scholarly journals Surface chromium single sites: open problems and recent advances

2012 ◽  
Vol 468 (2143) ◽  
pp. 2087-2098 ◽  
Author(s):  
Adriano Zecchina ◽  
Elena Groppo
Keyword(s):  
Ethylene Polymerization ◽  
Reaction Rate ◽  
Single Site ◽  
Polymerization Reaction ◽  
Detailed Knowledge ◽  
Open Problems ◽  
Initiation Mechanism ◽  
Characterization Methods ◽  
Polymerization Catalyst ◽  
Recent Advances

The results of decades of studies on the Phillips chromium (Cr)/silica polymerization catalyst are briefly summarized. The application of several characterization methods has allowed a detailed knowledge of the structure and reactivity of Cr centres to be obtained. In particular, many aspects of this apparently simple single-site catalyst, including the heterogeneity, the modification of the ligand sphere upon interaction with many molecules and the initiation mechanism of the ethylene polymerization reaction, have been clarified. It is shown that based on the acquired knowledge, it is now possible to proceed further towards the intelligent modification of the ligand sphere with the scope to increase the reaction rate and selectivity. It is also illustrated that, besides polymerization/oligomerization reactions, it is possible to extend the study of Cr II reactivity towards new reactions.

scholarly journals Photocatalytic Activity: Experimental Features to Report in Heterogeneous Photocatalysis

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1990 ◽  
Author(s):  
Md. Hoque ◽  
Marcelo Guzman
Keyword(s):  
Reaction Rate ◽  
Monochromatic Light ◽  
Heterogeneous Photocatalysis ◽  
Research Articles ◽  
Quantum Yields ◽  
Characterization Methods ◽  
Valuable Data ◽  
Photocatalytic Activities ◽  
Scientific Papers

Heterogeneous photocatalysis is a prominent area of research with major applications in solar energy conversion, air pollution mitigation, and removal of contaminants from water. A large number of scientific papers related to the photocatalysis field and its environmental applications are published in different journals specializing in materials and nanomaterials. However, many problems exist in the conception of papers by authors unfamiliar with standard characterization methods of photocatalysts as well as with the procedures needed to determine photocatalytic activities based on the determination of “apparent quantum efficiencies” within a wavelength interval or “apparent quantum yields” in the case of using monochromatic light. In this regard, an astonishing number of recent research articles include claims of highly efficient (photo)catalysts or similar terms about materials with superior or enhanced efficiency for a given reaction without proper experimental support. Consequently, the comparison of the efficiencies of photocatalysts may result as being meaningless, especially when reports are only based on expressions determining (1) a reaction rate per weight of catalyst or its surface area, (2) quantum efficiencies or quantum yields, and (3) turnover frequencies or turnover numbers. Herein, we summarize the standards needed for reporting valuable data in photocatalysis and highlight some common discrepancies found in the literature. This work should inform researchers interested in reporting photocatalysis projects about the correct procedures for collecting experimental data and properly characterizing the materials by providing examples and key supporting literature.

(Pyrazol-1-yl)carbonyl palladium complexes as catalysts for ethylene polymerization reaction

2013 ◽  
Vol 724 ◽  
pp. 95-101 ◽  
Author(s):  
Hosana D. Mkoyi ◽  
Stephen O. Ojwach ◽  
Ilia A. Guzei ◽  
James Darkwa
Keyword(s):  
Ethylene Polymerization ◽  
Palladium Complexes ◽  
Polymerization Reaction

scholarly journals Effects of Various Mixed Metal Chlorides- AlCl3 in TiCl4/MgCl2/THF Catalytic System on Ethylene Polymerization

2015 ◽  
Vol 14 (2) ◽  
pp. 12
Author(s):  
Nittaya Sudsong ◽  
Wanna Phiwkliang ◽  
Bunjerd Jongsomjit ◽  
Piyasan Praserthdam
Keyword(s):  
Catalytic System ◽  
Ethylene Polymerization ◽  
Catalyst System ◽  
Polymerization Reaction ◽  
Molar Ratio ◽  
Metal Chlorides ◽  
Mixed Metal ◽  
Icp Analysis ◽  
Co Addition

In this research, the modification of TiCl4/MgCl2/THF catalyst system with various metal chlorides was investigated on ethylene polymerization. Experimentally, metal chlorides (CaCl2, FeCl2 and ZnCl2) were simultaneously introduced different with TiCl4/MgCl2/THF catalyst. ICP analysis was used to determine the total amount of each metal in the catalyst. For polymerization reaction, TEA was used as cocatalyst and hexane was used as a medium solvent. The Al/Ti molar ratio was 140. The activity result of Ca-Al, Zn-Al and Fe-Al was 979, 1009 and 1476 kgPE/molTi.h, respectively. The coaddition of AlCl3 and FeCl2 in TiCl4/MgCl2/THF catalyst system exhibited the highest activity. It suggested that the co-addition of AlCl3 and FeCl2 has higher electronegativity (EN) and the radius of Fe2+ is closer to Mg2+ resulting in an increased efficiency of the THF removal. This result led to improve the catalyst performance.

Remote dibenzocycloheptyl substitution on a bis(arylimino)pyridyl-iron ethylene polymerization catalyst; enhanced thermal stability and unexpected effects on polymer properties

2021 ◽  
Author(s):  
Liwei Guo ◽  
Wenjuan Zhang ◽  
Furong Cao ◽  
Youshu Jiang ◽  
Randi Zhang ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Ethylene Polymerization ◽  
Chloride Complexes ◽  
Polymerization Catalyst ◽  
Polymer Properties

Four examples of para-dibenzocycloheptyl-substituted 2,6-bis(arylimino)pyridyl-iron(II) chloride complexes, [2,6-{(2-R1,4-(C15H13),6-R2C6H2)N=CMe}2C5H3N]FeCl2 (R1 = R2 = Me Fe1, Et Fe2, iPr Fe3, R1 = Me, R2 = Et Fe4), have been synthesized and characterized...

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