Chemisorption of methane over Ni/Al2O3 catalysts

Adsorption of methane as well as co-adsorption of methane and O-2 on Ni/Al2 O3 catalyst have been studied by in situ FT-IR spectroscopy. The reaction s tart temperature measurements indicate that the methane partial oxidation o ccurs at 230 degrees C. As the reduced Ni/Al2O3 was exposed to pure CH4, tw o bands for adsorbed methane were observed at 3005 and 2998 cm(-1), respect ively, which was confirmed by the appearance of two bands at 2242 and 2237 cm(-1) when CD4 was used. During temperature programmed (TP) dynamic proces s (in the presence of CH4), the intensities of the bands at 3005 and 2998 c m(-1) increased with increase in temperature, indicating that the amount of adsorbed methane increases with increasing temperature, which is indicativ e of chemisorption of methane. During TP dynamic process (in the co-presenc e of CH4 and O-2), two forms of chemisorbed methane are observed. The amoun t of chemisorbed methane increased with increasing temperature. At 250 degr ees C, the intensity of the band at 3015 cm(-1) for gaseous methane decreas ed remarkably and at the same time, CO, H-2, CO2 and H2O were detected in t he gas phase, indicating that the partial oxidation of CH4 occurs, which is in good agreement with the reaction start temperature observed above. Thes e results suggest that the dissociation of chemisorbed methane in the parti cipation of chemisorbed oxygen is a key step for methane partial oxidation. (C) 2000 Elsevier Science B.V. All rights reserved.