多元非晶态合金纳米管的可控制备及催化性能研究

Noncrystalline alloys have been found important applications in catalytic hydrogenation、dehydrogenation reactions and etc. due to their unique structures. Plenty of research reports have shown that the composition、structure and morphology of noncrystalline alloy have great influence on their catalytic performance. As indicated by our previous results, compared with common catalysts,nanotubular structured catalysts may show cooperativity between multiple binding sites and confinement effect, due to the distinctive nanosized bended structure and the nanosized confined space, respectively, which contribute to their high catalytic activity and special selectivity. So it will be very interesting explorative project to fabricate the noncrystalline alloys as nanotubes and further investigate their catalytic performance. In our previous studies, it had been found that the small-diameter nanotubes show better catalytic performance than big ones and the ternary NiPB noncrystalline alloy nanotubes was more stable than the binary NiB nanotubes, which indicated the importance of exploring the scientific problem about the confinement effect within nanotubes in the liquid reaction. .In this project we will further investigate the formation mechanism of these novel noncrystaline alloy nanotubes, to obtain a set of polynary noncrystalline alloy nanotubes with different tubular diameters and compositions, and make an intensive study of the relationship between the confinement effect and tubular diamenter, and the influence of polynary compositions on the stability, catalytic activity and selectivity of noncrystalline alloy nanotubes. We will also focus on developing excellent hydrogenation catalysts with industrial value for certain applications through optimizing the tubular diameter and composition.

非晶态合金具有独特的结构，在催化加氢、脱氢等反应中具有重要应用。其组成、结构和形貌对催化性能具有重要影响。将非晶态合金做成纳米管，系统调控其组成、结构和尺寸，并考察相应的催化性能是非常有意义的课题。如其纳米管内表面可能的多位点协同作用及限域环境，会对管内催化反应产生特殊的效应，可望获得高性能催化材料。本组前期工作已初步揭示了这一点，发现小管径的纳米管催化性能更优越，还发现三元NiPB纳米管比二元NiB纳米管更稳定，这些揭示了探讨液相反应中非晶态纳米管内限域效应这一科学问题的重要性。因此，本课题拟进一步研究合成机理，获得一系列管径与组成可调的多元非晶态合金纳米管，深入研究管径与限域效应，多元组成与纳米管稳定性、催化活性及选择性之间的关系，并针对应用目标调变管径尺寸、组成种类及比例，着力开发具有工业应用价值的选择性加氢催化剂。

本项目发展完善了多元非晶态合金纳米管的溶液化学合成路线，拓展了非晶态合金纳米管的种类，获得了丰富的三元、四元、甚至五元非晶态合金纳米管材料。在吐温系列非离子/樟脑磺酸阴离子混合表面活性剂与过渡金属盐溶液所形成的溶致层状液晶模板体系中加入硼氢化钠，制备了多元过渡金属与硼的非晶合金纳米管。其中过渡金属盐以Ni、Co、Fe、Cu、Zn等为主，也可加入P的前体盐类化合物如次亚磷酸钠，可以成功制备一系列Ni-Fe-Co-P-B、Co-Fe-P-B、Ni-Fe-P-B, Fe-Co-B、Co-Ni-B、Fe-Ni-B、Ni-Cu-B等多元非晶合金纳米管。基于一系列实验结果，揭示了这类反应的机制，发现溶致层状液晶模板的存在及其诱导生成纳米薄片前体是获得多元非晶态合金纳米管的关键，层中多种过渡金属离子及含磷的离子被硼氢化钠还原后生成多元非晶态合金纳米薄片前体的同时还产生氢气，导致层状液晶相解离，多元非晶态合金纳米薄片前体卷曲形成纳米管。在多元反应体系中，由于硼氢化钠、次亚磷酸钠与不同的金属离子之间存在多种竞争反应，使得反应中间体的结构和组成难以控制，容易生成一些纳米颗粒或金属纳米晶，使得多元非晶态合金纳米管的合成较为困难；同时这些竞争反应影响了最后纳米管材料中各个元素的含量。在此基础上通过细调合成参数并添加适当的稳定剂，可以得到稳定的多元（三元到五元）非晶态合金纳米管，并可在一定范围内调控其组成比例。催化性能对比研究表明，在一些加氢反应中多元非晶态合金纳米管不仅具有比相应的非晶态纳米颗粒更好的催化性能，而且呈现出四元>三元>二元的催化活性顺序；同时，调变种类和组成比例，可以得到稳定性更好且催化性能优于二元非晶态合金纳米管的三元或四元非晶态合金纳米管材料，展现出丰富的可能性和工业应用潜力。