Design of novel ceria-based nano-oxides for CO oxidation and other catalytic applications

Abstract

Carbon monoxide oxidation over various ceria-based solid solutions has been reviewed. The advantageous incorporation of various dopants in the ceria lattice (Ce_xM_1–xO₂; M = Zr and Hf, and Ce_xM_1–xO_2-_{<span style="font-family:Symbol;mso-ascii-font-family:" times="" new="" roman";="" mso-hansi-font-family:"times="" roman";mso-char-type:symbol;mso-symbol-font-family:="" symbol"="" lang="EN-GB">d</span>}; M = La and Pr) to improve oxygen storage capacity and CO oxidation activity have been addressed. Nanosized doped ceria solid solutions are synthesized by a newly developed coprecipitation method from ultrahigh dilute aqueous solutions. To establish the thermal stability, the synthesized materials have been calcined at 773 and 1073 K and thoroughly characterized by various state-of-the-art techniques. The structural features have been investigated by X–ray diffraction, transmission electron microscopy, Raman spectroscopy, UV–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and BET surface area. X-ray differaction and Raman Spectroscopic studies establish the formation of solid solutions and the TEM analysis specifies the nanosized nature of the mixed oxides. Further, the XPS and UV–vis DRS studies establish the existence of cerium in both 3+ and 4+ oxidation states and the presence of oxygen vacancies, respectively. Among various combinations, the ceria-hafnia solid solution exhibits the best oxygen storage capacity and excellent CO oxidation activity. As revealed by this model study, there is ample scope to design better materials for CO oxidation and related pollution abatement applications.