CO adsorption on Co(0001) revisited: High-coverage CO superstructures on the close-packed surface of cobalt

Weststrate, C.J.; Niemantsverdriet, J.W.

doi:10.1016/j.jcat.2022.03.005

Cited by 6 publications

(5 citation statements)

References 58 publications

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“…2085 cm –1 in this work) were attributed to 3-fold bonded CO, bridge-bonded CO on a well-perfect Pd surface, and linearly adsorbed CO on the low-coordinated Pd, respectively. , The absorption bands originating from the stretching vibration of CO adsorbed in the 3-fold and bridged configuration on the cobalt surface were separately located in the region of 1800–1900 cm –1 and centered at ca. 1927 cm –1 , partially overlapping with the features of 3-fold and bridge-bonded CO on Pd. , The weak carbonyl absorption band at 2024 cm –1 corresponded to CO linearly adsorbed on Co 0 in Pd/Co 3 O 4 -0. , For Pd/Co 3 O 4 -1 and Pd/Co 3 O 4 -6, the characteristic bands of CO adsorbed on Co 0 significantly intensified and underwent a progressive red-shift relative to Pd/Co 3 O 4 -0. The former was ascribed to the increased amount of surface Co 0 sites due to the high reduction degree of Co 3 O 4 , the latter derived from an enhanced electron back-donation from Co 0 to π* antibonding orbitals of CO, thereby lowering the frequencies of C–O bond stretching vibrations.…”

Section: Resultsmentioning

confidence: 93%

Constructing a Pd–Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Yuan,

Wang,

et al. 2023

ACS Appl. Mater. Interfaces

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Cobalt is an alternative catalyst for furfural hydrogenation but suffers from the strong binding of H and furan ring on the surface, resulting in low catalytic activity and chemoselectivity. Herein, by constructing a Pd−Co interface in cobalt oxidesupported Pd catalysts to tailor the d-band center of Co, the concerted effort of Pd and Co boosts the catalytic performance for the hydroconversion of furfural to cyclopentanone and cyclopentanol. The increased dispersion of Pd on acid etching Co 3 O 4 promotes the reduction of Co 3+ to Co 0 by enhancing hydrogen spillover, favoring the creation of the Pd−Co interface. Both experimental and theoretical calculations demonstrate that the electron transfer from Pd to Co at the interface results in the downshift of the d-band center of Co atoms, accompanied by the destabilization of H and furan ring adsorption on the Co surface, respectively. The former improves the furfural hydrogenation with TOF on Co elevating from 0.20 to 0.62 s −1 , and the latter facilitates the desorption of formed furfuryl alcohol from the Co surface for subsequently hydrogenative rearrangement of the furan ring to cyclopentanone on acid sites. The resultant Pd/Co 3 O 4 -6 catalyst delivers superior activity with a 99% furfural conversion and 85% overall selectivity toward cyclopentanone/cyclopentanol. We anticipate that such a concept of tailoring the d-band center of Co via interface engineering provides novel insight and feasible approach for the design of highly efficient catalysts for furfural hydroconversion and beyond.

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Section: Resultsmentioning

confidence: 93%

Constructing a Pd–Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Yuan,

Wang,

et al. 2023

ACS Appl. Mater. Interfaces

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“…A K-type thermocouple was spotwelded to the side of the crystal and was connected via small springs to the TCconnections located on the manipulator. From a comparison of the TP-XPS data recorded at FlexPES with in-house TPD data for CO desorption (reported in ref 18 ) a systematic offset of −10 K relative to the in-house data was found for the measurements performed at FlexPES. The temperature of TP-XPS data shown here was therefore corrected by +10 K to facilitate direct comparison.…”

Section: ■ Experimental Methodsmentioning

confidence: 95%

“…Temperature-programmed desorption and reaction experiments were performed using the setup described previously in refs. ,, The “shielded” quadrupole mass spectrometer (QMS) used to measure the water formation rate is located inside a separately pumped and moveable compartment with a 5 mm aperture that connects to the main chamber. Desorption signals and reaction products from other parts of the sample holder are largely suppressed when the sample is placed at 2 mm from the aperture.…”

Section: Experimental Methodsmentioning

confidence: 99%

Water and Hydroxyl Reactivity on Flat and Stepped Cobalt Surfaces

et al. 2023

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Hydroxyl adsorbates generally appear as transient species during water formation from adsorbed oxygen and hydrogen atoms on a metal surface, a reaction that is part of the catalytic cycle in various important surface-catalyzed reactions such as Fischer−Tropsch synthesis. In the present work, temperature-programmed desorption and in situ synchrotron XPS were used to study water adsorption and OH reactivity on a flat and a stepped cobalt single crystal surface. Water adsorbs intact on the flat Co(0001) surface and desorbs around 160 K. Electrons induce dissociation of water and produce OH species at low temperature. Hydroxyl species can also be formed by the reaction between O ad and H 2 O, but only for high initial oxygen coverage while low coverage O ad appears largely unreactive. Reactive hydrogen species (H atoms) produced by a hot tungsten filament hydrogenate adsorbed oxygen atoms at low temperature already and both OH ad and H 2 O are formed. In all cases, hydroxyl adsorbates react around 190 K to form water via 2 OH ad → H 2 O (g) + O ad associated with an activation barrier of 40−50 kJ mol −1 . Water readily dissociates on the step sites exposed by vicinal . A part of the OH ad species recombine to form water and oxygen between 200 and 300 K, while decomposition of OH ad into O ad and H ad dominates above 370 K. For catalysis, the high reactivity of step sites for water dissociation and the high stability of OH ad at these sites implies that O removal from these sites may be difficult and may limit the overall rate of Fischer−Tropsch synthesis on cobalt catalysts.

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“…117 In a follow-up study, new high-coverage structures were proposed above the 7/12 ML coverage typically found under Fischer−Tropsch conditions (Figure 6). 122 At higher coverages, the (2√3 × 2√3) R30°structure breaks up and boundary regions with higher coverage form in between, which is possible due to the formation of double bridge dicarbonyls. Around 0.63 ML, a phase transition is observed by LEED, resulting in a mixture of (2 × 2)-3CO structures with lower coverage boundary regions to relieve stress.…”

Section: Overlayers Of Comentioning

confidence: 99%

Section: Molecular Views Of the Active Site And Structure Of Co- And ...mentioning

confidence: 99%

Molecular Views on Fischer–Tropsch Synthesis

2023

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For nearly a century, the Fischer–Tropsch (FT) reaction has been subject of intense debate. Various molecular views on the active sites and on the reaction mechanism have been presented for both Co- and Fe-based FT reactions. In the last 15 years, the emergence of a surface-science- and molecular-modeling-based bottom-up approach has brought this molecular picture a step closer. Theoretical models provided a structural picture of the Co catalyst particles. Recent surface science experiments and density functional theory (DFT) calculations highlighted the importance of realistic surface coverages, which can induce surface reconstruction and impact the stability of reaction intermediates. For Co-based FTS, detailed microkinetic simulations and mechanistic experiments are moving toward a consensus about the active sites and the reaction mechanism. The dynamic phase evolution of Fe-based catalysts under the reaction conditions complicates identification of the surface structure and the active sites. New techniques can help tackle the combinatorial complexity in these systems. Experimental and DFT studies have addressed the mechanism for Fe-based catalysts; the absence of a clear molecular picture of the active sites, however, limits the development of a molecular view of the mechanism. Finally, direct CO2 hydrogenation to long-chain hydrocarbons could present a sustainable pathway for FT synthesis.

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CO adsorption on Co(0001) revisited: High-coverage CO superstructures on the close-packed surface of cobalt

Cited by 6 publications

References 58 publications

Constructing a Pd–Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Constructing a Pd–Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Water and Hydroxyl Reactivity on Flat and Stepped Cobalt Surfaces

Molecular Views on Fischer–Tropsch Synthesis

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