Quantum Theory of Dissociative Chemisorption on Metal Surfaces

Kroes, Geert–Jan; Groß, Axel; Baerends, E. J.; Scheffler, Matthias; McCormack, Drew A.

doi:10.1021/ar010104u

Cited by 173 publications

(95 citation statements)

References 70 publications

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“…26,35,59,66,83 In one case, the calculations 66 actually challenged the results of older experiments, 8,10 with newer experiments confirming the validity of the theoretical results. 59 Although 6D calculations have been performed for H 2 ϩPd(100) ͑Refs.…”

Section: Introductionmentioning

confidence: 79%

“…Thanks to the improved accuracy of density functional theory 76,77 ͑DFT͒ for determining potential energy surfaces ͑PESs͒ for H 2 ϩmetal systems, 26,78 -80 6D quantum dynamical calculations now yield quantitatively accurate results 26,67,[81][82][83] and are starting to offer a structured procedure for obtaining predictions for experiments. 26,35,59,66,83 In one case, the calculations 66 actually challenged the results of older experiments, 8,10 with newer experiments confirming the validity of the theoretical results.…”

Section: Introductionmentioning

confidence: 99%

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Signatures of site-specific reaction of H2 on Cu(100)

Somers

McCormack

Kroes

et al. 2002

The Journal of Chemical Physics

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Six-dimensional quantum dynamical calculations are presented for the reaction of (v, j) H 2 on Cu͑100͒, at normal incidence, for vϭ0 -1 and jϭ0 -5. The dynamical calculations employed a potential energy surface computed with density functional theory, using the generalized gradient approximation and a slab representation for the adsorbate-substrate system. The aim of the calculations was to establish signatures from which experiments could determine the dominant reaction site of H 2 on the surface and the dependence of the reaction site on the initial rovibrational state of H 2 . Two types of signatures were found. First, we predict that, at energies near threshold, the reaction of (vϭ1) H 2 is rotationally enhanced, because it takes place at the top site, which has an especially late barrier and a reaction path with a high curvature. On the other hand, we predict the reaction to be almost independent of j for (vϭ0) H 2 , which reacts at the bridge site. Second, we predict that, at collision energies slightly above threshold for which the reaction probabilities of the (vϭ0) and (vϭ1) states are comparable, the rotational quadrupole alignment of (vϭ1) reacting molecules should be larger than that of (vϭ0) reacting molecules, for jϭ1, 4, and 5. For ( j ϭ2) H 2 , the opposite should be true, and for ( jϭ3) H 2 , the rotational quadrupole alignment should be approximately equal for (vϭ1) and (vϭ0) H 2 . These differences can all be explained by the difference in the predicted reaction site for (vϭ1) and (vϭ0) H 2 ͑top and bridge͒ and by the differences in the anisotropy of the potential at the reaction barrier geometries associated with these sites. Our predictions can be tested in associative desorption experiments, using currently available experimental techniques.

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Section: Introductionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Signatures of site-specific reaction of H2 on Cu(100)

Somers

McCormack

Kroes

et al. 2002

The Journal of Chemical Physics

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“…In the "trivial" case of diatom (H 2 ), vibrational excitation significantly enhances reactivity because the internuclear distance is intimately associated with the reaction coordinate (31). The dissociative chemisorption of CH 4 is more complicated because of its many vibrational modes (22).…”

Section: Discussionmentioning

confidence: 99%

“…A full-dimensional quantum dynamical description of polyatomic dissociative chemisorption is still extremely challenging (31). In the case of CH 4 , for example, 15 degrees of freedom are needed on a rigid surface, rendering it difficult to develop an accurate, global high-dimensional PES (32)(33)(34) and to carry out quantum dynamical calculations.…”

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confidence: 99%

Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation

Jiang

Ren

Xie

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

117

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The dissociative chemisorption of water is an important step in many heterogeneous catalytic processes. Here, the mode selectivity of this process was examined quantum mechanically on a realistic potential energy surface determined by fitting planewave density functional calculations spanning a large configuration space. The quantum dynamics of the surface reaction were characterized by a six-dimensional model including all important internal coordinates of H 2 O and its distance to the surface. It was found that excitations in all three vibrational modes are capable of enhancing reactivity more effectively than increasing translational energy, consistent with the "late" transition state in the reaction path.heterogeneous catalysis | mode specific chemistry | reaction dynamics T he dissociative chemisorption of H 2 O on transition-metal surfaces, which produces chemisorbed H and OH species, is an important and often obligatory step in many heterogeneous catalytic processes, such as the water-gas shift (WGS) reaction and steam reforming (1). Given our dwindling fossil fuel resources and health-threatening pollution, these reactions have become increasingly important in generating environmentally friendly hydrogen fuels for various high-efficiency applications, such as fuel cells (2). In low-temperature WGS on copper catalysts, for example, the dissociative chemisorption of H 2 O has been identified as the rate-limiting step (3). A better understanding of the reaction dynamics and the ultimate control and/or enhancement of the process could potentially benefit many industrial processes that involve H 2 O. Despite our increasing understanding of the adsorption and dissociation of water on various metal surfaces, however, few experimental studies have been reported (to the best of our knowledge) on the dynamics of water-metal interaction, and none on dissociative chemisorption (4). In this work, we explore a potentially useful scheme based on mode selectivity to enhance dissociative chemisorption on a copper surface.Controlling reactivity of a chemical reaction by selecting reactant internal quantum states is a holy grail in chemical dynamics (5). This mode selectivity and related bond selectivity have been experimentally demonstrated for only a few reactive systems in the gas phase (6-13) and on surfaces (14-21). For example, it was shown that both the kinetics and dynamics of the H þ H 2 O reaction depend sensitively on the vibrational state of the H 2 O reactant (6). Similarly, different vibrational excitations of CH 4 have been demonstrated to have varying efficacies in promoting its dissociative chemisorption on transition-metal surfaces, some more effective than translational energy (22). These observations underscore the importance of quantum dynamical effects and inadequacy of statistically based transition state theory for describing mode-and bond-specific chemistry.A key question in mode-and bond-selective chemistry is whether energy in vibrational coordinates is more effective in promoting reaction than t...

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“…The use of BO to describe lattice motion in metals is, therefore, questionable [3,4]. In spite of this, BO has proven effective for the accurate determination of chemical reactions [5], molecular dynamics [6, 7] and phonon frequencies [9,8,10] in a wide range of metallic systems. Graphene, recently discovered in the free state [11,12], is a zero band-gap semiconductor [13], which becomes a metal if the Fermi energy is tuned applying a gate-voltage V g [14,12].…”

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confidence: 99%

Breakdown of the adiabatic Born–Oppenheimer approximation in graphene

Pisana¹,

Lazzeri²,

Casiraghi³

et al. 2007

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The Born-Oppenheimer approximation (BO) [1] is the standard ansatz to describe the interaction between electrons and nuclei. BO assumes that the lighter electrons adjust adiabatically to the motion of the heavier nuclei, remaining at any time in their instantaneous ground-state. BO is well justified when the energy gap between ground and excited electronic states is larger than the energy scale of the nuclear motion. In metals, the gap is zero and phenomena beyond BO (such as phonon-mediated superconductivity or phonon-induced renormalization of the electronic properties) occur [2]. The use of BO to describe lattice motion in metals is, therefore, questionable [3,4]. In spite of this, BO has proven effective for the accurate determination of chemical reactions [5], molecular dynamics [6, 7] and phonon frequencies [9,8,10] in a wide range of metallic systems. Graphene, recently discovered in the free state [11,12], is a zero band-gap semiconductor [13], which becomes a metal if the Fermi energy is tuned applying a gate-voltage V g [14,12]. Graphene electrons near the Fermi energy have twodimensional massless dispersions, described by Dirac cones. Here * acf26@eng.cam.ac.uk † francesco.mauri@impmc.jussieu.fr 1 we show that a change in V g induces a stiffening of the Raman G peak (i.e. the zone-center E 2g optical phonon [15,16]), which cannot be described within BO. Indeed, the E 2g vibrations cause rigid oscillations of the Dirac-cones in the reciprocal space [17]. If the electrons followed adiabatically the Dirac-cone oscillations, no change in the phonon frequency would be observed. Instead, since the electron-momentum relaxation near the Fermi level [18,19,20] is much slower than the phonon motion, the electrons do not follow the Dirac-cone displacements. This invalidates BO and results in the observed phonon stiffening. This spectacular failure of BO is quite significant since BO has been the fundamental paradigm to determine crystal vibrations from the early days of quantum mechanics [1,9,21,8,10]. Graphene samples are prepared by micromechanical cleavage of bulk graphite at the surface of an oxidized Si wafer with a 300 nm thick oxide layer, following the procedures described in Ref. [11]. This allows us to obtain graphene monocrystals exceeding 30 microns in size. By using photolithography, we then make Au/Cr electrical contacts, which enable the application of a gate voltage, V g , between the Si wafer and graphene (Fig. 1A,B). The resulting devices are characterized by electric-field-effect measurements [12,14,22], yielding a charge carrier mobility µ of 5,000 to 10,000 cm 2 /Vs at 295K and a zero-bias (V g =0) doping of ∼10 12 cm −2 [23]. This is reflected in the existence of a finite gate voltage V n at which the Hall resistance is zero and the longitudinal resistivity reaches its maximum. Accordingly, a positive (negative) V g -V n induces an electron (hole) doping, having an excess-electron surface-concentration of n=η(V g -V n ). The coefficient η ≈7.2 10 10 cm −2 /V is found from Hall effect measu...

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Quantum Theory of Dissociative Chemisorption on Metal Surfaces

Cited by 173 publications

References 70 publications

Signatures of site-specific reaction of H2 on Cu(100)

Signatures of site-specific reaction of H2 on Cu(100)

Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation

Breakdown of the adiabatic Born–Oppenheimer approximation in graphene

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Quantum Theory of Dissociative Chemisorption on Metal Surfaces

Cited by 173 publications

References 70 publications

Signatures of site-specific reaction of H2 on Cu(100)

Signatures of site-specific reaction of H2 on Cu(100)

Enhancing dissociative chemisorption of H 2 O on Cu(111) via vibrational excitation

Breakdown of the adiabatic Born–Oppenheimer approximation in graphene

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Product

Resources

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Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation