调变Ni/Mo/MgO催化剂中Ni/Mo比例可控合成薄壁碳纳米管(英文)

Synthesis of thin-walled carbon nanotubes from methane by changing the Ni/Mo ratio in a Ni/Mo/MgO catalyst

采用摩尔分数1%Ni及负载少量Mo的Ni/Mo/MgO催化剂裂解甲烷合成薄壁碳纳米管。通过SEM、TEM、XRD和Raman光谱表征方法研究了碳纳米管直径和催化剂中Ni/Mo比例关系。实验发现:通过控制Ni/Mo比例可以调变催化剂颗粒大小以及活性相。TEM及XRD表征发现,随着Ni/Mo比例的降低,金属Mo相逐渐从NiMo合金相中析出。NiMo合金相对应的活性组分颗粒很小,容易催化裂解甲烷形成薄壁碳纳米管;而后析出的Mo相则主要形成了大管径厚壁的碳纳米管。当Ni/Mo比例为6时可以高选择性地获得窄分布,内径为1.3nm,外径为3.0nm的薄壁碳纳米管。Raman光谱进一步验证了碳纳米管含有较少的缺陷。薄壁碳纳米管形成的关键因素主要体现为碳在其表面的快速扩散以及小颗粒的碳纳米管催化剂活性相控制。

Thin-walled carbon nanotubes （CNTs） were prepared from methane decomposition using Ni/Mo/MgO as catalysts loaded with 1% mole fraction of Ni and smaller proportion of Mo. The relationship between CNT diameter and Ni/Mo ratio was studied by SEM, TEM, XRD and Raman spectroscopy. The particle size and the active phase of the catalyst could be modulated by the Ni/Mo ratio. With decreasing Ni/Mo ratio, a NiMo alloy was first formed, and then an isolated Mo phase was formed on the catalyst, as characterized by TEM and XRD. The NiMo alloy, with very small size, was responsible for the growth of thin-walled CNTs , whereas, the Mo phase was related to the formation of large- diameter thick-walled CNTs. The thin-walled CNTs with outer diameter of 3.0nm and inner diameter of 1.3 nm could be obtained with high selectivity, a narrow diameter distribution, and high purity by controlling the Ni/Mo ratio at 6. Raman spectra confirmed the formation of thin-walled CNTs with few defects. The formation of thin-wailed CNTs was mainly attributed to a rapid surface diffusion and precipitation of carbon on the small metal alloy crystallites.