Studies On The Structure And Catalytic Performance Of The Ru Promoted Cobalt Based Fischer-Tropsch Synthesis Catalysts

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.