Organic compounds semiconductor-catalyzed

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. 

K. Tokumaru, H. Sakuragi, T. Kanno, T. Oguchi, H. Misawa, Y. Shimamura and Y. Kuriyama, in Semiconductor-Catalyzed Photoreactions of Organic Compounds, M.A. Fox ed., ACS Symposium Series No. 278, American Chemical Society, Washington, D.C. (1985), p. 43. 

In recent years, W/O microemulsions have found numerous applications as microreactors for specific reactions (for comprehensive reviews, see Refs. 94 and 95). Thus, it has been shown that hydrophilic enzymes can be solubilized without loss of enzymatic activity and used to catalyze various chemical and photochemical reactions [96,97]. Other interesting applications involve the polymerization of solubilizates in microemulsions [98] and the preparation of micro-porous polymeric materials by polymerization of single-phase microemulsions [99]. Furthermore, microemulsions have been used as microreactors for the synthesis of nanosized particles for various applications [93,95] such as metal clusters (Pt, Pd, Rh, Au) for catalysis [100,101], semiconductor clusters [102-104] (ZnS, CdS, etc.), silver halides [105], calcium carbonates, and calcium fiuoride [106]. Recently it was shown [107,108] that it is possible to use W/O microemulsions for the control of polymorphism of water-soluble organic compounds. In most of these appUcations, one or more reactants are solubilized within a microemulsion and then a reaction is initiated. Depending on its molecular structure. 

Stimulated by the early work of Bard et al. on the Ti02-catalyzed photo-Kolbe reaction [36], many papers appeared in subsequent years dealing with photocatalytic organic reactions [115] in the presence of colloidal or suspended semiconductor particles. They include cis-trans isomerizations [68, 93, 116-119], valence isomer-izations [120, 121], substitution and cycloaddition reactions [73, 80, 122-125], oxidations [126, 127], and reductions [128-130]. Characteristic of all these reactions is that in almost all cases well known compounds were formed, which were not isolated but only characterized by spectroscopic methods. The nature of the products can be rationalized within the mechanistic scheme of semiconductor photocatalysis type A, which means that at least one reduced and one oxidized compound are... 

The three types of solids, metals, covalent semiconductors or insulators, and ionic compounds (including oxides) have characteristic surface reactions. In organic catalysis only metals and ionics are considered (Table 6.5), while in CVD all three types of solid surfaces are of interest. Metals absorb hydrogen and nitrogen dissociatively while ionic substrates have redox reactions or acid/base reactions with molecules. Oxidation of gases is often catalyzed by the surface of metal oxides. So is deposition of oxides by oxidation and hydrolysis of metal-containing precursors. When mixed oxides (e.g., perovskites) are deposited care must be taken to ensure a sufficient availability of the separate components. 

---