High Temperature Stabilisation of Pores in Sol-Gel Titania in Presence of Silica

Sol-gel titania was prepared by the hydrolysis and condensation reaction of acetic acid modified titanium isopropoxide. Partially hydrolysed tetraethoxy silane was further added to this precursor in order to get titania-silica mixed oxides. The silica content was varied from 1% to 50%. The gels were characterised by thermal analysis, FTIR and XRD analysis. Surface area of titania with out any additive was 320 m2/g. This got considerably reduced to 56 m2/g on tempering at 550°C for a period of one hour and further to 29 m2/g on tempering for 32 hours at the same temperature. However, in the case of silica added samples the surface area becomes constant after one hour of tempering and remains nearly at the same value even up to 32 hours. While undoped titania retains only ∼10% of its initial surface area when tempered at 550°C over a period of 32 hours, a titania-1% silica composition retains up to 26% under identical conditions. This trend further increases with increase in silica content and for a composition titania-50% silica, retention of surface area is as high as ∼80%. Untempered titania and titania-silica samples are highly micro porous in nature. On tempering, titania samples become mesoporous. However a major fraction of the micro porosity is retained in the case of the titania-silica compositions, even after tempering for 32 hours at 550°C, which also contributes to their high surface area. The results of this study are discussed.