【作者】 蔡琴；

【导师】 李金林；

【作者基本信息】 中南民族大学 ， 物理化学， 2008， 硕士

【摘要】 费-托合成是将煤和天然气转化为洁净液体燃料油最有前途的方法之一。钴基催化剂因其具有催化活性高、水煤气变换活性低、长链烃选择性高、失活效率低等优点,越来越受到重视。由于SBA-15具有高的比表面积,孔径大小在5-30 nm范围内且可调控,孔道规整有序,并有较厚的孔壁和好的水热稳定性,可用作于费-托合成催化剂的载体。钌对SBA-15负载的钴基催化剂的催化性能方面的研究报道较少,用原位漫反射红外光谱技术研究钌助剂对SBA-15负载的钴基催化剂上CO吸附和合成气的费-托合成反应则未见文献报道。因此,本文选取SBA-15作为载体,用满孔浸渍法制备催化剂,重点研究钌负载量对SBA-15负载的钴基催化剂费-托合成催化性能的影响并采用X-射线衍射、H₂-程序升温还原、H₂-程序升温脱附、氧滴定等技术对催化剂进行了表征。此外采用CO为探针分子,用漫反射红外光谱法在原位条件下研究催化剂的吸附性能,同时考察不同钌助剂含量的SBA-15负载钴基催化剂表面CO加氢反应机理。催化剂费-托合成反应活性和选择性测试在典型的费-托合成条件下（230℃、10 bar）在固定床反应器上进行。综合表征结果及反应结果发现,钌助剂显著影响Co/SBA-15催化剂的结构、氧化钴物种的还原度和催化反应性能。（1）钌金属作氢溢流的桥梁,促进了催化剂上钴氧化物的还原,提高了催化剂的分散度,增加了活性中心的数量。且钌可以阻止钴与载体间的相互作用,促进氧化钴的还原。（2）不同钌含量的催化剂显示不同的催化活性。催化剂的催化活性随着钌含量的增加而提高。钌含量为0.5 wt%的Co/SBA-15催化剂表现出最高的费-托合成反应活性和长链烃选择性。（3）原位红外光谱研究表明,室温下CO在还原态催化剂表面主要以线式吸附和桥式吸附存在。在有H₂共吸附的情况下,H₂不仅使催化剂对CO的吸附能力大为增强,并显示出更多的吸附位。（4）不同钌含量的钴基催化剂还原后显示出不同的CO吸附性能。随着钌含量的增大,催化剂上桥式吸附和线性吸附发生了明显的变化。催化剂上存在桥式吸附和多种线性吸附,但只有特定的吸附位才对反应活性有显著影响。（5）还原态催化剂上合成气原位反应红外光谱研究表明,在钴金属表面CO并不是C-O键直接解离形成产物,而是先形成了羰基氢化物再发生解离。羰基氢化物是催化反应的重要中间体,与反应活性密切相关。羰基氢化物谱峰随温度升高红移的过程实际上是活性位上CO分子在H的作用下C-O键逐渐活化、减弱的过程。更多还原

【Abstract】 Fischer-Tropsch （F-T） synthesis is one of the most promising processes for coal and natural gas conversion to ultra-clean fuels at economically feasible cost. Supported cobalt catalysts are the preferred catalysts for the F-T synthesis of long-chain paraffins from natural gas because of its high activity, low water–gas shift activity, and relatively lower deactivation rate. SBA-15 is commonly used as the support material due to its high surface area,the hexagonal array of uniform tubular channel with pore diameters ranging from 5 to 30 nm, the thick pore walls and good hydrothermal stability.From a survey of the literatures, we found that there was little information focused on the effect of Ru promoter on the SBA-15 supported Co-based catalysts for FT synthesis. So the work focused on the effect of Ru promoter on the catalyst structure and its catalytic behavior on F-T synthesis for the Co/SBA-15 catalyst. A series of cobalt catalysts supported by SBA-15 with different Ru loading were prepared by incipient wetness impregnation method. X-ray diffraction （XRD）, Hydrogen Temperature programmed reduction （H₂-TPR）, Hydrogen temperature programmed desorption （H₂-TPD） and oxygen titration were used to characterize the catalysts. The adsorption and reaction properties of Co/SBA-15 catalysts were studied by in situ diffuses reflectance FTIR spectroscopy （DRIFTS） using CO and syngas as probe moleculars, and the reaction mechanism of CO hydrogenation on Co/SBA-15 catalysts with different Ru losding was also investigated by DRIFTS. The activity and selectivity for the F-T reaction were measured by using a fixed bed reactor under typical F-T synthesis conditions for cobalt catalysts （230℃and 10 bar）.Catalysis and characterization results showed that the Ru promoter influenced the structure, reducibility, and the F-T catalytic performance of SBA-15 supported cobalt catalysts strongly.（1） Ru acted as the soures of H₂ spill over process, it facilitated the reduction of cobalt oxide. It also improved the dispersion and increased the active numbers of the catalysts, and it reduced the interaction between cobalt and the support to inhance the reducibility（2） Catalysts with different Ru loading showed different catalytic properties. The catalytic reaction activity is enhanced with increasing Ru loading. The catalysts with 0.5%Ru loading displayed the highest F-T activity and highest C5+ selectivity inthe catalysts.（3） The results of DRIFTS at room temperature showed that the CO linear and bridge-type adsorption were occured on Co/SBA-15. In the presence of hydrogen, the hydrogen not only improved the CO adsorption, the catalysts also had more Co adsorption sites.（4） Catalysts with different Ru loading showed different CO adsorption properties. The linear and bridge-type CO adsorption changed significantly with increasing Ru loading. There are several types of adsorption sites on catalyst surface, but only the special adsorption sites could influence the activity.（5） The results of syngas TP-IR indicated that the C-O bond did not dissociate directly to form hydrocarbons on catalyst surface but via hydrocarbonyl. The hydrocarbonyl was intermediate species and could be observed from IR spectra during the catalytic reaction. With increasing temperatures, the peak of hydrocarbonyl shifted to low wavenumbers, indicating that the C-O bond became gradually weaker.更多还原