Platinum as catalyst

A similar experiment using platinum as catalyst yielded D2 as the initial product suggesting homolytic splitting on this surface with both adsorbed atoms exchanging rapidly with the water. 

There are different methods to cleave benzyl ether bonds. The most common one is hydrogenolysis with palladium on carbon or platinum as catalysts under H2 atmosphere. The standard solvents are ethanol or ethyl acetate. Pd is the preferred and milder one, because the use of Pt at any rate results in aromatic ring hydrogenation. Also a number of methods have been developed in which hydrogen is generated in situ, e. g. from cyclo-hexene, -hexadiene or formic acid (see Chapter 7). 

Teuber and Schmitt hydrogenated 5-methoxyindole over ruthenium dioxide in 90% ethanol at elevated temperature and pressure and obtained the corresponding octahy-droindole in a 79% yield (eq. 12.9).11 The hydrogenation was difficult to complete with platinum or rhodium-platinum as catalyst in acetic acid. 

Dehalogenations at saturated carbons are seen quite commonly with cyclic compounds of the type RCH2X. Equations 13.105,197 13.106,198 and 13.107199 are examples of such dechlorination, debromination, and deiodination, respectively, using palladium or platinum as catalyst. Equations 13.108200 and 13.109201 are those using Raney Ni. 

The product of the decomposition is, like in the Millennium Cell system, sodium metaborate. The system shows the same problems for the regeneration of NaBH4 from an aqueous solution of metaborate as described below. One advantage of the direct borohydride fuel cell systems is that platinum as catalyst is not needed. Unfortunately, depending on the temperature of the solution, some hydrogen gas is produced in a side reaction. However, this hydrogen can be piped out or can be used as additional fuel in a subsequent PEM fuel cell. 

The high-cost of materials and efficiency limitations that chemical fuel cells currently have is a topic of primaiy concern. For a fuel cell to be effective, strong acidic or alkaline solutions, high temperatures and pressures are needed. Most fuel cells use platinum as catalyst, which is expensive, limited in availability, and easily poisoned by carbon monoxide (CO), a by-product of many hydrogen production reactions in the fuel cell anode chamber. In proton exchange membrane (PEM) fuel cells, the type of fuel used dictates the appropriate type of catalyst needed. Within this context, tolerance to CO is an important issue. It has been shown that the PEM fuel cell performance drops significantly with a CO con-... 

Streptomycin trihydrochloride was hydrogenated in aqueous solution at atmospheric pressure using platinum as catalyst. - About one molar equivalent of hydrogen was absorbed to yield a product which formed a crystalline trihelianthate from which a white powder, designated... 

According to this, SO 3 should be dissociated 5 per cent, at 527° C. and a pressure of one atmosphere. This is in agreement with technical experience, as the temperature in the contact process (with platinum as catalyst) must not exceed 450°. According to the accurate iritourements of Bodenstein and Pohl, the degree of dissociation of SO3 at 500° is 8 7 per cent. 

Electrodes The porous electrodes consist of carbon cloths loaded with a mixture of platinum and Nafion. In order to achieve a good contact between the electrode, the catalyst, and the electrolyte, the electrodes are pressed on the electrolyte membrane, which acts as the supporting component. Other catalysts such as binary Pt-Ru mixtures and ternary systems such as Pt- Ru- Sn have been studied for better CO tolerance [8]. The current density voltage curves of Fig. 7 show the effect of CO on the performance of a cell with platinum as catalyst. Fig. 8 shows the higher catalytic... 

Catalytic Converters Catalytic converters on cars use the metals rhodium and platinum as catalysts to convert potentially dangerous exhaust gases to carbon dioxide, nitrogen, and water. Why don t cars need to have the rhodium and platinum replaced after they are used ... 

There are still important technological breakthroughs that must be achieved for the fuel cell technology to be a realistic option for mass production. The major challenge seems to be the fuel cell itself, which today is made with heavy use of platinum as catalyst and with insufficient durability. Cheaper and more accessible catalysts and longer durability are necessary to achieve comparable costs. The ideal solution is a two-way fuel cell that can serve as an electrolyser, that is, produce hydrogen from electricity, when it does not use hydrogen to produce electricity, but this still seems a rather distant option. 

Scott et al. [44] have designed two types of flow cells (1) parallel flow channel arrangement and (2) a spot design of a flow bed. These two types of flow cells are designed to test with electrodes made of Teflon and carbon with ruthenium and platinum as catalysts on electrodes. Teflon was used for the purpose of providing hydrophobic effect in the electrode. By making the electrode hydrophobic, the flow of methanol is improved. 

---