PYRIDINE AND AMMONIA AS PROBES FOR FTIR ANALYSIS OF SOLID ACID CATALYSTS

Pyridine and ammonia have been used as probe molecules for the quantit ative analysis of surface acidity of some solid catalysts by FTIR spec troscopy. For pyridine, a scale of acidity and an evaluation of the re lative acid strength at different temperatures (373-773 K) were obtain ed for both Bronsted- and Lewis-acid sites. Correlation was verified b etween the concentration of Bronsted sites and the catalytic activity of the catalysts examined for the dehydration of 2-(2-hydroxyethyl)pyr idine to 2-vinylpyridine. In contrast, ammonia was a much less reliabl e probe, mainly due to the overlapping of the resulting IR absorption bands. Moreover, it decomposed even at rather low temperatures, when a dsorbed onto the catalysts.