Ionic liquids are immobilized on a functionalized support which carries or contains one component of the ionic liquid, or a precursor to such a component. The ionic liquid may be immobilized via the anion by treating a support with an anion source, e.g., an inorganic halide, before the ionic liquid is applied or formed. Alternatively, the ionic liquid may be immobilized by having the cation covalently bound to the support, e.g., through silyl groups, or incorporated in the support by synthesizing the support in the presence of a suitable base. The immobilized ionic liquids are of use as catalysts, for example, for the Friedel-Crafts reaction, such as alkylation reaction.