Studies On Preparation, Characterization And Application Of Hexagonal Mesoporous Silicas Assembled By Two Metallic Elements

This paper investigates host-guest assembly approach to hexagonal mesoporous silicas (HMS) composite materials assembled by two metallic elements. The structures and nitrogen adsorption properties are studied. A experiment is made which the mesoporous composite materials synthesized is used as filter additive to reduce tar and carbon monoxide in the cigarette smoke.The cosolvent systems containing water-ethanol-(iso)propanol were used to assemble HMS silicas by means of ambient temperature synthetic method.The comparison was made which the template was removed by ethanol extraction with simply burned off by calcination at elevated temperature. In addition, the influence on typical HMS silicas preparation and physico-chemical characteristics of hexagonal mesophase were discussed. HMS silicas were prepared using the starting reaction mixture in a molar ratio of tetraehylorthosilicate/dodecylamine=4:1 and a volume ratio of (iso)propanol/ethanol/water=1.0:8.5:5.0. Wormhole HMS silicas which the template was removed by ethanol extraction with average BJH pore sizes to 4.5nm were assembled using (iso)propanol as a cosolvent. The specific surface area is 933.4m²/g and pore volume is 1.038cm³/g. The template was removed by ethanol extraction rather than by calcination.Ce/HMS silicas were synthesized by means of in-situ incorporation and post-assembly, respectively. Not only the calcined products illustrate HMS silicas typical properties, but also the framework structural contraction was stopped so that the calcined products assembled by cerium illustrated high thermal stability. The results demonstrate that post-assembly is superior to in-situ incorporation during producing mesoporous materials doped by metallic element.Ce,Al/SiO₂ supermicroporous materials were prepared with in-situ incorporation method, and its hydrothermal stability was discussed after cerium and aluminum were doped. The calcined products prepared illustrated high hydrothermal stability. Mesoporous silicas assembled by cerium and palladium were synthesized by way of post-assembly and impregnation. The mesostructures and morphology of the calcined products loaded by palladium species onto two kinds of carrier were studied. The ordered mesoporous silicas could be obtained with Ce/HMS silicas as the carrier, but microporous silicas could be produced by loading palladium species onto HMS silicas...