Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐Pore Zeolite SSZ‐13: High‐Capacity and High‐Efficiency Low‐Temperature CO and Passive NOx Adsorbers

Khivantsev, Konstantin; Jaegers, Nicholas R.; Kovařík, Libor; Hanson, Jonathan C.; Tao, Franklin Feng; Tang, Yu; Zhang, Xiaoyan; Koleva, Iskra Z.; Aleksandrov, Hristiyan A.; Vayssilov, Georgi N.; Wang, Yong; Gao, Feng; Szanyi, János

doi:10.1002/ange.201809343

Cited by 50 publications

(107 citation statements)

References 56 publications

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“…11). It was previously shown by us that Pd(II)-NO in SSZ-13 upon CO adsorption selectively forms Pd(II)(CO)(NO) complex [8,11] largely responsible for excellent performance of Pd(II)/SSZ-13 as a low temperature passive NOx adsorber (at 100 ⁰C). However, in this case, we observe the unselective formation of Pd(II)(CO)(NO) even at elevated CO pressures (up to 10 Tors dosed onto the sample).…”

Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 95%

“…The bands in this region belong to NO chemisorbed on cationic Pd. We have previously shown that although these bands fall in the region typical for linearly adsorbed NO, NO in fact binds with its unpaired electron forming a fully covalent bond with an electron given by Pd(II) [8,13,11]: the formation of the strong covalent Pd-N bond in the bent Pd-N-O fragment is the reason why Pd ions in zeolite can function as low-temperature passive NOx adsorbers, i.e. bind NO at 100 ⁰C and release it above ~200 ⁰C.…”

Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 97%

“…Using spectroscopy and DFT, we were able to identify different Pd(II)-NO complexes formed under various gas environments on BEA and SSZ-13 zeolites, including the first examples of Pd(II) carbonyl-olefin and Pd(II) nitrosyl-olefin species, in addition to Pd(II)-NO, Pd(I)-NO, Pd(II)(NO)2 (which forms only on BEA but not on SSZ-13) and Pd(II)(NO)(CO) (formed on all zeolites). [8,9,10,11] Here, we have a diversity of Pd(II) sites present including Pd(II) and Pd(II)-OH. NO adsorption on Pd(II)-OH leads to the formation of Pd(II)(OH)(NO) complex with NO band at 1810 cm -1 .…”

Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 99%

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The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

Khivantsev¹,

Jaegers²,

Kovařík³

et al. 2020

Preprint

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We successfully synthesized uniform SSZ-39 with an average crystal size of about a micron. Pd (0.7 - 3 wt%) was supported on SSZ-39 with Si/Al ratio ~12. The as-synthesized materials were characterized by FTIR, XRD, Helium Ion Microscopy, HAADF-STEM imaging, 27Al, 29Si and H solid state NMR spectroscopic techniques. FTIR studies with CO and NO probe molecules reveal that the 0.7 wt% Pd/SSZ-39 material with Si/Al ~12 has the majority of Pd dispersed atomically as isolated Pd(II) and Pd(II)-OH centers, and thus can be used as a low-temperature passive NOx adsorber. Pd(II)-NO, Pd(II)(OH)(NO) and Pd(II)(CO)(NO) complexes form during PNA in this material. We compare this PNA material directly with the Pd/SSZ-13 system (with Si/Al ratio ~12) and show its superior hydrothermal stability. Remarkably, Pd/SSZ-39 with Si/Al ratio ~12 survives hydrothermal aging up to 815 ºC in 10% H2O/Air vapor for 16 hours without significant loss in activity. The SSZ-39 crystal structure remains intact during hydrothermal aging up to 1,000 ºC as we elucidate it with XRD and HAADF-STEM imaging/EDS mapping. However, changes to the framework during such harsh hydrothermal treatment significantly change the NOx release profiles during PNA as evidenced by high-field 27Al NMR on fresh and aged Pd/SSZ-39 samples as well as PNA performance measurements. Besides PNA application, these hydrothermally very stable materials (3 wt% Pd on SSZ-39 with Si/Al ratio ~12) can be used as a robust methane combustion catalyst under industrially relevant conditions (GHSV~600,000hr-1). This catalyst shows minimal deactivation after both harsh hydrothermal aging at 750 and 800 ºC, and prolonged time on stream (105 hrs) at 425 ⁰C. In contrast, both 3wt% Pd/alumina and 3wt% SSZ-13 supported samples lose a significant portion of their activity.

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Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 95%

Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 97%

Section: Spectroscopic Investigation Of 07 Wt% Pd/ssz-39 Using Ftir mentioning

confidence: 99%

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The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

Khivantsev¹,

Jaegers²,

Kovařík³

et al. 2020

Preprint

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“…In order to get further insight into the effect of hydrothermal aging on the NOx storage/release (PNA) properties of aged materials, we performed studies under practically relevant conditions on the fresh and aged samples of 1-3 wt% Pd/SSZ-13 with Si/Al ~6, 12 and 30 as well as 1 wt% Pd/BEA with Si/Al ~12. The samples were prepared according to [35], in order to maximize Pd dispersion.…”

Section: Investigation Of Pna Performance Of Aged 1-3 Wt% Pd/ssz-13 Smentioning

confidence: 99%

“…NOx uptake [35,36,38]. Due to steam-treatment at such high temperatures (750 ºC), dealumination inevitably occurs (see NMR data above).…”

Section: Insight Into the Structural Changes Of Fresh And Hta Pd/ssz-mentioning

confidence: 99%

Palladium/ Zeolite Low Temperature Passive NOx Adsorbers (PNA): Structure-Adsorption Property Relationships for Hydrothermally Aged PNA Materials

Khivantsev¹,

Jaegers²,

Kovařík³

et al. 2019

Preprint

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Zeolites with different framework structures (SSZ-13, ZSM-5, BEA) but similar Si/Al ratios and Pd loading (~1 wt%) were synthesized and evaluated as low temperature passive NOx adsorbers (PNA). These materials exhibit high NOx adsorption efficiency with atomically dispersed Pd the active adsorption site. Hydrothermal aging at 750 ºC for 16 hours in the presence of 10% water vapor in air resulted in the formation of PdO nanoparticles in all three samples as evidenced by high energy XRD. Hydrothermal aging of the small-pore Pd/SSZ-13 (Si/Al = 6), which contain ~100-90% atomically dispersed palladium ions, decreases its PNA performance only by ~10-20%, indicating agglomeration of only ~10-20% of all atomically dispersed Pd into PdO. High-field solid state 27Al NMR studies on the fresh and aged samples substantiate dealumination and significant changes in the distribution of Al (and thus, Brönsted acid) sites after hydrothermal aging. FTIR measurements with NO probe molecule and titration of Brönsted acid sites with nitrosyl (NO+) ions further corroborate the 27Al NMR data. Because framework aluminum atoms are the anchoring sites for atomically dispersed Pd ions, their elution from the framework causes the loss of active atomically dispersed Pd species. With the aid of HAADF-STEM imaging and synchrotron XRD studies, we further confirm and visualize the fate of these Pd species – they agglomerate into PdO nanoparticles on the external surface of zeolite. Consequently, these changes lead to the decrease in PNA performance of these materials after hydrothermal aging. The thus formed agglomerates cannot be re-dispersed back to their ionic state due to the loss of framework Al T-sites and/or inherent stability of such large PdO particles. Our study demonstrates that, unlike in previous studies that found increased PNA performance upon HTA, high temperatures hydrothermal aging of PNA materials, that contain atomically dispersed Pd initially, results in a decrease in NOx storage efficiency due to the formation of PdO agglomerates. However, we also highlight the high hydrothermal stability of predominantly atomically dispersed 1-3 wt% Pd/SSZ-13 (Si/Al = 6), whose performance decreases only marginally after prolonged hydrothermal aging at 750 ºC. This study shows that hydrothermally stable passive NOx materials can be prepared using small-pore SSZ-13 zeolite.

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Atomic Insights into the Cu Species Supported on Zeolite for Direct Oxidation of Methane to Methanol via Low‐Damage HAADF‐STEM

Tang

Guo

et al. 2023

Advanced Materials

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Precise determination of the structure-property relationship of zeolite-based metal catalysts is critical for the development toward practical applications. However, the scarcity of real-space imaging of zeolite-based low-atomic-number (LAN) metal materials due to the electron-beam sensitivity of zeolites has led to continuous debates regarding the exact LAN metal configurations. Here, a low-damage high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging technique is employed for direct visualization and determination of LAN metal (Cu) species in ZSM-5 zeolite frameworks. The structures of the Cu species are revealed based on the microscopy evidence and also proved by the complementary spectroscopy results. The correlation between the characteristic Cu size in Cu/ZSM-5 catalysts and their direct oxidation of methane to methanol reaction properties is unveiled. As a result, the mono-Cu species stably anchored by Al pairs inside the zeolite channels are identified as the key structure for higher C1 oxygenates yield and methanol selectivity for direct oxidation of methane. Meanwhile, the local topological flexibility of the rigid zeolite frameworks induced by the Cu agglomeration in the channels is also revealed. This work exemplifies the combination of microscopy imaging and spectroscopy characterization serves as a complete arsenal for revealing structure-property relationships of the supported metal-zeolite catalysts.

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Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐Pore Zeolite SSZ‐13: High‐Capacity and High‐Efficiency Low‐Temperature CO and Passive NO_x Adsorbers

Cited by 50 publications

References 56 publications

The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

Palladium/ Zeolite Low Temperature Passive NOx Adsorbers (PNA): Structure-Adsorption Property Relationships for Hydrothermally Aged PNA Materials

Atomic Insights into the Cu Species Supported on Zeolite for Direct Oxidation of Methane to Methanol via Low‐Damage HAADF‐STEM

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