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Alternative TitleGraphitic Carbon Nitrides Preparation and Catalytic Synthesis of Cyclic Carbonates
Thesis Advisor成为国 ; 张锁江
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword环状碳酸酯   co2   g-c3n4   环加成反应   离子液体
Abstract环状碳酸酯的合成是固定转化CO2的原子经济性反应,产品环状碳酸酯应用广泛,需求量巨大。本文针对该反应非均相催化剂热稳定性差、载体活性位少等问题,通过对类石墨氮化碳材料(g-C3N4)前驱体筛选及制备条件调控,研究开发了具有高稳定性、多活性位的新型催化剂;此外,尝试通过添加离子液体来调控类石墨氮化碳材料的结构以期改善材料本身的催化性能。本文主要工作及创新性成果如下: 1. 无模板剂条件下分别由尿素、二氰二胺和三聚氰胺制备氮化碳材料,三种前驱体在一定条件下均能形成g-C3N4。材料催化CO2与环氧丙烷环加成的活性测试结果表明,空气氛围中以尿素为前驱体制备的氮化碳(u-g-C3N4)活性最高,在反应测试条件下可实现24 %的环氧丙烷转化率和99%的碳酸丙烯酯选择性。 2.尿素为前驱体不同温度下制备氮化碳材料(u-g-C3N4)。所制备的材料对环加成反应均表现出一定的催化活性:低温下制备的u-g-C3N4催化活性更高,u-g-C3N4-480在一定反应条件下可催化环氧丙烷转化率达58%,相同条件下可催化其他环氧底物转化率达90%以上;分析结果表明,不同温度下制得的u-g-C3N4具有不同的结晶度和聚合度及不同的孔结构和表面性质。边缘缺陷中未完全聚合的氨基基团是反应的催化活性位,低温下制备的材料边缘缺陷越多,因而活性更高。 3.三聚氰胺为前驱体不同离子液体(BmimBF4, BmimCl,EmimPF6, C8mimPF6, EmimBr)做发泡剂制备相应氮化碳材料。初步研究表明,发泡剂与前驱体的质量比影响g-C3N4结晶相的形成,不同离子液体发泡作用不同;BmimBF4不同添加比例下材料孔结构和聚合度不同,添加比例越小,材料大孔比例越大。
Other AbstractThe synthesis of cyclic carbonates is an atom economy reaction for CO2 fixation and conversion, of which the products are now in wide application and in high demand. Aimed at overcoming the disadvantages of the exsiting heterogeneous catalysts, such as poor thermal stability and scarce carrier active sites, new catalysts with higher stability and more active sites were studied and developed by screening the precursors and regulating preparation conditions of graphitic carbon nitrides (g-C3N4). Furthermore, ionic liquids were added in the process of carbon nitrides preparation to adjust g-C3N4 structure for better catalytic performance. The major work and innovative results for this thesis are as follows. 1. Template-free preparation of carbon nitrides from urea, dicyanodiamine or melamine was respectively conducted. The g-C3N4 phases could be achieved from the three different precursors under certain conditions. Catalytic evaluation results of prepared materials for CO2 cycloadditon with propylene oxide (PO) showed that the sample prepared from urea in air (u-g-C3N4) exhibited higher catalytic activity, with 24% PO conversion and 99% propylene carbonate (PC) selectivity under reaction conditions. 2. Graphitic carbon nitrides preparation from urea precursor (u-g-C3N4) were conducted under different temperatures. All the prepared u-g-C3N4 were active catalysts for the cycloaddition reaction. The u-g-C3N4 prepared under lower temperature showed a higher catalytic activity. Of all u-g-C3N4, u-g-C3N4-480 displayed the best catalytic performance, achieving 58% PO conversion and 99% PC selectivity. Under identical conditions, u-g-C3N4-480 was also effective for other substrates with more than 90% conversion of epoxides. The analysis results showed that u-g-C3N4 obtained under different temperatures owned different crystallinity and polymerization degree with different pore structures and surface groups, and the edge amino groups were regarded as active centers, which explains the higher activity of the sample prepared under lower temperature with larger amounts of edge amino groups. 3. Different carbon nitrides were respectively obtained from melamine with different kinds of ionic liquids (BmimBF4, BmimCl, EmimPF6, C8mimPF6, EmimBr) as foaming agents. The preliminary study showed that the mass ratio of foaming agent to precursor influenced the formation of g-C3N4 phases and different ionic liquids displayed different foaming effect. Besides, the pore structures and polymerization degree of materials changed with the mass ratio of BmimBF4 to melamine—more macropores were achieved under lower ratio.
Document Type学位论文
Recommended Citation
GB/T 7714
苏倩. 类石墨氮化碳材料的制备及其催化合成环状碳酸酯的研究[D]. 中国科学院研究生院,2014.
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