Mesoporous zirconium oxides: an investigation of physico-chemical synthesis parameters

摘要

A systematic kinetic study of mesoporous zirconia formation has been performed in order to optimize the synthesis conditions without addition of structure stabilizing agents such as sulfate or phosphate anions. We have investigated in particular the effect of synthesis time and temperature. On the basis of TEM, SEM XRD and N_2 adsorption-desorption results, a synthesis mechanism has been proposed. Low temperature or short duration afford supermicroporous materials and continuation of hydrothermal treatment makes the walls separating adjacent pores break down allowing the transformation to mesopores. The obtained materials have a uniform pore size and their surface can reach 400m~2/g. However, if hydrothermal treatment is performed at too high temperatures or for too long durations, mesoporous compounds are no longer obtained, but thermodynamically more stable crystalline zirconium oxides with very low specific surface area, namely the tetragonal and monoclinic forms, are the final phases that are more likely to appear.