A study of the surface acidity of acid-treated montmorillonite clay catalysts

The surface acidity of a series of commercial Slid Chemie acid-treated mont morillonite clays (K-catalysts) has been evaluated by a wide range of compl ementary experimental techniques. The different methods applied allow a rat her complete characterisation of the surface acidity providing a complete p icture of the Lewis/Bronsted acid strength/density of the surface sites. IR data show that the Bronsted sites on these catalysts are relatively weak a nd provide evidence for a slight increase of the strength and the density o f Bronsted sites in the order K5 < K10 <similar to> K20 < K30 in full agree ment with the trend in iso-butene conversion, which is a measure of the str ength and/or the abundancy of Bronsted sites. The apparent contradiction of these data with those obtained from the ammonia adsorption and iso-propano l conversion experiments can be explained by the structural and chemical mo dification of the clays upon acid treatment. (C) 2001 Elsevier Science B.V. All rights reserved.