Platinum-free catalysts

Hence, the rate depends only on the ratio of the partial pressures of hydrogen and n-pentane. Support for the mechanism is provided by the fact that the rate of n-pentene isomerization on a platinum-free catalyst is very similar to that of the above reaction. The essence of the bifunctional mechanism is that the metal converts alkanes into alkenes and vice versa, enabling isomerization via the carbenium ion mechanism which allows a lower temperature than reactions involving a carbo-nium-ion formation step from an alkane. 

Wu, M. Ma, T., Platinum-Free Catalysts as Counter Electrodes in Dye-Sensitized Solar Cells. ChemSusChem 2012, 5 1343-1357. 

Fig. 5. Isomerization rate versus pentene partial pressure (S4). Comparison of n-pentane isomerization rate over platinum-alumina catalyst with the rate of skeletal isomerization of 1-pentene over the platinum-free catalyst 372°C.

Morozan A, Jousselene B, Palacin S (2011) Low-platinum and platinum free catalysts for the oxygen reduction reaction at fuel cell cathodes. Energy Environ Sci 4 1238-1254... 

However, poor performances and reduced Hfetimes need to be overcome for the commercialization of adapted PEFCs. Alkaline direct ethanol fuel cells are favored because they feature an increased performance and allow the use of cheaper platinum-free catalysts. 

Platinum-free catalysts usually feature two general problems stability in acidic enviromnents, and that none of the alternatives has so far reached the activity level of platinum. The first criterion excludes almost all pure non-noble metals as well as their alloys, unless an extraordinary stability combined with a ehange of the non-noble properties can be observed. The leaching of metal ions from the catalyst catalyses the formation of hydrogen peroxide, which leads to a self-destroying oxidation of the catalyst and to membrane degradation. " ... 

Another outstanding characteristic of the platinum-rhenium catalyst is its low aging rate with respect to activity. Typical comparisons with conventional catalysts are shown in Figure 5 where operating conditions were essentially constant for the two types of catalysts. The comparisons obtained to date indicate that the catalyst life for the platinum—rhenium catalyst when operated to a given activity decline or temperature rise is about four times that of the conventional catalysts. Under these conditions the yield loss from the rhenium containing catalyst is considerably less than from the platinum catalyst. If the platinum—rhenium catalyst were allowed to operate to the same yield loss as the rhenium-free catalyst, the life would be considerably greater than the four times indicated above. 

Treatment of benzyl 2-(A-benzyloxycarbonyl)amino-2-deoxy-a-D-gluco-pyranoside with oxygen in the presence of platinum oxide catalyst causes oxidation at C6 hydrogenolysis of the substituents yields 2-amino-2-deoxy-D-glucuronic acid.64 Under similar conditions of oxidation, the A-acetyl derivative is less stable than the A-benzyloxycarbonyl derivative, and complete degradation of the molecule occurs. Glycosides of 2-amino-2-de-oxy-D-glucuronic acid are remarkably resistant to acidic hydrolysis, and the free acid itself is much more stable toward mineral acids than are other uronic acids. 

The experimental data presented in this paper demonstrates the potential of CuCl/HCl electrolysis for nuclear hydrogen production. The CuCl/HCl electrolysis reaction requires a cation exchange membrane in order to produce hydrogen at a current density that exceeds 0.1 A-cm-2. In order to carry out the hydrogen production reaction a platinum electro-catalyst is required. The copper(I) oxidation reaction, on the other hand, does not require a Pt catalyst. This reaction proceeds quite readily on Pt-free graphite electrodes. Methods to mitigate the passage of the copper ion species across the membrane need to be developed to maintain the performance of the cell at the desired level. 

Phosphine dissociation from platinum boryl intermediates (PPh3)2Pt(BCat)2 allows the coordination of an alkyne prior to the boryl transfer step. The diborylation of alkenes requires phosphine-free catalysts.45,46 Boron—boron bonds react with a,j8-unsaturated ketones with 1,4-addition.47... 

Many different routes are available for the synthesis of vinylboranes and several of them are shown in Scheme 7. Hydroboration and diboration reactions of alkynes and borylated alkynes provide access to the frill series of mono-, di-, tri-, and tetraborylated olefins. 1,2-Diborylated olefins (33) are obtained via diboration of alkynes and 1,1-diborylated olefins (34) are accessible through hydroboration of borylalkynes. An alternative route to 1,1-disubstituted products involves the diboration of carbenoids formed in situ from vinylhalides and butyl hthium. In certain cases, metal-catalyzed dehydrogenative borylation of olefins may be used. Borylalkynes serve as precursors to triborylated (35) and tetraborylated (36) olefins. Thus, the sparingly soluble tetraborylethylene derivative (36) forms in good yield through platinum-catalyzed diboration of diborylacetylene in toluene at 40 °C if the base-free catalyst [Pt(cod)2] is used. If the reaction, however, is performed at higher temperature, ftnther diboration of (36) leads directly to the hexaborylated ethane (23) shown above. Intramolecular B-O interactions were postulated for (36) based on HF-SCF calculations. ... 

Zabrodskii, A.G. et ah. Carbon supported polyaniline as anode catalyst pathway to platinum-free fuel cells, Technol. Phys. Lett., 32, 758, 2006. 

Several catalytic hydrogenations of aromatic rings in compounds containing free carboxyl groups are described (cf. method 4). Low-pressure hydrogenation over platinum oxide catalyst has been used. p-Toluic acid in acetic acid at 60° gives 4-methylcyclohexanecarboxylic acid (S>5%). 

Hydrogenation of the crystalline streptomycin trihydrochloride-calcium chloride double salt in aqueous solution with platinum oxide catalyst at atmospheric pressure or with Raney nickel catalyst at 100-140 atmospheres and 150° also yielded dihydrostreptomycin. Acid hydrolysis of dihydrostreptomycin gave streptidine and N-methyl-L-glucosamine. Hence, the reduction involved the nitrogen-free moiety, streptose. 

With the introduction of Pt/Re catalysts, it is possible to achieve the ensemble control with much smaller sulfur addition. The su1fur-free Pt/Re catalyst by itself has a higher relative activity for hydrogenolysis than a platinum catalyst. However, this is changed when sulfur Is present In the feed. Kughes has described the first observations in a pilot plant. The catalyst produced more methane than any other that had been tested, and the run would probably have been aborted if it had not been an ordinary catalyst screening test. However, after the first and second weeks on stream, the selectivity improved and finally became similar to that of a fresh platinum/ alumina catalyst and as the run continued, the catalyst proved to be more stable than any previous catalyst tested. These results were ascribed to the presence of sulfur in the feed and could be obtained even with very low sulfur contents, l.S ppm. ... 

It should be noted that since sulfur is a poison for the platinum-based catalysts used for these changes, the feed for the catalytic reformer has to be essentially sulfur free. Sulfur is removed by passing the feedstock through a cobalt/molybdenum catalyst bed in the presence of hydrogen, Avhich can come from the catalytic reformer. Carbon-bound sulfur is converted to hydrogen sulfide (Eq. 18.30). 

Kluksdahl, H.E., inventor Chevron Research Company, assignee. "Reforming a sulfur-free naphtha with a platinum-rhenium catalyst." U.S. Patent 3,415,737. 8 pages. 1968. 

Note the overall good performance of the rhodium free catalyst Pd-Ce, which showed almost the same characteristics as the fully promoted palladium catalyst Pd-Rh-Ce. Ceria addition also increased CgHg conversion of the platinum catalyst, but resulted in a lower N2-yield. Generally, the palladium catalysts Pd-Ce and Pd-Rh-Ce showed similar or even superior catalytic performance compared to Pt-Rh-Ce. 

Chen et al. [19] have reported very active, stable platinum nanopartide catalysts prepared by alcohol reduction of PtCls using poly(N-isopropylacrylamide) previously grafted on PS microspheres as stabilizing polymer. The observed catalytic activity in the hydrogenation of allyl alcohol was more than five times higher than with Pt/C. Moreover, it was possible to recycle the resin-based catalysts for at least six cycles, whereas Pt/C was not recyclable at all. When comparing the catalytic activity of free and heterogeneous colloidal platinum particles, only a small decrease in the reaction rate was observed. 

Alvarez, E., Blanco, J., Otero de Becerra, J., Olivares, J., Salvador, L. 2002. Platinum monolithic catalysts for SO2 abatement in Dust-Free Flue Gas from combustion units. Latin American Applied Research. 32,123-129. 

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