Platinum-ruthenium catalyst supported

It was seen when studying mixed systems Pt-WOj/C and Pt-Ti02/C that with increasing percentage of oxide in the substrate mix the working surface area of the platinum crystallites increases, and the catalytic activity for methanol oxidation increases accordingly. With a support of molybdenum oxide on carbon black, the activity of supported platinum catalyst for methanol oxidation comes close to that of the mixed platinum-ruthenium catalyst. 

Rauhe BR, Mclamon FR, Cairns EJ (1995) Direct anodic-oxidation of methanol on supported platinum ruthenium catalyst in aqueous cesium carbonate. J Electrochem Soc 142(4) 1073-1084... 

Figure 4.14. Arrhenius plot for methanol electrooxidation at 0.5 V vs. RHE using colloidal PtRu catalyst supported on Vulcan XC72. Electrolyte 1 M CH3OH - 0.5 M H2SO4. Scan rate 1 mV s . Pt Ru atomic ratios 2.33 1, , o 4 1 and Pt/C [96]. (With kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Elecfrooxidation of methanol at platinum-ruthenium catalysts prepared from colloidal precursors atomic composition and temperature effects, 33, 2003, 419-49, Dubau L, Coutanceau C, Gamier E, Leger J-M, Lamy C, figure 11.)...

Munke et al. [196] reported a technique (Figure 10.31) of in situ electrochemical FTIR and used it to study a real carbon-supported platinum + ruthenium catalyst. Different adsorptions were observed when methanol was electrooxidized at bulk Pt, Pt particles, and carbon-black-supported Pt -I- Ru electrodes, particularly with regard to the nature of the adsorbed CO species (Figure 10.32). 

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. 

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). 

Freifelder obtained an 82% yield of benzylhydrazine by hydrogenating a freshly prepared hydrazone over Pd-C in ethanol at 0.3 MPa H2 in less than 30 min.83 However, when the hydrazone was allowed to stand for several days to a week, the yield dropped to 45-48%. In the hydrogenation of phenylacetone hydrazone, Biel et al. observed that the formation of large amounts of jV,iV -bis(l -phenyl-2-propylidene)hydrazine took place when hydrogenation proceeded slowly and incompletely with such catalysts as Pd-C, rhodium, ruthenium, and platinum oxide, and with solvents such as alcohol, water, ethyl acetate, tetrahydrofuran, and dioxane. The A(A%disubstituted hydrazine was obtained when the hydrogenation proceeded slowly to completion, as over platinum oxide in aqueous acetic acid. With Raney Ni in ethanol, the azine and l-pheny-2-propylamine were formed almost exclusively. 1-Phenyl-2-propylhy-drazine was obtained in acceptable yields of 55-70% by use of platinum oxide or supported platinum in alcoholic acetic acid at a pressure of 13.8 MPa H2. The products obtained over platinum oxide in various conditions are summarized in eq. 8.40.78... 

The usefulness of rhodium catalysts is also seen in the hydrogenation of pyrogallol (eq. 11.19)101 and gallic acid (eq. 11.20)102 over 5% Rh-Al203 in ethanol. The all-m products were also obtained in higher yields than with supported palladium, platinum, or ruthenium catalysts. 

A homogeneous catalytic solution to the alcohol inhibition problem (see the discussion under Uncatalyzed chain reactions of the oxidation of alcohol intermediates, above) does not appear to have been found. However, the presence of a heterogeneous oxidative dehydrogenation catalyst has been reported to be effective in the direct oxidation of alcohols to carbonyls and acids [109, 110]. The mechanism probably involves preliminaiy heterogeneous (oxidative) dehydrogenation of carbinols to carbonyls. If the carbonyl is an aldehyde, it is readily converted to the acid. Platinum, palladium, ruthenium, rhodium, and iridium catalysts, supported on carbon, are reported to be active and selective catalysts for the purpose [109]. Promoters such as cobalt and cadmium have been reported to be effective additives. 

The reaction kinetics of the vapor-phase hydrogenation of benzene was studied on ruthenium, rhodium, palladium, and platinum catalysts supported on alumina at temperatures ranging from 25 to 225° and 1 atm. pressure. 

The catalytic activity of ruthenium, rhodium, platinum, and palladium catalysts supported on alumina for the vapor-phase hydrogenation of ben-... 

In all three MEAs the rate of methanol oxidation was facilitated by the platinum-ruthenium unsupported catalyst, which in the presence of CO as a byproduct of the reaction, exhibit an electrochemical activity higher than pure Pt. However, compared to Pt supported and unsupported catalysts, the electrochemically active surface area of PtRu alloys cannot be determined by hydrogen adsorption using cyclic voltammetiy due to the overlap of hydrogen and oxygen adsorption potentials, and the tendency for hydrogen to absorb in the ruthenium lattice [xvi]. However, under the same operation conditions, cyclic voltammetry can be used for qualitative estimation of the similarity in the PtRu anode layer properties. 

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