Sonochemically prepared Pt, Au and Pd nanoparticles were successfully immobilized onto TiO2 with the assistance of prolonged sonication. Their photocatalytic activities were evaluated in H2 production from aqueous ethanol solutions. Beside the sonochemical method, the conventional impregnation method was also employed to prepare photocatalysts. The sonochemically prepared catalysts showed higher activities than did the conventional ones. Their photocatalytic activities depended on the work functions and the dimensions of supported noble metal nanoparticles. Smaller Pt nanoparticles effectively restricted recombination of electrons and holes and provided H2 at a higher rate.

A simple and unique route to synthesize nanosize Pd particles using a zeolite support including a single-site Ti oxide moiety (TS-1) under UV-light irradiation has been developed. By the photoassisted deposition (PAD) method, a Pd precursor can be deposited directly on the photoexcited tetrahedrally coordinated Ti oxide moiety within the zeolite frameworks from an aqueous solution of Pd. The subsequent reduction with H2 generates the nanosized Pd metal particles with a narrow size distribution (PAD-Pd/TS-1). Characterization by XAFS and TEM analysis revealed that the size of the metal particles depends on the preparation methods and that the smaller sizes of Pd nanoparticles were formed on the photodeposited catalysts compared with the conventionally prepared impregnated catalysts. PAD also provides PdAu bimetallic nanoparticles from an aqueous solution of mixture of PdCl2 and HAuCl4. The catalytic activities in the direct synthesis of hydrogen peroxide (H2O2) using H2 and O2 gases under atmospheric pressure were strongly dependent on the preparation method and the presence of Au atoms. Here, both deposition of PdAu onto the TS-1 moiety under UV-light irradiation was the most efficient for the above reaction. The applicability of the present catalytic system is highlighted by the one-pot reaction of phenol using PAD-Pd/TS-1 in the presence of H2 and O2, in which both Pd nanoparticles and isolated Ti oxide moieties within the frameworks participate in the formation of H2O2 and oxidation of phenol, respectively.

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We now report the CO 2 -reduction performances of Pt-Ru/C electrocatalysts and power-generation characteristic of a polymer electrolyte fuel cell driven by feeding H 2 and CO 2 to the anode (Pt/C) and cathode (Pt-Ru/C), respectively. The CO 2 electroreduction was evaluated by the current-voltage relationships in combination with in-line mass spectrometry. The onset potentials for the CO 2 reduction are observed at 0.06-0.4 V vs. the reversible hydrogen electrode (RHE), and they depend on the Pt:Ru composition of the Pt-Ru/C cathode. Mass spectrometry revealed that a Pt-rich catalyst generates CH 4 , whereas this gas is not or slightly generated at a Ru-rich catalyst. Based on these results, two significant effects of a small amount of Ru doping to Pt were elucidated: (i) it allows H, which is used for H 2 evolution at the Pt/C, to be used for the CH 4 generation, and (ii) it decreases the adsorption energy of the CO 2 -reduced intermediate (CO) on the Pt. In the fuel cell test, the fuel cell effectively generates power by combining a Pt/C anode and a Pt 0.8 Ru 0.2 /C cathode rather than a Pt/C cathode. Consequently, we demonstrated that Pt 0.8 Ru 0.2 /C exhibits greater performances than Pt/C for the CO 2 reduction and power generation of the H 2 -CO 2 fuel cell.

The isolated and tetrahedrally coordinated metal oxide (Ti, V, Cr, Mo and W-oxides) moieties can be included in the silica matrixes of silica-based microporous zeolite and mesoporous silica materials and named as ''single-site photocatalysts''. Under UV-light irradiation these single-site photocatalysts form the charge transfer excited state, i.e., the excited electron-hole pair state which is located quite near to each other in different from the manner observed on semiconducting materials such as TiO 2 , and play a significant role in various photocatalytic reactions. These single-site photocatalysts not only can promote photocatalytic reactions but also can be utilized to synthesis of functional materials. The nano-sized metal catalyst and visible-light sensitive binary oxide photocatalyst can be synthesized on the excited single-site photocatalyst under UV-light irradiation. The transparent mesoporous silica thin film with single-site photocatalyst generates the super-hydrophilic surface. In this review, our recent applications of single-site photocatalysts to synthesis of the surface functional materials have been introduced.Keywords Single-site photocatalyst Á Zeolite Á Mesoporous silica Á Nano-sized metal Á Visible-light sensitive photocatalyst Á Mesoporous thin film Á Surface hydrophilic-hydrophobic property 1 Introduction

Supported Pd catalysts were synthesized using various semiconductor materials by a photo-assisted deposition method under UV-light irradiation. The Pd precursor was deposited and partially reduced by the direct interaction with the photo-excited state of the semiconductor materials, and subsequently transformed into metal particles by H(2) reduction. CO adsorption and Pd K-edge XAFS measurements demonstrated that the mean diameter of the deposited Pd particles can be controlled by the type of employed semiconductor materials. The catalytic activities in the direct synthesis of hydrogen peroxide (H(2)O(2)) using H(2) and O(2) gases under atmospheric pressure were strongly dependent on the type of supports. Here, the use of TiO(2) comprising a mixed phase of anatase and rutile was the most efficient based on the amount of Pd. The photo-assisted deposition also provides a simple and straightforward method to synthesize PdAu alloy nanoparticles. For the structural model of PdAu nanoparticles, we suggest that most of the Au atoms are preferentially located in the core region, whereas the Pd atoms are preferentially located in the shell region. The PdAu/TiO(2) catalysts prepared by the photo-assisted deposition method were shown to perform significantly better than the pure Pd/TiO(2) catalysts.