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

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 fir st treating with pure sulphuric acid titanium isopropoxide, grafting the ti tanium alkoxide sulphate on silica and again by steaming and calcinating th e product obtained. All the catalysts prepared have been characterized usin g different techniques such as: electrochemical potentiometric titrations t o evaluate the PZC (point of zero charge), the hydroxyl densities and the s urface dissociation equilibrium constants; TGA (thermal gravimetric analyse s) to evaluate the hydroxyl densities; TPD (thermal programmed desorption) of organic bases such as pyridine and lutidine; and XPS (X-ray photoemissio n spectroscopy). All catalysts have also been tested by determining the per formances in three different reactions: dehydration of methanol, epoxidatio n of cyclooctene with cumene hydroperoxide and isomerization of 1-butene to 2-butene. The behaviour of the catalysts prepared shows that grafting tita nium on silica strongly modifies the original surface and the catalysts obt ained with the mentioned grafting techniques are different from those obtai ned by impregnation and coprecipitation, (C) 1999 Elsevier Science B.V. All rights reserved.