Preparation Of Co/SiO₂Catalysts And Their Performances For Fischer-tropsch Synthesis

The abundant reserves of coal in our country have made it possible to developthe technology of the synthesis of liquid fuels based on Fischer-Tropsch synthesiswith syngas, which can effectively decrease the dependency on petroleum. The maincatalysts used in the industry for Fischer-Tropsch synthesis were iron-based catalystsand cobalt-based catalysts. The cobalt metal is the more active metal compared withthe iron metal for the hydrogenation of carbon monoxide. The traditional cobalt-basedcatalysts used in Fischer-Tropsch synthesis are supported catalysts (such as Co/SiO2,Co/Al2O3and so on). As the cobalt metals dispersed on the surface of the supports,the active component would be easy to grow because of migration and aggregation.Catalyst deactivation due to sintering is a major problem of the traditional supportedcobalt-based catalyst.In this paper, we prepared the size-controlled TTAB-capped Co3O4nanoparticleswith different chemical properties by using different facile methods. The TTABsurfactants were used to stabilize the Co3O4cubes and also used as structure-directingtemplates for the polymerization of silicates around the surface of Co3O4nanopariclesusing a sol-gel process. We prepared the Co3O4nanoparticles coated with amesoporous silica shell catalyst (Co3O4/SiO2) by using modified sol-gel process. Bymodulating the factors of template agent and solvents (water or alcohol), we preparedthe Co3O4/SiO2material with a mosaic structure. In addition, we prepared a novelregular hexagonal prism structure bilayer model catalyst with a double-channelstructure that consists of a Co3O4oxide metal core coated with a porous silica shell(Co3O4/SiO2) which exhibited an average particle size around2μm in diagonaldistance.Our results showed that the H2-TPR profiles of the novel serial classes ofCo3O4/SiO2catalysts made by modified sol-gel process had a lower reduction degreecompared to the traditional Co/SiO2catalyst made by impregnation method, whichindicated a higher strength of interaction between the Co3O4core and SiO2shellcompared to the traditional SiO2catalyst. In addition, we found that the bilayer modelcatalyst with regular hexagonal prism structure had a higher reduction degreecompared to the typical Co3O4/SiO2core shell catalyst, which indicated that the double-channel structure increased the reduction degree. Because the mass scale ofthe core shell Co3O4/SiO2material prepared is too small, it is not enough to makethem as catalysts used for Fischer-Tropsch synthesis.The catalytic properties of the cobalt and silica based mosaic structure catalystswith different loadings in Fischer-Tropsch Synthesis were evaluated in a fixed-bedreactor. Our results showed that the CO conversion of the mosaic structure FTScatalyst was improved13%compared to the traditional catalyst. Our results showedthat the mosaic structure FTS catalyst exhibited a narrow product distributioncompared to the traditional catalyst. The C5-C11selectivity and C12+selectivity of thetraditional catalyst were8.6%and84.0%respectively when the Co loading was20wt.%. The C5-C11selectivity and C12+selectivity of the mosaic catalyst were18.1%and72.6%respectively when the Co loading was20wt.%. The C5-C11selectivity andC12+selectivity of the mosaic catalyst were40.7%and49.9%respectively when theCo loading was50wt.%. In addition, the CH4selectivity of the mosaic catalyst waslower than8%.This is due to the spatial confinement effect and molecule shapeselectivity of the tailor-made encapsulated catalyst.