Activity-acidity relationship in zeolite ZSM-5. Application of Bronsted-type equations

In this paper the relation between activity and acidity in a variety of ZSM -5 zeolite catalysts, with different Si/Al ratios and different protonic co ntent, is analysed and a quantitative correlation is obtained. The acid sit e strength distribution was estimated using temperature-programmed desorpti on (TPD) of ammonia by applying a digital deconvolution method to the curve s. These data were then correlated with experimental catalytic activity dat a fbr the same catalysts towards n-heptane cracking reaction, by means of a Bronsted-type equation similar to the ones used for homogeneous acid catal ysis and already used for other zeolites. It can be noticed that the same t ypes of equation that are used for homogeneous acid catalysis also hold for heterogeneous acid catalysis and that the activation energy for ammonia de sorption can be used as acid-strength scale for the purpose of correlation with catalytic activity. (C) 2000 Elsevier Science B.V. All rights reserved .