On the roughness of the internal surface of MCM-41 materials studied by ¹²⁹Xe NMR

Different MCM-41 samples have been synthesized and characterized by N₂ adsorption-desorption at 77K, X-ray diffraction and ¹²⁹Xe-NMR spectroscopy. The unexpectedly high chemical shift of adsorbed xenon corresponds to a stronger xenon-surface interaction in MCM-41 than in zeolites. Coadsorption of water and xenon leads to a decrease in the ¹²⁹Xe chemical shift, which is interpreted in terms of a screening of the roughness of the surface. Coadsorption of benzene or cyclohexane shows that there are channel restrictions and, more generally, pore structure defects.