A characterization study of the surface acidity of solid catalysts by temperature programmed methods

The surface acidic properties of various solid catalysts (i.e., clay montmorillonite, acid modified smectite clay, HY zeolite, sulphate-promoted ZrO(2) (SO(4)(2-)/ZrO(2)) and Cs-exchanged dodecatungstophosphoric acid (H(0.5)Cs(2.5)PW(12)O(40))) have been comparatively evaluated by temperature programmed desorption (TPD) measurements of adsorbed NH(3), C(5)H(5)N and C(6)H(6). Mathematical analysis of TPD spectra of adsorbed ammonia indicates the presence of weak, medium and strong acid sites in all the catalysts. On the basis of the TPD patterns of NH(3), C(5)H(5)N and C(6)H(6), the nature (Bronsted and Lewis) of the acid sites has been ascertained. Catalytic measurements in CH(3)OH dehydration and benzene alkylation indicate that besides the acidic properties, the diffusional phenomena also play a key role on the reactivity of solid acid catalysts. The superior catalytic performance of the H(0.5)Cs(2.5)PW(12)O(40) system in the above reactions has been explained in the light of a pseudo-liquid behaviour. (C) 1998 Elsevier Science B.V.