Modified Metal Surfaces

1 Achiral Molecules on Achiral Surfaces - The Racemic Reaction 

In the Pt/a-ketoester [59, 60] and Ni/fS-ketoester [61] systems, the key step in achieving enantioselective behavior is the adsorption of chiral molecules (modifiers). It is widely proposed that the role of the modifier is to interact (via H-bonding) with a reactant molecule in order to stabilize the pro-(J ) adsorption geometry relative to the pro-(S) configuration (or vice versa). 

A clear problem of heterogeneous versus homogeneous systems is the fact that there are often many different active sites on a metal particle. In regions of the particle, which have low densities of chiral modifiers, the racemic reaction over the bare surface can compete strongly with the enantioselective reaction, leading to poor ee values. In the Ni/tartrate-type system, the loss of modifier over the course 

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The molecular chemisorption of CO on various alkali-modified metal surfaces has been studied extensively in the literature. It is well established that alkali modification of the metal surface enhances both the strength of molecular chemisorption and the tendency towards dissociative chemisorption. This effect can be attributed to the strongly electropositive character of the alkali, which results in donation of electron density from the alkali to the metal and then to the adsorbed CO, via increased backdonation into the... 

A general conclusion regarding H2 adsorption on alkali modified metal surfaces is that alkali addition results in a pronounced decrease of the dissociation adsorption rate of hydrogen as well as of the saturation coverage. 

On the contrary, on oxygen-modified metal surfaces where secondary reactions between the adsorbed oxygen and ethylene decomposition products can easily occur, the effect of oxygen on the adsorptive capacity of the... 

KOESTNER ET AL. Clean and Sulfur-Modified Metal Surfaces... 

Selective Reactions on Modified Metal Surfaces the Ligand Effect. 201... 

The large size of redox enzymes means that diffusion to an electrode surface will be prohibitively slow, and, for enzyme in solution, an electrochemical response is usually only observed if small, soluble electron transfer mediator molecules are added. In this chapter, discussion is limited to examples in which the enzyme of interest is attached to the electrode surface. Electrochemical experiments on enzymes can be very simple, involving direct adsorption of the protein onto a carbon or modified metal surface from dilute solution. Protein film voltammetry, a method in which a film of enzyme in direct... 

When extra oxygen species are coadsorbed with methanol, some modifications of the reaction steps are needed. Although a promotion effect of adsorbed oxygen atoms on formation of methoxy from methanol molecule has been reported on some oxygen-modified metal surfaces ... 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

Chirally Modified Metal Surface for Heterogeneous Asymmetric Hydrogenation 17... 

XPS measurements of chemically modified metal surfaces contain contributions from both surface and bulk metal atoms. The component due to surface molybdenum atoms was determined using a procedure established by Citrin et. al. (10) which is based on the changing contribution of surface and bulk components to the measured signal as a function of photoemission takeoff angle. The surface... 

I nvestigation of the stability of modified metal surfaces, the modification layer being as thin as one monolayer [103]. 

This chapter has been organized by considering several aspects. An introduction concerning the relevance of the electronic properties and applications of the azamacrocycles related to surface phenomena as well as the general aspects and characteristics of the vibrational techniques, instruments and surfaces normally used in the study of the adsorbate-surface interaction. The vibrational enhanced Raman and infrared surface spectroscopies, along with the reflection-absorption infrared spectroscopy to the study of the interaction of several azamacrocycles with different metal surfaces are discussed. The analysis of the most recent publications concerning data on bands assignment, normal coordinate analysis, surface-enhanced Raman and infrared spectroscopies, reflection-absorption infrared spectra and theoretical calculations on models of the adsorbate-substrate interaction is performed. Finally, new trends about modified metal surfaces for surface-enhanced vibrational studies of new macrocycles and different molecular systems are commented. 

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