Catalysts, for carbon dioxide reduction

Rasmussen, S.C., Richter, M.M., Yi, E., Place, H. and Brewer, KJ. (1990) Synthesis and characterization of a series of novel rhodium and iridium complexes containing polypyridyl bridging ligands Potential uses in the development of multimetal catalysts for carbon dioxide reduction. Inorg. Chem., 29, 3926—3932. 

Use of Stoichiometric Reactions in the Design of Redox Catalyst for Carbon Dioxide Reduction... 

Photochemical reduction systems (Figure 5.11) require efficient light harvesting, usually by a so-called dye or sensitizer, and efficient charge separation and energy utilization. Transition metal complexes, particularly tris(2,2 -bipyridine)ruthenium(ll), serve as sensitizers. The overall reaction carried out must be a useful one. That is, in addition to carbon dioxide reduction, the complementary oxidation process (which provides the electrons) should be a desirable one. Both reduction and oxidation processes generally require catalysis. For carbon dioxide reduction, a number of the catalysts used in electrochemical systems are also effective in photochemical systems, as outlined below. 

For synthetic fuels or energy-storage media to be produced electrochemically, it is necessary that the carbon dioxide reduction be conducted at potentials only slightly (not more than by 0.2 V) more negative than the corresponding equilibrium potential. To do this requires extensive research aiming at refining the catalysts and the conditions for this process. 

Fuel cell applications Manganese dioxide as a new cathode catalyst in microbial fuel cells [118] OMS-2 catalysts in proton exchange membrane fuel cell applications [119] An improved cathode for alkaline fuel cells [120] Nanostructured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell [121] Carbon-supported tetragonal MnOOH catalysts for oxygen reduction reaction in alkaline media [122]... 

Selective carbon dioxide reduction to CO has been accomplished in a non-aqueous medium that includes tricarbonyl (2,2 -bipyridinium) rhenium , /ac-Re(bpy) (CO)3X (X=Cl, Br) as light-active component and homogeneous catalyst for C02 reduction [183-185]. In dimethylformamide solutions that include TEOA as sacrificial electron donor, photosensitized reduction of C02 to CO proceeds with a quantum efficiency of

Mechanistic investigations have revealed that reductive ET quenching of the rhenium complex (Eq. (54)) yields the catalytic intermediate active in deoxygenation of C02. It has been suggested that carbon... 

Japanese researchers [248] have designed an apparatus for the electrochemical reduction of carbon dioxide employing ultrasound. The apparatus comprises an electrolytic cell containing C02-dissolved electrolytic solution, a porous Pt-group metal anode, a proton-conductive solid electrolyte having a porous metal cathode used as a catalyst for the electrochemical reduction of COz on one side and a second anode on the other side facing oppositely to the cathode, and an ultrasonic vibrator. C02 can be reduced effectively for a long time. 

Electrocatalysis at metal electrodes in aqueous (1.2) and non-aqueous ( ) solvents, phthalocyanine ( ) and ruthenium ( ) coated carbon, n-type semiconductors (6.7.8),and photocathodes (9,10) have been explored in an effort to develop effective catalysts for the synthesis of reduced products from carbon dioxide. The electrocatalytic and photocatalytic approaches have high faradaic efficiency of carbon dioxide reduction (1,6). but very low current densities. Hence the rate of product formation is low. Increasing current densities to provide meaningful amounts of product, substantially reduces carbon dioxide reduction in favor of hydrogen evolution. This reduction in current efficiency is a difficult problem to surmount in light of the probable electrostatic repulsion of carbon dioxide, or the aqueous bicarbonate ion, from a negatively charged cathode (11,12). 

Current developments in carbon dioxide reduction research is not enough for the real implementation of the process. The maximum yield has been reached up to some micromoles. Let s look at the present scenario, with the current pace, 1.1 x 108 kg of TiC>2 would be required for the production of methanol from carbon dioxide and water, assuming a catalyst activity of 1 pm ol product gcat 1 h"1 and production rate 1kg s"1 [19]. 

When Ag and Pd porphyrins were employed as catalysts for the electrochemical reduction of CO2 in dichloromethane, H2, and oxalic acid were the detected products, Table 7.4, the latter being a rare product. Qiu and Sawyer reported that alkalyated iron and cobalt porphrins dianioins electrocatalytically reduce carbon dioxide to give CO and... 

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