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One-step preparation of highly dispersed metal-supported catalysts by fluidized-bed MOCVD for carbon nanotube synthesis

机译：流化床MOCVD一步一步制备高分散金属负载催化剂用于碳纳米管合成

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摘要

A new technique of fluidized-bed metal-organic chemical vapour deposition (FB-MOCVD) is developed as a one-step method to prepare highly dispersed metal-supported catalysts for carbon nanotube synthesis. By using ultrafine powder of gamma-alumina (70 nm Sauter mean in size) as the support with Fe(CO)_5 and Mo(CO)_6 as the metal precursors, Fe/Al_2O_3, Mo/Al_2O_3 and Fe-Mo/Al_2O_3 catalysts have been prepared in an FB-MOCVD reactor. Compared with the conventional catalyst-preparation methods such as impregnation, ion exchange, co-precipitation and co-crystallization, the one-step FB-MOCVD technique is advantageous in many aspects. These include eliminating the solid-liquid separation and the subsequent operations of drying and high-temperature calcination/reduction, thus minimizing the aggregation or the crystalline size-growing problem for the supported metal particles caused by these operations. The metal-supported catalysts obtained by FB-MOCVD are characterized with various techniques including ICP-AES, SEM-EDX, XRD and nitrogen isothermal adsorption. Some catalysts are selected and used for carbon nanotube synthesis by CVD from acetylene (C_2H_2) in a fluidized bed at 650 or 850 deg C. The formation of the entangled multi-walled carbon nanotubes (MWNTs), around 50 nm in outer diameter and 10 nm in inner diameter, and several to tens of microns in length, has been confirmed by the TEM and SEM analyses. High CNT selectivity (> = 95 percent) with the carbon yield ranging widely from about 10 percent to over 60 percent, depending on the type of catalyst used and the CNT deposition temperature, has been demonstrated with TGA tests.
机译：开发一种新的流化床金属有机化学气相沉积（FB-MOCVD）技术，作为一步法制备用于碳纳米管合成的高度分散的金属负载催化剂。以Fe（CO）_5和Mo（CO）_6为金属前体，以γ-氧化铝超细粉末（平均Sauter尺寸为70 nm）作为载体，Fe / Al_2O_3，Mo / Al_2O_3和Fe-Mo / Al_2O_3催化剂已经在FB-MOCVD反应器中制备。与常规的催化剂制备方法（例如浸渍，离子交换，共沉淀和共结晶）相比，一步式FB-MOCVD技术在许多方面均具有优势。这些包括消除固液分离以及干燥和高温煅烧/还原的后续操作，从而使由这些操作引起的负载金属颗粒的聚集或晶体尺寸增长问题最小化。通过FB-MOCVD得到的金属负载的催化剂用ICP-AES，SEM-EDX，XRD和氮等温吸附等各种技术进行了表征。选择了一些催化剂，并将其用于在650或850℃的流化床中通过乙炔（C_2H_2）进行CVD合成碳纳米管的过程。缠结的多壁碳纳米管（MWNT）的形成，外径约为50 nm，10纳米TEM和SEM分析已证实其内径为100 nm，长度为数十至数十微米。 TGA测试表明，根据所用催化剂的类型和CNT的沉积温度，高CNT选择性（> = 95％），碳产率范围从大约10％到60％以上。

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