Recent advances in colloidal synthesis enabled the precise control of the size, shape and composition of catalytic metal nanoparticles, enabling their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here, we report the design of a high-temperature-stable model catalytic system that consists of a Pt metal core coated with a mesoporous silica shell (Pt@mSiO(2)). Inorganic silica shells encaged the Pt cores up to 750 degrees C in air and the mesopores providing direct access to the Pt core made the Pt@mSiO(2) nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt@mSiO(2) nanoparticles enabled high-temperature CO oxidation studies, including ignition behaviour, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt@mSiO(2) nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept used in the Pt@mSiO(2) core-shell catalyst can be extended to other metal/metal oxide compositions.

High performance catalysts are central for the development of new generation energy conversion and storage technologies. 1,2 While industrial catalysts can be optimized empirically by tuning the elemental composition, changing the supports, or altering preparation conditions in order to achieve higher activity and selectivity, these conventional catalysts are typically not uniform in composition and/or surface structure at the nano-to micro-scale. In order to significantly improve our capability of designing better catalysts, new concepts for the rational design and assembly of metal-metal oxide interfaces are desired. Metal nanocrystals with well-controlled shape and size are interesting materials for catalyst design from both electronic structure and surface structure aspects. 3,4,5 From the electronic structure point of view, small metal nanoclusters have size-dependent electronic states, which make them fundamentally different from the bulk. From the surface structure point of view, the shaped nanocrystals have surfaces with well-defined atomic arrangements. It has been clearly demonstrated by surface science studies in recent decades that the atomic arrangement on the crystal surface can affect catalytic phenomena in terms of activity, selectivity, and durability.

Hydrogen peroxide (H2O2) in water has been proposed as a promising solar fuel instead of gaseous hydrogen because of advantages on easy storage and high energy density, being used as a fuel of a one-compartment H2O2 fuel cell for producing electricity on demand with emitting only dioxygen (O2) and water. It is highly desired to utilize the most earth-abundant seawater instead of precious pure water for the practical use of H2O2 as a solar fuel. Here we have achieved efficient photocatalytic production of H2O2 from the most earth-abundant seawater instead of precious pure water and O2 in a two-compartment photoelectrochemical cell using WO3 as a photocatalyst for water oxidation and a cobalt complex supported on a glassy-carbon substrate for the selective two-electron reduction of O2. The concentration of H2O2 produced in seawater reached 48 mM, which was high enough to operate an H2O2 fuel cell.

The photocatalytic water oxidation to evolve O 2 was performed by photoirradiation (l > 420 nm) of an aqueous solution containing [Ru(bpy) 3 ] 2+ (bpy ¼ 2,2 0 -bipyridine), Na 2 S 2 O 8 and water-soluble cobalt complexes with various organic ligands as precatalysts in the pH range of 6.0-10. The turnover numbers (TONs) based on the amount of Co for the photocatalytic O 2 evolution with [Co II (Me 6 tren)(OH 2 )] 2+ (1) and [Co III (Cp * )(bpy)(OH 2 )] 2+ (2) [Me 6 tren ¼ tris(N,N 0 -dimethylaminoethyl) amine, Cp * ¼ h 5 -pentamethylcyclopentadienyl] at pH 9.0 reached 420 and 320, respectively. The evolved O 2 yield increased in proportion to concentrations of precatalysts 1 and 2 up to 0.10 mM. However, the O 2 yield dramatically decreased when the concentration of precatalysts 1 and 2 exceeded 0.10 mM. When the concentration of Na 2 S 2 O 8 was increased from 10 mM to 50 mM, CO 2 evolution was observed during the photocatalytic water oxidation. These results indicate that a part of the organic ligands of 1 and 2 were oxidized to evolve CO 2 during the photocatalytic reaction. The degradation of complex 2 under photocatalytic conditions and the oxidation of Me 6 tren ligand of 1 by [Ru(bpy) 3 ] 3+ were confirmed by 1 H NMR measurements. Dynamic light scattering (DLS) experiments indicate the formation of particles with diameters of around 20 AE 10 nm and 200 AE 100 nm during the photocatalytic water oxidation with 1 and 2, respectively. The particle sizes determined by DLS agreed with those of the secondary particles observed by TEM. The XPS measurements of the formed particles suggest that the surface of the particles is covered with cobalt hydroxides, which could be converted to active species containing high-valent cobalt ions during the photocatalytic water oxidation. The recovered nanoparticles produced from 1 act as a robust catalyst for the photocatalytic water oxidation.

We report the structure of the organic capping layers of platinum colloid nanoparticles and their removal by UV-ozone exposure. Sum frequency generation vibrational spectroscopy (SFGVS) studies identify the carbon-hydrogen stretching modes on poly(vinylpyrrolidone) (PVP), and tetradecyl tributylammonium bromide (TTAB) capped platinum nanoparticles. We found that the UV-ozone treatment technique effectively removes the capping layer, based on several analytical measurements including SFGVS, X-ray photoelectron spectroscopy, and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The overall shape of the nanoparticles was preserved after the removal of capping layers, as confirmed by transmission electron microscopy (TEM).SFGVS of ethylene hydrogenation on the clean platinum nanoparticles demonstrates the existence of ethylidyne and di--bonded species, indicating the similarity between single crystal and nanoparticle systems. TITLE RUNNING HEAD: Sum Frequency Generation and Catalytic Reaction Studies of the removal of the organic capping agents from Pt nanoparticles by UV ozone treatment.

This review describes homogeneous and heterogeneous catalytic reduction of dioxygen with metal complexes focusing on the catalytic two-electron reduction of dioxygen to produce hydrogen peroxide. Whether two-electron reduction of dioxygen to produce hydrogen peroxide or four-electron O2-reduction to produce water occurs depends on the types of metals and ligands that are utilized. Those factors controlling the two processes are discussed in terms of metal-oxygen intermediates involved in the catalysis. Metal complexes acting as catalysts for selective two-electron reduction of oxygen can be utilized as metal complex-modified electrodes in the electrocatalytic reduction to produce hydrogen peroxide. Hydrogen peroxide thus produced can be used as a fuel in a hydrogen peroxide fuel cell. A hydrogen peroxide fuel cell can be operated with a one-compartment structure without a membrane, which is certainly more promising for the development of low-cost fuel cells as compared with two compartment hydrogen fuel cells that require membranes. Hydrogen peroxide is regarded as an environmentally benign energy carrier because it can be produced by the electrocatalytic two-electron reduction of O2, which is abundant in air, using solar cells; the hydrogen peroxide thus produced could then be readily stored and then used as needed to generate electricity through the use of hydrogen peroxide fuel cells.

Structural characteristics of ceria−titania and vanadia/ceria−titania mixed oxides have been investigated using X-ray powder diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) techniques. The (1:1 mole ratio) mixed oxide was obtained by a coprecipitation method, and a nominal 5 wt % V2O5 was deposited over its surface by a wet impregnation technique. Both of the materials were then subjected to thermal treatments from 773 to 1073 K and were characterized by the above-mentioned techniques. The XRD results suggest that the CeO2−TiO2 mixed oxide calcined at 773 K primarily consists of poorly crystalline CeO2 and TiO2-anatase phases and that a better crystallization of these oxides occurs with increasing calcination temperature. The “a” cell-parameter values suggest some incorporation of titanium into the ceria lattice. Impregnation of vanadia on ceria−titania enhances the crystallization of CeO2 and TiO2 oxides. However, no crystalline V2O5 could be observed from XRD and RS measurements. Furthermore, the dispersed molecular vanadium oxide (polyvanadate), evidenced by Raman measurements, interacts preferentially with the CeO2 portion of the mixed oxides and forms the CeVO4 compound at higher calcination temperatures. The XRD and RS results provide direct evidence about the formation of CeVO4. The XPS electron-binding energies indicate that ceria, titania, and vanadia are mainly in their highest oxidation states, Ce(IV), Ti(IV), and V(V). The formation of Ce(III) has also been noticed in both CeO2−TiO2 and V2O5/CeO2−TiO2 samples at all temperatures.

Microstructure evolution of ceria-based mixed oxides CeO2−MO2 (M = Si4+, Ti4+, and Zr4+) after thermal treatments in the temperature range of 773−1073 K were investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other techniques. The CeO2−SiO2 was synthesized by a deposition precipitation method, and a coprecipitation procedure was adopted to make CeO2−TiO2 and CeO2−ZrO2 binary oxides. The XRD measurements revealed the presence of crystalline cubic CeO2 on the surface of SiO2 in CeO2−SiO2, CeO2 and TiO2 (anatase) in CeO2−TiO2, and Ce0.75Zr0.25O2 and Ce0.6Zr0.4O2 phases in CeO2−ZrO2 samples. The crystallinity of these phases increased as the calcination temperature increased. Estimations of the cell parameter a indicated an expansion of the CeO2 lattice in the case of CeO2−TiO2 samples, whereas a contraction was noted in the case of CeO2−ZrO2. Some incorporation of Si4+ ions into the CeO2 lattice was noted at higher calcination temperatures for the CeO2−SiO2 samples. Raman measurements revealed the presence of oxygen vacancies, lattice defects, and the displacement of oxide ions from their normal lattice positions in the case of the CeO2−TiO2 and CeO2−ZrO2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation statesSi4+, Ti4+, and Zr4+at the surface of the materials. Cerium is present in both Ce4+ and Ce3+ oxidation states, but in different proportions, depending on the mixed-oxide system and the calcination temperature used.