The adsorption of HAuCl(4), the typical precursor for gold grafting on metal oxide surfaces, is investigated on amorphous silica support. The adsorption of the precursor is investigated as a function of its chlorinated form, depending on the pH, using periodic DFT. The results are supported with experimental data based on catalytic probe reactions (acetonylacetone cyclization and oxidation of methanol). The location of chloride ions neighboring hydroxyls gives rise to generation of Bronsted basicity demonstrated by the methylcyclopentenone formation from acetonylacetone and CO(2) from methanol. The most stable grafting complex is formed by the AuCl(OH)(3)(-) precursor form on a chloride-free silica surface. The presence of Si-Cl groups at the surface destabilizes the grafting complex.