Ionic liquid immobilized catalysts were prepared by each of the grafting and impregnation methods on mesocellular foam silica (MCF) and amorphous silica, respectively, as support. 1-alkyl-3-methylimidazolium chloride was synthesized by the modified synthesis method. All the synthesized catalysts were characterized by SAXS, BET and element analysis. Ionic liquid could be loaded on the support much better by the grafting method than the impregnation method. The ionic liquid immobilized catalysts were applied to the alkylation of benzene with dodecene. The catalyst prepared by the grafting method on MCF showed a superior catalytic reaction performance compared to the one synthesized by the impregnation method and silica based catalyst. The conversion is high by virtue of the large amount of ionic liquid well dispersed on the support. The high selectivity to the linear alkyl benzene may be attributed to the product shape selectivity of the ionic liquid catalyst supported on MCF.