Ce or CeO2 is often added to Fe–Cr–Ni base alloys to enhance protective Cr2O3 ceramic scale formation. In high-temperature carbonaceous reducing environments, however, it is still unsolved that Ce-containing alloys often exhibited increased carburization and coke formation. This research is aimed at understanding the mechanism of Ce-enhanced coke formation. It was found that CeO2 can cause catalytic activation of chromium carbide for carbon growth by first forming CeCrO3 and then decomposing CeCrO3 into CeO2 and active nanosize chromium carbide particles; the latter has proven to be conducive to coke formation. These findings can be helpful for the design of alloys with better ceramic coating resistant to carbonaceous degradation and for the growth of graphitic nanostructures using Cr-related catalysts.