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Heterogeneous photocatalytic reactions

Recently was estimated an expected impact on the global chemistry of the atmosphere of the indirect heterogeneous photocatalytic reactions under the much more abundant near ultraviolet, visible and near infrared solar light [2]. As photocatalysts may serve atmospheric aerosols, i.e. ultrasmall solid particles that sometimes are embedded into liquid droplets. Aerosols are known to contain Ti02, Fc203, ZnO and other natural oxides, as well as metal sulfides of volcanic or antropogenic origin, that may serve as semiconductor photocatalysts (see Fig.5). Aerosols are known to be concentrated mainly in the air layers near the surface of the Earth, i.e. in the troposphere, rather than stratosphere. [Pg.49]

The electronic theory furnishes, as we have already seen, a general recipe for the consideration of heterogeneous photocatalytic reactions. This recipe was obtained in Section I of the present article. In Sections III, IV, and V it was applied to the reactions of hydrogen-deuterium exchange, oxidation of CO, and synthesis of hydrogen peroxide, respectively. These are the most thoroughly studied photocatalytic reactions. [Pg.204]

We thus see that the electronic theory of heterogeneous photocatalytic reactions not only makes an attempt to explain, from the unified point of view, a large amount of experimental data, often contradictory at first glance, but also predicts new effects awaiting experimental verification. No doubt, the photocatalytic effect on semiconductors which has only recently become the subject matter of scientific research requires further experimental and theoretical study. [Pg.206]

The influence of the size particles of catalysts on the chemical yields of heterogeneous photocatalytic reactions, has received little attention, however our results suggest that both factors, the size of grains and the concentration of catalyst, must play an important role for light scattering and reflexion pro cesses these factors can influence the quantum yields and consequently the che mical yields of the photogenerated products. [Pg.450]

Fig. 8.19 Schematic diagram of a flow-type reactor for heterogeneous photocatalytic reaction of NO,. Fig. 8.19 Schematic diagram of a flow-type reactor for heterogeneous photocatalytic reaction of NO,.
Sonophotocatalysis is photocatalysis with ultrasonic irradiation or the simultaneous irradiation of ultrasound and light with photocatalyst. Tnis method includes irradiation with alternating ultrasound and light. Ultrasound effects on heterogeneous photocatalytic reaction systems have been demonstrated by Mason,1 Sawada et al.,2) Kado et al.,3) and Suzuki et al.4) In these papers, not only acceleration of photocatalytic reactions but increase in product selectivity by ultrasonic irradiation has also been reported. It was postulated that ultrasound effects, such as surface cleaning, particle size reduction and increased mass transfer, were the result of the mechanical effects of ultrasound.1,5) Lindley reviewed these and other effects.5)... [Pg.108]

Heterogeneous photocatalytic reaction products and their production rates depend on the kind of photocatalysts. As noted above, each photocatalyst powder has different properties. In the case of the sonophotocatalytic reaction, products or their yields also depend on the kind of photocatalysts. The effect of surface area on product ratio was discussed in section (12.2.1C). The influence of surface area on product ratio was noted, but factors other than surface area must be introduced to explain the difference in product ratios. It is known that there are several crystal structures of Ti02. The major structures are anatase and rutile. 2... [Pg.112]

Gas-phase heterogeneous reactions have been carried out in a closed circulating system evacuable to high vacuum (Fig. 13.1). For heterogeneous photocatalytic reactions, a quartz reaction cell with flat bottom (R. C. in Fig. 13.1) has been used. When Pt/Ti02 powder is spread over the bottom of the cell followed by evacuation (this is referred to as dry state) and illuminated in the presence of gas-phase water, neither H2 nor 02 is observed. The same is true for... [Pg.119]

Fig. 13.1 Schematic diagram of the circulating reaction apparatus for heterogeneous photocatalytic reactions. R. C. Reaction cell, F Filter (UV-D33S + H20). Fig. 13.1 Schematic diagram of the circulating reaction apparatus for heterogeneous photocatalytic reactions. R. C. Reaction cell, F Filter (UV-D33S + H20).
Fujihira M, Satoh Y, OsaT. Heterogeneous photocatalytic reactions on semiconductor materials. III. Effect of pH and Cu2+ ions on the photo-Fenton type reaction. Bull Chem Soc Jpn 1982 55 666-71. [Pg.103]

Sclafani A, Palmisano L, Schiavello M. N2 photoreduction and phenol and nitrophenol isomers photooxidation as examples of heterogeneous photocatalytic reactions. Res Chem Intermed 1992 18 211-26. [Pg.165]

Navio, J.A., G. Colon, M. Trillas, J. Peral, X. Domenech, J.J. Testa, J. Padron, D. Rodriguez and M.I. Litter (1998). Heterogeneous photocatalytic reactions of nitrite oxidation and Cr(VI) reduction on iron-doped titania prepared by the wet impregnation method. Applied Catalysis B-Environmental, 16(2), 187-196. [Pg.435]

Siemon, U., D. Bahnemann, J.J. Testa, D. Rodriguez, M.I. Litter and N. Bruno (2002). Heterogeneous photocatalytic reactions comparing Ti02 and Pt/Ti02. Journal of Photochemistry and Photobiology A-Chemistry, 148(1-3), 247-255. [Pg.438]

The prototype of a heterogeneous photocatalytic reaction is based on the irradiation of particles of the semiconductor titanium dioxide (Ti02) in the presence of... [Pg.115]

One of the most significant points that we must consider in scientific studies, not limited to studies on photocatalysis, is distinction between evidence and consistency, as least as far as the author thinks. In other words, it is necessary to recognize every fact to be a necessary condition but not a sufficient condition in a strict scientific sense. For example, the fact that a reaction rate obeys the first-order rate law giving a linear relation in a plot of data as in Fig. 6 is only a necessary condition for a monomolecular reaction in homogeneous phase and also a necessary condition for heterogeneous photocatalytic reaction in diffusion-limited conditions or that in surface-reaction limited conditions with a Henry-type adsorption or a Langmuir-type adsorption in the lower-concentration region. [Pg.407]

In a heterogeneous photocatalytic reaction, in which multiple photons are absorbed due to the relatively large size of particles compared with the size of molecules, multiple-electron (positive hole) transfer may occiu. For example, photocatalytic silver metal deposition accompanied by molecular oxygen (O2) liberation proceeds with the following stoichiometry (28) ... [Pg.412]

Three components must be present in order for the heterogeneous photocatalytic reaction to take place an emitted photon (in the appropriate wavelength), a catalyst surface (usually a semi-conductor material) and a strong oxidizing agent (in most cases oxygen). Pasquali et al., (1996) indicated that absorbed photons should be considered to be a nonmaterial reactant, which, like other reacting species, must be present for the reaction to occur. [Pg.2]

The heterogeneous photocatalytic reaction can be represented as a number of mechanistic steps (Legrini et. ai, 1993 Hoffman et. al., 1995 Turchi and Ollis, 1990). [Pg.3]

Figure 19.1 Schematic representation of the excitation and deexcitation steps for electrons and holes in a heterogeneous photocatalytic reaction. (Reproduced with permission from A. L. Linsebigler et al., Chem. Rev. 1995, 95, 735.)... Figure 19.1 Schematic representation of the excitation and deexcitation steps for electrons and holes in a heterogeneous photocatalytic reaction. (Reproduced with permission from A. L. Linsebigler et al., Chem. Rev. 1995, 95, 735.)...
It has to be emphasized that most of the heterogeneous photocatalytic reactions include a formation of such substrate/catalyst complexes. [Pg.64]


See other pages where Heterogeneous photocatalytic reactions is mentioned: [Pg.451]    [Pg.26]    [Pg.400]    [Pg.412]    [Pg.244]    [Pg.166]    [Pg.218]    [Pg.219]    [Pg.221]    [Pg.223]    [Pg.225]    [Pg.151]    [Pg.290]    [Pg.249]    [Pg.451]    [Pg.256]   
See also in sourсe #XX -- [ Pg.249 ]




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