Interaction of CO2 with well-ordered iron sulfide films on Au(111)

Abstract

Iron sulfides are important in catalysis because of their abundance on earth and their catalytic activity. In Wächtershäuser’s origin of life theory, Fe/Ni sulfide deposits in and near to submarine hydrothermal vents (’black smokers’) catalyzed the production of first organic matter, and recent studies have indicated that iron sulfides might be able to activate CO2 towards conversion into chemicals such as methanol, formic acids and others. Here, we present a study of the interaction of carbon dioxide with well ordered iron sulfide films grown on Au(111). Since the as-prepared film proved to be rather non-reactive to the molecule, possibly because of the layer’s sulfide termination, we tried to modify the sulfide’s stoichiometry both by exposing it to atomic hydrogen and by adding metallic iron. Hydrogen is able to interact with the sulfur on the surface and to partially remove it, but the resulting surface is still not reactive towards CO2. X-ray photoemission results show that the addition of metallic iron is detrimental for the quality of the sample, giving rise to the admixture of substrate gold to the layer. Insertion of an FeO blocking layer between the sulfide and the gold substrate allowed the sulfide to become Fe-rich, enhancing its reactivity towards CO2, but it was not possible to completely prevent diffusion between the FeO layer and the substrate. However, we found that an increased iron content together with the presence of gold was able to activate the layer towards CO2.