BEHAVIOR OF CHROMIUM-OXIDE ON MGO OR MGF2

The molecular structure and oxidation state of the chromium oxide on M gO or MgF2 as a function of Cr loading were determined by XRD, Raman s pectroscopy, and XPS. The effects of preparation method and the acidit y of support were investigated. The Raman study on a series of chromiu m oxide supported on MgO prepared by an impregnation method showed tha t the chromium oxide was present as polychromate independent of Cr loa ding due to high acidity of the preparation solution. In samples prepa red by a precipitation method, the chromium oxide was present as monoc hromate at 5% Cr loading, as dichromate at 10% Cr loading, and as mono - and polychromate at 20% Cr loading due to a larger surface area of t he support prepared by this method. The chromium in CrO3/MgF2 was pres ent as polychromate and monochromate for impregnated and precipitated samples, respectively. The oxidation state of Cr(VI) on MgO is maintai ned independent of Cr loadings. When the 10 wt % Cr/MgO was calcined a t 800 degrees C, MgCr2O4 and Cr2O3 were formed. Preferred formation of MgCr2O4 was observed for the precipitated sample due to its larger su rface area compared to that of the impregnated sample.