Platinum/carbon

Diacetone-L-sorbose (DAS) is oxidized at elevated temperatures in dilute sodium hydroxide in the presence of a catalyst (nickel chloride for bleach or palladium on carbon for air) or by electrolytic methods. After completion of the reaction, the mixture is worked up by acidification to 2,3 4,6-bis-0-isoptopyhdene-2-oxo-L-gulonic acid (2,3 4,6-diacetone-2-keto-L-gulonic acid) (DAG), which is isolated through filtration, washing, and drying. With sodium hypochlorite/nickel chloride, the reported DAG yields ate >90% (65). The oxidation with air has been reported, and a practical process was developed with palladium—carbon or platinum—carbon as catalyst (66,67). The electrolytic oxidation with nickel salts as the catalyst has also... 

Fig 1. Electron micrograph of a platinum/carbon replica prepared by the fast-freeze, deep-etch, rotary-shadow replica technique printed in reverse contrast. Cell walls of onion parenchyma have an elaborate structure with many thin fibres bridging between thicker cellulosic microfibrils. Scale bar represents 200nm. 

The catalyst layer is the most expensive part of this fuel cell. It is made from a mixture of platinum, carbon powder, and PEM powder, bonded to a conductive carbon fiber cloth. We obtained ours from E-Tek Inc. The cost for an order of their ELAT catalyst cloth sheet includes a setup charge. So get together with others for a larger order if you want to keep costs down. We paid 360 for a piece of ELAT 15.2 centimeters by 15.2 centimeters [6 inches by 6 inches] including the 150 setup charge. This piece provides enough for about twelve disks. Each fuel cell requires two disks of ELAT and one larger disk of PEM to make the sandwich, so you can make six cells from this size... 

In the future it may be possible to reduce the cost by putting the catalyst coating directly on the PEM with a platinum-carbon ink, as practiced by Los Alamos National Laboratory. 

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. 

The temperature dependence of the selectivity for isomerization versus hydrogenolysis depends on the type of catalyst. Thus, over thick platinum film catalysts this selectivity was temperature independent for the reaction of the butanes and neopentane (24). However, in Boudart and Ptak s (122) reaction of neopentane over platinum/carbon the selectivity to isomerization decreased slightly with increasing temperature while Kikuchi et al. (128) found an increased trend for isomerization in the reaction of n-pentane over platinum/silica and platinum/carbon catalysts. 

Chemically, the platinum-carbon bond in iodo(trimethyl)-platinum(IV) is relatively nonreactive and is unaffected by water or oxygen. The iodine atoms may be replaced by other ions through simple metathetical reactions. 

The samples of BR-reconstituted vesicle (100 pg BR/1.5 mM lipid) were quick-frozen using the technique of Heuser [23], and fractured in a Balzers BAF 400D freeze-fracture apparatus (Balzers, Liechtenstein). The replicas were obtained by rotary shadowing with platinum/carbon of ca. 7 nm thick and carbon of ca. 25 nm, and then examined in a Philips CM200 Ultra Twin electron microscope at 200 kV. 

Electrochemical Instrumentation. For the Ru complexes, a 1 cm diameter platinum disk brazed onto a brass holder was used as a working electrode. It was masked with ChemGrip (a teflon based epoxy) except for the upper face. Prior to use, it was polished with 1 micron diamond paste (Buehler) and rinsed with water, acetone and methanol. The working electrode for each Os complex was the uppermost platinum layer of a platinum/carbon layered synthetic microstructure (LSM) (Energy Conversion Devices). The LSM consisted of 200 layer pairs of carbon and platinum whose thicknesses were 24.4 and 17.0 A, respectively and where platinum was the outermost layer. The LSM was placed in 1.0 M H2SO4 and cleaned... 

C Counter or Platinum, carbon or steel Similar to the Must be larger than W... 

Fig. 14.17 Relative current density for various anode compositions as a function of increasing CO concentrations added to a pure hydrogen feed to the anode / re = 840 mA cm-2, at 0.5 V, for platinum/carbon.

Lin, Y., et ah, Platinum/carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells. The Journal of Physical Chemistry B, 2005. 109(30) p. 14410-14415. 

Trimm, D. L. and B. J. Cooper. 1973. Propylene hydrogenation over platinum/carbon molecular sieve catalysts. J. Cat. 31 287-92. 

The triphenylphosphine complex 42 b reacts with bromine to give a platinum(IV) species 42f, assigned the cyclic structure with four platinum-carbon c-bonds. The reaction sequence here must begin with the attack of a bromine molecule on an uncoordinated olefin, as otherwise it is hard to see why two metal-carbon bonds are formed, and not one metal-carbon and one metal-bromine. 

Contrary to previous reports suggesting colloidal metal as the active species in Pt-catalyzed hydrosilylations, the catalyst was found to be a monomeric platinum compound with silicon and carbon in the first coordination sphere.615 The platinum end product at excess olefin concentration contains only platinum-carbon bonds, whereas at high hydrosilane concentration, it is multinuclear and also contains platinum-silicon bonds. An explanation of the oxygen effect in hydrosilylation was also given to show that oxygen serves to disrupt multinuclear platinum species that are formed when poorly stabilizing olefins are employed. 

The reaction in Eq. 13.5 can be thought of as an electrophilic attack by HgtUiotvlhe platinum-carbon bond. The oxidative addition reaction shows oxidation of Pt(II) to Pt(lV) with simultaneous expansion of the coordination number of Pt from A to 6. 

Platinum-carbon bond cleavage can be photoinduced. The photoinduced reductive elimination of cyanoalkanes from ftwis-PtH(R)(PPh3)2 (R = CH2CN, (CH2)2CN, (CH2)3CN) involves initial isomerization to the cis isomer prior to reductive elimination.563 Photolysis of platinacyclopentanes gives alkanes and alkenes.564... 

Assume that a disk-shaped electrode (gold, platinum, carbon, etc.) has been coated with a Film of poly (vinyl ferrocene) (Table 13.2). This can be accomplished by dissolving the polymer in chloroform, applying a drop of the solution to the electrode surface, and allowing the solvent to evaporate. The electrochemistry of the resulting polymer film-coated electrode can be investigated using the same electrochemical cell and equipment as described in the previous example. 

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