A comparative kinetic study of CH4 oxidation by NiO/Al2O3, Pt/Al2O3 and NiO-PtiAl2O3 catalysts

A NiO-Pt/a-Al2O3 oxidation-reduction catalyst (3%Ni and 0.1%Pt, C53-1, Catalyst and Chemicals Europe S.A.) is applied in industry (EKO refinery, Thessaloniki, Greece) for nitrogen gas production, through LPG combustion by atmospheric air. The aim of the present research work is to compare the kinetics of total oxidation of methane by the separate constituents of the above catalyst, as well as by the mixed catalyst. The a-alumina based NiO (3%Ni), Pt (0.1%Pt) and NiO-Pt (3%Ni, 0.1%Pt) catalysts were prepared by the impregnation method and characterized by BET, XRD and SEM-EDX. The activity tests show that activity follows the order, NiO-Pt>Pt>NiO. The reaction kinetics were measured at low partial pressures of oxygen and methane near the stoichiometric point. The kinetic results were interpreted with the Langmuir-Hinshelwood (L-H) and Elye-Riedel (E-R) mechanisms. The reaction follows an E-R mechanism on the NiO catalyst. On the Pt catalyst, reaction follows a mixed L-WE-R mechanism, but at low methane partial pressures and high oxygen partial pressures an E-R mechanism prevails. The reaction rate kinetic and adsorption constants and activation energies were calculated according to the above mechanisms. The validation of the proposed mechanisms was checked statistically and through thermodynamic consideration. The reaction rate over the Pt catalyst is considerably higher (ten times) than over the NiO catalyst at the stoichiometric point. The rate of the reaction over the mixed catalyst is the sum of the rates over the separate catalysts and a synergistic effect is not seems possible.