Pore size-controlled synthesis of molecular sieves and theirs difference in catalytic properties for Fischer–Tropsch synthesis

Three molecular sieves with different pore size distributions, i.e., mesopore (Al-MCM-41), micropore (ZSM-5) and hierarchical pore (HPMS), were synthesized under hydrothermal condition and characterized by N2 adsorption–desorption. Three cobalt-loaded catalysts, i.e., Co/Al-MCM-41, Co/ZSM-5 and Co/HPMS, were prepared by impregnating cobalt nitrate onto three molecular sieves, respectively, and characterized by X-ray diffraction, scanning electron microscopy, and H2 temperature-programmed reduction (H2-TPR). The H2-TPR results show that the reduction temperature of Co/HPMS is lower than those of Co/Al-MCM-41 and Co/ZSM-5, indicating that Co/HPMS has a better catalytic activity. The selectivity of three catalysts for Fischer–Tropsch synthesis was evaluated in a fixed-bed reactor, and the results show that the pore structure is of important influence on the product distribution. Co/HPMS exhibits significantly good selectivity of C5–11 and C12–18 hydrocarbons (up to 25.6 and 27.7 %, respectively), much higher than those of Co/Al-MCM-41 and Co/ZSM-5, due to the confinement effect of micropore and good diffusibility for long-chain hydrocarbons of mesopore in Co/HPMS.