Correlation of oxidation states of surface chromium species with ethylene polymerization activity for Phillips CrOx/SiO2 catalysts modified by Al-alkyl cocatalyst

In situ Raman spectroscopy studies on chromium oxide catalyst in an anhydrous hydrogen fluoride atmosphere

“…[7,8] For application in catalysis, chromium oxides are usually supported on inorganic oxides, such as magnesia [9] and alumina. [10,11] Supported chromium oxide catalysts are crucial in chemical reactions such as hydrogenation and dehydrogenation reactions of hydrocarbons, [12,13] dehydrocyclization of paraffin, [14] polymerization of olefins, [9] and especially in the synthesis of hydrofluorocarbons (HFCs) and other oxygen-depleting substance (ODS) substitutes. [8,9,15] It is found that the CrO x F y phase exhibits significantly higher catalytic activity in dismutation of CCl 2 F 2 and fluorination of CF 3 CH 2 Cl than the pure oxide (Cr 2 O 3 ) and fluoride (α-CrF 3 and β-CrF 3 ).…”

“…[10,11] Supported chromium oxide catalysts are crucial in chemical reactions such as hydrogenation and dehydrogenation reactions of hydrocarbons, [12,13] dehydrocyclization of paraffin, [14] polymerization of olefins, [9] and especially in the synthesis of hydrofluorocarbons (HFCs) and other oxygen-depleting substance (ODS) substitutes. [8,9,15] It is found that the CrO x F y phase exhibits significantly higher catalytic activity in dismutation of CCl 2 F 2 and fluorination of CF 3 CH 2 Cl than the pure oxide (Cr 2 O 3 ) and fluoride (α-CrF 3 and β-CrF 3 ). [16,17] Chung et al [16] explained that the relatively easy formation of labile fluorine on the catalyst surface was due to the stronger interaction between the valence band of CrO x F y and the antibonding orbitals of HF.…”

Chromium(III) complexes bearing 2-benzoxazolyl-6-arylimino-pyridines: Synthesis and their ethylene reactivity

“…In spite of their practical applications for the last 50 years, the active species and the polymerization mechanism of these catalysts are still unclear [2][3][4]. It is well known that heterogeneous catalysts result in multisite active species in olefin polymerization [5][6][7], however, homogeneous catalysts provide the opportunity in understanding the active species and polymerization/oligomerization mechanism which might be helpful in designing advanced catalysts [8][9][10].…”

Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding

“…During the first 5 min, the injection of the TEAl co-catalyst in heptane, for a Al:Cr molar ratio of 2, can be noted by the increase of the methyl and methylene stretching bands of these compounds in the 2800–3000 cm −1 CH stretching region. [24–28] It must be noted that the addition of TEAl did not lead to a significant decrease of the silanol and titanol groups, suggesting that the added TEAl was also consumed for the reduction of Cr 6+ to Cr 2+ , Cr 3+ and Cr 5+ species,[29–38] for the transformation of a portion of the polymerisation into the oligomerisation active sites as well as for the scavenging of poisons. [1] Flushing of heptane revealed complex vibrational features of TEAl in the CH stretching region, suggesting alkylation of some of the Cr sites.…”