Effects of Drying Conditions on the Synthesis of Co/SiO2 and Co/Al2O3 Fischer–Tropsch Catalysts

Abstract

The nanoscale distribution of the supported metal phase is an important property for highly active, selective, and stable catalysts. Here, the nanoscale redistribution and aggregate formation of cobalt nitrate during the synthesis of supported cobalt catalysts were studied. Drying over a range of temperatures in stagnant air resulted in cobalt particles (8 nm) present in large aggregates (30–150 nm). However, drying in a N2 flow resulted in cobalt nanoparticles distributed either in aggregates or uniformly on various SiO2 and γ-Al2O3 supports, critically dependent on the drying temperature. The mechanism of aggregation was studied through chemical immobilization of the precursor on a silica support after drying in a N2 flow. The aggregation behavior upon drying in a gas flow at temperatures below 100 °C showed a remarkable similarity to distributions obtained upon the dewetting of colloidal films, suggesting a physical process. Alternatively, by inducing decomposition of the cobalt nitrate above 100 °C be...