Core-level binding-energy shifts at surfaces and in solids

Nanoscale structural information underlies research aimed at fabricating catalysts in a more controlled way. Surface science methods can provide that information, but the complexity of heterogeneous systems in general hinders the application of these methods to their full potential. In the last decades, a solution to this problem has been found in the use of model systems, ranging from well-defined single crystals of the supported phase to films or particles of that phase on flat or spherical model supports. In this paper, we review the literature on the latter model systems, that is, particles on a model support. Attention is payed to both preparation and use of such model systems.

https://pure.tue.nl/ws/files/1495087/617871.pdf

Surface Science Approach to Modeling Supported Catalysts

A method for the highly sensitive determination of acetylcholine (ACh) and choline (Ch) that employs a graphite-like carbon film electrode containing 6.5% platinum (Pt) nanoparticles was developed for use as a detector in microbore liquid chromatography (LC) with a postcolumn enzyme reactor. The film electrode was prepared by RF cosputtering carbon and Pt, which requires only a one-step formation process. This method can control the Pt content of the film at a relatively low deposition temperature (below 200 degrees C). The average size of the Pt nanoparticles was 2.5 nm. The film electrode showed excellent electrocatalytic activity, high sensitivity, and negligible baseline drift when detecting hydrogen peroxide. The electrode was modified with glucose oxidase and responded rapidly to glucose with a much more stable baseline current than at a Pt bulk electrode based sensor. Therefore, it is appropriate to employ the electrode to detect trace amounts of biomolecules, such as neurotransmitters and hormones combined with various oxidase enzymes. We used the electrode as a detector for microbore LC and observed a low detection limit of 2.5 and 2.3 fmol (10-microL injection) for ACh and Ch, respectively, which is approximately 1 order of magnitude lower than that of a Pt bulk electrode.

Characterization of platinum nanoparticle-embedded carbon film electrode and its detection of hydrogen peroxide.

Publisher Summary The skeletal rearrangements of hydrocarbons represent an important class of reactions catalyzed by metal surfaces, that have few counterparts in homogeneous catalysis. The first examples of skeletal rearrangements on metals were reported by the Soviet school of catalysis. A major step in hydrocarbon chemistry is the finding that platinum, unlike palladium and nickel, selectively catalyzes the hydrogenolysis of cyclopentane hydrocarbons. At about 300°C, on the classical Zelinskii platinum-charcoal catalyst, cyclopentane yields n -pentane as sole reaction product, while palladized charcoal is completely inactive and nickel-alumina produces all the possible acyclic hydrocarbons, from methane to pentane. The predominant precursor species in skeletal rearrangements are metallocyclobutanes and metallocarbenes, which can be further dehydrogenated to metallocarbynes, dicarbenes, or carbene-olefin complexes, and react like the analogous species in coordination chemistry. Metallocyclobutane dismutation and the reverse reaction, carbene-olefin addition, are the two major steps in olefin metathesis, and dicarbene recombination also has an analogue in organometallic reactions.

Y. Takasu

Papers

Photoemission from palladium particle arrays on an amorphous silica substrate