Reversed-flow gas chromatography for studying heterogeneous catalysis

Abstract

The rate constants of surface-catalysed reactions can be determined in a gas-chromatographic column, containing the catalyst, by introducing the reactant as a pulse at a middle position of the column, and then repeatedly reversing the direction of flow of the carrier gas. Following each reversal of the gas flow, an extra function is recorded by the detector, and then the chromatographic signal returns to the original elution curve. The analytical mathematical expressions, describing the elution curves when the gas flow is reversed, are derived for a general case and then applied to two specific reaction schemes, namely a simple first-order reaction and two consecutive reactions. By plotting the logarithm of the area under the ‘extra peaks’ as a function of time when the respective reversal of the flow was made, the rate constants of the surface steps of the reaction can be extracted. Arrhenius plots constructed from these rate constants give the ‘true’ activation parameters, free from heats of adsorption.