Acid sites distribution and their influence on the catalytic properties of mesoporous H-AlMCM-41 and H-FeMCM-41

Abstract

The acid properties of mesoporous H-AlMCM-41 and H-FeMCM-41 catalysts were studied by temperature programmed desorption of ammonia. The results suggest the existence of four different types of acid sites. They are assigned to: (i) weak acid sites due to surface/terminal hydroxyl groups; (ii) moderate structural (Bronsted) acid sites associated with symmetrical tetrahedral AI(III) or Fe(III); (iii) strong structural (Bronsted) acid sites fi om a highly distorted tetrahedral AI(III) or Fe(III) and (iv) Lewis acid sites arising from tricoordinated Al(III) or Fe(III) in the framework. The t-butylation reaction of phenol over H-AlMCM-41 and H-FeMCM-41 showed high substrate conversion in the case of the former than the fatter. This could be attributed to presence of large excess of type (ii) and type (iii) acid sites in H-AlMCM-41.