Radiations induced catalysis

ZACHEIS, G. A., GRAY, K. A., KAMAT, P. V., Radiation-Induced Catalysis on Oxide Surfaces Degradation of Hexachlorobenzene on y-Irradiated Alumina Nanoparticles , J. Phys. Chem. B 1999,103, 2142-2150. 

Catalysis of Hg/I Exchange on Silica - A Radiation-Induced Catalyic Entity... 

Differential reactors are primarily used for studies of heterogeneous catalysis, Homogeneous reactions are very difficult to confine as sharply as necessary to a very small flow reactor. An exception are radiation-induced reactions (see comment in preceding section on tubular reactors). 

Ingold (6) did not review ascorbic acid per se, but did present a chapter on metal catalysis including the metal content of vegetable oils and the eflFect of valence state of the metals on oxidation of fats and oils. He reports cobalt, manganese, copper, iron, and zinc at the higher valences acted catalytically to oxidize many substrates. The author discussed the antioxidant activity of ascorbic acid in radiation-induced free radicals, fats in emulsions, fluid milk, and frozen fish. He also discussed the quandary of metal reactions vs. valence state. 

Marignier J.-L., Belloni J., Delcourt M.-O., Chevalier J.-P, New microaggregates of non noble metals and alloys prepared by radiation-induced reduction. Nature, 1985,317,344-345. Belloni J., Marignier J.-L., Delcourt M.-O., Minana M., Non noble metal catalytic microaggregates, a method for their preparation and their application in the catalysis ofthe photoreduction of water., US Pat. 1986, 4,629,709. Belloni J., Marignier J.-L., Delcourt M.-O., Minana M., New mono or multimetal microaggregates, a method for their preparation and their application in the catalysis of the photoreduction of water, US Patent 1987,4745094. 

In an earlier contribution (Volume 13 of the Advances), R. Coekel-bergs, A. Crucq, and A. Frennet wrote on Radiation Catalysis. In that case, emphasis was on the irradiated system reactants plus catalyst. In this volume, Ellison H. Taylor reviews the field of radiation-induced changes in electronic, chemical, and physical structure in solids and the resulting effects on their catalytic properties. The focal point in each case is different, yet taken together, they may challenge some readers to explore phenomenological overlaps. 

Confinement to the reactor is automatic in heterogeneous catalysis, and easily achieved for radiation-induced reactions, e.g., gas-phase chlorination of alkanes initiated by ultraviolet light. The reactor, usually a differential one, then is a cell in which the fluid passes through a beam of light. 

T. Mizota, S. Tsuneda, K. Saito and T. Sugo, Sulfonic Acid Catalysts Prepared by Radiation-Induced Graft Polymerization,. Catalysis, 149 (1994) 243. 

Thus over the course of half a century, the basic concepts of activated adsorption and active centers were made more precise by application of novel techniques In addition to the direct line work on catalysis, many scientific side lines were pursued photochemistry, discharge tube chemistry, radiation induced transformation, solid state chemical physics, and chemotherapy of cancer (113)... 

Vairavapandian, D., Vichchulada, P, Lay, M. D. 2008. Preparation and modification of carbon nanotubes Review of recent advances and applications in catalysis and sensing. Arud. Chem. Acta 626 (2) 119-129. Wang, H., Sun, X., Ye, Y., Qiu, S. 2006. Radiation induced synthesis of Pt nanoparticles supported on earbon... 

Reduction is the most common technique to prepare polymer-immobilized nanoparticles. Two different types of reduction can be considered. The first type, or the impregnation method, consists of the chemical reduction of metals from solutions or suspensions of their salts. Ammoniacal solutions of Cu, Cr, and Ag hydroxides are often used. Electrochemical or radiation-induced reduction in the presence of macroligands have also been employed. The reduction of mononuclear metal complexes chemically bound with polymers represent the second type. The impregnation method is more widely applied because it better meets the needs of catalysis. In particular, metal blacks, ultradispersed powders, etc. are prepared. For example, Raney nickel is stabilized by incorporating it into the silicone rubber "" followed by vulcanization at room temperature. 

In this paper the state of the art and perspectives will be discussed, of basic and applied photocatalysis and thermal catalysis induced by solar radiation, with the emphasis on the following areas ... 

PHOTOCATALYSIS AND THERMAL CATALYSIS INDUCED BY SOLAR RADIATION IN UTILIZATION OF SOLAR ENERGY... 

At present, thermal catalysis induced by solar radiation is more ready for potential practical use in the energy production industry of the future, than photocatalysis [7,9,29,30], Fig.7 illustrates the scheme of the pilot plant for thermocatalytic solar-to-chemical energy... 

The quantum yield 0 of a photophysical or photochemical event is a quantitative measure of the overall efficiency of this process (Braun et al., 1991). It is a unitless constant, which usually ranges from zero to one. However, some authors express 0 in units of mol einstein, which in fact is unit-less, because an einstein is defined as one mol of photons. Quantum yields greater than one indicate photo-induced chain reactions, which may involve radical species or photo-generated catalysis. Commonly used definitions of 0 are collected in Tab. 3-7. These definitions describe quantum yields of photophysical events and of photochemical reactions with regard to the reactant diminution or to the formation of the photoproduct Quantum yields may be dependent on the wavelength of the absorbed UV/VIS radiation, but many photochemical systems exist that have a constant quantum yield 0 over a defined wavelength range. Such chemical systems can be... 

Hj production on solid materials is indeed a particular case of energy redistribution in a multiphase system, which is sometimes also referred to as radiation catalysis the energy of ionising radiation absorbed in one phase can be delivered to the interface and can induce physical and chemical processes in the other phase. 

The hexapole technique has been extensively exploited for the study of oriented open shell molecules such as OH (see Ref [46] and references therein) and NO (see Ref [47] and references therein), the latter also for scattering on surfaces [48]. This is a very important topic, because the basic tool for enhancement of chemical reactivity is catalysis at surfaces. In Ref [49], for examples, the oxidation of Si (001) induced by incident energy of O2 molecules is studied by synchrotron radiation photoemission spectroscopy and mass spectrometry, a process of a kind which may show propensities regarding molecular orientation of O2 as it impinges on the surface, possibly controlled by techniques of the kind described in previous sections. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

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