TEM characterization of sol-gel-processed alumina–silica and alumina–titania nano-hybrid oxide catalysts

Alumina–silica nano-particle mixtures and alumina–titania nano-mixtures with molar ratios 3:1, 3:4 and 1:0.5, 1:5 were synthesized by a sol-gel technique, during which the co-precipitates are formed. The resolved precursor powder calcined at 400 °C was characterized by thermo-gravimetric analysis, BET specific surface area measurement, adsorption isotherm characteristics and transmission electron microscopy. The results show, that the specific surface area of alumina–silica gel decreases with increase of silica content. On the other hand, specific surface area increases with increase in the amount of Ttitania content, in the case of alumina–titania powder. Considerable extent of meso-porosity is developed in 3:1 composition compared with pure alumina. TEM micrographs show a highly homogeneous distribution of the constituent phases in all specimens. In alumina–titania samples fine uniform needle like particles of ∼10 nm size are observed, while for alumina–silica mixture having less silica content while for high silica containing sample, non-uniform needle like particles with particle sizes ranging from 20 to 75 nm are observed. The diffraction patterns also show more crystallinity for low silica content and high titania containing samples. Thus it is possible to synthesize materials with different porosity features and surface morphology, which may be having different applications by changing the ratio of individual components in a mixed oxide system.