Ceria-Manganese Mixed Oxides as Catalyst for Soot and Co Oxidation Activity

Abstract

Automobile exhaust catalysts, like three-way catalytic converters are known to use Ceria coating for the fine dispersion of Platinum Group Metals (PGM). The Ceria coating acts as an active support. PGMs have certain shortcomings, such as, high prices, sintering at relatively low temperatures, and fouling due to SO2. Doping Ceria with other metals, like in the present work Manganese, boosts its catalytic properties while lessening or negating any determinantal effects. Manganese-doped Ceria catalysts have been widely studied as a catalyst for a variety of applications due to their attractive properties attained due to synergy achieved by favorable defects, physicochemical, and morphological features aiding in the oxidation processes. A systematic study has been carried out in the present work to study the effect of Manganese doping in Ceria and its soot oxidation activity from nanostructured powder to CO oxidation activity on structured catalysts, i.e., catalyst coated on to an Alumina wash-coated Cordierite honeycomb substrate. The EDTA-Citrate method was the choice of synthesis method for the powder catalyst. Since the variation in the atomic radius of both cations (Ce and Mn) is very large, phase difference and the existence of multiple oxidation states in Manganese, a complete solid solution is not feasible over the entire range of Manganese doping into the Ceria lattice. Consequently, two series of nanostructured powder catalysts were obtained, namely, Ceria-rich Ceria-Manganese and Manganese-rich Ceria-Manganese mixed oxides, with interesting morphological features attained due to the solubility limits. Ceria-Manganese mixed oxides (nanostructured powder catalysts) were examined by XRD, Raman spectroscopy, BET and BJH, FESEM, and TEM characterization techniques. A dip-coating technique was employed for coating of the Cordierite honeycomb substrate. The structured catalysts were utilized for CO oxidation. The adherence of the coating was tested by ultrasonication. XRD, Raman spectroscopy, and BET analysis probed the physicochemical parameters. Digital optical microscopy, and FESEM analysis analyzed the morphological features. Overall, the thesis concentrates on developing compositions of Ceria-Manganese oxides for soot and CO oxidation activity for a Catalyzed Diesel Particulate Filter (CDPF).