双孔载体改性铜铁基低碳醇合成催化剂及其构效关系研究

Higher alcohols synthesis (HAS), as an important technology in the production of liquid fuels and chemicals from syngas derived from coal and biomass, is receiving a renewed interest for both industrial and academic applications because of the emergency of transportation fuel shortage in the whole world. In order to solve the key issues of the difficulty to adjust the synergy effect of Cu-Fe, low HAS activity and C2+OH selectivity over the Cu-Fe based catalyst, a support with a distinct bimodal pore structure is used to modify the catalyst, because the large pores provide pathways for rapid molecular transportation and small pores provide a large area of active surface, contributing to high diffusion efficiency and enhance dispersion of supported metal simultaneously. Adjustment mechanism of bimodal support nano-pore structure size, formation and variation of particle size of copper and iron species in the pore structures, diffusion and steric effect of H2 and CO probe molecules in the bimodal support, and regulatory mechanism of higher alcohols via modification of alkaline metals are investigated together for illustrating the synergy effect of Cu-Fe-bimodal support and establishing the relationship between the structure and HAS performance of the Cu-Fe bimodal catalyst. All of these studies provide the theoretical support for the industrial development and application of HAS catalysts with high activity and selectivity as well as excellent stability.

本项目针对Cu-Fe基催化剂双活性金属协同作用难于调控，低碳醇合成反应活性和高级醇产物选择性偏低的共性关键问题，提出利用具有不同纳米孔径结构的双孔载体来改性低碳醇合成反应活性位和高级醇产物分布的构思。通过大孔凝胶和小孔溶胶制备具有纳米孔径结构的双孔载体，探索双孔结构形成和孔径尺寸变化规律，研究双孔载体孔道限域效应对Cu、Fe双活性金属的颗粒尺寸调节机制，分析H2和CO等探针分子在不同孔道中的扩散和空间位阻效应，揭示甲醇活性中心Cu组元和碳链增长活性中心Fe组元与双孔载体的相互作用关系，阐明碱性金属对Cu-Fe协同作用的改性和高级醇产物的调节机理，构建Cu-Fe双活性组元微观结构与低碳醇合成反应性能的构效关系，为高活性高选择性具有优良稳定性的低碳混合醇催化剂的工业开发和应用提供基础理论支撑。

随着化石能源的日益减少，利用来源丰富的煤炭/生物质基含碳资源经合成气催化转化为低碳混合醇（C1-C5醇类）等洁净液体燃料，可缓减我国石油资源紧缺，是实现含碳资源高效洁净转化最为现实可行的途径之一。本项目针对Cu-Fe基催化剂双活性金属协同作用难于调控，低碳醇合成反应活性和高级醇产物选择性偏低的共性关键问题，提出利用具有不同纳米孔径结构的双孔载体来改性低碳醇合成反应活性位和高级醇产物分布的构思。通过溶胶-凝胶方法和超声浸渍法将大孔硅凝胶和小孔硅溶胶进行有效结合，合成出具有纳米孔径结构不一的双孔载体（小孔孔径16 nm，大孔孔径60 nm），通过改变双孔载体中大孔硅凝胶和小孔硅溶胶含量的比例可进一步调节纳米双孔结构尺寸分布；在此基础上采用等体积浸渍法在双孔载体孔道中引入Cu、Fe双活性金属研制出双孔载体改性的Cu-Fe基低碳醇催化剂，通过改变双孔载体孔道结构可以有效调节孔道中Cu、Fe双活性金属元素的粒径大小。催化剂中Fe/Cu比的增加有利于单质铜的分散和铁碳化物的生成，加强了大孔结构中Cu-Fe-载体间的相互作用，促进了低碳混合醇合成的反应活性和时空产率。在Cu-Fe双孔载体催化剂中添加Ca和Li助剂增加了表层CuO的含量而降低了Fe2O3物相的含量，这削弱了Cu-Fe双活性组元的作用力，促使了甲醇产物的生成。碱金属Na和K的添加则促使了催化剂表层Cu、Fe物种的生成，增加了双活性组元的活性位，加强了Cu-Fe之间的协同作用，促进了低碳醇合成的活性和高级醇产物的选择性。相比于其它碱性金属，K助剂的添加促使Cu-Fe双孔载体催化剂具有高的低碳醇合成活性和时空产率。在优化的Cu-Fe-K-双孔载体催化剂上，低碳醇反应活性可达56%，C2+OH/C1OH比例达到2.61。.在低碳混合醇液体燃料合成方面取得了一批具有理论和应用参考价值的创新性成果，发表了学术论文25篇，其中SCI/EI收录的高质量学术论文14篇，申请国家发明专利5项。参加国际应用能源及催化学术交流会议5次。培养博士研究生1名，硕士研究生2名。