scholarly journals Time-resolved in situ visualization of the structural response of zeolites during catalysis

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jinback Kang ◽  
Jerome Carnis ◽  
Dongjin Kim ◽  
Myungwoo Chung ◽  
Jaeseung Kim ◽  
...  

AbstractZeolites are three-dimensional aluminosilicates having unique properties from the size and connectivity of their sub-nanometer pores, the Si/Al ratio of the anionic framework, and the charge-balancing cations. The inhomogeneous distribution of the cations affects their catalytic performances because it influences the intra-crystalline diffusion rates of the reactants and products. However, the structural deformation regarding inhomogeneous active regions during the catalysis is not yet observed by conventional analytical tools. Here we employ in situ X-ray free electron laser-based time-resolved coherent X-ray diffraction imaging to investigate the internal deformations originating from the inhomogeneous Cu ion distributions in Cu-exchanged ZSM-5 zeolite crystals during the deoxygenation of nitrogen oxides with propene. We show that the interactions between the reactants and the active sites lead to an unusual strain distribution, confirmed by density functional theory simulations. These observations provide insights into the role of structural inhomogeneity in zeolites during catalysis and will assist the future design of zeolites for their applications.

1998 ◽  
Vol 547 ◽  
Author(s):  
R.I. Walton ◽  
T. Loiseau ◽  
R.J. Francis ◽  
D. O'Hare ◽  
G. Férey

AbstractThe hydrothermal crystallisation (130-180 °C) of three-dimensional open-framework gallium and aluminium oxyfluoro-phosphates with the ULM-3 and ULM-4 structures have been studied in situ for the first time. The in situ energy-dispersive X-ray diffraction method has allowed the formation of the crystalline products to be observed under hydrothermal conditions The integrated areas of the strongest Bragg reflections has allowed quantitative kinetic data to be extracted. The effect of temperature, phosphorus source, templating agent have been investigated. The nature of phosphorus source in the reaction mixture has been found to affect dramatically the course of reaction for certain combinations of amine and temperature. Previously unobserved transient crystalline phases have been seen during the production of ULM-3 gallium phosphates when P2O5 or polyphosphoric acid are used. The formation of these intermediates affects the kinetics of product growth. In the case of the aluminium ULM-3 materials reaction always proceeds via a crystalline intermediate whatever phosphorus source is used. The ULM-4 framework materials are found to always crystallise directly with no evidence for any intermediates. Kinetic data for each system have been modelled using standard solid-state chemistry expressions, and these calculations indicate the reactions to be diffusion controlled.


2021 ◽  
Author(s):  
Daniel Bregante ◽  
Laura Wilcox ◽  
Changming Liu ◽  
Christopher Paolucci ◽  
Rajamani Gounder ◽  
...  

Cu-exchanged zeolites activate dioxygen to form active sites for partial methane oxidation (PMO), nitrogen oxide decomposition, and carbon monoxide oxidation. Apparent rates of O<sub>2</sub> activation depend both on the intrinsic kinetics of distinct Cu site types and the distributions of such sites within a given zeolite, which depend on the density and arrangement of the framework Al atoms. Here, we use hydrothermal synthesis methods to control the arrangement of framework Al sites in chabazite (CHA) zeolites and, in turn, the distinct Cu site types formed. Time-resolved in situ resonance Raman spectroscopy reveals the kinetics of O<sub>2</sub> adsorption and activation within these well-defined Cu-CHA materials and the concomitant structural evolution of copper-oxygen (Cu<sub>x</sub>O<sub>y</sub>) complexes, which are interpreted alongside Cu(I) oxidation kinetics extracted from in situ X-ray absorption spectroscopy (XAS). Raman spectra of several plausible CuxOy species simulated using density functional theory suggest that experimental spectra (λ<sub>ex</sub> = 532 nm) capture the formation of mono(μ-oxo)dicopper species (ZCuOCuZ). Transient experiments show that the timescales required to form Cu<sub>x</sub>O<sub>y</sub> structures that no longer change in Ra-man spectra correspond to the durations of oxidative treatments that maximize CH<sub>3</sub>OH yields in stoichiometric PMO cycles (approximately 2 h). Yet, these periods extend well beyond the timescales for the complete conversion of the initial Cu(I) intermediates to their Cu(II) states (<0.3 h, reflected in XANES spectra), which demonstrates that Cu<sub>x</sub>O<sub>y</sub> complexes continue to evolve structurally following rapid oxidation. The dependence of ZCuOCuZ formation rates on O<sub>2</sub> pressure, H<sub>2</sub>O pressure, and temperature are consistent with a mechanism in which ZCuOH reduce to form ZCu<sup>+</sup> sites that bind molecular oxygen and form ZCu-O<sub>2</sub> intermediates. Subsequent reaction with proximate ZCu<sup>+</sup> form bridging peroxo dicopper complexes that cleave O-O bonds to form ZCuOCuZ in steps facilitated by water. These data and interpretations provide evidence for the chemical processes that link rapid and kinetically irrelevant Cu oxidation steps (frequently probed by XAS and UV-Vis spectroscopy) to the relatively slow genesis of reactive Cu complexes that form CH<sub>3</sub>OH during PMO. In doing so, we reveal previously unrec-ognized complexities in the processes by which Cu ions in zeolites activate O<sub>2</sub> to form active Cu<sub>x</sub>O<sub>y</sub> complexes, which under-score the insight afforded by judicious combinations of experimental and theoretical techniques.


2021 ◽  
Author(s):  
Daniel Bregante ◽  
Laura Wilcox ◽  
Changming Liu ◽  
Christopher Paolucci ◽  
Rajamani Gounder ◽  
...  

Cu-exchanged zeolites activate dioxygen to form active sites for partial methane oxidation (PMO), nitrogen oxide decomposition, and carbon monoxide oxidation. Apparent rates of O<sub>2</sub> activation depend both on the intrinsic kinetics of distinct Cu site types and the distributions of such sites within a given zeolite, which depend on the density and arrangement of the framework Al atoms. Here, we use hydrothermal synthesis methods to control the arrangement of framework Al sites in chabazite (CHA) zeolites and, in turn, the distinct Cu site types formed. Time-resolved in situ resonance Raman spectroscopy reveals the kinetics of O<sub>2</sub> adsorption and activation within these well-defined Cu-CHA materials and the concomitant structural evolution of copper-oxygen (Cu<sub>x</sub>O<sub>y</sub>) complexes, which are interpreted alongside Cu(I) oxidation kinetics extracted from in situ X-ray absorption spectroscopy (XAS). Raman spectra of several plausible CuxOy species simulated using density functional theory suggest that experimental spectra (λ<sub>ex</sub> = 532 nm) capture the formation of mono(μ-oxo)dicopper species (ZCuOCuZ). Transient experiments show that the timescales required to form Cu<sub>x</sub>O<sub>y</sub> structures that no longer change in Ra-man spectra correspond to the durations of oxidative treatments that maximize CH<sub>3</sub>OH yields in stoichiometric PMO cycles (approximately 2 h). Yet, these periods extend well beyond the timescales for the complete conversion of the initial Cu(I) intermediates to their Cu(II) states (<0.3 h, reflected in XANES spectra), which demonstrates that Cu<sub>x</sub>O<sub>y</sub> complexes continue to evolve structurally following rapid oxidation. The dependence of ZCuOCuZ formation rates on O<sub>2</sub> pressure, H<sub>2</sub>O pressure, and temperature are consistent with a mechanism in which ZCuOH reduce to form ZCu<sup>+</sup> sites that bind molecular oxygen and form ZCu-O<sub>2</sub> intermediates. Subsequent reaction with proximate ZCu<sup>+</sup> form bridging peroxo dicopper complexes that cleave O-O bonds to form ZCuOCuZ in steps facilitated by water. These data and interpretations provide evidence for the chemical processes that link rapid and kinetically irrelevant Cu oxidation steps (frequently probed by XAS and UV-Vis spectroscopy) to the relatively slow genesis of reactive Cu complexes that form CH<sub>3</sub>OH during PMO. In doing so, we reveal previously unrec-ognized complexities in the processes by which Cu ions in zeolites activate O<sub>2</sub> to form active Cu<sub>x</sub>O<sub>y</sub> complexes, which under-score the insight afforded by judicious combinations of experimental and theoretical techniques.


2020 ◽  
Author(s):  
Luzia S. Germann ◽  
Sebastian T. Emmerling ◽  
Manuel Wilke ◽  
Robert E. Dinnebier ◽  
Mariarosa Moneghini ◽  
...  

Time-resolved mechanochemical cocrystallisation studies have so-far focused solely on neat and liquid-assisted grinding. Here, we report the monitoring of polymer-assisted grinding reactions using <i>in situ</i> X-ray powder diffraction, revealing that reaction rate is almost double compared to neat grinding and independent of the molecular weight and amount of used polymer additives.<br>


2019 ◽  
Author(s):  
Hao Wu ◽  
Jeffrey Ting ◽  
Siqi Meng ◽  
Matthew Tirrell

We have directly observed the <i>in situ</i> self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. This work has elucidated one general kinetic pathway for the process of PEC micelle formation, which provides useful physical insights for increasing our fundamental understanding of complexation and self-assembly dynamics driven by electrostatic interactions that occur on ultrafast timescales.


Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1615
Author(s):  
Qiong Li ◽  
Jürgen Gluch ◽  
Zhongquan Liao ◽  
Juliane Posseckardt ◽  
André Clausner ◽  
...  

Fossil frustules of Ellerbeckia and Melosira were studied using laboratory-based nano X-ray tomography (nano-XCT), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Three-dimensional (3D) morphology characterization using nondestructive nano-XCT reveals the continuous connection of fultoportulae, tube processes and protrusions. The study confirms that Ellerbeckia is different from Melosira. Both genera reveal heavily silicified frustules with valve faces linking together and forming cylindrical chains. For this cylindrical architecture of both genera, valve face thickness, mantle wall thickness and copulae thickness change with the cylindrical diameter. Furthermore, EDS reveals that these fossil frustules contain Si and O only, with no other elements in the percentage concentration range. Nanopores with a diameter of approximately 15 nm were detected inside the biosilica of both genera using TEM. In situ micromechanical experiments with uniaxial loading were carried out within the nano-XCT on these fossil frustules to determine the maximal loading force under compression and to describe the fracture behavior. The fracture force of both genera is correlated to the dimension of the fossil frustules. The results from in situ mechanical tests show that the crack initiation starts either at very thin features or at linking structures of the frustules.


Carbon ◽  
2015 ◽  
Vol 87 ◽  
pp. 246-256 ◽  
Author(s):  
Périne Landois ◽  
Mathieu Pinault ◽  
Stéphan Rouzière ◽  
Dominique Porterat ◽  
Cristian Mocuta ◽  
...  

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