The Direct Study of Heterogeneous Catalysis by Gas-Solid Chromatography

Abstract

Heterogeneous catalysis may be investigated by using an adsorbent surface simultaneously as a catalyst and as a chromatographic column. The analysis leads directly to velocity constants for the surface reaction and hence to true activation energies. The most useful general technique is one in which the gas flow is stopped for defined intervals so that the reaction products formed in the stopped-flow intervals are eluted as sharp peaks. Various classes of reaction and the resulting reaction chromatograms are discussed and analysed. Experimental results are given for three elimination reactions on the surface of KCI/AI2O3. The direct chromatographic method requires only very small samples of reactant, makes possible the determination of very accurate velocity constants, and is of very wide application. Reaction rates are determined on surfaces which may be very finely characterised in terms of adsorption equilibria. The method could also be applied to homogeneous reactions occurring in the liquid film of a gas-liquid chromatographic column.