Reduction of H+ by TiO2 electrons (e(TiO2)(-)) in aqueous colloidal solution takes place in the presence of surface metal catalysts. The catalytic reduction gives rise to adsorbed hydrogen atoms. In the presence of Pd-0 or Pt-0, material balance shows that most of the adsorbed H atoms combine to molecular hydrogen. When the TiO2 nanoparticles are partially coated with Au-0 instead of Pd-0 or Pt-0, a higher than expected molecular hydrogen level is observed, attributed to a short chain reaction involving hydrogen abstraction from 2-propanol. This unusual hydrogen abstraction reaction has not been reported before. The mechanism and energy balance are discussed. The surface modification of TiO2 nanoparticles was carried out by reduction of K2PdCl4, H2PtCl6, or HAuCl4 with e(TiO2)(-). The latter had been generated through electron injection from hydrated electrons, hydrogen atoms, or 2- propanol radicals, produced by gamma or pulse radiolysis prior to the addition of the metal compounds. Upon addition of the metal compounds, immediate reactions take place producing metals clusters (M-0) by multistep reductions reactions on the TiO2 surface. The chemical kinetics involving the different metals and the reaction rate constant of e(aq)(-) and e(TiO2)(-) with AuCl4- is also reported.