Multiple adsorption of NO on Fe2+ cations in the a- and ß-Positions of ferrierite: An experimental and density functional study

Author(s)

Lubomir Benco, Tomas Bucko, Robert Grybos, Juergen Hafner, Zdenek Sobalik, Jiri Dedecek, Stepán Sklenak, J Hrusak

Abstract

Adsorption of NO on Fe-exchanged ferrierite is investigated by Fourier

transform infrared (FTIR) spectroscopy and ab initio periodic density

functional theory (DFT) calculations. The adsorption properties of

single Fe species located in the β- and α-site representing the two most

stable locations of the extraframework cation are probed. We consider a

divalent Fe(II) cation with two framework Al/Si substitutions, three

configurations with two Al atoms in the six-membered ring separated by

the −Si−O−Si− chain, and one configuration with two Al atoms in

different channels representing a low-Al zeolite. Upon adsorption of a

single NO molecule, a tetragonal pyramid forms with four in-plane Fe−O

bonds to the framework and one axial Fe−N bond. Upon adsorption of a

second NO molecule on a Fe²⁺ cation in the β-2, α-1, and α-2

sites, a cis tetrahedral complex is formed. In the most stable

configuration in the β-1 site, however, the planar Fe−O bonding is not

destroyed but is completed to a trans octahedral complex. The

tetrahedral complex contains an extraframework [Fe−(NO)₂]⁺

(dinitrosyl) particle, carrying only a single positive charge. Because

such a particle compensates only one Al/Si substitution, the resulting

charge imbalance induces a high chemical reactivity of the framework Al

sites. A third NO molecule therefore adsorbs on the activated oxygen

atoms next to the Al site whose charge remains unbalanced, and it is

oxidized to NO⁺. NO stretching frequencies of adsorption

clusters formed in Fe−FER are similar to those recorded on Fe−ZSM-5 and

Fe−silicatite. The calculated NO stretching frequencies agree well with

experimental data and support the proposed assignment to mono-, di-, and

trinitrosyl species. Before a trinitrosyl species is formed, one NO

molecule adsorbs on the Al site and converts to NO⁺. The calculated stretching frequencies of the NO⁺ cation agree with the IR band at 2000−2100 cm^-1.

Organisation(s)

Computational Materials Physics

External organisation(s)

Czech Academy of Sciences

Journal

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

Volume

111

Pages

9393-9402

No. of pages

10

ISSN

1932-7447

DOI

https://doi.org/10.1021/jp0724018

Publication date

2007

Peer reviewed

Yes

Austrian Fields of Science 2012

1030 Physics, Astronomy

Portal url

https://ucris.univie.ac.at/portal/en/publications/multiple-adsorption-of-no-on-fe2-cations-in-the-a-and-sspositions-of-ferrierite-an-experimental-and-density-functional-study(5560f688-cfec-42c1-ac11-c3be2b1e7605).html