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首页> 外文期刊>Catalysis science & technology >Creation of discrete active site domains via mesoporous silica poly(styrene) composite materials for incompatible acid-base cascade reactions
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Creation of discrete active site domains via mesoporous silica poly(styrene) composite materials for incompatible acid-base cascade reactions

机译：通过建立离散活性部位域介孔硅聚(苯乙烯)复合材料不兼容的酸碱级联的材料反应

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This work highlights the design and synthesis of bifunctional mesoporous silicate - polymer composite dual acid-base supported cascade catalysts. Compartmentalization of the two incompatible active sites is sought by segregating acid sites on the silica surface, and base sites within polymer chains and/or polymer domains. The ability to isolate and segregate active sites via control of the mesoporous silica pore size and polymer molecular weight is probed with silica samples functionalized by a grafting-to process. Supplemental activator and reducing agent (SARA) atom transfer radical polymerization is used to synthesize random copolymers containing protected primary amines. Thiol-ene 'click' chemistry facilitates silica functionalization via a convergent approach, with the ene-functionalized polymer end group and silica-grafted thiols forming SBA/MCM-SH-poly(styrene-co-2-(4-vinylbenzyl)isoindoline-1,3-dione). Polymer deprotection and thiol oxidation produces primary amine/sulfonic acid containing composite catalysts. With the polymer supported Lewis base and silica grafted Bronsted acid, the two-step deacetalization - Knoevenagel condensation cascade is explored to assess the ability of these polymer/silica hybrids to segregate active sites, allowing both acid and base site accessibility. Six composite catalysts are synthesized and tested in individual and cascade reactions with kinetic results demonstrating that lower molecular weight SBA-15-P1 and MCM-41-P1 catalysts outperform (higher turnover frequencies and initial rates) their higher molecular weight analogues, as well as a polymer-free system containing molecular active sites dispersed on the silica surface. Higher molecular weight composite catalysts perform more poorly due to limited chain solubility, mass transfer limitations, and poor catalyst accessibility. In many cases, the polymer chains effectively thread into the mesopores, with higher molecular weight polymers leading to pore blockage and inhibited mass transfer.
机译：这项工作突出的设计和合成双功能介孔硅酸盐-聚合物复合双酸碱支持级联催化剂。不相容的活动网站寻求隔离酸网站在二氧化硅表面,基地网站在聚合物链和/或聚合物域。通过控制介孔二氧化硅活跃的网站孔隙大小和聚合物分子量是探测与功能化的硅样品嫁接过程。还原剂(SARA)原子转移自由基使用聚合合成随机的包含主保护胺共聚物。Thiol-ene“点击”化学促进二氧化硅通过收敛的功能化方法,ene-functionalized聚合物集团和结束silica-grafted硫醇形成

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