Nanostructured MnOx as highly active catalyst for CO oxidation

• DOI: 10.1016/j.jcat.2011.11.014
• Publication Date: 2012-01-03T09:34:50Z
• Authors: Krisztina Frey; Viacheslav Iablokov; György Sáfrán; János Osán; István Sajó; Rafal Szukiewicz; Sergey Chenakin; Norbert Kruse
• Keywords: Nanocrystalline material; XANES; Stoichiometry; Oxidation state; X-ray absorption spectroscopy

Abstract Non-stoichiometric Mn-oxides (MnO x and MnO y ) were prepared by temperature-programmed oxidation (TPO) of Mn-oxalates, MnC 2 O 4 ·3H 2 O and MnC 2 O 4 ·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 μmol CO m −2 s −1 ) at 298 K. 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 MnO x . The Mn oxidation state in MnO x 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 MnO x , 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 Mn 3 O 4 phases were able to be identified in the regions between rods.