Nanostructured MnOx as highly active catalyst for CO oxidation

Non-stoichiometric Mn-oxides (MnOx and MnOy) were prepared by temperature-programmed oxidation (TPO) of Mn-oxalates, MnC2O4 center dot 3H(2)O and MnC2O4 center dot 2H(2)O. Both oxides provide high specific surface areas (525 m(2) g(-1) and 385 m(2) g(-1), respectively) and identical CO oxidation reaction rates of 10(-2) molecules nm(-2) s(-1) (0.017 mu mol(co) m(-2) s(-1)) at 298K. A spinodal transformation of oxalates into oxides was observed by transmission electron microscopy (TEM). The quantitative evaluation of TPO and temperature-programmed reduction with CO allowed x-values of 1.61,...,1.67 to be determined for MnOx. The Mn oxidation state in MnOx was found to be 3.4 +/- 0.1 by X-ray absorption near-edge structure analysis and X-ray photoelectron spectroscopy. In accordance with the high specific surface area and mixed-type I/IV adsorption isotherms of MnOx, high resolution TEM demonstrated the occurrence of nested micro-rod features along with nanocrystalline particles in the endings of the rods. After CO oxidation MnO and Mn3O4 phases were able to be identified in the regions between rods. (C) 2011 Published by Elsevier Inc.