| Fischer-Tropsch synthesis (FTS) is an important route to catalytically convert syngas (CO and H2) to clean fuels. For the development of Fischer-Tropsch catalysts, one of the most important goals is to develop the cobalt catalyst with high FTS reaction activity and high long chain hydrobarbon selectivity. In the present work, SNT was synthesized using CNT as a template, and used as a support to prepare cobalt and ruthenium catalysts.All cobalt catalysts were prepared by incipient wetness impregnation.All ruthenium catalysts were prepared by slurry impregnation. The catalysts were characterized using different techniques such as N2 physisorption measurement, X-ray diffraction (XRD), transmission electron microscopy(TEM), temperature-progra -mmed reduction (H2-TPR). The catalyst activity and selectivity were evaluated in a fixed-bed reactor under typical hydrocarbon synthesis conditions. The main results are as follows:1. For Ru/SNT catalysts, silica nanotube (SNT) was synthesized by using the carbon nanotube (CNT) as a template, the catalysts were prepared by slurry impregnation. Ruthenium particles were found to disperse mainly inside the nanotubes. The Ru/SNT catalyst had a good catalytic activity, while Ru/SiO2 catalyst showed a poor catalytic activity due to large Ru particles and the poor dispersion. The larger Ru particles are more selective for heavier hydrocarbons for F-T synthesis.2. Silica coated carbon nanotubes (SNT-CNT) and SNT were used to load cobalt catalyst in Fischer-Tropsch synthesis (FTS). The catalysts were also prepared by incipient wetness impregnation. The Co/SNT catalyst showed the best catalytic performance because of high degree of reduction. Co/SNT-CNT catalyst had a poor catalytic performance, which was attributed to the low BET specific surface area of SNT-CNT, the large cobalt particle and poor dispersion. The high CH4 selectivity of Co/CNT might be due to the small cobalt particle size as well as the ease of gasification of the carbon to produce CH4 under the hydrogen atmosphere.3. SiO2,SBA-15 and SNT were used as supports to prepare cobalt catalysts FTS. The catalysts were prepared by incipient wetness impregnation. The three catalysts in F-T synthesis showed the similar activity for FTS, but the selectivity was different. The Co/SNT catalyst showed the high C5+ selectivity and low CH4 selectivity. The cobalt particle size in Co/SNT is the largest among those catalysts, so the higher C5+ selectivity is thus expected. The Co/SiO2 catalyst showed the high CH4 selectivity, due to the unreduced cobalt oxides which can catalyze the WGS reaction, resulting in an increasing in H2/CO ratio on the catalyst surface. This led to both an increase in methane selectivity and CO2 selectivity. |
