Interaction of phenol with NaX zeolite as studied by 1H MAS NMR, 29Si MAS NMR and 29Si CP MAS NMR spectroscopy

The interaction of phenol with zeolite NaX has been studied by 1H and 29Si MAS and 29Si-CP-MAS NMR spectroscopy. A large displacement of the chemical shift of hydroxyl protons from 1.2 ppm in the crystalline state to about 9 ppm occurs upon H-bonding of phenol to basic oxygen atoms of the zeolite. An enhancement of the 29Si-CP-MAS signal is observed for the phenol loaded NaX zeolite and interpreted in terms of an interaction of the aromatic ring with either Na+ cations or oxygen atoms of the 12 member ring of the supercage. A small fraction of framework silicon atoms in four fold aluminum coordination, most likely Si atoms in four member ring positions of SIII or SIII’ sites, is electronically affected by interaction of phenol with Na+ ions located in these sites. After thermal treatment to 320°C part of the phenol is deprotonated and rearranges to linear Na+…−OPh complexes.