The impact of co-feeding carbon dioxide in Fischer–Tropsch-to-olefin catalysis: an inelastic neutron scattering study

The addition of CO₂ to a syngas feed stream in Fischer–Tropsch to Olefin (FTO) catalysis is investigated by means of inelastic neutron scattering (INS) spectroscopy using ambient pressure CO hydrogenation at 623 K as a test reaction. The principal objective being to explore how the presence of CO₂ affects the nature of a hydrocarbonaceous overlayer that forms during the conditioning phase of the catalytic process. The candidate FTO catalyst examined is Fe-based and doubly promoted with sodium (2000 ppm) and sulfur (100 ppm). Temperature-programmed oxidation profiles recorded after 3, 6, 12 and 24 h time-on-stream (T-o-S) reveal progressive carbon retention by the catalyst mainly in the form of amorphous carbon. The INS spectrum as a function of T-o-S confirms the presence of a hydrocarbonaceous overlayer, but with a much higher hydrogen concentration than previously observed for Fe-based FTO catalysts operating solely with a syngas feed. These preliminary results are considered with respect to a possible role for CO₂ perturbing the equilibrium between iron carbides and oxides.