(A) study on the synthesis and catalytic application of macrostructured biporous ailicate materials

Abstract

Inorganic materials having both mesopores and macropores should be very attractive for their applications in the area of adsorption, heterogeneous catalysis and separation due to their obvious advantages, i.e. high surface area of mesoporous structures and ease access to active sites of macroporous structures. Such silicate materials with bimodal pore size distribution have been synthesized by replicating the closed packed array of colloidal crystal and liquid crystal mesophase of surfactant. A new and simpler dual-templating method for preparation of macrostructured mesoporous silicate was used in this work. Monodispersed micron-sized polystyrene (PS) beads were added without any pre-arrangement directly to a gel solution prepared for the synthesis of mesoporous MCM-41. Different macropore structures were obtained due to different shrinking modes of macropores by varying the PS bead size, the Si:PS ratio and the reaction temperature. One of them termed skeletal structure (SkS) consists of continuous network partially filling the interstices around PS beads. The SkS is observed in the range of PS bead size around 200nm. When the PS bead size was lager, the wall of SkS became thicker and its structure was changed accordingly. It was found that the skeleton structure (SkS), shell structure (ShS) and residual volume structure (RVS) could coexist in a sample. Among these macrostructured MCM-41 powders, skeleton structured MCM-41 has high surface area, high mesopore volume and well defined macropore structure than other ones. Therefore, the potential of skeleton structured MCM-41 (Sk-MCM-41/PS) as new materials was tested for VOCs adsorption and selective catalytic reduction of NO by hydrocarbon. It was observed that the adsorption behavior of VOCs for Sk-MCM-41/PS was affected by the nature of macroporous structures and the Si/PS ratio. Sk-MCM-41/PS with hierarchically ordered macropores showed better adsorptive capability in VOCs adsorption compared to simple mes...