Iridium oxidation reactions

Depending on the fabrication techniques and deposition parameters, the pH sensitive slope of IrOx electrodes varies from near-Nemstian (about 59 mV/pH) to super-Nemstian (about 70mV/pH or higher). Since the compounds in the oxide layers are possibly mixed in stoichiometry and oxidation states, most reported iridium oxide reactions use x, y in the chemical formulas, such as lr203 xH20 and IrOx(OH)y. Such mixed oxidation states in IrOx compounds may induce more H+ ion transfer per electron, which has been attributed to causing super-Nerstian pH responses [41],... 

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Significant distinction in rate constants of MDASA and TPASA oxidation reactions by periodate ions at the presence of individual catalysts allow to use them for differential determination of platinum metals in complex mixtures. The range of concentration rations iridium (IV) rhodium (III) is determined where sinergetic effect of concentration of one catalyst on the rate of oxidation MDASA and TPASA by periodate ions at the presence of another is not observed. Optimal conditions of iridium (IV) and rhodium (III) determination are established at theirs simultaneous presence. Indicative oxidation reactions of MDASA and TPASA are applied to differential determination of iridium (IV) and rhodium (III) in artificial mixtures and a complex industrial sample by the method of the proportional equations. 

Fig. 26. Cyclic voltammogram of a thick anodic iridium oxide film (AIROF) in 0.5 mol L 1 H,S04. The reaction mechanism for coloration and Oz evolution is indicated.

Although the redox reaction mechanisms of iridium oxide are still not clear, most researchers believe that the proton exchange associated with oxidation states of metal oxides is one of the possible pH sensing mechanisms [41, 87, 100, 105], During electrochemical reactions, oxidation state changes in the hydrated iridium oxide layer are... 

Considering the H+ dependent redox reaction between two oxidation states of the iridium oxide as the basis of the pH sensing mechanism, the electrode potential changes to the hydrogen ion concentration are expressed by Nemstian equation ... 

Following on from stochiometric iridium-based C-H functionalizations, iridium-catalyzed reactions have been developed and can be combined with oxidation chemistry to enable the selective functionalization of aromatics. Moreover, these reactions can be performed under solventless conditions (Equations (91) and (92)). ... 

IRC (intrinsic reaction coordinate analysis), 45 Iridium oxide, amperometry, 650 Iron(II) compounds... 

Other electrocatalysts were considered for the electrooxidation of ethanol, such as rhodium, iridium or gold, " " leading to similar results in acid medium. The oxidation of ethanol on rhodium proceeds mainly through the formation of acetic acid and carbon monoxide. Two types of adsorbed CO are formed, i.e., linearly-bonded and bridge-bonded, in a similar amount, at relatively low potentials, then leading rapidly to carbon dioxide when the rhodium surface begins to oxidize, at 0.5-0.7 V/RHE. On gold in acid medium the oxidation reaction leads mainly to the formation of acetaldehyde. " " ... 

In the Ir-AljOa system migration does not play a role in crystallite growth when heating in an oxygen environment above 713 K. Sintering was inhibited by BaO, CaO, and SrO up to 923 K oxidative stabilization of iridium crystallites is consistent with the formation of an immobile surface iridate by reaction between a mobile molecular iridium oxide species and the well dispersed Group IIA oxide. 

The addition of ruthenium(lV) or iridium(lV) chloride complexes increased the rate of the oxidation reaction leading to the formation of the chloroalkanes [65], The selectivity of the oxidation in the presence of ruthenium(IV) (1° 2° ... 

Molecular oxygen adducts of transition metal complexes arc of interest and importance to catalytic processes and commercial oxidation processes, as well as being intermediates in oxidation reactions. Vaska " has reviewed the nature of dioxygen bound to transition metal complexes. All known iridium dioxygen complexes possess the peroxo structure (140). Experimental data reveal that the formation of covalent Ir—(O2) bonds on dioxygen addition to IrL, is accompanied by extensive redistribution of electrons, and the electron transfer is from the iridium to dioxygen. SCF-X -SW calculations on [Ir(02)(Ph3)4] and [Ir(Ph3)4] " indicate peroxo -metal bonding. ... 

Vukovic M. (1987) Oxygen evolution reaction on thermally treated iridium oxide films. J. appl. Electrochem. 17, 737-745. 

In Figure 14.4, the iridium oxidation state increases from (I) to (111), and the coordination number increases from 4 to 6. The new ligands add in a cis or trans fashion, with their orientation a function of the mechanistic pathway. The expansion of the coordination number of the metal brings the newly added ligands into close proximity to the original ligands this can enable reactions to occur between them. Such reactions are encountered frequently in the mechanisms of catalytic cycles. 

Morris ND, Suzuki M, Mallouk TE (2004) Kinetics of electron transfer and oxygen evolution in the reaction of Piu(bpy)3] with colloidal iridium oxide. J Phys Chem A... 

Although oxidation reactions of this type are generally associated with square-planar four-co-ordinate complexes, there are several examples of oxidative addition to five-co-ordinate species. In these systems, however, the mechanism may also be termed as oxidative elimination since the product is six co-ordinate and one of the ligands is displaced. The mechanism of silicon hydride addition to hydridocarbonyltris(triphenyl-phosphine)iridium(i) has been described, the reaction... 

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