Chemisorption of methane over Ni/Al 2O 3 catalysts

Abstract

Adsorption of methane as well as co-adsorption of methane and O 2 on Ni/Al 2O 3 catalyst have been studied by in situ FT-IR spectroscopy. The reaction start temperature measurements indicate that the methane partial oxidation occurs at 230°C. As the reduced Ni/Al 2O 3 was exposed to pure CH 4, two bands for adsorbed methane were observed at 3005 and 2998 cm −1, respectively, which was confirmed by the appearance of two bands at 2242 and 2237 cm −1 when CD 4 was used. During temperature programmed (TP) dynamic process (in the presence of CH 4), the intensities of the bands at 3005 and 2998 cm −1 increased with increase in temperature, indicating that the amount of adsorbed methane increases with increasing temperature, which is indicative of chemisorption of methane. During TP dynamic process (in the co-presence of CH 4 and O 2), 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 gaseous methane decreased remarkably and at the same time, CO, H 2, CO 2 and H 2O were detected in the gas phase, indicating that the partial oxidation of CH 4 occurs, which is in good agreement with the reaction start temperature observed above. These results suggest that the dissociation of chemisorbed methane in the participation of chemisorbed oxygen is a key step for methane partial oxidation.