Potassium promotion on CO hydrogenation on the χ-Fe 5 C 2 (111) surface with carbon vacancy

Zhao, Shu; Liu, Xing-Wu; Huo, Chun‐Fang; Li, Yongwang; Wang, Jianguo; Jiao, Haijun

doi:10.1016/j.apcata.2017.01.012

Cited by 16 publications

(10 citation statements)

References 47 publications

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“…Ojeda et al found that further hydrogenation of CHO over Fe(110) and Co(0001) surfaces form CH via CHO + H → CHOH → CH + OH, which agrees with the results obtained by Ozbek et al over C-vacant χ-Fe 5 C 2 (001). Additionally, Zhao et al found that CH x species are formed via CH x OH dissociation over K 2 O-doped χ-Fe 5 C 2 (111). Wang et al. − showed that CO activation prefers to form CH 2 via CHO + H → CH 2 O → CH 2 + O over the Cu(110), Cu(111) and Rh-/Co-monolayer modified Cu(111) surfaces.…”

Section: Resultsmentioning

confidence: 99%

Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis

et al. 2020

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This research is designed to fundamentally understand CO activation acting as a crucial step in the initiation of the Fischer–Tropsch (FT) process over Co2C catalyst, the intrinsic activity, and structural sensitivity of the catalyst, which is vital to its FT performance, but remains unclear. Accordingly, CO activation over the commonly exposed Co2C(101), (011), (010), (110), and (111) facets is investigated using density functional theory (DFT) calculations and microkinetic modeling. Results show that the CH monomer is the most abundant surface CH x species for CO activation over five Co2C facets, and the mechanism of CO activation and subsequent CH formation strongly depend on the Co2C facet. The formation rate of the CH monomer follows the order of (111) < (010) < (110) < (101) < (011). The (011) facet accounting for 35.21% of the surface is the most active for CO direct dissociation into C, followed by C hydrogenation to CH, which presents a comparable activity with the hexagonal close-packed (HCP) Co due to the presence of denser B5-type active sites. Further, Co2C is a multifunctional catalyst for the FT process because its facets exhibit a different catalytic activity toward CO dissociation to form the key CH monomer, and as a result, C2+ hydrocarbons and oxygenates can be formed depending on the relative reaction rate between CO insertion into CH x reaction and CH x –CH x coupling. The finding of this research may lead a new avenue for rational design of Co2C-based catalysts with desirable activities and product selectivity.

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Section: Resultsmentioning

confidence: 99%

Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis

et al. 2020

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“…Water dissociation is selected as a probe reaction for exploring the effects of promoters on catalytic performance due to their simplicity and necessity in surface reactions such as the water gas shift reactions, Fischer–Tropsch synthesis, and reactions in fuel cells. Most of the previous theoretical studies focus on the effect of alkali-metal additives facilitating C–O bond, O–O bond, and C–H bond cleavage on transition metal surfaces; − however, experimental studies rather than theoretical reports have been devoted to potassium effecting on O–H bond scission of H 2 O in the past few years. ,− The adsorption and dissociation of H 2 O on clean and K-covered Pt(111) were investigated by Bonzel et al utilizing Auger, X-ray, and ultra-violet photoemission spectroscopies. It was concluded by them that, on one hand, no dissociation of the adsorbed H 2 O was noted on heating to higher temperatures, but on the other hand, adsorbed K induces the dissociation of H 2 O to OH species at T = 100–320 K with a lower activation barrier than a barrier of 43 kJ/mol reported by Creighton et al for H 2 O dissociation in the temperature range 130–142 K on the O-covered Pt(111) surface.…”

Section: Introductionmentioning

confidence: 99%

Water Dissociation on Clean and Potassium Preadsorbed Transition Metals: A Systematic Theoretical Study

Wang

2018

J. Phys. Chem. C

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It is crucial to control the O−H bond cleavage on metal surfaces with preadsorbed potassium atoms in heterogeneous catalysis. On the basis of the density functional theory (DFT) calculations, the adsorption and dissociation of water on clean and potassium preadsorbed transition metal surfaces, including group 11 (Cu, Ag, and Au) and group 8−10 metal (Co, Ni, Ru, Rh, Pd, Ir, and Pt) surfaces, have been investigated systematically. The calculation results show that the presence of potassium atom enhances the binding strength of H 2 O but weakens the binding strength of OH. More importantly, it was found that the preadsorbed potassium can promote the catalytic activity of various metals for H 2 O dissociation to varying degrees and the more promoting ef fect of potassium on the water O−H bond scission occurs on the less chemically active transition metals. On the basis of electronic and geometric analysis, the physical origin of the promotion effect can be attributed to the dipole−dipole interactions like ((K δ+ -OH δ− )-(Au δ+ -OH δ− )), which stabilize the OH group and weaken the interaction between OH and H at the TS and thus facilitate the dissociation of water. The functional mechanism illuminated in this paper could be applicable to other electropositive additives like Na, Cs in the activation of the O−H bond involved in H 2 O or CH 3 OH.

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“…Further calculations revealed that K 2 O adsorption on χ-Fe 5 C 2 surfaces can greatly increase the effective hydrogenation barriers on the (100) and (110) facets, while slightly decreasing that on the (111) facet . In addition, the energy barriers for cleaving the C–O bonds in CH x OH ( x = 0–2) are reduced due to the increasing electrostatic interaction between the positively charged K δ+ and the negatively charged O δ− from CH x OH, which explains the contribution of K 2 O to the carburization process and long-chain hydrocarbon formation . Reaction pathway calculations and electronic structure analysis of Zn- and Na-modulated Fe 5 C 2 catalysts by Zhai et al showed that modulation of the electronic structure of the Fe 5 C 2 surface by Na facilitates CO activation, inhibits the hydrogenation of double bonds, and promotes the desorption of olefins.…”

Section: Introductionmentioning

confidence: 96%

“…20 In addition, the energy barriers for cleaving the C−O bonds in CH x OH (x = 0−2) are reduced due to the increasing electrostatic interaction between the positively charged K δ+ and the negatively charged O δ− from CH x OH, which explains the contribution of K 2 O to the carburization process and longchain hydrocarbon formation. 21 Reaction pathway calculations and electronic structure analysis of Zn-and Na-modulated Fe 5 C 2 catalysts by Zhai et al 22 showed that modulation of the electronic structure of the Fe 5 C 2 surface by Na facilitates CO activation, inhibits the hydrogenation of double bonds, and promotes the desorption of olefins. For Co 2 C, besides acting as electronic promoters, K and Na were indicted by experiments to also facilitate the formation and stabilization of Co 2 C nanoprisms, as only CoMn catalysts with alkali metal promoters stimulate the formation of the Co 2 C phase with specific exposed crystal facets, which are stable under FTS reaction conditions.…”

Section: ■ Introductionmentioning

confidence: 99%

Theoretical Insights into Morphologies of Alkali-Promoted Cobalt Carbide Catalysts for Fischer–Tropsch Synthesis

Zhang

Zhong

et al. 2021

J. Phys. Chem. C

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Co2C catalysts were found to be structure-sensitive during Fischer–Tropsch synthesis (FTS), and reaction-induced Co2C nanoprisms exposing the (101) and (020) facets exhibited superior olefin selectivity, low methane selectivity, and high activity under mild conditions. Alkali metal promoters benefit the formation and stabilization of Co2C nanoprisms, although mechanistic understanding and theoretical support are lacking due to the great complexity of this catalytic reaction and the difficulty in characterizing the detailed structural changes. Here, density functional theory (DFT) calculations and ab initio atomistic thermodynamics simulations are combined to elucidate the “promoter–structure” relationship of Co2C catalysts decorated with different alkali metal promoters. Co- and C-terminated and stoichiometric low-index surfaces including (020), (101), (111), (011), and (110) are considered. Evolution of the equilibrium morphology versus K2O coverage (θK2O) and carbon chemical potential (μC) as determined by the temperature, pressure, and the H2/CO ratio are predicted. We find that increasing θK2O facilitates the preferential exposure of the (020) and (101) facets with different terminations at diverse μC, which are the active surfaces for Fischer–Tropsch to olefins (FTO). For θK2O = 1/6 ML, these two surfaces are predicted to cover 100, 53.4, and 48.4% of the exposed surface area at μC of −7.5, −8.5, and −9.5 eV, respectively, compared with 8.6, 18.3, 26.2% without this promoter. The dominant exposure of these two facets explains the experimentally observed structure of Co2C nanoprisms with a parallelepiped shape. Additionally, the promotional effect extends the preference of most Co- and C-terminated facets over stoichiometric facets to a larger range of μC. Furthermore, Na, K, and Rb promoters are predicted to have stronger effects than Li in stabilizing these two facets, which is also consistent with available experimental observations. Insights from this theoretical work provide a rational understanding of the promotional effect of alkali metals on the morphology of the Co2C catalyst, which may facilitate the design of more efficient FTO catalysts with controlled surface structures.

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Potassium promotion on CO hydrogenation on the χ-Fe 5 C 2 (111) surface with carbon vacancy

Cited by 16 publications

References 47 publications

Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis

Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis

Water Dissociation on Clean and Potassium Preadsorbed Transition Metals: A Systematic Theoretical Study

Theoretical Insights into Morphologies of Alkali-Promoted Cobalt Carbide Catalysts for Fischer–Tropsch Synthesis

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Potassium promotion on CO hydrogenation on the χ-Fe 5 C 2 (111) surface with carbon vacancy

Cited by 16 publications

References 47 publications

Understanding the Key Step of Co2C-Catalyzed Fischer–Tropsch Synthesis

Understanding the Key Step of Co2C-Catalyzed Fischer–Tropsch Synthesis

Water Dissociation on Clean and Potassium Preadsorbed Transition Metals: A Systematic Theoretical Study

Theoretical Insights into Morphologies of Alkali-Promoted Cobalt Carbide Catalysts for Fischer–Tropsch Synthesis

Contact Info

Product

Resources

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Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis

Understanding the Key Step of Co₂C-Catalyzed Fischer–Tropsch Synthesis