Iridium, colloidal

Platinum colloid use H2PtCl6 C H2O Iridium colloid use H2lrCl6 C 4H2O... 

Colloids of metals with practically zero overpotential for Hj evolution such as platinum and iridium are very efficient at catalysing production. The transferred electrons are immediately converted into adsorbed H atoms which then undergo the Heyrovsky reaction to form Hj e + H -h H2. The gold microelectrode... 

Mevellec, V., Roucoux, A., Ramirez, E., Philippot, K. and Chaudret, B. (2004) Surfactant-stabilized aqueous iridium(O) colloidal suspension an effident reusable catalyst for hydrogenation of arenes in biphasic media. Advanced Synthesis and Catalysis, 346 (1), 72-76. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

A new class of heterogeneous catalyst has emerged from the incorporation of mono- and bimetallic nanocolloids in the mesopores of MCM-41 or via the entrapment of pro-prepared colloidal metal in sol-gel materials [170-172], Noble metal nanoparticles containing Mex-MCM-41 were synthesized using surfactant stabilized palladium, iridium, and rhodium nanoparticles in the synthesis gel. The materials were characterized by a number of physical methods, showed that the nanoparticles were present inside the pores of MCM-41. They were found to be active catalysts in the hydrogenation of cyclic olefins such as cyclohexene, cyclooctene, cyclododecene, and... 

Metals or Metal Oxides. Explosions result on contact with Ni powder, Hg, colloidal Ag, thallium powder, Zn powder, PbO, Pb304, and Na202 violent decomposition occurs with barium peroxide, CuO, impure Cr03, iridium dioxide, Pb02, Mn02, and V205 and with Fe powder contaminated with a trace of Mn02.3... 

In alkaline solution the activity of the colloidal platinum increases to a maximum with increase of alkalinity, and then decreases. In this respect it behaves in an analogous manner to certain inorganic ferments.9 Exposure to Rontgen rays retards the reaction.10 Colloidal rhodium,11 palladium, iridium,12 silver, and gold behave in an analogous manner... 

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. 

A characteristic property of the platinum metals consists in tin1 readiness with which they admit of being prepared in the colloidal stale as hydrosols. These latter possess powerful catalytic properties, and their accelerating influence upon the rate of decomposition of aqueous solutions of hydrogen peroxide has been carefully studied. The most, powerful catalyscr is colloidal osmium, followed in order of decreasing activity by platinum, palladium, and iridium.1... 

Osmium palladium platinum and ruthenium iridium rhodium.1 It is interesting to compare this order with that found for the activity of the colloidal metals in regard to the decomposition of hydrogen peroxide. The change in position of the osmium is remarkable. 

Colloidal osmium readily undergoes oxidation it catalvtieally assists the oxidation of unsaturated compounds by gaseous hydrogen. In this respect it is stated to be even more effective than the finely divided metal, but less active than either platinum or iridium. Carbon monoxide combines with oxygen, yielding the dioxide, when shaken at ordinary temperatures with the hydrosol of osmium.7... 

Colloidal Iridium is readily obtained by reducing an aqueous solution of the chloride with hydrazine hydrate14 or sodium amalgam,15 in the... 

Colloidal iridium may also be prepared by Bredig s method, which consists in sparking between iridium electrodes immersed in ice-cooled water. A current of 20 to 25 amperes at 220 volts gives satisfactory results.2 The colour of the hydrosol ranges from red to black, according to the method of preparation. A small current favours the formation of the black solution. 

Colloidal iridium readily decomposes hydrogen peroxide solution, the reaction being, as with platinum, mono-molecular the rate of decomposition is approximately proportional to the concentration of catalyst. Alkali does not affect the reaction velocity, but dilute acids accelerate it. Hydrogen sulphide, mercuric chloride, and certain other substances act as poisons.3 Colloidal iridium is less active, however, than platinum. 

Iridium Sesquioxide, Ir2Os, is obtained by igniting iridium sulphite, or by heating an alkali chloriridate with twice its weight of carbonate. The product is washed -with hot water, and the colloidal residue treated with a solution of ammonium chloride to effect its coagulation, and finally with nitric acid and dried, the acid serving to remove the last traces of alkali.2... 

When heated above 400° C. iridium sesquioxide decomposes, yielding metallic iridium and its dioxide, a little oxygen being likewise liberated. It dissolves in hydrochloric acid, yielding a colloidal solution. 

Iridium dioxide also exists in colloidal form in solutions obtained by dissolving the amorphous oxide in hydrochloric acid. 

It is a black, colloidal substance, soluble in aqua regia, giving an iridium chloride, and decomposable at high temperatures, yielding metallic iridium. 

Ir(OH)3] precipitates as a result of the reaction between K3[IrCl6] and KOH under a C02 atmosphere. The product is usually colloidal, and ranges in colour from yellow-green to blue-black. Iridium(III) hydroxo species (including [Ir(OH)6]3 and [Ir(0H)5(H20)]2 are thought to be present in alkaline solutions of lr203.310... 

The newer type of colloidal catalysts have been prepared containing palladium (4), platinum (4), rhodium (5), and iridium (6). A variety of synthetic polymers has been applied. Among those tested were polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polymethyl methacrylate (PMMA), and polymethyl acrylate (PAMA). In general, polyvinyl alcohol (4a) has been found most satisfactory. 

Perhaps H atoms produced by the catalytic cracking of H2 can be converted at high pH to e aq, because colloidal iridium has been shown to possess a high activity for hydrogenation of aromatic compounds in strongly alkaline solution (31). 

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