Effects of SO2/redox exposure on the microstructure of cerium–zirconium mixed metal oxides

Abstract Cerium–zirconium solid solutions were prepared and characterized to determine the effects of SO 2 /redox exposure on the microstructure of the crystallites. The mixed oxides were prepared via co-precipitation of cerium(IV) ammonium hydroxide and zirconium oxynitrate using ammonium hydroxide. The oxides were characterized prior to and after SO 2 exposure to discern the effects of temperature and SO 2 on crystallite properties. The samples were treated at 673 and 1073 K with a flow of 100 ppm SO 2 /balance N 2 with a concomitant redox pulse of 5% H 2 /balance N 2 and 5% O 2 /balance N 2 on 10 s intervals. The cubic crystalline structure (CaF 2 ) was observed and maintained for compositions ranging from 100 to 25 at.% cerium without indication of a separate tetragonal phase. While the cubic structure was maintained, the addition of zirconium in the cubic lattice reduced the cubic lattice parameter ( a 0 ) and the crystallite grain size. Under identical redox conditions and temperatures, exposure to SO 2 resulted in smaller grain sizes, as calculated by X-ray diffraction (XRD) and confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In addition, higher exposure temperatures resulted in larger crystallite grain sizes without altering the cubic lattice parameter. Auger electron spectroscopy (AES) confirmed the absence of surface sulfur species, indicating sulfur dioxide alters the microstructure of the crystallites under redox conditions without the formation of cerium–zirconium chemisorbed sulfur species.