An activated carbon Norit RX3 has been treated with acids (sulphuric, nitric and sulphonitric mixture). The modified activated carbons have been characterized by elemental analysis, point of zero Charge. N-2 adsorption, XPS and FTIR. The solids obtained have been used as acidic heterogeneous catalyst in the reaction between imidazole and haloalkanes. The reaction with 1-bromobutane yields an ionic liquid, N,N-di-n-butyl-imidazolium bromide (1). Reaction with 2-bromobutane and 1-chlorohexane yields the corresponding N-alkyl-imidazoles (2) and (3). Sulphuric acid treated carbon is the most active catalyst. (C) 2011 Elsevier B.V. All rights reserved.