Filter and buffer-pot confinement effect of hollow sphere catalyst for promoted activity and enhanced selectivity

Abstract

To efficiently utilize the catalyst active sites and simultaneously enhance target hydrocarbon selectivity in Fischer–Tropsch synthesis (FTS), herein, we demonstrate a promising Co–Al₂O₃ hollow-sphere catalyst prepared by a two-pot route including hydrothermal carbonization and wet impregnation. Benefiting by plentiful mesopores on the shell, reactants could access the cavity inside and the active sites on the inner surface for further FTS reaction. Compared with conventional solid catalyst, the hollow structure provided a “buffer-pot” effect, where feed gas and preliminary product from the shell could mix completely at a low flow rate. Heavy hydrocarbons were further confined, leading to enhanced formation of lighter C₅–C₁₁ components, which more readily escaped out through the mesoporous shell, which thus played a “filter” role. Additionally, increased acidity on the shell generated more iso-paraffins and olefins in the final product. This concept displayed a great superiority in improving active metal activity and selective production from multiple products compared with conventional supported catalysts.