基于非晶态Fe/Al_(2)O_(3)催化剂的乙烷催化裂解高效制备碳纳米管

Efficient Synthesis of Carbon Nanotubes by Catalytic Cracking of Ethane Based on Amorphous Fe/Al_(2)O_(3) Catalyst

通过共沉淀法和浸渍法分别制备了非晶态和晶态的Fe/Al_(2)O_(3)催化剂。采用X射线衍射、N_(2)吸附-脱附、H_(2)程序升温还原、扫描电镜-元素分布扫描等分析方法对催化剂样品进行表征,并通过固定床反应器评价了各催化剂上乙烷催化裂解合成碳纳米管(CNT)的反应性能。结果表明:非晶态催化剂具有更大的比表面积和更多的活性位点;在反应温度为700℃、催化剂装载量为1.5 g、乙烷进气量为90 mL/min的反应条件下,Fe/Al摩尔比为1/2的非晶态催化剂的碳纳米管产率可达27.7 g CNT/g CAT;非晶态催化剂合成的碳纳米管纯度高,管径集中分布在14~22 nm,石墨化程度高;相比于晶态催化剂,非晶态催化剂的无定形结构促进了活性组分的均匀分散,可在更大范围内调节金属原子组成,拥有更多的活性中心,具有更高的反应活性和碳纳米管产率。

Amorphous and crystalline Fe/Al_(2)O_(3) catalysts were prepared through co-precipitation and impregnation.Catalyst samples were characterized by X-ray diffraction,N_(2) adsorption-desorption,H_(2) temperature program reduction,scanning electron microscope and element distribution scanning.The performance of catalyst samples for catalytic cracking of ethane to synthesize carbon nanotubes(CNT)was evaluated using a fixed bed reactor.The results show that the amorphous catalyst has a larger specific surface area and more active sites.Under the reaction temperature of 700℃,catalyst loading capacity of 1.5 g and the ethane flow rate of 90 mL/min,the carbon nanotube yield of amorphous catalysts with a Fe/Al molar ratio of 1/2 can reach 27.7 g CNT/g CAT.The carbon nanotubes synthesized by amorphous catalyst exhibit high purity and high degree of graphitization,with outer diameters between 14 and 22 nm.Compared with crystalline catalyst,amorphous catalyst has higher reactivity and yield of carbon nanotubes because its amorphous structure can promote the uniform dispersion of active sites to have more active centers by adjusting the composition of metal atoms in a wider scope.