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H2O-Mediated CuOx Redispersion and Hydroxyl Reactivity for Enhancing NOx Reduction over Cu-SSZ-13
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PRE
AI
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段
J
DOI：10.1021/acs.est.5c12081.png)
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Abstract
En 中文
Traditional high-temperature hydrothermal aging commonly inhibits selective catalytic reduction of NOx with ammonia (NH3–SCR) over zeolite catalysts, but a comprehensive understanding of the water vapor effect remains elusive. Herein, by combining the experiment and ab initio molecular dynamics (AIMD) simulations, a promoted mechanism for NOx conversion by water molecules at moderate temperatures is proposed over the Cu-SSZ-13 zeolite. Upon introducing 10 vol % H2O, NOx conversion is enhanced by approximately 20% at 400 °C, while under 5 vol %H2O at 180 °C, the conversion increased from 70% to 80%. Acting as a reactant in the SCR and a ligand for active Cu sites, water vapor drives CuOx redispersion to isolated framework Cu2+ species on the zeolite, creating Lewis acid sites for NH3 activation and avoiding NH3 overoxidation in the high temperature, while its dissociation produces bridge and terminal hydroxyl groups for NH3 adsorption. Meanwhile, preferential coordination of H2O molecules at Cu sites triggers a shift in hydroxyl reactivity, from free H atom attacks on the coordinated hydroxyl in Cu(H2O)(OH) to proton transfer between the NNH+ transition state and free hydroxyl groups. This transformation effectively avoids deep energy wells and decreases the overall energy barrier. This research elucidates a distinct water-mediated mechanism over a Cu-exchanged zeolite for NH3–SCR.
Journal
E
IF:
11.3
Papers:
4.3W
Citations:
26.0W
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Cited Papers