Effect of chromium content on the corrosion resistance of ferritic stainless steels in sulfuric acid solution.

Due to recent increases in the price of Ni, steel use is currently undergoing a global shift from austenitic stainless steels to ferritic stainless steels. In this study, the corrosion behavior of four types ferritic stainless steels with different Cr contents was investigated to study the effect of Cr content on the corrosion resistance in a sulfuric acid solution. The polarization curves of the ferritic stainless steel with the highest Cr content indicated the best corrosion resistance. No corrosion was observed for the stainless steel with 24 mass% Cr after a potential sweep based on ex-situ SEM images. Corrosion resistivity was improved for high Cr content (>24 mass%) stainless steel because it is considered to form a stable passivation layer.

New route for the preparation of Pd and PdAu nanoparticles using photoexcited Ti-containing zeolite as an efficient support material and investigation of their catalytic properties.

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.

A new application of photocatalysts: synthesis of nano-sized metal and alloy catalysts by a photo-assisted deposition method.

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.

Synthesis of highly dispersed platinum nanoparticles on Ti-containing mesoporous silica using photo-assisted deposition.

A simple and unique route to synthesize the nano-size Pt particles using mesoporous silica support including single-site Ti-oxide moiety (Ti-HMS) under UV-light irradiation has been developed. By the photo-assisted deposition (PAD) method, a Pt precursor can be deposited from aqueous solution of H2PtCl6 directly on the photo-excited isolated Ti-oxide moiety. The subsequent reduction with H2 generates the nano-sized Pt metal particles (PAD-Pt/Ti-HMS). The deposition of Pt precursor onto the Ti-HMS can be recognized by the observation of the decrease in the intensity of the preedge in the Ti K-edge XANES spectrum, demonstrating that the Pt precursor underwent anchoring on the single framework Ti4+ center of Ti-HMS under UV-light irradiation. The lower intensity of the Pt-Pt bond of the PAD-Pt/Ti-HMS than that of Pt foil in the Fourier transforms of Pt L(III)-edge EXAFS spectra clearly suggests the formation of the Pt nanoparticles. The PAD-Pt/Ti-HMS exhibited the higher catalytic activity for the hydrogenation of nitrobenzene to aniline and the NO reduction than the catalyst prepared by the conventional impregnation.

Immobilization of noble metal nanoparticles on the surface of TiO2 by the sonochemical method: photocatalytic production of hydrogen from an aqueous solution of ethanol.

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.