Platinum oxygenation catalyst

Maye MM, Kariuiki NN, et al. 2004. Electrocatal3dic reduction of oxygen Gold and gold-platinum nanoparticle catalysts prepared by two-phase protocol. Gold Bull 37(3-4) 217-223. 

Since S03/H2S04 is clearly not the most desirable system for industrial applications, a formidable challenge is to find an oxidant that oxidizes Pt(II) much faster than S03 does, operates in an environmentally friendly solvent, and can be (like SVI/SIV) reoxidized by oxygen from air. Ideally, the reduced oxidant would get reoxidized in a continuous process, such that the oxidant acts as a redox mediator. In addition, the redox behavior has to be tuned such that the platinum(II) alkyl intermediate would be oxidized but the platinum(II) catalyst would not be completely oxidized. Such a system that efficiently transfers oxidation equivalents from oxygen to Pt(II) would be highly desirable. A redox mediator system based on heteropolyacids has been reported for the Pt-catalyzed oxidation of C-H bonds by 02, using Na8HPMo6V6O40... 

Another key part of a PEM membrane is the thin layer of platinum-based catalyst coating that is used. It makes up about 40% of the fuel cell cost. The catalyst prepares hydrogen from the fuel and oxygen from the... 

M. M. Maye, N. N. Kariuki, J. Luo, L. Han, P. Njoki, L. Wang, Y. Lin, H. R. Naslund, and C. J. Zhong, Electrocatalytic reduction of oxygen Gold and Gold-platinum nanoparticle catalysts prepared by two-phase protocol. Gold Bull. 37, 217-223 (2004). 

In an acidic medium, a PEMFC fed with ethanol allows power densities up to 60 mW cm to be reached at high temperatures (80-120 °C), but this needs platinum-based catalysts, which may prevent wider applications for portable electronic devices. On the other hand, in an alkaline medium, the activity of non-noble catalysts for ethanol or ethylene glycol oxidation and oxygen reduction is sufficient to reach power densities of the order of 20 mW cm at room temperature. This opens up the hope of developing SAMFCs that are particularly efficient for large-scale portable applications. 

The mechanism of this strongly inhibited reaction has not yet been explained in detail, even with platinum, the most intensively studied of all catalysts 26>. The results obtained to date show that the course of the reaction is not the same on all catalysts and that other factors, such as oxygen absorption on platinum metal catalysts, play an important part. In most of the reaction mechanisms hitherto formulated and discussed H2O2 occurs as an intermediate stage 26> ... 

At 500°C the reaction rate over the platinum electrode-catalyst appeared to be independent of the e.m.f. of the cell. At 550°C two reaction rate branches were observed, depending on whether the catalyst had been pretreated in oxidising or reducing conditions (see Figure 9). The e.m.f. of the cell also exhibited two branches dependent upon pretreatment (see Figure 9), in a similar manner to other SEP work on oxide catalysts.86,87 It was suggested that the catalyst state (i.e., catalyst oxygen content or 5) was a function of the catalyst history. Different catalyst states corresponded with different catalyst reactivities and the e.m.f. of the cell reflected the catalyst state. 

Mukesh, D., Kenney, C. N., and Morton, W. (1983). Concentration oscillations of carbon monoxide, oxygen and 1-butene over a platinum supported catalyst. Chem. Eng. Sci., 38, 69-77. 

It is well established that oxygen in the presence of platinum (Adams catalyst) can achieve specific oxidation of secondary alcohols by a preferential attack upon hydrogen in an equatorial position (25). Catalytic oxidation of methyl a- and /3-D-galactopyranoside (26), fallowed by catalytic reduction with hydrogen, led to the formation of methyl a- and /3-6-deoxy-D-galactopyranoside (D-fuco-pyranoside) in 15% and 35% yield, respectively. This oxidation-reduction sequence with selective oxidation at carbon 4 as the initial step is structurally closely related to the above described pathway for TDPG-oxidoreductase. 

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. 

Then, as described in US Patent 3,053,845, one hundred grams (0.278 mol) of 2-oxo-3-(N,N-diethylcarboxamido)-9,10-dimethoxy-l,2,3,4,6,7-hexahydro-llb-H-benzopyridocoline was dissolved in 1,500 ml of hot methanol and the resulting solution was allowed to cool to room temperature. After removal of all the dissolved oxygen therein by saturation of the solution with dry nitrogen, 5.0 grams of Adams platinum oxide catalyst was introduced into the system in one portion while still maintaining same under a nitrogen atmosphere. 

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