Steam Reforming and Graphite Formation on Ni Catalysts

Bengaard, Hanne Skov; Nørskov, Jens K.; Sehested, Jens; Clausen, Bjerne S.; Nielsen, Lars; Molenbroek, A.M.; Rostrup-Nielsen, J.R.

doi:10.1006/jcat.2002.3579

Cited by 1,014 publications

(838 citation statements)

References 105 publications

Supporting

Mentioning

761

Contrasting

Unclassified

Order By: Relevance

“…The initial catalysis of graphene formation on Ni under similar conditions has been described earlier, 15 and is thought to take place at step edges on the Ni surface. 16 The graphitising effect of Ni is clearly confirmed by the Raman spectra in Fig. 3.…”

mentioning

confidence: 64%

Gas phase controlled deposition of high quality large-area graphene films

Kumar

McEvoy

Lutz³

et al. 2010

Chem. Commun.

View full text Add to dashboard Cite

A gas phase controlled graphene synthesis resembling a CVD process that does not critically depend on cooling rates is reported. The controllable catalytic CVD permits high quality large-area graphene formation with deft control over the thickness from monolayers to thick graphitic structures at temperatures as low as 750 1C.Graphene has attracted enormous attention because of its exciting structural and electrical properties. 1 Extremely high mobilities 2 and a tunable band gap 3 make graphene potentially useful for innovative approaches to electronics 4 and sensing. 5 For these applications a scalable and reproducible method for graphene production is required. Mechanical exfoliation of graphite 6 and decomposition 7 of SiC surfaces upon thermal treatment have been the main sources for graphene, with limitations in quality and scalability. Solution-phase 8 and solvothermal syntheses of graphene 9 were a major improvement for processing, however for device fabrication, a reproducible method such as CVD yielding high quality films of controlled thickness is desirable. Recently, the formation of graphene under CVD-like conditions on Ir, 10a Ru, 10b Ni 11 and Cu 12 surfaces has been reported. Nevertheless, these processes are not conventional CVD since they rely on precipitation of carbon upon cooling and require high-quality substrates, elevated temperatures (B1000 1C) and accurate control over cooling rates.Here, we introduce a CVD process which produces high quality graphene with tunable thickness on Ni surfaces. We have synthesised large-area graphene films (41 cm 2 ) in a simple tubular CVD reactor using ethyne (acetylene) as precursor under varying CVD parameters. The nickel substrates were prepared by E-beam evaporation (Edwards Auto500) of Ni (200 nm) on thermally-grown silicon dioxide (300 nm). The substrates were introduced in a tube furnace heated to temperatures between 650 1C and 1000 1C. After reduction by a mixture of hydrogen and argon (1 : 1) for 5 min, Ar was shut off and acetylene was introduced, keeping the overall pressure between 0.5 and 5 Torr for various dwell times. The flow rate was nominally 60 sccm for acetylene and 180 sccm for hydrogen or argon, unless otherwise specified. The substrates were then cooled under nitrogen flow with rates exceeding 15 1C s À1 or as slow as 0.15 1C s À1 . For reference, bare SiO 2 substrates were also placed in the CVD chamber. A Zeiss Ultra FE SEM with an EDX detector was used for imaging the graphene layers directly on the substrates. Aberration-corrected HRTEM was carried out using an Oxford-JEOL JEM2200MCO FEGTEM/STEM fitted with two CEOS C s aberration correctors, operated at 80 kV. The samples for HRTEM were prepared by directly peeling off the carbon deposit from the substrate with a formvar film which then was deposited onto a TEM grid. Raman spectra were taken with a Jobin-Yvon Labram Raman spectrometer using an excitation wavelength of 633 nm, with a probe size of 2 mm. Typically, five Raman spectra were taken on each sample to confirm homogeneit...

show abstract

mentioning

confidence: 64%

Gas phase controlled deposition of high quality large-area graphene films

Kumar

McEvoy

Lutz³

et al. 2010

Chem. Commun.

View full text Add to dashboard Cite

show abstract

“…Step-edge formation energies based on theoretical calculations report values of 0.41 eV and 0.16 eV per Ni step-edge atom, 16,17 both less than the energy gained when binding carbon atoms to the step-edges. 15,16 Since nickel transport may proceed along the graphene-nickel interface, it is likely that a similar transport mechanism can also account for the transport of carbon atoms.…”

Section: Atomic-resolved Imaging Of Multilayered Carbon Nanofibermentioning

confidence: 99%

Mechanisms for catalytic carbon nanofiber growth studied byab initiodensity functional theory calculations

et al. 2006

View full text Add to dashboard Cite

Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported from the deposition site at the free nickel surface to the perimeter of the growing graphene layer via surface or subsurface diffusion. Three different processes are identified to govern the growth of graphene layers, depending on the termination of the graphene perimeter at the nickel surface, and it is argued how these processes may lead to different nanofiber structures. The proposed growth model is found to be in good agreement with previous findings.

show abstract

“…Model surfaces of the face-centered cubic crystal (fcc{211}) were used to represent the step sites, which was found to be the important active site for a number of catalytic reactions. 15,16,17,18 A (1×2) cell with 10 atomic layers in the (211) direction corresponding to 3 layers in the closepacked (111) direction was used to model the adsorbate-metal structures. The atoms in the bottom 7 layers of the slab were fixed to their bulk positions, while the atoms in the top 3 layers were allowed to relaxation during the calculations.…”

mentioning

confidence: 99%

Universal Brønsted-Evans-Polanyi Relations for C–C, C–O, C–N, N–O, N–N, and O–O Dissociation Reactions

Temel²,

et al. 2010

View full text Add to dashboard Cite

It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals. Keywords Density Functional Theory -Stepped surfaces -Coupling reactions -Bond breaking reactions -BEP relations -Scaling relationsTo bridge the gap between macroscopic properties of a catalyst, such as turn-over rates and selectivity and the microscopic properties obtained from electronic structure methods based on density functional theory (DFT), an in depth understanding of the underlying thermodynamics and kinetics of the corresponding metal surfaces is needed. Today, DFT has reached a level of sophistication where it can be used to describe complete catalytic reactions and hence provide an insight that pinpoints to the origin of the catalytic activity and selectivity. 1,2,3,4,5,6 However, extensive DFT calculations that eventually lead to this understanding are still computationally demanding. A simplification that connects the reactivity and selectivity of a catalytic surface to one or few descriptors is therefore extremely useful. Such a simplification, e.g. the Brønsted-Evans-Polanyi (BEP) relations, is able to show that the transition state energy of a reaction is linearly depending on the reaction energy. 7,8,9,10,11,12 * Corresponding author SLAC-PUB-14285 2 Herein, we investigate the transition state energies of a large number of essential bond breaking and forming reactions that play a key role in the catalytic transformation of a large fraction of base chemicals. The transition state energies investigated include C-C, C-O, C-N, N-O, N-N, and O-O coupling and have been calculated on different stepped surfaces of transition metals such as Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au. For a dissociation reaction (AB → A+B), the transition state energy (E ts ) is calculated by Equation (1), in which E ts/slab , E slab and E gas are the total energies of the slab with transition states, the clean slab, and the gas phase molecules relevant for the reactions, respectively. The dissociative adsorption energy (E diss ) is calculated by Equation (2), in which E A/slab and E B/slab are the total energies of the slab with adsorbates A and B, respectively.(1)All calculations were performed using the DACAPO plane-wave pseudo potential DFT code. 13 Ionic cores were described by ultrasoft pseudopotentials 14, and the Kohn-Sham one-electron valence states were expanded in a basis of plane wave functions with a cutoff energy up to 340 eV. For most adsorption systems, the surface Brillouin zone was sampled using a Monkhorst-Pack grid of size 4×4×1, while 2×3×1 was used for O 2 , and 8×6×1 was used for N 2 and NO as a test of the parameters. The self-consistent electron density was determined by iterative diagonalization of the Kohn-Sham Hamiltonian. A Fermi distribution for the population of...

show abstract

Steam Reforming and Graphite Formation on Ni Catalysts

Cited by 1,014 publications

References 105 publications

Gas phase controlled deposition of high quality large-area graphene films

Gas phase controlled deposition of high quality large-area graphene films

Mechanisms for catalytic carbon nanofiber growth studied byab initiodensity functional theory calculations

Universal Brønsted-Evans-Polanyi Relations for C–C, C–O, C–N, N–O, N–N, and O–O Dissociation Reactions

Contact Info

Product

Resources

About