Bing Xue,Lei Hui,Huaqin Yang,Yulai Zhao,Linxi Hou,Wei Li
A macroporous SiO2 (Macro-SiO2), which has uniformed macropores, an open-framework structure, and thin walls, was synthesized to support Ziegler–Natta catalysts. The immobilization behaviors of the Ziegler–Natta catalysts inside the Macro-SiO2 were investigated. Notable agglomerations of δ-MgCl2/titanium complex were observed because of the unconstrained environment of the Macro-SiO2. A highly superficial Ti content and a heterogeneously chemical structure of Ti active sites were thus achieved inside the Macro-SiO2. The ethylene polymerization results revealed that the Macro-SiO2/MgCl2/TiCl4 exhibited much higher catalytic activity (i.e., 12.1 × 106 g PE·(mol Ti·h)−1 or 17.8 × kg PE·(g cat·h)−1) than that of the traditional 955-SiO2 supported catalyst (i.e., 2.0 × 106 g PE·(mol Ti·h)−1 or 2.7 × kg PE·(g cat·h)−1). Finally, the fragmentation behavior of Macro-SiO2/MgCl2/TiCl4 was investigated during the polymerization. This unconstrained environment of Macro-SiO2 afforded fewer resistances to the diffusion of reactants and also the polymer growth.
Catalytic combustion is considered as one of the most efficient methods for soot removal. However, the limited contact area between soot and active site is a key restrictive factor for the present reaction, as soot particles (particle size > 25 nm) are usually difficult to enter the inner pores of general catalysts. In this work, we report a simple and economic strategy to synthesize macroporous SiO2 as the support for combustion catalysts so as to facilitate the mass transfer in the inner surface of the catalysts. The macroporous SiO2 could be synthesized rationally through controlling and adjusting the Si–OH dehydration condensation and neck growth during the sol–gel preparation process. The porosity of SiO2 influences catalytic activity greatly in the reaction of soot catalytic combustion. Furthermore, macroporous SiO2 supported Ag and K catalysts exhibit superior soot oxidation activity, showing important potentiality for future applications.
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