Influence of Crystallite Size on the Properties of Zirconia

Systematic studies on the properties of zirconia for catalytic applications revealed that the concentration of the stock solution, from which precipitation is carried out, strongly influence the crystallite size of the resulting zirconia. The crystallite size influences the BET surface area, the crystallization temperature, and the phase transition temperature. The findings of this study clarify the parameters governing the formation of specific phase with desired surface areas

Synthèse de zircones mésoporeuses de haute surface

Il est montré que des oxydes de zirconium mésoporeux et de haute surface spécifique peuvent être préparés à partir de l'hydrolyse de ZrOCl2 8 H2O, en présence de tensioactif (CTAB). Les hautes aires spécifiques sont attribuées à la formation de clusters agrégés sous la forme de petites particules. Le temps de réaction est le paramètre qui paraît gouverner l'obtention des hautes aires spécifiques ainsi que la structure cristalline des matériaux calcinés. Un mécanisme de synthèse prenant en compte ces différents paramètres et conduisant à la formation d'oxydes de zirconium divisés est proposé

Monoclinic and Tetragonal High Surface Area Sulfated Zirconias in Butane Isomerization: CO Adsorption and Catalytic Results

In the present study high surface area monoclinic and tetragonal sulfated zirconia samples both active in n-butane isomerization were prepared from the same hydroxide precursor in a novel one-step hydrothermal process. The process is studied via analysis of intermediate stages of the product formation. The monoclinic samples show a catalytic activity in n-butane isomerization lower by about a factor of 4 compared to the tetragonal samples, although the acidity as analyzed by CO adsorption was found to be similar. This suggests, that it is not only the acidity of sulfated zirconia that determines the catalytic performance. The results support the bimolecular mechanism, for which a favorable arrangement of surface groups is necessary. The surface structure of tetragonal zirconia seems to be better suited than that of the monoclinic zirconia, although the presented monoclinic zirconia performs substantially better than claimed in many publications, where the monoclinic phase is typically assumed to be inactive