【作者】 代威力；

【导师】 尹双凤；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2010， 博士

【摘要】 CO2是地球上储量最丰富、廉价、无毒和可再生的C1资源,如何在相对温和的条件下实现CO2的化学固定已成为国际上竞相研发的热点课题。迄今为止,以CO2为原料的工业化生产途径不多。利用CO2与环氧化物环加成合成环状碳酸酯是资源化CO2的有效途径之一。但是,所报导的催化剂体系大多存在活性不高和／或产物与催化剂的分离困难等不足。本论文的研究工作主要针对CO2与环氧化物环加成合成环状碳酸酯开发了多种高效均相和多相催化剂体系。第一类催化剂为含桥式N配位原子双酚盐配体的铋配合物,LnBiX(X：Cl、Br、I；n=1～5)和LnBi(OCH3)(n=1～5)。当以NaI作为助催化剂时,这些铋配合物均对CO2与环氧丙烷的环加成反应显示了较高的催化活性和选择性(>99.5%)。其中LnBiI(n=1～3)的催化活性最高,当反应温度120℃、CO2初始压力2.5 MPa和反应时间1 h时,碳酸丙烯酯产率可达95%以上。但由于这种催化剂易于水解,使得其应用受到限制。第二类催化剂为由ZnBr2与有机鳞盐组成的双组分环加成催化剂体系,其中ZnBr2-Ph4PI对二氧化碳与环氧化物之间的加成反应表现出较高的催化活性,而且ZnBr2-Ph4PI还具有很好的稳定性和重复使用性能,是一类具有应用前景的均相环加成催化剂。此外,详细考察了不同Zn2+盐、ZnBr2/Ph4PI摩尔比、反应条件及水对催化剂活性的影响,发现水对ZnBr2-Ph4PI催化剂体系具有重要的影响,即少量的水存在也会严重降低催化剂的活性。通过焙烧相应水滑石合成了第三类催化剂：Zn-Al-O复合氧化物及一系列碱土金属掺杂改性的Zn-M-Al-O(M=Mg、Ca、Sr、Ba)复合氧化物催化剂。这些催化剂对C02与环氧丙烷环的加成反应均具有较好的催化活性和选择性,其中Zn-Mg-Al-O(Zn/Mg=4.0、pH=10.未经水热处理)催化性能最好：在140℃、CO2初始压力2.5 MPa的条件下,反应12 h后碳酸丙烯酯产率和选择性分别可达88.8%和99.2%；而且Zn-Mg-Al-O催化剂还具有良好的稳定性和循环使用性能。Zn-Mg-Al-O催化剂兼具酸性和碱性。通过关联催化剂的性能和表面酸碱性之间的关系,还揭示了催化剂表面适中碱强度(6.1≤H0<8.9)的碱位更有利于环加成反应的进行。通过化学嫁接法和一步杂化法制备了第四类催化剂：SBA-15固载的羟基离子液体(3-(2-羟乙基)-1-丙基咪唑溴化物,HEPIMBr)催化剂,其中嫁接方法制备的催化剂(SBA-15-HEPIMBr)对二氧化碳和环氧化物之间的加成反应表现出很高的催化活性。例如,在140℃、CO2初始压力2.0 MPa和反应时间1 h的条件下,碳酸丙烯酯产率可达98.9%。还发现适量水的存在可显著改善SBA-15-HEPIMBr的催化活性,这与ZnBr2-Ph4PI催化剂显著不同。羟基基团的存在可能是这类羟基离子液体催化剂具有高活性的原因。另外,由于载体与HEPIMBr之间的协同作用,固载型的羟基离子液体具有比未固载的羟基离子液体(3-(2-羟乙基)-1-甲基咪唑溴化物)更高的催化活性。虽然由于活性组分的部分流失使得SBA-15-HEPIMBr在循环使用的初始阶段活性有所下降,但循环使用4次后催化剂活性可稳定在较高水平。为了进一步提高催化剂的稳定性和循环使用性能,以羟基离子液体功能化的三乙氧基硅烷和TEOS一起作为硅源,制备了杂化的SBA-15固载的羟基离子液体催化剂(H-SBA-15-HEPIMBr).虽然H-SBA-15-HEPIMBr的催化活性略低于SBA-15-HEPIMBr,但前者的稳定性和循环使用性能有了显著改善。第五类催化剂为聚二乙烯基苯固载的羟基离子液体催化剂。首先采用3-(2-羟基乙基)-1-乙烯基咪唑溴化物与二乙烯基苯共聚制得催化剂P-DVB-HEVIMBr。该催化剂对环加成反应具有较高的催化活性和稳定性。在循环使用6次后,其催化活性仅略有下降。为了进一步改善这类催化剂的活性和循环使用性能,还直接利用1-(3-氨丙基)咪唑功能化的聚二乙烯基苯与2-溴乙醇反应制得羟基离子液体嫁接的聚二乙烯基苯催化剂(PDVB-HEIMBr)。PDVB-HEIMBr比P-DVB-HEVIMBr以及文献上报道的多相环加成催化剂具有更高的催化活性,而且经过8次循环使用后,其活性没有下降。因此,这类催化剂具有良好的应用前景。此外,通过对比离子液体上不同官能团对催化剂活性的影响,探讨了羟基基团在反应中的作用,并提出了可能的反应机理。更多还原

【Abstract】 CO2 is an abundant, inexpensive, notoxic and renewable C1 resource. In the view of the concepts of "atom economy", "sustainable development", and "green chemistry", the chemical fixation of CO2 into valuable compounds under mild conditions is attracting much attention. However, there have been a few commercial processes that use CO2 as a feedstock so far. The synthesis of cyclic carbonates via the cycloaddition of CO2 to epoxides is one of the few processes that have been commercialized. Many catalysts have been reported to show catalytic activity towards this reaction, while most of them suffered from some shortcomings, such as low catalytic activity, and/or difficult separation of catalysts from products. In this study, several high-efficiency homogeneous and heterogeneous catalysts were designed and fabricated for the synthesis of cyclic carbonates from CO2 and epoxides.A series of novel bismuth compounds bearing a nitrogen-bridged bis(phenolato) ligand, LnBiX (X=Cl, Br, I; n=1～5) and LnBi(OCH3) (n=1～5) were firstly synthesized and examined for the cycloaddition reaction. In the presence of NaI as co-catalyst, the bismuth biphenolate complexes show high catalytic activity and selectivity (>99.5%) for the cycloaddition reaction of CO2 to propylene oxide (PO). LnBiI (n=1～3) is much superior to other bismuth complexes in catalytic efficiency, showing above 95% propylene carbonate (PC) yield at 120℃and 2.5 MPa CO2 initial pressure within 1 h. However, the stability of the bismuth compounds is not satisfactory, which will limit their applications.Subsquently, the two-component catalyst systems composed of zinc salts and different phosphonium salts were examined for the cycloaddition reaction. It was found that the ZnBr2-Ph4PI shows the best catalytic activity (e.g., giving TOF 6272 h-1 at 120℃and 2.5 MPa CO2 initial pressure when propylene oxide is used as substrate). Furthermore, the catalytic activity of ZnBr2-Ph4PI didn’t change after 10 recycles, showing good stability and reusability. A systematic investigation was also conducted on the effects of different zinc salts, ZnBr2/Ph4PI molar ratio, reaction parameters, and addition of water on the catalytic activity of ZnBr2-Ph4PI. It is noted that the presence of water even in trace amount has a negative effect on PO conversion.Heterogeneous catalysts of Zn-Al-O and alkaline-earth metal modified Zn-Al-O composite oxides (denoted as Zn-M-Al-O, M=Mg, Ca, Sr, Ba) were fabricated via calcination of the corresponding hydrotalcites. Among the synthesized composite oxides, Zn-Mg-Al-O (Zn/Mg=4.0, pH=10, without hydrothermal treatment) is the best in performance, showing PC yield of 88.8% and selectivity of 99.2% at 140℃and 2.5 MPa CO2 initial pressure within 12 h. Furthermore, the Zn-Mg-Al-O catalyst has good stability and reusability. The results of NH3- and CO2-TPD investigation indicate that the Zn-Mg-Al-O surface has both acid and basic sites. The basicity of the catalysts was measured by Hammett indicator method, and the results indicate that the sites of moderate basicity (6.1≤H0<8.9) are crucial to the reaction.In order to obtain high-efficiency heterognenous catalysts, SBA-15 immobilized hydroxyl ionic liquid (3-(2-hydroxyl-ethyl)-1-propyl-imidazolium bromide, HEPIMBr) catalysts were fabricated by grafting method. The catalyst (SBA-15-HEPIMBr) prepared by grafting method was found to show high catalytic efficiency. It gave 98.9% of PC yield at 140℃and initial CO2 pressure 2.0 MPa when propylene oxide was used as a substrate. Compared with that over ZnBr2-Ph4PI, the presence of a trace amount of water has positive effect on the cycloaddition reaction over SBA-15-HEPIMBr. The excellent performance of SBA-15-HEPIMBr is possibly related to the existence of OH groups. Furthermore, the SBA-15-HEPIMBr shows better catalytic performance than the pure hydroxyl ionic liquid (3-(2-hydroxyl-ethyl)-1-methyl-imidazolium bromide), possibly as a result of the synergistic effect between support and HEPIMBr. Although there was a distinct decrease of PC yield within the first three runs, the activity of SBA-15-HEPIMBr almost didn’t change after 4 runs. In order to improve the stability and reusability of the SBA-15 immobilized HEPIMBr catalyst, hybrid SBA-15 immobilized HEPIMBr catalyst (H-SBA-15-HEPIMBr) was also fabricated by one-pot synthesis method. Although the catalytic activity of H-SBA-15-HEPIMBr is lower than that of SBA-15-HEPIMBr, the former shows better stability and reusability.In addition,3-(2-hydroxyl-ethyl)-1-vinylimidazolium bromide was copolymerized with the cross-linked divinylbenzene (DVB) to prepare a polymer immobilized hydroxyl ionic liquid (P-DVB-HEVIMBr). The P-DVB-HEVIMBr shows good catalytic activity and stability for the cycloaddition reaction of CO2 to epoxides. After 6 runs, there was only a little decrease in the catalytic activity of P-DVB-HEVIMBr. Moreover, the hydroxyl ionic liquid-grafting polydivinylbenzene catalyst (PDVB-HEIMBr) was fabricated through the reaction of 1-(3-amino-propyl) imidazole-functionlized polydivinyl-benzene with 2-bromoethanol. It was found that the PDVB-HEIMBr exhibits better catalytic performance than P-DVB-HEVIMBr. Furthermore, there was no loss of catalytic activity of PDVB-HEIMBr even after 8 recycles. Therefore, it can be deduced that the PDVB-HEIMBr will find potential industrial applications in cyclic carbonates synthesis. Moreover, a possible reaction mechanism was proposed on the basis of the role of hydroxyl groups of the PDVB-HEIMBr catalyst.更多还原