Résumé High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m2/g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH3-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.
摘要 通过一种简单的溶胶-凝胶
水解过程,无需任何有机模板和
水热处理,制备了具有高比表面积的介孔
硅基催化剂。以工业大宗
化学品
硅酸乙酯-40作为
硅源,进行可控
水解,形成了具有极高比表面积(719 m²/g)的介孔
硅(孔径67 Å,孔体积1.19 cc/g)。介孔
硅的形成与
硅酸乙酯-40
硅源的聚合物性质有关,其在
水解和进一步缩合过程中形成长链
硅物种,阻碍了致密结构的形成,从而创造了大孔,形成了具有高比表面积的介孔
硅。
硅酸乙酯-40进一步用于通过简单的溶胶-凝胶
水解合成过程,在介孔
硅上负载
氧化钼纳米颗粒,制备固体酸催化剂。催化剂显示极高的酸性,由NH3-
TPD测定显示存在Lewis酸和Brønsted酸。这些催化剂在酯化反应中表现出极高的催化活性,这是一种典型的酸催化有机转化反应,涉及各种单和二
羧酸与一系列醇的反应。在催化反应中现场形成的
硅钼酸杂多阴离子被发现是这些反应的活性物种。
硅酸乙酯-40作为一种工业大宗
硅源,展现了其在更大规模、更低成本上作为
硅源,用于制备介孔
硅基异质催化剂的良好潜力。