Disclosing the Interaction between Carbon Monoxide and Alkylated Ti3+ Species: a Direct Insight into Ziegler-Natta Catalysis

Synthesis and Deconstruction of Polyethylene-type Materials

Polyethylene deconstruction to reusable smaller molecules is hindered by the chemical inertness of its hydrocarbon chains. Pyrolysis and related approaches commonly require high temperatures, are energy-intensive, and yield mixtures of multiple classes of compounds. Selective cleavage reactions under mild conditions ( Collapse

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Grants

• H2020 European Research Council

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Affiliation(s)

Simon T. Schwab Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Maximilian Baur Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Taylor F. Nelson Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Stefan Mecking Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany

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Study of the Chemical Activities of Carbon Monoxide, Carbon Dioxide, and Oxygen Traces as Critical Inhibitors of Polypropylene Synthesis

This study outlines the investigation into how the compounds CO2, CO, and O2 interact with the active center of titanium (Ti) on the surface of MgCl2 and how these interactions impact the productivity of the Ziegler-Natta catalyst, ultimately influencing the thermal stability of the produced polypropylene. The calculations revealed that the adsorption energies of Ti-CO2-CO and O2 were -9.6, -12.5, and -2.32 Kcal/mol, respectively. Using the density functional theory in quantum calculations, the impacts of electronic properties and molecular structure on the adsorption of CO, O2, and CO2 on the Ziegler-Natta catalyst were thoroughly explored. Additionally, the Gibbs free energy and enthalpy of adsorption were examined. It was discovered that strong adsorption and a significant energy release (-16.2 kcal/mol) during CO adsorption could explain why this gas caused the most substantial reductions in the ZN catalyst productivity. These findings are supported by experimental tests showing that carbon monoxide has the most significant impact on the ZN catalyst productivity, followed by carbon dioxide, while oxygen exerts a less pronounced inhibitory effect.

A Brief Review on Selected Applications of Hybrid Materials Based on Functionalized Cage-like Silsesquioxanes

Rapid developments in materials engineering are accompanied by the equally rapid development of new technologies, which are now increasingly used in various branches of our life. The current research trend concerns the development of methods for obtaining new materials engineering systems and searching for relationships between the structure and physicochemical properties. A recent increase in the demand for well-defined and thermally stable systems has highlighted the importance of polyhedral oligomeric silsesquioxane (POSS) and double-decker silsesquioxane (DDSQ) architectures. This short review focuses on these two groups of silsesquioxane-based materials and their selected applications. This fascinating field of hybrid species has attracted considerable attention due to their daily applications with unique capabilities and their great potential, among others, in biomaterials as components of hydrogel networks, components in biofabrication techniques, and promising building blocks of DDSQ-based biohybrids. Moreover, they constitute attractive systems applied in materials engineering, including flame retardant nanocomposites and components of the heterogeneous Ziegler-Natta-type catalytic system.

A Ziegler-type spherical cap model reveals early stage ethylene polymerization growth versus catalyst fragmentation relationships

Polyolefin catalysts are characterized by their hierarchically complex nature, which complicates studies on the interplay between the catalyst and formed polymer phases. Here, the missing link in the morphology gap between planar model systems and industrially relevant spherical catalyst particles is introduced through the use of a spherical cap Ziegler-type catalyst model system for the polymerization of ethylene. More specifically, a moisture-stable LaOCl framework with enhanced imaging contrast has been designed to support the TiCl₄ pre-active site, which could mimic the behaviour of the highly hygroscopic and industrially used MgCl₂ framework. As a function of polymerization time, the fragmentation behaviour of the LaOCl framework changed from a mixture of the shrinking core (i.e., peeling off small polyethylene fragments at the surface) and continuous bisection (i.e., internal cleavage of the framework) into dominantly a continuous bisection model, which is linked to the evolution of the estimated polyethylene volume and the fraction of crystalline polyethylene formed. The combination of the spherical cap model system and the used advanced micro-spectroscopy toolbox, opens the route for high-throughput screening of catalyst functions with industrially relevant morphologies on the nano-scale.

Ziegler-type polyolefin catalysts have proven to be hard to characterize. Here the authors present a model system consisting of patterned LaOCl spherical caps, simulating bulk particles while facilitating the use of micro(-spectro)scopic characterization techniques specifically aimed at surfaces.

Core-Shell-Structured Carbon Nanotube@VS4 Nanonecklaces as a High-Performance Cathode Material for Magnesium-Ion Batteries

As a typical layered transition metal chalcogenide, VS₄ is considered as a promising cathode material for advanced magnesium-ion batteries. However, the poor electronic conductivity and severe polarization effect restrict its practical applications. Herein, we report a betaine-assisted solvothermal strategy to coat VS₄ nanoblocks on the surface of carbon nanotubes (CNTs), obtaining unique core-shell-structured CNT@VS₄ nanonecklaces. As a result of the morphology-controlling effect of betaine, VS₄ exhibits an unusual nanoblock morphology, which renders abundant active sites and promotes the contact between the electrode and electrolyte. CNTs serve as a highly conductive skeleton, combining with the VS₄ nanoblocks and ensuring their uniform distribution. As a benefit from the synergistic effect of abundant active sites and electron-conductive highways, the as-synthesized CNT@VS₄ nanonecklaces manifest remarkable performance for magnesium storage, including a large reversible capacity of 170 mAh g^-1 at 0.1 A g^-1, outstanding cycle stability (76.3 mAh g^-1 after 800 cycles at 0.5 A g^-1), and superior rate performance (77.2 mAh g^-1 at 2 A g^-1).

Cr(III) Complexes Bearing a β-Ketoimine Ligand for Olefin Polymerization: Are There Differences between Coordinative and Covalent Bonding?

β-ketoimines are extensively applied for the synthesis of organometallic complexes intended as (pre)catalysts for a variety of chemical transformations. We were interested in the synthesis of two Cr complexes bearing a simple bidentate β-ketoimine (L), with different ligand binding modes, as well as their application as a precatalyst in the polymerization of olefins. Complex 1 (L2CrCl3) was obtained by direct reaction of L with CrCl3(THF)3, while, for the synthesis of complex 2 (LCrCl2), the ligand was first deprotonated with nBuLi, giving the β-ketoiminato ligand L─Li+, and then reacted with CrCl3(THF)3. Characterization of the complexes proved that the Cr(III) ion is coordinatively bonded to L in 1, while it is covalently bonded to L in 2. The complexes were then used as precatalysts for the polymerization of ethylene and various cyclic olefins. Upon activation with methylaluminoxane, both the complexes exhibited poor activity in the polymerization of ethylene, whilst they exhibit good productivity in the polymerization of cyclic olefins, affording semicrystalline oligomers, without a significant difference between 1 and 2. To gain more insight, we investigated the reaction of the complexes with the Al-cocatalyst by IR and UV-Vis spectroscopies. The results proved that, in case of 1, the Al-activator deprotonates the ligand, bringing to the formation of an active species analogous to that of 2.

Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts

Kinetics-based differences in the early stage fragmentation of two structurally analogous silica-supported hafnocene- and zirconocene-based catalysts were observed during gas-phase ethylene polymerization at low pressures. A combination of focused ion beam-scanning electron microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy (IR PiFM) revealed notable differences in the distribution of the support, polymer, and composite phases between the two catalyst materials. By means of time-resolved probe molecule infrared spectroscopy, correlations between this divergence in morphology and the kinetic behavior of the catalysts' active sites were established. The rate of polymer formation, a property that is inherently related to a catalyst's kinetics and the applied reaction conditions, ultimately governs mass transfer and thus the degree of homogeneity achieved during support fragmentation. In the absence of strong mass transfer limitations, a layer-by-layer mechanism dominates at the level of the individual catalyst support domains under the given experimental conditions.

Polyethylene materials with in-chain ketones from nonalternating catalytic copolymerization

[Figure: see text].

The cooperative role of innocent ligand in N-heterocyclic carbene manganese catalyzed carbon dioxide hydrogenation

The concept of Lewis acidic π* cooperation was proposed for innocent CO ligand in NHC–Mn catalyzed CO2 hydrogenation by systematic DFT studies.