Pore-structure stability of nanostructured rutile titania containing a “structure-directing second-phase stabilizer”

Metastable-to-stable transformation in oxides is always associated with a drastic reduction in surface area and/or porosity. Because of this, all earlier efforts to stabilize the pore-structure of oxides undergoing a metastable-to-stable phase transformation have been directed to retarding or preventing the transformation. Here we report the pore-structure stabilization of nanostructured titania by promoting the anatase-to-rutile transformation using a “structure-directing second-phase stabilizer.” In the present study pure titania transformed to more than 95% rutile and became completely dense at 800°C (near zero porosity), whereas titania containing 2.4 mol% tin oxide transformed to about 70% rutile already at 750°C, but retained a surface area as high as 16 m2/g. At 800°C it transformed to 100% rutile and still retained a surface area of about 8 m2/g.