High coverage CO adsorption and dissociation on the Co(0001) and Co(100) surfaces from DFT and thermodynamics

Chen, Congbiao; Wang, Qiang; Zhang, Riguang; Hou, Bo; Li, Debao; Jia, Litao; Wang, Baojun

doi:10.1016/j.apcata.2016.06.013

Cited by 24 publications

(10 citation statements)

References 59 publications

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“…It is strongly exothermic (−95 kJ/mol) and leaves the CO* molecule and the OH* fragment on the surface, both chemisorbed at a hollow site. CO* can hardly be dissociated into C* and O* on Co(0001) since this is a strongly endothermic and highly activated process (228 kJ/mol), in agreement with previous DFT studies . The adsorption energy of CO found by DFT at this low coverage of 1/9 ML (−176 kJ/mol) is in line with previous findings but seems strongly overestimated compared with our TPD data (−117 kJ/mol at most).…”

Section: Resultssupporting

confidence: 92%

“…CO* can hardly be dissociated into C* and O* on Co(0001) since this is a strongly endothermic and highly activated process (228 kJ/mol), in agreement with previous DFT studies. 55 The adsorption energy of CO found by DFT at this low coverage of 1/9 ML (-176 kJ/mol) is in line with previous findings but seems strongly overestimated compared with our TPD data (-117 kJ/mol at most). This discrepancy can be attributed to coverage, 6655 CO being strongly sensitive to lateral effects.…”

Section: Carboxyl Branchsupporting

confidence: 92%

“…At this temperature, carbon monoxide can dissociate to carbon and oxygen on Co(0001), and this process has been reported experimentally with binding energies reported at 284.3 and 531.0 eV, − respectively, in agreement with our observations. Note that the dissociation of CO on Co(0001) has been predicted as being extremely difficult, but perhaps steps, ad-atoms, defects, or a more complex mechanism is involved. Increasing the temperature up to 200 K, there is a decrease in the formate peak and a shift in the oxygen peak to 532.5 eV.…”

Section: Resultsmentioning

confidence: 99%

“…This discrepancy can be attributed to coverage, 6655 CO being strongly sensitive to lateral effects. 55,58 Thus, CO* does not dissociate and preferentially desorbs. The other fragment co-generated with CO* is the OH* species, which could be hydrogenated to yield water, recombining with an adsorbed hydrogen H* produced in the first step.…”

Section: Carboxyl Branchmentioning

confidence: 99%

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Adsorption and Decomposition of Formic Acid on Cobalt(0001)

et al. 2018

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Formic acid can undergo dehydration or dehydrogenation with variable selectivity over a range of metal catalysts. The selectivity among these reactions depends on the reaction mechanism and reaction conditions pertinent on each surface. This work provides mechanistic insight on the decomposition of formic acid on cobalt at high and low temperature regimes. The adsorption and decomposition of formic acid on a Co(0001) single crystal was studied in ultra-high vacuum by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Insight is provided using DFT calculations. In the low temperature regime, formic acid adsorbs molecularly on the surface at 130 K. Partial decomposition produces CO at 140 K, and at 160 K the decomposition of formic acid into formate, which is a thermodynamic sink, is dominant. Water can be formed at low temperature via bimolecular processes. At high temperature (>400 K) the similar barriers for decomposition of the formate species lead to the concomitant production of CO, CO2 and H2. The correlation between experiment and theory provides a framework for the interpretation of surface species and reaction path operating in different regimes.

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Section: Resultssupporting

confidence: 92%

Section: Carboxyl Branchsupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Section: Carboxyl Branchmentioning

confidence: 99%

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Adsorption and Decomposition of Formic Acid on Cobalt(0001)

et al. 2018

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“…This value is consistent with previous experiments on polycrystalline samples at room temperature and low CO partial pressure . Such low reactivity is explained by the high value of the CO dissociation free energy on terraces, leaving the steps as the most likely candidates for spontaneous dissociation. − …”

Section: Experimental Sectionsupporting

confidence: 91%

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

et al. 2018

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The irradiation with photons or electrons can dramatically influence the chemical stability of a molecule, either free or adsorbed on a surface, inducing its fragmentation or desorption. We revisit here the exostimulated dissociation of CO, a prototypical case, choosing hcp thin cobalt films as model support. Intense, microfocused soft X-rays or electron beams are used to locally stimulate CO dissociation. Fast-XPS gives direct access to the adsorbates’ chemical state and coverage during irradiation, enabling the kinetics of the process to be monitored in real time. The energy-dependent cross sections for photon and electron stimulated molecular dissociation and desorption are estimated for a fixed initial CO coverage of 1/3 ML. In the soft X-ray regime, the desorption channel always prevails over dissociation and is significantly enhanced above the O K edge. The relative dissociation probability increases steadily with increasing photon energy, reaching 30% at 780 eV. Furthermore, we show that low energy electrons in the range 50 to 200 eV dissociate CO more efficiently than X-rays. The prolonged irradiation of the Co surface in CO ambient is found to produce a continuous increase of the carbon coverage, initially promoting the formation of carbides and subsequently accumulating sp2 carbon on the surface. Far from being a detrimental effect, the CO stimulated dissociation can be exploited to lithographically graft carbon-rich microscopic patterns on Co, with resolution well into the nanometer scale. A brief thermal treatment following irradiation results in the formation of a graphitic carbon overlayer, which effectively protects Co from oxidation upon exposure to ambient conditions, preserving its out-of-plane magnetic anisotropy and domain configuration.

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Highly active and selective Co‐based Fischer–Tropsch catalysts derived from metal–organic frameworks

Pei

2017

AIChE Journal

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The design of supported Co‐based Fischer–Tropsch (F–T) catalysts with suitable reducibility, dispersion, loading, and nanoparticle structure is necessary so that high catalytic activity and selectivity for C5+ hydrocarbons can be achieved. Herein, we report that pyrolyzing a Co‐metal–organic framework‐71 precursor can provide porous carbon‐supported Co catalysts with completely reduced, well‐dispersed face‐centered cubic (FCC) Co nanoparticles (∼10 nm in average size). The catalysts can be further tailored dimensionally by doping with Si species, and the FCC Co nanoparticles can be partially transformed into hexagonal close‐packed Co via a Co2C intermediate. All the as‐prepared catalysts had extremely high Co site density (>3.5 × 10−4 mol/g‐cat.) because they had a high number of Co active sites and low mass. Aside from having high F–T activity and C5+ selectivity, with diesel fuels being the main constituents, they showed unprecedentedly high C5+ space time yields (up to 1.45 g/(g‐cat. h)) as compared to conventional Co catalysts. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2935–2944, 2017

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High coverage CO adsorption and dissociation on the Co(0001) and Co(100) surfaces from DFT and thermodynamics

Cited by 24 publications

References 59 publications

Adsorption and Decomposition of Formic Acid on Cobalt(0001)

Adsorption and Decomposition of Formic Acid on Cobalt(0001)

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

Highly active and selective Co‐based Fischer–Tropsch catalysts derived from metal–organic frameworks

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