Platinum with oxygen

Catalyst samples were pressed as a wafer in the stainless steel or perspex sample holder. It was calculated that, due to diffusion limitations, the aqueous samples needed at least 6 hours pretreatment in order to attain monolayer coverage of the platinum with oxygen or hydrogen throughout the sample. A pretreatment time of 20 hours was chosen. 

Hydroxylamine sulfate is produced by direct hydrogen reduction of nitric oxide over platinum catalyst in the presence of sulfuric acid. Only 0.9 kg ammonium sulfate is produced per kilogram of caprolactam, but at the expense of hydrogen consumption (11). A concentrated nitric oxide stream is obtained by catalytic oxidation of ammonia with oxygen. Steam is used as a diluent in order to avoid operating within the explosive limits for the system. The oxidation is followed by condensation of the steam. The net reaction is... 

Platinum Catalyst for Reductions (Coll. Vol. i, 452) Preparation from platinum black by heating with oxygen underpressure. Laffiteand Grandadam, Compt. rend. 200, 456 (193s). 

It is available commercially from several routes including as a product from the manufacture of sodium nitrate from sodium chloride and nitric acid, and from a process involving the passage of ammonia and air over heated platinum and treating the nitric oxide so formed with oxygen. 

In outline the procedure consists of carefully weighing about 5-10 mg of sample on to a shaped piece of paper (Fig. 3.11c) which is folded in such a way that the tail (wick) is free. This is then placed in a platinum basket or carrier suspended from the ground-glass stopper of a 500 mL or 1 litre flask. The flask, containing a few millilitres of absorbing solution (e.g. aqueous sodium hydroxide), is filled with oxygen and then sealed with the stopper with the platinum basket attached. 

Both rhodium (m.p. 1976°C, b.p. 3730°C) and iridium (m.p. 2410°C, b.p. 4130°C) are unreactive silvery metals, iridium being considerably more dense (22.65gem-3) than rhodium (12.41 gem-3), the densest element known apart from osmium. Both form fee (ccp) lattices and, like the other platinum metals, are ductile and malleable. Neither is affected by aqua regia and they only react with oxygen and the halogens at red heat. 

The fit of these equations to the data is very good, as seen in Fig. 18. These equations are valid to very small values of CO concentrations, where the reaction becomes first order with respect to CO. In a mixture of CO with oxygen, there should be a maximum in reaction rate when the CO concentration is at 0.2%, as shown in Fig. 19. When the oxidation of olefins and aromatics over a platinum loaded monolith is over 99% complete, the conversion of higher paraffins may be around 90% and the conversion of the intractable methane is only 10%. 

No experiments appear to have been made with such cells, although the equation has been verified with oxygen at different partial pressures in admixture with nitrogen, with platinum electrodes and hot solid glass as electrolyte (Haber and Moser). A similar case is that of two amalgams of a metal, of different concentrations, as electrodes, and a solution of a salt of the metal as electrolyte (G. Meyer, 1891). Here we must take the osmotic pressures of the metals in the amalgams, Pi, P2, and, for an 7i-valent metal ... 

Figure 1 shows AES data for the oxidized titanium surface before and after deposition of 30 X of platinum with the substrate held at 130 K. The platinum thickness was calculated from the attenuation of the oxygen AES signal assuming layered growth of the metal. From the spectra It Is clear that the platinum was sufficient to completely attenuate the underlaying features of the titanium oxide. 

Hwang JT, Chung JS. 1993. The morphological and surface properties and their relationship with oxygen reduction activity for platinum-iron electrocatalysts. Electrochim Acta 38 2715-2723. 

Except for dry incineration in a platinum crucible, oxygen-induced decomposition requires special apparatus in order to avoid the loss of volatile substances. Combustion of organic materials may be achieved with the... 

Platinum(II) Complexes with Oxygen-donor Ligands 709... 

There can be no doubt that even with a noble metal such as platinum, the surface can be heavily contaminated with carbon when the latter is used as a supporting material (51). This may be ameliorated by cautious treatment with oxygen which oxidizes this carbon impurity to carbon dioxide. Nevertheless, it is extremely doubtful if any platinum surface in platinum/carbon can be prepared without an appreciable, and perhaps substantial, amount of impurity. 

---