H2SO4和Al2（SO4）3改性中孔分子筛Al-MCM-41及其催化性能

用SO24-物质的量相同的H2SO4和Al2(SO4)3分别对Al-MCM-41进行改性,得到样品SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41。采用X射线多晶衍射(XRD)、红外光谱(FTIR)、N2吸附-脱附和NH3程序升温脱附(NH3-TPD)等测试技术对样品进行表征。分别用H2SO4、MCM-41、Al-MCM-41、SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41催化合成丙酸香叶酯,比较了它们的催化性能。结果表明,H2SO4和Al2(SO4)3改性对Al-MCM-41中孔分子筛结构影响不明显,都可提高其酸性,改性后中孔分子筛的骨架仍保持着六方介孔结构,孔径、孔容和比表面积有所降低,但用Al2(SO4)3改性的分子筛酸性和催化性能更强;SO42-/Al-MCM-41的酸催化活性主要源于SO42-与分子筛表面硅羟基作用形成的双齿螯合配位结构,而Al/SO42-/Al-MCM-41的酸催化活性一方面来自SO24-与分子筛表面硅羟基作用形成的双齿螯合配位结构,另一方面,也来自与分子筛骨架接枝的铝,使其产生了更多的Brnsted酸中心。

H2SO4 and Al2 ( SO4 ) 3 Modifying Mesoporous Molecular Sieves Al-MCM-41 and Their Catalytic Performances

The SO2-4/Al-MCM-41 and Al/SO2-4/Al-MCM-41 were prepared through modificaiton of Al-MCM-41 with H2SO4 and Al2(SO4)3 with the same amounts of SO2-4,respectively.The structures of two samples were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),N2 adsorption-desorption and NH3 temperature program desorption(NH3-TPD).The catalytic performances of H2SO4,MCM-41,Al-MCM-41,SO2-4/Al-MCM-41 and Al/SO2-4/Al-MCM-41 were investigated in the catalytic synthesis of geranyl propionate.The results showed that the H2SO4 and Al2(SO4)3 modification have no obvious influence on the structure of Al-MCM-41.Both modification methods can improve the acidity of catalysts.The modified mesoporous molecular sieves still possess the hexagonal mesoporous structure.Meanwhile,the pore diameter,specific pore volume and specific surface decrease relatively.The mesoporous molecular sieves modified with Al2(SO4)3 provides stronger acidity and higher catalytic performances than those modified with H2SO4.The catalytic activity of SO2-4/Al-MCM-41 was generated mainly from the double teeth chelating coordination structure formed by SO2-4 and Si-OH of molecular sieves surface.The catalytic activity of Al/SO2-4/Al-MCM-41 was generated mainly from the double teeth chelating coordination structure formed by SO2-4and Si-OH of molecular sieves surface.On the other hand,the Brnsted acid sites produced from the Al grafting on framework of molecular sieves also provided catalytic activity.