A new process for 1-butene/isobutane alkylation to yield C-8-alkylates is described using binary mixtures of certain acidic imidazolium ionic liquids (ILs) and strong acids such as sulfuric or trifluoromethanesulfonic (triflic) acid. Equivalent or better conversion (>95%), C-8-alkylates selectivity (>70%) and trimethylpentane/dimethylhexane selectivity (TMP/DMH > 7) were achieved with the IL/acid mixtures over the pure acids themselves. Six types of substituted 3-methyl-imidazolium ionic liquids were investigated, wherein acidity is imparted via either the cation with sulfonic acid groups or the anion (hydrogen sulfate) or both. Long-term studies up to 30+ recycles indicate that the catalyst stability was increased by sometimes greater than 30+% with the IL/acid mixtures over the pure acid. The ionic liquid is believed to tune the acidity, solubility, and interfacial properties, resulting in these enhanced results. In addition, this concept could also be applicable to Friedel-Crafts alkylation, acylation chemistries, or other acid-catalyzed reactions. (c) 2009 Elsevier Inc. All rights reserved.