Synthesis And Catalysis Of Mesoporous Titanosilicate Nanoparticles

In recent years, mesoporous nanoparticles have been gradually attracted moreattention in the field of materials. Among all metal elements, titanium has been moststudied because titanium-containing mesoporous molecular sieves are highly active inmany selective oxidations. However, the particle size of present mesoporous molecularsieves is scaled in micrometer, which greatly limits the diffusion of reactants incatalysis.In our work, Ti-MCM-41and mesoporous titanosilicate nanoparticles weresuccessfully prepared by using cationic polymers PDD-AM or PDADMAC viahydrothermal synthesis method, whose particle size is less than100nm. The nanopar-ticles were charaterized by XRD、SEM、IR、UV-vis and N2adsorption-desorptionmeasurements. It has been revealed that the amount of cationic polymers has a biginfluence on the size and order of the mesoporous titanosilicate nanoparticles. MorePDADMAC leaded to the damage of ordered structure of mesopores in titanosilicatenanoparticles. However, ordered Ti-MCM-41nanoparticles could be prepared in thepresence of hydrogen peroxide and n-hexane. To evaluate the catalytic activity of theprepared mesoporous titanosilicate nanoparticles, they were used as heterogeneouscatalysts in the epoxidation of cyclohexene with hydrogen peroxide. Compared withconventional Ti-MCM-41, Ti-MCM-41nanoparticles are more active and selective tothe product epoxide, which are due to the small particle size, resulting in improveddiffusion of reactants and the epoxide in the short mesopore channels. In addition, wealso adopted the hydrothermal synthesis method to prepare MTS-1nanoparticles withintraparticle mesopores in the presence of cationic polymer PDADMAC. In theepoxidation of cyclohexene, MTS-1nanoparticles showed much higher catalyticconversions than nanosized TS-1crystals, which is comparable to Ti-MCM-41. Theresults indicate that the intraparticle size favors the diffusion of bulky reactants on thenanoparticles.