basal (001) plane. Activating the basal (001) plane could improve the catalytic performance of the FeS material towards CO2 activation and reduction reactions. Herein, we report dispersion-corrected density functional theory (DFT-D3) calculations of the adsorption of CO2 and the elementary steps involved in its reduction through the reverse water-gas shift reaction on a defective FeS (001) surface containing sulfur vacancies. The exposed Fe sites resulting from the creation of sulfur vacancies are shown to act as highly active sites for CO2 activation and reduction. Based on the calculated adsorption energies, we show that the CO2 molecules will outcompete H2O and H2 molecules for the exposed active Fe sites if all three molecules are present on or near the surface. The CO2 molecule is found to weakly physisorb (−0.20 eV) compared to the sulfur-deficient (001) surface where it adsorbs much strongly, releasing adsorption energy of −1.78 and −1.83 eV at the defective FeS (001) surface containing a single and double sulfur vacancy, respectively. The CO2 molecule gained significant charge from the interacting surface Fe ions at the defective surface upon adsorption, which resulted in activation of the C–O bonds confirmed via vibrational frequency analyses. The reaction and activation energy barriers of the elementary steps involved in the CO2 hydrogenation reactions to form CO and H2O species are also unraveled.
Highlights
The conversion of CO2 into fuels and chemicals is a promising process towards achieving green energy [1,2,3,4]
A comprehensive analyses of the structural geometries, electronic properties, and the reaction mechanisms associated with CO2 adsorption and its hydrogenation reactions on the sulfur-deficient FeS (001) surface was performed, using dispersion-correction density functional theory calculations
It is demonstrated that the presence of sulfur vacancies promotes CO2, and H2 adsorption and activation on the FeS (001) basal plane
Summary
The conversion of CO2 into fuels and chemicals is a promising process towards achieving green energy [1,2,3,4]. The surfaces of ferrous sulfide minerals are posited to have acted as heterogeneous catalysts for CO2 reduction, catalyzing the reaction of CO2 and H2 to form small organic molecules in the primordial ocean [7,8,9,10,11] It has been suggested by Russell et al that iron sulfide phases such as mackinawite (FeS), greigite (Fe3 S4 ), and violarite (FeNi2 S4 ) may have played important catalytic roles in prebiotic chemistry [9]. The surfaces of these minerals are structurally similar to the primary active sites, (Fe,Ni)S clusters, of natural enzymes such as carbon monoxide dehydrogenase (CODH), which efficiently and reversibly catalyze the reduction of CO2 to CO [12,13]. We discuss the thermodynamics and calculated activation energy barriers of the elementary steps involved in CO2 reduction through the reverse water–gas shift reaction (CO2 + H2 → CO + H2 O) on the defective FeS (001) surface
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