SBA-15分子筛羟基结构性质及其催化活性的理论研究

采用密度泛函方法对SBA-15分子筛簇模型化合物进行了计算模拟,重点研究了簇模型化合物羟基的几何构型和电子结构性质。从键级、前线分子轨道、静电势和质子化能等方面探讨了表面羟基的酸碱及氧化还原性质。分子筛模型化合物的静电势图显示SBA-15分子筛表面孤立羟基的H原子为分子筛表面的L酸性位,而氢键羟基的O原子则为分子筛表面的B碱性位。分子筛的前线分子轨道研究发现,表面羟基是分子筛表面的氧化还原活性位。计算得到的羟基SiO-H键级及形成的氢键键级分别在0.677 5～0.710 5和0.055 7～0.092 6范围,计算羟基OH的质子化能在1 471～1 589 kJ.mol-1范围。考察分子筛表面的质子化能显示未参与形成氢键的羟基H质子具有较强的B酸性。

Structure and Catalytic Properties of the SiO-H Groups on SBA-15 Molecular Sieve: A Density Functional Theory Study

A DFT study on the structural and catalytic properties of the SiO-H groups on SBA-15 molecular sieve was carried out. The geometry and IR spectra data calculated are identical to the experimental data. The electrostatic potential maps of the model clusters show that the H atoms of the single O-H groups on the surface of SBA-15 are the L acid sites and the O atoms of the hydrogen-bonded O-H groups are the B basic sites. The frontier molecular orbitals demonstrate that the hydroxyl groups on the surface of SBA-15 provide the oxidability. Further, the strength of the B acid on the surface of SBA-15 was discussed by means of the deprotonation energy and Mayer bond order.