Platinum on activated carbon

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Liquid-solid-gas where the solid is normally a catalyst such as in the hydrogeneration of amines, using a slurry of platinum on activated carbon as a catalyst. 

For selective oxidations in the carbohydrate field, Heyns and coworkers have investigated the use of platinum catalysts in different forms. For reactions in which further oxidation of the desired product is probable (as, for example, in the oxidation of ketose and pentose derivatives ), a milder catalyst of 5 to 10% platinum on activated carbon is recommended. Care must be taken in the preparation of the catalyst otherwise, it is difficult to obtain catalysts of reproducible activity. The platinum is deposited on the carbon by hydrogenation or by reduction with formaldehyde or hydrazine sulfate. The catalyst prepared through formaldehyde... 

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

Palladium and platinum (5—10 wt % on activated carbon) can be used with a variety of solvents as can copper carbonate on siHca and 60 wt % nickel on kieselguhr. The same is tme of nonsupported catalysts copper chromite, rhenium (VII) sulfide, rhenium (VI) oxide, and any of the Raney catalysts, copper, iron, or nickel. 

Liquid film state under reactive distillation conditions for the dehydrogenation of decalin on platinum supported on active carbon and boehmite... 

Once the reaction kinetics were determined and the appropriate reaction conditions were set, the analyses of different catalysts was launched. A variety of different heterogeneous catalysts were evaluated for the deprotection of 20 mmol Cbz-glycine (1, R=-H). Catalysts composed of different platinum group metals supported on activated carbon were evaluated as well as palladium supported on alumina. Figure 5 confirms that Pd supported on activated carbon is indeed the catalyst of choice for this type of hydrogenolysis reaction. 

Adora, S. Soldo-Olivier, Y. Faure, R. Durand, R. Dartyge, E. Baudelet, F. Electrochemical Preparation of Platinum Nanocrystallites on Activated Carbon Studied by X-ray Absorption Spectroscopy. J. Phys. Chem. B 2001, 103, 10489-10495. 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

It has been discovered that the performances of platinum and palladium catalysts may be improved by promotion with heavy metal salts. However, there is little information available about the role and chemical state of the promoter 8,9). We have recently found that a geometric blocking of active sites on a palladium-on-activated carbon catalyst, by lead or bismuth, suppresses the by-product formation in the oxidation of l-methoxy-2-propanol to methoxy-acetone 10). 

Commercial catalytic hydrogenations of unsaturated compounds use Raney nickel or—less commonly—Pt catalyst supported on active carbon. Electrocatalytic hydrogenation can be performed at platinized platinum or other platinum-metal electrodes. Adsorbed hydrogen atoms are the active reactant in catalytic as well as in electrocatalytic hydrogenation. 

The catalyst contained 10% platinum deposited on activated carbon. This high platinum content (20 times more than in the commercial catalyst) made the activity of the catalyst more stable, thus facilitating the studies of kinetics. The surface of platinum in 1 g of the catalyst measured by hydrogen chemisorption was 2 m2. Since the concentrations of H2 and NO in the... 

The foregoing discussion serves to show that disordered carbon structures are oxidized more readily than well-ordered graphite planes and that dislocations and active sites provide nucleation points for attack of the carbon crystallite. Another factor that must be considered is that dispersed electrocatalysts, such as platinum, on the carbon surface are not benign. The electrocatalysts interact with the carbon causing local oxidation or corrosion, i.e., the platinum catalyzes the corrosion of the carbon itself. In the presence of oxygen, which is the condition under which the electrocatalyst will operate, reduction intermediates from the oxygen (e.g., HOj) can have an accelerated corrosion effect. 

Palladium, Pd, and platinum, Pt, usually on activated carbon or asbestos, are catalysts for the dehydrogenation of hydroaromatic and some heterocyclic compounds to aromatic compounds. The reaction takes place at high temperatures (300-350 °C), and consequently, side reactions such as rearrangements often take place [495, 496, 497, 945, 946, 947, 948], The catalytic dehydrogenations played a very important role in the elucidation of terpene and alkaloid structures. Because spectroscopic methods, especially NMR spectroscopy, can help to determine structures much more reliably, catalytic dehydrogenation over palladium and platinum are rare nowadays. 

Figure 11 shows conversion to iso-heptanes to be negligible for (0.5 wt. %) platinum supported on activated carbon (Pt/C) as the only catalyst, and also for (0.4 wt. %) platinum on silica-gel (Pt/Si02). No detectable conversion was obtained with silica-alumina. A mechanical mixture of either of the Pt-bearing particles with silica-alumina of about 150 m.Vg-surface area, both in millimeter diameter particle size (1000m), immediately resulted in appreciable isomerization ( SiAl with Pt/C SiAl with Pt/Si02). Isomerization increases rapidly for smaller component particle sizes, of 70/i and S i diameters. It approaches the performance of a silica-alumina that has been directly impregnated with platinum, and which has... 

Z.D. Wei, H.T. Guo, Z.Y. Tang, Methanol electro-oxidation on platinum and platinum-tin alloy catalysts dispersed on active carbon. J. Power Sources 1996, 58(2), 239-242. 

In the patent specification [147] there data on the chemical attachment to hydridesilica surface in the presence of the Reney nickel, chloroplatinic acid or metallic platinum deposited on activated carbon as a catalyst of the following unsaturated functional compounds divinylbenzene, ethylene glycol diacrylate, acetylene, allyl alcohol, allyl glycidyl ether, allyl isocyanate, acrylic acid. The chemical reactions result in the transformation of Si-H bonds of hydridesilica surface into Si-C bonds. Such transformations may be also classified as processes of solid-phase catalytic hydrosilylation of functional olefins. 

Macias-Perez, M.C., Salinas Martinez de Lecea, C., and Linares-Solano, A. (1997). Platinum supported on activated carbon cloths as catalyst for nitrobenzene hydrogenation. Appl. Catal. A Gen., 151, 461-75. 

Oxygen Electrocatalytic Properties Oxygen Reduction. Figure 8 compares steady-state polarization curves for the electroreduction of Op on a typical pyrochlore catalyst, Pb2(Rui.42Pbo.53)06.5 15 w/o platinum on carbon. The latter was considered representative of conventional supported noble metal electrocatalysts. The activities of both catalysts are quite comparable. While the electrodes were not further optimized, their performance was close to the state of the art, considering that currents of 1000 ma/cm could be recorded, at a relatively moderate temperature (75 C) and alkali concentration (3M KOH). Also, the voltages were not corrected for electrolyte resistance. The particle size of the platinum on the carbon support was of the order of 2 nanometers, as measured by transmission electron microscopy. 

Catalytic oxidation of vicinal diols to a-hydroxy carboxylates was performed by Prati and Rossi [82] in alkaline aqueous solution with gold-based catalysts prepared by deposition-precipitation with sodium carbonate from HAUCI4 solutions on active carbon suspension. The 1 % Au/C catalysts had remarkable properties compared with conventional Pt/C and Pd/C catalysts in terms of selectivity and stability. Thus, Table 1 shows that at pH 8,1,2-propanediol was very selectively oxidized to lactic acid, which indicates that gold was more selective than platinum and palladium in the oxidation of the primary alcohol function. The activity of gold catalysts was also very stable as a function of conversion or after several recycles, indicating that gold is less sensitive to over-oxidation and/or self-poisoning than platinum and palladium. 

Platinum supported on niobium oxide phases also exhibits high activity for oxygen reduction, despite a 50 to 150 fold decrease in platinum compared to the standard 10 weight % platinum on Vulcan carbon. 

Figure 15.12 Platinum vanadium on activated carbon catalyst for the selective hydrogenation of nitroaromatic groups. The percentages present the yield of the desired product.

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