SPECTROSCOPIC CHARACTERIZATION OF THE FE ZRO2 SYSTEM .1. CO ADSORPTION/

The problem of oxide-oxide interaction has been studied on the Fe2O3/Z rO2 system reduced and outgassed under vacuum between 500 and 773 K. T he techniques utilized were UV-vis reflectance, volumetric, TEM, and m ainly FTIR spectroscopy of adsorbed CO. Whereas CO is not adsorbed on oxidized samples, the depletion under vacuum of oxygen from the sample reduced at 500 K produces a coordinative unsaturation (cus) on the fe rric surface ions with lowering of the oxidation number and reversible adsorption of CO at v = 2150, 2138, and 2124 cm(-1). The reduction at 623-773 K favors further reduction to a highly dispersed FeO-like pha se spread on the support; the frequencies of reversibly adsorbed CO ar e red-shifted up to 2080 cm(-1) and are the fingerprints of a high het erogeneity of Fe-x+ (x approximate to 2) sites. However, the oxide-oxi de interaction hinders an easy reduction to Fe-0 even at 773 K; at thi s temperature only small quantities of carbonylic clusters and of CO a dsorbed on more extended iron faces, with vCO = 2100-1970 cm(-1), are formed at room temperature. The oxidation at 473 K fully eliminates th e process of reduction and of oxide-oxide interaction.