Studies On Ruthenium And Cobalt Supported On The Ordered Mesoporous Carbon Material For Application In Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) technology for the production of liquid fuels by natural gas, coal, and biomass has received extensive attention. Although iron and cobalt are the more common metals for FTS, Ru catalysts possess higher intrinsic activity and produce higher molecular weight hydrocarbons. Thus, Ru catalysts are usually utilized as the model catalysts for the development of promising novel FTS catalysts. In order to eliminate the metal-support interaction when investigating the effect of the pore structure of the support and the active metal phase on the catalytic properties of a catalyst for FTS, the carbon materials are widely utilized, owing to the inertness, unique structure, high surface area, and physicochemical property.In this work, ordered mesoporous carbons with different pore sizes have been synthesized using SBA-15 as a hard template. Ruthenium nanoparticles were embedded on the carbon walls of the ordered mesoporous carbon material. Characterization technologies including power X-ray diffraction (XRD), nitrogen adsorption-desorption, and transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H2-TPR), hydrogen temperature programmed desorption (H2-TPD) were used to scrutinize the catalysts. The catalyst activity for FTS was measured in a fixed bed reactor. The effect of supports, pore sizes, and prepared methods for catalysts on the structure and FTS performance of the catalysts have been investigated. The main results are as follows:1. The Ru-OMC catalyst exhibited highly ordered mesoporous structure and large surface area, indistinguishable with those of the OMC material. Furthermore, the embedded Ru-OMC catalyst displayed much better FTS performance than the Ru/OMC catalyst which was prepared with conventional impregnation approach. It may be that the Ru-C interaction could prevent Ru nanoparticles from aggregation. In addition, the formation of some kind of electron-deficient sheets on the interfacial contact might impede the oxidation of Ru particles, and help the transfer of the spilled-over hydrogen which in turn stimulates the hydrogen disassociation on the Ru active sites. However, the methane selectivity of the Ru-OMC catalyst is relatively high. This occurrence appears to be rational if the hydrogen disassociation does is improved on Ru-OMC due to the existence of electron deficient sheets which is not the case with Ru/OMC. Then the higher H2/CO ratio in the pore channels of Ru-OMC catalyst should boost both overall FTS activity and methane selectivity. 2. Ru nanoparticles embedded on the walls of the ordered mesoporous carbon materials with different pore sizes were prepared and investigated as catalysts for the FTS. All the catalysts have retained the ordered mesostructure of OMC. Compared to the catalysts with smaller pores, the catalysts with larger pores led to larger Ru nanoparticle sizes. The catalytic activity and C5+ selectivity were found to increase with increasing pore size, but the methane selectivity showed opposite trend. It is considered that the activity and hydrocarbon selectivity depend more on the effect of the pore size than the Ru particle size. These changes may be explained in terms of the special environment of the active sites and diffusion of the products in the pores of the catalysts.3. Co catalysts supported on SBA-15, C-SBA-15, and OMC were prepared by incipient wetness impregnation. The doping of carbon impacted catalytic performance. The catalyst with the carbon-doped SBA-15 was more easily reducible and improved the dispersion of the metal cobalt, resulting in higher FTS activity and higher C5+ selectivity. However, for the Co/OMC catalyst, the lowest FTS activity might develop from that the cobalt oxides formed are too small due to OMC with high surface area and rich porous structures, and thus being subject to more rapid aggregation and deactivation during the reaction. In addition, a portion of cobalt oxides within the pore size are more difficult reducible, resulting in a decrease in catalytic activity.