PREPARATION AND CHARACTERIZATION OF CHROMIUM-OXIDE SUPPORTED ON ZIRCONIA

Chromium oxide/zirconia was prepared by dry impregnation of powdered Zr(OH), with an aqueous solution of (NH4)2CrO4. The characterization of prepared samples was performed using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and differential thermal analysis (DTA), and by measurement of the surface area. The addition of chromium oxide to zirconia shifted the transitions of ZrO2 from the amorphous to the tetragonal phase and from the tetragonal to the monoclinic phase to higher temperatures due to the strong interaction between chromium oxide and zirconia; and the specific surface area of the samples increased in proportion to the chromium-oxide content. Since the ZrO2 Stabilizes supported chromium oxide, chromium oxide was well dispersed on the surface of zirconia, and alpha-Cr2O3 was only observed at calcination temperatures above 1173 K. Upon the addition of only small amounts of chromium oxide (1 wt % Cr) to ZrO2, both the acidity and acid strength of the samples increased remarkably, showing the presence of two kinds of acid sites on the surface of CrOx/ZrO2 (Bronsted and Lewis acid sites).