Adsorption of NO on Cu-SAPO-34 and Co-SAPO-34: A Periodic DFT Study

Author(s)

Ellie Uzunova, Hans Mikosch, Juergen Hafner

Abstract

The location of Cu(I), Cu(II), and Co(II) cations at the extraframework

sites of metal cation exchanged SAPO-34 as well as their adsorption

properties toward NO are studied by periodic DFT calculations with the

PW91 functional. The relative stability of configurations with variable

positions of the Si → P substitutions and cation sites was examined;

structures with the divalent cation located in proximity to closely

spaced negative framework charges were of highest stability. The highest

adsorption capacities of the divalent Cu and Co cations were determined

for an environment with Si → P substitutions separated in the unit

cells, but the interaction between the cation and the more distant

negative charges is important for the formation of a stable adsorption

complex. The Cu(I)−NO configuration in SAPO-34 is bent, with an angle

∠Cu(I)−N−O of 141.0°. This enables an interaction of the dz²

state of the cation with both the σ and π* molecular orbitals.

Backdonation to the π* state leads to a red-shift of the NO stretching

frequency by ∼100 cm^-1, in good agreement with experiment.

For divalent metal cations Cu(II) and Co(II), the highest adsorption

energies are related to wider ∠M(II)−N−O angles, shorter M(II)−N bonds,

and a slightly weakened N−O bond, indicating a significant electrostatic

contribution (ion-dipole interactions) to the bonding and a much less

pronounced d_π → π* back-donation, as reflected by an almost unchanged NO stretching frequency.

Organisation(s)

Computational Materials Physics

External organisation(s)

Bulgarian Academy of Sciences (BAS), Technische Universität Wien

Journal

The Journal of Physical Chemistry Part C (Nanomaterials and Interfaces)

Volume

112

Pages

2632–2639

No. of pages

ISSN

1932-7447

DOI

https://doi.org/10.1021/jp0774903

Publication date

2008

Peer reviewed

Yes

Austrian Fields of Science 2012

104017 Physical chemistry

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