Development of Heterogeneous Metathesis Catalysts with Nanopores

烯烃歧化反应是通过过渡金属络合物或钼、钨的氧化物进行的。在复分解反应的非均相催化剂中，稀土系催化剂是公认的强效催化剂。例如，负载型Re_2O_7对简单烯烃的液相歧化反应表现出比MoO_3和WO_3催化剂更高的活性。虽然Re基催化剂对烯烃歧化反应具有很高的潜力，但它们存在着严重的缺点，即在没有R4Sn和R4Pb等添加剂的情况下，对官能化的烯烃反应活性很低。1991年，据报道，有机金属甲基三氧杂环芳烃(MTO)仅在固体酸SiO_2-Al_2O_3表面能顺利地诱导官能化烯烃的歧化反应。然而，催化剂载体SiO_2-Al_2O_3中Re物种的性质和作用还没有完全阐明。在本研究中，我们发现氯化锌修饰的介孔氧化铝具有较高的比表面积、相对均匀的介孔和Lewis酸性，并且掺杂MTO的MTO/ZnCl2//Meso-Al_2O_3比Herrmann的MTO/SiO_2-Al_2O_3(MTO/SiO_2-Al_2O_3)体系对官能化烯烃歧化反应的催化性能更好。在我们的催化体系中，ZnCl2//Meso-Al_2O_3不仅能将MTO固定在固体表面，而且还能活化MTO，从而加速官能化烯烃的歧化反应。

Olefin metathesis reactions have been performed by transition metal complexes or oxides of molybdenum and tungsten. Among heterogeneous catalysts for metathesis, it is well known that rhenium-based catalysts are powerful ones. For example, supported Re_2O_7 shows higher activity for liquid-phase metathesis reactions of simple olefins than MoO_3 and WO_3 catalysts. Although rhenium-based catalysts have high potential for olefin metathesis, they have serious drawbacks of little activity toward functionalized olefins without help of additives such as R4Sn and R4Pb. In 1991, organometallic methyltrioxorhenium (MTO) was reported to smoothly induce the metathesis of functionalized olefin only on the surface of a solid acid, SiO_2-Al_2O_3. However, the nature of the rhenium species and the role of the catalyst carrier, SiO_2-Al_2O_3, have not been fully illuminated. In this study, we found that a zinc chloride-modified mesoporous alumina, ZnCl_2//meso-Al_2O_3, with a high surface area, relatively uniform mesopores, and Lewis acidic character was developed, and that MTO doped on the alumina, MTO/ZnCl_2//meso-Al_2O_3, demonstrated higher catalytic performance for the metathesis of functionalized olefins than Herrmann's system of MTO on SiO_2-Al_2O_3 (MTO/SiO_2-Al_2O_3). In our catalytic system, ZnCl_2//meso-Al_2O_3 not only immobilizes MTO on its solid surface, but also activates MTO enough to accelerate the metathesis of functionalized olefins.