Applied Catalysis A: General 270 (2004) 113–120 Three-element mixed oxides: a new approach to basic catalysts Cristina Flego a,∗ , Giovanni Cosentino b , Marco Tagliabue a a EniTecnologie SpA, via Maritano 26, I-20097 S. Donato Mil. (MI), Italy b C.I.R.A. SCpA, via Maiorise s.n.c., I-81043 Capua (CE), Italy Received in revised form 27 April 2004; accepted 28 April 2004 Available online 5 June 2004 Abstract A series of three-element mixed oxides (IA) x (IIA) y AlO z 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 N 2 adsorption/desorption isotherms, the basicity distribution by CO 2 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 mol/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. © 2004 Elsevier B.V. All rights reserved. Keywords: Mixed oxides; Basicity; Multivariate methods; CO 2 adsorption; Side-chain methylation of toluene 1. Introduction The application of sol–gel chemistry to the preparation of binary mixed oxides has been widely investigated [1]. Mixed oxides approach a homogeneous composition at the molecular scale and show a peculiar behaviour com- pared to the original pure oxides, due to the combination of dissimilar components in the same three-dimensional macro-molecular network. These mixed oxides play a cen- tral role in chemical and petrochemical processing and catalysis [2] as acid catalysts (e.g. silica-alumina gel [3]), oxidation catalysts (e.g. titania-silica gel [4]), fuel cell ma- terials (e.g. Ce–Zr–Ca oxides [5]) and supports [6]. By contrast, the application of sol–gel procedure in the synthe- sis of basic materials (e.g. Mg/Al mixed oxides) has been scarcely considered [7–9]. In particular, the effect of com- bining two different basic elements (e.g. alkali, alkali-earth metals) in an aluminium-based oxide has not yet been in- vestigated. In fact, as the presence of alkali-earth metals in ∗ Corresponding author. Tel.: +39-0252046678; fax: +39-0252056364. E-mail address: cflego@enitecnologie.eni.it (C. Flego). mixed oxides has been already proved to confer basic char- acter [7,8], the introduction by sol–gel synthesis of alkali metals is unusual [9], in spite of their specific high basicity. Reactivity and basicity of the mixed oxides are greatly influenced by both the preparation procedure (e.g. co-precipitation, sol–gel, grafting) and the synthesis vari- ables (e.g. composition, nature and amount of the elements, metal precursor, reaction temperature, stirring speed, age- ing, drying/calcinations, etc.) [1], their evaluation being money- and time-consuming process. For the study of so complex chemical systems, the application of the multivari- ate approach has been effectively suggested [10,11]. Specif- ically, the multivariate approach is based on the application of mathematical and statistical methods for the a priori selection of sets of informative experiments. Multivariate methods can be used for data modelling as well. This work reports the synthesis, physicochemical charac- terisation and catalytic testing of three-element basic mixed oxides (IA) x (IIA) y AlO z . The synthesis was performed by sol–gel method in the presence of a gelling agent (tetrapropy- lammonium hydroxide (TPAOH)). Among the numerous parameters that may influence this kind of synthesis, five variables related to the chemical composition of the mother 0926-860X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2004.04.035