Carbon-Induced Surface Transformations of Cobalt

Zhang, Xueqing; Santen, van R.A.; Hensen, Emiel J. M.

doi:10.1021/cs501484c

Cited by 49 publications

(48 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Theoretical studies have shown agreement with the high Θ C values on fcc Co under FT conditions, and that CO or deposited carbon can induce restructuring . Recent work by van Helden et al.…”

Section: Figurementioning

confidence: 80%

Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time‐Resolved Chemical Transient Kinetics

et al. 2017

View full text Add to dashboard Cite

The Fischer-Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer-Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H /CO=2. Large differences in carbon coverage (Θ ) were observed for the two catalysts: the 4.3 nm Co catalyst has a Θ less than one while the 9.5 nm Co catalyst supports a Θ greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B -B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes.

show abstract

Section: Figurementioning

confidence: 80%

Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time‐Resolved Chemical Transient Kinetics

et al. 2017

View full text Add to dashboard Cite

show abstract

“…In this process the number of adsorption sites decreases: three rows of terrace sites are converted to one row of B5 sites and one row of F4 sites. Since various carbon-containing 6 species adsorb strongly on Co, [11][12][13][14][15][16][17] it is natural to ask whether strong adsorption and high coverage at the new step sites could overcome the large energy penalty to create steps. To evaluate the effect of adsorbates, the stability of C, CH, and CH 2 at the steps (Figure 2), as well as the adsorption of CO on terraces and steps ( Figure 3) was computed to find a combination that could overcome the step creation penalty.…”

Section: Resultsmentioning

confidence: 99%

Origin of the Formation of Nanoislands on Cobalt Catalysts during Fischer–Tropsch Synthesis

et al. 2015

View full text Add to dashboard Cite

Cobalt catalysts undergo a massive reconstruction under Fischer-Tropsch conditions, resulting in the formation of uniform nano-islands. It is unclear what drives the formation of these islands, since it is highly unfavorable for clean surfaces. Using density functional theory, we show that the formation of islands and steps is driven by the embedding of carbon in an unusual square-planar form at the B5 step sites. Though carbon is not a typical oxidant for metals, it oxidizes cobalt at those sites. This strengthens CO adsorption, which further favors the formation of islands and steps. The oxidation of cobalt by carbon is predicted to be experimentally detectable as a 2 eV shift in the Co 2p binding energy.

show abstract

“…8,9 The open surface structure is often more catalytically active than those with closely packed surface atoms. Depending on the reaction conditions, a different coverage of adsorbates may be formed.…”

Section: Introductionmentioning

confidence: 99%

A DFT study of H-dissolution into the bulk of a crystalline Ni(111) surface: a chemical identifier for the reaction kinetics

Shirazi

Bogaerts

Neyts

2017

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

In this study, we investigated the diffusion of H-atoms to the subsurface and their further diffusion into the bulk of a Ni(111) crystal by means of density functional theory calculations in the context of thermal and plasma-assisted catalysis. The H-atoms at the surface can originate from the dissociative adsorption of H 2 or CH 4 molecules, determining the surface H-coverage. When a threshold H-coverage is passed, corresponding to 1.00 ML for the crystalline Ni(111) surface, the surface-bound H-atoms start to diffuse to the subsurface. A similar threshold coverage is observed for the interstitial H-coverage. Once the interstitial sites are filled up with a coverage above 1.00 ML of H, dissolution of interstitial H-atoms to the layer below the interstitial sites will be initiated. Hence, by applying a high pressure or inducing a reactive plasma and high temperature, increasing the H-flux to the surface, a large amount of hydrogen can diffuse in a crystalline metal like Ni and can be absorbed. The formation of metal hydride may modify the entire reaction kinetics of the system. Equivalently, the H-atoms in the bulk can easily go back to the surface and release a large amount of heat. In a plasma process, H-atoms are formed in the plasma, and therefore the energy barrier for dissociative adsorption is dismissed, thus allowing achievement of the threshold coverage without applying a high pressure as in a thermal process. As a result, depending on the crystal plane and type of metal, a large number of H-atoms can be dissolved (absorbed) in the metal catalyst, explaining the high efficiency of plasma-assisted catalytic reactions. Here, the mechanism of H-dissolution is established as a chemical identifier for the investigation of the reaction kinetics of a chemical process.

show abstract

Carbon-Induced Surface Transformations of Cobalt

Cited by 49 publications

References 40 publications

Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time‐Resolved Chemical Transient Kinetics

Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time‐Resolved Chemical Transient Kinetics

Origin of the Formation of Nanoislands on Cobalt Catalysts during Fischer–Tropsch Synthesis

A DFT study of H-dissolution into the bulk of a crystalline Ni(111) surface: a chemical identifier for the reaction kinetics

Contact Info

Product

Resources

About