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Published on: August 18, 2020
Nitrogen oxide reaction with six-atom silver clusters supported on LTA zeolite
Amgalanbaatar Baldansuren1, Rüdiger-A Eichel, Emil Roduner
1Institut für Physikalische Chemie, Universität Stuttgart, D-70569, Stuttgart, Germany.
Physical Chemistry Chemical Physics : PCCP
|July 30, 2009
Summary
Silver catalysts in LTA zeolite form unique Ag(6)(+) clusters. These clusters interact with nitrogen monoxide (NO) and nitrogen dioxide (NO2), revealing insights into catalytic reactions and molecular dynamics.
Area of Science:
- Materials Science
- Catalysis
- Spectroscopy
Background:
- Silver-containing LTA zeolites are synthesized via aqueous ion exchange.
- Characterization reveals a specific paramagnetic Ag(6)(+) cluster after oxidation and reduction.
- This cluster structure is crucial for understanding its reactivity.
Purpose of the Study:
- To investigate the interaction of Ag(6)(+) clusters with nitrogen monoxide (NO) and nitrogen dioxide (NO2).
- To elucidate the structural and dynamic properties of adsorbed NO and NO2 on the silver catalyst.
- To determine the kinetic parameters and activation energy for the rotational motion of adsorbed NO2.
Main Methods:
- Preparation of silver-containing LTA zeolite catalysts using aqueous ion exchange.
- Characterization of silver clusters using Continuous Wave Electron Paramagnetic Resonance (CW-EPR) and Hyperfine Sublevel Correlated Spectroscopy (HYSCORE).
- Analysis of EPR lineshapes to study molecular dynamics and determine kinetic parameters.
Main Results:
- A well-defined, isolated Ag(6)(+) paramagnetic cluster was formed.
- Upon NO addition, the Ag(6)(+) cluster spectrum vanished, replaced by signals attributed to adsorbed NO and NO2.
- Hyperfine interactions indicated NO binding to a silver nucleus and proximity to a second nitrogen spin.
- NO2 exhibited temperature-dependent rotational dynamics, with axially symmetric to isotropic diffusion observed between 30-125 K.
Conclusions:
- The Ag(6)(+) cluster in LTA zeolite readily interacts with NO, forming adsorbed species.
- EPR spectroscopy effectively probes the binding and dynamics of NO and NO2 on silver catalysts.
- The study provides activation energy for NO2 rotational motion, contributing to understanding catalytic mechanisms.
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