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Temperature-dependent dynamics of NH3-derived Cu species in the Cu-CHA SCR catalyst

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Abstract

The Cu-exchanged CHA zeolite (Cu-CHA) is a promising catalyst for the NH3-assisted selective catalytic reduction (NH3-SCR) of harmful nitrogen oxides (NOx, x = 1, 2), combining high hydrothermal stability with good performance in the 200–550 °C range. Despite many recent breakthroughs in the molecular-scale understanding of this catalyst, several open questions remain to ultimately unravel the NH3-SCR mechanism across the operation-relevant temperature range. In this context, we apply in situ XAS and UV-vis–NIR spectroscopy to assess the nature and thermal stability of NH3-derived Cu-species in a commercial Cu-CHA deNOx catalyst. Both techniques evidence fast and complete ‘solvation’ by NH3 of the framework-coordinated CuII and CuI ions formed upon thermal activation of the catalyst. Our results confirm that NH3 desorption at T > 200 °C is accompanied by CuII → CuI reduction phenomena, while the compresence of pre-adsorbed NH3 with gas-phase NO greatly enhances the reduction rate and efficiency. By applying state-of-the-art multivariate curve resolution (MCR) analysis, we elaborate these insights in a quantitative picture of Cu-speciation during NH3 temperature-programmed desorption (TPD) and surface reaction (TPSR) experiments. MCR analysis confirms recent theoretical predictions for the thermal stability of [CuI(NH3)2]+ species and allows us to experimentally identify the framework-coordinated Ofw–CuI–NH3 intermediate formed upon desorption of a NH3 ligand from [CuI(NH3)2]+.

Graphical abstract: Temperature-dependent dynamics of NH3-derived Cu species in the Cu-CHA SCR catalyst

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Publication details

The article was received on 30 Nov 2018, accepted on 21 Feb 2019 and first published on 21 Feb 2019


Article type: Paper
DOI: 10.1039/C8RE00322J
Citation: React. Chem. Eng., 2019, Advance Article

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    Temperature-dependent dynamics of NH3-derived Cu species in the Cu-CHA SCR catalyst

    E. Borfecchia, C. Negri, K. A. Lomachenko, C. Lamberti, T. V. W. Janssens and G. Berlier, React. Chem. Eng., 2019, Advance Article , DOI: 10.1039/C8RE00322J

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