Mechanism of CH4 activation on a monomeric Zn2+-ion exchanged in MFI-Type zeolite with a specific Al arrangement: Similarity to the activation site for H2

Akira Oda, Hiroe Torigoe, Atsushi Itadani, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

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30 Citations (Scopus)

Abstract

In this work, we used both experimental and density functional theory (DFT) calculation methods to examine the mechanism of CH4 activation taking place on the Zn2+ ion exchanged MFI-type zeolite (ZnMFI). The heterolytic dissociation of CH4 on ZnMFI around 300 K was observed experimentally, causing the appearance of IR bands at 3615, 2930, and 2892 cm-1. The first band can be assigned to the OH stretching vibration associated with the formation of the Brønsted acid site and the latter to the C-H stretching modes ascribable to the -[ZnCH3]+ species. Combining the IR spectroscopy with a DFT calculation, it is apparent that the heterolytic C-H bond dissociation of CH4 has an activation energy of 15 kJ mol-1 and takes place on a monomeric Zn2+ at the M7S2 site. The M7S2 site has a specific Al arrangement in MFI and exhibits a pronounced reactivity for the H-H bond cleavage of H2, even at room temperature. In addition, to our knowledge, we are the first to succeed in explaining the dissociation process of CH4 by applying natural bond orbital (NBO) and interaction localized orbital (ILO) analyses to the present system; the donation interaction from the CH4-σ(C- H) orbital to the Zn-4s orbital triggers the cleavage of the C-H bond of CH 4 under mild conditions.

Original languageEnglish
Pages (from-to)19525-19534
Number of pages10
JournalJournal of Physical Chemistry C
Volume117
Issue number38
DOIs
Publication statusPublished - Sep 26 2013

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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