Ni修饰多壁碳纳米管材料的制备及表征研究

Preparation and Characterization of a Material of Carbon Nanotubes Decorated by Nickel

采用化学还原沉积法将少量镍负载分散到多壁碳纳米管(MWCNT,简写为CNT)上,制得一系列不同Ni载量的x%(质量百分数)Ni/CNT复合材料;利用多种谱学工具(如TEM,SEM、XRD、H2 TPD和CO TPD)对其物化性能进行表征,结果表明,所制得沉积镍颗粒粒径在～10nm量级;H2 TPD和CO TPD测试结果表明,经Ni修饰的CNT比单纯CNT对H2和CO具有更强的吸附活化能力,其所促进的Cu基催化剂对CO加氢成甲醇的催化活性比无CNT促进或单纯CNT促进的同类催化剂均明显提高.

By using chemical reduction-deposition method,a metallic nickel-decorated multi-walled carbon nanotube material,symbolized as x%Ni/CNTs,was prepared.TEM and XRD measurements demonstrated that the metallic nickel was evenly coated onto the carbon nanotube substrate,with granule-diameter of the Ni_x^0-crystallites at ～12 nm.The H_2-TPD and CO-TPD measurements showed that the modification of metallic nickel to the CNTs resulted not only in a significant increase in the total amounts of its adsorbing hydrogen and CO,but also in pronounced enhance of the proportion of the dissociatively adsorbed hydrogen H(a) and strongly chemisorbed CO(a) in their respective total amount of adsorption.With this composite nano-carbon material as an additive,a co-precipitated Cu_6Zn_3Al_1-12.5%(8%Ni/CNT) catalyst was prepared.The assay of its catalytic activity for methanol synthesis from syngas showed that under the reaction conditions of 2.0 MPa,V(H_2)/V(CO)/V(CO_2)/V(N_2)=62/30/5/3,GHSV=2 700 mL(STP)·h^(-1)·(g-catal.)^(-1),the observed CO conversion and methanol STY reached 34% and 442 mg·h^(-1)·(g-catal.)^(-1),which was about 38% and 17% higher than those over the Cu_6Zn_3Al_1 and Cu_6Zn_3Al_1-12.5%CNT catalysts, respectively,at the respective optimal operation temperature,513 K and 503 K.The results of the present work indicated that the nickel-modified CNTs could serve as a promoter more excellent than the simple CNTs.Its unique feature of promoting adsorption/spillover of hydrogen and CO would be beneficial to generating microenvironments with higher stationary-state concentration of active hydrogen-adspecies and chemisorbed CO(a) on surface of the functioning catalyst,and thus be favorable to increasing the rate of the CO hydrogenation reactions.