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[Display omitted] Synthetic strategies in the preparation of embedded structure, impregnated, and precipitated catalysts have an important effect on the Fe-SiO 2 interaction, morphology, and catalytic performance. • Sintering of iron species is effectively inhibited by SiO 2 shell in Fe@Si catalyst. • Fe-SiO 2 interaction can be manipulated by preparation strategies. • The properties and catalytic performance of Fe-Si FTS catalysts are governed by the configuration and Fe-SiO 2 interaction. The physico-chemical properties of SiO 2 -promoted Fe-based Fischer-Tropsch synthesis catalysts were traditionally considered to be governed by Fe-SiO 2 interaction. Here we found that the configuration between SiO 2 and iron species also played a pivotal role in determining the structure and thus FTS performance of the catalysts. Fe@Si catalyst with embedded structure, impregnated Fe/Si catalyst as well as precipitated Fe-Si catalyst was fabricated by different methods respectively, and they were thoroughly characterized by multiple techniques. The results indicated that, despite the weaker Fe-SiO 2 interaction, the construction of SiO 2 shell outside the iron species core in Fe@Si catalyst strongly inhibited the reduction of iron oxides due to the confining effect of SiO 2 shell, which increased the diffusion resistance of H 2 O generated in the reduction process. However, the sintering of iron species was effectively hindered even during FTS reaction by the physical separation of SiO 2 shell. In contrast, iron species in impregnated Fe/Si and precipitated Fe-Si catalyst experienced aggregation with different degrees. The reduction behavior of these two catalysts were well correlated with the strength of Fe-SiO 2 interaction. The FTS performance showed that both Fe@Si and Fe/Si catalyst exhibited higher initial activity but deactivated gradually, while the activity of Fe-Si catalyst displayed an opposite trend. These phenomena were discussed in terms of the variation of iron carbides content at different stages, which was determined not only by Fe-SiO 2 interaction, but also by the manner that SiO 2 and iron species constructed. The present study contributed a new understanding of the structure-performance relationship for SiO 2 -promoted Fe-based FTS catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Real space evidence of p4g(2 × 2) Fe 2 C and Co 2 C surface carbides. • Tip-sample distance dependent STM imaging of Fe 2 C. • Fe 2 X (X = B, C, N, O) with increasing electrons the reconstruction becomes less favourable. Thin FCC (1 0 0) iron and cobalt carbide films were prepared on Cu(1 0 0) to study the connection between their structure, electronic properties and stability. We present the first detailed, real space experimental confirmation of the C-induced clock reconstruction on the FCC(1 0 0) surfaces of iron and cobalt. Both Fe and Co surface carbides show p4g (2 × 2) surface reconstruction with tetracoordinated square planar carbon and pure FCC (1 0 0) metal layers underneath. Combining tip-sample distance dependent STM imaging with theoretical calculations we present different imaging modes of Fe 2 C. Using a combination of angle-resolved x-ray photoelectron spectroscopy (AR-XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and theoretical calculations we provide detailed electronic and structural models for Fe 2 C and Co 2 C p4g (2 × 2) surface carbides and other 2D Fe 2 X interstitial compound systems. In various Fe 2 X (X = B, C, N, O) surface compounds moving to the right in the periodic table with increasing electrons the reconstruction becomes less favorable, while iron carbide shows the highest stability. [ABSTRACT FROM AUTHOR]

Sn-containing Fe 5 C 2 interface not only can boost the rates of oxygen removal but also restrain the coke deposition by elevating the barrier of nucleation, which stabilizes the active iron carbide structure and enhanced the stability remarkablely. [Display omitted] • Oxygen removal by carbon oxide is facilitated for Fe-Sn interface； • Coking deposition was inhibited remarkably for Fe-Sn bimetallic catalysts; • Catalytic stability was significantly enhanced for Sn0.25 and Sn0.50 catalysts; • Provided a strategy to construct durable catalysts under the perspective of oxygen removal and coking resistance. Comprehending deactivation mechanisms and constructing durable Fe-based catalysts remain a substantial challenge for Fischer-Tropsch synthesis. In this contribution, the effects of Sn promoter on the structure and catalytic performance of Fe-based catalysts were investigated systematically. The catalytic stability was enhanced significantly for 100Fe/0.25Sn and 100Fe/0.50Sn catalysts, reducing the deactivation rate almost four-fold and seven-fold respectively. Combined with several characterizations and DFT calculation, it has been confirmed that Sn-containing Fe 5 C 2 interface not only can boost the rates of oxygen removal but also restrain the coke deposition by elevating the barrier of nucleation, which stabilizes the active iron carbide structure and inhibits the deactivation efficiently. This study may broaden the understanding of enhanced stability during Fe-based FTS under the perspective of oxygen removal and coking resistance and provide a strategy to construct durable catalysts. [ABSTRACT FROM AUTHOR]

A theoretical chemistry approach combining Wulff construction, density functional theory, and microkinetics enables revealing the nature of facet-dependent key elementary reactions on single-phase iron carbide at single particle level, complementary to current limited understanding of this issue in experimental exploration of iron-catalyzed Fischer-Tropsch Synthesis. • Intrinsic catalysis of a single-phase iron carbide particle in FTS was studied. • Neither too strong nor too weak H adsorption is favorable for CH 4 formation. • Coupling of two H-deficient hydrocarbon intermediates is more facile. • The surface (111) and (10 1 -) are kinetically more viable for C 2 formation. • CH 4 formation is kinetically more facile on surface (010), (110) and (11 1 -). Elucidation of intrinsic working principle of single-phase iron carbide and its facet-dependent catalytic behavior remains a substantial challenge in iron-catalyzed Fischer-Tropsch synthesis. Here, we provided in-depth understanding of the iron carbide phase-dependent and facet-dependent properties on theoretically established Fe 5 C 2 particle model through an approach combining Wulff construction, density functional theory, and microkinetics. We studied two key probe reactions, C 2 formation via C 1 +C 1 coupling and CH 4 formation, by monitoring surface-dependent thermodynamics and microkinetics. Integration of results thereby allows us to assess the macroscopic catalytic properties at single particle level and evaluate contribution from individual exposed surface. The surface (111) and (10 1 -) are kinetically more viable for C 2 formation, whereas CH 4 formation is kinetically more facile on surface (010), (110) and (11 1 -). This study enriches the knowledge of the intrinsic working mechanism for single-phase iron carbide and provides fundamental insights into rational design of improved iron-based Fischer-Tropsch synthesis catalysts. [ABSTRACT FROM AUTHOR]