Chemisorption of methane over Ni/Al2O3 catalysts
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文摘
Adsorption of methane as well as co-adsorption of methane and O2 on Ni/Al2O3 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/Al2O3 was exposed to pure CH4, 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 CD4 was used. During temperature programmed (TP) dynamic process (in the presence of CH4), 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 CH4 and O2), 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, 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 suggest that the dissociation of chemisorbed methane in the participation of chemisorbed oxygen is a key step for methane partial oxidation.