Partial oxidation and chemisorption of methane over Ni/Al2O3 catalysts

Abstract

Partial oxidation of methane, adsorption of methane as well as co-adsorption of methane and O2 on Ni/Al2O3 catalyst have been studied by continuous flow micro-reactor and in situ FT-IR spectroscopy. The results show that with increasing temperature and space velocity, the CH4 conversion and CO and H2 selectivities increased and CO2 selectivity decreased. With the decrease of CH4/O2 ratio, the methane conversion and CO2 selectivity increased while the CO and H2 slectivities decreased. The onset of activity for methane partial oxidation occur at 230 °C. As reduced Ni/Al2O3 was exposed to pure CH4, the two bands for adsorbed methane were observed at 3005 and 2998 cm−1 respectively. During TP (in CH4) dynamic process, the intensities of the bands at 3005 and 2998 cm−1 increased with increase in temperature, indicating that the amount of adsorbed methane increase with increasing temperature which is indicative of chemisorption of methane. During TP (in CH4 and O2) dynamic process, two forms of chemisorbed methane are observed. The amount of chemisorbed methane increased with increasing temperature. At 250°C, the intensity of the band at 3015 cm−1 for free methane decreased remarkably and at the same time, CO, H2, CO2 and H2O were detected in the gas phase, indicating that the partial oxidation of CH4 occurs, which is in good agreement with the reaction start temperature observed above. These results indicate that the dissociation of chemisorbed methane dissociation in presence of chemisorbed, oxygen is a key step for methane partial oxidation.