Supporting mechanism of non‐toxic chromium (III) acetate on silica for preparation of Phillips ethylene polymerization catalysts

Abstract

Phillips catalyst is an important kind of industrial polyethylene catalyst. As early as in the late 1970s, CrO 3 was substituted by chromium (III) acetate for the preparation of Phillips catalyst on the industrial scale owing to health and environmental considerations. There is still considerable research focusing on the relations between the preparation process and catalyst properties in academics. In this work, the supporting mechanism of chromium (III) acetate on silica has been studied by Thermogravimetry-Differential Thermal Analysis (TG-DTA), and Electron Spin Resonance (ESR), in comparison with that of supporting CrO 3 on SiO 2 . The basic chromium (III) acetate supported on high surface area silica gel decomposed differently from that for bulk basic chromium acetate when decomposition temperature was decreased by 15• C. The decomposition temperature was 299• C for Cr 3 (OH) 2 (Ac) 7 /SiO 2 catalyst precursor, which would be firstly transferred into CrO 3 followed by supporting on silica surface as chromate species. The further weight loss came from thermal inductive reduction of chromate species into Cr 2 O 3 , which was also supported by the results of colors of catalysts. Moreover, with the increase of chromium loading of Cr 3 (OH) 2 (Ac) 7 /SiO 2 , such thermal inductive reduction became more severe. ESR spectra of Cr 3 (OH) 2 (Ac) 7 /SiO 2 and CrO 3 /SiO 2 catalyst precursors showed that a small amount of supported Cr 5+ can exist stably on silica gel surface at temperatures higher than 200

Comparison of Support Effects on Phillips and Metallocene Catalysts

“…For Phillips catalysts, the calcination temperature is one of the most powerful variables in determining activity [3,21,110]. In addition to oxidizing the Cr [111], high temperatures are thought to remove OH ligands, and add stress to the -O-Cr-O-bonds as illustrated in Scheme 1. With silica as the support, the activity first develops after calcination at about 400 • C, and it continues to rise up to the point of sintering, usual around 900 • C. Other supports also tend to follow this trend, although the activity can vary widely.…”

“…Chromium catalysts were made by impregnating these supports, prior to calcination, with a methanol solution of chromium acetate [111,113]. Then they were dried in a vacuum oven, followed by calcination as indicated.…”

Covalent immobilization of metal–organic frameworks onto the surface of nylon—a new approach to the functionalization and coloration of textiles

“…Herein, we report a novel approach for covalently immobilizing MOF particles onto textiles. MIL-101 (Cr) (denoted as MIL-101), a typical MOF which comprises a nontoxic chromium(III) 33 cluster and benzene-1,4-dicarboxylate ligand and possesses a high surface area and good chemical stability 34 35 36 37 , was coated onto nylon fabric with 2-hydroxyethyl acrylate (HEA); then, co-graft polymerization was initiated by γ-ray irradiation, as illustrated in Fig. 1 .…”