Characterization of the porosity developed in a new titania-alumina catalyst support prepared by the sol gel route

Titanium oxide (TiO₂) is a good candidate for support of hydrotreating catalysts but has the disadvantage of presenting a low surface area and a poor thermal stability when compared with Al₂O₃. A mixed TiO₂-Al₂O₃ support was proposed as an alternative that is expected to be free from these drawbacks. The variation during firing of the nanoporous texture of supports composed of TiO₂-Al₂O₃, TiO₂ and Al₂O₃ was studied by small-angle X-ray scattering (SAXS). The supports were prepared by the sol-gel route using Ti and Al isopropoxides. We have particularly analyzed the effects of acid and basic hydrolysis on the nanostructural features of catalyst supports fired at different temperatures. The nanopore radius distribution functions were determined from SAXS results assuming a simple model of spherical nanopores embedded in a homogeneous solid matrix. The modal pore radius in both pure TiO₂ and pure Al₂O₃ supports grows from 1.3 to 2.2 nm as the firing temperature increases from 673 to 973 K. On the other hand, the modal pore radius in the mixed TiO₂-Al₂O₃ support remains below 1.2 nm over the same range of firing temperatures. These results demonstrate the good thermal stability of the nanoporous texture of mixed TiO₂-Al₂O₃ supports.