Introduction of chromium species into the (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta catalyst for better catalytic performance

•A novel Cr-modified (SiO2/MgO/MgCl2)·TiClx ZN catalyst is developed.•Effects of Cr-modification on the ethylene polymerization are studied.•Cr-modification leads to 13% increase in polymerization activity.•Cr-modification leads to 40% increase in hydrogen response.•Cr-modification leads to 20% increase in incorporated SCBs with better SCBD.

A novel chromium-modified (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta ethylene polymerization catalyst with improved catalytic properties is successfully developed. The catalyst is prepared through co-impregnation of water-soluble magnesium and chromium compounds with SiO2 followed by calcination in dry air and refluxing reaction with TiCl4 to synthesize magnesium dichloride in situ, and the supporting of titanium species is also accomplished simultaneously. By characterization of the catalysts and the polymers, several key factors such as cocatalyst concentration, the addition amount of chromium species, the effect of hydrogen and 1-hexene in ethylene polymerization are systematically investigated. Compared with the original (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta catalyst, the novel Cr-modified catalyst with proper initial addition amount of chromium shows better catalytic performance with 13% higher activity, 40% higher hydrogen response, and 20% higher 1-hexene incorporation ability with better short chain branch distribution.

Graphical abstractNovel chromium-modified (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta polyethylene catalysts with improved catalytic properties are successfully developed and systematically investigated. The Cr-modified catalyst with proper addition amount of chromium shows better catalytic performance with 13% higher activity, 40% higher hydrogen response, and 20% higher 1-hexene incorporation ability with better short chain branch distribution.Figure optionsDownload full-size imageDownload as PowerPoint slide