Acetone condensation as a model reaction for the catalytic behavior of acidic molecular sieves: a UV–Vis study

Abstract

The aldol condensation is taken as a model reaction in order to study both the acid site density and the pore dimension on a variety of acidic molecular sieves (small-, medium-, large-pore zeolites and amorphous micro-, mesoporous silica–aluminas). Adsorption-reaction experiments of acetone are followed by UV–Vis spectroscopy. The main evidences obtained in this work allow us to relate: (i) the shift of the UV signal of acetone in the earliest stage of reaction to the strength of the Brønsted acid sites of the molecular sieves; (ii) the acetone conversion at 21°C to the density of the Brønsted acid sites; (iii) the product distribution to the dimensions of the pores of the molecular sieves. Medium pore zeolites give phorone as final product, while zeolites with large channels and mesoporous silica–aluminas favor the formation of isophorone.