Temperature-dependent dynamics of NH3-derived Cu species in the Cu-CHA SCR catalyst. Issue 6 (8th March 2019)

• Record Type: Journal Article
• Authors: Borfecchia, Elisa; Negri, Chiara; Lomachenko, Kirill A.; Lamberti, Carlo; Janssens, Ton V. W.; Berlier, Gloria
• Is Part Of: Reaction chemistry & engineering. Volume 4:Issue 6(2019)
• Page Start: 1067
• Page End: 1080
• Publication Date: 2019-03-08
• Subjects: Reaction mechanisms (Chemistry) -- Periodicals; Chemical engineering -- Periodicals; Chemical engineering; Reaction mechanisms (Chemistry); Periodicals; 547.705
• DOI: 10.1039/c8re00322j
• Languages: English
• ISSNs: 2058-9883

Abstract

Abstract : In situ XAS and UV-vis–NIR spectroscopy shed light on Cu-speciation during NH3 temperature-programmed desorption and surface reaction (TPSR) over a commercial Cu-chabazite deNO x catalyst, expanding the fundamental knowledge required to unravel the NH3 -SCR mechanism across the whole operation-relevant temperature range. 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 (NO x, 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 deNO x catalyst. Both techniques evidence fast and complete 'solvation' by NH3 of the framework-coordinated Cu II and Cu I ions formed upon thermal activation of the catalyst. Our results confirm that NH3 desorption at T > 200 °C is accompanied by Cu II → Cu I 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 [Cu I (NH3 )2 ] + species and allows us to experimentally identify the framework-coordinated Ofw –Cu I –NH3 intermediate formed upon desorption of a NH3 ligand from [Cu I (NH3 )2 ] + .