Structure and catalytic performance of cobalt Fischer Tropsch catalysts supported by periodic mesoporous silicas

Abstract

The structure of cobalt catalysts supported by periodic mesoporous silicas at different stages of preparation was characterized by XRD, N 2 adsorption, XPS, in situ X-ray absorption and TGA. It was shown that the size and reducibility of supported cobalt particles were strongly affected by porous structure; larger and more easily reducible particles being detected in wider pore silicas. Cobalt dispersion was found to be controlled by silica pore sizes even at high cobalt contents (up to 30 wt.%) It was shown that catalytic behavior of cobalt supported mesoporous silicas in Fischer Tropsch synthesis strongly depended on cobalt dispersion and catalyst porous structure. Wide pore SBA-15 supported Co catalysts were found to be much (about 5–10 times) more active than narrow pore MCM-41 supported catalysts with the same cobalt content. Product distribution was found to be a function of cobalt particle sizes and cobalt reducibility. Fischer Tropsch reaction rates increased monotonically with increase in cobalt content up to 30 wt %, whereas product distributions for completely reduced wide pore catalysts were nearly the same at high and low cobalt loadings.