The characteristics of the superficial structure of a hydrophobic silica subjected to treatment at various temperatures and heating times, and of the Rh catalysts supported on the silica, are studied by FTIR. The catalysts obtained have different dispersions that depend on the superficial methoxyl fraction of the support, and are independent of the superficial OH groups. This procedure for changing the metal dispersion is different from the pretreatment of the catalyst reported previously.