clay interlayers is too narrow to accommodate large molecules such as capric acid, resulting in apparent poor activity of the photocatalyst. Studies to confirm this idea are under way.

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020ChemInform Abstract The surface chemistry of water adsorbed on HZSM5 and a series of alkali-metal ZSM5 is studied at pressures between 10-5 and 1 mbar by using mainly time-resolved transmission absorption IR spectroscopy for analysis. At low pressures (< 10-4 mbar) the most important adsorption sites are Lewis acid sites (octahedrally coordinated Al), whereas at higher pressures strong Bronsted acid sites (bridging hydroxyl) are more important sites for adsorption. Up to a gravimetrically determined number of three adsorbed H2O per strong Bronsted site, bands attributed to hydroxonium ions can be observed. On Li-, Na-, and KZSM5, adsorption of isolated H2O molecules on alkali-metal cations dominates at pressures < 10-2 mbar. At higher equilibrium pressures a second shell of H2O molecules is built up. With Rb-and CsZSM5 interactions between H2O molecules are of high importance for adsorption at H2O equilibrium pressures < 10-2 mbar.

The use of time resolved FTIR spectroscopy for characterizing time dependent adsorbate concentrations has been demonstrated with the examples of adsorption/desorption of ammonia and of adsorption and reactions of propan-2-ol. Adsorption sites and adsorbate structures are discussed.