A DFT study towards dynamic structures of iron and iron carbide and their effects on the activity of the Fischer-Tropsch process

Qiang Yin; Hanqing Wang; Jinping Zhao; Chengjun Li; Yu Mao

doi:10.1039/d3ra06467k

A DFT study towards dynamic structures of iron and iron carbide and their effects on the activity of the Fischer-Tropsch process

RSC Adv. 2023 Nov 22;13(48):34262-34272. doi: 10.1039/d3ra06467k. eCollection 2023 Nov 16.

Authors

Qiang Yin^{1

2}, Hanqing Wang^{3

2}, Jinping Zhao³, Chengjun Li³, Yu Mao⁴

Affiliations

¹ Department of Forestry Engineering, School of Materials Science and Engineering, Central South University of Forestry & Technology Changsha China.
² Hunan Engineering Research Centre of Full Life-cycle Energy-efficient Buildings and Environmental Health, Central South University of Forestry and Technology Changsha Hunan China.
³ School of Civil Engineering, Central South University of Forestry & Technology Changsha China hqwang@csuft.edu.cn.
⁴ School of Chemical Sciences, University of Auckland Auckland 1010 New Zealand yu.mao@auckland.ac.nz.

Abstract

The Fe-based Fischer-Tropsch synthesis (FTS) catalyst shows a rich phase chemistry under pre-treatment and FTS conditions. The exact structural composition of the active site, whether iron or iron carbide (FeC_x), is still controversial. Aiming to obtain an insight into the active sites and their role in affecting FTS activity, the swarm intelligence algorithm is implemented to search for the most stable Fe(100), Fe(110), Fe(210) surfaces with different carbon ratios. Then, ab initio atomistic thermodynamics and Wulffman construction were employed to evaluate the stability of these surfaces at different chemical potentials of carbon. Their FTS reactivity and selectivity were later assessed by semi-quantitative micro-kinetic equations. The results show that stability, reactivity, and selectivity of the iron are all affected by the carbonization process when the carbon ratio increases. Formation of the carbide, a rather natural process under experimental conditions, would moderately increase the turnover frequency (TOF), but both iron and iron carbide are active to the reaction.