KINETICS OF CARBON FORMATION FROM CH4-H2 MIXTURES ON NICKEL ALUMINA CATALYST

The kinetics of carbon formation from CH4-H-2 mixtures diluted with N2 on a steam reforming catalyst of Ni/Al2O3-CaO were studied in the temperature range 838-938 K at atmospheric pressure. It was found that the product formed deactivates the catalyst. Carbon deposition rates were interpretated using a kinetic equation with separable variables of the type r = r*alpha. The reaction rate r* increased with increasing partial pressure of methane and decreased with increasing partial pressure of hydrogen. The experimental data were fitted by a Langmuir-Hinshelwood expression which takes into account competitive adsorption of hydrogen and hydrocarbon. The activity factor-alpha was dependent on the time, temperature and methane and hydrogen partial pressures. Temperature programmed reactions of the coked catalysts with hydrogen allowed us to distinguish two types of deposits of different reactivities.