By simple impregnation and hydrothermal treatment, MgO supported iron catalysts were obtained that were used for carbon nanotube (CNT) growth from chemical vapor deposition with methane as the carbon source. Single/double/multi-walled CNTs (S/D/MWCNTs) were selectively synthesized on the Fe/MgO catalyst with different iron loadings. When the iron loading was low (0.5%), the iron atom distributed on the MgO support was sintered to iron nanoparticles with a size of 0.8-1.2 nm under the growth conditions. This catalyst promoted the formation of SWCNTs, which was attributed to the surface diffusion of carbon atoms on it. The selectivity for SWCNTs in the as-grown product from the 0.5%Fe/MgO catalyst was 90%, and the carbon mass yield was 19 times that of the active phase. When the iron loading was increased to 3%, larger iron catalyst particles of about 2.0 nm were formed. On this catalyst, there was more bulk diffusion of carbon, and DWCNTs became the main products due to the combination of both surface and bulk diffusion. With the iron loading was further increasing, iron particles from 1 to 8 nm were formed, which promoted the growth of MWCNTs together with S/DWCNTs. With increasing iron amount on the porous MgO support, the diameter, wall number, and proportion of semiconducting CNTs also increased. This provides a controllable way to selectively grow S/D/MWCNTs on a large scale in a fluidized bed to meet critical needs for CNTs in applications.%通过浸渍及水热处理获得MgO负载的Fe基催化剂,并将其用于化学气相沉积过程裂解甲烷获得碳纳米管. 结果表明,单/双/多壁碳纳米管可选择性地生长在Fe负载量不同的Fe/MgO催化剂上. 当Fe负载量仅为0.5%时,铁原子在载体表面烧结为0.8～1.2 nm的铁颗粒,碳在这种小颗粒上以表面扩散为主,导致单壁碳纳米管形成,并且单壁碳纳米管的选择性高达90%. 当Fe负载量提高到3%时,铁原子聚集成约2.0 nm的颗粒,在化学气相沉积中生长碳纳米管时,碳在Fe催化剂颗粒中的体相扩散的贡献增大,在表相扩散和体相扩散的共同作用下,双壁碳纳米管的选择性显著增高. 当进一步增加Fe负载量时,铁原子烧结形成1～8 nm的颗粒,经过化学气相沉积,在催化剂上生长了单、双、多壁碳纳米管. 随着Fe在MgO载体上负载量的增加,管径、管壁数以及半导体管的含量都增加. 本研究提供了一种适合大批量选择性生长单/双/多壁碳纳米管的方法.
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