Effect of strain on the performance of iron-based catalyst in Fischer-Tropsch synthesis Yingying Xue a,b , Hui Ge a , Zheng Chen a,b , Yongbiao Zhai c , Juan Zhang a , Jiaqiang Sun a , Mohamed Abbas a,d , Ke Lin e , Wentao Zhao e , Jiangang Chen a,⇑ a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China b University of Chinese Academy of Sciences, Beijing 100049, China c College of Electronic Science and Technology, Shenzhen University, Shenzhen 518060, China d Ceramics Department, National Research Centre, El Bohouth Str, 12622 Cairo, Egypt e San Ju Environment Company, Beijing 100080, China article info Article history: Received 19 September 2017 Revised 27 November 2017 Accepted 17 December 2017 Keywords: Strain FTS d-Band DFT calculations abstract The role of strain on metal catalysis has been widely investigated by theoretical calculations. It is hard to prove by direct experimental strategies. In this work, we show how the strain can be adjusted experimen- tally to modulate Fischer-Tropsch synthesis (FTS) activity. The strain value is derived from the X-ray diffraction (XRD) line broadening method. The d-band occupancy (n d ) is calculated semi-quantitatively by magnetic characterization on a vibrating sample magnetometer (VSM). A volcano curve is correlated between strain and FTS activity. The combination of physical property such as mechanics, magnetization, hardness and density functional theory (DFT) calculations is proposed to elucidate a general strain induced reactivity behavior. Such a strain dependent behavior is related to the variation in d-band elec- tronic property of the metal. Ó 2018 Elsevier Inc. All rights reserved. 1. Introduction The role of strain in tuning metal surface catalysis has devel- oped rapidly over the past decade [1–7], including hydrogenolysis reaction, oxygen reduction reaction, methanol synthesis and methanation reaction. Three fundamental factors have been iden- tified in theoretical literatures as playing a crucial role in strain mediated surface chemistry: band coupling [8], mechanical work [9,10] and surface tension mediated charge effects [11,12]. Strain induced variations in the d-band structure influence adsorbate- metal bonding state through the adsorbate valence orbital with metal d orbital band coupling. The coupling of the applied stress field to the adsorbate-induced relaxation (a strain field) brings about a distinct mechanical work term. Moreover, the strain induced shifts in the electrode potential or adsorption enthalpy mediated by the surface tension affect the energy of charged spe- cies, most readily demonstrated in electrochemistry [11,13]. Gen- erally, strain in metal can be introduced by ball-milling [14], doping [15–17], alloying [18–20], adding template agent [6,21], exerting high pressure [22] and ion sputtering [2]. These methods modify the structure through a combination of plastic deformation and elastic strain. The elastic strain emerges along with applied external forces. The plastic deformation is manifested in lattice defect, such as dislocations and magnetostriction. This type of strain is often called residual strain (the strain remaining in a body after the additional stress has been removed, and the retained portion is as strain associated with dislocations). Dislocations emit at a surface where they present step-like structures. These steps are preferential adsorption sites on a catalyst for the adsorbed molecular species [23,24]. In fact, the correlation between strain and the adsorption energy on various metals has been confirmed by density functional (DFT) calculations. To gain insight into the theory by experimental strategies, researchers have investigated the strain effect on single crystal [1] or metal catalysts [25]. Nevertheless, the single crystal model deviates from the real catalysis environment. Other researchers have involved the conventional supported metal catalysts, which introduce the strain indirectly, and also contain complex factors, such as strong metal-support interaction (SMSI), dispersion, poros- ity and particle size effect. Curtin and Francis [10] reported the possibility of using strain as a tool to achieve continuous control over methanation reactivity over Ni, Ni 3 Fe, NiFe catalysts. The experimental work performed by Fernandez et al. involved strain-enhanced activity for Ni-based ethane hydrogenolysis https://doi.org/10.1016/j.jcat.2017.12.017 0021-9517/Ó 2018 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: #27 Taoyuan South Road, Yingze District, Taiyuan 030001, China. E-mail address: chenjg@sxicc.ac.cn (J. Chen). Journal of Catalysis 358 (2018) 237–242 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat