The Effect of Surface Geometry of Copper on Dehydrogenation of

Article pubs.acs.org/JPCC

The Effect of Surface Geometry of Copper on Dehydrogenation of Benzotriazole. Part II Anton Kokalj,*,† Sebastijan Peljhan,†,§ and Jože Koller‡ †

Department of Physical and Organic Chemistry, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia Chair of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia

‡

S Supporting Information *

ABSTRACT: Dehydrogenation of benzotriazole (BTAH)an outstanding corrosion inhibitor for copperon low Miller index surfaces of copper and under-coordinated defects thereon has been characterized using density functional theory calculations. The issue of dehydrogenation is of importance, because benzotriazole bonds strongly to copper surfacesa requirement for successful competition with corrosive speciesonly in dehydrogenated (or deprotonated) form. The calculated dehydrogenation activation energy of weakly chemisorbed BTAHoriented with the molecular plane perpendicular to the surfaceis about 1.1 eV on Cu(111), whereas, on more open Cu(100) and step-edges, the activation energy decreases to values closely below 1.0 eV. On the other hand, dehydrogenation activation energies of physisorbed BTAHoriented with the molecular plane parallel to the surfaceare found to be considerably smaller; the smallest calculated value is 0.73 eV. We also find that dehydrogenation barriers decrease with increasing molecular coverage. The effect of aqueous solvent on dehydrogenation of adsorbed BTAH is also considered, and calculations suggest that, in some cases, water molecules may aid the dehydrogenation by reducing the activation energy. Our calculations, therefore, suggest that dehydrogenation of BTAH can be feasible on more open or defective surfaces of copper, whereas, on densely packed Cu(111), it is hindered, because there the desorption energy of about 0.6 eV is considerably smaller.

1. INTRODUCTION This is the second part of the two-part series of articles (Part I: DOI 10.1021/jp409717e) about the role of surface geometry of copper on adsorption and dehydrogenation of benzotriazole (BTAH), which is an outstanding corrosion inhibitor for copper.1−4 There are a number of reportssee, e.g., a review of Finšgar and Milošev4 and references thereinconcerning the nature of the corrosion inhibiting behavior of benzotriazole; however, the structure of the adsorbed BTAH still comes up for the discussion and it is not completely resolved. Several issues concerning the geometry and energetics of BTAH adsorbed on copper surfaces were already discussed on the basis of DFT (density functional theory) modeling in our previous papers5−8 and those of others.9−11 In particular, in one of our studies, the role of surface geometry of copper on the adsorption bonding of the standalone neutral BTAH molecule was addressed,8 whereas, in the present two-part series of articles, we extent that study8 and address the effect of surface geometry of copper on (i) dehydrogenation reaction barrier of BTAH, (ii) adsorption energy of resulting dehydrogenated benzotriazole, and (iii) relative strength of benzotriazole−copper versus chloride− copper bonding. The last two issues were considered in the Part I,12 whereas the first issue is considered in the current paper. The reason the issue (ii) was considered before the issue © 2013 American Chemical Society

(i) is that adsorption structures of dehydrogenated and neutral benzotriazole are required for the calculation of dehydrogenation reaction barriers, while the issue (iii) was considered in Part I (DOI 10.1021/jp409717e) because corrosion is usually promoted by some reactive corrosive species and the inhibitive effect of benzotriazole on the corrosion of copper in chloride media has been often investigated (e.g., see ref 4). This makes the comparison between the adsorption bonding of benzotriazole and chloride on copper surfaces rather relevant. In Part I,12 we showed that chemisorptive bonding of benzotriazole and Cl increases as the coordination number of surface Cu atoms involved in the adsorption site decreases. The bonding enhancement is the strongest for dehydrogenated (deprotonated) benzotriazole, which indicates its tendency to passivate the reactive under-coordinated defective surface sites. Indeed, dehydrogenated (deprotonated) benzotriazole bonds considerably stronger to copper surfaces than the neutral BTAH and can rival the strength of Cl−surface interaction.6,12 While at the metal/vacuum interface, the Cl bonds stronger to copper surfaces than dehydrogenated benzotriazolealthough Received: September 30, 2013 Revised: December 10, 2013 Published: December 12, 2013 944

dx.doi.org/10.1021/jp409719c | J. Phys. Chem. C 2014, 118, 944−954

The Journal of Physical Chemistry C

Article

water interface is far more appropriate to consider than the solid/gas (or solid/vacuum) interface. For this reason, the effect of water solvent on dehydrogenation barriers is also discussed and roughly estimated.

the bonding difference between the two reduces as the coordination number of surface Cu atoms decreases approximate implicit solvent calculations reveal that aqueousphase adsorption of deprotonated BTA− is more exothermic than that of Cl−, mainly because the chloride anion is much smaller and solvates considerably stronger in water than the BTA−.6,12 These findings suggest that the deprotonated form of benzotriazole is likely the actual active species for inhibiting the corrosion.6 This proposition is strongly supported by experimental evidence; namely, benzotriazole is a less efficient inhibitor in acidic solutions,13−16 where the amount of deprotonated species is decimated, and, moreover, 1-methylbenzotriazole is ineffective in preventing the corrosion of copper,17 because the substitution of acidic hydrogen by the methyl group prevents the formation of the deprotonated form of benzotriazole. Benzotriazole can, therefore, compete with Cl− only when it is stripped of its H1 atom (Lewis structures of neutral and deprotonated forms of benzotriazole are shown in Figure 1). In

2. TECHNICAL DETAILS 2.1. Computational. DFT calculations were performed with the plane-wave pseudopotential method as implemented in the PWscf code from the Quantum ESPRESSO distribution,22 using the ultrasoft pseudopotentials23,24 and plane-wave basis set with a kinetic energy cutoff of 30 Ry (240 Ry for the charge density), while molecular graphics were produced by the XCRYSDEN25 graphical package. We used the PBE26 and reparametrized PBE-D′ energy functionals; the latter includes a semiempirical dispersion correction of Grimme.27,28 Because the original PBE-D functional overestimates adsorption energies on metal surfaces, a reparameterized version was used (see ref 5; the prime in the PBE-D′ label is used to indicate the reparameterization of the original method). Surfaces were modeled by periodic slabs with the in-plane lattice spacing fixed at the calculated equilibrium Cu bulk lattice parameter (3.67 Å for PBE29 and 3.64 Å for PBE-D′5). For further computational details, see the Part I of this two-part article series.12 Unless explicitly stated otherwise, the presented results refer to the PBE functional. 2.2. Definitions and Energy Equations. Even though the metal/water interface would be more appropriate in the context of benzotriazole as a corrosion inhibitor, the calculations were, nevertheless, performed at the metal/vacuum interface due to obvious modeling reasons. The adsorption energies were calculated as

Figure 1. Lewis structures of neutral BTAH molecule (left) and its deprotonated BTA− form (right). Numbering of atoms is also indicated.

principle, this can be achieved either by deprotonation in solution BTAH(aq) ⇄

− BTA (aq)

+

+ H(aq)

Eads = E X/surf − (Esurf + E X )·

where the subscript X stands for adsorbate (X  BTAH, BTA⊙, or H) and EX, Esurf, and EX/surf are the total energies of isolated adsorbate (molecule or atom), Cu slab, and adsorbate/ Cu−slab systems, respectively. In the case of radicals, the adsorption energy will be designated as E⊙ ads to emphasize that it is calculated with respect to the radical in the initial state; the E⊙ ads, therefore, measures the binding energy of the radical to the surface. Dehydrogenation reactions were modeled as the minimum energy paths (MEPs) connecting the reactants (initial state, IS) with the products (final state, FS), using the climbing-image nudged elastic band (CI-NEB) method.30,31 The configuration of maximum energy along the MEP is identified as the transition state (TS), the energy difference of which with respect to the IS gives the activation energy, E* = ETS − EIS. For the precise location of the TS, the threshold for the magnitude of the atomic forces was set below 50 meV/Å. Dehydrogenation reaction energies, ΔEdeh, can be calculated either as a difference between the energy of FS and IS, i.e.

(1) −

followed by subsequent adsorption of BTA or by dehydrogenation of adsorbed BTAH on the surface of copper: ⊙ ⊙ BTAH(ads) ⇄ BTA (ads) + H(ads)

(3)

(2)

In the last reaction, the positive and negative signs are omitted in favor of the ⊙ sign to indicate the radical character; the actual charge of the adsorbed species depends on the electronegativity difference between the adsorbate and the metal surface,18 and according to our previous calculations, the BTA adsorbed onto Cu(111) is only partially negatively charged by about half an electron.6 The subject of the current paper is to explore the feasibility of dehydrogenation reaction 2 on copper surfaces. The issue of dehydrogenation is motivated by observation that transition metals are very effective catalysts for cleaving the X−H bonds (where X is, e.g., C, N, O, or S). For example, the dehydrogenation of ammonia can occur on the open Cu(110) surface.19 Similarly, it has been demonstrated that under-coordinated defects on copper surfaces are reactive enough to dehydrogenate unsaturated organic molecules.20 Indeed, under-coordinated surface defects are generally known to be more reactive for breaking chemical bonds;21 hence, the role the surface defects play in reaction 2 should be also addressed. It should be noted that, due to obvious modeling reasons, the presented calculations refer to the metal/vacuum interface. However, with respect to corrosion and its inhibition, the solid/

ΔEdeh = E FS − E IS

(4)

or from the adsorption (binding) energies of BTAH ⊙ H⊙ BTA⊙ (EBTA ads ), and H (Eads) as ⊙

(EBTAH ads ),

⊙

BTA H N1−H BTAH ΔEdeh = [Eads + Eads + D bond ] − Eads

(5)

DN1−H bond

where is the calculated N1−H bond dissociation energy of BTAH, 4.72 eV. In this paper, only dehydrogenation reaction energies will be considered; hence, the notation of ΔEdeh can be 945



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Figure 2. Structural characteristics of different identified adsorption modes of neutral8 (a−c) and dehydrogenated12 (d−f) benzotriazole: (a) Weakly chemisorbed modes of BTAH bonded perpendicularly to the surface via triazole nitrogen atoms (dN−Cu stands for N−Cu bond length). (b) Physisorption mode with BTAH molecular plane nearly parallel to the surface. (c) Strongly bonded parallel adsorption mode of BTAH on Cu(110) with the molecule roughly oriented along the [001] direction; this mode is ascribed as apparent chemisorption + physisorption mode (labeled as “apparent chem+phys”).8 (d) BTA⊙ bonded perpendicularly as bridge−N2+N3. (e) Highly tilted mode of chemisorbed BTA⊙ on Cu(100) bonded via N1+N2+N3 atoms and (f) bonded parallel onto Cu(110) and oriented roughly along the [001] direction.12

simplified to ΔE. The difference between eq 4 and eq 5 is that the latter allows (in principle) the calculation of ΔE at the limit of zero coverage (i.e., at infinite separation of adsorbates). It is should be noted that, among various terms of eq 5, the EBTAH ads by far the most susceptible to surface coverage; hence, values extrapolated to zero coverage by the method of ref 32 will be used. To facilitate the presentation, we will also use the Θ and NC labels. Θ is the surface coverage (defined as the inverse of the number of surface Cu atoms per adsorbate), and NC is the average coordination number of Cu atoms involved in the adsorption site. Benzotriazole adsorption geometries will be designated as site−atomlist, where site designates the site on the surface to which the molecule bonds with the atoms specified by atomlist. For example, designation bridge−N2+N3 specifies the molecule adsorbed over the bridge site with N2 and N3 atoms attached to the surface.

3. RESULTS AND DISCUSSION 3.1. Adsorption of BTAH, BTA⊙, and H. The adsorption of neutral BTAH, dehydrogenated BTA⊙, and H on low Miller index copper surfaces and under-coordinated defects thereon was considered in our previous publications.8,12 Here, only the principal findings are briefly summarized, because they are required for better comprehension of dehydrogenation of benzotriazole. Structural characteristics of different identified adsorption modes of neutral and dehydrogenated benzotriazole are pictured in Figure 2, magnitudes of adsorption energies as a function of coordination number of surface Cu atoms involved in the adsorption site are shown in Figure 3, and various considered surface structuresflat facets and under-coordinated defectsof copper are shown in Figure S1 in the Supporting Information. The neutral BTAH can either weakly chemisorb in an upright geometry via triazole nitrogen atoms with the N−Cu distances of about 2.1 Å (Figure 2a) or physisorb nearly parallel to copper surfaces (Figure 2b) with the molecule−surface height ranging from about 2.6 Å on Cu(110) to 3 Å on Cu(111).8 Among the perpendicular modes, the bridge− N2+N3 is the stablest, whereas the less stable top−N2 is of appropriate geometry for dehydrogenation, because its H1 atom points toward the surface and can be released to the surface during the reaction (Figure 2a; the difference in stability between the top−N2 and bridge−N2+N3 modes is about 0.1 and 0.2 eV on Cu(111) and Cu(100),8 respectively). As evident from Figure 3, the magnitude of chemisorption energy

Figure 3. Low coverage adsorption energy magnitudes of BTAH, BTA⊙, and H as a function of coordination number of surface Cu atoms; data taken from refs 8 and 12. The PBE adsorption energies are designated by solid symbols (H, BTAH⊥, and BTA⊙ ⊥ ), while the PBED′ adsorption energies are labeled by open symbols (BTAH∥ and apparent chem+phys BTAH∥).

increases as passing from densely packed Cu(111) (−0.60 eV, PBE value) to more open surfaces and low-coordinated defects (−1.26 eV at addimer defect, PBE value), whereas the physisorption energy is similar on all three low Miller index surfaces (being about −0.7 eV as calculated by PBE-D′ functional); a notable exception is the BTAH adsorbed parallel onto Cu(110) and oriented along the [001] direction (Figure 2c), which displays a remarkably stronger adsorption energy of −1.3 eV (PBE-D′ value), and a considerably smaller average molecule−surface height of about 2.3 Å. This mode was ascribed as apparent chemisorption+physisorption mode.8 In contrast to neutral BTAH, dehydrogenated BTA⊙ strongly chemisorbs to copper surfaces and the magnitude of the chemisorption energy increases as the coordination number of surface Cu atoms involved in the adsorption site decreases (Figure 3), i.e., from −2.8 eV on Cu(111) to −3.8 eV on the 946



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Figure 4. PBE reaction energies, ΔE, for dehydrogenation of weakly chemisorbed BTAH: (a) ΔE extrapolated to the limit of zero surface coverage, calculated by eq 5, on perfect Cu surfaces and under-coordinated surface defects (labeled according to Figure S1 in the Supporting Information). (b) ΔE on Cu(100), calculated by eq 4, as a function of surface coverage (the upper x axis states the corresponding supercells). Two sets of points are plotted, which correspond to product BTA⊙+H coadsorbed to either adjacent (stars) or distant sites (squares). The curves are drawn to guide the eye.

low-coordinated addimer defect (PBE values).12 In addition to perpendicular modes (Figure 2d), also the parallel (Figure 2f) or highly tilted (Figure 2e) adsorption modes were identified. While the PBE functional slightly favors the perpendicular modes, the PBE-D′ slightly prefers the parallel (or highly tilted) modes.12 As for the adsorption of H, Figure 3 reveals that its adsorption energy is rather insensitive to surface geometry, being about −2.5 eV (PBE value);12 a similar insensitive trend was also observed for H on Rh surfaces.33 Among the considered species, the neutral BTAH displays by far the strongest dependence of adsorption energy on surface coverage due to its large permanent dipole moment (4.1 D), which results in repulsive and long-range dipole−dipole interactions between perpendicularly adsorbed BTAH molecules, whereas, for parallely adsorbed BTAH, they are far less important and slightly attractive at higher coverages8,32 (see Figure S2 in the Supporting Information). On the other hand, lateral dipole−dipole interactions are not significant for BTA⊙ due to considerable adsorption-induced charge transfer, which greatly reduces the dipole.6 Also, the adsorption energies of H are not very sensitive to surface coverage.12 Concerning the use of PBE and PBE-D′ functionals, the following points should be noted. For parallel adsorption modes of neutral BTAH, the PBE-D′ functional should be more appropriate than the PBE, because, for these physisorption modes, the semiempirical dispersion correction is crucial (the inability of the PBE to describe the dispersion interaction gives the Eads of merely −0.1 eV).8 The situation is less clear for dehydrogenated BTA⊙, which chemisorbs strongly. Namely, it is known that the PBE often overestimates the chemisorption bonding;34,35 hence, the PBE-D′ would overestimate even more in such cases. However, for parallel (or highly tilted) adsorption modes, the dispersion interactions are more important than for perpendicular modes due to larger molecular contact area with the surface; hence, even if the absolute values of PBE-D′ are inferior to PBE ones, the PBE-D′ may more appropriately capture the relative stability between the perpendicular and the parallel (or highly tilted) adsorption modes. For these reasons, the perpendicular modes are

preferentially treated with the PBE and the parallel (or highly tilted) modes with the PBE-D′ functional. 3.2. Dehydrogenation of Benzotriazole. The fact that dehydrogenated BTA⊙ interacts much stronger with copper surfaces than neutral BTAH opens a question whether BTAH would dehydrogenate on the surface (cf. reaction 2). Note that surface dehydrogenation reactions are known to closely follow the linear Brønsted−Evans−Polanyi (BEP) relation,36 which associates the activation energy (E*) with the reaction energy (ΔE), E* = a + bΔE; hence, the more exothermic is the ΔE, the smaller is the E*. This relationship helps to explain why the low-coordinated defects are known for their increased reactivity toward bond-breaking; namely, they also bind adsorbates stronger. According to current calculations, the dehydrogenation of benzotriazole is slightly endothermic on Cu(111) and about athermic on Cu(100) and Cu(110) surfaces at the limit of very small surface coverage; indeed, as shown in Figure 4a, the exothermicity of dehydrogenation increases as the coordination number of surface Cu atoms involved in adsorption site decreases. Dehydrogenation also becomes more exothermic at larger molecular surface coverages (see Figure 4b), because the lateral interactions are strongly repulsive and long ranged for perpendicularly adsorbed BTAH and much less so for the adsorbed BTA⊙. Apart from this coverage effect, the trend of ΔEdeh is given by variations of the adsorption energies of neutral and dehydrogenated benzotriazole, because the adsorption energy of H is rather insensitive to surface geometry (see Figure 3). The increasing exothermicity of ΔEdeh, therefore, stems from the fact that the magnitude of the adsorption energy increases more rapidly for dehydrogenated BTA⊙ than for neutral BTAH as the coordination number decreases. Indeed, the average slope of the |Eads| curve, Δ|Eads|/ ΔNC, in Figure 3, is 0.20 and 0.14 eV for BTA⊙ and BTAH, respectively. 3.2.1. Dehydrogenation of Perpendicularly Chemisorbed BTAH. As the activation energy calculations are computationally at least an order of magnitude more demanding than the structural relaxations, we calculated the E* for just a subset of surface geometries shown in Figure S1 in the Supporting Information, and the corresponding results for dehydrogen947



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Table 1. PBE Calculated Activation (E*) and Reaction (ΔE) Energies for Dehydrogenation of Weakly Chemisorbed BTAH Bonded Perpendicularly to the Copper Surface (Values in Parentheses Are the PBE-D′ Values)c surface geometry (111) (100) (111)/(111) (100)/(110)

NC 9 8 7 6

Θ (ML) a

1/16 1/16a 1/16a 1/15b

Θ (10−2 Å−2)

BTAH ads. mode

BTA⊙ ads. mode

E* (eV)

ΔE (eV)

1.07 (1.09) 0.93 (0.95) 1.07 0.99

top−N2 top−N2 top−N2 top−N2

SB−N2+N3 SB−N2+N3 SB−N2+N3 LB−N2+N3

1.14 (1.17) 0.96 (0.93) 0.97 0.96

+0.14 (+0.17) −0.09 (−0.15) −0.32 −0.36

Calculated with the (4×4) supercell. bCalculated with the 25 03 supercell. cDehydrogenation does not proceed from the stablest bridge−N2+N3 mode, but from the top−N2 mode (both shown in Figure 2a), and the corresponding E* and ΔE are reported with respect to this latter mode. The resulting BTA⊙ is always adsorbed in bridge−N2+N3 mode (shown in Figure 2d). Reaction energies are calculated according to eq 4, and surface coverages are reported in relative ML and absolute Å−2 units. Labels SB and LB refer to short-bridge and long-bridge sites, respectively (these sites are designated graphically in Figure S1 in the Supporting Information). a

( )

activation energies are about 0.1 eV larger than the PBE-D′ ones. This discrepancy is not unreasonable, because the PBED′ predicts significantly smaller molecule−surface height, which facilitates the N1−H bond-breaking, whereas, in the PBE calculations, the molecules have to first approach closer to the surfacewhich costs some extra energy due to Pauli repulsionand only then the N1−H bond-breaking is initiated. The activation energies of parallel adsorption modes of BTAH are smaller than those for perpendicular modes (cf. Tables 1 and 2), and on Cu(100) and Cu(110), the values are considerably below 1 eV. Note that, for each surface, the E* values at two different coverages are reported, because we observed that the dehydrogenation barrier decreases with increasing surface coverage. This is, to some extent, surprising, becausein contrast with the perpendicularly adsorbed BTAHthe lateral interactions between parallelly physisorbed BTAH molecules are slightly attractive8 (this coverage dependence is illustrated in Figure S2 in the Supporting Information). The reason appears to be connected to the BEP principle; namely, despite the weak attraction between physisorbed BTAH molecules, the exothermicity of dehydrogenation nevertheless increases with increasing surface coverage, as evidenced by ΔE values reported in Table 2. An example of the atomic-scale mechanism of dehydrogenation of parallelly physisorbed BTAH is shown in Figure 6a. According to PBE-D′ results, the dehydrogenation would be quite feasible on Cu(110) at room temperature, where the competing desorption energy of BTAH of about 1.3 eV is considerably larger, whereas, on Cu(111), the dehydrogenation would be less feasible, despite the relatively small E* values, because the competitive desorption energy is even smaller, about 0.7 eV.8 3.3. Dehydrogenation vs Desorption of BTAH. The above consideration of competitive dehydrogenation versus desorption of BTAH was based on the corresponding activation energies. Activation energy is only one component, although very important, of the van’t Hoff−Arrhenius equation for the reaction rate constant k; i.e., k = v exp[−E*/(kBT)]. The other component is the preexponential factor, v, which can be according to transition-state theoryassociated with the vibrational frequency of the initial state along the reaction coordinate, whereas kB and T are the Boltzmann constant and temperature, respectively. It is known that the preexponential factors for desorption are usually 1−3 orders of magnitude larger than the preexponential factors for dehydrogenation of the same molecule37 (see also ref 38 for a detailed discussion on preexponential factors). At room temperature (T ≈ 300 K), this amounts to the activation energy difference of 0.06−0.18

ation of perpendicularly adsorbed BTAH are reported in Table 1. Because of the reasons described in section 3.1, the majority of presented results were calculated with the PBE functional, whereas two cases were also calculated with the PBE-D′ functional for the sake of comparison, and it can be seen that the two functionals give very similar results. Activation energy for dehydrogenation of weakly chemisorbed BTAH is calculated to be about 1.1 eV on Cu(111) and decreases to values closely below 1.0 eV on more open Cu(100) and on (111)/(111) and (100)/(110) step edges. These results, therefore, confirm the BEP-based anticipation that the activation energy of dehydrogenation reduces as passing from densely packed Cu(111) to more open surfaces and low-coordinated defects. An example of the atomic-scale reaction mechanism is shown in Figure 5a, which shows the snapshots of IS, TS, and FS structures for dehydrogenation of perpendicularly chemisorbed BTAH on Cu(100). The reaction proceeds from the BTAH bonded with the N2 atom onto the top site; note that this mode, denoted as top−N2, is inferior to the stablest bridge−N2+N3 mode (for details, see our previous study8). In the course of reaction, the BTAH swings over the top site and, at a given point, the N1−H bond starts to break and the N1−Cu bond starts to form, eventually resulting in coadsorbed bridge−N2+N1 bonded BTA⊙ and off-hollow H (note that bridge−N2+N1 mode is symmetrically equivalent to bridge−N2+N3). Current results reveal that dehydrogenation of weakly chemisorbed BTAH is kinetically hindered. This is particularly true on close-packed Cu(111), because the calculated E* of 1.14 eV is appreciable and cannot be easily overcome at room temperature (see section 3.3 below) and, moreover, because the E* is also considerably larger than the desorption energy (Edes ≤ 0.6 eV); for nonactivated adsorption, the Edes = −Eads. However, on more open surfaces and under-coordinated defects, dehydrogenation barriers become smaller and desorption energies larger. 3.2.2. Dehydrogenation of Parallelly Physisorbed BTAH. Dehydrogenation reactions were also calculated for parallelly adsorbed BTAH geometries that result in highly tilted or even parallel bonded BTA⊙ shown in Figure 2e,f. The resulting dehydrogenation barriers on Cu(111), Cu(100), and Cu(110) are summarized in Table 2. In contrast to the case of perpendicular modes of BTAH, here, the majority of presented results were calculated with the PBE-D′ functional, becauseas described in section 3.1this functional gives more appropriate description of the parallel physisorption modes. However, two examples were also calculated with the plain PBE functional for the sake of comparison; the corresponding 948



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Figure 5. Top and side views of optimized structures of initial, transition, and final states for dehydrogenation (N−H bond-breaking) of weakly chemisorbed BTAH on Cu(100): (a) standalone adsorbed BTAH and (b) adsorbed BTAH interacting with coadsorbed water molecule. Activation energies and N−Cu, O−Cu, N−H, and N···H bond lengths are also stated.

methanol (O−H bond scission) on Cu(110)39 and for the dehydrogenation of NH 3 on Rh(111). 40 As for the preexponential factors of desorption, the values of 1016 s−1 or larger are known for desorption of alkanes (CNH2N+2, N ≥ 6) from various surfaces,41,42 whereas the value of 1017 s−1 was reported for desorption of flat-lying benzene on Pd(111).43 On the basis of these values, it seems reasonable to assumefor the sake of discussionthe values of ≈1013 s−1 and ≳ 1016 s−1 for the preexponential factors of dehydrogenation and

eV. Dehydrogenation is, therefore, competitive with desorption only when its activation energy is by such an adequate amount smaller than the desorption energy. The preexponential factors for dissociation of adsorbed molecules at low coverage are often below the value of kBT/h ≈ 1013 s−1,37 where h is Planck’s constant. Nevertheless, DFTcalculated preexponential factors for cleavage of O−H and N− H bonds of adsorbed molecules are close to this value; e.g., the v = 2 × 1013 s−1 was reported for the dehydrogenation of 949



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Table 2. As in Table 1 but Calculated with the PBE-D′ Functional for the Parallel Physisorption Modes of BTAH (the PBE Values Are Stated in Parentheses)f surface geometry

NC

(111)

9

(100)

8

(110)

7

Θ (ML) a

1/16 1/9b 1/15c 1/9b 1/8d 1/6e

Θ (10−2 Å−2)

BTAH ads. mode

BTA⊙ ads. mode

E* (eV)

ΔE (eV)

1.09 1.94 1.01 1.68 (1.65) 1.34 1.77 (1.74)

≈ Figure 2b ≈ Figure 2b ≈ Figure 2b ≈ Figure 2b Figure 2c Figure 2c

≈ Figure 2e ≈ Figure 2e Figure 2e Figure 2e Figure 2f Figure 2f

0.96 0.85 0.86 0.73 (0.83) 0.82 0.75 (0.91)

−0.02 −0.14 −0.31 −0.46 (−0.21) −0.04 −0.16 (−0.17)

Calculated with the (4×4) supercell. bCalculated with the (3×3) supercell. cCalculated with the 25 03 supercell. dCalculated with the 14 20 supercell. eCalculated with the 13 20 supercell. fThe notation “≈ Figure” means “similar as in Figure”.

( )

a

(

)

( )

Figure 6. As in Figure 5, but calculated with the PBE-D′ functional for the parallelly physisorbed BTAH on Cu(111).

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Figure 7. Reaction energy profiles for adsorption and subsequent dehydrogenation of benzotriazole on copper surfaces; for perpendicular modes, the PBE (top panels) and, for parallel modes, the PBE-D′ (bottom panels) results are presented. The zero energy corresponds to gas-phase benzotriazole. Reddish rectangles drawn on top of the TS positions indicate an energy equivalent of 0.2 eV that accounts for the estimated difference in prefactors between dehydrogenation and desorption at T = 300 K (see text). The short blue dashed lines (top panels) correspond to adsorption energies of BTAH⊥ extrapolated to zero coverage.

desorption of BTAH, respectively. These values, therefore, imply that, for dehydrogenation to be competitive with desorption at room temperature, its activation energy should be about 0.2 eV smaller than the desorption energy. A typical time scale (τ) of an elementary reaction event can be estimated as τ = v−1 exp[E*/(kBT)]. At T = 300 K, the kBT is 0.026 eV. Hence, a typical τ for dehydrogenation with v = 1013 s−1 and E* = 1.15 eV is on the order of 2 × 106 s ≈ 1 month and, for dehydrogenation with E* = 1.0 eV, it is on the order of 2 h, whereas, for E* = 0.8 eV, it is on the order of 1 s. These time scales imply that dehydrogenation of weakly chemisorbed BTAH would be kinetically hindered on Cu(111) at room temperature, but on more open surfaces and undercoordinated defects, it would be much more facile. However, on many of these sites, the desorption of BTAH is favored with respect to dehydrogenation; the interplay between the desorption and the dehydrogenation can be appreciated from Figure 7, which plots the corresponding reaction energy profiles. A notable exception is the so-called apparent chemisorption+physisorption mode of parallel BTAH on Cu(110), for which the competing desorption energy of 1.3 eV is considerably larger than the dehydrogenation activation energy of about 0.8 eV. For the majority of other cases, the dehydrogenation would be achievable by continually populating the adsorption state. Although the majority of BTAH molecules would desorb, occasionally also dehydrogenation would occur. On the basis of presented results, we can, therefore, infer that dehydrogenation of BTAH should be feasible on copper surfaces. This inference is strongly supported by experimental findings. Indeed, it has been often claimed that the H1 atom of benzotriazole is removed upon chemisorption on copper surfaces even under ultra-high-vacuum (UHV) conditions.44−47

Very recently, Grillo et al.47 showed by means of STM (scanning tunneling microscopy) and RAIRS (vibrational spectroscopy) not only that benzotriazole adsorbs as BTA− on the copper surface under UHV conditionsnote that we showed by DFT modeling6 that, for gas-phase adsorption, it is more appropriate to refer to BTA⊙ insteadbut also that the chemisorption initially takes place at the step-edge defects, which is in agreement with the current calculations (e.g., see Figure 3). 3.4. Effect of Water on Dehydrogenation Barrier. The above-discussed dehydrogenation activation energies were calculated at the metal/vacuum interface, but in the context of BTAH as corrosion inhibitor, the metal/water interface is more appropriate, because corrosion takes place at this phase boundary. It should be noted that benzotriazole stripped from its H1 atom is the relevant building unit also for the formation of organometallic complexes with copper, whose formation has been often considered as a very important factor for achieving the corrosion inhibitory effect1,4,48,49 (for corresponding DFT modeling of such complexes, see Part I12 and refs 6 and 11). For this reason, an effort has been undertaken to roughly estimate the effect of water on the dehydrogenation reaction barrier. We followed the method used in our previous studies,6,50 which describes the solvent implicitly by the continuum solvation model.51 It should be noted that water interacts weakly with the hydrophobic metals, such as copper, and, moreover, flat copper facets are not expected to easily dissociate water molecules;52,53 these circumstances, therefore, alleviate some problems associated with the use of the implicit solvent model in the current case. In addition, we also modeled the interaction between BTAH and an explicit water molecule in the coadsorbed state, an approach along the lines used by 951



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Michel et al.54 Finally, we combined the two approaches, where the coadsorbed BTAH and H2O molecules were immersed into implicit solvent. The molecular structure of BTAH is suitable for the formation of intermolecular hydrogen bonds. For example, BTAH forms N−H···H bonds in its crystal structure55 and it can also form intermolecular hydrogen bonds with water molecules, where it acts as either hydrogen bond acceptor (O− H···N) or hydrogen bond donor (N−H···O). To estimate how such intermolecular bonding would affect the dehydrogenation activation energy, the reaction was recalculated by adding to the model an explicit water molecule that acted as hydrogen bond donor. Two examples were considered: dehydrogenation of BTAH weakly chemisorbed perpendicularly to Cu(100) and physisorbed parallel to Cu(111). The IS, TS, and FS structures of the former are shown in Figure 5b. In the IS structure, the BTAH and water molecules are coadsorbed onto top sites of nearest-neighbor Cu atoms such that an intermolecular hydrogen bond develops with the H···N bond length of 1.76 Å. This bond shortens to 1.73 Å at the TS and to 1.68 Å at the FS, indicating that it becomes stronger as the reaction proceeds. As a result, the activation energy lowers considerably, from 0.96 eV (for standalone BTAH) to 0.77 eV (for coadsorbed BTAH + H2O), a reduction of 0.19 eV. A very similar effect of water molecule as hydrogen bond donor on reduction of the dehydrogenation barrier was observed previously by Michel et al.54 for dissociation of the O−H bond of ethanol on Rh(111). The opposite, but twice smaller, effect is observed for dehydrogenation of BTAH physisorbed parallel to Cu(111), where activation energy, calculated by the PBE-D′ functional, increases from 0.96 eV (for standalone BTAH) to 1.04 eV (for coadsorbed BTAH + H2O), an enhancement of 0.08 eV. The corresponding IS, TS, and FS structures are shown in Figure 6b. As for the implicit description of aqueous solvent, the effect of water solvent on E* was estimated by calculating TS/metal IS/metal ΔE* ≈ ΔGsolv − ΔGsolv

The implicit solvent model, therefore, predicts a considerably smaller effect of water on the dehydrogenation barrier of BTAH than the explicit H2O + BTAH calculation. This is perhaps not surprising. Namely, a single water molecule is rather flexible and can well optimize its interaction with the BTAH molecule, whereas, in aqueous phase, the pertinent water molecule would be less flexible due to other surrounding water molecules and its interaction with the BTAH would be compromised, because it would need to coordinate the interaction with both BTAH and with other water molecules. On the other hand, the implicit solvent model may have some difficulties to properly describe the solute−solvent intermolecular hydrogen bonding.51 Hence, the values resulting from the two different approaches can be roughly seen as upper and lower bounds to the effect of water on the dehydrogenation barrier. On this basis, it can be concluded that the discussion of the preceding section about the feasibility of dehydrogenation of BTAH on copper remains valid.

4. CONCLUSION Dehydrogenation of benzotriazole on low Miller index surfaces of copper and under-coordinated defects thereon has been characterized using DFT calculations. We have shown that the calculated activation barriers are small enough for dehydrogenation of BTAH to be facile at room temperature on copper surfaces, except on perfect facets of densely packed Cu(111). However, on many investigated surface geometries, the desorption of BTAH is estimated to be more probable than the dehydrogenation, implying that dehydrogenation would be achievable by continually populating the adsorption state; although the majority of BTAH molecules would desorb, occasionally also dehydrogenation would occur. Once the molecule is dehydrogenated, it bonds very strongly to copper surface and can rival with corrosive species, such as chloride ions.12 Current findings, therefore, not only support the experimental observations that the H1 atom of benzotriazole is removed prior or subsequent to chemisorption on copper surfacesor else the molecule would adsorb very weaklybut also provide atomic-scale insight into the mechanism of how the H1 atom is detached from the BTAH molecule adsorbed on copper surfaces.

(6)

where ΔGsolv terms designate solvation free energies of corresponding systems, while IS/metal and TS/metal indicate the molecule/metal system in initial-state and transition-state geometry, respectively (e.g., as shown in Figure 5). The ΔGsolv terms were evaluated by utilizing cluster models of the surface, which are built by cutting the optimized structures as obtained from the gas-phase slab calculations. A two-layer Cu(100)[30,20] cluster was used (shown in Figure S3 in the Supporting Information), where the subscripts indicate the number of Cu atoms in the first and second (100) layers. This cluster is large enough to well accommodate the adsorbed molecule. The soobtained cluster was then immersed into implicit solvent with the geometry kept fixed, and the ΔGsolv terms were calculated by the COSMO method56 as implemented in the NWChem code57 (for further computational details, see ref 58). The effect of aqueous solvent on the dehydrogenation barrier was evaluated by the described implicit solvent model for the two examples shown in Figure 5, that is, for standalone chemisorbed BTAH and for coadsorbed BTAH + H2O on Cu(100). For standalone chemisorbed BTAH on Cu(100) (shown in Figure 5a), the implicit solvent model predicts a very small reduction of E*, ΔE* = −0.02 eV, whereas, for coadsorbed BTAH + H2O (shown in Figure 2b), the effect of implicit solvent on E* is predicted to be even smaller, ΔE* ≈ 0.01 eV.

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ASSOCIATED CONTENT

S Supporting Information *

Figures S1, S2, and S3. The first figure shows various considered surface geometries and designation of bridge adsorption sites, the second figure shows the dependence of adsorption energy of neutral BTAH on the surface coverage, and the third figure displays the Cu(100)[30,20] cluster used for the implicit solvent COSMO calculations. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +386-1-477-35-23. Fax: +386-1-477-38-22. E-mail: tone. [email protected]. URL: http://www.ijs.si/ijsw/K3-en/Kokalj. Present Address §

BIA Separations d.o.o., Mirce 21, SI-5270 Ajdovščina, Slovenia. Notes

The authors declare no competing financial interest. 952



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et al. QUANTUM ESPRESSO: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys.: Condens. Matter 2009, 21, 395502. Code available from http://www.quantumespresso.org/. (23) Vanderbilt, D. Soft Self-Consistent Pseudopotentials in a Generalized Eigenvalue Formalism. Phys. Rev. B 1990, 41, 7892−7895. (24) Ultrasoft pseudopotentials for H, C, N, O, and Cu were taken from the Quantum Espresso PseudoPotential download page: http:// www.quantum-espresso.org/pseudopotentials (files: H.pbe-rrkjus.UPF, C.pbe-rrkjus.UPF, N.pbe-rrkjus.UPF, O.pbe-rrkjus.UPF, and Cu.pbe-d-rrkjus.UPF). (25) Kokalj, A. Computer Graphics and Graphical User Interfaces as Tools in Simulations of Matter at the Atomic Scale. Comput. Mater. Sci. 2003, 28, 155−168. Code available from http://www.xcrysden.org/. (26) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (27) Grimme, S. Semiempirical GGA-Type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787−1799. (28) Barone, V.; Casarin, M.; Forrer, D.; Pavone, M.; Sambi, M.; Vittadini, A. Role and Effective Treatment of Dispersive Forces in Materials: Polyethylene and Graphite Crystals as Test Cases. J. Comput. Chem. 2009, 30, 934−939. (29) Peljhan, S.; Kokalj, A. Adsorption of Chlorine on Cu(111): A Density-Functional Theory Study. J. Phys. Chem. C 2009, 113, 14363− 14376. (30) Henkelman, G.; Jonsson, H. Improved Tangent Estimate in the Nudged Elastic Band Method for Finding Minimum Energy Paths and Saddle Points. J. Chem. Phys. 2000, 113, 9978. (31) Henkelman, G.; Uberuaga, B. P.; Jonsson, H. A Climbing Image Nudged Elastic Band Method for Finding Saddle Points and Minimum Energy Paths. J. Chem. Phys. 2000, 113, 9901. (32) Kokalj, A. Electrostatic Model for Treating Long-Range Lateral Interactions between Polar Molecules Adsorbed on Metal Surfaces. Phys. Rev. B 2011, 84, 045418. (33) Kokalj, A.; Bonini, N.; Sbraccia, C.; de Gironcoli, S.; Baroni, S. Engineering the Reactivity of Metal Catalysts: A Model Study of Methane Dehydrogenation on Rh(111). J. Am. Chem. Soc. 2004, 126, 16732−16733. (34) Hammer, B.; Hansen, L. B.; Nørskov, J. K. Improved Adsorption Energetics within Density-Functional Theory Using Revised Perdew-Burke-Ernzerhof Functionals. Phys. Rev. B 1999, 59, 7413−7421. (35) Alaei, M.; Akbarzadeh, H.; Gholizadeh, H.; de Gironcoli, S. CO/ Pt(111): GGA Density Functional Study of Site Preference for Adsorption. Phys. Rev. B 2008, 77, 085414. (36) Michaelides, A.; Liu, Z.-P.; Zhang, C. J.; Alavi, A.; King, D. A.; Hu, P. Identification of General Linear Relationships between Activation Energies and Enthalpy Changes for Dissociation Reactions at Surfaces. J. Am. Chem. Soc. 2003, 125, 3704−3705. (37) Campbell, C. T.; Sun, Y.-K.; Weinberg, W. Trends in Preexponential Factors and Activation Energies in Dehydrogenation and Dissociation of Adsorbed Species. Chem. Phys. Lett. 1991, 179, 53−57. (38) Zhdanov, V. Arrhenius Parameters for Rate Processes on Solid Surfaces. Surf. Sci. Rep. 1991, 12, 185−242. (39) Mei, D.; Xu, L.; Henkelman, G. Potential Energy Surface of Methanol Decomposition on Cu(110). J. Phys. Chem. C 2009, 113, 4522−4537. (40) Popa, C.; Offermans, W. K.; van Santen, R. A.; Jansen, A. P. J. Ab Initio Density-Functional Theory Study of NHx Dehydrogenation and Reverse Reactions on the Rh(111) Surface. Phys. Rev. B 2006, 74, 155428. (41) Tait, S. L.; Dohnálek, Z.; Campbell, C. T.; Kay, B. D. n-Alkanes on Pt(111) and on C(0001)/Pt(111): Chain Length Dependence of Kinetic Desorption Parameters. J. Chem. Phys. 2006, 125, 234308. (42) Fichthorn, K. A.; Miron, R. A. Thermal Desorption of Large Molecules from Solid Surfaces. Phys. Rev. Lett. 2002, 89, 196103.

ACKNOWLEDGMENTS This work has been supported by the Slovenian Research Agency (Grant Nos. J1-2240 and P2-0148).

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REFERENCES

(1) Cotton, J. B.; Scholes, I. R. Benzotriazole and Related Compounds as Corrosion Inhibitors for Copper. Br. Corros. J. 1967, 2, 1−5. (2) Poling, G. Reflection Infra-Red Studies of Films Formed by Benzotriazole on Cu. Corros. Sci. 1970, 10, 359−370. (3) Antonijevic, M. M.; Petrovic, M. B. Copper Corrosion Inhibitors. A Review. Int. J. Electrochem. Sci. 2008, 3, 1−28. (4) Finšgar, M.; Milošev, I. Inhibition of Copper Corrosion by 1,2,3Benzotriazole: A Review. Corros. Sci. 2010, 52, 2737−2749. (5) Kokalj, A.; Peljhan, S. Density Functional Theory Study of ATA, BTAH, and BTAOH as Copper Corrosion Inhibitors: Adsorption onto Cu(111) from Gas Phase. Langmuir 2010, 26, 14582−14593. (6) Kokalj, A.; Peljhan, S.; Finšgar, M.; Milošev, I. What Determines the Inhibition Effectiveness of ATA, BTAH, and BTAOH Corrosion Inhibitors on Copper? J. Am. Chem. Soc. 2010, 132, 16657−16668. (7) Kokalj, A.; Kovačević, N.; Peljhan, S.; Finšgar, M.; Lesar, A.; Milošev, I. Triazole, Benzotriazole, and Naphthotriazole as Copper Corrosion Inhibitors: I. Molecular Electronic and Adsorption Properties. ChemPhysChem 2011, 12, 3547−3555. (8) Peljhan, S.; Kokalj, A. DFT Study of Gas-Phase Adsorption of Benzotriazole on Cu(111), Cu(100), Cu(110), and Low Coordinated Defects Thereon. Phys. Chem. Chem. Phys. 2011, 13, 20408−20417. (9) Jiang, Y.; Adams, J. B. First Principle Calculations of Benzotriazole Adsorption onto Clean Cu(111). Surf. Sci. 2003, 529, 428−442. (10) Jiang, Y.; Adams, J. B.; Sun, D. Benzotriazole Adsorption on Cu2O(111) Surfaces: A First-Principles Study. J. Phys. Chem. B 2004, 108, 12851−12857. (11) Chen, X.; Häkkinen, H. Divide and Protect: Passivating Cu(111) by Cu-(Benzotriazole)2. J. Phys. Chem. C 2012, 116, 22346− 22349. (12) Peljhan, S.; Koller, J.; Kokalj, A. The Effect of Surface Geometry of Copper on Adsorption of Benzotriazole and Cl. Part I. J. Phys. Chem. C 2014, DOI: 10.1021/jp409717e (preceding article). (13) Musiani, M.; Mengoli, G.; Fleischmann, M.; Lowry, R. An Electrochemical and SERS Investigation of the Influence of pH on the Effectiveness of Some Corrosion Inhibitors of Copper. J. Electroanal. Chem. 1987, 217, 187−202. (14) Al-Kharafi, F. M.; Ateya, B. G. Effect of Sulfides on the Electrochemical Impedance of Copper in Benzotriazole-Inhibited Media. J. Electrochem. Soc. 2002, 149, B206−B210. (15) Brunoro, G.; Parmigiani, F.; Perboni, G.; Rocchini, G.; Trabanelli, G. Corrosion Inhibition of OFHC Copper by Prefilming with Organic Compounds. Br. Corros. J. 1992, 27, 75−79. (16) Tommesani, L.; Brunoro, G.; Frignani, A.; Monticelli, C.; Colle, M. D. On the Protective Action of 1,2,3-Benzotriazole Derivative Films against Copper Corrosion. Corros. Sci. 1997, 39, 1221−1237. (17) Törnkvist, C.; Thierry, D.; Bergman, J.; Liedberg, B.; Leygraf, C. Methyl Substitution in Benzotriazole and Its Influence on Surface Structure and Corrosion Inhibition. J. Electrochem. Soc. 1989, 136, 58− 64. (18) Kokalj, A. On the HSAB Based Estimate of Charge Transfer between Adsorbates and Metal Surfaces. Chem. Phys. 2012, 393, 1−12. (19) Guo, X.-C.; Madix, R. J. Site-Specific Reactivity of Oxygen at Cu(110) Step Defects: An STM Study of Ammonia Dehydrogenation. Surf. Sci. 1996, 367, L95−L101. (20) Kravchuk, T.; Vattuone, L.; Burkholder, L.; Tysoe, W. T.; Rocca, M. Ethylene Decomposition at Undercoordinated Sites on Cu(410). J. Am. Chem. Soc. 2008, 130, 12552−12553. (21) Hammer, B.; Nørskov, J. K. Theoretical Surface Science and CatalysisCalculations and Concepts. Adv. Catal. 2000, 45, 71−129. (22) Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; 953



Article

(43) Rocklein, M. N.; Arnold, T. V.; Gerth, C. M.; Land, D. P. The Desorption Kinetics of Flat-Lying Benzene from Palladium (111). J. Phys. Chem. B 2004, 108, 1009−1013. (44) Fang, B.-S.; Olson, C. G.; Lynch, D. W. A Photoemission Study of Benzotriazole on Clean Copper and Cuprous Oxide. Surf. Sci. 1986, 176, 476−490. (45) Walsh, J. F.; Dhariwal, H. S.; Gutirrez-Sosa, A.; Finetti, P.; Muryn, C. A.; Brookes, N. B.; Oldman, R. J.; Thornton, G. Probing Molecular Orientation in Corrosion Inhibition via a NEXAFS Study of Benzotriazole and Related Molecules on Cu(100). Surf. Sci. 1998, 415, 423−432. (46) Nilsson, J. O.; Törnkvist, C.; Liedberg, B. Photoelectron and Infrared Reflection Absorption Spectroscopy of Benzotriazole Adsorbed on Copper and Cuprous Oxide Surfaces. Appl. Surf. Sci. 1989, 37, 306−326. (47) Grillo, F.; Tee, D. W.; Francis, S. M.; Fruchtl, H.; Richardson, N. V. Initial Stages of Benzotriazole Adsorption on the Cu(111) Surface. Nanoscale 2013, 5, 5269−5273. (48) Cotton, J. B. Control of Surface Reactions on Copper by Means of Organic Reagents. In Proceedings of the 2nd International Congress on Metallic corrosion; N.A.C.E: New York, 1963. (49) Rubim, J.; Gutz, I.; Sala, O.; Orville-Thomas, W. Surface Enhanced Raman Spectra of Benzotriazole Adsorbed on a Copper Electrode. J. Mol. Struct. 1983, 100, 571−583. (50) Kovačević, N.; Kokalj, A. The Relation between Adsorption Bonding and Corrosion Inhibition of Azole Molecules on Copper. Corros. Sci. 2013, 73, 7−17. (51) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical Continuum Solvation Models. Chem. Rev. 2005, 105, 2999−3094. (52) Michaelides, A.; Alavi, A.; King, D. A. Insight into H2O-Ice Adsorption and Dissociation on Metal Surfaces from First-Principles Simulations. Phys. Rev. B 2004, 69, 113404. (53) Hodgson, A.; Haq, S. Water Adsorption and the Wetting of Metal Surfaces. Surf. Sci. Rep. 2009, 64, 381−451. (54) Michel, C.; Auneau, F.; Delbecq, F.; Sautet, P. C−H versus O− H Bond Dissociation for Alcohols on a Rh(111) Surface: A Strong Assistance from Hydrogen Bonded Neighbors. ACS Catal. 2011, 1, 1430−1440. (55) Krawczyk, S.; Gdaniec, M. Polymorph β of 1H-Benzotriazole. Acta Crystallogr., E 2005, 61, O2967−O2969. (56) Klamt, A.; Schuurmann, G. COSMO: A New Approach to Dielectric Screening in Solvents with Explicit Expressions for the Screening Energy and Its Gradient. J. Chem. Soc., Perkin Trans. 2 1993, 799−805. (57) Valiev, M.; Bylaska, E. J.; Govind, N.; Kowalski, K.; Straatsma, T. P.; van Dam, H. J. J.; Wang, D.; Nieplocha, J.; Apra, E.; Windus, T. L.; de Jong, W. NWChem: A Comprehensive and Scalable OpenSource Solution for Large Scale Molecular Simulations. Comput. Phys. Commun. 2010, 181, 1477−1489. Code available from http://www. nwchem-sw.org/. (58) COSMO56 calculations were performed with the Gaussian-typeorbital basis set using the NWChem code.57 The 6-311++G(d,p) basis set was used for H, C, N, and O atoms, whereas, for Cu, the modified all-electron TZVP basis set of Ahlrichs59 was used with the outer s, p, and d exponents reoptimized for Cu(111).60 (59) Schäfer, A.; Huber, C.; Ahlrichs, R. Fully Optimized Contracted Gaussian Basis Sets of Triple Zeta Valence Quality for Atoms Li to Kr. J. Chem. Phys. 1994, 100, 5829−5835. (60) Finšgar, M.; Lesar, A.; Kokalj, A.; Milošev, I. A Comparative Electrochemical and Quantum Chemical Calculation Study of BTAH and BTAOH as Copper Corrosion Inhibitors in Near Neutral Chloride Solution. Electrochim. Acta 2008, 53, 8287−8297.

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The Effect of Surface Geometry of Copper on Dehydrogenation of

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