Reaction mechanism of partial oxidation of methane to synthesis gas over supported Ni catalysts

A mechanistic study on the partial oxidation of methane to synthesis gas (H-2 and CO) was conducted with supported nickel catalysts. To investigate the reaction mechanism, pulse experiments, O-2-TPD, and a comparison of the moles of reactants and products were carried out. From the O-2-TPD experiment, it was observed that the active catalyst in the synthesis gas production desorbed oxygen at a lower temperature. In the pulse experiment, the temperature of the top of the catalyst bed increased with the pulses, whereas the temperature of the bottom decreased. This suggests that there are two kinds of reactions, that is, the total oxidation of methane (exothermic) at the top and reforming reactions (endothermic) at the bottom. From the comparison of the moles of reactants and products, it was found that the moles of CO2, CH4 and H2O decreased as the moles of H-2 and CO increased. The results support the mechanism that synthesis gas is produced through a two-step reaction mechanism: the total oxidation of methane to CO2 and H2O takes place first, followed by the reforming reaction of the produced CO2 and H2O with residual CH4 to form synthesis gas.