Effects of preparation conditions on pore structure and crystal phase of mesoporous zirconia

Mesoporous zirconia was prepared by the hydrolysis of zirconium tetrapropoxide (ZTP). Crystal structure of zirconia was controlled by using different hydrolysis procedures. A large amount of water and subsequent calcination led to the formation of mesoporous monoclinic zirconia with the pore size of 20 nm, while non-porous tetragonal zirconia was prepared with a small amount of water. Mesoporous tetragonal zirconia with controlled pore size was prepared from ZTP and carboxylic acids with different alkyl-chain length. The average pore size of the tetragonal zirconia increased from 4.8 to 7.5 nm with increasing alkyl-chain length of carboxylic acids. A complex of ZTP and carboxylic acid formed a hexagonal mesophase at the molar ratio of carboxylic acid to ZTP≥1.5. The lattice parameter of the hexagonal mesophase increased with increasing alkyl-chain length of carboxylic acid. The hexagonal mesophase, however, disappeared when the precursor melted over 58°C. The calcined zirconia consisted of the aggregates of crystallites, and the mesopores were located at interparticles. The appropriate coordination state and alkyl-chain length of carboxylic acid are probably effective in preparing mesoporous tetragonal zirconia and controlling the mesopores.