Temperature-dependent dynamics of NH 3 -derived Cu species in the Cu-CHA SCR catalyst

The Cu-exchanged CHA zeolite (Cu-CHA) is a promising catalyst for the NH 3 -assisted selective catalytic reduction (NH 3 -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 NH 3 -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 NH 3 -derived Cu-species in a commercial Cu-CHA deNO x catalyst. Both techniques evidence fast and complete ‘solvation’ by NH 3 of the framework-coordinated Cu II and Cu I ions formed upon thermal activation of the catalyst. Our results confirm that NH 3 desorption at T > 200 °C is accompanied by Cu II → Cu I reduction phenomena, while the compresence of pre-adsorbed NH 3 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 NH 3 temperature-programmed desorption (TPD) and surface reaction (TPSR) experiments. MCR analysis confirms recent theoretical predictions for the thermal stability of [Cu I (NH 3 ) 2 ] + species and allows us to experimentally identify the framework-coordinated O fw –Cu I –NH 3 intermediate formed upon desorption of a NH 3 ligand from [Cu I (NH 3 ) 2 ] + .