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

Abstract

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 N 2 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 H 2 temperature-programmed reduction (H 2 -TPR). The H 2 -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 C 5-11 and C 12-18 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.

Preparation and Characterization of Hierarchical Pore Molecular Sieve with Large Pore Size

“…Those drawbacks of mesoporous molecular sieve and microporous zeolite limit their applications, especially in Fischer-Tropsch (F-T) synthesis. Hierarchical porous molecular sieve (HPMS) has proper meso/micropore size distribution and high hydrothermal stability, and could overcome the drawbacks of mesoporous molecular sieve and microporous zeolite [1][2][3]. Hence, it is an important approach to control the F-T synthesis product distribution via suitable catalyst using HPMS as a support.…”