Hydrocarbons photocatalytic oxygenation

A mechanism has been proposed to explain the heterogeneous photocatalytic oxidation of hydrocarbons in oxygen-containing solutions at platinized Ti02. This is based on the photogeneration of hydroxyl radicals at the Ti02 surface [equations (2)—(4), where h" = hole]. However, another paper suggests that the... 

Photocatalytic Oxygenation of Hydrocarbons on T OJ ron-Porphyrin Hybrid Catalysts. 

The C—H bond can be activated by a metal complex, particularly when the complex plays the role of catalyst or photocatalyst. The reactions of hydrocarbons with metal complexes occur at low temperatures and can be selective. There are different pathways for C—H bond activation (i) by low-valence metal complexes, (ii) by high-valent metal-oxo compounds, (iii) by molecular oxygen and oxygen atom donors, (iv) by biological oxidation, or (v) by photocatalytic enhancement (21). 

UV irradiation of Ti02 containing a sufficient amount of H2O in the presence of unsaturated hydrocarbons such as CsHg and C4H6 leads to the formation of hydrogenolysis reaction products and oxygen-containing products (214, 242, 243). As shown in Fig. 52, the rates of these photocatalytic reactions increase when the ionization potential of the reactants decreases (224). 

Photocatalytic activation of allyl and benzyl ethers results either in carbon-carbon coupling or oxygenation [148-151]. The photocatalyst used for these conversions can be generated in situ, by photolysis of a zinc dithiolene salt, by preformed catalysts, or by particles supported within surfactant vesicles. Radical intermediates formed by hydrogen abstraction by photogenerated hydroxyl or hy-droperoxyl radicals may also be important in the photoelectrochemically induced oxidation of hydrocarbons. In the Ti02-sensitized photooxidation of toluene to cresols, for example, a photo-Fenton (radical) type mechanism has been suggested [150]. ... 

Figure 28. Photocatalytic hydrocarbon oxidation using visible light and molecular oxygen.

In situ FTIR and diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) studies deal mainly with photocatalytic oxidation or reduction of nitric oxide (NO) as important pollutant and green house gas as well as the depollution or selective oxidation of organics such as olefinic, aliphatic, aromatic, and oxygenated hydrocarbons. 

The carbonylation of hydrocarbons serves as an important catalytic methodology both for extending the carbon backbones of organic compounds and for adding oxygen functional groups such as alcohols, aldehydes or carboxylic acids. Hydroformylation of alkenes (eq. 23) is carried out in various thermal catalysis schemes [87] and photocatalytic examples have been described (see below) [88,89],... 

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