Preparation And Characterization Of Highly Dispersed Co-based Fischer-Tropsch Synthesis Catalysts

The supported cobalt is one of important Fischer-Tropsch synthesis （FTS） catalysts, its catalytic activities and selectivities (i.e. CH₄%, C₅₊%) are strongly depended on the metallic Co sites dispersions and densities. How to prepare highly dispersed and reduced Co-based catalysts is a hot topic for FTS Co-based catalysts currently.We reported here to prepare highly dispersed and reduced Co-based catalysts by using unmodified and cheap SiO₂ as support. This allows to breaking of the dispersion-reducibility dependence inherent to small cobalt particle supported on oxidic carriers, and improving Co utilization efficiency and decreasing catalyst cost.Using inorganic salt as raw material （Ru as promoter）, these highly dispersed Co-based catalysts could be prepared successfully by dispersing of polymer-metallic ion clusters, pre-formed in aqueous solution containing organic solvent and polymer, on a SiO₂ support. The impacting factors on catalysts dispersions and reducibilities had been systematically studied. Our conclusions were reported as followings:（1） The addition of polymer with low molecular weight （amu.≤400） led to highly dispersed Co clusters (D_Co<10nm) on unmodified SiO₂. Trace Ru promoter （Ru/Co=0.07） was essential to improve catalysts reducibilities.（2） The addition of same type of polymer with high molecular weight （amu.≥1000） resulted in unexpected large Co clusters (D_Co>10nm). However, they demonstrated good reducibilities at lower temperature. Also, the reduction behaviors of these catalysts resembled to that of unsupported Co₃O₄, indicating the weak interaction between support and cobalt oxide.（3） According to FT-IR and TEM results, it appeared that metallic ions (Co^m+, Ruⁿ⁺) did not convert to metallic particles in solution. We proposed that they may adsorb on polymer chain to form polymer-metallic ion clusters.（4） Compared with coventional impregnation method, the presence of polymer in current preparation not only prevented paticles agglomeration and sinter, leading to highly dispersed metal oxides clusters on support, but also avoid the blocking of pore channels in support during calcination. This improved effective surface area of catalysts.The successful preparation of highly dispersed and reduced Co-based catalysts on unmodified SiO₂ offers an effective way to improve Co utilization efficiency and fundamental understand the strong interaction between metal oxide and oxidic support. Therefore, this study provides valuable data for preparing FTS Co-based catalysts with better performance.