| 1. |
- Chen, Lin, 1990, et al.
(författare)
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Activation of oxygen on (NH3–Cu–NH3)+ in NH3-SCR over Cu-CHA
- 2018
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 358, s. 179-186
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Tidskriftsartikel (refereegranskat)abstract
- Cu-CHA materials are efficient catalysts for NH 3 –SCR of NO x in oxygen excess. A crucial step in the reaction is oxygen (O 2 ) activation, which still is not well understood. Density functional theory calculations in combination with ab initio thermodynamics and molecular dynamics are here used to study O 2 dissociation on Cu(NH 3 ) 2 + species, which are present under NH 3 –SCR conditions. Direct dissociation of O 2 is found to be facile over a pair of Cu(NH 3 ) 2 + complexes whereas dissociation on a single Cu(NH 3 ) 2 + species is unlikely due to a high activation energy. The presence of NO promotes oxygen dissociation on both single and pairs of Cu(NH 3 ) 2 + complexes. Nitrites and nitrates are easily formed as O 2 dissociates, and NO adsorption over nitrates leads to facile formation of NO 2 . The results stress the importance of ligand-stabilized Cu species in Cu-CHA catalysts for NH 3 –SCR.
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| 2. |
- Chen, Lin, 1990, et al.
(författare)
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Effect of Al-distribution on oxygen activation over Cu-CHA
- 2018
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:8, s. 2131-2136
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Tidskriftsartikel (refereegranskat)abstract
- Cu(NH 3 ) 2 + -pairs in chabazite (CHA) have been suggested to activate oxygen during lowerature selective catalytic reduction of nitrogen oxides with ammonia (NH 3 -SCR). As charge neutrality requires that each Cu-complex is associated with a framework Al, the Al-distribution may affect Cu(NH 3 ) 2 + -pair formation and subsequent oxygen activation. Here, density functional theory calculations in combination with ab initio molecular dynamics simulations are used to explore Cu(NH 3 ) 2 + -pair formation and oxygen activation in Cu-CHA. The Al-distribution is found to markedly affect the probability for Cu(NH 3 ) 2 + -pair formation. Moreover, the molecular dynamics simulations reveal a low-energy reaction path for O 2 activation and dissociation. The facile O 2 dissociation suggests that Cu-pair formation rather than O 2 activation governs the lowerature NH 3 -SCR activity. The results indicate that precise synthesis of Cu-exchanged chabazite with respect to Al-distribution may enhance the catalytic activity.
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| 3. |
- Sloth Madsen, Marianne, et al.
(författare)
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Determination of rate constants for the uptake process involving SO2 and an aerosol particle. A quantum mechanics/molecular mechanics and quantum statistical investigation
- 2008
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 348:1-3, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined quantum mechanics/molecular mechanics and quantum statistical investigation of the interactions between a Molecule (SO2) and an aerosol particle including rate constants for the uptake process. A coupled cluster/molecular mechanics method including explicit polarization is used along with a quantum statistical method for calculating sticking coefficients. The importance of the polarization of the classical subsystem (the aerosol particle), the size of the classical subsystem and the size of one-electron basis sets are studied. The interaction energy is divided into van der Waals, electrostatic and polarization contributions. Relevant binding sites for the evaluation of the sticking coefficient are identified. These are classified into three groups according to the strength of the molecule-aerosol particle interaction energy. The identification of binding sites provides relevant information used in the quantum statistical method and thereby knowledge of the magnitude of the sticking coefficients for the different binding sites along with the total rates for the uptake processes between the aerosol particle and the SO2 molecule.
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