Pyrochlores ruthenate

Lead-Ruthenate Pyrochlore Modified Nafion Membrane for Tunable Heterogeneous Catalytic Oxidation... 

Lead-Ruthenate Pyrochlore Modified Nafion Membrane. 

S. Venkatesan, A. S. Kumar, J.-M. Zen, A Rugged Lead-ruthenate pyrochlore Membrane Catalyst for Highly Selective Oxidation of Alcohols, J. Mol. Catal. A Chem. 250 (2006) 87-93. 

Increasing the temperature of synthesis results in enhanced crystallinity as would be anticipated because of improved reaction kinetics. However, this observation is also consistent with a crystallization mechanism involving solubility. Furthermore, as the temperature increases so does the equilibrium concentration of lead in solution thus with all else held constant, increased temperature of reaction results in a smaller lattice parameter for the product lead ruthenate pyrochlore. 

One additional parameter that affects the solubility of lead ruthenate pyrochlores in alkali is the extent of lead substitution on the B-site. The greater the substitution (i.e. the larger x is in formula 1), the higher the solubility of the pyrochlores is in alkali 2). If it is assumed that a solution-reprecipitation mechanism of synthesis is operative, the stoichiometry-dependent solubility could explain why it becomes significantly more difficult to crystallize lead ruthenate directly out of alkaline solution when x <0.3. 

Figure 9 illustrates the O2 electroreduction activity of a number of lead ruthenate pyrochlores, Pb2(Ru2-xPbx)06.5> here 0 < x < 1.0. These data demonstrate that catalysts of roughly equivalent activity can be synthesized over the entire compositional range. In two examples where the activity was noticeably lower (x = 0.04 and x 0.98), the synthesis conditions were such that the surface areas of... 

---