The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH3-TPD, molecular NH3 desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na+ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH3 on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al3+ for tetrahedral Si will be favorable to NH3 adsorption. (c) 2005 Elsevier B.V All rights reserved.