An efficient methodology to synthesize highly active Pd nanoparticles using a single-site photocatalyst under UV-light irradiation has been developed for the synthesis of hydrogen peroxide (H2O2) from H-2 and O-2. By the photo-assisted deposition (PAD) method, Pd precursor can be deposited directly on the photo-excited tetrahedrally coordinated metal-oxide moiety within the silica frameworks, and subsequently transformed into Pd nanoparticles by H-2 reduction. The mean diameter of the deposited Pd particles determined by CO adsorption and the catalytic activities in the direct synthesis of H2O2 were strongly dependent on the preparation method and kind and/or amount of metal-oxide moieties. Here, the use of Ti-containing mesoporous silica (Ti/Si = 0.01) acted as a most efficient support for the above reaction. The PAD method also provides PdAu bimetallic nanoparticles from an aqueous solution of mixture of PdCl2 and HAuCl4. The PdAu/Ti-MCM-41 catalyst prepared by the PAD method was shown to perform significantly better activity than the pure Pd/Ti-MCM-41.