Methanol on Co(0001): XPS, TDS, WF and LEED results

Habermehl-Cwirzen, Karin; Lahtinen, Jouko; Hautojärvi, P.

doi:10.1016/j.susc.2005.08.033

Cited by 32 publications

(45 citation statements)

References 21 publications

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“…As shown in Fig. 5, the higher forward barriers for H-assisted CO activation and methanol formation are in agreement with these experimental observations, be it that these were made on Co(0 0 0 1) surfaces [63][64][65].…”

Section: Ch 3 Oh Formationsupporting

confidence: 87%

“…The energy diagram given in Fig. 5 also agrees qualitatively with experimental observations where formaldehyde or methanol decomposition has been studied on cobalt surfaces [63,64]. These surface science studies report that methanol adsorbs as methoxy, CH 3 O, which is stable up to 300 K. Further heating decomposes the methoxy into CO and H 2 , which is the rate-limiting step.…”

Section: Ch 3 Oh Formationsupporting

confidence: 84%

See 1 more Smart Citation

Methane, formaldehyde and methanol formation pathways from carbon monoxide and hydrogen on the (0 0 1) surface of the iron carbide χ-Fe5C2

Özbek

Niemantsverdriet

2015

Journal of Catalysis

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a b s t r a c tFormation of CH x (O) monomers and C 1 products (CH 4 , CH 2 O, and CH 3 OH) on C-terminated v-Fe 5 C 2 (0 0 1) (Hägg carbide) surfaces of different carbon contents was investigated using periodic DFT simulations. Methane (CH 4 ) as well as monomer (CH x ) formation follows a Mars-van Krevelen-like cycle starting with the hydrogenation of surface carbidic carbon, which is regenerated by subsequent CO dissociation, while oxygen is removed as H 2 O. In cases where surface carbon is readily available, the apparent barrier for CH 4 formation was found to be $95 kJ/mol. However, different rate-determining steps show that different propagation mechanisms may be possible for actual chain growth, depending on the carbon content of the surface. Hydrogen addition to CO forms formyl (HCO), which is a precursor for both H-assisted CO activation and oxygenate formation. Further hydrogenation of HCO yields adsorbed formaldehyde and methoxy, rather than hydroxymethyl (HCOH) that would give C-O bond splitting. Full hydrogenation to gas-phase methanol faces a high barrier, suggesting that CH x O species may be involved in higher oxygenate formation in a full Fischer-Tropsch mechanism or that the C-O bond does not break until the CHO fragment has been incorporated in a C 2 species, a route for which precedents are available in the literature.

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Section: Ch 3 Oh Formationsupporting

confidence: 87%

Section: Ch 3 Oh Formationsupporting

confidence: 84%

Methane, formaldehyde and methanol formation pathways from carbon monoxide and hydrogen on the (0 0 1) surface of the iron carbide χ-Fe5C2

Özbek

Niemantsverdriet

2015

Journal of Catalysis

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“…[23] These results indicate a desorption limitation also for hydrogen formation, which implies that the dehydrogenation process itself takes place below 300 K on both metals. For Pd nanoparticles, Schauermann et al reported a decreasing intensity for IR bands belonging to vibrations of the methanol molecules and the formation of carbon monoxide bands between 200 and 230 K. [21] No significant traces of other dehydrogenation products, such as formaldehyde, were found in our TPD data, which agrees with published results for Pd nanoparticles, [21] PdA C H T U N G T R E N N U N G (100) single crystals, [20] and CoA C H T U N G T R E N N U N G (0001) [23] that reported neither water nor methane but only complete dehydrogenation products.…”

Section: Resultsmentioning

confidence: 89%

“…[22] For Co, on the other hand, the picture is less complete, because only results for the (0001) surface can be found in the literature, where carbon monoxide and hydrogen were the only detected decomposition products. [23] For the methanol decomposition process, it is also of relevance whether carbon monoxide can dissociate on the metal surfaces, because this would lead to a direct junction of the two pathways resulting in more carbon formation at the expense of the carbon monoxide yield. On Pd, carbon monoxide dissociation plays, at least under UHV conditions, only a negligible role according to results for single-crystalline surfaces.…”

Section: Introductionmentioning

confidence: 99%

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

et al. 2008

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Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh-vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core-shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature-programmed desorption of methanol and carbon monoxide and by X-ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C--O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C--O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous-flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high-pressure conditions.

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“…Acquiring fundamental understanding of the reaction networks of methanol on cobalt is important for further development of processes such as methanol synthesis from syngas, production of formaldehyde and for operation of direct methanol fuel cells. On the other hand, methanol may also serve as a simple model compound for the study of the oxidation of other more complex alcohols like ethanol and glycerol [20]. The aim of this work is to probe if cobalt undergoes dynamic variations under reaction conditions and to understand the role of different cobalt oxidation states to the reaction pathways.…”

Section: Introductionmentioning

confidence: 99%

Methanol oxidation over model cobalt catalysts: Influence of the cobalt oxidation state on the reactivity

Zafeiratos

Dintzer

Teschner

et al. 2010

Journal of Catalysis

117

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X-ray photoelectron and absorption spectroscopies (XPS and XAS) combined with on-line mass spectrometry were applied under working catalytic conditions to investigate the methanol oxidation on cobalt. Two cobalt oxidation states (Co3O4 and CoO) were prepared and investigated as regards their influence on the catalytic activity and selectivity. In addition adsorbed species were monitored in the transition of the catalyst from the non-active to the active state. It was unequivocally shown that the surface oxidation state of cobalt is readily adapted to the oxygen chemical potential in the CH3OH/O2 reaction mixture. In particular, even in rich to oxygen mixtures the Co3O4 surface is partially reduced, while the degree of surface reduction is higher as the methanol concentration in the mixture increases. The reaction selectivity depends on the cobalt oxidation state with the more reduced samples favouring the partial oxidation of methanol to formaldehyde. In the absence of oxygen, methanol is effectively reducing cobalt to the metallic state, promoting also hydrogen and CO production. Direct evidence of methoxy and formate species adsorbed on the surface upon reaction was found by analysing the O 1s and C 1s photoelectron spectra. However, the surface coverage of those species was not proportional to the catalytic activity, indicating that in the absence of surface oxygen, these species might act also as reaction inhibitors.

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Methanol on Co(0001): XPS, TDS, WF and LEED results

Cited by 32 publications

References 21 publications

Methane, formaldehyde and methanol formation pathways from carbon monoxide and hydrogen on the (0 0 1) surface of the iron carbide χ-Fe5C2

Methane, formaldehyde and methanol formation pathways from carbon monoxide and hydrogen on the (0 0 1) surface of the iron carbide χ-Fe5C2

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

Methanol oxidation over model cobalt catalysts: Influence of the cobalt oxidation state on the reactivity

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