Platinum activating crystals

Since oxidation of methanol is an electrocatalytic reaction with different adsorption steps, interactions of the adsorbed species with the metallic surface are important. Using platinum single-crystal electrodes, it has been proven that the electrooxidation of methanol is a surface-sensitive reaction. The initial activity of the Pt(llO) plane is much higher than that of the other low-index planes, but the poisoning phenomenon is so rapid that it causes a fast decrease in the current densities. The... 

FIGURE 1.10 Current intensity versus electrode potential voltammetric profile for platinum single crystals, Pt(100) (cooled in air) with blue lines, Pt(110) with black lines and Pt(lll) in red lines, in 0.5 M sulfuric acid solution run at 0.05 V s 1 at room temperature. A difference with respect to the early single crystal preparation method by Will [18] is that the ones reported here are those obtained by Clavilier early in 1980. After 50 years of the first paper by Will on the use of single crystals for the oxygen electroreduction reaction and his finding of the given preferred activities on (111) and (100) planes, the industry still uses polycrystalline surfaces. 

Figure 7.38. The structure sensitivity of dehydrocyclization of alkanes to aromatic hydrocarbons. The bar graphs compare reaction rates for n-hexane and n-heptane catalyzed at 573 K and atmospheric pressure over the two flat platinum single-crystal faces with different atomic structure. The Pt surface with a hexagonal atomic arrangement is several times more active than the surface with a square unit cell over a wide range of reaction conditions [155].

Heterogeneous nucleation on active sites Real surfaces, for instance obtained with melt-grown gold, silver, or platinum single-crystal electrodes, exhibit various sites and structural imperfections of different dimensionahty, such as kinks, vacancies, monatomic steps, reconstructed surface domains, 2D islands, and holes [2, 129, 130]. Defining the number of active sites S under particular experimental conditions as No, one may consider the heterogeneous nucleation process as the successive incorporation of monomers Ml into site-confined clusters S — Mi... 

Tremiliosi G, Kim H, Chrzanowski W, Wieckowski A, Grzybowska B, Kulesza P (1999) Reactivity and activation parameters in methanol oxidation on platinum single crystal electrodes decorated by ruthenium adlayers. J Electroanal Chem 467 143-156... 

It was established that platinum single crystals served as excellent model catalysts LEED provided structural information, flat terraces could be prepared with steps one atom high, kink sites could be introduced and their catalytic activity recognized... The concept of structural sensitivity could be examined at the atomic level for the first time. Surface science has provided a remarkably detailed picture of catalysis on single metal crystals under conditions of high vacuum. 

The reaction by itself is best studied by means of model investigations on platinum single-crystal stufaces steps and terraces on the surface are thereby the most active spots, leading to a preferred reaction on these places. ... 

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