Iridium black

The results obtained with nickel raised the question whether the relation found between rate of exchange and particle size holds also for other metals of group VIII. We therefore carried out the benzene-D2 reaction on some iridium catalysts widely differing in particle size. We chose iridium because we knew from earlier experiments that iridium black gives a very characteristic cyclohexane isotopic distribution pattern with a maximum for C6H4Ds, whereas the patterns of Ni, Ru, Pd, and Pt show a maximum for the d6 compound. 

Two of the three catalysts, viz, Ir-8 and Ir-45, have also been used in the infrared experiments. Ir-600 is an iridium-black catalyst. Figure 15 shows the cyclohexane isotopic distributions for the iridium catalysts. 

Iridium black is only slightly soluble in aqua regia. When fused with alkalies and alkaline nitrates or NuTT. the metal is converted to an aetd-soluhle form. The metal at red heal reacts to a small extent with O., S. and P. At elevated temperature, die metal is attacked by CL and F-When fused with NaCl and treated with Cli, the water-soluble sodium hexachloroiridaletIVi. NadrCI,.. is formed. 

Iridium Black.204 Iridium(III) hydroxide is reduced in water at 90°C and 8 MPa H2 for 40 min, in the same way as in the preparation of osmium black. The iridium(III) hydroxide is prepared by adding an aqueous lithium hydroxide solution dropwise to an 1% aqueous solution of water-soluble iridium(III) chloride, IrCl3 3H20, at 90-95°C until the pH of the solution becomes 7.5-7.8 under stirring. By keeping the solution at the same temperature under stirring, the precipitate of iridium(III) hydroxide is separated out from its colloidal solution. The precipitate is collected, washed repeatedly with hot water, and then dried in vacuo. 

The substrate (0.5 ml) was hydrogenated over 5 mg of iridium black in 7 ml t-BuOH at 80°C and 4.9 MPa H2. The same catalyst, prepared from the iridium hydroxide precipitated at pH 7, was used throughout the experiments. 

Indium Black consists of an indefinite mixture of finely divided iridium and its oxides,12 and is obtained by reducing iridium compounds. For example, the sesquioxide dissolved in alkaline solutions yields a deposit of iridium black on boiling with alcohol, the latter being oxidised to formic acid and aldehyde. 

Iridium black is soluble in aqua regia, and like its platinum analogue possesses considerable catalytic activity.13 For example, it converts ozone into oxygen, hypochlorites into chlorides, and free oxygen and chlorine water into hydrochloric acid and oxygen. 

Iridium black has been used for producing a black colour in the decoration of porcelain.5... 

By dissolving iridium black or the dioxide in hydrochloric acid. The solution is concentrated and any trichloride converted into tetrachloride by addition of aqua regia. The product is dried in vacuo, whereby a brownish black amorphous residue is obtained which is very hygroscopic and soluble in water. 

CATALYSTS Chlorotrisftriphenylphos-phine)rhodium(I). (S)-a-(R)-2-Di-phenylphosphinoferrocenyl ethyldl-methylamine. Hydridotrisftriisopropyl-phosphine)rhodium(I). Iridium black. 2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane. Lindlar catalyst. Nickel-Alumina. Palladium catalysts. Raney nickel. Rhodium oxide-Platinum oxide. 

Hydrogenation catalyst. Iridium black is a highly selective hydrogenation catalyst. Yamamoto and Sham used this catalyst to effect the remarkably stereoselective (>98%) hydrogenation of 1 to 2. Mixtures of stereoisomers are obtained when 1 is hydrogenated with palladium on charcoal or Raney nickel. 

Halogen Electrodes.—The determination of the standard potentials of the halogens is simple in principle it involves measurement of the potential of a platinum electrode, coated with a thin layer of platinum or iridium black, dipping in a solution of the halogen acid or a halide, and surrounded by the free halogen. The uncertainty due to liquid junction can be avoided by employing the appropriate silver-silver halide or mercury-mercurous halide electrode as reference electrode. In practice, however, difficulties arise because of the possibility of the reactions... 

Iridium black effects the stereoselective ( 98%) complete hydrogenation of 4 to 5, whereas mixtures of isomers are obtained when 4 is hydrogenated with Pd-on-carbon or finely divided Ni ... 

Hydrogenation of the tricyclic diene 1 over palladium on carbon yields the product of 1,4-addition with a tetrasubstituted double bond 2, which is extremely resistant to further hydrogenation. In contrast, hydrogenation with Adams catalyst affords 9-pupukeanone (3)5. Iridium black as catalyst gives the latter product with excellent diastereoselectivity (yield not reported d.r. >98 2)6. 

Iridium black like rhodium black has been used in producing black colours in the decoration of porcelain. 

Challenges in the Assembly of Membrane Electrode Assemblies for Regenerative Fuel Cells using Pt/C, Iridium Black, and lr02 Catalysts... 

Use of Unsupported Anode Catalysts (Iridium Black) and the Effect of Water Flow Rate and Water Purity... 

FIGURE 8.8 (a) MEA 28 and 29 current density measured at 40°C, and (b) comparison of the current density for various MEA made with iridium black as the anode catalyst using a potential of —1.7V. 

This series of MEAs did not show any improvement over the iridium black catalyst (MEAs 25, 28, and 29) and is either due to the GDL, catalyst loading on the GDL, catalysts dispersion method or the different catalysts used. Iridium oxide catalysts have been shown to outperform iridium black, and Pt/C catalysts in SPE electrolyzers [1,2,7,18,21], and the loadings between the different MEAs were similar, thus the likely difference is due to the use of the Etek GDL. 

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