The kinetics of carbon deposition has been investigated on a supported nickel catalyst for steam reforming of naphtha and the mechanism has been described. The following experimental conditions were applied: 1.01×10^5Pa and 823-948K. Empirical rate equations of carbon deposition with H2O were obtained while empirical rate equations of carbon deposition without H2O were also given only for comparison. In the experimental temperature range, the deep dehydrogenation of adsorbed naphtha is still suggested as the rate limiting step of carbon deposition reaction, but the study revealed that H2O on Ni-surface was dissociatively adsorbed. As a result, the order of steam partial pressure changes from -1 to -0.62 and the effect of hydrogen on carbon deposition increases at the same time. The analysis of mechanism further explains why H2 can speed the carbon deposition. So far as the reason for the formation of apparent negative activation energy is concerned, it has been argued about for a long time, but no agreement has been made yet. The observations are shown to be best explained with the cooperative effects including pyrolysis reaction, adsorption and steam reforming reaction.

Key words: REACTION MECHANISM, CATALYST, NICKEL, REACTION KINETICS, METHYLBENZENE, ACTIVATION ENERGY