Synthesis And Characterization Of Ti-MCM-48Catalyst In Olefins Epoxidation

Olefins epoxides are widely used in many chemical fields such as fine chemical productions, food additives, drugs, perfume materials etc, because the epoxides are very important intermediates in organic synthesis process. The epoxidation of olefins is the main avenue for preparing olefins epoxides, and the most frequently used catalytsts in the reaction are titanium-containing silicas molecular sieves. The catalytic activities of titanium silicalite zeolites, such as TS-1and TS-2, are limited by their small micropore openings in epoxidation of bulky molecules; but otherwise, titanium-containing mesoporous molecular sieves (Ti-MSs) present higer catalytic activity, due to their huge specific surface and larger pore size. Because its three-dimensional channel system can improve the transmission rate of substances, Ti-MCM-48has several advantages over other Ti-MSs. But the catalytic performance of Ti-MCM-48is restricted by its poor surface hydrophobicity. There were two ways to increase the catalytic activity, the one was introducing fluoride to enhance surface hydrophobicity; the other was adding F127for reducing particle size. Finally, the catalytic performance of Ti-MSs was tested by the reaction of styrene epoxidation. The main research contents are listed below.(1) There were two different methods for preparing Ti-MSs, one was direct synthesis, the other was postsynthesis; and the samples synthesized by posrtreatment possessed higer catalytic activity.(2) Firstly, MCM-48samples were synthesized with fluoride by traditional hydrothermal method; then titanium atoms were incorporated into the framework forming tetrahedrally coordinated Ti by posttreament method. Compared to fluorine-free, the samples with fluoride had good catalytic effect on styrene epoxidation, with styrene conversion57.03%and styrene oxide selectivety increasing from1.68%to10.12%.(3) The species of fluoride were main influencing factors for the samples properties. As a conclusion, Ti-MSs with KF were convenient to their catalytic activity than NaF, and the styrene oxide yield raised notably, from8.76%to13.22%. The species of titanium source could affect the catalytic performance of Ti-MSs. In conclusion, TIP was better for the catalytic property than TBOT.(4) Ti/Si molar ratio could also affect the samples properties. When the ratio was0.01, the catalytic activity of Ti-MCM-48was higest; when the molar ratio was0.005, the catalytic active sites for shortage resulted in poor catalytic properties; when the ratio was0.02, the forming non-framework titanium reduced the catalytic activity of the smaples.(5) Nanospheres of Ti-MSs, which ranged from70nm to500nm, were synthesized with TIP at room-temperature, using CTAB and F127as double-template. The experimental results showed that the samller diameter of Ti-MSs spheres was, the better catalytic performance of samples could be. Comparing to traditional hydrothermal method, the room temperature systhesis process with F127had many advantages, such as the method was simple in operation and saved power consumption, but more importantly, the Ti-MSs with smaller particle size could achieve higher catalytic activity.