Shinri Sato

Photocatalytic activity of NOx-doped TiO2 in the visible light region

When powdered TiO2 was prepared from a commencal titanium hydroxide by calcination, its color turned to pale yellow at around 400°C and this yellow-colored TiO2 showed higher photocatalytic activity for oxygen isotope equilibration and the oxidation of carbon monoxide and ethane than standard TiO2 in the visible light region (434 nm). The spectral sensitization of TiO2 in this case was concluded to be due to NOx impurity which was formed from NF4OH used in the preparation of titanium hydroxide.

Photolysis of water over metallized powdered titanium dioxide

Photolysis of gas-phase water has been carried out on NaOH-coated Rh/TiO2 and Pd/TiO2 catalysts. Hydrogen and oxygen were simultaneously produced on both catalysts and the stoichiometric composition (H2/O2= 2) was obtained for most of the catalysts. The rate of water photolysis strongly depended upon the amount of NaOH loaded and the pressure of water vapour. The photolysis rate on the Rh/TiO2 catalyst was maximized at 15 wt % of NaOH coating and at ca. 2 Torr of water-vapour pressure. The photocatalytic activity depended upon the kind of metal deposited as well as the source of TiO2. Rh was more active but Pd was less active than Pt, which was tested previously. The highest formal quantum yield was ca. 29% when the Rh/TiO2 catalyst was used. The dependences of the photolysis rate on light intensity, wavelength and thermal back reaction rate have also been studied.

Surface isocyanate intermediate formed during the catalytic reduction of nitrogen oxide in the presence of oxygen and propylene

IR spectroscopic measurements have revealed that an IR band ascribable to adsorbed isocyanate species grows up when alumina-supported Cu-Cs oxide catalyst is exposed to a mixture of NO, O2 and C3H6 at room temperature and subsequently heated to 400 °C in vacuum. The species produces N2, CO2 and CO in the ratio of ca. 2:1:1 in the presence of NO at 350°C. Alumina and alumina-supported Cu oxide catalyst are less active for the formation of isocyanate species.

Possible role of isocyanate species in NOx reduction by hydrocarbons over copper-containing catalysts

The behavior of an isocyanate intermediate (-NCO) formed during NOx reduction has been studied on alumina-supported CuCs oxide catalyst in the presence of oxygen and hydrocarbons (propene, acetylene, propane and n-heptane) using infrared spectroscopy. While a reaction involving NO, O2 and acetylene needs some heat treatment to produce the isocyanate species on the catalyst, no heat treatment is required in the NO/O2/propene or n-heptane system. No isocyanate intermediate is formed in a NO/O2/propane system by an ordinary procedure. Adsorbed water on the catalyst surface is found to suppress the formation of the isocyanate species. This inhibition effect is smaller in the acetylene or n-heptane containing system than in the propene containing system. The role of isocyanate species is discussed with reference to results for the practical reduction of NOx.

Photoelectrochemical preparation of Pt/TiO2 catalysts

PtTiO2(anatase) catalysts were prepared by the photoelectrochemical deposition of Pt from hexachloroplatinic acid solution, and their properties for CO and H2 adsorption were characterized by infrared spectroscopic and volumetric methods. Although the dispersion of Pt deposit depends on the commercial source of TiO2, the photodeposition of Pt followed by photoreduction with the aid of a sacrificial reducing agent leads to a good result, but the photoelectroplating of Pt in the presence of the reducing agent tends to lower Pt dispersion. The photoimpregnation of hexachloroplatinic acid followed by calcination in air and reduction in H2 prepares well-dispersed PtTiO2 catalysts irrespective of the source of TiO2.

Activity enhancement of copper-containing oxide catalysts by addition of cesium in the reduction of nitric oxide

Catalytic reduction of nitric oxide in the presence of propylene and oxygen over alumina and copper-containing oxide catalysts has been studied. The optimum temperature for this reaction is dependent upon the composition of the catalysts: ≈ 640 K on Cu-Cs/Al2O3, ≈ 680 K on Cu/Al2O3, and ≈ 780 K on Al2O3. IR spectroscopic measurements show that an isocyanate (−NCO) intermediate formed on Cu-Cs/Al2O3 is more reactive with NO to give N2 than the intermediate produced on Al2O3 and Cu/Al2O3. Electron donation from Cs to Cu may activate the intermediate.

Photochemical properties of ultrathin TiO2 films prepared by chemical vapor deposition

Abstract Thin films of TiO 2 were prepared on fused silica and titanium substrates by chemical vapor deposition (CVD) using Ti[OCH(CH 3 ) 2 ] 4 under conditions of anatase formation. The UV—visible transmission spectrum of the film deposited on the fused silica substrate showed an absorption edge 30 nm shorter than that of anatase powder. This blue shift may be attributed to size quantization, i.e. the film may consist of extremely small TiO 2 particles. The absorption edge shifted to slightly longer wavelength upon heating the film in air at high temperatures. The photocatalytic property of the film was examined using the photodeposition reaction of silver from aqueous AgNO 3 . The silver photodeposition rate increased with the calcination temperature, maximizing at around 400°C and then decreasing at higher temperature. To compare the photocatalytic property with the photoelectrochemical property, photocurrents were measured in a KOH solution using the film deposited on the titanium substrate. They decreased after calcination at temperatures above 400°C. Compared to bulk TiO 2 , the wavelength dependence of the current was shifted to considerably shorter wavelengths, in agreement with the absorption spectrum.

Photocatalytic activities of indium oxide powder prepared from indium hydroxide

Although commercial indium oxide showed little photocatalytic activity, indium hydroxide was photoactive, when calcined, for oxygen isotope equilibration and oxidation of CO and C2H6 even in the visible light region. The activity for oxygen isotope equilibration increased with increasing calcination temperature and reached a maximum at a calcination temperature of about 200 °C, while the activity for the photo-oxidation was maximized by calcination at about 300 °C. At calcination temperatures above 600 °C, however, the photoactivities for all the reactions dropped almost to zero. X-ray diffraction as well as diffuse reflectance spectroscopy revealed that indium hydroxide was converted at about 200 °C into indium oxide, and the particle size of indium oxide increased upon calcination at higher temperatures. When the samples calcined at temperatures above 500 °C were platinized, hydrogen photoevolution was observed from aqueous methanolic solution.

ZEKE electron spectroscopy of alkylbenzene-argon van der Waals complexes

Van der Waals (vdW) complexes of a series of alkylbenzenes (benzene, toluene, ethylbenzene, and n-propylbenzene) formed with Ar in supersonic jets have been studied with two-color zero-kinetic-energy (ZEKE) electron spectroscopy combined with a PFI (pulsed field ionization) method. The shifts in adiabatic ionization energies (I ) due to complex a 21 formation have been determined as 2128 and 2112 cm for ethylbenzene-Ar and n-propylbenzene-Ar, respectively, with respect to the bare molecules. These shifts have been reproduced qualitatively in terms of atom-atom Lennard-Jones (LJ) potentials incorporating charge-charge-induced-dipole interactions. Some low-frequency ZEKE bands due to vdW vibrations have been observed for benzene-Ar for the first time. However, no vdW vibrational structures appear in ZEKE electron spectra both for ethylbenzene-Ar and n-propylbenzene-Ar. The absence of vdW vibrational structure in the spectra may be probably due to a steric hindrance between Ar and the alkyl group. This has been supported also by the present LJ potential calculations. Furthermore, for toluene-Ar, it has been found that upon ionization the relative position of Ar is shifted along the direction of the C-C(H ) bond.

Mechanism of the photolysis of iron pentacarbonyl adsorbed on a Pt surface

Abstract Photolysis of Fe(CO) 5 adsorbed on a Pt surface was investigated by IR reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD) technique, and X-ray photoelectron spectroscopy (XPS). Although no photoproducts are detected by IRAS, TPD and XPS spectra show that a partly decarbonylated species is formed by irradiation and its Fe/CO ratio is approximately 1:4. Because IRAS is selectively sensitive to vibrational modes perpendicular to a metal surface, these results indicate formation of Fe(CO) 4 as an intermediate species with a square planar structure parallel to the surface. The intermediate Fe(CO) 4 species decomposes completely with rise in temperature up to 300 K. Such instability of the intermediate is responsible for the absence of Fe 2 (CO) 9 or Fe 3 (CO) 12 produced typically by the Fe(CO) 5 photolysis over insulator surfaces, in the gas or liquid phase, or in low temperature matrices.