Physico-chemical properties of alumina supports modified with silicon alkoxides

In order to study the influence of the addition of silicon alkoxides on the physico-chemical properties of alumina, several types of alkoxides have been used as reagents during the alumina synthesis. Different parameters were studied: (i) the chain length of the alkoxide, tailored using either tetramethoxysilane, tetraethyl orthosilicate, trimethoxypropylsilane or trimethoxyoctylsilane; (ii) the presence of one or two amino groups using either 3-aminopropyltrimethoxysilane or 3-(2-aminoethylamino)propyltrimethoxysilane. The results showed that functionalized precursors with small chain lengths led to small and spherical Al2O3 crystallites, corresponding to narrow size distributions of mesopores. However, the composition and polarity of the functionalized chain must be considered in order to obtain a correct templating. The porosity of the samples seemed to stem exclusively from the presence of voids between the crystallites. The incorporation of Si onto alumina was correlated with the reactivity of the silicon precursor. Introducing Si increased the resistance of the material to sintering processes, as shown by a higher specific surface area and a higher purity of the gamma-Al2O3 phase after treatment at 1200 degrees C compared to the pure alumina sample.