Chiral BINAP-based hierarchical porous polymers as platforms for efficient heterogeneous asymmetric catalysis

手性多孔有机聚合物具有较高的稳定性和催化活性,广泛用于多相不对称催化中.目前研究多集中在合成具有微孔结构的聚合物,而少有具有多种孔道结构(包含介; 孔和微孔)的聚合物的报道.之前我们报道了乙烯基修饰的BINAP配体,; (S)-5,5-divinyl-BINAP,将其与不同单体共聚后得到了一系列具有不同孔结构的有机聚合物.其负载的Rh基催化剂在苯乙烯不对称氢甲酰; 化反应中,表现出比均相更高的产物对映体选择性.本文采用不同的溴代步骤,合成了(S)-4,4-divinyl-BINAP配体.将这两种具有乙烯基官; 能团的手性配体按相同的摩尔比与二乙烯基苯(DVB)共聚,得到两种不同的有机聚合物.负载[RuCl_2(benzene)]_2后,分别得到Ru/4; -BINAP@POPs和Ru/5-BINAP@POPs-l.采用一锅法合成了催化剂Ru/5-BINAP@POPs-2;以[RuCl_2(p-cy; me)]_2和RuCl_3分别合成了Ru/5-BINAP@POPs-3和Ru/5-BINAP@POPs-4催化剂.; N_2物理吸附结果显示,Ru/4-BINAP@POPs和Ru/5-BINAP@POPs-l催化剂具有相似的孔道结构;而采用一锅法合成的Ru/5-; BINAP@POPs-2催化剂的介孔孔径较大.4-BINAP@POPs和5-BINAP@POPs聚合物的~(13)C核磁显示,其均在145,13; 7和128 ppm处有明显的吸收峰,可归结为萘环和苯环上的碳振动峰;在44.0; ppm处的峰归属为亚甲基上的碳振动峰;~(31)P核磁显示,在聚合物中P基本没有被氧化.将所得到的Ru/POPs催化剂应用于乙酰乙酸甲酯的多相不; 对称加氢反应中,Ru/5-BINAP@POPs-1催化剂具有与Ru/4-BINAP@POPs更快的反应速率.在相同反应条件下,催化剂活性大小为R; u/5-BINAP@POPs-l > Ru/5-BINAP@POPs-3 > Ru/5-BINAP@POPs-4 >; Ru/5-BINAP@POPs-2.另外Ru/5-BINAP@POPs-1催化剂对beta-酮酸酯有着较好的底物适应性,且在釜式反应中可循环使用; 6次而活性基本不变.分析发现,使用前后的催化剂均没有明显的Ru-Ru键的存在.表明Ru金属高度分散于催化剂上,且具有较高的稳定性,金属不易聚集,; 这也是其具有高活性和稳定性的原因.Two vinyl-functionalized chiral 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) ligands, (S)-4,4'-divinyl-BINAP and (S)-5,5'-divinyl-BINAP, were successfully synthesized. Chiral BINAP-based porous organic polymers (POPs), denoted as 4-BINAP@POPs and 5-BINAP@POPs, were efficiently prepared via the copolymerization of vinyl-functionalized BINAP with divinyl benzene under solvothermal conditions. Thorough characterization using nuclear magnetic resonance spectroscopy, thermogravimetric analysis, extended X-ray absorption fine structure analysis, and high-angle annular dark-field scanning transmission electron microscopy, we confirmed that chiral BINAP groups were successfully incorporated into the structure of the materials considered to contain hierarchical pores. Ru was introduced as a catalytic species into the POPs using different synthetic routes. Systematic investigation of the resultant chiral Ru/POP catalysts for heterogeneous-asymmetric hydrogenation of beta-keto esters revealed their excellent chiral inducibility as well as high activity and stability. Our work thereby paves a path towards the use of advanced hierarchical porous polymers as solid chiral platforms for heterogeneous asymmetric catalysis. (c) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.Chinese Academy of Sciences [XDB17020400

Porous Rh/BINAP polymers as efficient heterogeneous catalysts for asymmetric hydroformylation of styrene: Enhanced enantioselectivity realized by flexible chiral nanopockets

不对称氢甲酰化是合成具有单一光学活性物质(如光学活性的醛、alpha-氨基酸和醇等)最为重要的反应之一.尽管不对称氢甲酰化反应的研究超过40年,; 但仍然是催化体系中具有挑战性的课题.该反应涉及到产物的化学选择性、立体选择性和对映体选择性的优化.目前,在Rh催化体系中,使用磷-亚磷酸酯手性配; 体或双亚磷酸酯配体可以在不对称氢甲酰化反应中取得优异的催化性能.然而在Rh/手性双膦配体催化体系中,不对称氢甲酰化反应性能通常很低.以BINAP; 配体为例,负载Rh金属后,在催化苯乙烯不对称氢甲酰化反应中,产物的ee值只有25%.同时,由于均相催化体系存在催化剂回收和产物提纯等问题,因此有; 必要研究多相不对称氢甲酰化反应催化剂.本文使用乙烯基修饰的BINAP配体5,5'-divinyl-BINAP与具有不同结构的共聚单体二乙烯基苯或; 1,3,5-三乙烯基苯基苯共聚,得到具有不同孔结构的聚合物Poly-1和Poly-2.为了比较,利用线性共聚单体乙二醇二甲基丙烯酸甲酯与乙烯基; BINAP共聚得到聚合物Poly-3.上述三种聚合物材料负载金属Rh后,用作苯乙烯不对称氢甲酰化反应的催化剂.固体13C核磁分析表明,三种聚合物; 材料负载金属后仍然保持较为稳定的C骨架结构.通过31P核磁可以看到,嵌入在材料骨架中的BIANP仍然保持未被氧化的状态.N2物理吸附结果发现Po; ly-1和Poly-2具有较大的比表面积和孔体积,而; Poly-3的比表面积最小.热重分析显示,这些材料具有较高的热稳定性.在不同反应溶剂中催化剂活性差异较大.通过优化反应温度和合成气压力后,催化剂; Rh/Poly-1在80 °C和0.2; MPa下产物的对映体选择性可高达58.9%,支链醛与直链醛的比值为8.5;而在相同反应条件下,均相催化剂Rh-BINAP的ee值仅为35.3%,; 但高于Rh/Poly-3.这是由于三个多相催化剂骨架中BINAP周围环境不同所致.前两个催化剂中,BINAP与空间位阻较大的单体相连接,使得反应; 底物按照特定方向与催化活性位点接触,形成了类似于手性口袋的结构.而Rh/Poly-3中,BIANP周围是线性的共聚单体,不能形成有效的手性口袋结; 构.Rh/Poly-1重复使用7次后,催化活性没有显著下降.拓展X射线吸收精细结构表征结果表明,Rh/Poly-1催化剂使用前没有Rh-Rh键存; 在,但经重复使用后,Rh金属部分聚集,生成了Rh-Rh键.球差电镜照片也证实了这一点.A new chiral monomer, (S)-5,5'-divinyl-BINAP, was successfully synthesized and embedded into two different porous organic polymers (Poly-1 and Poly-2). After loading a Rh species, the catalysts were applied for the heterogeneous asymmetric hydroformylation of styrene. Compared with the homogeneous BINAP analogue, the enantioselectivity of Rh/Poly-1 catalyst was drastically increased by approximately 70%. The improved enantioselectivity of the porous Rh/BINAP polymers was attributed to the presence of flexible chiral nanopockets resulting from the increased bulk of the R groups near the catalytic center. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.Strategic priority Research Program of the Chinese Academy of Sciences; [XDB17020400

Photoelectrochemical Reduction of CO2 over Graphene-Based Composites: Basic Principle, Recent Progress, and Future Perspective

面对日益严重的化石能源消耗和温室效应问题,二氧化碳还原正成为一个重要的全球性研究课题,其通过消耗二氧化碳来生成可用于能源供应的产物。光电催化技术; 同时利用光能和外部电压,是一种用于二氧化碳还原的可行且有效的途径。因为石墨烯具有增强二氧化碳吸附和促进光生电子转移的特性能够提升石墨烯基复合电极; 的性能,所以引入石墨烯用于调优光电催化二氧化碳还原体系已经引起了广泛关注。本篇综述详细陈述了石墨烯基复合材料应用于光电二氧化碳还原的基本原理,电; 极制备方法以及目前的研究进展。我们也对这个蓬勃发展的领域未来可能会遇到的机遇和挑战进行了展望,同时提出了潜在可行的革新策略用于提升光电二氧化碳还; 原方面的研究。In response to aggravated fossil resources consuming and greenhouse effect, CO2 reduction has become a globally important scientific issue because this method can be used to produce value-added feedstock for application in alternative energy supply. Photoelectrocatalysis, achieved by combining optical energy and external electrical bias, is a feasible and promising system for CO2 reduction. In particular, applying graphene in tuning photoelectrochemical CO2 reduction has aroused considerable attention because graphene is advantageous for enhancing CO2 adsorption, facilitating electrons transfer, and thus optimizing the performance of graphene-based composite electrodes. In this review, we elaborate the fundamental principle, basic preparation methods, and recent progress in developing a variety of graphene-based composite electrodes for photoelectrochemical reduction of CO2 into solar fuels and chemicals. We also present a perspective on the opportunities and challenges for future research in this booming area and highlight the potential evolution strategies for advancing the research on photoelectrochemical CO2 reduction.National Natural Science Foundation of China [U1463204, 20903023,; 21173045]; Award Program for Minjiang Scholar Professorship; Natural; Science Foundation of Fujian Province [2012J06003, 2017J07002];; Independent Research Project of State Key Laboratory of Photocatalysis; on Energy and Environment [2014A05]; first Program of Fujian Province; for Top Creative Young Talents; Open Research Project of State Key; Laboratory of Physical Chemistry of Solid Surfaces of Xiamen University; [201519]; Program for Returned High-Level Overseas Chinese Scholars of; Fujian provinc

Fe, N, S-doped porous carbon as oxygen reduction reaction catalyst in acidic medium with high activity and durability synthesized using CaCl2 as template

燃料电池是一种可将化学能通过电催化反应直接转化成电能的装置,具有能量密度高和清洁无污染等优点.燃料电池阴极氧还原反应(ORR)的动力学较迟缓,是; 电池能量效率损失的主要原因.目前ORR催化活性最高的是铂基催化剂,但由于贵金属铂价格昂贵,储量稀少,且对燃料小分子渗透的抗性较差,严重制约了燃料; 电池的大规模应用.因此,高性能、低成本的非贵金属催化剂成为燃料电池领域的研究热点.本文选用含氮量高达45%的三聚氰胺-甲醛树脂为碳源和氮源,Fe; (SCN)_3为铁源和硫源,以CaCl_2为模板,在高温和铁的催化作用下将树脂碳化,经酸洗和二次热处理工艺,制备出铁、氮、硫共掺杂的多孔碳(Fe; NS-PC).干燥后的CaCl_2颗粒可防止树脂在高温下交联形成块状碳颗粒,同时起到造孔模板的作用.CaCl_2颗粒在温和条件下即可除去,无需强; 腐蚀性条件,因此不会对催化活性中心造成破坏.在Fe/N/C催化剂中掺杂S可进一步提高催化活性,不添加碳载体可避免低活性的碳载体降低质量活性,多孔; 结构可促进传质,充分利用活性位点.我们优化了热处理温度,并对催化剂的结构、组分及催化性能等进行了表征分析.结果表明,热处理温度为900; °C时,可将树脂完全转化成多孔碳,并获得较高的杂原子掺杂量,可达到最优活性.CaCl_2为模板剂可避免使用强腐蚀性试剂去除模板,有利于保留活性位; ,并得到多孔结构.FeNS-PC-900的比表面积可达775; m~2/g.得益于原位掺杂的合成工艺,各掺杂元素在多孔碳表面均匀分布.在酸性介质中,FeNS-PC-900的半波电位可达到0.811; V,仅比商业Pt/C催化剂低78 mV;在0.8 V电位下的质量活性为10.2; A/g,表现出优异的催化活性.经过10000圈加速衰减测试后,其半波电位仅下降了20 mV,在0.75 V电位下持续放电10000; s后,其ORR电流仍保持初始电流的84.4%,具有比Pt/C更加优异的稳定性.以FeNS-PC-900为阴极催化剂的质子交换膜燃料电池的最大功率; 密度可达到0.49 W/cm~2,并在0.6 V电压下持续放电10; h后,其电流仍可保持初始电流的65%,表现出良好的应用潜力.FeNS-PC-900具有高掺杂含量、高比表面积和多孔结构,并且杂原子在催化剂表面均; 匀分散,在半电池和燃料电池测试中都表现出优异的催化活性和稳定性,表明其是一种非常有潜力应用于燃料电池的非贵金属氧还原催化剂.Proton exchange membrane fuel cells suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) and the high cost of Pt catalysts. In the present work, a high-performance ORR catalyst based on Fe, N, S-doped porous carbon (FeNS-PC) was synthesized using melamine formaldehyde resin as C and N precursors, Fe(SCN)(3) as Fe and S precursors, and CaCl2 as a template via a two-step heat treatment without a harsh template removal step. The results show that the catalyst treated at 900 degrees C (FeNS-PC-900) had a high surface area of 775 m(2)/g, a high mass activity of 10.2 A/g in an acidic medium, and excellent durability; the half-wave potential decreased by only 20 mV after 10000 potential cycles. The FeNS-PC-900 catalyst was used as the cathode in a proton exchange membrane fuel cell and delivered a peak power density of 0.49 W/cm(2). FeNS-PC-900 therefore has good potential for use in practical applications. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.National Basic Research Program of China [2015CB932303]; National; Natural Science Foundation of China [21373175, 21621091