Modified Brønsted type equation with ammonia as probe molecule: quantitative acidity-activity relationship for pyridine synthesis with ZSM-5 catalyst

Abstract

The acid site strength distribution of a series of ZSM-5 zeolite catalyst with different Si/Al ratios is quantificationally measured by temperature-programmed desorption of ammonia. The activation energy for ammonia desorption is not only a practical scale of acidity but also has a definite catalytic meaning in the Bronsted equation of acid catalysis. The activation energy for ammonia desorption was first correlated with experimental catalytic activity data of aldehyde and ammonia condensation reaction over ZSM-5 by means of a quantitative equation. An improved Bronsted equation was established. It can be concluded that different strength acid sites have different effect coefficients for the pyridine synthesis. The acid sites on which the activation energy of ammonia desorption is 150 kJ is the highest active sites for the reaction. The Bronsted-type relations can be used as a way to fast improve catalyst for pyridine synthesis.