Silica-supported metallocene catalyst poisoning: The effect of surface modification on the efficiency of the catalytic system

Ullmann, Marcius A.; Bernardes, Arthur A.; Santos, João Henrique Zimnoch dos

doi:10.1016/j.colsurfa.2018.12.039

Cited by 12 publications

(7 citation statements)

References 69 publications

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“…Several methods have been proposed in the literature to alleviate the formation of catalyst fines in gas-phase polymerization using antistatic agents, − catalyst poison in the form of a liquid or gas, − or small amounts of liquid hydrocarbon or mineral oil. − In all of these methods, a small amount of agent is used to coat and deactivate the active sites at the surface of the catalyst particle prior to the main reaction while leaving the interior active sites intact. A reduction in the number of active sites at the surface of the particle by increasing the contact time and allowing them to access the interior may remove the need of using such additives.…”

Section: Results and Discussionmentioning

confidence: 99%

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

2022

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This work presents the experimental investigation of the effects of intraparticle catalyst site distribution on the catalyst particle fragmentation in gas-phase ethylene polymerization over a silica-supported metallocene catalyst (rac-dimethylsilylbis(2-methyl-4-phenylindenyl)-dimethyl zirconium) with methylaluminoxane (MAO) as a cocatalyst. The supported catalysts with different spatial distributions of Al and Zr were prepared by varying the catalyst immobilization conditions, and the catalyst metal distributions were analyzed using the focused ion beam (FIB) and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDX) techniques. The experimental data showed that impregnation time and catalyst solution concentration had strong effects on the radial distributions of Zr in silica particles and fines formation during the gas-phase polymerization of ethylene. The supported catalyst with a high Zr concentration near the exterior region of a catalyst particle generated more fines than a supported catalyst with uniformly distributed Zr during the gas-phase polymerization, suggesting that the optimal distribution of catalyst sites needs to be considered in designing the silica-supported catalyst for improved control of polymer particle morphology.

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Section: Results and Discussionmentioning

confidence: 99%

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

2022

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“…Finally, Ullmann et al immobilized Cp 2 ZrC l2 on SiO 2 by using two different methods: direct grafting and via entrapment within the silica matrix by a NHSG route, modifying the surface of the latter with various metal salts (Cr, Mo, and W). 145 They found that the NHSG approach allowed the incorporation of Lewis acid sites while supporting the catalyst by entrapping in a single gelation step. It was suggested that the higher activities of these entrapped systems could be related to the Lewis acid sites on the surface, which prevented them from deactivation through poisoning.…”

Section: Nonhydrolytic Sol−gel Methodsmentioning

confidence: 99%

“…All catalysts were active and selective to acrolein due to the high proportion of Brønsted acid sites, and the authors concluded that the one-pot nonhydrolytic sol–gel route was an effective synthetic method to obtain active, selective, and stable catalysts for the aerobic transformation of glycerol to acrolein. Finally, Ullmann et al immobilized Cp 2 ZrC l2 on SiO 2 by using two different methods: direct grafting and via entrapment within the silica matrix by a NHSG route, modifying the surface of the latter with various metal salts (Cr, Mo, and W) . They found that the NHSG approach allowed the incorporation of Lewis acid sites while supporting the catalyst by entrapping in a single gelation step.…”

Section: Nonhydrolytic Sol–gel Methodsmentioning

confidence: 99%

Encapsulation Methods for Control of Catalyst Deactivation: A Review

et al. 2020

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One of the most significant challenges in the use of heterogeneous catalysts is the loss of activity and/or selectivity with time on stream, and researchers have explored different methods to overcome this problem. Recently, the coating of catalysts to control their deactivation has generated much research traction. This Review is aimed at studying different encapsulation techniques employed for controlling catalyst deactivation. Focus is given to the prevention of irreversible modes of deactivation, such as sintering and leaching. In this Review, we elaborate on different entrapment methods used to protect catalysts from deactivation in both liquid and gas reaction media. Relevant probe reactions are discussed with emphasis on the catalyst activity and stability. Challenges associated with those processes are also described with emphasis on the mass transfer limitations as a result of the coverage of the active sites. Finally, some future perspectives and areas for possible improvement are highlighted.

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“…SAXS allows to measure the radii of gyration (Rg) of particles and calculate the primary particle diameter (C.Dp M ) of catalyst, thus C.Dp M = 2Rg (5/3) 0.5. [21,52,74] Other studies using the SAXS technique have been reported the radius of gyration (Rg) of 14.8-20.3 nm, [78] 6.86-14.36 nm, [40] and 6.0-10.1 nm [79] of silica-based catalysts for ethylene polymerization.…”

Section: Chemcatchemmentioning

confidence: 99%

Supported Catalyst (nBuCp)₂ZrCl₂ on Nano/Micro Domains for High Performance Ethylene Polymerization

2023

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Silica-based supports known as structured-mixed supports were evaluated in ethylene polymerization. These supports exhibit local surface heterogeneity due to the in situ growth of nanoparticles under the surface. Standard (N) and hybrid (NTw and NPu) nanosilicas were synthesized by a sol gel method. The metallocene (nBuCp) 2 ZrCl 2 catalyst was immobilized onto nanosilicas and onto the structured-mixed support (MN, MNTw, and MNPu). The zirconocene active sites on the nanoparticles exhibited high activity (5,071 kg.mol Zr À 1 .h À 1 .bar À 1 with NPu) using Pluronic® L-31 (Pu). An excellent catalytic performance (10,777 kg.mol Zr À 1 .h À 1 .bar À 1 ) was achieved when Zr was incorporated on a structured-mixed support, and a polymer with high molecular weight (Mw up to 224 kg.mol À 1 ), broad polydispersion (Mw. Mn À 1 = 3.1), high melting temperature (Tm = 142 °C), and crystallinity (Xc = 76 %) was generated using Tween®80 (Tw). The results showed that support characteristics, such as a large surface area, surface fractal structure, functionalization of nanoparticles with Tw or Pu, and nano/microdomains, influenced the nature and distribution of active sites, leading to a robust catalytic system that is easily synthesized. Silica-based nano/microparticles pretreated with Tween®80 are an adequate candidate for new catalytic supports for ethylene polymerization.

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Silica-supported metallocene catalyst poisoning: The effect of surface modification on the efficiency of the catalytic system

Cited by 12 publications

References 69 publications

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

Encapsulation Methods for Control of Catalyst Deactivation: A Review

Supported Catalyst (nBuCp)₂ZrCl₂ on Nano/Micro Domains for High Performance Ethylene Polymerization

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Silica-supported metallocene catalyst poisoning: The effect of surface modification on the efficiency of the catalytic system

Cited by 12 publications

References 69 publications

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

Encapsulation Methods for Control of Catalyst Deactivation: A Review

Supported Catalyst (nBuCp)2ZrCl2 on Nano/Micro Domains for High Performance Ethylene Polymerization

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Product

Resources

About

Supported Catalyst (nBuCp)₂ZrCl₂ on Nano/Micro Domains for High Performance Ethylene Polymerization