2.2. Catalyst preparation
The preparation procedure of the bimetallic “two-in-one” catalyst is as follows. 100 ml TiCl4 was added into a 500 ml reactor and was cooled to −20 ◦C. 5 g spherical support of MgCl2·EtOH was added into the reactor and the reaction system was stirred for 1 h. Then the temperature was raised to 60 ◦C and 1.25 g of 9,9-bis(methoxymethyl) fluorene (BMMF) was introduced into the reactor. After that, the temperature was raised to 120 ◦C slowly and the whole system was stirred for 2 h. TiCl4 was removed by filtration and 100 ml fresh TiCl4 was added into the reactor again and the reaction system was stirred for another 2 h. TiCl4 was