Platinum-carbon, catalysts, structure

Catalytic hydrogenation has been applied to materials of widely varying molecular weights and structures. Thus, materials such as wood, rubber, vitamins, proteins, steroids, elastomers, cotton linters, and nylon are typical of the variety of compounds subjected to the reaction. Further, nitric oxide on hydrogenation over a platinum-carbon catalyst yields hydrox-ylamine—such a process has commercial possibilities. 

It is well established that oxygen in the presence of platinum (Adams catalyst) can achieve specific oxidation of secondary alcohols by a preferential attack upon hydrogen in an equatorial position (25). Catalytic oxidation of methyl a- and /3-D-galactopyranoside (26), fallowed by catalytic reduction with hydrogen, led to the formation of methyl a- and /3-6-deoxy-D-galactopyranoside (D-fuco-pyranoside) in 15% and 35% yield, respectively. This oxidation-reduction sequence with selective oxidation at carbon 4 as the initial step is structurally closely related to the above described pathway for TDPG-oxidoreductase. 

H. E. van Dam, A. P. G. Kieboom, and H. van Bekkum, Platinum/carbon oxidation catalysts. 7. Glucose-1-phosphate oxidation on platinum-on-carbon catalysts side-reactions and effects of catalysts structure on selectivity, Reel. Trav. Chim. Pays-Bas, 108 (1989) 404 107. 

Hydrogenation of 4-diisopropylamino-2-phenyl-2-pyridin-2-yl-butyramide over platinum oxide catalyst reduced the pyridine ring to a piperidine to give 4-diisopropylamino-2-phenyl-2-piperidin-2-yl-butyramide as a white solid, MP 107°-108°C. Structure was confirmed by proton, carbon-13-NMR spectra and by elemental analysis. 

The electro-catalytic oxidation of hydrogen, and reduction of oxygen, at carbon supported platinum based catalysts remain essential surface processes on which the hydrogen PEM fuel cell relies. The particle size (surface structure) and promoting component (as adsorbate or alloy phases) influence the activity and tolerance of the catalyst. The surface chemical behavior of platinum for hydrogen, oxygen, and CO adsorption is considered, in particular with respect to the influence of metal adsorbate and alloy components on close packed and stepped (defect) platinum surfaces. Dynamical measurements (employing supersonic molecular beams) of the... 

A.B. Kooh, W.J. Han, R.G. Lee, R.F. Hicks "Effect of Catalyst Structure and Carbon Deposition on Heptane Oxidation over Supported Platinum and Palladium", J. Catal. 130, 374-391,1991. 

Figure 9-2 shows the discharge curve of borosilicate electrode versus the standard carbon electrode of the H-Tec fuel cell. The load across the fuel cell for this test is 10 Q, resulting in a discharge of 100 mA cm. The cermet electrode demonstrates minimal increases of impedance over the discharge period and the higher overall voltage. The maximum developed by borosihcate substrate is 0.3489 V. This demonstrates that Ag metallization with a platinum/ruthenium catalyst can be developed as a cathode structure in DMFCs. 

For many years it has been well known that CO electrooxidation on platinum is a structure-sensitive reaction. Studies with singlecrystal electrodes have shown that the kinetic parameters depend not only on the surface composition of the catalyst but also on the symmetry of the surface and that the presence of steps and defects alters significandy the reaction rate. As a consequence, the surface structure of the nanoparticles should also affect the performance for the oxidation of CO. Understanding how the different variables affect CO oxidation on Pt nanoparticles dispersed on carbon requires the control of the platinum surface in a similar way as has been achieved for single-crystal electrodes. In this sense, the influence of the surface site distribution on CO oxidation using nanoparticles of well-defined... 

Active carbons have played a key role in heterogeneous catalysis as support of precious novel nanoparticles (NPs), such as palladium, platinum, and gold. Starting in the 1990s, novel allotropic forms of carbon displayed better-defined structure than active carbons. They are available widely in nature and can be supplied commercially. This has triggered an interest for comparing active carbons with carbon allotropes until finally controls have been shown that these carbons have intrinsic active sites. The chapter covers state of the art in the use of graphene either as carbon catalyst or as support of metal NPs. 

To improve effectiveness of the platinum catalyst, a soluble form of the polymer is incorporated into the pores of the carbon support structure. This increases the interface between the electrocatalyst and the solid polymer electrolyte. Two methods are used to incorporate the polymer solution within the catalyst. In Type A, the polymer is introduced after fabrication of the electrode in Type B, it is introduced before fabrication. 

Carbon corrosion and platinum dissolution in the acidic electrolyte at elevated temperatures are well recognized from the early years of research on PAFCs and are definitely relevant to HT-PEMFCs based on the acid-doped FBI membranes. Both mechanisms are enhanced at higher temperatures and higher electrode potentials. This should be taken into account when platinum alloy catalysts are considered for the HT-PEMFC. More efforts are also needed to develop resistant support materials based on either structured carbons or non-carbon alternatives. 

Anodes are usually very similar to, if not identical to those that serve as cathodes. Anodes that operate on reformed-hydrocarbon fuels, which contain some carbon monoxide, generally utilize a platinum-alloy catalyst to enhance co-tolerance. The catalyst-layer structure is sometimes altered between anodes and cathodes to adjust their respective hydrophobicity and reactant-diffusion properties. The thickness of the catalyst layer typically ranges from 10 to 20 tm, that of the substrate from 0.1 To 0.5 mm (uncompressed). 

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