The properties of silica, such as: low price, thermal stability, hardness, chemical resistance and nontoxicity make it one of the most frequently applied catalyst support. It has been shown that the activity of palladium catalysts for benzene, toluene and xylene hydrogenation is consistently higher with acidic supports than those with neutral silica [1,2]. For this reason modification of silica in order to generate the acidic properties seems to be especially interesting.
In this work, commercial silica (SiO2) was modified using aqueous solution of ammonium fluoride (SiO2-F) and ammonium chloride (SiO2-Cl). The resulting materials were used as supports for iridium active phase. The catalysts containing 1 wt.% of iridium supported on silica were prepared by conventional impregnation method using hexachloroiridic acid as metal precursor. The prepared catalysts and supports were characterized by N2 adsorption/desorption measurements and H2-TPR. The mean size of metal particles was determined by hydrogen chemisorption measurements. The acidity of modified SiO2 was estimated by means of temperature-programmed desorption of ammonia (NH3-TPD). The effect of acidity of supports on the activity of iridium catalysts for toluene hydrogenation was studied. The catalyst supported on silica modified using ammonium fluoride is the most active.