Temperature-Programmed Desorption of Benzene on Mesoporous Si−MCM-41, Na−AlSi−MCM-41, and H−AlSi−MCM-41

Temperature-programmed desorption (TPD) of benzene on Si−MCM-41, Na−AlSi−MCM-41, and H−AlSi−MCM-41 mesoporous materials from 323 to 673 K at different linear heating rates (5, 10, 20, and 25 K min - 1 ) and that on Si−MCM-41 at different adsorbate loadings (0.45−10.7 μmol g - 1 ) has been investigated. 1 H− 29 Si cross polarization magic angle spinning NMR and IR of the Si−MCM-41 showed the presence of a large number of terminal Si−OH groups. All the TPD spectra have multiple peaks (four for Si−MCM-41 and five for H (or Na)−AlSi−MCM-41), indicating presence of different types of benzene adsorption sites on these mesoporous materials. Heat of adsorption of benzene corresponding to the different TPD peaks, estimated from the TPD peak maximum temperatures measured at the different heating rates, was found to be in the following order: Si−MCM-41 < H−AlSi−MCM-41 < Na−AlSi−MCM-41. The TPD peak multiplicity for Si−MCM-41 is reduced with decreasing the adsorbate loading, indicating induced surface heterogeneity due to the adsorbate at its higher loadings.