STRUCTURAL-CHANGES OF TITANIUM-OXIDE INDUCED BY CHROMIUM ADDITION AS DETERMINED BY AN X-RAY-DIFFRACTION STUDY

An X-ray diffraction study has been carried out on a series of polycry stalline TiO2 (anatase) catalysts containing Cr(III) at different atom ic concentrations (0.2-5.0 at,%), prepared by a coprecipitation method , Analysis of the variation of the unit cell parameters of chromium-do ped anatase with respect to pure anatase has allowed us to estimate th e solubility limit for the system at around 1.4 at.%. There is no evid ence for the existence of a separate crystalline chromium oxide phase. Temperature effects on the cell parameter and on the anatase-rutile t ransformation rate were also analyzed, An increase in temperature prod uced release of the chromium from the solid solution. At the same time , an acceleration in the rate of the anatase-to-rutile phase transitio n was observed. (C) 1995 Academic Press, Inc.