New insights into the catalytic mechanism of VOCs abatement over Pt/Beta with active sites regulated by zeolite acidity

Applied Catalysis B Environment and Energy, Год журнала: 2023, Номер 334, С. 122811 - 122811

Опубликована: Апрель 26, 2023

Язык: Английский

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Dynamic Copper Site Redispersion through Atom Trapping in Zeolite Defects

Journal of the American Chemical Society, Год журнала: 2024, Номер 146(12), С. 8280 - 8297

Опубликована: Март 11, 2024

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains challenge often limits their use due to irreversible structural changes the catalyst. Here, we report zeolite-based copper which oxide agglomerates formed after reaction can be repeatedly redispersed back single sites using an oxidative treatment air at 550 °C. Under different environments, single-site Cu–Zn–Y/deAlBeta undergoes dynamic structure oxidation state that tuned promote formation key active while minimizing through Cu sintering. For example, Cu2+ reduces Cu1+ catalyst pretreatment (270 °C, 101 kPa H2) further Cu0 nanoparticles under conditions (270–350 7 EtOH, 94 or accelerated aging (400–450 H2). After regeneration °C air, agglomerated CuO was dispersed presence absence Zn Y, verified imaging, situ spectroscopy, catalytic rate measurements. Ab initio molecular dynamics simulations show solvation monomers water facilitates transport zeolite pore, condensation monomer with fully protonated silanol nest entraps reforms structure. The capability nests trap stabilize oxidizing could extend wider reactions allows simple strategy catalysts.

Язык: Английский

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Dynamic Evolution of Zeolite Framework and Metal-Zeolite Interface

ACS Catalysis, Год журнала: 2022, Номер 12(9), С. 5060 - 5076

Опубликована: Апрель 14, 2022

Zeolites and metal-zeolites are a class of porous materials that have been widely utilized in industry. So far, several fundamental questions relating to the dynamic evolution zeolite framework metal-zeolite interface remain unanswered. Contrary classical view zeolites as static, rigid, changeless material, atoms foreign metals can dynamically interconvert under pretreatment or reaction conditions, making it difficult identify real active centers mechanisms. With development characterization techniques theoretical calculations, more profound understanding at atomic scale has achieved. This critical Review will feature recent progress metal-zeolites, mainly focusing on T–O–T bonds breaking formation, metal valence state transformation, phase evolution, migration. We compare these proposed mechanisms analyze their suitability distinct experimental conditions. highlight identification sites catalytic mechanism should be cautious consider Finally, we summarize usages limitations different characteristic techniques, propose some future research directions about hope bridge gaps between knowledge achieved characterizations nature guide zeolite-based synthesis, modification, application.

Язык: Английский

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Cold-Start NO_x Mitigation by Passive Adsorption Using Pd-Exchanged Zeolites: From Material Design to Mechanism Understanding and System Integration

Environmental Science & Technology, Год журнала: 2023, Номер 57(9), С. 3467 - 3485

Опубликована: Фев. 21, 2023

It remains a major challenge to abate efficiently the harmful nitrogen oxides (NOx) in low-temperature diesel exhausts emitted during cold-start period of engine operation. Passive NOx adsorbers (PNA), which could temporarily capture at low temperatures (below 200 °C) and release stored higher (normally 250–450 downstream selective catalytic reduction unit for complete abatement, hold promise mitigate emissions. In this review, recent advances material design, mechanism understanding, system integration are summarized PNA based on palladium-exchanged zeolites. First, we discuss choices parent zeolite, Pd precursor, synthetic method synthesis Pd-zeolites with atomic dispersions, review effect hydrothermal aging properties performance Pd-zeolites. Then, show how different experimental theoretical methodologies can be integrated gain mechanistic insights into nature active sites, storage/release chemistry, as well interactions between typical components/poisons exhausts. This also gathers several novel designs modern exhaust after-treatment systems practical application. At end, challenges, important implications, further development real application Pd-zeolite-based mitigation.

Язык: Английский

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Progress and future challenges in passive NO adsorption over Pd/zeolite catalysts

Catalysis Science & Technology, Год журнала: 2021, Номер 11(18), С. 5986 - 6000

Опубликована: Янв. 1, 2021

Proposed NO adsorption cycles over Pd/zeolite materials.

Язык: Английский

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Unravelling Phosphorus-Induced Deactivation of Pd-SSZ-13 for Passive NO_x Adsorption and CO Oxidation

ACS Catalysis, Год журнала: 2021, Номер 11(22), С. 13891 - 13901

Опубликована: Ноя. 1, 2021

Phosphorus (P) originating from lubricant oil additives or biofuels is an emerging chemical poison in catalytic systems for automotive exhaust after-treatment. Here, we demonstrate that P-poisoning led to severe deactivation of small-pore Pd-SSZ-13 zeolites (with CHA framework) as passive NOx adsorbers (PNA) and CO oxidation catalysts cold-start purification applications. Deactivation mechanisms were unraveled by comparatively examining the P-free P-loaded using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), temperature-programmed reduction hydrogen (H2-TPR), pulse adsorption, desorption NH3 a probe molecule (NH3-TPD), ultraviolet/visible light (UV/vis) spectroscopy, situ diffuse relectance infrared Fourier transform (DRIFTS). The loss isolated Pd sites─namely, [Pd(OH)]+ Pd2+ (located eight- six-membered rings framework, respectively)─was revealed be largely responsible adsorption oxidation. In DRIFTS studies NO suggest was more susceptible than Pd2+. Specifically, migration cationic exchange sites zeolite surface, forming inactive metaphosphate (i.e., [Pd(OH)]+PO3–) bulk PdOx species at high temperatures. contrast, proceeded via sequential transformation first, then [Pd(OH)]+PO3– PdOx. This study provides comprehensive mechanistic understanding on P-poisoning, may guide design high-performance, phosphorus-resistant Pd-zeolite

Язык: Английский

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Interconversion of Atomically Dispersed Platinum Cations and Platinum Clusters in Zeolite ZSM-5 and Formation of Platinum gem-Dicarbonyls

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(30), С. 13874 - 13887

Опубликована: Июль 19, 2022

Catalysts composed of platinum dispersed on zeolite supports are widely applied in industry, and coking sintering during operation under reactive conditions require their oxidative regeneration, with the cycling between clusters cations. The intermediate species have remained only incompletely understood. Here, we report an experimental theoretical investigation structure, bonding, local environment cationic ZSM-5, which key intermediates this cycling. Upon exposure to O2 at 700 °C, fragmentation occurs, Pt2+ ions stabilized six-membered rings that contain paired aluminum sites. When exposed CO mild conditions, these form highly uniform gem-dicarbonyls, can be converted H2 Ptδ+ monocarbonyls. This conversion, weakens platinum-zeolite is a first step toward migration aggregation into clusters. X-ray absorption infrared spectra provide evidence reductive transformations various gas environments. chemistry general, as shown by observation gem-dicarbonyls several commercially used zeolites (ZSM-5, Beta, mordenite, Y).

Язык: Английский

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

The Journal of Physical Chemistry C, Год журнала: 2022, Номер 126(3), С. 1439 - 1449

Опубликована: Янв. 14, 2022

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

Язык: Английский

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Identification of Highly Selective Surface Pathways for Methane Dry Reforming Using Mechanochemical Synthesis of Pd–CeO₂

ACS Catalysis, Год журнала: 2022, Номер 12(20), С. 12809 - 12822

Опубликована: Окт. 7, 2022

The methane dry reforming (DRM) reaction mechanism was explored via mechanochemically prepared Pd/CeO2 catalysts (PdAcCeO2M), which yield unique Pd–Ce interfaces, where PdAcCeO2M has a distinct and higher reactivity for DRM relative to traditionally synthesized impregnated (PdCeO2IW). In situ characterization density functional theory calculations revealed that the enhanced chemistry of can be attributed presence carbon-modified Pd0 Ce4+/3+ surface arrangement, Pd–CO intermediate species strong Pd–CeO2 interactions are activated sustained exclusively under conditions. This arrangement leads highly selective pathways prefer direct oxidation CHx CO, identified on using isotope labeled diffuse reflectance infrared Fourier transform spectroscopy highlighting linear bound metallic C-modified Pd, leading adsorbed HCOO [1595 cm–1] as key intermediates, stemming from associative CO2 reduction. milled materials contrast strikingly with processes observed IW samples (PdCeO2IW) competing reverse water gas shift predominates.

Язык: Английский

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Palladium nanoparticles anchored on silanol nests of zeolite showed superior stability for methane combustion

Applied Catalysis B Environment and Energy, Год журнала: 2024, Номер 356, С. 124221 - 124221

Опубликована: Май 21, 2024

Язык: Английский

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