Jump to main content
Jump to site search


Origin of enhanced Brønsted acidity of NiF-modified synthetic mica–montmorillonite clay

Author affiliations

Abstract

The Brønsted acidity of synthetic mica–montmorillonite (SMM) clay was studied by periodic DFT calculations. Different structural models were compared to determine the Brønsted acidity of protons of the SMM clay based on (i) isomorphous substitution of Si4+ by Al3+ in the tetrahedral silicate layer and additional NiF-doping (ii) in the platelets and (iii) at the edge terminations of the clay platelets. The acid strength was judged from the computed adsorption energies of ammonia and pyridine. The SMM acidity is mainly determined by the composition of the clay platelets. The strongest acidity is found in structures in which octahedral [AlO]+ is replaced by [NiF]+ adjacent to tetrahedral [Si–(OH)–Al] moieties in the tetrahedral layer. For the Brønsted acid sites in the interlayer of SMM, modification with either Ni2+ or F in the octahedral layers has only a minor influence on the acidity. Our data indicate that Brønsted acid sites, properly modified in the second coordination shell by electron-withdrawing F, in the interlayer and at defect sites at the edges of clay platelets (intralayer sites) can contribute to the enhanced acidity in NiF-modified SMM. Although the predicted acidity of SMM by ammonia adsorption is higher than that of faujasite zeolite, the reactivity judged from propene protonation demonstrates that zeolites are more reactive than clays. This difference seems to be the result of the curved nature of the micropores of zeolites, which stabilizes the transition states for an acid-catalyzed reaction more than flat surfaces of clays do.

Graphical abstract: Origin of enhanced Brønsted acidity of NiF-modified synthetic mica–montmorillonite clay

Back to tab navigation

Supplementary files

Publication details

The article was received on 08 Oct 2017, accepted on 19 Nov 2017 and first published on 28 Nov 2017


Article type: Paper
DOI: 10.1039/C7CY02053H
Citation: Catal. Sci. Technol., 2018, Advance Article
  • Open access: Creative Commons BY license
  •   Request permissions

    Origin of enhanced Brønsted acidity of NiF-modified synthetic mica–montmorillonite clay

    C. Liu, E. A. Pidko and E. J. M. Hensen, Catal. Sci. Technol., 2018, Advance Article , DOI: 10.1039/C7CY02053H

    This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material.

    Reproduced material should be attributed as follows:

    • For reproduction of material from NJC:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.
    • For reproduction of material from PCCP:
      [Original citation] - Published by the PCCP Owner Societies.
    • For reproduction of material from PPS:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC.
    • For reproduction of material from all other RSC journals:
      [Original citation] - Published by The Royal Society of Chemistry.

    Information about reproducing material from RSC articles with different licences is available on our Permission Requests page.

Search articles by author

Spotlight

Advertisements