Center for Molecular Modeling - R. Millan

Mobility and Reactivity of Cu+ Species in Cu-CHA Catalysts under NH3-SCR-NOx Reaction Conditions: Insights from AIMD Simulations

cnudde — Fri, 17 Sep 2021 15:35:11 +0000

R. Millan, P. Cnudde, V. Van Speybroeck, M. Boronat

JACS Au (Journal of the American Chemical Society)

1 (10), 1778–1787

2021

Abstract

The mobility of the copper cations acting as active sites for the selective catalytic reduction of nitrogen oxides with ammonia in Cu-CHA catalysts varies with temperature and feed composition. Herein, the migration of [Cu(NH3)2]+ complexes between two adjacent cavities of the chabazite structure, including other reactant molecules (NO, O2, H2O, and NH3), in the initial and final cavities is investigated using ab initio molecular dynamics (AIMD) simulations combined with enhanced sampling techniques to describe hopping events from one cage to the other. We find that such diffusion is only significantly hindered by the presence of excess NH3 or NO in the initial cavity, since both reactants form with [Cu(NH3)2]+ stable intermediates which are too bulky to cross the 8-ring windows connecting the cavities. The presence of O2 modifies strongly the interaction of NO with Cu+. At low temperatures, we observe NO detachment from Cu+ and increased mobility of the [Cu(NH3)2]+ complex, while at high temperatures, NO reacts spontaneously with O2 to form NO2. The present simulations give evidence for recent experimental observations, namely, an NH3 inhibition effect on the SCR reaction at low temperatures, and transport limitations of NO and NH3 at high temperatures. Our first principle simulations mimicking operating conditions support the existence of two different reaction mechanisms operating at low and high temperatures, the former involving dimeric Cu(NH3)2-O2-Cu(NH3)2 species and the latter occurring by direct NO oxidation to NO2 in one single cavity.

Gold Open Access

DOI

http://dx.doi.org/10.1021/jacsau.1c00337

Theoretical and Spectroscopic Evidence of the Dynamic Nature of Copper Active Sites in Cu-CHA Catalysts under Selective Catalytic Reduction (NH3–SCR–NOx) Conditions

cnudde — Thu, 03 Dec 2020 08:53:24 +0000

R. Millan, P. Cnudde, A.E.J. Hoffman, C.W. Lopes, P. Concepcion, V. Van Speybroeck, M. Boronat

Journal of Physical Chemistry Letters

11, 23, 10060-10066

2020

Abstract

The dynamic nature of the copper cations acting as active sites for selective catalytic reduction of nitrogen oxides with ammonia is investigated using a combined theoretical and spectroscopic approach. Ab initio molecular dynamics simulations of Cu-CHA catalysts in contact with reactants and intermediates at realistic operating conditions show that only ammonia is able to release Cu+ and Cu2+ cations from their positions coordinated to the zeolite framework, forming mobile Cu+(NH3)2 and Cu2+(NH3)4 complexes that migrate to the center of the cavity. Herein, we give evidence that such mobilization of copper cations modifies the vibrational fingerprint in the 800–1000 cm–1 region of the IR spectra. Bands associated with the lattice asymmetric T-O-T vibrations are perturbed by the presence of coordinated cations, and allow one to experimentally follow the dynamic reorganization of the active sites at operating conditions.

DOI

http://dx.doi.org/10.1021/acs.jpclett.0c03020

Machine Learning Assisted Decoding of Light Olefin Transport in Cage-Based Zeolites

cnudde — Tue, 14 Oct 2025 09:00:37 +0000

P. Cnudde, R. Millan, M. Boronat, V. Van Speybroeck

ISBN/ISSN:

Talk

Conference / event / venue

21st International Zeolite Conference

Dalian, China

Sunday, 13 July, 2025 to Friday, 18 July, 2025