Insight into hydrothermal aging effect on deactivation of Pd/SSZ-13 as low-temperature NO adsorption catalyst: Effect of dealumination and Pd mobility

Applied Catalysis B Environment and Energy, Journal Year: 2021, Volume and Issue: 286, P. 119874 - 119874

Published: Jan. 13, 2021

Language: Английский

---

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, Journal Year: 2022, Volume and Issue: 144(30), P. 13874 - 13887

Published: July 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).

Language: Английский

---

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

The Journal of Physical Chemistry C, Journal Year: 2022, Volume and Issue: 126(3), P. 1439 - 1449

Published: Jan. 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.

Language: Английский

---

Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NO_x Reduction over Cu-SSZ-13 Zeolites by In Situ UV–Vis Spectroscopy and Time-Dependent DFT Calculation

Environmental Science & Technology, Journal Year: 2023, Volume and Issue: 57(33), P. 12465 - 12475

Published: Aug. 9, 2023

The low-temperature mechanism of chabazite-type small-pore Cu-SSZ-13 zeolite, a state-of-the-art catalyst for ammonia-assisted selective reduction (NH3-SCR) toxic NOx pollutants from heavy-duty vehicles, remains debate and needs to be clarified further improvement NH3-SCR performance. In this study, we established experimental protocols follow the dynamic redox cycling (i.e., CuII ↔ CuI) Cu sites in during catalysis by situ ultraviolet-visible spectroscopy infrared spectroscopy. Further integrating spectroscopic observations with time-dependent density functional theory calculations allows us identify two cage-confined transient states, namely, O2-bridged dimers μ-η2:η2-peroxodiamino dicopper) proximately paired, chemically nonbonded CuI(NH3)2 sites, confirm pair as precursor dimer. Comparative experiments reveal particularly high reactivity pairs NO-to-N2 at low temperatures. Our study demonstrates direct evidence formation paired CuI under zeolite confinement provides new insights into monomeric-to-dimeric transformation completing cycle over Cu-SSZ-13.

Language: Английский

---

Coal fly ash and bottom ash low-cost feedstocks for CO2 reduction using the adsorption and catalysis processes

The Science of The Total Environment, Journal Year: 2023, Volume and Issue: 912, P. 169179 - 169179

Published: Dec. 9, 2023

Language: Английский

---

Structural changes to molybdenum and Brønsted acid sites in MFI zeolites during methane dehydroaromatization reaction-regeneration cycles

Journal of Catalysis, Journal Year: 2024, Volume and Issue: 430, P. 115335 - 115335

Published: Feb. 1, 2024

Language: Английский

---

Progress in the construction strategy of noble metal active sites for zeolite-based PNA and VOCs catalysts

Green Energy & Environment, Journal Year: 2024, Volume and Issue: unknown

Published: June 1, 2024

Zeolite-loaded noble metal catalysts have demonstrated excellent performance in addressing cold-start automotive exhaust NOx emissions and catalytic oxidation of VOCs applications. Pd Pt are the most commonly used active metals PNA VOC catalysts, respectively. However, despite same metal/zeolite composition, efficient sites for been viewed as mainly Pd2+ Pt0, respectively, both which different from each other. As a result, various methods need to be applied dope zeolitic support respectively usages. No matter type species is needed, common requirement that should highly dispersed zeolite stay stable. The purpose this paper review progress synthetic means zeolite-coated (Pd, Pt, etc.) effective or catalysts. To give better understanding relationship between introduced methods, contributed adsorption (PNA) deep were first summarized compared. Then, based on above discussion, detailed construction strategies elaborated terms routes, precursor selection, carrier requirements. It hoped will contribute adsorption/catalysis zeolites provide promising design adsorption/catalysts with high activity, selectivity stability.

Language: Английский

---

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

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(22), P. 13891 - 13901

Published: Nov. 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

Language: Английский

---

Investigation of NO adsorption and desorption phenomena on a Pd/ZSM-5 passive NOx adsorber

Applied Catalysis B Environment and Energy, Journal Year: 2021, Volume and Issue: 298, P. 120561 - 120561

Published: July 28, 2021

Language: Английский

---

Experimental and Theoretical Characterization of Rh Single Atoms Supported on γ-Al₂O₃ with Varying Hydroxyl Contents during NO Reduction by CO

ACS Catalysis, Journal Year: 2022, Volume and Issue: 12(19), P. 11697 - 11715

Published: Sept. 12, 2022

Oxide-supported Rh catalysts are important components of commercial three-way for pollution abatement. Despite their universal application, many mysteries remain about the active structure on oxide supports as these materials often contain a mixture nanoparticles and single-atom species same support, even after aging. Probe molecule Fourier transform infrared (FTIR) spectroscopy in this work shows that atomically dispersed γ-Al2O3 prefer to strongly bind CO when exposed NO mixtures light-off reduction occurs at temperatures similar desorption, suggesting first rate-determining step NO–CO reactions may be desorption from dicarbonyl complexes, Rh(CO)2. Two sets symmetric asymmetric stretching frequencies associated with distinct Rh(CO)2 observed FTIR spectra 2084/2010 2094/2020 cm–1. During temperature ramps, latter pair bands cm–1 converts 463 K before all disappear 573 K. Bands then appear range 1975–1985 monocarbonyl, Rh(CO), upon disappearance bands, desorbs sequentially by forming Rh(CO) intermediates. Combined DFT experiments suggest local OH coverage surface distinguishes two species: higher frequency resides less hydroxylated region migrates more temperatures, causing vibrational decrease ∼10 high coverage, consistent predicted trend binding energies. Because coincidence reduction, support hydroxylation Rh1/γ-Al2O3 likely affects both kinetics studies which enabled model developed here.

Language: Английский

---