Abstract: A series of iron carbides with single-phases, including ε-Fe₂C, χ''-Fe₅C₂, and θ-Fe₃C, were synthesized in different carbonization gases either in higher or lower CO part pressure. After passivation, the iron carbides were characterized by N₂ physical adsorption, Mössbauer spectroscopy, temperature-programmed desorption, and laser Raman spectroscopy. The effects of carbonization gases and temperature on the structure properties of the iron carbides were obvious, especially for carbonization temperature. Carbonization gas with higher CO part pressure and higher temperature both enhances the carbon deposition on the iron carbides surface. It is interesting to note that the carbon deposition increases firstly with the rise of temperature and then decreases. The differences in structure and carbon deposition on iron carbides result in varied adsorption properties. Fe₂C synthesized at lower temperature (200 ^oC) was highly susceptible to dissociative adsorption of CO on its surface, while Fe₃C prepared under lower CO part pressure showed the highest desorption of adsorbed CO. The ability of dissociative adsorption of CO on the iron carbides prepared under other condition reduces probably because of carbon deposition.

Key words: single-phase, iron carbide, carbon deposition, carbon monoxide, adsorption performance