An EPR and NMR study on Mo/HZSM-5 catalysts for the aromatization of methane: Investigation of the location of the pentavalent molybdenum


Vu Thi Thu Ha V. T. T. H. , Sarioglan A. , Erdem-Senatalar A., Ben Taarit Y.

Journal of Molecular Catalysis A: Chemical, vol.378, pp.279-284, 2013 (Journal Indexed in SCI Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 378
  • Publication Date: 2013
  • Doi Number: 10.1016/j.molcata.2013.06.020
  • Title of Journal : Journal of Molecular Catalysis A: Chemical
  • Page Numbers: pp.279-284

Abstract

EPR and Al-27 NMR were used to probe the nature of the phases that formed during the conversion of methane at high temperature on the Mo/HZSM-5 catalyst. It was shown that ammonium 6-molybdoaluminate III supported over silica gave rise, when reduced, to an EPR signal due to Mo5+ ions with the odd electron interacting with the nonzero nuclear spin of aluminum in much the same way as in HZSM-5. Therefore, the occurrence of this particular spin interaction should not be taken as evidence of the location of the Mo5+ ions at the exchange sites of the zeolites. Rather, combined Al-27 NMR and EPR investigation of the reduction of a pure polycrystalline aluminum molybdate suggested that the observed signal in the case of the zeolite composite catalyst was due to Mo5+ ions formed within the Al-2(MoO4)(3) extra phase that formed upon dealumination of the zeolite in the presence of molybdenum. (c) 2013 Elsevier B.V. All rights reserved.