Abstract
Microcalorimetry has been used with several metallic oxides (MgO, SiO2, SiO2-Al2O3, Al2O3, Bi3FeMo2 O12, TiO2) and zeolites (Y-and ZSM-5-types in their Na and H forms) for the measurement of the differential heat of adsorption of probe molecules, acidic and basic in nature. Small probe molecules have been chosen, namely NH3 and CO2, in order to avoid diffusion limitation, particularly for small pore zeolites. It was observed that acidification of zeolite not only created strong acidic sites but also a few strong basic sites. On Al2O3 both strong acidic and basic sites were evidenced, whereas only strong basic sites were detected on MgO. Few weak acid sites were observed on Bi3FeMo2O12 catalysts and some acidic and basic sites were detected on silica. TiO2 (either anatase or rutile) presents a few and very weak acid sites. However, activation in air at 400°C created some strong acid sites. Correlation with peculiar catalytic properties involving the presence of both acidic and basic sites and with the electron donor and electron acceptor properties of oxides may be envisaged.
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