InCl_3/HMS介孔催化剂的结构及其催化烷基化作用特征

Structure and Catalytic Features of InCl_3 Impregnated Mesoporous HMS Solid Catalysts for Alkylation Reaction of Acromatic Compounds

介孔固体烷基化催化剂的研究和开发是现今催化和环境等领域的重要课题之一。以人工合成HMS(hexagonalmesoporoussilica)介孔新材料为载体,采用浸渍蒸发法制备了InCl3/HMS负载型介孔固体催化剂,应用XRD和N2等温吸附技术表征了该催化剂介孔结构特征,考察了InCl3负载量、活性前驱物、反应温度、反应物和催化剂重复使用等不同条件下InCl3/HMS催化剂催化烷基化反应的作用特征。研究结果表明,制备的InCl3/HMS催化剂仍具有介孔结构,孔径介于2.0～2.3nm;活性组分InCl3负载量与催化烷基化活性相关,在负载量为1.41mmolInCl3·(gHMS)-1载体时,催化剂活性最高;过多的InCl3负载量,催化剂孔容和比表面积的降低,说明InCl3积聚于HMS载体孔道内,降低了催化活性;HMS负载不同活性组份前驱物ZnCl2和InCl3后,对于苯和苄氯烷基化反应的活性为InCl3/HMS>ZnCl2/HMS;在InCl3/HMS催化剂上,苯与苄氯烷基化催化反应(苯过量)符合一级动力学方程;在同样的InCl3/HMS催化剂上,对苯和不同取代苯的烷基化反应的催化反应活性高低次序为苯>甲苯>对二甲苯;初步研究了重复使用的催化剂活性变化,结果说明催化剂表现出较好的可重复使用性。这些结果还初步表明InCl3/HMS催化烷基化机理可能在于催化剂表面的氧化还原作用。

By using synthetic hexagonal mesoporous silica (HMS) as catalyst supports, InCl3 impregnated mesoporous HMS solid catalysts were prepared through impregnation-evaporation method. The XRD and N2 adsorption-desorption techniques were employed to characterize the pore structure of the catalysts. The effect of conditions of preparation and reaction, such as InCl3 loadings, active precursors, reaction temperature and catalyst reuse on the catalytic activity in the reaction of benzene benzylation with benzyl chloride was investigated. It was found that the HMS-supported catalysts prepared maintain mesoporous structures with pore size in the range of 2.0-2.3 nm. The supported catalyst prepared shows a maximum catalytic activity when its InCl3 loading is 1.14 mmol InCl3 &middot (gHMS)-1, and the more InCl3 loading may decrease the catalytic activity by choking up the pores of the catalyst with the excess InCl3 loading. When using the InCl3/HMS catalyst prepared, the reaction rate of catalytic benzene benzylation with excess benzene fits the pseudo first-order reaction rate equation, As to the effect of different metal chloride precursors, the catalytic activity of mesoporous solid catalyst using InCl3 as precursor is higher than that of using ZnCl2 as precursor, i.e., the benzylation activity of InCl3/HMS catalyst is higher than that of ZnCl2/HMS catalyst. The catalytic activity of InCl3/HMS catalyst for the benzylation of different substituted aromatic reactants is in the order of benzene > toluene > xylene, which is different from that of the classical acid catalyzed Friedel-Crafts benzylation reaction. InCl3/HMS catalysts can be reused several times with stable catalytic alkylation activity of more than 80%. The experiment results show that the mechanism of the benzylation reaction with InCl3/HMS catalyst might be based on the redox reaction on the surface of the catalyst.