Carbonate, photochemical reduction

Kuwabata S, Nishida K, Tsuda R, Inoue H, Yoneyama H (1994) Photochemical reduction of carbon dioxide to methanol using ZnS microcrystaUite as a photocatalyst in the presence of methanol dehydrogenase. J Electrochem Soc 141 1498-1503... 

Electrochemical reduction of carbon dioxide has found no extensive application so far, yet it is of great interest for scientists in the fields of theoretical and applied electrochemistry. To a certain extent, it is analogous to the photochemical carbon dioxide reduction, but it involves no chlorophyll and yields simpler products. In recent years some books and reviews on this topic have been published (e.g., Taniguchi, 1989 Sullivan et al., 1993 Bagotsky and Osetrova, 1995). 

Lehn and Ziessel166 have also developed systems for the photochemical reduction of C02. These systems are similar to those represented by Fig. 18. Visible-light irradiation of C02-saturated aqueous acetonitrile solutions containing Ru(bpy)2+ as a photosensitizer, cobalt(II) chloride as an electron acceptor, and triethyl-amine as a sacrificial electron donor gave carbon monoxide and... 

The photochemical reduction of particulate and of dissolved iron(III) is coupled to the oxidation of a reductant, i.e., of dissolved organic carbon. 

For a fuel, an electron source is needed. Water is the ultimate electron source from an economical point of view. Water photolysis is the simplest among the chemical conversion systems of solar energy. Photochemical reduction of nitrogen or carbon dioxide to produce ammonia or hydrocarbons with the electrons from water is also an attractive system of conversion. 

Although water photolysis is the simplest photochemical conversion system, carbon dioxide reduction is still an attractive research subject as a synthetic model for C02 reduction in photosynthesis. There are numerous reports on chemical and photochemical C02 reduction,245 but it is not the aim of this chapter to review these works. 

Photochemical reduction of C02 was also achieved in the presence of the p-type semiconductor (copper oxide) or silicon carbide electrodes [97]. Irradiation of this system generates methanol and methane as the main products in the case of CuO electrode whereas hydrogen (with efficiency about 80%), methanol (16%), methane, and carbon monoxide in the case of SiC electrode. Also Ti02/CuO systems appeared relatively efficient (up to 19.2% quantum yield) in photocatalytic C02 to CH3OH reduction [98]. 

The Mehler reaction is a photochemical reduction of O2 to H2O2 or H2O in photosystem I (Box 35.2). Mehler activity is thought to be a mechanism for energy dissipation under high tight intensities or when carbon frxation is limited by supply... 

The electrochemical or photochemical reduction of CO2, when catalyzed by ruthenium complexes, also produces formic acid derivatives. Furthermore, ruthenium-catalyzed electrochemical reduction of CO2 can provide carbon-carbon bond-forming reactions. Although at present the efihciency of such electrochemical and photochemical reactions does not appear to be satisfactory for use as a new tool in large-scale organic synthesis, the chemistry suggests that these methodologies may someday be useful in organic synthesis. 

Photochemical carbon dioxide reduction with metal complexes Differences between cobalt and nickel macrocycles... 

Our research focuses on mechanistic and kinetic studies of photochemical and electrochemical CO2 reduction that involves metal complexes as catalysts. This work makes use of UV-vis, NMR, and FTIR spectroscopy, flash photolysis, pulse radiolysis. X-ray diffraction, XANES (X-ray absorption near-edge spectroscopy) and EXAFS (extended X-ray absorption fine structure). Here we summarize our research on photochemical carbon dioxide reduction with metal macrocycles. 

The challenging photochemical reduction of carbon dioxide to formate is catalyzed by Ru" [111] (cf. Section 3.3.4). For example, with the 2,2 -bipyridine-ruthenium(II) complex the active species is formed by photolabilization. Water renders the system more efficient with quantum yields up to 15%. Methanol is the photoproduct when CO2 is reduced with Ti02 in propene carbonate/2-propanol... 

Trimethylene-2,2 -bi-l,8-naphthyridine with [Re(CO)5Br] in heptane gives the bidentately coordinated complex 27 (960M3463). Compounds of the same composition, [Re(CO)3(LL)Cl] (LL = 3,3,-dimethylene-2,2,-biquinoline) can be prepared similarly (94IC2341). / -(2,6-di-2-pyridyl-4-pyridyl)phenol reacts with [Re(CO)5Cl] and forms complex 28 with bidentate coordination of the ligand (92JPP(A)259). The product is active in the electro- and photochemical reduction of carbon dioxide. Species [Re(CO)3(2,7-bis(2,-pyridyl)-l,8-naphthyridine)Br] is known (83ICA(76)L29). 

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