Preparation of ordered mesoporous ceria with enhanced thermal stability

The use of neutral surfactants to form a thermally stable ordered mesoporous ceria phase is reported. The judicious choice of cerium acetate as the inorganic framework precursor and the inorganic to surfactant ratio in the preparation mixture allowed the condensation of acetate derived inorganic polymer chains about the surfactant phase to form a regular mesoscopically ordered inorganic-organic matrix. Even at the low temperature processing conditions used to prepare the hybrid matrix the cerium precursor was seen to form the fluorite type structure of CeO2. Careful thermal processing of the matrix allowed the subsequent densification (of the pore walls) of the inorganic component and removal of the organic component so that a high quality ordered and truly crystalline mesoporous ceria was formed. The calcination procedure used resulted in a reduction of the long-range order of the pore channels (as evidenced by powder X-ray diffraction) whilst maintaining directionally aligned mesoporous channels as observed by transmission electron microscopy. These ordered pore structures remained even after high temperature ageing. The templating route adopted was found to allow the facile low temperature removal of surfactant due to the hydrogen bonding nature of the surfactant-ceria interaction. Differential scanning calorimetery (DSC) data are consistent with some amount of rapid ceria lattice reduction (Ce4+ to Ce3+) at the surface related to the presence of intimate organic-inorganic interactions most likely the result of hydrogen bonds that exist between the surfactant and the ceria lattice. Any reduction of the ceria pore wall surface during the initial thermal processing is rapidly re-oxidised by rapid mass transport of gas phase oxygen molecules through the open pore system during the process of template removal. The material maintained high surface areas after calcination up to temperatures of 873 K. The preparation of high surface area ceria with a stable uniform array of pores is significant and may allow the development of novel catalytic applications for ceria.