摘要
以不同配比的乙二醇(EG)/水溶液作溶剂,用初湿含浸法制备了Co粒子尺寸分别为6、8、12、19 nm的Co/Si O2模型催化剂.采用N2物理吸附、X射线粉末衍射(XRD)、透射电子显微镜(TEM)、程序升温脱附(TPD)、漫反射红外光谱(DRIFTS)、程序升温表面反应(TPSR)等表征和微分固定床反应器费托(F-T)反应评价实验,考察了Co粒子尺寸对F-T反应性能的影响.评价结果显示随着Co粒子尺寸的增大,CO转化率降低,表观TOF在Co粒子尺寸为8 nm时出现高点.TPD和DRIFTS研究结果表明:较小的Co粒子对CO的吸附和解离能力较强,其表面碳物种会覆盖部分表面活性位,使有效反应位点减少;较大Co粒子对CO的吸附能力较弱,表面C*较易脱附及CO*/Cos比例较高,导致催化剂加氢能力减弱,CO2的选择性增高.当Co粒子尺寸为8 nm左右时,COads和C*在Co粒子表面吸附强度适中并且比例恰当,使得催化剂表现出较高的F-T活性和产物选择性.
The effects of cobalt particle size are still controversial for whether it influences Fischer-Tropsch synthesis （F-T synthesis） behavior intrinsically. In the F-T synthesis, a large number of different reaction pathways as well as multitude of products does result in many difficulties in the search for the intrinsic causes. The adsorption and dissociation of CO and H2 is a key step for Fischer-Tropsch synthesis. So the effects are trying to be explained by means of exploring the relationship between the adsorbed behavior of CO and H2 and cobalt particle size. In this work, four Co/SiO2 catalysts with different co- balt particle sizes, named 6, 8, 12, 19 nm, were prepared by incipient wetness impregnation using ethylene glycol （EG） and water mixture as a solvent. The catalysts were characterized by N2 physisorption, X-Ray powder diffraction （XRD）, trans- mission electron microscopy （TEM）, temperature programmed desorption （TPD）, diffuse reflectance infrared Fourier trans- form spectroscopy （DRIFTS） and temperature programmed surface reaction （TPSR）, and their Fischer-Tropsch reactivity were tested in a micro-fixed bed reactor. The F-T synthesis test showed that the catalysts with larger cobalt particle size had lower CO conversion, but their apparent Turnover Frequency （TOF） displayed a maximum for the catalyst with cobalt parti- cle size of 8 nm. TPD and DRIFTS results indicated that both the adsorption and dissociation of CO were stronger on smaller cobalt particle, while some of the active sites could be blocked by carbon species on the surface, thus decreased the effective active sites. The adsorption of CO were weaker on larger cobalt particle and the formed C＊ species were easily desorbed, exhibiting higher CO＊/Cos ratio on the surface. Therefore tower activity and higher CO2 selectivity were observed. It is sug- gested that the catalyst with medium cobalt particle size can produce medium adsorbability of CO and proper amount of COabs （surface adsorbed CO） and C＊ spe
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2015年第7期690-698,共9页
Acta Chimica Sinica
基金
国家自然科学基金(No.21273261)资助~~
