Sol-gel synthesis and properties of unsupported and supported mesoporous ceria membranes

Unsupported ceria membranes were prepared from three different cerium oxide sols (commercial sol, cerous sol and ceric sol). XRD data show that the ceria membranes derived from all sols after drying at room temperature or calcination at a high temperature exhibit fluorite type structure. The final calcined product from all ceria sols is Ce⁴⁺ oxide compound. Ceria samples derived from commercial sol contain fairly dense particles with a very low surface area, and those derived from cerous and ceric sols give very high surface area with desired pore structure as mesoporous membranes. Cerous sol is however stable at very low concentration and is ineffective to use for making supported ceria membrane. Ceric sol is stable at high concentration (around 1 M) and provides unsupported ceria membranes with desired pore structure. Micron-thick ceria films could be coated on macroporous α-alumina support with the high concentration ceric sol after the support was chemically treated sequentially with a hot acid and base. The supported ceria membranes are crack-free and pinhole-free, and exhibit fluorite type structure. Compared to a similar sol-gel derived mesoporous zirconia membrane, the supported mesoporous ceria membrane has similar pore size (about 3.2 nm), smaller tortuosity factor (2.7) and larger porosity (54%).