Platinum oxidation

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on siHca or alumina (50). The operating temperatures range from 500—595°C... 

Platin-oxyd, n. platinum oxide, specif, platinic oxide, platinum(IV) oxide. -oxydul, n. platinous oxide, platinum(II) oxide, -oxy-dulverbindung, /. platinous compoimd, platinum (II) compound, -oxydverbindung, /. platinic compound, specif, platinum (IV) compound. 

M. Peuckert, and H.P. Bonzel, Characterization of oxidized platinum surfaces by X-ray photoelectron spectroscopy, Surf. Sci. 145, 239-259 (1984). 

M. Peuckert, and H. Ibach, Vibrational spectra of an oxidized platinum electrode, Surf. Sci. 136, 319-326(1984). 

Angerstein-Kozlowska H, Conway BE, Sharp WBA. 1973. Real condition of electrochemically oxidized platinum surfaces 1. Resolution of component processes. J Electroanal Chem 43 9 36. 

See Other METAL OXIDES, OXIDANTS, PLATINUM COMPOUNDS... 

Data from Ref. 126, obtained using an oxidized platinum rotating disk working electrode at 1 mM sample and 10 mM Et4NC104 in dry CH3CN at a rotation speed of 25 s... 

Electrochemical Syntheses of Partially Oxidized Platinum Complexes 13... 

ELECTROCHEMICAL SYNTHESES OF PARTIALLY OXIDIZED PLATINUM COMPLEXES... 

Fig. 28. Data recorded for CO oxidation on platinumfl 1 0) with an STM in a flow reactor. The upper panel shows mass spectrometer signals recorded directly from the reactor cell. The STM images show the surface morphology at different stages, corresponding to the curves in the mass spectrometer signal. High CO oxidation activity was correlated with the observation of a rough, oxidic platinum surface. With permission from Reference (163).

Similar to (SN)t in their one-dimenston.il conductivity properties arc the stacked columnar complexes typified by [Pl(CN)j i. These square planar ions adopt a closely spaced parallel arrangement, allowing for considerable interaction among the d i orbitals of the platinum atoms. These orbitals are normally filled with electrons, so in order to get a conduction band some oxidation (removal of electrons) must take place. This may be readily accomplished by adding a little elemental chlorine or bromine to the pure tetracyanoplatinate salt to get stoichiometries such as K-.[Pt(CN)jBr0, in which the platinum has an average oxidation state of +2.3. The oxidation may also be accomplished electrolytically. as in the preparation of Rbj(Pt(CN)4J(FHF)04 (Fig. 16.8). which has a short Pt—Pi separation. The Pt—Pt distance is only 280 pm. almost as short as that (bund in platinum metal itself (277 pm) and in oxidized platinum "pop complexes (270 to 278 pm see Chapter l5).4- Cold-bronze materials of this type were discovered as early as 1842. though they have been little understood until recent times. The complexes behave not only as one-dimensional conductors, but... 

Rotating optically semii-transparent electrodes for spectroelectro-chemical or photoelectrochemical studies can be fabricated by vapour deposition techniques on a quartz substrate. In this way, tin oxide, platinum and gold electrodes, amongst others, can be made. Electrical contact is with silver paint. 

Platinum(ll) hydroxide is made by adding KOH to a solution of platinum 11) chloride. 1 he unstable black powder is easily oxidized by air and must therefore be handled in an inert atmosphere. In hoi alkali or HC1, it disproportionates into the platinum(IV) compound and the metal. Very careful dehydration results in tire formation of a gray pov/dcr that approaches the composition of platinum(II) oxide. Platinum(II) oxide can also be made by combining the elements at 420 440 C at an 0> pressure of 8 atm. 

CH3OH molecules, which is facilitated by the spontaneous hydration of these proton exchanged oxides. Platinum loading enhances the activity for all compounds. Considerable activity has been observed towards 02 evolution from aqueous AgN03, though the activity is much less than that of Ti02. This is attributed to the intercalated Ag4 cations that work probably as recombination centers for electrons and holes. 

The rubidium salt Rbii67[Pt(C204)2]1.5H20 (RbOP) is a compound exhibiting a commensurate 2kF structure and, therefore, the distortion of the Pt chain has been determined precisely.66 The unit cell contains a distorted nonlinear sixfold Pt atom chain and involves six fPt(C204)2]1-67" units in one repeating unit of 17.11 A. There are three independent Pt—Pt distances of 2.716, 2.830 and 3.015 A. The Pt—Pt distance of 2.717 A is the shortest spacing so far observed in partially oxidized platinum complexes and it is shorter than the 2.77 A interatomic distance in Pt metal. 

F. Sperner and W. Hohmann, Rhodium-Platinum Gauzes for Ammonia Oxidation, Platinum Metals Review. Volume 20, Number 1, DD. 2-20 (1976). 

Some cases of catalyst deactivation by over-oxidation platinum leaching, platinum particle growth and site coverage during reductive pretreatment as well as during reaction were presented for the oxidation of ethanol and methyl-a-D glucopyranoside (MGP) in combination with the use of various catalyst characterization techniques. 

For spectroelectrochemical and photoelectrochemical studies, optically semi-transparent electrodes have been fabricated by vapour deposition techniques on glass or quartz substrates (Chapter 12). Tin and indium oxides, platinum, and gold have been used. 

The investigations of platinum pyrochlores have demonstrated the effectiveness of high pressure techniques in the synthesis of anhydrous oxides when one or both reactants have limited thermal stability. The bulk of the work reported here represents a continuation of an exploration of metal oxide-platinum oxide systems at high pressure. 

Voorhees and Adams141 obtained an active platinum black from the platinum oxide prepared by fusing a mixture of chloroplatinic acid and sodium nitrate at 500-550°C. The platinum oxide is readily reduced to an active black with hydrogen in a solvent in the presence or absence of substrate. The platinum oxide-platinum black thus prepared has been shown to be very active in the hydrogenation of various organic compounds and is now widely used as Adams platinum oxide catalyst. Frampton et al. obtained a platinum oxide catalyst of reproducible activity by adding a dry powder of a mixture of 1 g of chloroplatinic acid and 9 g of sodium nitrate in its entirety to 100... 

Platinous Oxide, Platinum Monoxide, PtO, is produced2 in the anhydrous condition in the form of superficial blackening when platinum, either in the form of sponge or of thin foil, is heated m dry oxygen at about 450° 0., the product containing as much as 43 per cent, of oxide. 

---