Unpromoted and K-promoted Ni/Al2O3 catalysts were prepared, calcined at 400 or 700 degrees C, and subsequently reduced at 500 or 800 degrees C. Cyclopentane hydrogenolysis was carried out within the 370-500 degrees C temperature range to obtain a carbon deposit. After coking, the catalysts were regenerated by carbon gasification in H-2 at 800 degrees C. TPO of the carbon deposits was carried out, and the filaments were examined by SEM and TEM. The structural parameters (particle size, degree of nickel reduction, promotion by K) as well as the hydrogen flow rate showed marked effects on both the coking and the regeneration. The catalysts coked at high temperature (approximate to 480 degrees C) form very stable carbon filaments whose gasification requires both a high temperature (800 degrees C) and a high H-2 flow rate. On the contrary, these which are coked at a lower temperature (420-460 degrees C) form filaments much more readily gasified by H-2.