Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 144, Issue 28, Pages 12816-12824Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.2c03877
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Funding
- NationalNaturalScienceFoundationofChina [21920102005, 21835002, 21621001, 91961119]
- 111Project [B17020]
- National Engineering Laboratory [NELMS2020A01]
- Centre for Highresolution Electron Microscopy (CEM) [EM02161943]
- Shanghai Tech University [SPSTAIC10112914]
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The incorporation of Sm ions into Cu-SSZ-13 zeolites enhances the NH3-SCR performance by facilitating the formation of active [ZCu(2+)(OH)](+) ions and stabilizing them through electrostatic interaction, as evidenced by a series of experimental and theoretical studies.
The incorporation of secondary metal ions into Cu-exchanged SSZ-13 zeolites could improve their catalytic properties in selective catalytic reduction of NOx with ammonia (NH3-SCR), but their essential roles remain unclear at the molecular level. Herein, a series of Cu-Sm-SSZ-13 zeolites have been prepared by ion-exchanging Sm ions followed by Cu ions, which exhibit superior NH3-SCR performance. The NO conversion of Cu-Sm-SSZ-13 is nearly 10% higher than that of conventional Cu-SSZ-13 (175-250 degrees C) after hydrothermal ageing, showing an enhanced low-temperature activity. The Sm ions are found to occupy the six-membered rings (6MRs) of SSZ-13 by X-ray diffraction Rietveld refinement and aberration-corrected scanning transmission electron microscopy. The Sm ions at 6MRs can facilitate the formation of more active [ZCu(2+)(OH)](+) ions at 8MRs, as revealed by temperature-programmed reduction of hydrogen. X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicate that there exists electron transfer from Sm3+ to [ZCu(2+)(OH)](+) ions, which promotes the activity of [ZCu(2+)(OH)](+) ions by decreasing the activation energy of the formation of intermediates (NH4NO2 and H2NNO). Meanwhile, the electrostatic interaction between Sm3+ and [ZCu(2+)(OH)](+) results in a high-reaction energy barrier for transforming [ZCu(2+)(OH)](+) ions into inactive CuOx species, thus enhancing the stability of [ZCu(2+)(OH)](+) ions. The influence of the ion-exchanging sequence of Sm and Cu ions into SSZ-13 is further investigated by combining both experiments and theoretical calculations. This work provides a mechanistic insight of secondary ions in regulating the distribution, activity, and stability of Cu active sites, which is helpful for the design of high-performance Cu-SSZ-13 catalysts for the NH3-SCR reaction.
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