A Static Method Coupling Calorimetry and Volumetry

The simultaneous assessment of the adsorbed quantity of a suitable probe molecule and the heats evolved at increasing coverage makes it possible to picture the heterogeneity of the surface (structural and/or chemical) by processing the overall set of combined volumetric and calorimetric data. 

A system that links microcalorimetry to the volumetric measurement of quantities of adsorbed reactants makes it possible to study gas-solid interactions and catalyhc reactions. This system works under stahc vacuum. The admission of gases into the calorimeter can be performed either in a discontinuous way (by successive doses) by means of a valve, or in a continuous manner by means of a capillary. The classical technique of adsorption calorimetry by doses is the most appropriate way to measure the energy of interaction between the adsorbed species and the catalyst. If the surface can be a priori considered as heterogeneous, the heat of adsorption, the amount adsorbed and the kinetics of adsorption must be measured for very small successive doses of the adsorbate so as to obtain accu- 

From these two types of isotherm (calorimetric and volumetric) the internal 

When there are several possible adsorption mechanisms (e.g. reversible and irreversible adsorption), these isotherms can be used to evaluate the sequence and the importance (number of active sites and bond energy) of the different processes. 

The variation of the differential heat of adsorption (Q = AQuy/Anj ) as a function of coverage is an indication of the homogeneity or heterogeneity of the adsorption sites. 

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