Thermal Stability and Dispersion Behavior of Nanostructured CexZr1-xO2 Mixed Oxides over Anatase-TiO2: A Combined Study of CO Oxidation and Characterization by XRD, XPS, TPR, HREM, and UV-Vis DRS

A study has been undertaken on the thermal stability and dispersion behavior of nanostructured CexZr1-xO2 mixed oxides over anatase-TiO2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported CexZr1-xO2 mixed oxide was also synthesized by coprecipitation method for the purpose of comparison. The structural/morphological characterization was performed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS). UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and temperature-programmed reduction (TPR) techniques. XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 phase at 773 K and incorporation of more zirconium into the ceria lattice at higher temperatures. HREM analysis conformed highly dispersed Ce-Zr nano-oxides over anatase-TiO2 support having the sizes in the range of 3-5 nm at 773 K. At hi-her temperatures, a slight increase in the crystallite size(5-10 nm) has been observed. The XPS measurements revealed the stabilization of Ce3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV-vis DRS studies showed that oxygen to metal (Ce4+/Ce3+) charge-transfer transitions Occur at lower wavelengths in the case of CexZr1-xO2/TiO2 compared to pure CexZr1-xO2. TPR experiments revealed that the surface reduction of CexZr1-xO2,/TiO2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported CexZr1-xO2.