Metal ion-exchanged clay composites such as M-II-Mont and M-II-Mont (AT) where M = Zn and Cd, Mont = montmorillonite clay of the types Mont, (SWy-2) and Mont2 (Neelkanth), and AT = acid treated have been synthesized, characterized and evaluated as catalysts for Friedel-Crafts reaction particularly for benzylation of benzene. XRD study reveals that, in general, the basal spacing (d(001)) increases as the interlayer cations of Na-Mont or H+-Mont are exchanged with Zn2+ or Cd2+ ions and interlamellar spacings are maintained in the range 3.9-5.3 and 4.3-6.0 Angstrom, respectively, at room temperature. The basal spacing (d(001)) of Mont(1) supported composites are higher than Mont(2) and therefore substantiate the advantage of the former over the latter in preparing metal ion-exchanged clay composites useful as solid acid catalysts. During the initial benzylation reactions, Cd2+-exchanged composites, in general, show higher activity but in the long run Zn2+-exchanged clays exhibit higher catalytic activities. In general, acid treated metal ion-exchanged clay composites exhibit higher catalytic activity than non-acid treated ones because the former show higher surface area as well as higher acid sites. (C) 2004 Elsevier B.V. All rights reserved.