Promotion of graphitic carbon oxidation via stimulating CO2 desorption by calcium carbonate.

Carbon oxidation has two stages, the first is the formation of surface oxides and the second is the gasification of the surface oxides to CO2. Calcium carbonate (CaCO3) was used to catalyze the gasification of the surface oxides. The catalytic effect of on graphite oxidation and its catalytic mechanism were studied by using thermogravimetric technique and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that characteristic temperature (T50) of graphite oxidation with CaCO3 was 946 K, 113 K lower than that of graphite only. DRIFTS analysis results show that surface oxides (adsorbed CO2 and carbonate CO32-) were formed on the graphite surface at a temperature above 473 K, carbonate products on graphite surface disappeared when CaCO3 was present; formation of CO32- on CaCO3 surface was confirmed, this CO32- may be more easily gasified into gaseous CO2. The kinetic analysis results showed that CaCO3 promoted graphite oxidation has an activation energy of 74.3 kJ mol-1, far lower than that of graphite (148 kJ mol-1).