H-1 MAS NMR studies of molecules adsorbed on activated zeolites

The aim of this paper is to study the interaction of organic molecules with zeolites of different pores sizes (NaY, dealuminated ZSM-5, and H-ZSM-5) p retreated under conditions which led to various catalytically active sites. The behavior of the adsorbed molecules is investigated by means of high-re solution H-1 MAS NMR spectroscopy. The measurements demonstrate that comple x adsorption interactions occur between adsorbed 2-butene or acetone molecu les and the OH groups in the zeolites which also have a strong influence on the activity of the catalytic sites. During the adsorption of the molecule s on differently activated zeolites the H-1 MAS NMR spectra show changes wh ich can be attributed to catalytic conversions, where Bronsted and Lewis ac idic sites of the zeolite catalysts are involved. A proton transfer from th e bridging AlOHSi groups of the zeolite framework to the adsorbed 2-butene molecules can be clearly detected. The results for the system acetone/dealu minated ZSM-5 and acetone/H-ZSM-5 point, in particular, to the role of Lewi s acid centers which may be formed in the zeolites during the applied pretr eatment procedure. (C) 2001 Academic Press.