Uniform synthesis of palladium species confined in a small-pore zeolite <i>via</i> full ion-exchange investigated by cryogenic electron microscopy

Kim, Yongwoo; Sung, Jae Hyuck; Kang, Sungsu; Lee, Jaeha; Kang, Min-Ho; Hwang, Sungha; Park, Ha Young; Kim, Joodeok; Kim, Younhwa; Lee, Eunwon; Park, Gyeong‐Su; Kim, Do Heui

doi:10.1039/d1ta00468a

Cited by 25 publications

(26 citation statements)

References 60 publications

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“…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 a bulk technique such as EXAFS and XRD. PdO particles are readily reduced at lower temperatures compared to charge compensating Pd 2+ ions. ,, When dehydrated Pd/SSZ-13 is exposed to CO at 15 °C, only slight CO 2 formation is observed, probably due to PdO reduction (Figure b). The main reduction peak is found around 270 °C, which is much higher than the temperature where NO x uptake is conducted during PNA.…”

Section: Resultsmentioning

confidence: 98%

“…PdO particles are readily reduced at lower temperatures compared to charge compensating Pd 2+ ions. 30,49,50 When dehydrated Pd/SSZ-13 is exposed to CO at 15 °C, only slight CO 2 formation is observed, probably due to PdO reduction (Figure 7b). The main reduction peak is found around 270 °C, which is much higher than the temperature where NO x uptake is conducted during PNA.…”

Section: Resultsmentioning

confidence: 99%

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Elucidating the Role of CO in the NO Storage Mechanism on Pd/SSZ-13 with in Situ DRIFTS

et al. 2022

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Pd-ion-exchanged zeolites have emerged as promising materials for the adsorption and oxidation of air pollutants. For lowtemperature vehicle exhaust, dispersed Pd ions can adsorb NO x even in H 2 O-rich exhaust containing carbon monoxide. To understand this phenomenon, changes in the Pd ligand environment have to be monitored in situ. Herein, we directly observe the activation of hydrated Pd ion shielded by H 2 O into a carbonyl−nitrosyl complex Pd 2+ (NO)-(CO) in SSZ-13 zeolite. The subsequent thermal desorption of ligands on the Pd 2+ (NO)(CO) complex proceeds to nitrosyl Pd 2+ rather than to carbonyl Pd 2+ under various conditions. Thus, CO molecules act as additional ligands to provide an alternative pathway with a lower energy barrier in accelerating NO adsorption on hydrated Pd 2+ ions through the Pd 2+ (NO)(CO) complex. 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 temperatures as high as 500 °C, while water makes it possible at near RT. However, the primary NO adsorption sites are Pd 2+ ions even in gases containing CO and water. These findings clarify additional mechanistic aspects of the passive NO x adsorption (PNA) process and will help extend the NO x adsorption chemistry in zeolite-based adsorbers to practical applications.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Elucidating the Role of CO in the NO Storage Mechanism on Pd/SSZ-13 with in Situ DRIFTS

et al. 2022

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“…Recently, Pd-exchanged zeolites were proposed as promising materials for this technology. , Highly dispersed Pd ions at exchange sites of a zeolite have been suggested as active sites for NO x storage at low temperatures . Subsequently, many research groups have studied NO x adsorption/desorption properties over Pd zeolites. − Small-pore Pd-SSZ-13 with chabazite (CHA) topology showed advantageous NO x release temperatures and higher hydrothermal stability compared to medium- and large-pore Pd zeolites. , …”

Section: Introductionmentioning

confidence: 99%

Computational Study of Noble Metal CHA Zeolites: NO Adsorption and Sulfur Resistance

et al. 2022

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Noble metal-exchanged small-pore molecular sieves with chabazite topology are promising materials for automotive cold-start NO x emission control applications. A combination of first-principles thermodynamics and density functional theory was applied for the prediction of monomeric palladium, platinum, and ruthenium species formed in 1Al or 2Al sites of six-/eight-membered rings of the SSZ-13 framework in the presence of SO 2 , NO, O 2 , and H 2 O at temperatures between 0 and 1100 K. Calculations using gradient-corrected Perdew−Burke−Ernzerhof (PBE) functional and hybrid Heyd−Scuseria−Ernzerhof (HSE06) functional showed that the binding energy of NO adsorbed on Pd, Pt, or Ru ions is a strong function of exchange−correlation functional. Use of the PBE functional overestimated the binding strengths of NO to Pd, Pt, or Ru ions compared to the HSE06 functional. While PBE led to the adsorption of two NO per Pd, Pt, or Ru ion, HSE06 predicted the adsorption of a single NO. Isolated Pd, Pt, or Ru ions in 1Al sites tended to bind NO stronger than their counterparts in 2Al sites. Both functionals revealed that Pd and Pt ions have more similarities in terms of both NO adsorption and sulfur resistance compared to Ru ions. The results of this study are beneficial for further modeling of passive NO x adsorbers with improved properties to deliver cleaner tailpipe emissions during engine cold start.

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“…[31][32][33][34][35][36][37] In zeolite-based PNAs (SSZ-13, ZSM-5, BEA) Pd ions efficiently trap NO in nitrosyl complexes, i.e., Pd 2+ -NO. [38][39][40][41][42][43][44][45][46] However, water is always present in the exhaust gas mixture making Pd ions hydrated, i.e., Pd 2+ (H2O)n, which prevents the coordination of NO molecules. Recently we have reported on the excellent PNA performance of Pd/FER materials.…”

Section: Introductionmentioning

confidence: 99%

Unusual water-assisted NO adsorption over Pd/FER calcined at high temperatures: The effect of cation migration

Song

Khivantsev

et al. 2022

Applied Catalysis B: Environmental

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Uniform synthesis of palladium species confined in a small-pore zeolite via full ion-exchange investigated by cryogenic electron microscopy

Abstract: Uniformly dispersed palladium species in small-pore zeolite are successfully prepared for catalytic applications, and are investigated by advanced microscopic methods.

Cited by 25 publications

References 60 publications

Elucidating the Role of CO in the NO Storage Mechanism on Pd/SSZ-13 with in Situ DRIFTS

Elucidating the Role of CO in the NO Storage Mechanism on Pd/SSZ-13 with in Situ DRIFTS

Computational Study of Noble Metal CHA Zeolites: NO Adsorption and Sulfur Resistance

Unusual water-assisted NO adsorption over Pd/FER calcined at high temperatures: The effect of cation migration

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