Dissociation of CH4 on Ni(111) and Ru(0001)

Egeberg, Rasmus; Ullmann, S.; Alstrup, I.; Mullins, C. Buddie; Chorkendorff, Ib

doi:10.1016/s0039-6028(01)01428-5

Cited by 99 publications

(120 citation statements)

References 27 publications

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“…Edge and corner atoms, with fewer Ru neighbors than those on terraces, bind CH x and H more strongly and apparently decrease the energy required to form the relevant transition state for C-H bond activation. 36 No previous literature reported systematic Ru dispersion effects on CH 4 reaction rates, but similar effects of coordinative unsaturation were previously reported on other metal surfaces. [24][25][26][27][28]50,51 .…”

Section: Reforming Reactionssupporting

confidence: 66%

“…42 It is not certain that these findings are relevant to Ru surfaces and to the steady-state behavior of catalytic Ru clusters. Figure 6 shows Arrhenius plots for CH 4 decomposition data on 3.2 wt % Ru/Al 2 O 3 , from the present study, together with CH 4 decomposition rates on Ru (0001) 36 38 Thus, it appears that the type of defect sites responsible for CH 4 activation on large single crystals are not available on small Ru metal clusters, even though surfaces of small clusters are often described as quite rough and densely populated by coordinatively unsaturated sites. One possibility is that this description becomes inappropriate at high temperatures, because of the tendency of small metal clusters to melt, at least in near-surface regions, well below the melting temperature of the corresponding bulk metal.…”

Section: Resultsmentioning

confidence: 69%

“…Activation energies for CO 2 4 activation on Ru (0001) from the amount of carbon deposited after various elapsed times. 36 Even lower values (36.1 kJ/mol) were measured by others on similar Ru (0001) surfaces from electron energy loss measurements of chemisorbed carbon 37 and on Ru/SiO 2 (29 kJ/mol) using a pulse microreactor. 38 Density functional theory (DFT) led to 85 kJ/mol 39 and 78 kJ/mol 40 estimates of activation energies for CH 4 activation on Ru (0001) surfaces.…”

Section: Resultsmentioning

confidence: 78%

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Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

2004

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Kinetic and isotopic tracer and exchange measurements were used to determine the identity and reversibility of elementary steps required for CH 4 reforming reactions on Ru-based catalyst. These studies provide a simple mechanistic picture and a unifying kinetic treatment for CH 4 /CO 2 and CH 4 /H 2 O reforming reactions and CH 4 decomposition. Forward kinetic rates were measured from net rates by correcting for the approach to equilibrium, after ruling out transport artifacts using pellet and bed dilution tests. The kinetic processes involved are exclusively limited by C-H bond activation, and CH 4 reaction rates are unaffected by the identity or the concentration of co-reactants (H 2 O, CO 2 ). Similar normal kinetic isotopic effects (k C-H /k C-D ) 1.40-1.51) were measured for CO 2 reforming, H 2 O reforming, and CH 4 decomposition, consistent with kinetically relevant C-H bond activation steps. The ratio of CH 4 /CD 4 cross-exchange to methane chemical conversion rates during the reaction of CO 2 reforming with CH 4 -CD 4 mixtures was 0.05, suggesting that steps involving C-H bond activation are essentially irreversible. Binomial D-atom distributions in dihydrogen and water were obtained during reactions of CH 4 /CO 2 /D 2 mixtures, and their D-contents were identical to those expected from complete equilibration between D 2 and H-atoms from reacted CH 4 , indicating that H-OH and H-H recombination steps are quasi-equilibrated. Reactions of 12 CH 4 / 12 CO 2 / 13 CO mixtures gave identical 13 C contents in CO and CO 2 , even far away from the CO 2 reforming equilibrium; thus, CO 2 activation is reversible and quasi-equilibrated during CO 2 reforming on Ru-based catalysts, as expected from the kinetic irrelevance of co-reactant activation steps. These conclusions suggest that water-gas shift reactions are also equilibrated, as confirmed by chemical analyses of reaction products. Forward CH 4 turnover rates increased with increasing Ru dispersion, but they were essentially unaffected by the identity of the support. This behavior reflects the higher reactivity of coordinatively unsaturated surface atoms, prevalent in small Ru clusters, for C-H bond activation reactions, as previously inferred from the effect of crystal orientation on CH 4 activation rates.

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Section: Reforming Reactionssupporting

confidence: 66%

Section: Resultsmentioning

confidence: 69%

Section: Resultsmentioning

confidence: 78%

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Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

2004

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“…The deactivation of Ni/SiC due to carbon deposition cannot be avoided. With the aid of density functional theory method, it was found that Ni (1 1 0) surface has a stronger tendency for carbon deposition than Ni (1 1 1) surface during methane dissociation, which decreases the stability of the catalyst [54,55]. This is ascribed to the fact that the activation energy barrier for CH 4 dissociative adsorption on Ni (1 0 0) surface is 0.61 eV, much lower than that on Ni (1 1 1) surface (0.77 eV).…”

Section: Introductionmentioning

confidence: 99%

Dielectric barrier discharge plasma for preparation of Ni-based catalysts with enhanced coke resistance: Current status and perspective

et al. 2015

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“…The dissociative adsorption of methane on Ni catalysts has been studied by different authors, showing that the estimated value of the energetic barrier of methane dissociation on Ni (100) crystal surface faces were 0.28 eV 27 and 0.54 eV 28 and for Ni (111) crystal surface 0.77eV. 29 Theoretical calculations indicated energetic barriers in the range of 0.69 ± 0.04 eV for methane dissociation on Ni (100) surfaces. 30 In fact, calculations 31 by density functional theory (DFT) estimated energy value of 0.60 eV on Ni (100) surface; however, the presence of oxygen inhibits the methane dissociation, which is attributed to the decreasing interaction between CH 3 and H atoms with the substrate.…”

Section: Activitymentioning

confidence: 99%

Activation of Methane on NiO Nanoparticles with Different Morphologies

Martins¹,

Schmal²

2014

Journal of the Brazilian Chemical Society

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Superfícies nanoestruturadas podem ser definidas como substratos tendo como principal característica dimensões na faixa de 1-100 nm. O recente interesse nestes sistemas é baseado no fato de que novas e interessantes propriedade (catalíticas, magnéticas, ferroelétricas, mecânicas, óticas e eletrônicas) são desenvolvidas como resultado da redução da dimensão destes substratos. Neste trabalho descreve-se a decomposição catalítica do metano em hidrogênio e nanofilamentos de carbono em catalisadores não suportados de Ni preparados por metodologias distintas. Catalisador de Ni suportado em zircônia foi usado para comparação dos resultados. Para os catalisadores não suportados, observou-se forte dependência da atividade do catalisador com o tamanho da partícula do óxido precursor e sua morfologia. Apesar de todos terem apresentado dimensões na faixa de nanopartículas, somente os preparados usando etileno glicol, NiEG, e rota hidrotérmica, NiHT, exibiram a mesma performance que o catalisador suportado (atividade e estabilidade), 25NiZ. O catalisador sintetizado em presença de dimetilglioxima, NiDMG, foi o menos ativo e desativou com o tempo em operação. Nanostructured surfaces can be defined as substrates in which the typical features have dimensions in the range of 1-100 nm. The recent focus of interest in these systems is based on the fact that interesting novel properties (catalytic, magnetic, ferroelectric, mechanical, optical and electronic) are developed as a result of the dimension reductions of these substrates. This paper describes the catalytic methane decomposition into hydrogen and carbon nanofilaments on unsupported Ni catalysts prepared from different methodologies, with controlled particle size and morphologies. Ni catalyst supported on zirconia was also used for performance comparison. For the unsupported catalysts, it was observed strong dependency of catalyst activities with particle size of nickel oxide precursors and their morphologies. Although all of them presented crystallite sizes with nanometric dimensions, only those prepared with ethylene glycol, NiEG, and by hydrothermal condition, NiHT, exhibited the same performance as the supported catalyst (activity and stability), 25NiZ. Catalyst synthesized in the presence of dimethylglyoxime, NiDMG, was less active and deactivated with time on stream.

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Dissociation of CH4 on Ni(111) and Ru(0001)

Cited by 99 publications

References 27 publications

Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

Dielectric barrier discharge plasma for preparation of Ni-based catalysts with enhanced coke resistance: Current status and perspective

Activation of Methane on NiO Nanoparticles with Different Morphologies

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