A Comparative Ambient Pressure X-ray Photoelectron and Absorption Spectroscopy Study of Various Cobalt-Based Catalysts in Reactive Atmospheres

Turczyniak, Sylwia; Luo, Wen; Papaefthimiou, Vasiliki; Ramgir, Niranjan S.; Haevecker, Michael; Machocki, Andrzej; Zafeiratos, Spyridon

doi:10.1007/s11244-015-0531-5

Cited by 27 publications

(36 citation statements)

References 57 publications

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“…The XPS results recorded after the ESR reaction at a stoichiometric (3:1) H 2 O/EtOH molar ratio ( T =420 °C, p total =1 atm, t =1 h) show a partially reduced ceria support and metallic Co with traces of CoO x (Figure a and b). Notably, compared to the state before ESR (reduced samples; Figure ), the stoichiometric reaction mixture seems to be more efficient to reduce ceria than H 2 , which is in agreement with previous reports . However, it is different for Co as its oxidation state remains almost the same as that before the reaction (cf.…”

Section: Resultssupporting

confidence: 91%

“…Notably, the intensity of the fitted Co II component is comparable to the noise level of the spectra in Figure b, therefore, the determined Co II contribution might be encumbered with a meaningful error. The spectra obtained proved that similar to the results of in situ XPS studies and in contrast to the results of ex situ XPS studies, it is possible to maintain Co efficiently mainly in a metallic form if it predominates.…”

Section: Resultssupporting

confidence: 75%

“…The oxidation state of Co under the ESR reaction conditions has been the subject of many studies . The evidence for the co‐existence of both forms of Co (metallic and cobalt(II) oxide) under the reaction conditions has been provided by using various techniques .…”

Section: Introductionmentioning

confidence: 99%

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Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

et al. 2017

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only substantial factor in the overall ESR process. Other important factorst hat influence the catalytic activity and selectivity are the morphology and textural properties of the support. [3,13,20] Soykal and co-workersi nvestigated the influence of the particle size (3.5and 120 nm) [3,21] and morphology [11] on the reducibility of ceria and its catalytic performance under the ESR conditions.R egardless of whether ceria wasp re-reduced or not, it converged to the same oxidation state (a mixture of Ce IV and Ce III )a tagiven temperature and exhibited as imilar ESR performance;h owever,ahighly dispersed cerias upport produced much more ethylene than its poorly dispersed counterpart. [3,21] In contrastt ot he studies presented by Soykal et al., [3,21] the results of da Silva et al. [54] and Laosiripojana and Assabumrungrat [20] showed that al ow-surface-area ceria exhibited ah igh selectivity to ethylene, whereas its high-surface-areac ounterpart was selective towards acetaldehyde. [54] However,t he authors agreed [21,54] that the use of nano-sized ceria ensures ah igher ethanol conversion and hydrogen yield. Therefore, any discrepancy between differentr esults, [3,8,13,21] although they concern ESR performed over Co/CeO 2 catalysts, may arise from differences in the morphology and catalytic properties of the ceria support used.Ag reat number of studies focus on the role of Co and on the ceria oxidation state in the ESR reaction, [2,3,7,8,10,11,21,29] whereas only af ew aim to explain the role of surface-adsorbed hydroxyl species, or generally speaking, surface-adsorbed oxygen-containing species. [44,[55][56][57] da Silva et al. [43] suggested that hydroxyl groups adsorbed on the ceria surfacea ssist in coke removal from Co, whereas another group [1] highlighted that ah igh concentration of surface-adsorbed oxygen-containing speciesm ay also induce the oxidation of the metal surface. In the second case, it is clear that adsorbed speciesw ould influence the catalysts electivity and, [48] therefore, play an important role in the ESR. de Lima et al. [55] presented as cheme of the transformation of ethoxy speciesi nw hich dehydrogenated species( acetyl species) undergo support-induced oxidation by the formation of acetates with oxygen-containing species( OH or surfaceo xygen adatoms). Acetate speciesc an be further oxidisedb yt he surface-adsorbed oxygen-containing species to carbonates followed by decomposition to CO 2 .It is generally accepted that promotersi mprove the stability of catalysts. Promoters (e.g.,a lkali metals,s uch as Na [58,59] and K, [22-24, 31, 60-62] and noble metals, such as Rh [7,10,40,63] and Pt) [62,64] are used widely to improvec atalytic activity [24,59] and extend the catalyst lifetime by making sintering [47] and carbon formation [23,24,31,59,60] more difficult. Snoeck et al. [65] examined the effect of the Kl oading on Ni catalysts on the rate of carbon gasification. Their findings showed that the most satisfactory results were obtained with a1 .6-2 wt %K 2 Oc ontent. Ogo et al. [23] sho...

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Section: Resultssupporting

confidence: 91%

Section: Resultssupporting

confidence: 75%

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Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

et al. 2017

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“…Here we observed that annealing of Co/ZnO in low‐pressure H 2 involves two parallel processes: reduction by gas‐phase H 2 up to 250 °C (CoO+H 2 →Co+H 2 O) and a dominant interfacial oxidation at higher temperature (e.g. Co+ZnO→Co x Zn 1− x O) . In the case of an “inert” SiO 2 support, the interfacial oxidation does not occur and cobalt oxide is reduced by gas‐phase H 2 or by simple thermal decomposition.…”

Section: Resultsmentioning

confidence: 81%

Graphene‐Coated ZnO and SiO₂ as Supports for CoO Nanoparticles with Enhanced Reducibility

Luo

Zafeiratos

2016

ChemPhysChem

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The insertion of a graphene layer between cobalt and a substrate modifies the morphology and the oxidation/reduction properties of supported cobalt particles. Co forms a relatively flat structure on ZnO and SiO , whereas individual Co nanoparticles are formed after graphene coating of these substrates. The graphene layer moderates the formation of cobalt oxide in 5×10 mbar O and promotes the reduction of oxidized Co in H at lower temperature. Angle-resolved XPS measurements indicate that this is mainly a consequence of the restricted interaction of cobalt with the oxide supports. After the low-pressure redox treatments, the graphene layer maintains a relatively high quality with a small number of defect sites.

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“…However the formation of unreducible mixed oxides between metal catalyst and support during the preparation and the reaction process has been blamed for irreversible deactivation of the catalyst . Similarly, while ZnO and CeO 2 are considered to have potentially promising applications in ethanol steam reforming reaction, the oxidation of active metal sites (such as Co) by the support decreases the catalytic activity . In the case of photocatalytic reactions, TiO 2 is the most widely studied material, but engineering of its band‐gap to absorb more in the visible electromagnetic radiation region remains a difficult problem.…”

Section: Introductionmentioning

confidence: 99%

A Brief Review of the Synthesis and Catalytic Applications of Graphene‐Coated Oxides

Luo

Zafeiratos

2017

ChemCatChem

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The potential applications of graphene‐based materials in catalysis have been intensively studied owing to the unique 2D structure of graphene and its superior physicochemical properties. Recently, graphene‐coated oxide composites have been fabricated and tested as catalysts or catalytic supports, demonstrating a significant improvement on the catalytic performance. This article briefly reviews the recent progress in the design and fabrication of graphene‐coated oxides including wet transfer, chemical vapor deposition and self‐assembly methods. The applications of these materials in catalysis as well as the role of graphene in the modification of oxide properties and the enhancement of catalytic activity are also discussed.

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A Comparative Ambient Pressure X-ray Photoelectron and Absorption Spectroscopy Study of Various Cobalt-Based Catalysts in Reactive Atmospheres

Cited by 27 publications

References 57 publications

Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

Graphene‐Coated ZnO and SiO₂ as Supports for CoO Nanoparticles with Enhanced Reducibility

A Brief Review of the Synthesis and Catalytic Applications of Graphene‐Coated Oxides

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A Comparative Ambient Pressure X-ray Photoelectron and Absorption Spectroscopy Study of Various Cobalt-Based Catalysts in Reactive Atmospheres

Cited by 27 publications

References 57 publications

Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

Surface State and Catalytic Performance of Ceria‐Supported Cobalt Catalysts in the Steam Reforming of Ethanol

Graphene‐Coated ZnO and SiO2 as Supports for CoO Nanoparticles with Enhanced Reducibility

A Brief Review of the Synthesis and Catalytic Applications of Graphene‐Coated Oxides

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Graphene‐Coated ZnO and SiO₂ as Supports for CoO Nanoparticles with Enhanced Reducibility