ACID SITES DISTRIBUTION AND THEIR INFLUENCE ON THE CATALYTIC PROPERTIES OF MESOPOROUS H-AlMCM-41 AND H-FeMCM-41

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 (Brønsted) acid sites associated with symmetrical tetrahedral Al(III) or Fe(III); (iii) strong structural (Brønsted) acid sites from a highly distorted tetrahedral Al(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 latter. This could be attributed to presence of large excess of type (ii) and type (iii) acid sites in H-AlMCM-41.