BRONSTED ACIDITY IN HY ZEOLITES MEASURED BY IR STUDY OF PYRIDINE ADSORPTION - INFLUENCE OF STERIC EFFECTS

The formation of pyridinium ions upon pyridine sorption on HY samples of varying Al composition has been studied by IR spectroscopy. It is d emonstrated that HY supercages cannot accommodate more than four pyrid inium ions. This property is shown to affect the ability of LF protons to migrate towards positions accessible to pyridine and form pyridini um ions. The mode of interaction of LF hydroxyls with pyridine is disc ussed in the light of both steric and electrostatic parameters.