Janus-Pickering乳液界面催化苯部分加氢制环己烯

The partial hydrogenation of benzene to cyclohexene is a route with relatively simple process and high atom economy, which has important social significance and economic value for extension of coal chemical industry chain. Benzene normally prefer to be hydrogenated to cyclohexane rather than to stay in cyclohexene because the thermodynamic properties of cyclohexane is more stable than cyclohexene. Studies have shown that the water-phase systems can accelerate desorption of cyclohexene from the catalyst surface to prevent further hydrogenation, affording high cyclohexene selectivity to some extent. However, the aqueous reaction systems surfer from inhomogeneous distribution of oil and water, and high mass transport resistance, seriously hindering the rapid diffusion of benzene and cyclohexene, which directly affects the matching between the diffusion rate and the surface catalytic reaction rate. As a result, the cyclohexene yield has not yet broken through 60%. To this end, this application will prepare dumbbell-shaped, interface-active Janus catalysts, and thereby construct a novel Pickering emulsion catalysis system that possesses a high level of water/oil mixing, a large reaction interface area and short diffusion distance, so as to accelerate the diffusion of hydrogen, benzene and cyclohexene, and furthermore improve the cyclohexene selectivity and yield. Also, this application will elaborate the underlying correlations among catalyst surface properties, catalyst structures, emulsion properties and catalytsis results, to provide theoretical basis and technical support for extending industrial chain of benzene in coal chemical engineering.

苯部分加氢制环己烯是过程简单、原子经济性高的反应路线，对延伸煤化工产业链有重要的经济价值。由于环己烷的热力学性质比环己烯更稳定，通常情况下苯加氢容易生成环己烷而难以停留在环己烯。研究表明，水相反应体系能促使环己烯分子从催化剂表面迅速脱附，阻止其进一步加氢，在一定程度上提高环己烯的选择性。然而，在这种水相反应体系中油水分布不均匀、传质阻力大，阻碍了苯、环己烯分子快速扩散，直接影响扩散速率与表面催化反应速率的匹配，导致环己烯的收率突尚未突破60%。申请提出制备哑铃状Janus界面活性催化剂，以构建Pickering乳液催化新体系，利用Janus-Pickering乳液体系油水混合均匀、界面大、分子扩散距离短的原理，加速苯、环己烯分子在反应体系中的扩散，进一步提高环己烯的选择性和收率，并建立催化剂组成、结构、乳液界面性质与催化反应结果的内在联系，为延伸煤化工苯板块的产业链提供理论基础和技术支撑。

由苯部分加氢制环己烯是一条原料价格低廉、过程简单、原子经济性好、附加值高的路线，是山西省煤化工发展的五条重要主线之一。相比于传统水相催化体系，Pickering 乳液体系具有更大的反应界面和更短的分子扩散距离。该项目重点开展了Janus界面催化剂制备及其Pickering乳液体系中苯部分加氢制环己烯研究，利用双模板法制得具有界面活性的哑铃状Janus材料，对哑铃状Janus材料液-液界面组装行为进行了研究，发现Janus粒子的乳液界面脱附能是各向同性粒子脱附能的3.2倍, 首次定量地证实了Janus粒子Pickering乳液的稳定性远高于各向同性粒子，显著提高了Pickering乳液的稳定性。在此基础上，构建了苯部分加氢制环己烯的Pickering催化体系，考察了乳液类型、乳滴大小、乳滴距离等条件变化对苯转化率和环己烯收率的影响；通过优化条件，苯加氢制环己烯的收率高达43%，高于同类两相催化体系的结果（37%），实现了预期的目标。进一步从分子水平上建立了催化反应结果与油水界面上扩散动力学的联系，揭示了高选择性的原因，研究还表明Pickering乳液可以精确控制两相反应的关键参数，实现催化反应性能的调控，为高效绿色催化合成奠定了基础，同时为延伸山西煤化工苯板块的产业链提供理论基础和技术支撑。相关研究成果共发表SCI论文11篇，发表于J. Am. Chem. Soc.、Angew. Chem. Int. Ed.、Langmuir、ChemCatChem、ACS Appl. Mater. Interfaces、J. Mater. Chem. A等期刊。