Preparation and properties of new acid catalysts obtained by grafting alkoxides and derivatives on the most common supports. Part III – grafting titanium alkoxides and sulphate derivatives on silica

Abstract

Some catalysts have been prepared by grafting different amounts of titanium isopropoxide dissolved in toluene on a silica support and by steaming and calcinating the products obtained. A catalyst has been prepared also by first treating with pure sulphuric acid titanium isopropoxide, grafting the titanium alkoxide sulphate on silica and again by steaming and calcinating the product obtained. All the catalysts prepared have been characterized using different techniques such as: electrochemical potentiometric titrations to evaluate the PZC (point of zero charge), the hydroxyl densities and the surface dissociation equilibrium constants; TGA (thermal gravimetric analyses) to evaluate the hydroxyl densities; TPD (thermal programmed desorption) of organic bases such as pyridine and lutidine; and XPS (X-ray photoemission spectroscopy). All catalysts have also been tested by determining the performances in three different reactions: dehydration of methanol, epoxidation of cyclooctene with cumene hydroperoxide and isomerization of 1-butene to 2-butene. The behaviour of the catalysts prepared shows that grafting titanium on silica strongly modifies the original surface and the catalysts obtained with the mentioned grafting techniques are different from those obtained by impregnation and coprecipitation.