FTIR SPECTROSCOPIC AND H-1 MAS NMR-STUDIES OF THE INFLUENCE OF LATTICE CHEMISTRY AND STRUCTURE ON BRONSTED ACIDITY IN ZEOLITES

The influence of the Si/Al ratio, of the nature of the T-atom and of t he pore size on the acidic strength of Bronsted sites in zeolites has been investigated using changes of the vibrational properties of Brons ted OH(OD) groups and a shift change of Bronsted protons in nuclear ma gnetic resonance upon adsorption of weak bases. Deuterated acetonitril e and trichloro-acetonitrile have been chosen to probe the acidic stre ngths of ZSM-5, FeZSM-5, mordenite and zeolite Y, which are often used as catalysts. From the results of the FTIR and H-1 MAS NMR studies it can be concluded that the chemical composition of the lattice dominat es the acidic strength of the Bronsted sites in zeolites. Differences in structure or pore size play a much smaller role.