A purified natural clay and the material obtained by acid treatment with sulphuric acid have been pillared with mixed solutions containing Al and Fe, Ti or Cr. The intercalation gives solids of high surface area, stable up to 773 K. The acid properties have been determined by calorimetric adsorption of ammonia. Several parameters determine the acidity of the pillared samples: the temperature of calcinations, the nature of the pillars and the type of clay. The distribution of acid strengths measured on these clays is comparable to that of zeolites, the AlTi clays showing the highest acidity. The catalytic properties have been determined for the alkylation of aromatics by benzylchloride. In spite of their lower acidity, the most active clays are those containing Fe. The same phenomenon is observed with benzene, chlorobenzene, or anisole as substrate. This lack of correlation of activity for alkylation and acidity is attributed to the initiation of the reaction by the oxidation of benzylchloride by Fe3+. (c) 2005 Elsevier B.V. All rights reserved.