High Catalytic Activity in CO Oxidation over MnO x Nanocrystals Viacheslav Iablokov • Krisztina Frey • Olga Geszti • Norbert Kruse Received: 29 October 2009 / Accepted: 29 November 2009 / Published online: 16 December 2009 Ó Springer Science+Business Media, LLC 2009 Abstract 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 m 2 /g. Annealing at 798 K rather than 633 K produced well crystalline Mn 2 O 3 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. Keywords Manganese oxides  Microrods  Nanocrystals  CO oxidation  Oxalate precipitation 1 Introduction Current efforts in increasing both, the activity and the selectivity of solid oxidation catalysts are based on intro- ducing concepts of nanotechnology into the procedures of catalyst preparation. With regard to CO oxidation, large attention is devoted to oxide-supported noble metals both in fundamental and applied research. According to Haruta et al. [1], nano-sized gold particles supported on reducible oxides are highly active in the CO oxidation reaction far below room temperature. The group of Somorjai [2, 3], in studies with Rh-based model catalysts, report the shape of the nano-sized metal particles to play a decisive role in determining the selectivity of CO oxidation with NO. While in some cases of catalysis by metals the strong influence of the particle size and shape has been success- fully demonstrated, this is much less so for metal oxide systems. Mn-oxides, for example, may exhibit high activity in CO oxidation, however, no clear microstructural corre- lation seems to be established despite the observation of nanorods and nanosized-particles of various chemical composition. Klier et al. [4] and Kanungo [5] find high catalytic activity over bulk MnO 2 at 293 K and 353 K, respectively. Luo et al. [6] report on the synthesis, prop- erties and catalytic performance of octahedral molecular Electronic supplementary material The online version of this article (doi:10.1007/s10562-009-0244-0) contains supplementary material, which is available to authorized users. V. Iablokov  K. Frey  O. Geszti  N. Kruse Chemical Physics of Materials, Universite ´ Libre de Bruxelles, CP 243, Brussels 1050, Belgium K. Frey (&) Department of Surface Chemistry and Catalysis, Institute of Isotopes, Konkoly Thege Miklo ´s u ´t 29/33, 1121 Budapest, Hungary e-mail: frey@mail.kfki.hu O. Geszti Research Institute for Technical Physics and Materials Science, Konkoly Thege Miklo ´s u ´t 29/33, 1121 Budapest, Hungary 123 Catal Lett (2010) 134:210–216 DOI 10.1007/s10562-009-0244-0