Structural and chemical disorder of cryptomelane promoted by alkali doping: Influence on catalytic properties

V. P. Santos*, O. S.G.P. Soares, J. J.W. Bakker, M. F.R. Pereira, J. J.M. Órfão, Jorge Gascon Sabate, F. Kapteijn, J. L. Figueiredo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

118 Scopus citations

Abstract

Different amounts of cesium (0.8-1.3 at.%) and lithium (up to 0.5 at.%) were introduced in the tunnel structure of cryptomelane in order to tailor its physical and chemical properties. The mechanism by which cryptomelane accommodates these alkali cations is different; Li occupies mainly empty sites by a redox-type reaction, while Cs is ion-exchanged by H 3O + cations. The adsorption of these alkali metals into cryptomelane was highly selective and is dictated by the solvation energy and ionic radius. Extrinsic defects (e.g. positive holes and oxygen vacancies) are created upon doping, enhancing the redox-properties of cryptomelane. The basicity of the framework also increases when Cs and Li are incorporated. The catalytic properties of this material were tested in the oxidation of ethyl acetate, and greatly improved after doping. The observed activity increase is explained by the redox and basic properties of the modified materials. The amount of cesium loaded has no effect on the activity, as a result of pore mouth catalysis.

Original languageEnglish (US)
Pages (from-to)165-174
Number of pages10
JournalJournal of Catalysis
Volume293
DOIs
StatePublished - Sep 1 2012

Keywords

  • Alkali doping
  • Cryptomelane
  • Oxidation
  • VOC

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

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