Photocatalytic hydrogenation of organic compounds

Photocatalytic hydrogenation of organic compounds in membrane reactors... 

Suggest additives apart from hydrogen peroxide that can accelerate photocatalytic oxidation of organic compounds in aqueous suspensions of Ti02-... 

The use of a photocatalytic system in the hydrogenation of organic compounds makes... 

For each subject, the author s opinion is presented about the practical consequences for the photocatalytic removal of organic compounds or, in the case of Ti02 with metal deposits, for hydrogen formation. 

Many fewer photocatalytic organic reductions have been reported. Reductions of organic substrates are less thoroughly studied, largely because of the early emphasis on the use of organic compounds as oxidizable source for the production of hydrogen gas. Nonetheless, some examples do exist, such as the hydrogenation of olefins, vinyl ethers, and a, S-unsaturated enones and alkynes [166, 167]. Similarly, other multiple bonds can be reduced, e.g., the N=N double bond of diaryl azo compounds [168] or carbonyl C=0 bonds [169, 170]. 

At present, several stable photocatalytic systems for production of hydrogen from water and organic compounds are made of semiconducting oxides and suitable proton reducing catalyzer. An efficient electron transfer between inorganic semiconductor and bacterial hydrogenase was shown to result in hydrogen photoproduction. 

Photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated (Sun and Pignatello, 1995). In addition to the dominant hydroxyl radical mechanism, Sun and Pignatello found evidence that direct hole oxidation may be the mechanism for the photocatalytic degradation of some organic compounds. The assumed mechanism for this oxidation is H+ acting as an electron-transfer oxidant, while O behaves like a free OH and abstracts H or adds to C=C multiple bonds. Hole oxidation has been used to explain the oxidation of oxalate and trichloroacetate ions, which lack abstractable hydrogens or unsaturated C-C bonds. Whether the reaction... 

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