By using operando Raman spectroscopy (ORS), we investigated the panoramic structure evolution of an iron oxide (a-Fe 2 O 3 ) catalyst, which is used for the production of olefins via Fischer-Tropsch (FTO). During activation in different atmospheres and reaction at 260 8C and 3.0 MPa, a-Fe 2 O 3 was only partially transformed into g-Fe 2 O 3 by H 2 pretreatment; meanwhile, a transformation of a-Fe 2 O 3 !g-Fe 2 O 3 !Fe 3 O 4 !Fe 5 C 2 was observed in both CO and syngas (H 2 /CO). Combining with other techniques such as XRD, TEM, XPS and TPSR, we reveal that assembles of various iron oxides (g-Fe 2 O 3 , Fe 3 O 4 , Fe carbide, and their combinations) are responsible for FTO. Especially, the preliminary relationship of catalyst structure and performance relating to the production of olefins directly from syngas was established. Such a study is critical for further understanding of the FTO reaction and other catalytic reactions.The iron-based Fischer-Tropsch synthesis (FTS) is a key platform for synthesizing liquid fuels or other value-added chemicals. [1][2][3] The structure evolution of iron catalysts for FTS has been studied by both academia and industry for almost 100 years. [4] It is well known that several phases (iron carbides, metallic iron, and magnetite) are produced during the reaction, and all of them have been suggested to be active for FTS. [5] On the other hand, the complexity of "real world" catalysts often precludes a detailed knowledge of the evolution of their microscopic structures and a related reaction mechanism because of the limitation of instruments.Owing to the development of surface-sensitive techniques and high-performance computers in last decades, the "operando" techniques [6][7][8][9] for the simultaneous determination of the dynamic structure of working catalysts in FTS and the catalytic performance has been developed. [10][11][12][13] A great effort (see the Supporting Information, Table S1) has been contributed to the study of the iron-based FTS using in situ or operando techniques, such as XAS, [10,14,15] IR, [16] MES, [12] XRD, [17][18][19][20] XPS [21] and STXM, [22] Raman, [23] and so on. Up to date, to the best of our knowledge, the structure evolution of iron oxide catalysts op-erating under industrial conditions (high pressure, high temperature) is rarely reported. [24] Operando Raman spectroscopy (ORS) has proven to be a powerful approach by operating over a broad temperature range 25-1000 8C and pressure range 0.1-10.0 MPa. It is even sensitive to a tiny modification of the structure that results from heat-and/or reaction-induced roughening on catalysts, while the Raman signal is less affected by the presence of H 2 O and other gases. [25][26][27] However, most of the hitherto successful applications of this technique are concentrated on several relative simple or moderate (e.g., ambient pressure) reactions, such as propane ammoxidation, [28] propane oxidative dehydrogenation, [29,30] and CO oxidation. [31] For complex reactions under harsh conditions such as FTS, ORS has be...
Density functional theory (DFT) calculations were used to study C2 oxygenate from syngas over bimetallic Co/Cu catalysts. The thermodynamics and kinetics for all possible elementary steps involved in the formation of C2 oxygenate from syngas have been investigated on both pure and Cu-doped Co(0001) surfaces. By comparing the results on two surfaces, the role of copper in improving the selectivity toward C2 oxygenates has been identified as two aspects: (1) controlling the Co ensemble size and blocking the active sites for C–O bond cleavage, which results in inhibition of CH x coupling to hydrocarbons; (2) providing undissociated CO/HCO as well as reducing the barriers for HCO insertion toward the formation of oxygenate precursors. With the combination of the mechanistic study and the charge analysis on the bimetallic surface, we conclude that the nature of the copper promotion is mainly a geometric effect rather than an electronic effect.
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