Various halide salts with different alkyl lengths were allowed to intercalate into the layer structure of sodium montmorillonite clay through an ion exchange reaction. Intercalation of 1-hexadecyl-3-methylimidazolium chloride, hexadecyltrimethylammonium bromide, dihexadecyldimethylammonium bromide, and tributylhexadecylphosphonium bromide could expand the spacing of the silicate layers from 12 to 37-41 angstrom (measured by X-ray diffraction). The modified clays were pretreated with the pyridine hydrochloride/AlCl3 mixture and used for suitably supporting a chloroaluminate ionic liquid catalyst for the isomerization of endo-tetrahydrodicyclopentadiene into the corresponding exo-isomer. Nearly quantitative conversion to the desired product and nearly quantitative selectivity were observed for the newly developed clay-supported ionic liquid catalysts, which were proven to be recyclable. (C) 2009 Elsevier B.V. All rights reserved.