Metal supported platinum-ruthenium catalysts

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

The choice of the metals is strictly related to the catalytic application. As we shall show later, the catal54ic reaction most commonly investigated with polymer supported M / CFP catalysts is hydrogenation (Table 3). The overwhelming majority of catalytic studies concerns the hydrogenation of alkenes and by far the most commonly employed metal is palladium, followed by platinum. Examples of rhodium and ruthenium hydrogenation catalysts supported on pol5uneric supports are very rare. 

The most widely used method for adding the elements of hydrogen to carbon-carbon double bonds is catalytic hydrogenation. Except for very sterically hindered alkenes, this reaction usually proceeds rapidly and cleanly. The most common catalysts are various forms of transition metals, particularly platinum, palladium, rhodium, ruthenium, and nickel. Both the metals as finely dispersed solids or adsorbed on inert supports such as carbon or alumina (heterogeneous catalysts) and certain soluble complexes of these metals (homogeneous catalysts) exhibit catalytic activity. Depending upon conditions and catalyst, other functional groups are also subject to reduction under these conditions. 

Palladium gave the highest activity of all the platinum group metals evaluated platinum, rhodium and ruthenium exhibited very poor activity. The choice of support was also demonstrated to be very important the activated carbon supported Pd catalyst showed a nearly fourfold increase in activity than did Pd supported on alumina. 

The feasibility of carbon-supported nickel-based catalysts as the alternative to the platinum catalyst is studied in this chapter. Carbon-supported nickel (Ni/C, 10 wt-metal% [12]), ruthenium (Ru/C, 10 wt-metal% [12]), and nickel-ruthenium composite (Ni-Ru/C, 10 wt-metal%, mixed molar ratio of Ni/Ru 0.25,1,4, 8, and 16 [12]) catalysts were prepared similarly by the impregnation method. Granular powders of the activated carbon without the base pretreatment were stirred with the NiCl2, RuC13, and NiCl2-RuCl3 aqueous solutions at room temperature for 24 h, respectively. Reduction and washing were carried out in the same way as done for the Pt/C catalyst. Finally, these nickel-based catalysts were evacuated at 70°C for 10 h. 

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. 

The co-existence of at least two modes of ethylene adsorption has been clearly demonstrated in studies of 14C-ethylene adsorption on nickel films [62] and various alumina- and silica-supported metals [53,63—65] at ambient temperature and above. When 14C-ethylene is adsorbed on to alumina-supported palladium, platinum, ruthenium, rhodium, nickel and iridium catalysts [63], it is observed that only a fraction of the initially adsorbed ethylene can be removed by molecular exchange with non-radioactive ethylene, by evacuation or during the subsequent hydrogenation of ethylene—hydrogen mixtures (Fig. 6). While the adsorptive capacity of the catalysts decreases in the order Ni > Rh > Ru > Ir > Pt > Pd, the percentage of the initially adsorbed ethylene retained by the surface which was the same for each of the processes, decreased in the order... 

The per cent of dicyclohexylamine formed in hydrogenation of aniline increases with catalyst in the order ruthenium < rhodium platinum, an order anticipated from the relative tendency of these metals to promote double bond migration and hydrogenolysis (30). Small amounts of alkali in unsupported rhodium and ruthenium catalysts completely eliminate coupling reactions, presumably through inhibition of hydrogenolysis and/or isomerization. Alkali was without effect on ruthenium or rhodium catalysts supported on carbon, possibly because the alkali is adsorbed on carbon rather than metal (22). 

Physico-chemical and catalytic properties of zirconia supported ruthenium and ruthenium-platinum catalysts were investigated. In order to improve the ruthenium stability a second noble metal, namely platinum, was introduced into the catalyst. Ten catalysts, consisting of zirconia supported Ru and/or Pt were prepared. 

Investigation of supported ruthenium phase stability was based on atomic absorption spectroscopy (AAS) measurements of the active metal loading variation in catalysts caused by different pre-treatment procedures. Ruthenium stabilisation in the presence of platinum was verified by temperature programmed reduction (TPR) experiments. Finally, the stabilising influence of Pt on Ru catalysts was evidenced using methylcyclopentane (MCP) hydrogenolysis as model reaction. 

The modification of platinum catalysts by the presence of ad-layers of a less noble metal such as ruthenium has been studied before [15-28]. A cooperative mechanism of the platinurmruthenium bimetallic system that causes the surface catalytic process between the two types of active species has been demonstrated [18], This system has attracted interest because it is regarded as a model for the platinurmruthenium alloy catalysts in fuel cell technology. Numerous studies on the methanol oxidation of ruthenium-decorated single crystals have reported that the Pt(l 11)/Ru surface shows the highest activity among all platinurmruthenium surfaces [21-26]. The development of carbon-supported electrocatalysts for direct methanol fuel cells (DMFC) indicates that the reactivity for methanol oxidation depends on the amount of the noble metal in the carbon-supported catalyst. 

We are investigating bifunctional catalysts in which one component of the catalyst adsorbs or oxidizes CO and the other component dissociates water. Our present research is focusing on metal-support combinations to promote this bifunctional mechanism. The metallic component is chosen to adsorb CO at intermediate adsorption strengths (platinum [Pt], Ru, palladium [Pd], PtRu, PtCu, cobalt [Co], ruthenium [Ru], silver [Ag], iron [Fe], copper [Cu], and molybdenum [Mo]). The support is chosen to adsorb and dissociate water, typically a mixed-valence oxide with redox properties or oxygen... 

This new single-step synthesis unites the simplicity of preparation and lower production costs, with the outstanding properties of the final catalysts. By the single-step procedure proposed here, deposition of dispersed nanoparticles of noble metals on ceramic supports with customised textural properties and shape was achieved. Noble metals including platinum, palladium, rhodium, ruthenium, iridium, etc. and metal oxides including copper, iron, nickel, chromimn, cerium oxides, etc on sepiolite or its mixtures with alumina, titania, zirconia or other refractory oxides have been also studied. 

Coq, Figueras and their associates have conducted wide-ranging investigations of surface modification of supported platinum, rhodium, and especially ruthenium catalysts by treating them when hydrided with alkyl compounds of aluminium, zinc, antimony, germanium, tin or lead. The purpose of this work was to explore the locations of the modifying atoms on the surface of the active metal particles, and to see whether in any case there was evidence for the selective blocking of sites on either low co-ordination number... 

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