Ruthenium oxide , pyrochlor

J.-M. Zen, C.-B. Wang, Oxygen Reduction on Ruthenium Oxide Pyrochlore Produced in a Proton Exchange Membrane, J. Electrochem. Soc. 141 (1994) 38-39. 

J.-M. Zen, C.-W. Wang, Determination of Dissolved Oxygen by Catalytic Reduction on a Nafion /Ruthenium Oxide Pyrochlore Chemically Modified Electrode, J. Electroanal. Chem. 368 (1994) 251—256. 

J.-M. Zen, A. S. Kumar and J.-C. Chen, Electrochemical Behavior of Lead-Ruthenium Oxide Pyrochlore Catalyst Redox Characteristics in Comparison with that of Ruthenium Dioxide, J. Mol. Catal. A Chem. 165 (2001) 177-188. 

An improved adsorption of DNA bases has been observed at a chemically modified electrode based on a Nafion/ruthenium oxide pyrochlore (Pb2Ru2-x FhxOj-y modified GC (CME). Nafion is a polyanionic perfiuorosulfonated ionomer with selective permeability due to accumulation of large hydrophobic cations rather than small hydrophilic ones. The Nafion coating was demonstrated to improve the accumulation of DNA bases, while the ruthenium oxide pyrochlore proved to have electrocatalytic effects towards the oxidation of G and A. The inherent catalytic activity of the CME results from the Nafion-bound oxide surface being hydrated. The catalytically active centers are the hydrated surface-boimd oxy-metal groups which act as binding centers for substrates [50]. 

Zen, J.M., Kumar, A.S., and Chen, J.C., Electrochemical behavior of lead-ruthenium oxide pyrochlore catalyst Redox characteristics in comparison with that of ruthenium dioxide, J. Mol. Catal. A, 165, 177, 2001. 

It should be noted that the exact cation stoichiometry of the product is highly sensitive to the exact metal concentration of the ruthenium source solution and temperature and pH of the reaction medium (inadvertent increases in both of these parameters lead to increased solubility of lead in the alkaline reaction medium and consequently yield solid products of lower lead ruthenium ratios). While synthesis of a pure lead ruthenium oxide pyrochlore is relatively easy, the precise cation stoichiometry of the product is a property that is not always easy to control. A relatively quick check on the cation stoichiometry of the lead ruthenium oxide product can be obtained, however, by using the correlation between lattice parameter and composition that is displayed in Fig. 1. When lattice parameter and cation stoichiometry are independently determined, the relationship shown in Fig. 1 also provides an assessment of product purity since data points that show significant departures from the displayed linear correlation indicate the presence of impurity phases. The thermal stability of the lead ruthenium oxides decreases with increasing occupancy of tetravalent lead on the octahedrally coordinated site, but all of the ruthenium oxide pyro-chlores described are stable to at least 350° in oxygen. 

Enzyme-like behavior was observed for electrocatalyt-ic oxidation on Nafion/lead-ruthenium oxide pyrochlore chemically modified electrodes.Nafion is loaded with lead(II) and ruthenium(III) cations by ion exchange, and then their oxides are prepared by in situ precipitation in such a way that the catalytically active sites remain... 

Zen J -M and Wang C W (1994) Oxygen reduction on ruthenium oxide pyrochlore produced in a proton exchange membrane, J. Electrochem. Soc., 141, pp. L51-L52. 

PbO , Lead oxide solid solns. with ruthenium oxide (RujOj), pyrochlore, 22 69... 

RU2O3, Ruthenium oxide, solid solns. with lead oxide Pb02, pyrochlore, 22 69 RU2O3C14H12, Ruthenium, p-carbonyl-p.-methylene-bis[carbonyl(it -cyclopen-tadienyl)-, 25 182... 

The catalysts are high surface area ruthenium pyrochlore oxides having the general formula A2+xRu2-x 7-y (A=Pb>Bi 0selective oxidation of cydohexane-1,2-diol to adipate (reaction 20) under mild conditions (25-95 13). 

T. R. Felthouse, P. B. Fraundorf, R. M. Friedman, and C. L. Schosser, Expanded lattice ruthenium pyrochlore oxide catalysts. I. Liquid-phase oxidations of vicinal diols, primary alcohols, and related substrates with molecular oxygen, J. Catal., 127 (1991) 393 120. 

A2Pt207, similar to those reported for tin, ruthenium, titanium, and several other tetravalent ions. Trivalent ions which form cubic platinum pyrochlores range from Sc(III) at 0.87 A to Pr(III) at X.14 A. Distorted pyrochlore structures are formed by lanthanum (1.18 A) and by bismuth (1.11 A). Platinum dioxide oxidizes Sb203 to Sb2(>4 at high pressure. The infrared spectra and thermal stability of the rare earth platinates have been reported previously and will not be repeated here, except to point out the rather remarkable thermal stability of these compounds decomposition to the rare earth sesquioxide and platinum requires temperatures in excess of 1200 °C. 

Vicinal diols have been cleaved with molecular oxygen using a ruthenium pyrochlore oxide catalyst. Cyclohexane-1,2-diol was oxidized to adipic acid in 72% yield with this catalyst system (Eqn. 21.38). Cyclohexanone was also converted to adipic acid under these conditions. 5... 

Perhaps the most important synthesis parameter affecting the crystallization of pyrochlore from alkaline solution is the oxidizing potential within the reaction medium. It is observed that this parameter has dramatic effects on both crystallinity and extent of ruthenium substitution by Pb . For example, a synthesis in which O2 is bubbled into the reaction medium will yield a well crystallized pyrochlore 2-3 times faster than a synthesis where O2 sparging is not provided. Crystalline pyrochlores cannot be obtained under any synthesis conditions (except those that are electrochemically assisted) when N2 sparging is used. The necessity for relatively oxidizing conditions in order to yield crystalline expanded pyrochlores is consistent with the hypothesis that these pyrochlores do... 

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