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Abstract
The diffusion of ammonia in commercial NH3-SCR catalyst Cu-CHA was measured and compared with H-CHA using quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations to assess the effect of counterion presence on NH3 mobility in automotive emission control relevant zeolite catalysts. QENS experiments observed jump diffusion with a jump distance of 3 Å, giving similar self-diffusion coefficient measurements for both Cu- and H-CHA samples, in the range of ca. 5–10 × 10−10 m2 s−1 over the measured temperature range. Self-diffusivities calculated by MD were within a factor of 6 of those measured experimentally at each temperature. The activation energies of diffusion were also similar for both studied systems: 3.7 and 4.4 kJ mol−1 for the H- and Cu-chabazite respectively, suggesting that counterion presence has little impact on ammonia diffusivity on the timescale of the QENS experiment. An explanation is given by the MD simulations, which showed the strong coordination of NH3 with Cu2+ counterions in the centre of the chabazite cage, shielding other molecules from interaction with the ion, and allowing for intercage diffusion through the 8-ring windows (consistent with the experimentally observed jump length) to carry on unhindered
Original language | English |
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Pages (from-to) | 17159-17168 |
Number of pages | 10 |
Journal | Physical Chemistry Chemical Physics |
Volume | 18 |
Issue number | 26 |
Early online date | 1 Jun 2016 |
DOIs | |
Publication status | Published - 14 Jul 2016 |
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Dive into the research topics of 'Ammonia mobility in chabazite: insight into the diffusion component of the NH 3-SCR process'. Together they form a unique fingerprint.Projects
- 1 Finished
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The UK Catalysis Hub
Davidson, M. (PI)
Engineering and Physical Sciences Research Council
1/06/13 → 30/11/18
Project: Research council