Phase transformation of iron oxide to carbide and Fe3C as an active center for the RWGS reaction†
Abstract
Iron based catalysts have been widely used in CO2 hydrogenation reactions and phase transformation during hydrogenation has been noted. Herein, iron oxide was observed to be in situ carburized into Fe3C, and Fe3C was identified as the active and stable phase during the reverse water gas shift (RWGS) reaction. Factors such as the reduction degree of iron oxide and reaction temperatures were revealed to affect the phase transformation from iron oxide to Fe3C. The feed gas ratio of H2/CO2 had a decisive effect on the in situ formation of Fe3C and an optimized ratio of 2 was crucial to avoid the excessive oxidation or reduction of carbide. Ex situ synthesized Fe3C via CO carbonization had an inferior catalytic performance compared with the in situ generated Fe3C due to the unexpected but inescapable carbon deposition.