The present invention provides technology for controlling, or tuning, the catalytic activity of gold provided upon nanoporous supports such as those derived from nanoparticulate, crystalline titania. In some aspects of practice, the surface of nanoparticulate media incorporated into a catalyst system of the present invention is provided with chemical modifications of the surface that dramatically suppress the ability of the resultant catalyst system to oxidize hydrogen. Yet, the system still readily oxidizes CO. In other words, by selecting and/or altering the nanoparticulate surface via the principles of the present invention, PROX catalysts are readily made from materials including catalytically active gold and nanoparticulate media. Additionally, the nanoparticulate support also may be optionally thermally treated to further enhance selectivity for CO oxidation with respect to hydrogen. Such thermal treatments may occur before or after chemical modification, but desirably occur prior to depositing catalytically active gold onto the support incorporating the nanoparticles.