水促进Co／Mo／Al2O3催化剂上碳纳米管的生长  

Water-Assisted Growth of Carbon Nanotubes over Co/Mo/Al_2O_3 Catalyst

作　　者：崔超婕[1] 骞伟中[1] 魏飞[1] 

机构地区：[1]北京市绿色反应工程与工艺重点实验室,清华大学化工系,北京100084

出　　处：《物理化学学报》2011年第10期2462-2468,共7页Acta Physico-Chimica Sinica

基　　金：国家重点基础研究发展规划项目(973)(201lCB932602);国家自然科学重点基金(20736007,20736004)资助~~

摘　　要：对水促进Co/Mo/Al_2O_3催化剂裂解乙烯生长碳纳米管(CNTs)的研究发现,通入体积分数((?))为0.6%的水蒸汽在1h内可将CNTs的生长倍率从3.7 g·g^(-1)提高至70 g·g^(-1).水的作用在于恢复被无定形碳包覆的催化剂颗粒的活性,水的加入量由于其积碳(促进固体碳生成)和消碳(去除固体碳)的竞争作用存在最佳值,不同反应时间下乙烯的转化率与有效催化剂含量的分析表明,在CNTs生长后期,水的催化促进作用减弱.将催化剂的相对性与CNT聚团的相对密度关联发现,反应后期的CNTs主要在聚团内部缠绕生长,催化剂被包覆失活,拉曼测试与差热热重分析表明,生长阻力导致所得CNTs缺陷增多,CNT聚团密度变化与CNT缺陷间存在对应关系.聚团内外CNTs的生长阻力不同,生长倍率不同,导致产品纯度不均匀.We studied the growth of carbon nanotubes （CNTs） over a Co/Mo/AI203 catalyst by decomposing ethylene with or without the assistance of water. The optimal amount of water was determined to be 0.6% （co） since excess water removed the amorphous carbon around the catalysts and also directly etched the CNTs at high temperature. Under this condition, the yield of CNTs can be increased from 3.7 g.g^-1, based on the mass of catalyst, to 70 g .g^-1 within 1 h. The time-dependent online conversion of ethylene and the ratio of effective catalysts suggested that the effect of water is insignificant in the final growth period of the CNTs compared to that at the beginning. The correlation between the relative activity of the catalyst and the relative density of the CNT agglomerate suggests that the lack of growth volume inside the CNT agglomerate results in a gradual deactivation of the catatyst in the final CNT growth period. Raman characterization suggests that the degree of CNT defects increases with the bulk density of the CNT agglomerates since the mechanical resistance that is exposed on CNTs inside the agglomerate increases with reaction time. Thermal-gravimetric analysis indicates that the purity of CNTs ranges from 95.0% to 99.9% for a product with average purity of 99.2%. The non-uniform purity of the CNTs is due to the difference in mechanical resistance inside and outside the CNT agglomerate. The growth of CNTs outside the agglomerate is nearly free of mechanical resistance compared to that inside the agglomerate and, consequently, results in a high yield and high purity for the CNTs. These results suggest that it is necessary to control the agglomerate size and the structure, and to use a reactor with a large reactor volume for the growth of CNTs with low resistance and with high yield.

关 键 词：碳纳米管:水: 生长倍率:聚团结构:堆积密度:缺陷 

分 类 号：O643.36[理学—物理化学]