Chemical looping combustion (CLC) of coal has received increasing interest in recent years. However, few attempts have been made to examine the effects of CO2 atmosphere and K2CO3 addition on the reduction rate, the oxygen transport capacity (OTC), and the sintering of the oxygen carrier when coal is used directly in CLC. In this work, these issues for Fe2O3 and the CuO oxygen carriers were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The TGA results indicate that the reduction rates can be increased by either the CO2 atmosphere or the K2CO3 additive due to the enhanced CO2 gasification of coal char. Detailed analyses demonstrate that the CO2 atmosphere affects the OTC and the sintering of the oxygen carrier by thermodynamic restrictions. The CO2 atmosphere has no effect on the OTC of the CuO oxygen carrier, and there are no significant differences in sintering between the residues obtained under CO2 and N-2 atmospheres. However, the CO2 atmosphere limits the OTC of the Fe3O4 oxygen carrier within the transformation Fe2O3-Fe3O4, and the sintering could be moderated because of the higher sintering resistance of Fe3O4. The K2CO3 addition does not affect the OTC because the catalyst has no impact on the equilibrium but promotes the sintering of the oxygen carrier due to its low Tammann temperature. Although severe sintering could be caused by the K2CO3 addition, the catalytic effect can be observed during several redox cycles.