Mesoporous Titanium Silica Molecular Sieve Synthesized With Mixed Template And Their Styrene Oxidation Properties

Styrene epoxides are widely used as intermediates in fine chemicals industries for the production of perfume materials, anthelmintics, drugs, sweeteners, etc. The catalytic potential of titanium-containing mesoporous silica (Ti-MS) is demonstrated by its facile catalyst epoxidation of alkenes with aqueous hydrogen peroxide as oxidant. Ti-MS has widely applied in bulk molecular catalysis due to size-tunable mesopores. Mixed surfactant template was proposed to improve the hydrophobic properties and decrease the particle size of Ti-MS. The main research contents are listed below.Highly ordered mesoporous MCM-48molecular sieve has been successfully synthesized using mixed surfactant of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) as templates at low surfactant-to-silica ratio (molar) of0.177. The possible formation mechanism of MCM-48using mixed surfactant template had been discussed according to Gibbs free energy theory and surfactant packing parameter theory. Titanium-containing mesoporous silica was synthesized through one-pot method, which showed better catalyst activity in styrene oxidation than titanium-containing mesoporous silica synthesized with CTAB as single template.Two method were proposed to improve the effective active site. The first method was to control the outer particle diameter of ordered mesoporous titanium silica submicrometer-spheres (Ti-MSS) using nonionic surfactant P123as particle dispersing agent at room temperature. The particle size was controlled ranging from400to80nm by adjusting the P123concentration. By adding P123in the solution for synthesis mesoporous silica using CTAB as template, P123assembled structures will interact with silica spices through intermolecular hydrogen bond leading to the formation of nano-scale particles. The second method was to synthesis core-shell materials with thin mesoporous shell using CTAB/P123as template. Nano-sized Ti-MSSs of about80nm demonstrated the optimized performance for styrene oxidation with styrene conversion44.7%, benzaldehyde selectivety82.2%and styrene oxide17.7%.Hollow mesoprous silica sphere with particle size of about300nm was obtained while adding anionic sodium dodecyl sulfate(SDS) in the solution for synthesis mesoporous MCM-48molecular sieve. The molar composition of surfactant mixture was SDS:CTAB=0.164. When the molar composition of surfactant mixture was CTAB:SDS:P123=1:0.164:0.78, hollow mesoprous silica sphere with particle size of about150nm was obtained. Mesoprous titanium-silica materials with CTAB/SDS mixed surfactant showed lower styrene conversion compared with mesoprous titanium-silica materials using CTAB/P123as template, but the selectivity to styrene oxide improved from17.7%to23.9%.The hydrophobic properties of mesoporous silica were improved by adding NaF in synthesis process. Hydrophobic mesoporous titanium-containing silica was obtained with best styrene conversion of24.5%and styerene oxide yield of10%as the molar ratio of Ti/NaF/SiO2was0.01:0.1:1. Hydrophobic Ti-MCM-48with particle size of about300nm was synthesized by adding NaF using CTAB as template at room temperature. The conversion of Ti-MCM-48to styrene decreased after adding NaF.