کد مقاله کد نشریه سال انتشار مقاله انگلیسی ترجمه فارسی نسخه تمام متن
6455402 1419757 2017 15 صفحه PDF سفارش دهید دانلود رایگان
عنوان انگلیسی مقاله ISI
Active sites formation and their transformations during ethylene polymerization by the Phillips CrOx/SiO2 catalyst
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موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی کاتالیزور
پیش نمایش صفحه اول مقاله
Active sites formation and their transformations during ethylene polymerization by the Phillips CrOx/SiO2 catalyst
چکیده انگلیسی


- Many potential initiation and propagation mechanisms are computationally studied.
- Cr(II), Cr(III), Cr(III)OH and Cr(V) oxide species are considered as the precursors.
- Cr(III)OH and Cr(III) vinyl sites can be effective for ethylene polymerization.
- Silica defect sites can play a role in transformation of Cr(II) to Cr(III) species.

The nature of the active sites and the mechanism of ethylene polymerization over the Phillips CrOx/SiO2 catalyst are still under debate. In this work, a number of potential initiation, propagation and termination mechanisms for ethylene polymerization are investigated using density functional theory and cluster models. Cr(II), Cr(III), Cr(III)OH and Cr(V) oxide species are considered as the active site precursors. It is predicted that the oxachromacycle ring expansion mechanism is more probable than the routes involving Si(OH)Cr(II)-vinyl or Si(OH)Cr(III)-vinyl sites. We also show that the hydroxylated Cr(III)OH species, further transforming into the active Cr(III) vinyl sites, can be effective for ethylene polymerization. Additionally, we propose that defect sites in the amorphous silica framework can play a role in low-temperature transformation of the Cr(II) species into the active Cr(III) sites. A potential polymerization mechanism involving minor Cr(V) oxide species is also calculated.

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ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Catalysis - Volume 352, August 2017, Pages 314-328
نویسندگان
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