Macromol. React. Eng. 6/2013

Meisterová, Lucie; Zubov, Alexandr; Smolná, Klára; Štěpánek, František; Košek, Juraj

doi:10.1002/mren.201370015

Cited by 5 publications

(4 citation statements)

References 0 publications

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“…A variety of samples can be imaged under ambient conditions at 2D and 3D spatial resolutions of up to 150 nm and 170 nm, respectively [33–35] . Specifically in the context of supported olefin polymerization catalysts, the technique delivers comprehensive information on the extent and magnitude of large‐scale fragmentation phenomena (i. e., crack formation and propagation) and the 3D structure and phase distribution of individual particles [2,4,36,37] – more so than other laboratory‐based techniques such as SEM, which only yields 2D information [11,17,19,38–42] …”

Section: Introductionmentioning

confidence: 99%

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

et al. 2022

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Strict morphological control over growing polymer particles is an indispensable requirement in many catalytic olefin polymerization processes. In catalysts with mechanically stronger supports, e. g., polymerization-grade silicas, the emergence of extensive cracks via the sectioning fragmentation mechanism requires severe stress build-up in the polymerizing catalyst particle. Here, we report on three factors that influence the degree of sectioning in silica-supported olefin polymerization catalysts. Laboratory-based X-ray nano-computed tomography (nanoCT) and focused ion beam-scanning electron microscopy (FIB-SEM) were employed to study catalyst particle morphology and crack propagation in two showcase catalyst systems, i.e., a zirconocene-based catalyst (i.e., Zr/MAO/SiO 2 , with Zr = 2,2'biphenylene-bis-2-indenyl zirconium dichloride and MAO = methylaluminoxane) and a Ziegler-Natta catalyst (i.e., TiCl 4 / MgCl 2 /SiO 2 ), during slurry-phase ethylene polymerization. The absence of extensive macropores in some of the catalysts' larger constituent silica granulates, a sufficient accessibility of the catalyst particle interior at reaction onset, and a high initial polymerization rate were found to favor the occurrence of the sectioning pathway at different length scales. While sectioning is beneficial for reducing diffusion limitations, its appearance in mechanically stronger catalyst supports can indicate a suboptimal support structure or unfavourable reaction conditions.

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Section: Introductionmentioning

confidence: 99%

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

et al. 2022

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“…Last but not least, laboratory‐based computed tomography (CT), an absorption contrast‐based technique, represents an accessible alternative to synchrotron‐based methods for characterizing pristine and polymerized catalyst particles [28,48,64–66] . Nano‐computed tomography (nanoCT) has been reported to deliver sub‐180 nm resolutions for different silica‐supported olefin polymerization catalysts (Figure 8), as determined via Fourier shell correlation analysis (FSC) [48] .…”

Section: Assessing the Morphology And Activity Of Supported Olefin Po...mentioning

confidence: 99%

Visualizing the Structure, Composition and Activity of Single Catalyst Particles for Olefin Polymerization and Polyolefin Decomposition

Werny,

Meirer,

Weckhuysen

2023

Angew Chem Int Ed

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The structural and morphological characterization of individual catalyst particles for olefin polymerization, as well as for the reverse process of polyolefin decomposition, can provide an improved understanding for how these catalysts operate under reaction conditions. In this review, we discuss an emerging toolbox of chemical imaging techniques that is suitable for investigating the chemistry and reactivity of related catalysts. While synchrotron‐based X‐ray microscopy still provides spatial resolutions in 2D and 3D, a number of laboratory‐based techniques, most notably focused ion beam‐scanning electron microscopy, confocal fluorescence microscopy, infrared photoinduced force microscopy and laboratory‐based X‐ray nano‐computed tomography, have helped to expand the arsenal of tools available to scientists in catalysis and polymer science. In terms of future research, the review outlines the role and impact of in situ and operando (spectro‐)microscopy experiments, involving sophisticated reactors as well as online reactant and product analysis, to obtain real‐time information on the formation, decomposition, and mobility of polymer phases within catalyst particles. Furthermore, the potential of fluorescence, X‐ray and optical microscopy is highlighted for the high‐throughput characterization of olefin polymerization and polyolefin decomposition catalysts.

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“…[10,12,18] The phenomenon is called replication. In some investigations on heterogeneous polymerization of olefins, the bulk of the particles appeared dense, [12,17,18] while in other cases, it was porous, [7,24,25] however, porosity decreased with time for both porous and dense particles. Researchers have also found out for porous polymer particles that there are always wide macrocracks extended from surface to the center of the particles.…”

Section: Doi: 101002/mren202100021mentioning

confidence: 99%

A Multipore Model for Heterogeneous Catalytic Polymerization: Structure–Performance Relationships

Sheikhzadeh

Pourmahdian

2021

Macro Reaction Engineering

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A novel single-particle model is developed for the physicochemical processes involved in the heterogeneous catalytic polymerization. The model considers the reaction kinetics together with the detailed initial pore structure and explicitly describes the support fragmentation. It captures some of the most widely observed morphological features of heterogeneous catalysis for both before and after starting fragmentation, including the possibility of occurrence of both known fragmentation mechanisms. All the monomer mass conservation equations are solved using a robust semianalytical approach. The results show that the catalyst pore structure, which can be tuned during chemical preparations, has a vital role in determining the catalyst performance through changing the contribution of each of the two fragmentation mechanisms in the overall fragmentation process and that decreasing the propagation rate constant and/or increasing diffusion coefficient intensifies the continuous bisection mechanism. A potential fragmentation index is proposed in order to relate the fragmentation phenomenon to structural features of the catalyst. By defining a weighted average fill factor, it is shown that the fragmentation index is in fact a measure of how much the pores closer to the center relative to the pores closer to the surface are filled up at the fragmentation moment.

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Macromol. React. Eng. 6/2013

Cited by 5 publications

References 0 publications

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

Visualizing the Structure, Composition and Activity of Single Catalyst Particles for Olefin Polymerization and Polyolefin Decomposition

A Multipore Model for Heterogeneous Catalytic Polymerization: Structure–Performance Relationships

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