Biomimetic CO oxidation below −100 °C by a nitrate-containing metal-free microporous system

Khivantsev, Konstantin; Jaegers, Nicholas R.; Aleksandrov, Hristiyan A.; Kovařík, Libor; Derewinski, Miroslaw A.; Wang, Yong; Vayssilov, Georgi N.; Szanyi, János

doi:10.1038/s41467-021-26157-3

Cited by 11 publications

(9 citation statements)

References 40 publications

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“…We have also monitored the change in the number of Bronsted acid sites upon steaming of the H-MFI zeolite by replacing H + ions with NO + ions and monitoring both the position and intensity the N-O stretching vibration in the IR spectrum [ 17 , 18 , 19 , 20 ]. Changes in the intensity of this IR feature can be used to monitor the variation in the number of Bronsted acid sites as a result of steaming, while the change in the position of the IR band would provide evidence for the change in acidity of the remaining acid site.…”

Section: Resultsmentioning

confidence: 99%

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

et al. 2022

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Steamed zeolites exhibit improved catalytic properties for hydrocarbon activation (alkane cracking and dehydrogenation). The nature of this practically important phenomenon has remained a mystery for the last six decades and was suggested to be related to the increased strength of zeolitic Bronsted acid sites after dealumination. We now utilize state-of-the-art infrared spectroscopy measurements and prove that during steaming, aluminum oxide clusters evolve (due to hydrolysis of Al out of framework positions with the following clustering) in the zeolitic micropores with properties very similar to (nano) facets of hydroxylated transition alumina surfaces. The Bronsted acidity of the zeolite does not increase and the total number of Bronsted acid sites decreases during steaming. O5Al(VI)-OH surface sites of alumina clusters dehydroxylate at elevated temperatures to form penta-coordinate Al1O5 sites that are capable of initiating alkane cracking by breaking the first C-H bond very effectively with much lower barriers (at lower temperatures) than for protolytic C-H bond activation, with the following reaction steps catalyzed by nearby zeolitic Bronsted acid sites. This explains the underlying mechanism behind the improved alkane cracking and alkane dehydrogenation activity of steamed zeolites: heterolytic C-H bond breaking occurs on Al-O sites of aluminum oxide clusters confined in zeolitic pores. Our findings explain the origin of enhanced activity of steamed zeolites at the molecular level and provide the missing understanding of the nature of extra-framework Al species formed in steamed/dealuminated zeolites.

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Section: Resultsmentioning

confidence: 99%

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

et al. 2022

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“…This remarkable property of Co/SSZ-13(Sr) material, thus, prompted us to load 1.7 wt% Pd in its micropores and study its PNA properties and hydrothermal stability of the resulting Pd-containing SSZ-13 composite [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Indeed, the sample shows excellent PNA performance after loading Pd in it (Fig.…”

Section: Investigation Of Hydrothermal Stability and Pna Performance ...mentioning

confidence: 99%

“…Emissions during vehicle cold start, however, remain a challenge. To circumvent this challenge, Pd/zeolite materials (passive NOx adsorbers) have been introduced industrially that adsorb NO strongly as Pd(II)-NO, Pd(I)-NO, Pd(II)(OH)(NO) and Pd(II)(NO)(CO) complexes (depending on Pd speciation in zeolites) at low temperatures (80-130 ⁰C) during cold start and then release them at higher temperatures (>170-180 ⁰C) when downstream SCR catalysts become very active [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. The main challenge for application of Metal/zeolite materials for industrial vehicle use has always been their hydrothermal stability.…”

Section: Introductionmentioning

confidence: 99%

Increasing Al-pair abundance in SSZ-13 zeolite via zeolite synthesis in the presence of alkaline earth metal hydroxide produces hydro-thermally stable Co-, Cu- and Pd-SSZ-13 materials

Khivantsev

Derewinski

Jaegers

et al. 2022

Preprint

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Replacing alkaline for alkaline-earth metal hydroxide in the synthesis of siliceous SSZ-13 zeolite (Si/Al~10) yields SSZ-13 with novel, advantageous properties. Its NH4-form ion-exchanges higher amount of isolated divalent M(II) ions than the conventional one: this is the consequence of increased number of Al pairs in the structure induced by the +2 charge of Sr(II) cations in the synthesis gel that force two charge-compensating AlO4- motives to reside closer together. We characterize the +2 state of Co(II) ions in these materials with infra-red spectroscopy and X-ray absorption spectroscopy measurements, and show their utility for NOx pollutant adsorption from ambient air: the ones derived from SSZ-13 with higher Al pair content contain more isolated cobalt(II) and thus, perform better as ambient-air NOx adsorbers. Notably, Co(II)/SSZ-13 with increased number of Al pairs is significantly more hydrothermally stable than its NaOH-derived analogue. Loading Pd(II) into Co-SSZ-13(Sr) produces an active NOx adsorber (PNA) material that can be used for NOx adsorption from simulated diesel engine exhaust. The critical issue for these applications is hydrothermal stability of Pd-zeolites. Pd/SSZ-13 synthesized in the presence of Sr(OH)2 does not lose its PNA capacity after extremely harsh aging at 850 and 900 ⁰C (10 hours in 10% H2O/air flow) and loses only ~55% capacity after hydrothermal aging at 930 ⁰C. This can be extended to other divalent metals for catalytic applications, such as copper: we show that Cu/SSZ-13 catalyst can survive hydrothermal aging at 920 ⁰C without losing its catalytic properties, metal dispersion and crystalline structure. Thus, we provide a new, simple, and scalable strategy for making remarkably (hydro)thermally stable metal-zeolite materials/catalysts with a number of useful applications.

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“…Sacrificial ammonia reductant is used, and this catalytic reaction is effective at temperatures starting >170 • C with state-of-the-art catalyst formulations. Significant advances have been achieved in understanding the fundamental nature of catalytic SCR reaction on Cu/SSZ-13 and Cu/BEA zeolitic systems [1][2][3][4][5][6][7][12][13][14][15][16][17][18][19][20][21][22]. Although Cu/SSZ-13 catalysts show excellent activity above 200 • C, no catalysts were shown to be active at lower temperatures.…”

Section: Introductionmentioning

confidence: 99%

Increasing Al-Pair Abundance in SSZ-13 Zeolite via Zeolite Synthesis in the Presence of Alkaline Earth Metal Hydroxide Produces Hydrothermally Stable Co-, Cu- and Pd-SSZ-13 Materials

Khivantsev,

Derewinski,

Kovarik

et al. 2024

Catalysts

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Replacing alkaline for alkaline-earth metal hydroxide in the synthesis gel during the synthesis of siliceous SSZ-13 zeolite (Si/Al~10) yields SSZ-13 with novel, advantageous properties. Its NH4-form ion-exchanges higher amount of isolated divalent M(II) ions than the conventional one: this is the consequence of an increased number of Al pairs in the structure induced by the +2 charge of Sr(II) cations in the synthesis gel that force two charge-compensating AlO4− motives to reside closer together. We characterize the +2 state of Co(II) ions in these materials with infra-red spectroscopy and X-ray absorption spectroscopy measurements and show their utility for NOx pollutant adsorption from ambient air: the ones derived from SSZ-13 with higher Al pair content contain more isolated cobalt(II) and, thus, perform better as ambient-air NOx adsorbers. Notably, Co(II)/SSZ-13 with an increased number of Al pairs is significantly more hydrothermally stable than its NaOH-derived analogue. Loading Pd(II) into Co-SSZ-13(Sr) produces an active NOx adsorber (PNA) material that can be used for NOx adsorption from simulated diesel engine exhaust. The critical issue for these applications is hydrothermal stability of Pd-zeolites. Pd/SSZ-13 synthesized in the presence of Sr(OH)2 does not lose its PNA capacity after extremely harsh aging at 850 and 900 °C (10 h in 10% H2O/air flow) and loses only ~55% capacity after hydrothermal aging at 930 °C. This can be extended to other divalent metals for catalytic applications, such as copper: we show that Cu/SSZ-13 catalyst can survive hydrothermal aging at 920 °C without losing its catalytic properties, metal dispersion and crystalline structure. Thus, we provide a new, simple, and scalable strategy for making remarkably (hydro)thermally stable metal-zeolite materials/catalysts with a number of useful applications.

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Biomimetic CO oxidation below −100 °C by a nitrate-containing metal-free microporous system

Cited by 11 publications

References 40 publications

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

Increasing Al-pair abundance in SSZ-13 zeolite via zeolite synthesis in the presence of alkaline earth metal hydroxide produces hydro-thermally stable Co-, Cu- and Pd-SSZ-13 materials

Increasing Al-Pair Abundance in SSZ-13 Zeolite via Zeolite Synthesis in the Presence of Alkaline Earth Metal Hydroxide Produces Hydrothermally Stable Co-, Cu- and Pd-SSZ-13 Materials

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