Hybrid Organic-Inorganic Active Sites for Selective Heterogeneous Catalysis

非均相催化的新兴应用需要开发新的材料，i)在相对较低的温度下提供高的催化剂选择性和活性，以避免关键化学中间体的背景降解反应，ii)在水和恶劣的有机溶剂环境中不发生浸出/降解。本工作通过设计和合成由多功能有机活性位点组成的多相催化剂，解决了上述(i)和（ii）的迫切需求。这些活性位点的有机成分固有地使它们具有水解稳定性，同时为控制功能提供分子结构的可定制性。本研究的智力价值在于实现了有机酸碱活性位点合成的新兴概念，作为高选择性、活性和健壮的非均相催化剂的相关前体，这些催化剂由有机-无机杂化材料组成。这项工作特别利用了二氧化硅表面上的催化位点的限制，并使用杯芳烃作为组织支架和限制实体来控制所产生的限制官能团的反应性。在杯芳烃接枝后，锚定杯芳烃在无机氧化物表面的侧向复分解聚合合成了由固定化催化活性位点组成的坚固的二维交联聚合物。这种聚合物是不溶性的，因此即使在恶劣的溶剂环境下，如高温和含水溶剂系统，也有望具有防浸性。初步实验旨在证明概念的证明，旨在证明在各种溶剂环境中使用可回收催化剂的强大和高度选择性的醛醇缩合活性，这是精细化学品和生物精炼的关键反应，以及基于该概念合成对映选择性酸碱双功能催化剂。这些目标需要开发含有酸性功能的杯芳烃活性位点，以及含有碱的位点，这些都可以使用我们研究小组最近开发的程序来实现。酸活性位点将研究与生物精炼有关的反应，如酯交换和酯水解。我们进一步开发了无机氧化物表面的模式方法，使用二氧化硅作为模型无机氧化物，具有两个不同的化学官能团，因为在此过程中发现的位点分离方法可能普遍适用于与其他转化相关的其他催化系统，例如涉及负载金属和无机氧化物纳米颗粒的催化系统。这些研究活动广泛地影响着未来催化剂设计和合成科学家的培训，特别强调具有设计的纳米级结构和连通性的杂化有机-无机催化剂的结构表征和功能评估。研究生和本科生的培训将特别强调招收女性和少数民族学生。外联活动包括K-12部分，重点是鼓励太平洋岛民少数民族从事化学科学和工程的研究，通过向高中生发表关于未来方向和研究挑战的鼓舞人心的研究报告，同时展示如何将科学发现用于创造新技术和理解。

0854560 KatzEmerging applications of heterogeneous catalysis require the development of new materials that i) afford high catalyst selectivity and activity at the relatively low temperatures required to avoid background degradation reactions of critical chemical intermediates, and ii) function without leaching/degradation in aqueous and harsh organic solvent environments. This work addresses the pressing needs in (i) and (ii) above via the design and synthesis of heterogeneous catalysts consisting of multifunctional organic active sites. The organic component of these active sites inherently lends them to being hydrolytically stable while simultaneously providing tailorability of molecular structure for control of function. The intellectual merit of this research is to implement emerging concepts in the synthesis of organic acid and base active sites as relevant precursors for highly selective, active, and robust heterogeneous catalysts, which consist of a hybrid organic-inorganic material. The work specifically exploits the confinement of catalytic sites on the surface of silica and control reactivity of the resulting confined functional groups using calixarenes as an organizational scaffold and confinement entity.Upon calixarene grafting, lateral metathesis polymerization of anchored calixarenes on the inorganic-oxide surface synthesizes a robust two-dimensional crosslinked polymer consisting of immobilized catalytically active sites. This polymer is insoluble and is therefore expected to be leach-proof even under severe solvent environments, such as those involving high temperatures and aqueous solvent systems. Preliminary experiments aimed at demonstrating proof of concept are geared towards demonstrating robust and highly selective aldol condensation activity, a reaction that is key to fine chemicals and biorefining, in a variety of solvent environments using a recoverable catalyst, as well as the synthesis of enantioselective acid-base bifunctional catalysts based on this concept.These goals require the development of confined calixarene active sites containing acidic functionality, as well as sites containing base, which are attainable using procedures recently developed by our research group. Acid active sites will be investigated for reactions relevant to biorefining such as transesterification and ester hydrolysis. We further develop approaches to pattern the surface of an inorganic oxide, using silica as a model inorganic-oxide, with two disparate chemical functional groups, because methods of site isolation discovered during this process are likely to be generally applicable to other catalytic systems of relevance to other transformations, such as those involving supported metal and inorganic-oxide nanoparticles. The research activities broadly impact the training of future scientists in catalyst design and synthesis, with specific emphasis on structural characterization and functional assessment of hybrid organic-inorganic catalysts with designed nanoscale structure and connectivity. The training of graduate and undergraduate students will have special emphasis placed on the recruitment of female and minority students. Outreach activities include a K-12 component, with a focus on encouraging Pacific Islander minorities to pursue study of the chemical sciences and engineering, through inspirational research presentations to high-school students on the topic of future directions and challenges in and research while simultaneously providing a demonstration of how scientific discoveries can be used for creating new technology and understanding.