Surface Oxidized Fe-S catalyst for the Liquid Phase Hydrogenation of CO2

Rapidly increasing anthropogenic carbon dioxide (CO2) emissions, coupled with irreversible climate change and depleting fossil fuels reserves, has significantly increased the drive for CO2 utilization. Iron sulfide as a catalyst for the hydrogenation of CO2 has been discussed in the literature for decades, especially in an origin-of-life context, however little experimental evidence exists in the literature for its feasibility. Here we report the catalytic properties of pyrrhotite (Fe1-xS) for the hydrogenation of CO2 into formate under mild, alkaline conditions at 125 oC and 20 bar (CO2:H2, 1:1). Controlled surface oxidation of pyrrhotite, via high temperature calcination, increased the surface oxygen species that in turn resulted in an increased catalytic activity, with the optimum calcination temperature being 200 oC. X-ray based characterisation methods in combination with computational studies, allowed us to identify surface S-Fe-O moieties as active sites for the reaction.