Influence of solvent on selective catalytic reduction of nitrogen oxides with ammonia over cu-cha zeolite

Abdul Nasir, Jamal, Guan, Jingcheng, Keal, Thomas W., Desmoutier, Alec W., Lu, You, Beale, Andrew M., Catlow, Charles ORCID: https://orcid.org/0000-0002-1341-1541 and Sokol, Alexey A. 2023. Influence of solvent on selective catalytic reduction of nitrogen oxides with ammonia over cu-cha zeolite. Journal of the American Chemical Society 145 , pp. 247-259. 10.1021/jacs.2c09823

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Abstract

The copper-exchanged zeolite Cu-CHA has received considerable attention in recent years, owing to its application in the selective catalytic reduction (SCR) of NOx species. Here, we study the NH3-SCR reaction mechanism on Cu-CHA using the hybrid quantum mechanical/molecular mechanical (QM/MM) technique and investigate the effects of solvent on the reactivity of active Cu species. To this end, a comparison is made between water- and ammonia-solvated and bare Cu species. The results show the promoting effect of solvent on the oxidation component of the NH3-SCR cycle since the formation of important nitrate species is found to be energetically more favorable on the solvated Cu sites than in the absence of solvent molecules. Conversely, both solvent molecules are predicted to inhibit the reduction component of the NH3-SCR cycle. Diffuse reflectance infrared fourier-transform spectroscopy (DRIFTS) experiments exploiting (concentration) modulation excitation spectroscopy (MES) and phase-sensitive detection (PSD) identified spectroscopic signatures of Cu-nitrate and Cu-nitrosamine (H2NNO), important species which had not been previously observed experimentally. This is further supported by the QM/MM-calculated harmonic vibrational analysis. Additional insights are provided into the reactivity of solvated active sites and the formation of key intermediates including their formation energies and vibrational spectroscopic signatures, allowing the development of a detailed understanding of the reaction mechanism. We demonstrate the role of solvated active sites and their influence on the energetics of important species that must be explicitly considered for an accurate understanding of NH3-SCR kinetics.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry Cardiff Catalysis Institute (CCI)
Publisher:	American Chemical Society
ISSN:	0002-7863
Funders:	EPSRC
Date of First Compliant Deposit:	12 January 2023
Date of Acceptance:	22 December 2022
Last Modified:	11 May 2023 09:26
URI:	https://orca.cardiff.ac.uk/id/eprint/155812

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