Mechanism for Cu-enhanced hydrothermal stability of Cu-CHA for NH3-SCR
Journal article, 2024

Exposure of acidic zeolite-based catalysts to water at high temperatures generally leads to deactivation due to dealumination. In Cu-CHA zeolite, which is a preferred catalyst for the selective catalytic reduction of NO by NH3 (NH3-SCR), the acidic protons in the zeolite are partially exchanged by Cu ions. The presence of Cu has been measured to reduce the rate of dealumination, thus stabilizing the catalyst. To understand the stabilizing effect of Cu, density functional theory calculations, ab initio thermodynamics and microkinetic modeling are used to compare the reaction mechanism for the dealumination of H-CHA to Cu-CHA. For H-CHA, we find that dealumination leads to the formation of mobile Al(OH)3H2O (extra-framework aluminum) species, whereas for Cu-CHA, formation of framework bound Cu-Al species is thermodynamically preferred over Al(OH)3H2O, which results in the increased stability of Cu-CHA. The formation of mobile Al(OH)3H2O in Cu-CHA is, moreover, associated with a high energy barrier. The phase diagrams show the formation of Al(OH)3H2O and Al2O3 from H-CHA and that high temperatures favor the formation of Al2O3. For Cu-CHA, high temperatures lead to the formation of CuO and Al2O3, which is favored over Al(OH)3H2O + CuO. The microkinetic model shows that the formation of Al(OH)3H2O in the presence of water starts at 380 K and 800 K in H-CHA and Cu-CHA, respectively. Additionally, the time evolution of the Al(OH)3H2O coverage at 923 K reveals that the process of dealumination is significantly faster for H-CHA as compared to Cu-CHA, which is in accordance with the measured increased stability.

Author

Shivangi Singh

Chalmers, Physics, Chemical Physics

Umicore

Ton Janssens

Umicore

Henrik Grönbeck

Chalmers, Physics, Chemical Physics

Catalysis Science and Technology

2044-4753 (ISSN) 2044-4761 (eISSN)

Vol. 14 12 3407-3415

KCK - Kompetenscentrum Katalys 2022-2026

Umicore Denmark ApS (KCK2022-2026), 2022-01-01 -- 2026-12-31.

Johnson Matthey (2500123383), 2022-01-01 -- 2026-12-31.

Volvo Group (PO:2435702-000), 2022-01-01 -- 2026-12-31.

Scania CV AB (Dnr:2021-036543Pnr:52689-1), 2022-01-01 -- 2026-12-31.

Preem (KCK2022-2026), 2022-01-01 -- 2026-12-31.

Cu-CHA zeolite-based catalysts for the selective catalytic reduction of NOx in exhaust diesel gas: addressing the issue of Sulfur Stability (CHASS)

European Commission (EC) (EC/H2020/955839), 2021-06-01 -- 2025-05-31.

Subject Categories

Inorganic Chemistry

Materials Chemistry

Organic Chemistry

DOI

10.1039/d4cy00373j

More information

Latest update

6/29/2024