Showing papers by "Masatake Haruta published in 1995"

Photoassisted hydrogen production from a water-ethanol solution: a comparison of activities of AuTiO2 and PtTiO2

Abstract: A comparison of the photocatalytic activity for H 2 generation between AuTiO 2 and PtTiO 2 has been made. The deposition of Au and Pt was carried out using TiO 2 powders in aqueous suspensions containing HAuCl 4 ·4H 2 O or H 2 PtCl 6 ·6H 2 O by deposition-precipitation (DP), impregnation (IMP), photodeposition (FD) and, in the case of Au, by mixing TiO 2 with colloidal gold suspensions (MIX). The main reaction products obtained from the irradiation of an aqueous 5 M C 2 H 5 OH suspension containing AuTiO 2 or PtTiO 2 were hydrogen, methane, carbon dioxide and acetaldehyde. Small amounts of acetic acid were also detected. The overall activity of Au samples was generally about 30% lower than that of Pt samples. The activity of Au samples strongly depended on the method of preparation and decreased in the order AuTiO 2 -FD>AuTiO 2 -DP>AuTiO 2 -IMP>AuTiO 2 -MIX. The activities of the platinum samples were less sensitive to the preparation method and decreased in the order PtTiO 2 -FD>PtTiO 2 -DP≈PtTiO 2 -IMP. Gold and platinum precursors calcined in air at 573 K showed the highest activity towards H 2 generation, followed by a decline in activity with increasing calcination temperature. The H 2 yield was found to be dependent on the metal content on TiO 2 and showed a maximum in the ranges 0.3–1 wt.% Pt and 1–2 wt.% Au. The exposed surface area of gold had only a small influence on the rate of hydrogen generation. On the other hand, the rate of H 2 production was strongly dependent on the initial pH of the suspension. pH values in the range 4–7 gave better yields, whereas highly acidic and basic suspensions resulted in a considerable decrease in the H 2 yield.

Carbon dioxide and carbon monoxide hydrogenation over gold supported on titanium, iron, and zinc oxides

Abstract: Gold deposited on TiO2, Fe2O3, ZnO and ZnFe2O4 with high dispersion was found to be active for the hydrogenation of both carbon dioxide and carbon monoxide at temperatures between 150 and 400°C. Over the above catalysts, methanol was produced more readily from carbon dioxide than from carbon monoxide. In particular, Au/ZnO and Au/ZnFe2O4 showed high methanol selectivities from carbon dioxide, which were comparable to those obtained for copper catalysts. As for methanol synthesis from carbon monoxide, only Au/ZnO gave appreciable yields with similar selectivity as copper catalysts. The comparison between experimental and thermodynamic data proved that over all the catalysts except for Au/TiO2 three reactions, namely between carbon dioxide and methanol, carbon monoxide and methanol, carbon dioxide and carbon monoxide, simultaneously reached equilibria at temperatures above 300°C and that the methanol yield decreased with further increase in temperature. Hydrocarbons were formed at high temperatures and the resulting water was also involved in the above equilibria. As a main hydrocarbon product, methane was obtained much more selectively from carbon dioxide than from carbon monoxide. Ethane and propane were also produced from carbon dioxide and carbon monoxide over gold supported on reduced iron oxides.

Large third-order optical nonlinearities in transition-metal oxides

Abstract: ADVANCES in the field of optical computing1–3 will require the development of materials that combine a large nonlinear optical response with a fast response time. For many applications, this translates into a third-order nonlinear optical susceptibility, χ(3), in excess of 10−8 e.s.u., and a response time faster than lO ps (ref. 4). Although a wide range of inorganic5–18 and organic19–21 materials have been found to exhibit a large χ(3), either the response times tend to be far too slow or the materials are not sufficiently stable for device applications. Recently, the transition-metal oxide Fe2O3 was found to have a large χ(3) (ref. 22). Here we show that oxides of several other 3d transition metals show a similarly large nonlinear optical response; moreover, we find that a significant contribution to the overall χ(3) (∼10−8 e.s.u. in the case of V2O5) has a response time of the order of 35 ps.

Preparation of nanometer gold strongly interacted with TiO2 and the structure sensitivity in low-temperature oxidation of CO

Abstract: Gold can be deposited on TiO2 as hemispherical fine particles with diameters smallerthan 4nm by deposition precipitation. Gold hydroxide precipitates with high and homogeneous dispersion on TiO2, most probably on specific surface sites, in the pH range 6 to 10. The calcination of TiO2 with Au(OH)3 in reducing gas atmospheres, such as H2 and CO led to smaller gold particles than in air. In the case of Au/TiO2 samples prepared by deposition precipitation, the catalytic activity for low-temperature CO oxidation was very high and could be observed even at temperatures below 0°C. Physically mixed Au/TiO2 samples though of much lower catalytic activity, showed gradual improvement with increasing calcination temperature. An increase in calcination temperature not only caused particle coagulation but also brought about a stronger interaction with the TiO2 support. The above results therefore indicate that the catalytic activity of Au/TiO2 is sensitive to the structure of the perimeter interface between Au and TiO2.

Method for production of alcohol, ketone, and aldehyde by oxidation of hydrocarbon

Abstract: An alcohol or a ketone or a mixture thereof is produced from a saturated hydrocarbon or an epoxide is produced from an unsaturated hydrocarbon by passing a mixture comprising of molecular hydrogen, the saturated or unsaturated hydrocarbon and oxygen through a bed of a catalyst comprising a titanium dioxide carrier and ultrafine gold particles deposited on the carrier, thereby effecting the oxidation of the hydrocarbon with oxygen.

An IR study of CO-sensing mechanism on Au/ZnO

Abstract: An FTIR and quadrupole mass study of the adsorption and oxidation of CO on an Au/ZnO sample with 16 O 2 and 18 O 2 is presented. The results indicate that CO adsorbed on gold sites at the perimeter interface with ZnO reacts with surface lattice oxygens at the oxide surface to form carbonate-like intermediates. This reaction and the decomposition of the intermediates can be assumed to be mainly responsible for the conductivity changes of the semiconductive metal oxide caused by CO in air. Oxygen, present in the mixture and adsorbed on gold vicinal sites, makes the nucleophilic attack of surface oxygens on the CO easier as a consequence of an electron-withdrawing effect. This effect produces a positivization of the carbon of adsorbed CO by an inductive effect and activates the reactivity of support lattice oxygens on the CO.

Optical CO detection by use of CuO/Au composite films

Abstract: Composite films consisting of a thin CuO layer and ultrafine Au particles have been found to be usable for the optical detection of CO in air. The optical absorption of CuO/Au composite films increases due to CO and recovers reversibly in air free of CO. The largest absorbance change due to CO is in the 700-800 nm wavelength region, with the absorbance change enhanced by increasing temperature or increasing CO concentration. We assume that the absorbance change of the CuO/Au film occurs due to the change in the electronic structure of the ultrafine Au particles as a result of their interactions with atmospheric gas.

Formation of Propylene Oxide by the Gas-Phase Reaction of Propane and Propene Mixture with Oxygen

Abstract: The homogeneous gas-phase reaction of propane and propene with molecular oxygen was investigated at 360-520°C under atmospheric pressure using a quartz reactor in a continuous-flow system. At a high concentration (65 vol%) and low conversions of hydrocarbons, the overall oxidation rate and the selectivity to propylene oxide were markedly enhanced by mixing propane and propene. At a specific propane/propene ratio, for example 10:3, the net conversion of propene was found to become zero at around 450°C, indicating that the consumption of propene was compensated by the formation from propane and only propane substantially reacted to form propylene oxide and the others. The major product was propylene oxide, and its selectivity exceeded 30%. Other products were ethylene, CO, acetaldehyde, methane, CO 2 , acrolein, propanal, methanol, and so forth

Catalytic methanol decomposition to carbon monoxide and hydrogen over NiSiO2 of high nickel content

Abstract: The methanol decomposition to carbon monoxide and hydrogen is catalyzed at 250°C over nickel-silica composites prepared by the sol-gel method while the activity is increased with increase in the content of nickel up to 40 wt%. The activity of nickel supported on silica prepared by the conventional impregnation technique is also increased with the nickel content but almost reaches a plateau at the nickel content of 10 wt%. The maximum activity found with the former is significantly higher than that with the latter.

Effect of the Addition of Nitrogen Dioxide on the Gas-Phase Partial Oxidation of Methane with Oxygen under Normal Pressures

Abstract: The addition of NO2 to the gas-phase reaction of CH4 with O2 conducted under normal pressures at temperatures of 400∼460 °C enhances the partial oxidation of methane with improved selectivities to organic products

Formation of methanol by the gas phase partial oxidation of methane under normal pressures

Abstract: Even under normal pressures (1.5–3.0 atm), methanol is formed by the gas phase reaction of methane with oxygen in a flow quartz reactor at 425–490 °C with methanol selectivities exceeding 30% at a methane conversion of 5%.

Nonlinear optical materials and process for producing the same

Abstract: There are provided a third-order nonlinear optical material comprising a film formed on the surface of a transparent substrate and consisting essentially of an oxide of a metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni and Cu; and a third-order nonlinear optical material of the type as described above wherein the film additionally contains a metal selected from the group consisting of Au, Ag and Cu in the form of particles dispersed therein and having a particle size of at most 500 nm. The present invention also provides a process for producing a third-order nonlinear optical material by dispersing and depositing in a transparent matrix an oxide of a metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni and Cu in the form of particles having a particle size of at most 500 nm; a process of the type as described above wherein a metal selected from the group consisting of Au, Ag and Cu in the form of particles having a particle size of at most 500 nm is simultaneously dispersed and deposited in a transparent matrix. The present invention further provides third-order nonlinear optical materials produced according to the process of the present invention.