Photocatalysis, of hydrogenation

H. Harada (2001)Isolation of hydrogen from water and for artificial seawater by sono-photocatalysis using alternating irradiation method Int J. Hydrogen Energy, 26 3003-2007... 

Another important photocatalytic application is the synthesis of hydrogen from water. However, low solar efficiency and photocorrosion have proven to be hindrances limiting the process economics of photocatalysis [325], The most efficient systems to date consist of compound semiconductor heterostructures that operate with efficiencies of approximately 16%, however, cost and stability are still problematic [325],... 

Applications of titania nanotube arrays have been focused up to now on (i) photoelectrochemical and water photolysis properties, (ii) dye-sensitized solar cells, (iii) photocatalysis, (iv) hydrogen sensing, self-cleaning sensors, and biosensors, (v) materials for photo- and/or electro-chromic effects, and (vi) materials for fabrication of Li-batteries and advanced membranes and/or electrodes for fuel cells. A large part of recent developments in these areas have been discussed in recent reviews.We focus here on the use of these materials as catalysts, even though results are still limited, apart from the use as photocatalysts for which more results are available. 

The formation of halohydrins can be promoted by peroxidase catalysts.465 Recently 466 it has been shown that photocatalysis reactions of hydrogen peroxide decomposition in the presence of titanium tetrachloride can produce halohydrins. The workers believe that titanium(IV) peroxide complexes are formed in situ, which act as the photocatalysts for hydrogen peroxide degradation and for the synthesis of the chlorohydrins from the olefins. The kinetics of chlorohydrin formation were studied, along with oxygen formation. The quantum yield was found to be dependent upon the olefin concentration. The mechanism is believed to involve short-lived di- or poly-meric titanium(IV) complexes. 

Zinc containing zeolites exhibit potential applications in optics, electronics, sensors and photocatalysis [1]. In catalytic applications, the addition of Zn produces an increase in both the catalytic activity and the selectivity towards aromatization of small alkanes in catalytic reforming reactions [2,3]. Zinc species promote dehydrogenation reactions avoiding the preferential removal of hydrogen by transfer to hydroearbon... 

Arthur J. Nozik is a senior research fellow with the Basic Science Division of the National Renewable Energy Laboratory (NREL). He received his B.S.Ch. from Cornell University in 1959 and his M.S. in 1962 and his Ph.D. in 1967 in physical chemistry from Yale University. Since receiving his Ph.D., Dr. Nozik has worked at NRL, where he has conducted research in nanoscience, photoelectrochemistry, photocatalysis, and hydrogen energy systems. He has served on numerous scientific review panels and received several awards in solar energy research. He is a senior editor of the Journal of Physical Chemistry, a fellow of the American Physical Society, and a member of the American Chemical Society, the American Association for the Advancement of Science, the Materials Research Society, the Society of Photo Optical Instrument Engineers, and the Electrochemical Society. 

For the last two decades, attention has been focused on redressing the ozone depletion in the earth s protective layer. It is believed that chlorine radicals dissociated from chlorofluorocarbons (CFCs), upon irradiation of sun s UV in the stratosphere, promotes the ozone depletion. Hence, in addition to development of CFC alternatives there is an urgent need for the safe disposal of CFCs. Several processes such as pyrolysis, incineration, photocatalysis, oxidative destruction over metal oxide or zeolite catalysts and destruction at very high temperatures ( by plasma technique ) are reported in the literature for the disposal of CFCs[ 1-5]. But all these processes yield harmful products like CO, HF/F2 etc. Catalytic conversion of chlorinated organics in presence of hydrogen seems to be a better technique as it yields either hydrofluorocarbons(HFCs) or hydrochlorofluorocarbons(HCFCs) whose ozone depletion potential is either zero or very low and yet most of these products act as CFC alternatives. 

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