Översikt
- Datum:Startar 23 januari 2026, 10:00Slutar 23 januari 2026, 13:00
- Plats:PJ-salen, Origohuset, Fysik, Chalmers.
- Opponent:Prof. William S. Epling, Department of Chemical Engineering, University of Virginia, USA
- AvhandlingLäs avhandlingen (Öppnas i ny flik)
Selective catalytic reduction using ammonia (NH3-SCR) is a critical technology for the control of NOx emissions from lean-burn engines. Cu-exchanged chabazite (Cu-CHA) materials are currently the preferred catalysts for NH3-SCR thanks to their excellent activity and selectivity at low temperatures. However, Cu-CHA suffers from deactivation due to water inhibition, hydrothermal aging, and sulfur poisoning. In this thesis, detailed mechanisms for the three deactivation paths are studied by density functional theory (DFT) based kinetic modeling and reactor experiments.
At low-temperature (200 °C), high partial pressures of H2O inhibits the NH3-SCR by competing with NO and NH3 for adsorption on active Cu sites. At high-temperature (>650 °C), H2O causes hydrothermal aging, primarily through dealumination, i.e., removal of framework Al thereby Brønsted acid sites (BAS). DFT calculations reveal similar fourstep hydrolysis pathways for dealumination in H-CHA and Cu-CHA, with extra-framework Al(OH)3(H2O) formed in H-CHA and Al(OH)3(H2O) together with Cu–Al species in Cu-CHA. The higher dealumination barriers in Cu-CHA and the thermodynamic stability of Cu–Al formation explain the experimentally observed enhanced stability of CHA in the presence of Cu. Dealumination of H-CHA is quantified by NH3-Temperature-Programmed Desorption (NH3-TPD) and 27Al Nuclear Magnetic Resonance (27Al-NMR) measurements. A quantitative comparison shows that NH3-TPD overestimates dealumination via a self-exchange reaction in which extra-framework Al(OH)3(H2O) accepts protons from neighboring BAS, leading to an apparent loss of acidity without framework Al removal.
Hydrothermal aging affects the kinetics of NH3-SCR at low-temperature (200 °C). Experiments show two different deactivation mechanisms attributed to loss of BAS and decreased formation of [Cu2(NH3)4O2]2+, which is a key intermediate for low-temperature SCR. Hydrothermal aging affects SO2 deactivation marginally, indicating that SO2 deactivation is largely independent of hydrothermal aging.
The proposed deactivation mechanism links loss in SCR performance to changes in Brønsted acid site and Cu speciation for each type of deactivation. The work provides mechanistic insights to improve catalyst durability during water-induced deactivation at
high temperatures, high pressures and SO2 exposure.
At low-temperature (200 °C), high partial pressures of H2O inhibits the NH3-SCR by competing with NO and NH3 for adsorption on active Cu sites. At high-temperature (>650 °C), H2O causes hydrothermal aging, primarily through dealumination, i.e., removal of framework Al thereby Brønsted acid sites (BAS). DFT calculations reveal similar fourstep hydrolysis pathways for dealumination in H-CHA and Cu-CHA, with extra-framework Al(OH)3(H2O) formed in H-CHA and Al(OH)3(H2O) together with Cu–Al species in Cu-CHA. The higher dealumination barriers in Cu-CHA and the thermodynamic stability of Cu–Al formation explain the experimentally observed enhanced stability of CHA in the presence of Cu. Dealumination of H-CHA is quantified by NH3-Temperature-Programmed Desorption (NH3-TPD) and 27Al Nuclear Magnetic Resonance (27Al-NMR) measurements. A quantitative comparison shows that NH3-TPD overestimates dealumination via a self-exchange reaction in which extra-framework Al(OH)3(H2O) accepts protons from neighboring BAS, leading to an apparent loss of acidity without framework Al removal.
Hydrothermal aging affects the kinetics of NH3-SCR at low-temperature (200 °C). Experiments show two different deactivation mechanisms attributed to loss of BAS and decreased formation of [Cu2(NH3)4O2]2+, which is a key intermediate for low-temperature SCR. Hydrothermal aging affects SO2 deactivation marginally, indicating that SO2 deactivation is largely independent of hydrothermal aging.
The proposed deactivation mechanism links loss in SCR performance to changes in Brønsted acid site and Cu speciation for each type of deactivation. The work provides mechanistic insights to improve catalyst durability during water-induced deactivation at
high temperatures, high pressures and SO2 exposure.
