Mx-Oy-Siz bonding models for silica-supported Ziegler-Natta catalysts

Liu, Jia-Chu

doi:10.1002/(sici)1099-0739(199904)13:4<295::aid-aoc845>3.0.co;2-r

Cited by 23 publications

(12 citation statements)

References 14 publications

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“…The vibrational band at 1209 cm –1 is assigned to Si–O vibrations that arise due to the oxidation of the silicon powder with H 2 O exposures. , This peak grows rapidly during the first 10 TiO 2 ALD cycles, and then the growth slows at higher TiO 2 ALD film thicknesses. The bands at 940 and 1048 cm –1 are assigned to Si–O–Ti vibrations resulting from the mixing of TiO 2 and SiO 2 at the interface. , These vibrational bands also do not increase further as TiO 2 ALD continues past 30 cycles.…”

Section: Resultsmentioning

confidence: 96%

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Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂

et al. 2021

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A combined computational and experimental study is employed to understand the competition between self-limiting (SL) and chemical vapor etch (CVE) reactions to design an atomic layer etch (ALE) process. The pulses in an ALE process have to be self-limiting; i.e., the reactions should reach saturation after sufficient pulse time. By comparing the reaction free energies of corresponding SL and CVE reactions using density functional theory (DFT), the temperature and pressure conditions can be predicted that favor the SL or CVE reactions. The etching of TiO2 when exposed to HF gas is utilized as a test case. Simulations reveal that when TiO2 is exposed to reactant HF at a pressure of 0.2 Torr, the SL reaction removing H2O at 0.01 Torr and fluorinating the surface is preferred up to 87 °C (360 K). At higher temperatures, continuous removal of TiO2 by CVE occurs according to the reaction TiO2 + HF → TiF4 + H2O subject to kinetic activation barriers. Experimental results from in situ Fourier transform infrared (FTIR) spectroscopy and quadrupole mass spectrometry (QMS) are compared with the theoretical predictions. In good agreement with theory, the FTIR spectroscopy studies revealed an onset of spontaneous etching (CVE) at temperatures around 80–90 °C. In addition, the QMS analysis observed TiF4 and H2O as the etch products, further validating the calculations. The calculations also predicted that an increase in the reactant gas pressure would enhance etching at high temperatures. The low computational cost of this theoretical approach allows for rapid screening of etch reagents and prediction of the temperature/pressure windows where the reactions will be in the SL or CVE regimes.

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Section: Resultsmentioning

confidence: 96%

“…The bands at 940 and 1048 cm −1 are assigned to Si−O−Ti vibrations resulting from the mixing of TiO 2 and SiO 2 at the interface. 46,47 These vibrational bands also do not increase further as TiO 2 ALD continues past 30 cycles.…”

Section: IIImentioning

confidence: 90%

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂

et al. 2021

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“…Recently, the use of polyhedral oligomeric silsesquioxane (POSS) to develop heterogeneous ZN catalysts has become increasingly attractive since its various organic substituents can provide different chemical properties while its oligomerization can form rigid blocks at the nanoscale. − Our previous works have demonstrated that simultaneous introduction of POSS and MgCl 2 can give rise to well-defined POSS/MgCl 2 nanoaggregates, which indicates the promising potential of POSS in effectively tuning the distribution of active titanium species . Herein, taking advantage of the self-nucleation behavior of trisilanol POSS molecules (see Figure S1 for their structure), we report a novel type of porous MgCl 2 /THF/TiCl 4 -based microspheres with in situ formed POSS inner cores and rhombic MgCl 2 outer layers.…”

Section: Introductionmentioning

confidence: 99%

Revealing the Dynamic Behaviors of Tetrahydrofuran for Tailoring the Active Species of Ziegler–Natta Catalysts

Liang

Chen

et al. 2021

ACS Catal.

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A full elucidation of chemisorbed donor behavior is of fundamental importance for tailoring the active species but has not yet been achieved for Ziegler–Natta catalysts. Herein, by exploiting the self-nucleation of polyhedral oligomeric silsesquioxane (POSS) molecules, we present porous microspheres assembled from rhombic MgCl2 nanocrystals with layered laterals. The as-formed POSS–MgCl2 aggregation, after immobilization of TiCl4, shows considerable catalytic activity toward ethylene polymerization, synthesizing ultrahigh molecular weight polyethylene with enhanced processability and mechanical properties as well as reduced entanglement. By tracing catalyst synthesis and titanium activation with in situ spectroscopy, surface approaches, and density functional theory calculations, we acquired fundamental insight into the active role of THF on the MgCl2 surface. We experimentally demonstrate (i) the full coverage of THF on the lateral surfaces of MgCl2 crystals; (ii) the partial desorption and migration of THF on the surfaces owing to its high mobility, resulting in the regeneration of unsaturated Mg2+ sites and the subsequent formation of TiCl4–THF complexes during titanation; and (iii) the active participation of THF in the final active sites (i.e., after activation). The whole data set clearly demonstrates that the dynamic adsorption of donors directly affects the structure and performance of the active species, offering a perspective on the interactions between donors and other components.

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“…Titansiloxanes are of considerable scienti c and practical interest. They are widely used as Ziegler-Natta catalysts [17], catalysts for oxidation and polymerization [18][19][20], and epoxidation [21,22]. In addition, they are precursors of materials for medicine and microbiology.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Polyphenylsilsesquioxane With Various β-diketonate Complexes of Titanium By Mechanochemical Activation

Libanov

Капустина²,

Шапкин³

et al. 2022

Preprint

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In the present work, we studied the interaction of polyphenylsilsesquioxane with various β-diketonate complexes of titanium by mechanochemical activation. Polyphenylsilsesquioxane, bis-(2,4-pentanedionate) titanium dichloride, bis-(1-phenyl-1,3-butanedionate) titanium dichloride and bis-(1,3-diphenyl-1,3-propanedionate) titanium dichloride were used as starting reagents. Synthesis products were studied by various chemical and physicochemical methods of analysis. The composition of the obtained compounds has been determined. It is shown that under conditions of mechanochemical activation, high molecular weight products with a Si/Ti ratio different from the specified ones are formed. In addition, under the action of mechanical stresses, the initial titanium complexes (with the exception of acetylacetonate) polymerize with the formation of coordination high-molecular compounds, which are destroyed by the addition of ethyl alcohol. The work is fundamental and contributes to the understanding of the mechanisms of mechanochemical synthesis. The work is aimed at finding effective and environmentally friendly methods for the synthesis and modification of elementorganic high-molecular compounds.

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Mx-Oy-Siz bonding models for silica-supported Ziegler-Natta catalysts

Cited by 23 publications

References 14 publications

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂

Revealing the Dynamic Behaviors of Tetrahydrofuran for Tailoring the Active Species of Ziegler–Natta Catalysts

Interaction of Polyphenylsilsesquioxane With Various β-diketonate Complexes of Titanium By Mechanochemical Activation

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Mx-Oy-Siz bonding models for silica-supported Ziegler-Natta catalysts

Cited by 23 publications

References 14 publications

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO2

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO2

Revealing the Dynamic Behaviors of Tetrahydrofuran for Tailoring the Active Species of Ziegler–Natta Catalysts

Interaction of Polyphenylsilsesquioxane With Various β-diketonate Complexes of Titanium By Mechanochemical Activation

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Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂

Prediction and Validation of the Process Window for Atomic Layer Etching: HF Exposure on TiO₂