NOx uptake and release on Pd/SSZ-13: Impact Of Feed composition and temperature

Gupta, Abhay; Kang, Sung Bong; Harold, Michael P.

doi:10.1016/j.cattod.2020.01.018

Cited by 70 publications

(150 citation statements)

References 34 publications

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“…15 This complex was consistently observed for other Pd/zeolites, including BEA, SSZ-39, and FER, and was suggested to be responsible for NO storage with the aid of static IR. [17][18]31 Meanwhile, several studies raised the possibility that the reducing effect of CO on Pd 2+ ions could be responsible for promotion of NO adsorption by CO. [32][33][34] The existence of Pd 2+ (NO)(CO) complex under practical conditions was also observed: however, some groups observed the complex but some did not in the in situ DRIFTS experiments. [35][36][37] In this study, we performed systematic diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements over Pd/SSZ-13 materials to understand how CO promotion occurs during NO adsorption and to elucidate the role of Pd 2+ (NO)(CO) complex in passive NOx adsorption.…”

Section: Introductionmentioning

confidence: 93%

“…Several studies have emphasized the reduction of Pd 2+ ions in Pd/SSZ-13 by CO and attempted to correlate it with the promoting effect of CO on NO storage. [33][34] To thoroughly examine this possibility, temperature-programmed reduction of Pd/SSZ-13 with CO was performed in the DRIFTS-MS setup (Figure 7). Pd/zeolites usually contain some small PdO clusters inside the zeolite channels and/or at the exterior of zeolite particles, which are hard to detect by bulk technique such as EXAFS and XRD.…”

Section: Conversion Of Pd 2+ -Carbonyl To Pd 2+ (No)(co) Complexmentioning

confidence: 99%

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Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Song

Khivantsev

Wang

et al. 2021

Preprint

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Pd ion exchanged zeolites emerged as promising materials for the adsorption and oxidation of air pollutants. For low-temperature vehicle exhaust, dispersed Pd ions are able to adsorb NOx even in H2O-rich exhaust in the presence of carbon monoxide. In order to understand this phenomenon, changes in Pd ligand environment have to be monitored in-situ. Herein, we directly observe the activation of hydrated Pd ion shielded by H2O into a carbonyl-nitrosyl complex Pd2+(NO)(CO) in SSZ-13 zeolite. The subsequent thermal desorption of ligands on Pd2+(NO)(CO) complex proceeds to nitrosyl Pd2+ rather than to carbonyl Pd2+ under various conditions. Thus, CO molecules act as additional ligands to provide alternative pathway through Pd2+(NO)(CO) complex with lower energy barrier for accelerating NO adsorption on hydrated Pd2+ ion, which is kinetically limited in the absence of CO. We further demonstrate that hydration of Pd ions in the zeolite is a prerequisite for CO-induced reduction of Pd ions to metallic Pd. The reduction of Pd ions by CO is limited under dry conditions even at a high temperature of 500°C, while water makes it possible at near RT. However, the primary NO adsorption sites are Pd2+ ions even in gases containing CO and water. These findings clarify additional mechanistic aspects of the passive NOx adsorption (PNA) process and will help extend the NOx adsorption chemistry in zeolite-based adsorbers to practical applications.

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Section: Introductionmentioning

confidence: 93%

Section: Conversion Of Pd 2+ -Carbonyl To Pd 2+ (No)(co) Complexmentioning

confidence: 99%

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Song

Khivantsev

Wang

et al. 2021

Preprint

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“…[ 13,15 ] However, the reaction and simulation results in some works proposed that Pd 2+ was reduced to Pd + by NO, which stored the NO as Pd + (NO). [ 73,74 ] On the other hand, two kinds of Pd cations, that is, Pd 2+ and Pd(OH) + , were believed existing in Pd/SSZ‐13. [ 74–76 ] However, the difference between the two kinds of Pd cations on NO adsorption was still ambiguous.…”

Section: Zeolite Support Catalystsmentioning

confidence: 99%

“…[ 73,74 ] On the other hand, two kinds of Pd cations, that is, Pd 2+ and Pd(OH) + , were believed existing in Pd/SSZ‐13. [ 74–76 ] However, the difference between the two kinds of Pd cations on NO adsorption was still ambiguous.…”

Section: Zeolite Support Catalystsmentioning

confidence: 99%

“…[ 13 ] Khivantsev et al [ 77 ] also observed the Pd 2+ (CO)(NO) complex would be also formed on the Pd/Beta catalyst as corroborated by FTIR results in the presence of CO and NO, which was believed to relate to the improved NO adsorption capacity of Pd/Beta. However, Gupta et al [ 74 ] proposed that the reduction of Pd(OH) + , which was seriously inhibited on NO adsorption by H 2 O, to Pd + by CO contributing to the increased NO adsorption capacity of Pd/SSZ‐13. The evidence to support the proposal is the detection of CO 2 during NO+CO adsorption at 100°C.…”

Section: Zeolite Support Catalystsmentioning

confidence: 99%

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Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

Wang

Yong

Rong

et al. 2020

J Chinese Chemical Soc

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In the practical applications, a high portion of the NO x is emitted without purification in the cold start period of engine because the selective catalytic reduction (SCR) or NO x storage and reduction (NSR) catalysts are not warmed up. Passive NO x absorbers (PNA) were proposed earlier to store the NO x at low temperatures and release the stored NO x during warm-up period when the SCR and NSR catalysts downstream are functional, while this concept just attracted great interests recently to meet the extra stringent requirement of governmental emissions regulations. A plant of PNA catalysts, showing different NO adsorption/release characteristics, was disclosed. This review summarizes the recent progress in the development of PNA catalysts. The characteristics of NO adsorption/release on precious metal (i.e., Pt, Pd) loading Al 2 O 3 support catalysts, CeO 2 support catalysts, and zeolite support catalysts are summarized and compared.

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Coaxial 3D Printing Enabling Mn/CHA@Pd/CHA Zeolite‐Based Core–Shell Monoliths for Efficient Passive NO_x Adsorbers

Li,

Wei,

Zhang

et al. 2024

Adv Funct Materials

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Pd‐based zeolites are extensively used as passive NOx adsorbers (PNA) for cold‐start NOx emissions to meet stringent emission regulations. However, optimizing adsorber design to reduce Pd usage with substitution by non‐noble metals that are prone to suffer from H2O remains a significant challenge. Herein, the core–shell Mn/CHA@Pd/CHA zeolite monoliths based on non‐noble metal/zeolite core are constructed using coaxial 3D printing technology and identified as efficient passive NOx adsorbers for the first time. In the Mn/CHA@Pd/CHA monolith, the Pd/CHA shell effectively protected the Mn active sites in the core from H2O, while the integration of the Mn/CHA core not only introduced efficient storage sites but also facilitated NOx desorption, thereby achieving comparable adsorption properties and increased the NOx desorption efficiency by 35% at 350 °C compared with that of Pd/CHA monolith. Furthermore, some non‐noble metal‐based zeolites (e.g., Co/CHA, Mn/MFI, Mn/BEA) and Pd‐based zeolites (e.g., Pd/AEI) are also employed as cores and shells respectively to fabricate a series of core–shell zeolite monoliths via coaxial 3D printing, highlighting the benefits of incorporating non‐noble metals into Pd‐based zeolites for improving adsorption and desorption behaviors. This work provides a promising strategy for designing cost‐effective PNA materials and contributes to improving the exhaust after‐treatment technology.

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NOx uptake and release on Pd/SSZ-13: Impact Of Feed composition and temperature

Cited by 70 publications

References 34 publications

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

Coaxial 3D Printing Enabling Mn/CHA@Pd/CHA Zeolite‐Based Core–Shell Monoliths for Efficient Passive NO_x Adsorbers

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NOx uptake and release on Pd/SSZ-13: Impact Of Feed composition and temperature

Cited by 70 publications

References 34 publications

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

Coaxial 3D Printing Enabling Mn/CHA@Pd/CHA Zeolite‐Based Core–Shell Monoliths for Efficient Passive NOx Adsorbers

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Coaxial 3D Printing Enabling Mn/CHA@Pd/CHA Zeolite‐Based Core–Shell Monoliths for Efficient Passive NO_x Adsorbers