Theory

The method of investigation the catalytic activity of the solid by the dissociation of CsCl molecules8 offers a number of significant advantages.9 CsCl is the simplest molecule with one break up channel only. One of the dissociation products, the Cs atom, has a low ionization potential (VCs = 3.89 eV), and under conditions where VCs is less than the substrate work function (this requirement is met on the surface of high melting point metals, graphite and many others) each Cs ad atom desorbs from the surface of heated adsorbent as Cs+ ion (the mechanism of ion formation is surface ionization10).

If a beam of CsCl molecules of flow density vCsCl strikes the surface of the solid the not dissociated molecules with flow density vCsCl escape rapidly, then the degree of dissociation y = (vCsCl - vCsCl ) / vCsCl will be a measure of the catalytic activity in question. Measuring under conditions of complete ionization ( VCs « p ), the current density of the Cs+ ions desorbing from the surface one can calculate Y, as j = e • (v CsCl - v CsCl ) = e • v CsCl • y.

At adsorption CsCl molecules, on many metal (Ir, W, Mo, Re, Pt, Pd, Rh) surfaces at T > 800 K, y = 1. Graphite stands out in its unique catalytic passivity: indeed, one monolayer of graphite on rhenium y reduces from 1 to 10-3-10-6.n

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