Development of Supported Metal Catalysts to Produce Carbon Nanotubes from Hydrocarbons under Mild conditions

我们一直在开发一种简便的方法来制备贵金属纳米颗粒。我们应用这种尺寸精确控制的金属纳米颗粒作为催化剂的活性物种来制备多壁碳纳米管(MWNT)。在Au/SiO_2-Al_2O_3或Pd/Al_2O_3催化剂上进行乙炔裂解，得到以下结果：(1)在Au/SiO_2-Al_2O_3催化剂上，在550℃的极低温度下形成了多壁碳纳米管。(2)考察了催化剂-载体的作用，发现SiO_2-Al_2O_3具有最佳的多壁碳纳米管的形成性能。(3)随着温度的升高，形成高度堆积的片层和弯曲结构的多壁碳纳米管。(4)当Au的负载量超过5wt%时，Au纳米粒子在SiO_2-Al_2O_3上的烧结和多壁碳纳米管的形成被抑制。(5)当Au与载体之间的相互作用很强时，形成了开放的多壁碳纳米管。Pd催化剂(1)在700℃时，不同Pd尺寸的Pd/Al_2O_3生成不同直径的MWNTs。(2)碳纳米丝主要是在低温下生成的。在高温下可得到结晶程度较高的多壁碳纳米管。

We have been developing facile method to produce noble metal nanoparticles by liquid preparation method. We have applied such metal nanoparticles with precisely controlled sizes as active species of catalysts to produce multi-walled carbon nanotubes (MWNT). Acetylene was decomposed over Au/SiO_2-Al_2O_3 or Pd/Al_2O_3 and following results are obtained :1.Au catalyst(1)MWNTs were formed at very low temperature of 550℃ over Au/SiO_2-Al_2O_3 catalyst. No report appeared for the formation of MWNTs over Au catalyst.(2)Effects of catalyst-support was investigated and SiO_2-Al_2O_3 showed the best performance to form MWNTs.(3)By an increase in temperature, MWNTs with highly stacked lamellae and bent structure was produced.(4)Supported amount of Au over 5wt% causes sintering of Au nanoparticles on SiO_2-Al_2O_3 and formation of MWNTs was inhibited.(5)When interaction between Au and support was strong, open-end MWNT was formed, while Au particle was encapsulated at the closed end of MWNT when the interaction was weak.2.Pd catalyst(1)Pd/Al_2O_3 with different Pd sizes produced MWNTs with different diameters depending on sizes of Pd at 700℃.(2)Carbon nanofilament was mainly produced at low temperature. Highly crystallized MWNT was produced at high temperature.