# Highly Flowable Nano TiO2/Porous Organic Polymer (POP) Supports for Efficient Metallocene Catalysts
## 3 Results and Discussion
### Ethylene Polymerization and Kinetic Curve of the Supported Metallocene Catalysts  
In order to investigate the effect of the inorganic-organic supports, the metallocene complex (n-BuCp)\({}_{2}\)ZrCl\({}_{2}\) and the MAO cocatalyst were immobilized in the prepared TiO\({}_{2}\)/POP composites, and then ethylene polymerization was conducted to evaluate their catalytic activity and kinetic behaviors using the produced (n-BuCp)\({}_{2}\)ZrCl\({}_{2}\)/MAO@TiO\({}_{2}\)/ POP catalysts. From the ethylene polymerization results listed in Table 4, all four TiO\({}_{2}\)/POP supports supported metallocene catalysts achieved higher catalytic activity compared to the silica gel-supported commercial catalysts, indicating that the TiO\({}_{2}\)/POP composites could act as an excellent metallocene support in terms of ethylene polymerization. POP-7 obtained the highest catalytic activity of 4794 Kg PE/mol Zr.bar.h and productivity of 389 g PE/g cat, respectively, which is above the twice of the silica gel-supported counterpart. Moreover, POP-6 gained higher ethylene polymerization activity with low SSA (136 m\({}^{2}\)/g) than POP-4 with relatively higher SSA (204 m\({}^{2}\)/g), and we can infer that the pore structure of the support might not be the determinant factors of the catalyst polymerization activity. Apart from the Al/Zr ratio discussed in other literature and our previous work, the TiO  
Figure 7: SEM images of TiO\({}_{2}\) and the prepared TiO\({}_{2}\)/POP particles. (**a**,**b**) TiO\({}_{2}\) nanoparticles; (**c**,**d**) POP-6; (**e**,**f**) POP-7. might play an important role to influence the active sites for ethylene polymerization. The prepared TiO\({}_{2}\)/POP composites obtained improved activity compared to the POP support without TiO\({}_{2}\) reported in our previous work, despite that the bulk densities of the prepared PE were still below that of the silica gel. To evaluate the ethylene polymerization kinetics, 2.0 kg hexane, 20 mL TEAL (10% wt in hexane), and 0.67g Zr/MAO@POP-7 catalyst were added into a 10 L stainless steel autoclave, and then ethylene was fed into the reactor constantly to maintain 6 bar ethylene partial pressure at 80 \({}^{\circ}\)C for 2 h. After the polymerization, 2142 g dry PE powder with higher ethylene polymerization activity (3197 g PE/g cat) was collected. As for the prepared TiO\({}_{2}\)/POP supports, the ethylene polymerization conditions seemed to play a significant role in the bulk density of the produced polymer. In the ethylene polymerization kinetic curve of Zr/MAO@POP-7 catalyst, the bulk density of the produced ethylene homopolymer improved dramatically from 0.24 to 0.36 g/mL in higher ethylene partial pressure and polymerization activity. Significantly, the catalyst showed no obvious decay of ethylene consumption during the polymerization as illustrated in Figure 8a, and the formed Zr\({}^{*}\) active sites in the Zr/MAO@POP catalyst were stable and suffered no apparent deactivation during the ethylene polymerization at about 80 \({}^{\circ}\)C [35]. As a comparison, 2283 g dry PE powder with 0.42 g/mL bulk density was obtained from 0.83 g commercial catalyst. The polymerization activity of the Zr/MAO/POP-7 catalyst (6562 kg PE/mol Zr.bar.h) was still higher than the silica gel-based metallocene