H_2SO_4 and Al_2(SO_4)_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.