The contact of Pd(AcO)(2) in solution with thiouric tethered to a silica led to the formation of supported nanoparticles (ca. 2 nm in size) active in the Heck reaction, quite sensitive to the palladium leaching. A stable supported phase was obtained by subsequent calcination, but the catalytic activity resulted strongly dependent on the calcination temperature. Such a behaviour was related to differences in the surface structure of the supported particles, as those monitored by IR spectroscopy of CO adsorbed on catalysts reduced at various temperatures.