High Catalytic Activity in CO Oxidation over MnO x Nanocrystals
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Manganese oxides of various stoichiometry were prepared via Mn-oxalate precipitation followed by thermal decomposition in the presence of oxygen. A non-stoichiometric manganese oxide, MnO x (x = 1.61…1.67) was obtained by annealing at 633 K and demonstrated superior CO oxidation activity, i.e. full CO conversion at room temperature and below. The activity gradually decreased with time-on-stream of the reactants but could be easily recovered by heating at 633 K in the presence of oxygen. CO oxidation over MnO x in the absence of oxygen proved to be possible with reduced rates and demonstrated a Mars—van Krevelen—type mechanism to be in operation. A TEM structural analysis showed the MnO x phase to form microrods with large aspect ratio which broke up into nanocrystalline manganese oxide (MnO x ) particles with diameters below 3 nm and a BET specific surface area of 525 m2/g. Annealing at 798 K rather than 633 K produced well crystalline Mn2O3 which showed lower CO oxidation activity, i.e. 100% CO conversion at 335 K. The catalytic performance in CO oxidation of various Mn-oxides either studied in this work or elsewhere was compared on the basis of specific reaction rates.
KeywordsManganese oxides Microrods Nanocrystals CO oxidation Oxalate precipitation
V. Iablokov gratefully acknowledges PhD. financial support by “ARC” (Communauté Française de Belgique). K Frey has been awarded a grant for short-term post-doctoral research at the ULB which is likewise acknowledged. We also acknowledge the technical help of I.E. Sajó for providing XRD characterisation. We are also grateful to the Hungarian Science and Research Fund OTKA grant No. NNF 78837.
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