RETENTION BEHAVIORS OF CARBON-CONTAINING SPECIES IN AS-PREPARED, WATER-TREATED, AND TRANSITION-METAL-CONTAMINATED ZRO2 GELS

Retention behaviours of carbon-containing species in ZrO2 gels derived from the Zr-n-propoxide-acetylacetone-water-isopropanol system have been studied by the Fourier transform infrared (FT-IR) pellet technique. The carbon retention patterns based on evolution of FT-IR spectra at different calcination temperatures for ZrO2 gels are examined in detail. It is found that the carbon retention behaviours for as-prepared gels and for thermal, water and transition metal (Ni2+) pre-treated ZrO2 gels differ. For most captured carbon species, for example, solvent isopropanol and additive acetylacetone, carbon can be depleted at a relatively low temperature of about 400 degrees C. However, for lattice-included species, especially those incorporated into the lattice during the phase transition, a temperature around 900 degrees C is needed to eliminate carbon in the gels. In the study of the effect of moisture on gel calcination, it is found that water treatment alone does not provide new routes for carbon retention in as-prepared ZrO2 gels. However, when gels are pre-treated with Ni2+ and water, new forms of carbon-containing species can be observed. These forms are attributed to an inter-diffusion of Ni2+ and ZrO2 matrix and the catalytic effect of the resultant solid solution, NiO-ZrO2, on the retained carbon species.