The model compounds for horseradish peroxidase (HRP) is reported, based on the association of H2O2 with iron and manganese porphyrins immobilized onto a functionalized silica gel. The models were developed in an attempt to find a biomimetical compound for systems containing heme groups. The ortho-dianisidine is a useful substrate model compound for checking the ability of degradation promoted by delignificant natural enzymes. The heterogeneous catalysts were obtained by grafting of three metalloporphyrins: (Fe(TFPP)-iron porphyrin from the 5,10,15,20-tetrakis (pentafluorophenyl) porphyrin-and Mn(TCPP) and Fe(TCPP), iron and manganese porphyrins from the 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin), onto the modified surface of silica gel. The oxidation of ortho-dianisidine was monitored by UV-Vis spectroscopy at room temperature using different ratios of catalyst, oxidant and substrate. At high H2O2 concentration, the perhalogenated iron porphyrin Fe(TFPP) produced best results, showing a turnover number of about 1100. This value was higher than those obtained for Fe(TCPP) and Mn(TCPP) systems. (C) 2002 Elsevier B.V. All rights reserved.