The Preparation And Characterization Of Mesoporous Molecular Sieves AlMCM-41 In Buffer Solutions

Application of pure silica MCM-41 is limited,because of low ionexchange capacity,bad hydrothermal stability and weak acidity. Incorporation of heteroatom into MCM-41 has been investigated in order to improve the acidic strength and enhance its catalytic activity.This paper was about the direct synthesis of A1MCM-41 to obtain mesoporous molecular sieves A1MCM-41 in buffer solution.Buffer solution can adjust pH automatically.The products were characterized by SAXRD,BET,TEM and IR.The mesoporous molecular sieves A1MCM-41 were hydrothermally synthesized with different Si/Al ratios using water glass as silica source, sodium aluminate as aluminum source,and cetyltrimethylammonium bromide as structure template.Combination with results of SAXRD,TEM and IR spectra,the crystallinity of A1MCM-41 decreased with the increase of aluminum content.Sample was exchanged with different cations.The performance of water absorption of the A1MCM-41 was studied and their regeneration ability was observed.The results illustrated that the performance of H₂O adsorption of A1MCM-41 decreased with the decreasing hydration energy ions extra-framework in the same groups. The H₂O adsorption of capacity of HA1MCM-41 was the highest,so was the regeneration ability.The mesoporous molecular sieves A1MCM-41 were hydrothermally synthesized in NH3·H₂O-NH₄Cl and Na₂B₄O₇·10H₂O buffer solutions using water glass,sodium aluminate and cetyltrimethylammonium bromide.In NH₃·H₂O-NH₄Cl buffer solution,the effects of Si/Al ratio, aging temperature and pH value on formation of A1MCM-41 was studied. The highest crystallinity of A1MCM-41 with Si/Al ratio of 25 was obtained under the conditions of aging temperature at 25℃,pH of 9.5.In Na₂B₄O₇·10H₂O buffer solution,effects of the content of Al and pH value on formation of mesoporous molecular sieves A1MCM-41 was investigated.A1MCM-41 with the highest crystallinity was obtained in Si/Al ratio of 25 and pH of 9.5.The hydrothermal stability of aluminosilicate MCM-41(A1MCM-41) was determined in vapour water.Results showed that the hydrothermal stability of A1MCM-41 synthesised in buffer solution was higher than that in aqueous solution,and A1MCM-41 synthesised in buffer solution Na₂B₄O₇·10H₂O was higher than that in NH₃·H₂O-NH₄Cl.The effects of Al content,temperature of vapour and pH on the hydrothermal stability of the molecular sieves was studied as well.The highest hydrothermal stability of A1MCM-41 was obtained in the conditions of pH=9.5 and Si/Al=25.(100)face of A1MCM-41 kept certain relatively intensity after hydrothermal treatment at 700℃for 4h,but its structrue was completely collapsed at 800℃.