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147 results on '"Huo, Chun-Fang"'

35. Hunting the Correlation between Fe5C2Surfaces and Their Activities on CO: The Descriptor of Bond Valence

Author

He, Yurong, Zhao, Peng, Meng, Yu, Guo, Wenping, Yang, Yong, Li, Yong-Wang, Huo, Chun-Fang, and Wen, Xiao-Dong

Abstract

To hunt the correlation between the surfaces of Fe5C2and their corresponding activities, the CO adsorption and dissociation on a series of both low ((010), (001), (110), (111), (111̅)) and high Miller index surfaces of Fe5C2((221), (4̅11), and (510)) surfaces are systemically investigated. For the CO adsorption, configurations with bonding to surface Fe sites are much stronger than that on C sites. For the CO dissociation, direct C–O cleavage can take place on the (221), (510), (010), and (111̅) surfaces due to the low activation energy. More importantly, to correlate the surface character and the activity of CO dissociation we proposed a concept of sum bond valence. It is found that the adsorbed CO with more bond valence can dissociate easier, and a linear relationship between the activation energies and the CO bond valence can be established. It can be inferred that the activity of Fe5C2surfaces for CO dissociation strongly relies on the binding characteristics. The relatively stable (100) and (111) surfaces are not active for direct CO dissociation. In this work, the CO bond valence is suggested to be an important descriptor to correlate complicated surfaces and their activities. Furthermore, such a finding can guide the rational design of catalysts with desired activities.

Published
2024
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36. Iron Carbides in Fischer–Tropsch Synthesis: Theoretical and Experimental Understanding in Epsilon-Iron Carbide Phase Assignment

Author

Liu, Xing-Wu, Cao, Zhi, Zhao, Shu, Gao, Rui, Meng, Yu, Zhu, Jian-Xin, Rogers, Cameron, Huo, Chun-Fang, Yang, Yong, Li, Yong-Wang, and Wen, Xiao-Dong

Abstract

As active phases in low-temperature Fischer–Tropsch synthesis for liquid fuel production, epsilon iron carbides are critically important industrial materials. However, the precise atomic structure of epsilon iron carbides remains unclear, leading to a half-century of debate on the phase assignment of the ε-Fe2C and ε′-Fe2.2C. Here, we resolve this decades-long question by a combined theoretical and experimental investigation to assign the phases unambiguously. First, we have investigated the equilibrium structures and thermal stabilities of ε-FexC (x= 1, 2, 2.2, 3, 4, 6, 8) by first-principles calculations. We have also acquired X-ray diffraction patterns and Mössbauer spectra for these epsilon iron carbides and compared them with the simulated results. These analyses indicate that the unit cell of ε-Fe2C contains only one type of chemical environment for Fe atoms, while ε′-Fe2.2C has six sets of chemically distinct Fe atoms.

Published
2024
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37. When Density Functional Approximations Meet Iron Oxides

Author

Meng, Yu, primary, Liu, Xing-Wu, additional, Huo, Chun-Fang, additional, Guo, Wen-Ping, additional, Cao, Dong-Bo, additional, Peng, Qing, additional, Dearden, Albert, additional, Gonze, Xavier, additional, Yang, Yong, additional, Wang, Jianguo, additional, Jiao, Haijun, additional, Li, Yongwang, additional, and Wen, Xiao-Dong, additional

Published
2016
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40. Suppression by Pt of CO adsorption and dissociation and methane formation on Fe5C2(100) surfaces.

Author

He, Yurong, Zhao, Peng, Liu, Jinjia, Guo, Wenping, Yang, Yong, Li, Yong-Wang, Huo, Chun-Fang, and Wen, Xiao-Dong

Abstract

To understand the chemical origin of platinum promotion effects on iron based Fischer–Tropsch synthesis catalysts, the effects of Pt on CO adsorption and dissociation as well as surface carbon hydrogenation on the Fe5C2(100) facet with different surface C* contents have been studied using the spin-polarized density functional theory method. CO dissociation initiating from diverse sites was calculated through both direct and H-assisted pathways via the CHO intermediate. On the perfect (100) surface, CO can hardly dissociate, and the surface carbon can be facially hydrogenated to CH4. On the C*-defect and C*-free (100) surfaces, CO can strongly adsorb on the C* vacant sites and direct dissociation is favored to occur. The activity is higher with the decrease of the surface carbon content. When platinum atoms are added on the surfaces, the C*-vacancies have a higher activity for CO dissociation than the new sites generated by Pt adsorption. However, both the CO dissociation and the surface carbon consumption through CH4 formation are hindered. The evolution of surface carbon is predicted to be suppressed by the addition of Pt on the Fe5C2(100) surface. [ABSTRACT FROM AUTHOR]

Published
2018
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42. CO Direct versus H-Assisted Dissociation on Hydrogen Coadsorbed χ-Fe5C2Fischer–Tropsch Catalysts

Author

He, Yurong, Zhao, Peng, Yin, Junqing, Guo, Wenping, Yang, Yong, Li, Yong-Wang, Huo, Chun-Fang, and Wen, Xiao-Dong

Abstract

The CO activation mechanism on the χ-Fe5C2Fischer–Tropsch synthesis catalysts is studied by spin-polarized density functional theory calculations. A series of low ((100), (010), (001), (110), (111), and (111̅)) and high ((221), (4̅11), and (510)) Miller index surfaces are intensively investigated. Both the direct and H-assisted pathways through HCO, COH, HCOH, and CH2O intermediates are systematically examined on the hydrogen coadsorbed surfaces. Different activity and activation mechanisms are determined on the various surfaces as well as the varying sites. It is found that the high-index Fe5C2(510) and the relatively unstable (010) and (221) surfaces are active for direct CO dissociation due to the existence of the highly activated sites. H-assisted dissociation pathways are preferred on the Fe5C2(010), (110), (4̅11), (111̅), and (111) surfaces with the moderate stability. On the relatively stable (100) surface, CO dissociation can hardly take place. Such discrimination for the activity and the CO activation mechanisms on various Fe5C2facets might guide the rational design of catalysts with desired activities.

Published
2018
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