新戊基钛在MCM-41表面的接枝反应及产物性质

采用原位红外光谱法在真空系统中考察了MCM-41分子筛表面与四新戊基钛Ti(CH2CMe3)4的反应,发现这个反应可在室温下定量进行,得到表面新戊基钛(≡Si－O)2Ti(CH2CMe3)2. 这种表面新戊基钛很容易与CH3OH、H2O和O2进一步发生反应分别得到(≡Si－O)2Ti(OCH3)2、(≡Si－O)2Ti(OH)2和(≡Si－O)2Ti(OCH2CMe3)2等表面化合物.在氧气中焙烧由(≡Si－O)2Ti(CH2CMe3)2水解所得的(≡Si－O)2Ti(OH)2可制得表面含钛MCM-41介孔分子筛（Ti-MCM-41）.元素分析、低温N2吸附-脱附、紫外可见漫反射光谱、X射线粉末衍射和FTIR等表征结果表明,接枝反应和后续的处理不破坏分子筛的介孔结构; Ti-MCM-41的比表面积和孔直径较MCM-41略有降低; Ti原子在Ti-MCM-41表面以TiO4四面体配位状态分散,并对乙烯氧化有较明显的光催化活性.论文还通过对Ti-MCM-41与水热合成骨架含钛[Ti]-MCM-41结构和光催化活性的比较,对分子筛类材料光催化作用机制进行了分析探讨.

Preparation and Property of a MCM-41Surface Neopentyl-titanium and Surface Titanium Oxides

The grafting of tetraneopentyl-titanium onto the surface of MCM-41 mesoporous molecular sieves prior to pretreatment at 500 ℃ under 10－2 Pa vacuum generated a well-defined bigrafted surface complex (≡Si－O)2Ti(CH2CMe3)2.The (≡Si－O)2Ti(CH2CMe3)2 readily reacts with CH3OH,H2O and O2 to produce (≡Si－O)2Ti(OCH3)2,(≡Si－O)2Ti(OH)2 and (≡Si－O)2Ti(OCH2CMe3)2 at room temperature, respectively. Further calcination in oxygen at 500 ℃ of the hydrolyzed products,(≡Si－O)2Ti(OH)2,resulted in surface titanium oxides. All the above reactions were followed by in situ FTIR and the resulted products were characterized by elemental analysis, XRD, nitrogen adsorption, FTIR and DRS. It is showed that the grafting reaction and post-treatments did not affect the characteristic structure of MCM-41.The surface area and pore diameter of the Ti-MCM-41 are slightly less than that of MCM-41.The Ti atoms are tetrahedrally coordinated on the surface of MCM-41.Catalytic test revealed that the Ti-MCM-41 has evident photocatalytic activity toward ethylene. The reason for photocatalytic activity of the molecular sieve was discussed by comparing for the structure and properties of Ti-MCM-41 with that of [Ti]-MCM-41.