Photocatalytic conversion

The advantages of microreactors, for example, well-defined control of the gas-liquid distributions, also hold for photocatalytic conversions. Furthermore, the distance between the light source and the catalyst is small, with the catalyst immobilized on the walls of the microchannels. It was demonstrated for the photodegradation of 4-chlorophenol in a microreactor that the reaction was truly kinetically controlled, and performed with high efficiency [32]. The latter was explained by the illuminated area, which exceeds conventional reactor types by a factor of 4-400, depending on the reactor type. Even further reduction of the distance between the light source and the catalytically active site might be possible by the use of electroluminescent materials [19]. The benefits of this concept have still to be proven. 

SCHEME 3. Photocatalytic Conversion of Methane. e>g = electron in conduction band, h = positive hole in valance band, MV = methylviologen. 

Previous research by our groiqD [6] has confirmed literature reports [1,2] that it is possible to photolyze methane, saturated with water vapcff, to produce methanol and hydrogen. In a modification of the above ejq)eriment, we were also able to photolyze methane sparged throu a photochemical reactor filled with water. Recently, we began investigating the photocatalytic conversion of methane in water. 

Yahaya, A.H., Gondal, M.A., and Hameed.A. (2004) Selective laser enhanced photocatalytic conversion of C02 into methanol. Chemical Physics Letters, 400 (1-3), 206-212. 

The are two possibilities, the direct solar into electricity conversion (photovoltaic) and the solar into chemical energy conversion (solar fuels), e.g., the production of H2 by water splitting or the photocatalytic conversion of C02 into chemi-... 

CQDs can be efficient chromophores for photon harvesting and photoconversion [55] and it was shown that photogenerated electrons could be transferred to gold or platinum nanoparticles for the photocatalytic conversion of carbon dioxide and splitting of water for hydrogen generation [55,56], In both cases, CQDs similar to titania... 

Taylor, C.E. (2005). Photocatalytic conversion of methane contained in methane hydrates. Topics in Catalysis, 32 (3-4), 179-184. 

Meteorites, atmospheric radiation and, 3 299 Meteorology, radiation and, 3 293 Methacrylic esters, photocatalytic conversion, 43 431 Methane... 

Very recently, a major revision of the chemical pathways operating in the photocatalytic conversion of organic substrates was undertaken. Tliese studies were carried out through very careful product analysis [58,59], by using selected substrates with similar chemical properties but different sorption behavior [60], or by surface modification through complexation by redox inactive species [61,62]. 

A. Photocatalytic Conversion of Chlorine-Containing Organic Compounds ON Titanium Oxide... 

Gas-phase oxidation of methane could be enhanced by the addition of a small amount of NO or N02 in the feed gas.1077 Addition of methanol to the CH4-02-N02 mixture results in a further increase in methane reactivity.1078 Photocatalytic conversion of methane to methanol is accomplished in the presence of water and a semiconductor photocatalyst (doped W03) at 94°C and atmospheric pressure.1079 The yield of methanol significantly increased by the addition of H202 consistent with the postulated mechanism that invokes hydroxyl radical as an intermediate in the reaction. 

Photocatalytic Conversion of Solar Energy. Heterogeneous, Homogeneous and Molecular Structurally-Organized Systems. K. I. Zamaraev and V. N. Parmon (Eds.), Nauka, Novosibirsk (1991) (in Russian). 

The photocatalytic conversion rate increases with the increase of the oxygen partial pressure. The typical explanation is that oxygen acts as an electron scavenger, thus reducing the rate of electron-hole recombination (Chen and Ray, 1999). 

Figures 21a, b show the 4-CP, 4-CC, and HQ concentrations derived from inserting the estimated parameters in the kinetic model and a comparison with the experimental data under different operating conditions. Symbols correspond to experimental data and solid lines to model predictions calculated with Equations (64)-(66) and Equations (71)-(74). Eor these experimental runs, the RMSE was less than 14.4%. These experimental 4-CC and HQ concentrations are in agreement with the proposed kinetic mechanism of parallel formafion of fhe intermediate species (Figure 16), and also with the series-parallel kinetic model reported by Salaices et al. (2004) to describe the photocatalytic conversion of phenol in a slurry reactor under various operating conditions. ...

Chapter 7 reports a scaling-up procedure for photocatalytic reactors. The described methodology uses a model which involves absorption of radiation and photocatalyst reflection coefficients. The needed kinetics is obtained in a small flat plate unit and extrapolated to a larger reactor made of three concentric photocatalyst-coated cylindrical tubes. This procedure is applied to the photocatalytic conversion of perchloroethylene in air and to the degradation of formic acid and 4-chlorophenol in water. 

Overoxidation, sometimes to the point of complete mineralization, is often observed in water. Of course, this complete destruction of organic materials is useful if the goal is a photocatalytic conversion that results in purification of a water stream, but for selective organic redox chemistry of use to the synthetic organic chemist, this lack of control can be disastrous. 

Scheme 8. Photocatalytic conversion from methacrylic esters to malonate species.

Abstract Background The conversion of carbon dioxide into worthwhile chemicals through photo-catalysis has been a matter of attraction for the last four decades among the scientific community. However, the conversion rate has not yet been achieved to the desired efficiency due to the inevitable barriers associated with the process making it as a Holy Grail. This presentation deals with the identification and critical evaluation of the hurdles that pulls back the photocatalytic processes on track and the recent advances in the scientific field that pertain to the photocatalytic conversion of carbon dioxide in the near future. 

The hydrogen ion is reduced to H2 with a rate of 69 pL h-1 cm-2. Kim et al also studied the nafion layer-enhanced photocatalytic conversion of CO2 [181]. The main role of nafion membrane is to enhance the proton activity. It also prevents the reoxidation of the CO2 reduction products. The current efficiency of solar fuel cells restricts this process from real-life implementation. 

Varghese, O. K. Paulose, M. LaTempa, T. J. Grimes, C. A. High-Rate Solar Photocatalytic Conversion of C02 and Water Vapor to Hydrocarbon Fuels. Nano Lett., 2009, 9, 731—737. 

Hou, W. Hung, W. H. Pavaskar, P. Goeppert, A. Aykol, M. Cronin, S. B. Photocatalytic Conversion of C02 to Hydrocarbon Fuels via Plasmon-Enhanced Absorption and Metallic Interband Transitions. ACS Catal., 2011,1, 929-936. 

Izumi, Y. Recent Advances in the Photocatalytic Conversion of Carbon Dioxide to Fuels with Water and / or Hydrogen Using Solar Energy and beyond. Coord. Chem. Rev., 2013,257,171—186. 

Zhang, X. Han, F. Shi, B. Farsinezhad, S. Dechaine, G. P. Shankar, K. Photocatalytic Conversion of Diluted C02 into Light Hydrocarbons Using Periodically Modulated Multiwalled Nanotube Arrays. Angew. Chem., Int. Ed., 2012,51,12732—12735. 

Teramura, K. Wang, Z. Hosokawa, S. Sakata, Y. Tanaka, T. A Doping Technique that Suppresses Undesirable H2 Evolution Derived from Overall Water Splitting in the Highly Selective Photocatalytic Conversion of C02 in and by Water. Chem. Eur. J., 2014, 20, 9906-9909. 

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