焙烧温度对碳纳米管钴基费托合成催化剂的影响

Effect of Calcination Temperature on Cobalt-Carbon Nanotube Composite Catalyst for Fischer-Tropsch Reaction

摘要:

通过浸渍法制备了不同焙烧温度的碳纳米管钴基费托合成催化剂〔CAT (X)，X =250、300、350、400、450、 500℃〕，利用热重分析、氮气物理吸附-脱附、X射线衍射、氢气程序升温还原、扫描电镜、透射电镜和X射线光电子能谱等考察了焙烧温度对催化剂热稳定性、结构、物相、还原度及费托合成反应性能的影响。结果表明：载体碳纳米管在500℃以下可以稳定存在；焙烧温度在250~500℃时，催化剂的比表面积在79.78~85.23 m2/g内，孔容在0.6~0.7 m3/g内，孔径在28.9~33.4 nm内，其中经350℃焙烧的催化剂比表面积为79.782 m2/g，孔容为0.6664 m3/g，孔径为33.410 nm；在350℃焙烧后，催化剂表面钴主要有Co3O4和CoO两种存在形式，晶粒细小，尺寸分布窄。程序升温还原测试和费托合成反应性能评价结果显示，350℃焙烧的催化剂还原温度最低，一氧化碳转化率最高，为12.5%。

Abstract:

A series of Co/CNT catalysts with different calcination temperature were prepared by the impregnation method to investigate the impact of different calcination temperature on the thermal stability, structure, phase, reduction degree and Fischer-Tropsch synthesis reaction activity. The catalyst characterization techniques include differential thermogravimetric analysis (TGA), nitrogen physisorption, X-ray diffraction (XRD), temperature program reduction (TPR), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). These characterization results show that carbon nanotube was stable below 500℃. When calcined at 250~500℃, surface area of the catalysts is in the range of 79.78~85.23 m2/g, pore volume in the range of 0.6~0.7 m3/g, and pore diameter in the range of 28.9~33.4 nm. The largest pore size is found when calcined at 350℃. When calcined at 350℃ the main phase of the catalyst is Co3O4 and CoO. The resulted crystallite size is relatively small, and crystallite size distribution is relatively narrow. TPR results and Fischer-Tropsch synthesis reaction data show that calcination at 350℃ lead to the lowest reduction temperature and highest CO conversion (12.5%).