Acta Phys. -Chim. Sin. ›› 2005, Vol. 21 ›› Issue (11): 1223-1228.doi: 10.3866/PKU.WHXB20051106

• ARTICLE • Previous Articles     Next Articles

UBI-QEP Analysis for the Mechanism of Fischer-Tropsch Synthesis

CHANG Jie; TENG Bo-tao; XIANG Hong-wei; LI Yong-wang; SUN Yu-han   

  1. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001; Graduate School of the Chinese Academy of Sciences, Beijing 100049
  • Received:2005-03-22 Revised:2005-05-16 Published:2005-11-15
  • Contact: XIANG Hon-gwei

Abstract: The unity bond index-quadratic exponential potential (UBI-QEP) model is used to evaluate the heat of chemisorption of adsorbed species and activation barriers for the elementary reactions in the mechanisms for Fischer-Tropsch synthesis (FTS) reaction over a model catalyst Co(0001), including carbide mechanism, hydroxycarbene mechanism, and CO insertion mechanism. It is demonstrated that the reaction pathway for the formation of hydrocarbons proposed in the carbide mechanism is energetically favorable. The insertion of CO is the pathway for the formation of oxygenations. Dissociation of adsorbed CO and hydrogenation of Cads have higher activation barriers than other elementary steps in the reaction pathway. The energetically preferred pathway to initiate the carbon chain growth is via insertion of CH2, ads intermediate into the carbon-metal bond of CH3, ads or CH2, ads group. The activation barrier for termination of carbon chain propagation by β-H elimination is lower than hydrogenation. The olefins and oxygenates in the primary products during FTS are apt to conduct the secondary reaction via readsorption on the catalyst surface because of its low active energies. Compared with Fe/W(110), the activation barriers for CHx, ads hydrogenations and CH2, ads insertion are lower on Co(0001), which results in higher selectivity of methane and more yield of heavy hydrocarbons.

Key words: Fischer-Tropsch synthesis, Co(0001) single crystal surface, UBI-QEP model, Reaction mechanism