Palladium on graphite

The catalyst used throughout this study was a 1% w/w palladium on graphite powder (S.A. 10 mV ) supplied by Johnson Matthey. 2-nitroacetophenone, 3-nitroacetophenone and 4-nitroacetophenone (all Aldrich >99 %) were used without further purification. No significant impurities were detected by GC. Gases (BOG, >99.99 %) were used as received. 

The use of catalysts that are supported on a solid phase is becoming increasingly popular. Such procedures allow for catalyst recycling and also reduce the levels of palla-dium/phosphine contamination in the final product. The use of palladium on graphite or alumina has been reported to be effective for catalyzing the reaction between allyl acetate and the enolate derived from diethylmalonate. ... 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

The reduction of 2- and 4-cyanopyridine to the aminomethylpyridine was mentioned in Part I. 3-Aminomethylpyridine has been prepared from 3-cyanopyridine in an electrocatalytic reduction in aqueous hydrochloric acid solution, using an electrode consisting of a thinly deposited layer of palladium black on graphite. The reduction proceeds with electrolytically generated hydrogen not via an electron transfer to the substrate.418... 

Table 1 compares the results from the selective hydrogenation of citral, at a variety of pressures and temperatures in both ionic liquids and organic solvents using palladium supported on carbon (Pd/C) and platinum supported on graphite (Pt/G). It is clear that the ionic liquid systems are highly selective solvents for the reduction of C=C without any reduction of the carbonyl group over palladium and similar selectivities can be achieved for the carbonyl group over platinum. 

A slurry catalyst of palladium supported on graphite is used and the liquid phase reaction is carried out at 170 C (340°F) and 10-17 bars (150-250 psig). Three reactors are used in series and overall conversions of 99.9% are achieved. The catalyst is recovered from the reactor effluent by centrifugation and recycled to the first reactor. 

ILs have been used in the electrosynthesis of nanostructures the preparation of various metallic nanoparticles, such as palladium [14], iridium [15], or semiconductor nanoparticles, such as stable Ge-nanoclusters [16], have been described. In some cases, wire-like structures were obtained, for instance Ti nanowires formed on graphite by electroreduction, as described by Freyland et al. [17]. In aU these cases, mainly the large electrochemical window and the relatively high polarity of ILs are exploited. 

Noble metals are eatalytieally very active, and many studies have been earried out on their surfaces, espeeially platinum, palladium, and rhodium. Noble metals have been used as polycrystalline metals or monocrystals, metal blacks, metals supported on graphite, microparticles ineorporated into redox active polymers, ete. The activity of these materials towards the electrocatalytieal hydrogenation depends mainly on the nature of the metal, pH, and supporting electrolyte, and the state of the surface. 

The direct electrooxidation of aqueous E>-g]uconic acid to l>arabinose on graphite has been performed in a very simple apparatus which may be suitable for practical application. The electrocatalytic oxidation of sucrose on smooth, lead-modified platinum electrodes has been examined with a view to finding experimental conditions for the selective electrosynthesis of value-added compounds. A paper in Bulgarian on the electrooxidation of diacetone-L-sorbose at low current densities in a nickel oxide electrolizer has been publi ed. The influence of the rize of palladium particles and their location on the support on their activity in the oxidation of glucose has been examined. An investigation of the effect of tonperature and pH on the platinum-catalysed oxidation of sucrose showed that changes in temperature affect mainly the reaction rate, where changes in pH alter the selectivity. ... 

Scheuermann GM, Rumi L, Sterner P, Bannwarth W, Miilhaupt R (2009) Palladium nanoparticles on graphite oxide and its functionalized graphene derivatives as highly active catalysts for the Suzuki—Miyaura coupling reaction. J Am Chem Soc 131 8262-8270... 

Umani-Ronchi and his co-workers have prepared various new active metals that consist of highly dispersed palladium or nickel on graphite and which selectively catalyse the semi-hydrogenation of acetylenes to Z-olefins. A different catalyst for the same process can be prepared by successive treatment of chloromethylated polystyrene beads with anthranilic acid and palladium chloride. Alternatively, acetylenes can be reduced to Z-oIefins by a catalytic transfer process using sodium phosphinate as the hydrogen donor and an easily prepared lead- or mercury-modified palladium catalyst. ... 

Gopakumar TG, Lackinger M, Hackcat M, Miller F, Hietschold M (2004) Adsmption of palladium phthalocyanine on graphite STM and T.EED study. J Phys Chem B 108 7839-7843... 

Electron-beam physical vapor deposition (EB-PVD) of rhenium on graphite has been demonstrated at The Pennsylvania State University. With EB-PVD technology, two or more materials ean be co-evaporated or deposited in layers to form functionally tailored coatings with improved properties and performance. Because rhenium is compatible not only with carbon but with platinum, palladium, ihodium, ruthenium, osmium, and iridium, it follows that EB-PVD technology can produce coatings with improved rhenium properties. For instance, deposition by electron-beam co-evaporation of rhenium with iridium will most likely provide high-temperature oxidation resistance. (Note that, presently, high-temperature, 2500 K, oxidation resistance is commercially achieved by vapor deposition of 50- to 250-pm-thick iridium films on rhenium.2... 

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

On the other hand, the inclusion of electrocatalytically active metal nanocrystals (graphite-supported palladium, platinum, and ruthenium or gold nanocrystals) allowed... 

The palladium and magnesium nitrates modifier has a substantial equalising effect on the atomisation temperature of the nine elements investigated. The optimum atomisation temperature for all but one element (thallium) is between 1900 and 2100 °C. This means that all elements can be determined at a compromise atomisation temperature of 2100 °C with a minimum sacrifice in sensitivity. Such uniform conditions for as many elements as possible are of vital importance if simultaneous multielement furnace techniques are envisaged. Moreover, in conventional graphite furnace AAS, uniform conditions for a number of elements can greatly facilitate and simplify daily routine analysis. 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

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