单相碳化铁的制备及其表面吸附性质

在不同CO分压下制备了ε-Fe2C,X″-Fe5C2和θ-Fe3C等系列单相碳化铁,经钝化处理后采用低温N2物理吸附、穆斯堡尔谱、激光拉曼光谱和程序升温脱附技术进行了详细的表征.结果发现,碳化气氛,尤其是碳化温度对所得碳化铁结晶度有所影响.碳化铁表面的积碳程度随碳化气氛中CO分压的升高而增高,而随碳化温度的升高呈抛物线形式增高;不同碳化条件下生成的碳化铁晶型和表面积碳的差异导致其织构性质及其吸附CO的能力不同,低温(200℃)碳化生成的Fe2C表面解离吸附CO的能力显著强于其他碳化铁;低碳气氛中生成的Fe3C上CO的解离脱附量最大;其他条件下生成的碳化铁因表面吸附活性位的破坏和大量沉积碳的生成

Synthesis of Single-Phase Iron Carbides and Their Adsorption Performance

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,M?ssbauer 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.