The present review devoted to the complete oxidation of CO using alkali- and alkaline-earth metal (AM/AEM)-modified ceria supported/mixed with noble metal and non-noble metal (NM). The AM/AEM-modified Ce supported/mixed with noble metal showed comparable CO oxidation with unmodified catalyst. However, AM/AEM modified NM showed higher CO oxidation at lower temperature compared to the unmodified catalyst. The AM and AEM modifications were responsible for the formation of oxygen vacancies in Ce, which leads to the decrease in the CO and O$_2$ activation barrier. The dissociative oxygen adsorption on AM/AEM-modified Ce-supported/mixed with NM favours the CO oxidation at a lower temperature. However, AM/AEM-modified Ce-supported/mixed with noble metal showed CO adsorption with formation of superoxy and peroxy species, which leads to the comparable oxidation activity. The plausible mechanism for CO oxidation is explained in detail with correlation to the characterizations.

The series of bimetallic Co and Mn supported on hydroxyapatite (HAp) catalysts were prepared by successive deposition method and examined for CO oxidation. The catalysts are characterized in detail and correlated to oxidation activity. The X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction characterization showed the presence of more facile Co$^{2+}$, Mn$^{3+}$ and adsorbed oxygen. The attenuated total reflection-Fourier transform infrared demonstrated the adsorption of water on active sites of catalyst was responsible for the shifting of activity towards higher temperatures. The Co$_{0.4}$/Mn$_{0.1}$ /HAp catalyst showed lower activation energy for CO oxidation compared to the monometallic catalysts. Interaction between Mn, Co and HAp could be responsible for the existence of Co$^{2+}$, Mn$^{3+}$ and adsorbed oxygen, which are active species for CO oxidation.