An investigation of submicrostructural evolution of freshly precipitated ZrO2 in digestion for ultrafine sulfated ZrO2 catalysts by SAXS technique

Coupled with XRD, BET, and TEM, the small-angle X-ray scattering (SAXS) technique has been effectively used to probe and characterize the submicrostructure of freshly precipitated hydrous zirconia and its evolution during digestion. It has been found that fresh hydrous zirconia particles possess an average diameter of about 5 nm and rather rough surfaces describable in terms of fractal concepts. The digestion of zirconia precipitates at 100 degrees C with their mother liquors may remarkably smooth the particles' rough surface and provoke fractal aggregation of the particles but make little change in average particle dimensions. A local dissolution-reprecipitation mechanism is regarded as a basic process to accompany particle surface smoothing, particle aggregation, and coarsening at the neck areas between joint particles, which may greatly strengthen the particle networks and enhance their resistance to crumbling while calcinated at high temperatures. On the basis of the submicrostructural features unraveled by SAXS, a coherent and significant physical picture has been raised out to demonstrate and interpret the relationship underlying the submicrostructure, the surface area variation, and the heating behavior of hydrous zirconia precipitates.