Takashi Ibusuki

Heterogeneous photocatalytic oxidation of benzene, toluene, cyclohexene and cyclohexane in humidified air: comparison of decomposition behavior on photoirradiated TiO2 catalyst

Abstract Gas–solid heterogeneous photocatalytic decomposition of benzene, toluene, cyclohexane and cyclohexene over TiO 2 was studied at room temperature, and their reactivities were compared. Catalyst deactivation was ascribed to the formation of the carbon deposits on TiO 2 surface, and the formation and decomposition behavior of the carbon deposits affected the decomposition rate. Deactivated TiO 2 catalysts were photochemically regenerated in the presence of water vapor, and the carbon deposits were decomposed to CO x .

Photochemical Reduction of CO2 Using TiO2: Effects of Organic Adsorbates on TiO2 and Deposition of Pd onto TiO2

Reduction of CO(2) using semiconductors as photocatalysts has recently attracted a great deal of attention again. The effects of organic adsorbates on semiconductors on the photocatalytic products are noteworthy. On untreated TiO(2) (P-25) particles a considerable number of organic molecules such as acetic acid were adsorbed. Although irradiation of an aqueous suspension of this TiO(2) resulted in the formation of a significant amount of CH(4) as a major product, it was strongly suggested that its formation mainly proceeded via the photo-Kolbe reaction of acetic acid. Using TiO(2) treated by calcination and washing procedures for removal of the organic adsorbates, CO was photocatalytically generated as a major product, along with a very small amount of CH(4), from an aqueous suspension under a CO(2) atmosphere. In contrast, by using Pd (>0.5 wt %) deposited on TiO(2) (Pd-TiO(2)) on which organic adsorbates were not detected, CH(4) was the main product, but CO formation was drastically reduced compared with that on the pretreated TiO(2). Experimental data, including isotope labeling, indicated that CO(2) and CO(3)(2-) are the main carbon sources of the CH(4) formation, which proceeds on the Pd site of Pd-TiO(2). Prolonged irradiation caused deactivation of the photocatalysis of Pd-TiO(2) because of the partial oxidation of the deposited Pd to PdO.

Photocatalytic reduction of carbon dioxide to methane and acetic acid by an aqueous suspension of metal-deposited TiO2

Deposition of a metal on TiO2 considerably accelerated photocatalytic reduction of carbon dioxide to methane and/ or acetic acid, and product distribution was dependent on the kind of metal on the surface of TiO2.

Efficient photocatalytic CO2 reduction using [Re(bpy) (CO)3{P(OEt)3}]+

Abstract [Re(bpy) (CO)3{P(OEt)3}]+ (1+) (bpy, 2,2′-bipyridine) is the most efficient homogeneous photocatalyst for the selective reduction of CO2 to CO reported to date. Both the quantum yield and turnover number of the photocatalytic reaction are strongly dependent on the irradiation light intensity and wavelength because of the unusual stability of the one-electron-reduced species [Re(bpy.−) (CO)3{P(OEt)3}] (1).

Toluene oxidation on u.v.-irradiated titanium dioxide with and without O2, NO2 OR H2O at ambient temperature

Abstract As an example of transformation and decomposition of environmental organic chemicals on a solid surface, the photo-oxidation of toluene on titanium dioxide (TiO2) was studied. The rate of the photo-oxidation was much greater than that in the homogeneous gas phase reaction. The photocatalytic activity of TiO2 was remarkably changed with O2, NO2 and H2O concentration in the gas phase. The results were discussed in terms of the nature and the amount of the active species formed on the TiO2 surface.

Photocatalytic decomposition of benzene over TiO2 in a humidified airstream

Photocatalytic decomposition of benzene over TiO2 in the gas phase at room temperature was studied with a fixed-bed flow reactor. In a humidified airstream ([H2O]=2.2%), benzene was efficiently decomposed to CO2 and CO with the selectivities of 93 and 7%, respectively. The selectivities were almost independent of the benzene conversion, indicating that CO is not the intermediate of CO2 in the reaction. The selectivity of CO was in the range of 7–10% with varying concentration of O2, H2O, and benzene. The formation of phenol and brownish carbonaceous matter attributable to polymeric products was observed on the catalyst surface. In the absence of O2, benzene oxidation did not proceed at all, showing that O2 is essential for the reaction. The presence of H2O not only suppressed the formation of the carbon deposits on the catalyst surface, but also accelerated the decomposition of them to CO2 and CO. Diffuse reflectance IR study showed that the presence of H2O regenerated the surface hydroxyl groups of TiO2 which were consumed in the photoreaction. With increase in the benzene concentration, the benzene conversion was decreased and the amount of carbon deposits on the catalyst surface was increased.

Performance evaluation of a hybrid system comprising silent discharge plasma and manganese oxide catalysts for benzene decomposition

A hybrid system comprising a silent discharge plasma reactor (SDR) and manganese oxide (MnO/sub 2/) catalyst was used for the decomposition of benzene in air. The benzene conversion was greatly enhanced by combining MnO/sub 2/ with the SDR in the latter part. The MnO/sub 2/ catalyst decomposed benzene by using ozone (O/sub 3/) that was formed in the SDR as the oxidant precursor. With an increase in the amount of water vapor in air, the benzene conversion was decreased, due to the deactivation of high-energy electrons, the diminished formation of O/sub 3/ in SDR, and decreased activity of MnO/sub 2/ for the benzene oxidation with O/sub 3/. The only products of the reaction were CO/sub 2/ and CO. The carbon mass balance was not perfect due to the deposition of intermediates on MnO/sub 2/ during the reaction. The intermediates were subsequently decomposed to CO/sub 2/ and CO by MnO/sub 2/ in the presence of O/sub 3/. In dry air, the selectivities to CO/sub 2/ and CO were 70% and 30%, respectively, and were almost independent of specific energy density. The CO/sub 2/ selectivity was improved to 90% by humidifying the background air.

The surface structure of titanium dioxide thin film photocatalyst

Abstract The surface structure of TiO2 thin film photocatalyst was successfully controlled by the sol-gel method with a polymer doped dip-coating process. The thin films prepared were either transparent or translucent depending on the molecular weight of the polymer doped. The surface of the transparent thin films looked plain consisting of uniformly aggregated nanometer size TiO2 particles, while the translucent thin film was formed with cubic-like crystalline TiO2 at a micrometer level. The specific surface area of the transparent thin film was almost the same as that of the translucent one. All the thin film photocatalysts had an anatase structure with similar crystallinity. Both the transparent and translucent films showed catalytic activity for NOx elimination from air. The activity was almost equal to the commercial photocatalyst P25.

Sulfur dioxide oxidation by oxygen catalyzed by mixtures of manganese(II) and iron(III) in aqueous solutions at environmental reaction conditions

The reaction kinetics of SO2 oxidation by oxygen catalyzed by mixtures of Mn(II) and Fe(III) in aqueous solutions over a wide range of pH from 2.6 to 6.5 have been studied at low concentrations of S(IV) and the metal ions. The catalytic synergism between the two catalysts as a function of [Mn(II)]. [Fe(III)] has been confirmed. The following rate expression is obtained with a rate constant of ks = (3.6 ± 0.6) × 1010/mole s−1−d[S(IV)]dt = ks[Mn(II)]·[Fe(III)]·[S(IV)] at a pH of 4.2 and a temperature of 23.8°C. The pH and temperature dependences of the reaction rate have also been evaluated. The reaction mechanism is briefly discussed on the basis of the rate law and the activation energy for this reaction.

The stabilization of active oxygen species by Pt supported on TiO2

Abstract Pt/TiO2 was active for the oxidation of CO to CO2 in the dark at ambient temperature after UV irradiation. Pure TiO2 was inactive and the presence of Pt supported on TiO2 was indispensable for the reaction. Based on the ESR study, it was found that Pt deposited on TiO2 stabilized the O− and O3− species photoformed on the TiO2, and they were responsible for the CO oxidation.