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 Ce x Zr 1− x O 2 mixed oxides over anatase-TiO 2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported Ce x Zr 1− x O 2 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 Ce 0.75 Zr 0.25 O 2 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-TiO 2 support having the sizes in the range of 3−5 nm at 773 K. At higher temperatures, a slight increase in the crystallite size (5−10 nm) has been observed. The XPS measurements revealed the stabilization of Ce 3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV−vis DRS studies showed that oxygen to metal (Ce 4+ /Ce 3+ ) charge-transfer transitions occur at lower wavelengths in the case of Ce x Zr 1− x O 2 /TiO 2 compared to pure Ce x Zr 1− x O 2 . TPR experiments revealed that the surface reduction of Ce x Zr 1− x O 2 /TiO 2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported Ce x Zr 1− x O 2 .