Isopropanol Dehydration to Propylene: The Impact of Acid–Base Sites Strength, Dispersion and Nature

ABSTRACT Three bulk oxides were studied to elucidate the dependence of the surface mechanism involved in the dehydration of isopropanol to propylene. Niobium oxide (acid), magnesium oxide (basic) and alumina (amphoteric) were selected for this study due to their distinct acid–base properties. The complementarity of infrared and microcalorimetry methods was used to accurately correlate surface properties with catalytic activity. The latter were evidenced using a reactor inside a microcalorimeter linked to gas chromatography and subsequent kinetic computations. Acid sites are essential for isopropanol to coordinatively adsorb and initiate a surface reaction under catalytic conditions. A solely basic surface exhibits isopropanol physical adsorption under continuous inert flow, with no surface reaction. The presence of both acidic and basic sites allows for easier dissociation of the alcohol. The synergetic effect of acid–base pairs on isopropanol adsorption and conversion is confirmed by the study of amorphous silica–alumina. Surface hydroxyls are also involved in the adsorption. The effective activation energy determined by advanced kinetic computations suggests a first order mechanism on acidic surfaces. On the amphoteric solid, the results suggest the presence of both second order and first‐order elimination mechanism. The water produced during the reaction shown to alter the surface properties and reaction pathway. These results highlight the important role of acid–base site strength, nature and distribution and their synergetic effect on reaction mechanisms.