Synthesis of Nanocrystalline Powders in the CeO_2-Al_2O_3 System by the Citrate Sol-Gel Method

摘要

Weakly aggregated, highly dispersed precursor powders with a specific surface area of 350-360 m(2)/g have been prepared by the citrate sol-gel method in the CeO2 ZrO2 -Al2O3 system. Heat treatment of the precursors in the temperature range 700-1000 degrees C led to the formation of powders based on a fluorite-like Ce0.7Zr0.3O2 solid solution with a crystallite size under 30 nm. The presence of alumina has been shown to inhibit the Ce0.7Zr0.3O2 crystallite growth process. Using low-temperature nitrogen adsorption measurements, we have studied texture characteristics of the powders obtained at 1000 degrees C: they have a specific surface area of 90 and 105 m(2)/g and a specific pore volume of up to 0.380 cm(3)/g, with a unimodal pore size distribution in the range 2.5-10 nm. We examine the effect of thermal "aging" at a temperature of 1000 degrees C for 50 h on the structure and particle size of the powders. Based on the experimental data obtained, we propose a process for the synthesis of nanocrystalline mesoporous powders in the CeO2 ZrO2 -Al2O3 system for the preparation of supports of an active phase (Pt, Pd, or Rh) in three-way catalysts.