Cold-Start NO<sub><i>x</i></sub> Mitigation by Passive Adsorption Using Pd-Exchanged Zeolites: From Material Design to Mechanism Understanding and System Integration

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Ammonia-mediated selective catalytic reduction (NH 3 -SCR) is currently the key approach to abate nitrogen oxides (NO x ) emitted from heavyduty lean-burn vehicles. The state-of-art NH 3 -SCR catalysts, namely, copper ionexchanged chabazite (Cu-CHA) zeolites, perform rather poorly at low temperatures (below 200 °C) and are thus incapable of eliminating effectively NO x emissions under cold-start conditions. Here, we demonstrate a significant promotion of low-temperature NO x reduction by reinforcing the dynamic motion of zeolite-confined Cu sites during NH 3 -SCR. Combining complex impedancebased in situ spectroscopy (IS) and extended density-functional tight-binding molecular dynamics simulation, we revealed an environment-and temperaturedependent nature of the dynamic Cu motion within the zeolite lattice. Further coupling in situ IS with infrared spectroscopy allows us to unravel the critical role of monovalent Cu in the overall Cu mobility at a molecular level. Based on these mechanistic understandings, we elicit a boost of NO x reduction below 200 °C by reinforcing the dynamic Cu motion in various Cu-zeolites (Cu-CHA, Cu-ZSM-5, Cu-Beta, etc.) via facile postsynthesis treatments, either in a reductive mixture at low temperatures (below 250 °C) or in a nonoxidative atmosphere at high temperatures (above 450 °C).

“…), in which the dynamics of single-atom metal sites (Cu, Ni, Ag, Pd, etc.) play a substantial role, as well. − …”

Section: Environmental Implicationsmentioning

confidence: 99%

Copper Site Motion Promotes Catalytic NO_x Reduction under Zeolite Confinement

Chen,

Khetan,

Lei

et al. 2023

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“…In our previous work, a coupled absorption–photoreduction system is developed, where the introduction of the Fe(II) ethylenediaminetetraacetic acid [Fe(II)EDTA] complex is beneficial for NO absorption, which increases the concentration of the soluble NO reactant for continuous NO reduction . However, the coexistence of NO and SO 2 pollutants in the flue gas raises great concern for their simultaneous removal and utilization. − Thus, the potential impact of SO 2 poison on NO absorption and reduction should be identified.…”

Section: Introductionmentioning

confidence: 99%

Continuous NO Upcycling into Ammonia Promoted by SO₂ in Flue Gas: Poison Can Be a Gift

Chen

Wang

et al. 2023

Although ammonia (NH3) synthesis efficiency from the NO reduction reaction (NORR) is significantly promoted in recent years, one should note that NO is one of the major air pollutants in the flue gas. The limited NO conversion ratio is still the key challenge for the sustainable development of the NORR route, which potentially contributes more to contaminant emissions rather than its upcycling. Herein, we provide a simple but effective approach for continuous NO reduction into NH3, promoted by coexisting SO2 poison as a gift in the flue gas. It is significant to discover that SO2 plays a decisive role in elevating the capacity of NO absorption and reduction. A unique redox pair of SO2–NO is constructed, which contributes to the exceptionally high conversion ratio for both NO (97.59 ± 1.42%) and SO2 (99.24 ± 0.49%) in a continuous flow. The ultrahigh selectivity for both NO-to-NH3 upcycling (97.14 ± 0.55%) and SO2-to-SO4 2– purification (92.44 ± 0.71%) is achieved synchronously, demonstrating strong practicability for the value-added conversion of air contaminants. The molecular mechanism is revealed by comprehensive in situ technologies to identify the essential contribution of SO2 to NO upcycling. Besides, realistic practicality is realized by the efficient product recovery and resistance ability against various poisoning effects. The proposed strategy in this work not only achieves a milestone efficiency for NH3 synthesis from the NORR but also raises great concerns about contaminant resourcing in realistic conditions.

“…The increasingly stringent regulations on diesel vehicles pose higher requests for after-treatment systems. , In recent decades, many efforts have been devoted to alleviating nitrogen oxides (NO x ) emitted from lean-burn engines. , The selective catalytic reduction with ammonia (NH 3 -SCR) has been proven to be efficient for reducing the NO x emissions from diesel vehicles at temperatures above 200 °C. , As for the NO x emissions during the cold start (<200 °C), passive NO x adsorber (PNA) is proposed as a promising technology for the abatement of NO x at temperatures below 200 °C. − …”

Section: Introductionmentioning

confidence: 99%

Na Cocations and Hydrothermal Aging Cooperatively Boost the Regeneration of Phosphorus-Poisoned Pd/SSZ-13 for Passive NO_x Adsorption

Li,

Ding,

Hao

et al. 2023

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Pd/SSZ-13 has been proposed as a passive NO x adsorber (PNA) for low-temperature NO x adsorption. However, it remains challenging for Pd/SSZ-13 to work efficiently when suffering from phosphorus poisoning. Herein, we report a simple and efficient strategy to regenerate the phosphorus-poisoned Pd/SSZ-13 based on the cooperation between hydrothermal aging treatment and Na cocations. It was found that hydrothermal aging treatment enabled the redispersion of Pd and P-containing species in phosphorus-poisoned Pd/SSZ-13. Meanwhile, the presence of Na cocations significantly reduced the formation of AlPO4 and retained more paired Al sites for highly dispersed Pd2+ ions, which was of great importance for the recovery of adsorption performance. To our satisfaction, the restoration ratio of the adsorption capacity of poisoned Pd/SSZ-13 was >90% after regeneration. Strikingly, the NO x adsorption activities of phosphorus-poisoned Pd/SSZ-13 with phosphorus loadings of 0.2 and 0.4 mmol g–1 almost completely recovered upon regeneration. This study demonstrates the promoting effect of Na cocations on the regeneration of phosphorus-poisoned Pd/SSZ-13 by hydrothermal aging treatment, which provides useful guidance for the design of PNA materials with excellent durability for cold-start application.