Temperature programmed desorption, reduction, oxidation and flow chemisorption for the characterisation of heterogeneous catalysts. Theoretical aspects, instrumentation and applications

Some aspects related to catalysts characteristic and behaviour will be trea ted such as determination of metal surface area and dispersion, spillover e ffect and synterisation. A detailed description of the available techniques will follow, taking in consideration some aspects of the gas-solid interac tions mechanisms (associative/dissociative adsorption, acid-base interactio ns, etc.). Every technique will be treated starting from a general descript ion of the related sample pretreatment, due to the fundamental importance o f this step prior to catalysts characterisation. The analytical theories wi ll be described in relation to static and dynamic chemisorption, thermal pr ogrammed desorption and reduction/oxidation reactions. Part of the paper wi ll be dedicated to the presentation of the experimental aspects of chemisor ption, desorption and surface reaction techniques, and the relevant calcula tion models to evaluate metal surface area and dispersion, energy distribut ion of active sites, activation energy and heat of adsorption. The combination of the described techniques and the integration of the expe rimental results produce a detailed picture of the investigated catalyst, a llowing a better comprehension of the reaction mechanisms in complicated pr ocesses and a detailed characterisation of catalyst activity and selectivit y. Most of the experimental results shown in the present paper have been ob tained in the application lab of CE Instruments (ThermoQuest S.p.A.), Milan - Italy. All the graphs related to static volumetric chemisorption have be en obtained by the adsorption apparatus Sorptomatic 1990, while the graphs related to TPD, TPR/O and pulse chemisorption analyses with the dynamic app aratus TPDRO 1100.