Novel Cr/Ti bimetallic polyethylene catalysts synthesized through introduction of chromium species into the (SiO2/MgR2/MgCl2)·TiClx Ziegler-Natta catalyst

Abstract A series of novel Cr/Ti bimetallic polyethylene catalysts were successfully synthesized for the first time through introduction of chromium species into the (SiO 2 /MgR 2 /MgCl 2 )·TiCl x Ziegler-Natta catalysts. The bimetallic catalysts, which showed high activity, were simply prepared by refluxing titanium choloride with chromium modified silica gel/alkyl Mg adducts. Moreover, the effects of chromium content and calcination temperature were investigated in detail. The results obtained in the study were used to systematically discuss a clear relationship between the catalyst preparation condition and the relative performance of different metal active centers. Factors including surface hydroxyl content, catalyst performance in homo-polymerization, ethylene/1-hexene copolymerization were systematic investigated. Comparably, the chromium modified catalyst shows catalytic performance with 89% higher activity, 41.5% higher hydrogen response and 46.3% higher 1-hexene incorporation than the original (SiO 2 /MgR 2 /MgCl 2 )·TiCl x Ziegler-Natta catalyst. A new schematic model was proposed to explain the accelerated activation process of the bimetallic catalysts with kinetic and SEM results: chromium active sites on the outer surface of support react 10 times quicker than Ti active sites initially and help to crack the catalyst particle in the first stage; then the released inner surface active sites start to accelerate the polymerization reaction in the second stage.