Influence of Alkylaluminum Co-catalysts on TiCl4 Transalkylation and Formation of Active Centers C* in Ziegler-Natta Catalysts

2013 ◽  
Vol 7 (3-4) ◽  
pp. 146-154 ◽  
Author(s):  
Heinrich Trischler ◽  
Wolfgang Schöfberger ◽  
Christian Paulik
Keyword(s):  
Active Centers ◽  
Co Catalysts ◽  
Ziegler Natta Catalysts

In Situ and Ex Situ Microscopic Study of Propylene Polymerization With Heterogeneous Mgcl2-Supported Ziegler-Natta Catalysts

2000 ◽  
Vol 6 (S2) ◽  
pp. 33-34
Author(s):  
V. Oleshko ◽  
P. Crozier ◽  
R. Cantrell ◽  
A. Westwood
Keyword(s):  
Large Scale ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
Light And Electron Microscopy ◽  
High Surface Area ◽  
Propylene Polymerization ◽  
Ex Situ ◽  
Co Catalysts ◽  
Ziegler Natta Catalysts

The large-scale commercial production of polyolefins by catalytic Ziegler-Natta polymerization have stimulated the development of the third, fourth and fifth generation heterogeneous catalysts comprising high surface area defective MgCl2 with TiCl4, electron donors, and AlR3-co-catalysts. In spite of intensive research over the years, the present level of understanding of the catalysts is still incomplete because of their complex composition leading to a multitude of local active site environments. The aim of this work is to provide a new insight into the process via in situ video microscopy of gas phase propylene polymerization over MgCl2-supported Ziegler-Natta catalysts combined with ex situ characterization by light and electron microscopy techniques (SEM, TEM, HRTEM, STEM, PEELS and windowless EDX). Procedures for catalyst synthesis are described elsewhere. The catalysts were stored in a dry box under a He atmosphere (<lppm H2O/O2). Samples were transferred to specimen holders in the dry box and then transferred into the microscopes under high purge N2 conditions to prevent poisoning of the catalysts by air and moisture.

scholarly journals Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

2020 ◽  
Author(s):  
Anton Ashuiev ◽  
mathieu humber ◽  
sebastien norsic ◽  
jean blahut ◽  
david gajan ◽  
...  
Keyword(s):  
Active Sites ◽  
Atomic Scale ◽  
Paramagnetic Species ◽  
Polymerization Catalysts ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Joint Application ◽  
Spectroscopic Signatures ◽  
Electron Paramagnetic ◽  
Ziegler Natta Catalysts

Despite decades of extensive studies, the atomic-scale structure of active sites in heterogeneous Ziegler-Natta (ZN) catalysts remains elusive and a matter of debate. Here, the structure of polymerization ZN catalysts is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl<sub>3</sub> so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Notably, we show that EPR and NMR spectroscopy of the activated ZN catalysts enables to observe paramagnetic species whose amount increases in conjunction with the catalytic activity. The joint application of 2D HYSCORE experiments and DFT calculations reveals the presence of bimetallic alkyl-Ti(III),Al complexes that are assigned to the catalytic centers of MgCl<sub>2</sub>-supported Ziegler-Natta catalysts

scholarly journals Carbon Monoxide Promotes the Catalytic Hydrogenation on Metal Cluster Catalysts

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Ruixuan Qin ◽  
Pei Wang ◽  
Pengxin Liu ◽  
Shiguang Mo ◽  
Yue Gong ◽  
...  
Keyword(s):  
Catalytic Hydrogenation ◽  
Metal Cluster ◽  
Hydrogenation Reaction ◽  
Metal Catalysts ◽  
Binding Energies ◽  
Single Atom ◽  
Surface Binding ◽  
Active Centers ◽  
Promoting Effect ◽  
Co Catalysts

Size effect plays a crucial role in catalytic hydrogenation. The highly dispersed ultrasmall clusters with a limited number of metal atoms are one candidate of the next generation catalysts that bridge the single-atom metal catalysts and metal nanoparticles. However, for the unfavorable electronic property and their interaction with the substrates, they usually exhibit sluggish activity. Taking advantage of the small size, their catalytic property would be mediated by surface binding species. The combination of metal cluster coordination chemistry brings new opportunity. CO poisoning is notorious for Pt group metal catalysts as the strong adsorption of CO would block the active centers. In this work, we will demonstrate that CO could serve as a promoter for the catalytic hydrogenation when ultrasmall Pd clusters are employed. By means of DFT calculations, we show that Pdn n=2‐147 clusters display sluggish activity for hydrogenation due to the too strong binding of hydrogen atom and reaction intermediates thereon, whereas introducing CO would reduce the binding energies of vicinal sites, thus enhancing the hydrogenation reaction. Experimentally, supported Pd2CO catalysts are fabricated by depositing preestablished [Pd2(μ-CO)2Cl4]2- clusters on oxides and demonstrated as an outstanding catalyst for the hydrogenation of styrene. The promoting effect of CO is further verified experimentally by removing and reintroducing a proper amount of CO on the Pd cluster catalysts.

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