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April, 1945 POLAROGRAPHIC REDUCTION OF THE PLATINWM METALS 547 in size of the central atom or to radical differences in the reaction mechanism. The first possibility can be better evaluated only when more data are available on additional members of the tetra-alkyl groups. As for the second alternative, a more thorough examination of the decomposition of tetraethyl lead would undoubtedly yield valuable information concerning its mechanism and energy of activation.summary The thermal decomposition of tetramethyltin has been investigated between 440 and 493" over a range between 5 and 185 mm. initial pressure.By the criteria of half-life periods, times for a given fractional pressure increase and initial rates, the reaction was found to be predominantly of the first order above 80 mm. initial pressure. At lower initial pressures the order increases, approaching that of second.The specific velocity constant of the prima process was found to be KO = 8.32 X 1021 e-82,400/R?Rate constants calculated by an indirect method agreed well with those obtained directly. The reaction was found to be homogeneous once the reaction vessel was thoroughly coated with a deposit of tin and carbon.Nitric oxide produced no inhibition but instead caused a slight catalytic acceleration of the primary process.Chemical analyses made over the entire range of decomposition revealed the predominant gaseous product to be methane, together with some hydrogen and ethylene. Tin and carbon were also found as a deposit on the walls.Based upon the kinetic data and the chemical analyses, a probable reaction mechanism was proposed.An explanation is offered for the changes in activation energy observed in going from the methyl to ethyl to propyl tetra-alkyls thus far investigated.In a previous communication' the polarographic reduction of rhodium compounds was discussed in detail. In the present paper similar work is extended to the other platinum metals. With the exception of a recent paper on the polarographic reduction of osmium tetroxide12 the only published work in this field seems to be that dealing with catalytic hydrogen waves produced in acid solutions containing small amounts of the platinum metal chlorides.304Theory It was shown in the previous paper' that although rhodium trichloride itself was rapidly decomposed by mercury, complex salts of *rhodium could be obtained which were stable toward rnercury, and which were reducible a t the dropping electrode. In the present work it is shown that the other platinum metals also form stable complexes, which in some cases give polarographic steps.In order to calculate n, the number of electrons involved in each reduction step, the IlkoviP equation was applied and the log plot calculated in the previously described way. As explained before, in the calculation of the diffusion coefficient of a complex metal ion conductivity data for similar (1) Willis, THIS JOURNAL, 66, 1067 (1944). (2) Crowell, Heyrovsky, and Engelkemeir, iLid., 68, 2888 (1941). (3) Herasymenko and Slendyk, Coll. Cscch. Chem. Comm....

Nickel catalysts, supported on alumina, silica, and molybdena, have been prepared by impregnation and co-crystallization. In the precursor state the catalysts were characterised by UVÈvisible spectroscopy, thermogravimetric analysis/di †erential thermal analysis (TGA/DTA), and X-ray photoelectron spectroscopy (XPS). The nickel was principally in the 2] oxidation state with an octahedral coordination. However, the ligand sphere surrounding the nickel ion was sensitive to the support, indicating that the species on the di †erent supports were not identical thus suggesting a metal complexÈsupport interaction. Reduction was followed by temperature programmed reduction (TPR) and TGA, the results of which indicated that reduction and decomposition of nickel nitrate occurred simultaneously. X-ray di †raction (XRD) analysis revealed that, with the sample, no hydrogen bronze was formed on reduction. The reduced catalysts were Ni/MoO 3 characterised by carbon monoxide chemisorption, carbon dioxide chemisorption, and by reaction of buta-1,3diene with dihydrogen. In the absence of a dihydrogen stream it was found that the catalysts adsorbed no carbon monoxide due the presence of sub-monolayer quantities of surface oxygen. The extent of the oxygen was quantiÐed by exchange with isotopically labelled carbon dioxide. Di †erences in the electronic nature of the nickel between the sample and the other catalysts were revealed by their behaviour towards buta-1,3-Ni/MoO 3 diene hydrogenation.