SURFACE CHARACTERIZATION OF CHROMIUM OXIDE-ZIRCONIA CATALYST

Chromium oxide-zirconia catalysts were prepared by dry impregnation of powdered Zr(OH)4 with an aqueous solution of (NH4)2CrO4. The surface characterization of prepared catalysts was performed by using Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and by the measurement of surface area. The addition of chromium oxide to zirconia shifted the phase transitions Of ZrO2 from amorphous to tetragonal and from tetragonal to monoclinic to higher temperatures due to the interaction between chromium oxide and zirconia. Since the ZrO2 dispersed chromium oxide, alpha-Cr2O3 was observed only at the calcination temperature above 1173 K. In the treatments by oxygen, hydrogen, carbon monoxide, and n-hexane the reduction-oxidation between Cr(VI) and Cr(III) is reversible, as observed by XPS and IR. Upon the addition of only a small amount of chromium oxide (1 wt % Cr) to ZrO2, both the acidity and acid strength of catalyst increased remarkably, showing the presence of Bronsted and Lewis acid sites on the surface of CrO(x)/ZrO2.