Platinum oxide composition

Other workers (165) used X-ray photoelectron spectroscopy (XPS) to examine the influence of ammonia oxidation on the surface composition of alloy gauzes. After several months on stream, the surface was covered by the same types of highly faceted structures noted by others. As illustrated in Fig. 14, XPS analysis provides evidence that the top microns, and in particular the top 100 A of the surface, were enriched in rhodium. This enrichment was attributed to the preferential volatilization of platinum oxide. The rhodium in the surface layers was present in the oxide form. Other probes confirm the enrichment of the surface in rhodium after ammonia oxidation (166). Rhodium enrichment has been noted by others (164, 167), and it has been postulated that in some cases it leads to catalyst deactivation (168). 

Hydrogenation of cinnamaldehyde to 3-phenylpropionaldehyde over palladium catalyst may be accompanied by the formation of 3-phenyl-1-propanol and propyl-benzene,218 although the formation of 3-phenylpropionaldehyde usually predominates.219,220 The composition of the products are widely affected by the nature of palladium catalysts, solvents, supports, and additives.216,221 The hydrogenation over Pd-Al203 in ethanol or over Pd-kieselguhr in acetic acid gave 3-phenylpropionalde-hyde quantitatively at room temperature and atmospheric pressure. The addition of a 1 1 ratio of ferrous chloride to palladium also resulted in quantitative formation of 3-phenylpropionaldehyde in the hydrogenation over 5% Pd-C in methanol.221 This result was contrasted with those obtained with platinum oxide where iron additives led... 

Hydrogenation of dihydrostreptobiosamine hydrochloride and of streptobiosamine hydrochloride with platinum oxide catalyst resulted in the absorption of one and two moles of hydrogen, respectively. Acetylation of the products yielded in each case a crystalline compound which, however, was not the expected heptaacetyltetrahydrostreptobiosamine, but a base hydrochloride of the composition CjaHjoOgN(CH3C0)6-HC1-CjHsOH. The mole of ethanol, which could not be removed by drying... 

Since on pure platinum, methanol oxidation is strongly inhibited by poison formation, bimetallic catalysts such as PtRu or PtSn, which partially overcome this problem, have received renewed attention as interesting electrocatalysts for low-temperature fuel cell applications, and consequently much research into the structure, composition, and mechanism of their catalytic activity is now being undertaken at both a fundamental and applied level [62,77]. Presently, binary PtRu catalysts for methanol oxidation are researched in diverse forms PtRu alloys [55,63,95], Ru electrodeposits on Pt [96,97], PtRu codeposits [62,98], and Ru adsorbed on Pt [99]. The emphasis has recently been placed on producing high-activity surfaces made of platinum/ruthenium composites as a catalyst for methanol oxidation [100]. 

PtO2 (752, 757), similar to some electrochemical oxygen layers. Figure 12 shows a possible structure of platinum oxides on various planes (752). The [1(X)] plane has a PtOj composition (752,757), while the bulk corresponds to a PtO oxide. Present information does not unambiguously point toward either surface oxide formation or chemisorption. Because of the apparent similarity of some surface oxygen species on catalysts and electrocatalysts, coordinated efforts in both fields using standardized techniques and procedures could resolve uncertainties. 

Timperman L, Lewera A, Vogel W, Alonso-Vante N (2010) Nanostructured platinum becomes alloyed at oxide-composite substrate. Electrochem Commun 12(12) 1772-1775... 

Manufacture of wire from platinum/metal oxide composites, T. Eckhardt, H. Manhardt, and D. F. Lupton, Materialwissenschaft und Werkstofftechnik, 2008, 12, 933. 

Wen TT, Xue C, Li Y et al (2012) Reduced graphene oxide-platinum nanoparticles composites based imprinting sensor for sensitively electrochemical analysis of 17 beta-estradiol. J Electroanal Chem 582 121-127... 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Silver-containing catalysts are used exclusively in all commercial ethylene oxide units, although the catalyst composition may vary considerably (129). Nonsdver-based catalysts such as platinum, palladium, chromium, nickel, cobalt, copper ketenide, gold, thorium, and antimony have been investigated, but are only of academic interest (98,130—135). Catalysts using any of the above metals either have very poor selectivities for ethylene oxide production at the conversion levels required for commercial operation, or combust ethylene completely at useful operating temperatures. 

Alloys with ruthenium Additions of ruthenium have a most marked effect upon the hardness of platinum, but the limit of workability is reached at about 15% ruthenium, owing to the fact that ruthenium belongs to a crystallographic system different from that of platinum. Apart from a somewhat greater tendency to oxide formation at temperatures above 800°C, the resistance to corrosion of ruthenium-platinum alloys is comparable to that of iridium-platinum alloys of similar composition. 

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

A sophisticated quantitative analysis of experimental data was performed by Voltz et al. (96). Their experiment was performed over commercially available platinum catalysts on pellets and monoliths, with temperatures and gaseous compositions simulating exhaust gases. They found that carbon monoxide, propylene, and nitric oxide all exhibit strong poisoning effects on all kinetic rates. Their data can be fitted by equations of the form ... 

---