Work function chemisorption induced

The last point is confirmed by measuring the work function changes upon CO chemisorption on clean and alkali-promoted metal surfaces. Figures 2.16 and 2.17 show the work function changes induced by CO adsorption on a K/Pt(lll) and on a Na/Ru(1010) surface respectively, for various alkali... 

One of the most striking results is that of C2H4 oxidation on Pt5 where (xads,o ctact = -1, i.e. the decreases in reaction activation energy and in the chemisorptive bond strength of oxygen induced by increasing work function ethylene epoxidation and deep oxidation on Ag.5... 

There is very little experimental evidence pointing to enrichment in solid solutions. Bouwman et al. 15) studied the surface composition of Ag-Pd alloys by measuring the changes in work function of the alloys upon adsorption of CO. The result they obtained after brief exposition to CO at room temperature is shown in Fig. 5. Since the dependence on alloy concentration is nonlinear in the silver concentration, enrichment in silver is concluded, this enrichment being a function of the concentration of the alloys. After 16 hours exposure to a CO atmosphere Bouwman et al. found an additional increase in work function, which they ascribed to chemisorption-induced enrichment... 

The main difference with respect to the previous case is that the binding energy is now of 27 kcal/mol. This fact is attributed to a deaease in the surface work function induced by K atoms and shows the importance of K coverage on the chemisorption of C02. ... 

An alternative interpretation of the phenomenon of metal-support interactions induced by doping of semiconductive carriers with aliovalent cations is based on the theory of electrochemical promotion or the NEMCA effect. According to this interpretation, the charge carriers transported from the carrier to the metal particles are oxygen ions, which diffuse to the surface of the metal particles, thus altering the surface work function and, subsequently, chemisorptive and catalytic parameters. Work is currently in progress to elucidate the mechanism of induction of metal-support interactions by carrier doping. 

The opposite situation from weak interaction of inert gases with the surface space charge is surface ionization, when the adsorbate is ionized by the substrate. This typically occurs in alkali-metal adsorption on transition-metal surfaces. In the more usual situation with chemisorbed molecules, only partial charge transfer occurs to or from the substrate to the molecule. If the negative pole of the molecule points toward the vacuum, the induced electric fields cause an increase in the work function. Table 5.4 lists the work-function changes obtained by the chemisorption of several molecules on rhodium. 

Let us discuss the model that is commonly used to interpret the chemisorption-induced changes in work function, along with some of the experimental results. 

The observed phenomena are very similar to the effects on chemisorptive bond strength induced via electrical polarization (0.3 V/A) and concomitant work-function change on well-characterized surfaces under UHV conditions. ... 

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