稻草和稻草灰合成中孔分子筛MCM-41及性能分析

Synthesis of Mesoporous Molecular Sieves MCM-41 Using Rice Straw and Rice Straw Ash and Its Property Analysis

以稻草(RS)和稻草灰(RSA)为硅源合成了中孔分子筛RS-MCM-41和RSA-MCM-41,并将其与以水玻璃(SDS)为硅源合成的中孔分子筛SDS-MCM-41进行了比较;采用接枝法对RSA-MCM-41进行改性以提高其酸性,制备了RSA-Al40/MCM-41和RSA-Al10/MCM-41(Si和Al的物质的量比分别为40∶1和10∶1),用于催化合成丙酸香叶酯(GP)。样品的XRD、FT-IR、NH3-TPD、N2吸附-脱附和气相色谱(GC)等分析结果表明:RS-MCM-41和RSA-MCM-41尽管具有中孔分子筛的六方介孔结构以及良好的长程有序性和结晶度,但用其催化合成GP,与SDS-MCM-41一样,活性都较弱;通过接枝法将改性铝以铝氧四面体接枝引入到分子筛骨架上,铝的接枝对中孔分子筛的结晶不利,但可使其表面产生更多的Brnsted酸中心;铝的接枝量越多,分子筛的催化活性就越强;RSA-Al10/MCM-41催化合成GP的转化率可达54.47%,选择性为74.82%。

The mesoporous molecular sieves RS-MCM-41 and RSA-MCM-41 were synthesized using rice straw （RS） or rice straw ash （RSA） as silica source. The differences between these two catalysts and SDS-MCM-41 catalyst synthesized from sodium sili- cate （SDS） were compared. The acidity of RSA-A140/MCM-41 and RSA-All0/MCM-41 were promoted by grafting AI with 40 and 10 of Si/A1 mole ratio. After that, they were used as solid acid catalyst for synthesis of geranyl propionate （GP）. The struc- tures of the synthesized molecular sieves were characterized by XRD, FT-IR, NH3-TPD, and N： adsorption-desorption. The structure of RS-MCM-41, RSA-MCM-41 and SDS-MCM-41 are shown in similar hexagonal mesoporous structure, good long- range order and crystallinity. However, all the catalysts showed low catalytic activities in synthesis of GP. Aluminum can be in- troduced into the framework of molecular sieves by grafting method as aluminum oxygen tetrahedron. After grafting, aluminium has negative influence on the crystallization of mesoporous molecular sieves, but it has positive influence on the amount of Br6nsted acid sites on MCM-41 surface. The more of aluminium grafted, the stronger catalytic activity of molecular sieves is. The conversion of 54.47% and selectivity of 74.82% in synthesis of GP can be achieved with RSA-Al10/MCM-441 catalyst.