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N-H Bond Activation in Ammonia by TM-SSZ-13 (Fe, Co, Ni, Cu) Zeolites: A First-Principles Calculation

Abstract

N-H activation is crucial for NH3-assisted selective catalytic reduction (SCR) and selective catalytic oxidation (SCO) of NH3 in exhaust emission treatment of the diesel engine. Copper-exchanged CHA-type zeolites show high performance for the N-H activation, however, the atomic-level understanding of activation mechanism is inaccessible. In this work, we use density functional theory (DFT) calculations to investigate the origin of high activity through electronic structures, magnetic properties and N-H bond of NH3 activation on the naked Cu2+ as active site in Cu-SSZ-13. Fe, Co, Ni-SSZ-13 were also systematically studied as comparison. The incorporation of transition metal ions leads to high-spin d-states around the Fermi level. The magnetic moment of 3.858, 2.889, 1.920 and 0.946 μB is observed for Fe, Co, Ni, and Cu-SSZ-13, respectively. A distorted square planar crystal field is found. For Cu-SSZ-13, the electron configurations of Cu2+ ensure the lowest unoccupancy of b1g (dx2−y2), enabling to receive electrons from base NH3 and thus activate the N-H bond with a barrier of 1.26 eV significantly lower than that in Fe, Co, Ni-SSZ-13. These findings may provide fundamental insights on the high activity and selectivity of Cu-SSZ-13 catalysts for NOx removal and NH3 oxidation at high temperature.

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Publication details

The article was received on 08 Oct 2018, accepted on 04 Dec 2018 and first published on 05 Dec 2018


Article type: Paper
DOI: 10.1039/C8CP06263C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    N-H Bond Activation in Ammonia by TM-SSZ-13 (Fe, Co, Ni, Cu) Zeolites: A First-Principles Calculation

    W. Wang, L. Wang and H. Chen, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP06263C

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