Three-element mixed oxides: a new approach to basic catalysts Original Research Article

A series of three-element mixed oxides (IA)x(IIA)yAlOz was prepared by sol–gel method, adopting a multivariate experimental design strategy in order to explore in a rational way the effects of preparation parameters on textural and basic properties. The textural properties were determined from N2 adsorption/desorption isotherms, the basicity distribution by CO2 chemisorption and temperature programmed desorption. Besides, the reactivity of toluene in the side-chain alkylation with methanol was taken as a measure of the acid–basic character of these oxides. The prepared three-element mixed oxides showed good basicity (>300 μmol/g) and textural properties among the mesoporous materials. Density and strength of the basic sites of the materials were related to the synthesis parameters by applying the multivariate analysis to data modelling. For example, the presence of large amount of alkali metals, IA/Al=0.30, was related to the increased density of medium-strong basic sites. The product distribution of the model reaction confirmed the presence of weak and very strong basic sites, the former responsible of aromatic ring alkylation and the latter of styrene synthesis.