Ab Initio Molecular Dynamics Study of Dissociative Chemisorption and

Article pubs.acs.org/JPCC

Ab Initio Molecular Dynamics Study of Dissociative Chemisorption and Scattering of CO2 on Ni(100): Reactivity, Energy Transfer, Steering Dynamics, and Lattice Effects Xueyao Zhou,† Brian Kolb,‡ Xuan Luo,† Hua Guo,‡ and Bin Jiang*,† †

Department of Chemical Physics, School of Chemistry and Materials, University of Science and Technology of China, Hefei, Anhui 230026, China ‡ Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States ABSTRACT: The dissociative chemisorption of polyatomic molecules on metal surfaces has attracted much interest in recent years due to their industrial and fundamental importance. Comparing with extensively studied systems such as methane and water, however, dissociative chemisorption of CO2, which is important for CO2 activation, has so far received scant attention. We recently reported vibrational enhancement of the dissociative chemisorption of CO2 on a rigid Ni(100) surface using a nine-dimensional potential energy surface (PES) based on a large number of density functional theory calculations. However, that PES is incapable of describing the lattice motion and energy transfer between this heavy molecule and the surface. To overcome these limitations, we present here ab initio molecular dynamics results for CO2 scattering and dissociation. In addition to formation of adsorbed O and CO, CO2 is found to have a large trapping probability in a chemisorption well, along with a substantial amount of energy loss to surface phonons. The lattice and dynamical steering effects are found to be quite different from what have been observed for direct dissociative chemisorption of methane and water.

I. INTRODUCTION Recent years have witnessed significant advances in our understanding of dissociative chemisorption (DC) dynamics of small polyatomic molecules, such as methane and water, on transition metal surfaces.1−4 The practical importance of these reactions derives from the fact that they are key steps in many industrial heterogeneous catalytic processes such as steam reforming and water-gas shift reactions. Experimental studies of quantum state selective reactivity measurements based on molecular beam techniques allowed the determination of the relative efficacy of various forms of energy in promoting the DC process. For example, it has been firmly established from careful measurements that the dissociative sticking probability of methane on metal surfaces can be substantially enhanced by vibrational excitations, and sometimes the enhancement can be more pronounced than that by the same amount of translational energy.5−16 More recently, excitations of the asymmetric stretching mode of water were also found to promote its DC on Ni(111) more effectively than translation.17 These intriguing mode-specific phenomena have stimulated a large number of theoretical studies focusing on quantum/ classical dynamics on high-dimensional Born−Oppenheimer potential energy surfaces (PESs),17−33 lattice effects,34−41 and nonadiabatic effects.42,43 The large set of data has helped the development of new paradigms to rationalize the observed mode specificity,3,4,44 which in turn have shed valuable light onto the nonstatistical nature of the multidimensional dynamics in these systems at gas−metal interfaces. © XXXX American Chemical Society

Surprisingly, the DC dynamics of CO2 to form adsorbed O and CO has been seldom studied, despite its importance in heterogeneous catalysis and greenhouse gas reduction.45 Different from methane and water, CO2 is made of heavy atoms and its dissociation pathway is indirect, usually involving a precursor state in a chemisorption well. The molecule is thus expected to undergo significant energy exchange with surface phonons and/or electron−hole pairs, particularly in the chemisorption well. The potentially long residence time in the precursor state near the metal surface could induce significant energy randomization, which might make the process approaching the statistical limit. Hence, mode specificity is not a foregone conclusion. Thus far, only two molecular beam studies have been reported, concerning the CO2 DC on the Ni(100)46 and Si(111)-7×7 surfaces,47 respectively. Both experimental investigations concluded that the CO2 DC is activated by both vibrational and translational energies. Later, nondissociative adsorption dynamics of CO2 on Pt(111) and Pd(111)48 and on Cu(110)49 was examined, where significant trapping was observed and the trapping probabilities decrease quickly with an increasing incident energy. More recently, the interaction of CO2 with Ni(110) was also investigated.50,51 Theoretically, energetics of the CO2 adsorption and dissociation pathways Received: December 17, 2016 Revised: February 9, 2017 Published: February 21, 2017 A

DOI: 10.1021/acs.jpcc.6b12686 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Ni(100) surface was modeled with four layers of a 3 × 3 unit cell, with 15 Å separating the slab from its periodic image. The first Brillouin zone was sampled with a 3 × 3 × 1 k-point mesh by the Monkhorst−Pack scheme.76 The three top layers of Ni atoms were allowed to move in both energy and AIMD calculations. In our previous work, two near isoenergetic saddle points have been located along the dissociation pathway of CO2 on rigid Ni(100).62 (A very low diffusion barrier (TS2) is neglected in our discussion.) One is an “early” barrier (TS1) from the physisorption to chemisorption well, while the other is a “late” barrier (TS3) responsible for the C−O bond cleavage. To consider the lattice effects, stationary point geometries and energies were reoptimized with the top three layers relaxed, and saddle points were located by using the dimer method77 and confirmed with frequency calculations. To simulate the effect of the surface temperature in experiment (407 K),46 we follow a procedure similar to that of Kroes and co-workers.13,64,68 First, the bulk lattice parameter was multiplied by a factor of 1.0068 (3.545 Å) due to a small expansion (0.684%) observed in experiment78 at this temperature compared to that at 0 K (3.521 Å at 0 K). The initial coordinates were chosen as the relaxed bare surface atomic positions, and their velocities were randomly sampled from the Maxwell−Boltzmann distribution with the initial temperature set as twice of the target temperature, followed by an equilibration run in the microcanonical (NVE) ensemble for 2 ps with a 1 fs time step. An extra 1 ps propagation was performed to confirm that equilibration was indeed reached, and 1000 subsequent configurations were saved for simulating the collision event. The mean surface temperature for the last 1 ps propagation is 402 K with a standard deviation of 50 K, which is close to the value expected (σT = T/(3Natoms)1/2 ≈ 45 K, Natoms is the number of moving atoms). The initial coordinates and velocities of the CO2 molecules were sampled with a QCT method by using a modified VENUS program.79 In the QCT sampling, the CO2 molecule was initiated at 6.0 Å above the Ni(100) surface with random orientation. Its center of mass (COM) was randomly chosen to cover the unit cell and its velocity assigned with a fixed translational energy normal to the surface (Ei). In simulation of the molecular beam experiment, the ro-vibrational states of CO2 were sampled from the Boltzmann distribution at the corresponding nozzle temperature, TN. Specifically, four sets of conditions were investigated: (I) Ei = 1.08 eV with TN = 300 K, (II) Ei = 1.08 eV with TN = 1000 K, (III) Ei = 0.78 eV with TN = 300 K, and (IV) Ei = 0.78 eV with TN = 1000 K. 300 AIMD trajectories were computed for (I) and (II) and 800 for (III) and (IV). These AIMD trajectories were propagated using the Verlet algorithm in VASP, with maximum propagation time of 3 ps and time step of 1 fs. The total energy was well conserved within ∼10 meV for most trajectories. A trajectory was considered “reactive” if one of the C−O bonds in CO2 molecule became larger than 2.5 Å, while “scattered” when the molecule was reflected back beyond 6.1 Å above the surface with the velocity pointing away from the surface. Otherwise, the trajectory was considered “trapped” and terminated after 3 ps.

have been mapped out by means of the density functional theory (DFT).4,50,52−61 However, such information, while valuable, does not provide details of dynamics. Indeed, as shown below, a low-barrier pathway is not always associated with a facile reaction. Very recently, we reported the first global nine-dimensional potential energy surface (PES) for the CO2 DC on rigid Ni(100),62 fit to a large number of DFT points. Two nearly isoenergetic barriers along the reaction pathway have been identified: one connects a shallow physisorption well to a much deeper chemisorption well, and the other is associated with the C−O bond cleavage from the molecular chemisorption well to dissociated products. Using a quasi-classical trajectory (QCT) method, the DC dynamics was investigated on this PES. Our results indicated that each of two barriers controls the reactivity in a certain energy range. Strong vibrational enhancement and mode specificity were found, but the vibrational efficacy depends on the translational energy. Comparing to experiment,46 the sticking coefficients were too low by roughly 1 order of magnitude, though the trend of vibrational and translational activations was reproduced. One possible reason for this experiment−theory discrepancy is obviously the neglect of surface motions. Indeed, lattice effects have been found to be remarkably important in the DC of molecules such as methane and water, particularly at low energies.23,40 Because of the small mass difference between CO2 (m ≈ 44) and Ni (M ≈ 58), a large amount of energy transfer is expected between the molecule and surface, even in the hard sphere collision limit according to the simple Baule formula.63 Unfortunately, such energy transfer cannot be taken into account in our rigid surface model. Energy transfer between the impinging molecule and surface phonons can however be included in a straightforward albeit computationally expensive method, namely ab initio molecular dynamics (AIMD), in which the potential energies and forces are calculated on the fly using DFT along the nuclear trajectories. As demonstrated in a variety of systems,13,29,64−71 AIMD simulations of gas−surface collisions with a statistically meaningful number of trajectories have become possible thanks to the increase of computer power. For “heavy” molecules like CO2 studied here, quantum effects are expected to be small, and as a result a classical treatment of the dynamics should be accurate. Jackson and co-workers have recently suggested that AIMD is probably the best route for further studying the DC of CO2.4 In the present work, we report an extensive AIMD study of the energy transfer and lattice effects in the reactive/ nonreactive scattering of CO2 on Ni(100). Our results indicate a large kinetic energy loss of the molecule upon collision, leading to significant trapping of CO2 in the chemisorption well. The calculated dissociative sticking probabilities are higher than those obtained in the frozen surface model but still much lower than the experimental ones. Finally, the influence of lattice motions and dynamical steering is also discussed.

II. THEORY All AIMD and plane-wave DFT calculations were performed using the Vienna Ab Initio Simulation Package (VASP).72,73 The generalized gradient approximation (GGA) was employed,74 with the Perdew−Burke−Ernzerhof (PBE) functional.74 Core electrons were described with the projector augmented wave (PAW) method,75 and the Kohn−Sham oneelectron wave functions were expanded in a plane-wave basis set up to 400 eV. A Fermi smearing of 0.1 eV was used. The

III. RESULTS AND DISCUSSION A. Reaction Pathway. We first compare the minimumenergy path (MEP) of CO2 DC on rigid and movable Ni(100) surfaces in Figure 1. The chemisorption well is lowered by 0.08 B


Article


atom (Ni5) shifts up by ∼0.1 Å with a force of 0.50 eV/Å. However, TS3 is a very “late” barrier and lies roughly over the hollow site where the molecule interacts with the nearest four Ni atoms, two of which pucker up by 0.12 Å with forces of 0.65 eV/Å and the other two by ∼0.07 Å and forces of ∼0.42 eV/Å. These displacements and forces are at the same level with these in H2O/Ni(111) system17,24,31 but somewhat weaker than these in CH4/Ni(111) and CH4/Ni(100).37,38,40 Our results are found to be consistent with those of Jackson and coworkers.4 B. Dissociation, Trapping, and Scattering. Since the CO2/Ni mass ratio is close to unity, CO2 molecules colliding with the Ni surface are expected to lose a significant amount of energy to lattice phonons. Consequently, they can then be trapped in the chemisorption well and eventually equilibrate with the substrate, in addition to scattering and dissociation. This trapping process was not fully considered in the rigid surface simulation because of the absence of surface phonons, but the movable surface atoms in AIMD calculations can readily accommodate trapping by providing an energy sink. Figure 3

Figure 1. Reaction path for CO2 dissociative chemisorption on the rigid (blue) and relaxed (black) Ni(100) surfaces. Energies in eV.

eV on movable surface, which features a bent CO2 with significant negative charge (i.e., CO2δ−) resulting from electron transfer from the metal surface. The existence of multiple transition states and chemisorption wells for CO2 on low-index Ni surfaces has been observed and discussed, and high mobility of the CO2δ− moiety was expected given the low diffusion barriers.4,51,60−62 The relaxation of the surface atoms has a small effect on the initial barrier (TS1) for the formation of the molecular CO2 chemisorption species but impacts significantly the dissociation barrier (TS3) for C−O bond breaking. Specifically, the classical barrier height of TS1 (0.21 eV) is lowered by only 0.03 eV while that for TS3 (0.09 eV) by 0.14 eV due to surface relaxation, and increasing the number of kpoints was found to lower the barrier height of TS3 by ∼0.04 eV but have negligible effect on TS1, in good agreement with those reported by Jackson and co-workers.4 This suggests a stronger coupling between the lattice motion and the reaction coordinate at TS3 than TS1, which can be clearly seen in Figure 2. Here, we follow Jackson et al.,4 who described the molecule− lattice coupling at the transition state in terms of displacements of surface atoms when surface is relaxed and forces on the surface atoms when the surface is frozen. TS1 is located above the bridge site in the entrance channel where only a single Ni

Figure 3. Probabilities for the reaction, scattering and trapping events at incidence energies of 0.78 and 1.08 eV, with nozzle temperatures of 300 and 1000 K.

displays the probabilities for dissociative sticking, trapping, and scattering for different incident energies and nozzle temperatures. In all cases, roughly half of molecules are trapped after 3 ps while at most 10% of molecules adsorb on the surface dissociatively as O and CO, and the rest are scattered back to the gas phase. This is in sharp contrast to our earlier rigid surface calculations, in which almost no trapping was found.62 The significant trapping here underscores the substantial amount of energy loss from the molecule to the surface phonons. Unlike direct DC processes involving water or methane,13,42 the DC of CO2 on average takes a much longer time. Figure 4 shows the lifetime distributions of the reactive and scattered trajectories at two energies and TN = 1000 K. We count the lifetime, i.e., the residence time of CO2 near the surface, starting from the time when the trajectory enters the surface region (with the molecular center passes through TS1 with a negative velocity) to the time when it exits (with the molecular center passes through TS1 with a positive velocity). For a reactive event, the finishing point corresponds to the end of the trajectory since the molecule is always near the surface in such a case. It is quite clear that both types of trajectories spend on average a significant time in the chemisorption well near the

Figure 2. Geometries of the two main transition states for CO2 dissociative chemisorption on relaxed Ni(100). The arrows represent the displacements (in Å) and the directions of the forces (in eV/Å, in parentheses) on the surface atoms (see text). The bottom panels show the top view of the transition states with the CO bond lengths marked. C


Article


Figure 4. Lifetime distributions (see text for the definition) of reactive and scattered trajectories at two incidence energies.

surface. The lifetime distributions at two energies peak at about 200 fs and extend to ∼1.8 ps for scattered trajectories, while the reactive ones are more widely distributed although the statistics are not as good. This is very different from the DC of water or methane, which is largely direct upon impact and finished within roughly 200 fs.13,42 The direct dissociation channel is still present for CO2, but it represents only a portion of the total reaction. At Ei = 1.08 eV, for example, the fastest dissociation occurs at ∼100 fs while scattering at ∼50 fs. If those trajectories with lifetimes smaller than 400 fs are crudely considered as direct, their respective percentages are 54% and 81%. The proportion of direct trajectories could become lower considering that part of the currently trapped trajectories may eventually react or scatter in a longer propagation time, which should be classified as indirect ones. The difference in the DC mechanism stems apparently from the dominant chemisorption well in the case of CO2 on Ni(100), which provides an obligatory intermediate for all three processes, namely scattering, dissociation, and of course trapping. Many trajectories entering the well spend significant residence times in the chemisorption well, waiting for energy to accumulate in the particular reaction coordinate associated with either TS1 or TS3. The strong interaction between the molecule and surface atoms in this well allows energy redistribution, analogous to the intramolecular vibrational energy redistribution (IVR) in gas phase systems.80 If the energy randomization in the precursor state were complete, the probabilities for the scattering and dissociation would be determined by statistical theory. In this statistical limit, the dissociation channel is expected to be preferred because its corresponding barrier (TS3) is much lower than that for scattering (TS1). A simple RRKM theory81 calculation indeed confirms that the rate for dissociation should be about 2−3 times larger than that of desorption in the energy range of interest. However, the AIMD results in Figure 3 clearly indicate dissociation is actually a minor channel. This suggests that the energy randomization in the chemisorbed complex is incomplete, and the reaction is not entirely statistical. This conclusion would predict the retention of some form of mode specificity, which is examined below. Figure 5 compares the AIMD dissociative sticking probabilities with previous static surface results62 and experimental data.46 The surface motions included in AIMD modestly promote the reactivity, consistent with the lower barrier at TS3 when surface is relaxed. In addition, the experimental trend is reproduced by both the AIMD and static surface results, e.g., a higher nozzle temperature which means larger populations of vibrationally excited states of CO2 gives rise to a higher

Figure 5. Comparison of calculated results of dissociative sticking probabilities for CO2 on Ni(100), based on the rigid surface model (triangles) and AIMD with surface relaxed (squares) with experimental ones (circles). The surface temperature is 407 K.

dissociation probability. The enhancement of reactivity by vibrational excitations of CO2 provides further evidence that the DC dynamics is not completely statistical. A vibrational state resolved calculation of the dissociative sticking probability would be desirable but is not considered here as the AIMD method is too computationally expensive. Quantitatively, the AIMD dissociative sticking coefficients are still way below the experimental data,46 and the enhancement from TN = 300 to 1000 K seems to be too small. The DC of CO2 thus provides an interesting example of low reactivity for a surface reaction with low reaction barrier, which underscores the importance of dynamics. It should, however, be noted that the trajectories that are classified as “trapped” here may eventually react or desorb in a longer time frame. As a result, the “trapping” fraction reported here should be considered as the upper limit. This overestimation of “trapping” probability could lead to a larger dissociation probability, improving the agreement with experiment. On the other hand, the possibility of experimental errors cannot be completely ruled out as the measurement of small sticking coefficients for an atmospherically omnipresent molecule is not an easy task. C. Energy Transfer to Lattice. The energy transfer from the impinging molecule to the lattice can often be estimated on the basis of the Baule model,63 in which the energy transfer depends on the initial incidence energy Ei and the mass ratio between the molecule and the surface atom μ = mCO2/mNi

ΔE = 4μE i /(1 + μ)2 D

(1) DOI: 10.1021/acs.jpcc.6b12686 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article


times (0.4 ps) residence times. In some sense, the latter should probably be better considered as desorption rather than scattering. These results are consistent with what was observed for N2 scattering on W(110).67,71 This is also apparent in the angular distribution of the scattered molecule, as shown in Figure 6. In particular, the scattered CO2 molecules with long residence times near the surface have a much broader angular distribution, suggesting the molecule has partially lost its memory on the incidence angle. D. Steering Effect. Next, we check for possible dynamical steering effects, given the long time scale of the CO2 DC as discussed above. Figure 7 shows the initial lateral positions of

Because of momentum conservation, the CO2 molecule is according to this model to lose nearly all its incidence energy to the Ni(100) surface, i.e., ΔE ≈ 0.98Ei, given the similar masses of the molecule and surface atom. In practice, Figure 6 shows

Figure 6. Distributions of translational energy transfer (ΔE) of scattered CO2 molecules (a, b), with the two subgroups separately shown for those trajectories with residence times of 0.4 ps and longer (c, d), and scattering angle distributions separated with the same time intervals (e, f) at Ei = 1.08 eV (left panels) and Ei = 0.78 eV (right panels).

Figure 7. Initial lateral positions of the molecular COM in the unit cell for trapped and scattered trajectories (open black circles) and reactive trajectories (solid red circles).

the total translational energy transfer (ΔE = Ei − Ef, where Ef is the final translational energy for the scattered trajectory) distributions computed from the scattered CO2 for Ei = 0.78 and 1.08 eV with TN = 300 K. The results for TN = 1000 K are quite similar and thus not shown. The energy loss spreads in a very wide range, with a small tail of negative values, which implies net energy flow from the surface to the molecule. In general, a larger initial translational energy will shift the final distribution toward higher energy. The mean energy transfer is about 0.38 and 0.65 eV for Ei = 0.78 and 1.08 eV, respectively. This amount of energy transfer is significant, about 50−60% of the incidence energy, but is still much smaller than that estimated in the Baule limit. Our results are similar to those in the N2 scattering on the W(110) surface67,71 and HCl/DCl from the Au(111) surface,69,70,82 where AIMD predicted significantly less energy transfer than the Baule model. These observations indicate that the Baule model, which simplifies the gas−surface collision with a binary collision of two hard spheres, should be considered as just an upper bound of the energy transfer for the heave molecule−surface scattering. As discussed above, the scattering of CO2 from the Ni(100) surface can be roughly divided into the direct and indirect channels, corresponding to e.g. trajectories of lifetimes shorter and longer than 0.4 ps, respectively. Figure 6 shows the distributions of translational energy transfer in the two channels. Not surprisingly, molecules scattered after short

the COMs of molecules in the unit cell. In general, the reactive trajectories seem to distribute all around without too much preference toward any specific site. When the molecules reach the impact point, which is defined as the point when one of the CO bonds just stretches over the transition-state (TS3) value, i.e., 1.82 Å, their COMs are all confined near the hollow site, as evidenced in Figure 8 for TN = 300 K. This can be clearly seen in the distribution of the lateral distance ρ between the COM of the molecule and the nearest top site, as shown in Figure 8. For reactive trajectories, a significant shift from an initially uniform distribution to a narrower one with very large ρ values at the impact point is observed for both incidence energies of 0.78 and 1.08 eV. For scattered trajectories, we define the impact point at where the molecular COM moves over the TS1 (z > 2.45 Å) with positive velocity. Interestingly, although ρ distributions in the beginning and the impact point look quite similar, both of which reasonably match the uniform distribution in a unit cell, the absolute diffusion distance of the molecule on the surface can be very large. Indeed, we find that upon impact the CO2 molecule may migrate across the unit cells, which have a lattice constant of 2.507 Å, leading to a remarkable travel distance up to 8 Å from its initial position for both reactive and scattered trajectories, as displayed in Figure 9. Such a large diffusion length was predicted for systems of CO2 E


Article


averaging approximation, for which quantum mechanical treatments have proven to be quite accurate.24−26 Indeed, in these cases, the high barrier and relatively small surface corrugation prevail as the barrier height varies within 0.2−0.3 eV from site to site. In the current system, however, it is found that the dissociation barrier changes substantially from one site to another. For example, the dissociation barrier (TS3) optimized on our static CO2/Ni(100) PES62 exactly over top, bridge, and hollow sites is 1.12, 0.86, and 0.44 eV, respectively, compared to the global one of 0.23 eV, suggesting significant corrugation of the dissociation bottleneck. This is likely to hold with surface relaxation. On the other hand, the diffusion barrier among various sites are relatively low.62 As a result, chemisorbed CO2 molecules tend to diffuse around within the chemisorption well in search for the minimum-energy barrier toward dissociation (i.e., the hollow sites in different unit cells). This mechanism thus rules out a sudden treatment of the dynamics for this system.

IV. CONCLUDING REMARKS AIMD calculations have been carried out for the dissociative chemisorption and scattering of CO2 on Ni(100). Different from extensively studied direct dissociation processes, the CO2 dissociation pathway is dominated by a chemisorption well, which makes the dissociation indirect and more complex. The molecule impinging on the surface endures a large energy loss to the surface phonons. Because of the deep chemisorption well near the surface, the molecule is found to spend a significant residence time in the well before it can either dissociate or desorb. The energy loss of the scattered CO2, which is substantial, correlates with the lifetime in the well. In addition, a large portion stays trapped in the precursor state at 3 ps. However, the energy of the chemisorbed species is not completely randomized, as a significant increase of the dissociative chemisorption probability is found at higher nozzle temperatures, suggesting vibrational enhancement. In addition, the dissociation remains a minor channel despite its lower barrier than that for desorption. The calculated dissociative sticking probability is found to increase somewhat relative to that obtained from a frozen surface model, thus suggesting a notable role of surface motion. However, the theoretical predictions are all well below the experimental values. One possible source of the experiment− theory discrepancy is the functional used in the DFT calculations. It might also be desirable for experimentalists to reconfirm the data that are more than 20 years old. Even considering the experimentally measured reactivities, this reaction is still quite inefficient, despite the low barrier. The studies reported here clearly demonstrated the importance of dynamics in multidimensional space. This example thus raises the question on the common practice of using barrier height to model kinetics in surface reactions. The dissociative chemisorption of CO2 on Ni(100) provides thus a very different paradigm from that of water and methane, where the dissociation is rather fast and direct. The presence of a significant chemisorption well plays not only the role of a gateway for the final dissociation but also serves as an intermediate for scattering/desorption back to the gas phase. The relatively long residence time in the chemisorption well might also induce additional dissipation via the surface electron−hole pairs.83 Such a dissipation channel, which has been found to be negligible in direct dissociation,42,43,70,84 could reduce the dissociative sticking probability more in the

Figure 8. Left panels: lateral positions of the molecular COM in the unit cell for the reactive trajectories at the impact site (solid red circles) and in the beginning (open blue circles). Right panels: distributions of the lateral distance ρ between the molecular COM and the nearest top site for the reactive trajectories in the beginning (dotted blue line) and at impact point (solid blue line) and for scattered trajectories in the beginning (dotted red line) and at impact point (solid red line). The exactly uniform distribution is shown for comparison. The impact site for the reactive trajectory is defined as where either CO bond stretches to the TS3 value and for the scattered trajectory as where the molecular COM moves over the TS1 with positive velocity.

and low-index Ni surfaces60,61 and has never been seen in previous studies for water or methane DC.13,32,33,68 In relatively direct DC events for methane and water on metal surfaces, previous AIMD13,33 and QCT32 studies have suggested minor steering, which has led to a sudden site-

Figure 9. Distributions of the absolute distance between the molecular COM in the initial position and the impact site, which may exceed the length of the unit cell representing diffusion across unit cells. F


Article


(13) Nattino, F.; Ueta, H.; Chadwick, H.; van Reijzen, M. E.; Beck, R. D.; Jackson, B.; van Hemert, M. C.; Kroes, G.-J. Ab initio molecular dynamics calculations versus quantum-state-resolved experiments on CHD3 + Pt(111): New insights into a prototypical gas−surface reaction. J. Phys. Chem. Lett. 2014, 5, 1294−1299. (14) Hundt, P. M.; van Reijzen, M. E.; Ueta, H.; Beck, R. D. Vibrational activation of methane chemisorption: The role of symmetry. J. Phys. Chem. Lett. 2014, 5, 1963−1967. (15) Hundt, P. M.; Ueta, H.; van Reijzen, M. E.; Jiang, B.; Guo, H.; Beck, R. D. Bond-selective and mode-specific dissociation of CH3D and CH2D2 on Pt(111). J. Phys. Chem. A 2015, 119, 12442−12448. (16) Dombrowski, E.; Peterson, E.; Del Sesto, D.; Utz, A. L. Precursor-mediated reactivity of vibrationally hot molecules: Methane activation on Ir(111). Catal. Today 2015, 244, 10−18. (17) Hundt, P. M.; Jiang, B.; van Reijzen, M.; Guo, H.; Beck, R. D. Vibrationally promoted dissociation of water on Ni(111). Science 2014, 344, 504−507. (18) Jiang, B.; Ren, X.; Xie, D.; Guo, H. Enhancing dissociative chemisorption of H2O on Cu(111) via vibrational excitation. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 10224−10227. (19) Jiang, B.; Liu, R.; Li, J.; Xie, D.; Yang, M.; Guo, H. Mode selectivity in methane dissociative chemisorption on Ni(111). Chem. Sci. 2013, 4, 3249−3254. (20) Shen, X. J.; Lozano, A.; Dong, W.; Busnengo, H. F.; Yan, X. H. Towards bond selective chemistry from first principles: methane on metal surfaces. Phys. Rev. Lett. 2014, 112, 046101. (21) Jiang, B.; Guo, H. Dynamics of water dissociative chemisorption on Ni(111): Effects of impact sites and incident angles. Phys. Rev. Lett. 2015, 114, 166101. (22) Shen, X. J.; Chen, J.; Zhang, Z. J.; Shao, K. J.; Zhang, D. H. Methane dissociation on Ni(111): A fifteen-dimensional potential energy surface using neural network method. J. Chem. Phys. 2015, 143, 144701. (23) Farjamnia, A.; Jackson, B. The dissociative chemisorption of water on Ni(111): Mode- and bond-selective chemistry on metal surfaces. J. Chem. Phys. 2015, 142, 234705. (24) Jiang, B.; Song, H.; Yang, M.; Guo, H. Quantum dynamics of water dissociative chemisorption on rigid Ni(111): An approximate nine-dimensional treatment. J. Chem. Phys. 2016, 144, 164706. (25) Zhang, Z.; Liu, T.; Fu, B.; Yang, X.; Zhang, D. H. First-principles quantum dynamical theory for the dissociative chemisorption of H2O on rigid Cu(111). Nat. Commun. 2016, 7, 11953. (26) Shen, X.; Zhang, Z.; Zhang, D. H. Communication: Methane dissociation on Ni(111) surface: Importance of azimuth and surface impact site. J. Chem. Phys. 2016, 144, 101101. (27) Liu, T.; Zhang, Z.; Fu, B.; Yang, X.; Zhang, D. H. Mode specificity for the dissociative chemisorption of H2O on Cu(111): a quantum dynamics study on an accurately fitted potential energy surface. Phys. Chem. Chem. Phys. 2016, 18, 8537−8544. (28) Liu, T.; Zhang, Z.; Fu, B.; Yang, X.; Zhang, D. H. A sevendimensional quantum dynamics study of the dissociative chemisorption of H2O on Cu(111): effects of azimuthal angles and azimuthal angle-averaging. Chem. Sci. 2016, 7, 1840−1845. (29) Fuchsel, G.; Thomas, P. S.; den Uyl, J.; Ozturk, Y.; Nattino, F.; Meyer, H.-D.; Kroes, G.-J. Rotational effects on the dissociation dynamics of CHD3 on Pt(111). Phys. Chem. Chem. Phys. 2016, 18, 8174−8185. (30) Jiang, B.; Guo, H. Origin of steric effects in methane dissociative chemisorption. J. Phys. Chem. C 2016, 120, 8220−8226. (31) Jiang, B.; Guo, H. Towards an accurate specific reaction parameter density functional for water dissociation on Ni(111): RPBE versus PW91. Phys. Chem. Chem. Phys. 2016, 18, 21817−21824. (32) Jiang, B.; Guo, H. Quantum and classical dynamics of water dissociation on Ni(111): A test of the site-averaging model in dissociative chemisorption of polyatomic molecules. J. Chem. Phys. 2015, 143, 164705. (33) Jackson, B.; Nattino, F.; Kroes, G.-J. Dissociative chemisorption of methane on metal surfaces: Tests of dynamical assumptions using

current system and move further from the available experimental values. Thus, additional investigations on this dissipative channel are needed. Despite the insights gained in this and earlier work, our understanding of this important surface reaction prototype is still far from completion.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (B.J.). ORCID

Hua Guo: 0000-0001-9901-053X Bin Jiang: 0000-0003-2696-5436 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (Grants 21573203 and 91645202 to B.J.) and the US National Science Foundation (Grant CHE1462019 to H.G.). We thank Bret Jackson and Ludo Juurlink for several useful discussions. The calculations were performed at the Supercomputing Center of University of Science and Technology of China and National Supercomputing Center in Guangzhou.

■

REFERENCES

(1) Juurlink, L. B. F.; Killelea, D. R.; Utz, A. L. State-resolved probes of methane dissociation dynamics. Prog. Surf. Sci. 2009, 84, 69−134. (2) Chadwick, H.; Beck, R. D. Quantum state resolved gas-surface reaction dynamics experiments: a tutorial review. Chem. Soc. Rev. 2016, 45, 3576−3594. (3) Jiang, B.; Yang, M.; Xie, D.; Guo, H. Quantum dynamics of polyatomic dissociative chemisorption on transition metal surfaces: Mode specificity and bond selectivity. Chem. Soc. Rev. 2016, 45, 3621− 3640. (4) Guo, H.; Farjamnia, A.; Jackson, B. Effects of lattice motion on dissociative chemisorption: Toward a rigorous comparison of theory with molecular beam experiments. J. Phys. Chem. Lett. 2016, 7, 4576− 4584. (5) Juurlink, L. B. F.; McCabe, P. R.; Smith, R. R.; DiCologero, C. L.; Utz, A. L. Eigenstate-resolved studies of gas surface reactivity: CH4(v3) dissociation on Ni(100). Phys. Rev. Lett. 1999, 83, 868−871. (6) Beck, R. D.; Maroni, P.; Papageorgopoulos, D. C.; Dang, T. T.; Schmid, M. P.; Rizzo, T. R. Vibrational mode-specific reaction of methane on a nickel surface. Science 2003, 302, 98−100. (7) Smith, R. R.; Killelea, D. R.; DelSesto, D. F.; Utz, A. L. Preference for vibrational over translational energy in a gas-surface reaction. Science 2004, 304, 992−995. (8) Maroni, P.; Papageorgopoulos, D. C.; Sacchi, M.; Dang, T. T.; Beck, R. D.; Rizzo, T. R. State-resolved gas-surface reactivity of methane in the symmetric C-H stretch vibration on Ni(100). Phys. Rev. Lett. 2005, 94, 246104. (9) Juurlink, L. B. F.; Smith, R. R.; Killelea, D. R.; Utz, A. L. Comparative study of C-H stretch and bend vibrations in methane activation on Ni(100) and Ni(111). Phys. Rev. Lett. 2005, 94, 208303. (10) Bisson, R.; Sacchi, M.; Dang, T. T.; Yoder, B.; Maroni, P.; Beck, R. D. State-resolved reactivity of CH4(2v3) on Pt(111) and Ni(111): Effects of barrier height and transition state location. J. Phys. Chem. A 2007, 111, 12679. (11) Bisson, R.; Sacchi, M.; Beck, R. D. Mode-specific reactivity of CH4 on Pt(110)-(1 × 2): The concerted role of stretch and bend excitation. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82, 121404. (12) Chen, N.; Huang, Y.; Utz, A. L. State-resolved reactivity of methane (ν2 + ν4) on Ni(111). J. Phys. Chem. A 2013, 117, 6250− 6255. G


Article

The Journal of Physical Chemistry C quantum models and ab initio molecular dynamics. J. Chem. Phys. 2014, 141, 054102. (34) Nave, S.; Jackson, B. Methane dissociation on Ni(111): The effects of lattice motion and relaxation on reactivity. J. Chem. Phys. 2007, 127, 224702. (35) Tiwari, A. K.; Nave, S.; Jackson, B. Methane dissociation on Ni(111): A new understanding of the lattice effect. Phys. Rev. Lett. 2009, 103, 253201. (36) Tiwari, A. K.; Nave, S.; Jackson, B. The temperature dependence of methane dissociation on Ni(111) and Pt(111): Mixed quantumclassical studies of the lattice response. J. Chem. Phys. 2010, 132, 134702. (37) Jackson, B.; Nave, S. The dissociative chemisorption of methane on Ni(100): Reaction path description of mode-selective chemistry. J. Chem. Phys. 2011, 135, 114701. (38) Jackson, B.; Nave, S. The dissociative chemisorption of methane on Ni(111): The effects of molecular vibration and lattice motion. J. Chem. Phys. 2013, 138, 174705. (39) Han, D.; Nave, S.; Jackson, B. Dissociative chemisorption of methane on Pt(110)-(1 × 2): Effects of lattice motion on reactions at step edges. J. Phys. Chem. A 2013, 117, 8651−8659. (40) Nave, S.; Tiwari, A. K.; Jackson, B. Dissociative chemisorption of methane on Ni and Pt surfaces: Mode-specific chemistry and the rffects of lattice motion. J. Phys. Chem. A 2014, 118, 9615−9631. (41) Shen, X.; Zhang, Z.; Zhang, D. H. CH4 dissociation on Ni(111): a quantum dynamics study of lattice thermal motion. Phys. Chem. Chem. Phys. 2015, 17, 25499−25504. (42) Jiang, B.; Alducin, M.; Guo, H. Electron−hole pair effects in polyatomic dissociative chemisorption: Water on Ni(111). J. Phys. Chem. Lett. 2016, 7, 327−331. (43) Luo, X.; Jiang, B.; Juaristi, J. I.; Alducin, M.; Guo, H. Electronhole pair effects in methane dissociative chemisorption on Ni(111). J. Chem. Phys. 2016, 145, 044704. (44) Guo, H.; Jiang, B. The sudden vector projection model for reactivity: Mode specificity and bond selectivity made simple. Acc. Chem. Res. 2014, 47, 3679−3685. (45) Freund, H. J.; Roberts, M. W. Surface chemistry of carbon dioxide. Surf. Sci. Rep. 1996, 25, 225−273. (46) D’Evelyn, M. P.; Hamza, A. V.; Gdowski, G. E.; Madix, R. J. Dynamics of the dissociative adsorption of CO2 on Ni(100). Surf. Sci. 1986, 167, 451−473. (47) Lorraine, P. W.; Thoms, B. D.; Machonkin, R. A.; Ho, W. Translationally and vibrationally activated reaction of CO2 on Si(111)7 × 7. J. Chem. Phys. 1992, 96, 3285−3297. (48) Kao, C.-L.; Carlsson, A.; Madix, R. J. The adsorption dynamics of molecular carbon dioxide on Pt(1 1 1) and Pd(1 1 1). Surf. Sci. 2002, 497, 356−372. (49) Funk, S.; Hokkanen, B.; Wang, J.; Burghaus, U.; Bozzolo, G.; Garcés, J. E. Adsorption dynamics of CO2 on Cu(110): A molecular beam study. Surf. Sci. 2006, 600, 583−590. (50) Ding, X.; De Rogatis, L.; Vesselli, E.; Baraldi, A.; Comelli, G.; Rosei, R.; Savio, L.; Vattuone, L.; Rocca, M.; Fornasiero, P.; et al. Interaction of carbon dioxide with Ni(110): A combined experimental and theoretical study. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 195425. (51) Dri, C.; Peronio, A.; Vesselli, E.; Africh, C.; Rizzi, M.; Baldereschi, A.; Peressi, M.; Comelli, G. Imaging and characterization of activated CO2 species on Ni(110). Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82, 165403. (52) Choe, S. J.; Kang, H. J.; Park, D. H.; Huh, D. S.; Park, J. Adsorption and dissociation reaction of carbon dioxide on Ni(1 1 1) surface: molecular orbital study. Appl. Surf. Sci. 2001, 181, 265−276. (53) Wang, S.-G.; Cao, D.-B.; Li, Y.-W.; Wang, J.; Jiao, H. Chemisorption of CO2 on nickel surfaces. J. Phys. Chem. B 2005, 109, 18956−18963. (54) Wang, S.-G.; Liao, X.-Y.; Cao, D.-B.; Huo, C.-F.; Li, Y.-W.; Wang, J.; Jiao, H. Factors controlling the interaction of CO2 with transition metal surfaces. J. Phys. Chem. C 2007, 111, 16934−16940.

(55) Cao, D. B.; Li, Y. W.; Wang, J. G.; Jiao, H. J. CO2 dissociation on Ni(211). Surf. Sci. 2009, 603, 2991−2998. (56) Liu, C.; Cundari, T. R.; Wilson, A. K. CO2 reduction on transition metal (Fe, Co, Ni, and Cu) surfaces: In comparison with homogeneous catalysis. J. Phys. Chem. C 2012, 116, 5681−5688. (57) Muttaqien, F.; Hamamoto, Y.; Inagaki, K.; Morikawa, Y. Dissociative adsorption of CO2 on flat, stepped, and kinked Cu surfaces. J. Chem. Phys. 2014, 141, 034702. (58) Fan, C.; Zhu, Y.-A.; Yang, M.-L.; Sui, Z.-J.; Zhou, X.-G.; Chen, D. Density functional theory-assisted microkinetic analysis of methane dry reforming on Ni catalyst. Ind. Eng. Chem. Res. 2015, 54, 5901− 5913. (59) Lin, W.; Stocker, K. M.; Schatz, G. C. Reducing CO2 to CO and H2O on Ni(110): The influence of subsurface hydrogen. J. Phys. Chem. C 2016, 120, 23061−23068. (60) Czelej, K.; Cwieka, K.; Kurzydlowski, K. J. CO2 stability on the Ni low-index surfaces: van der Waals corrected DFT analysis. Catal. Commun. 2016, 80, 33−38. (61) Czelej, K.; Cwieka, K.; Wejrzanowski, T.; Spiewak, P.; Kurzydlowski, K. J. Decomposition of activated CO2 species on Ni(110): Role of surface diffusion in the reaction mechanism. Catal. Commun. 2016, 74, 65−70. (62) Jiang, B.; Guo, H. Communication: Enhanced dissociative chemisorption of CO2 via vibrational excitation. J. Chem. Phys. 2016, 144, 091101. (63) Baule, B. Theoretische behandlung der erscheinungen in verdünnten Gasen. Ann. Phys. 1914, 349, 145−176. (64) Nattino, F.; Díaz, C.; Jackson, B.; Kroes, G.-J. Effect of surface motion on the rotational quadrupole alignment parameter of D2 reacting on Cu(111). Phys. Rev. Lett. 2012, 108, 236104. (65) Marashdeh, A.; Casolo, S.; Sementa, L.; Zacharias, H.; Kroes, G. J. Surface Temperature Effects on Dissociative Chemisorption of H2 on Cu(100). J. Phys. Chem. C 2013, 117, 8851−8863. (66) Blanco-Rey, M.; Juaristi, J. I.; Díez Muiño, R.; Busnengo, H. F.; Kroes, G. J.; Alducin, M. Electronic friction dominates hydrogen hotatom relaxation on Pd(100). Phys. Rev. Lett. 2014, 112, 103203. (67) Nattino, F.; Costanzo, F.; Kroes, G. J. N2 dissociation on W(110): An ab initio molecular dynamics study on the effect of phonons. J. Chem. Phys. 2015, 142, 104702. (68) Nattino, F.; Migliorini, D.; Kroes, G.-J.; Dombrowski, E.; High, E. A.; Killelea, D. R.; Utz, A. L. Chemically accurate simulation of a polyatomic molecule-metal surface reaction. J. Phys. Chem. Lett. 2016, 7, 2402−2406. (69) Kolb, B.; Guo, H. Communication: Energy transfer and reaction dynamics for DCl scattering on Au(111): An ab initio molecular dynamics study. J. Chem. Phys. 2016, 145, 011102. (70) Füchsel, G.; del Cueto, M.; Díaz, C.; Kroes, G.-J. Enigmatic HCl + Au(111) reaction: A puzzle for theory and experiment. J. Phys. Chem. C 2016, 120, 25760−25779. (71) Nattino, F.; Galparsoro, O.; Costanzo, F.; Muino, R. D.; Alducin, M.; Kroes, G. J. Modeling surface motion effects in N2 dissociation on W(110): Ab initio molecular dynamics calculations and generalized Langevin oscillator model. J. Chem. Phys. 2016, 144, 244708. (72) Kresse, G.; Furthmuller, J. Efficient iterative schemes for ab initio total-energy calculations using plane wave basis set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169−11186. (73) Kresse, G.; Furthmuller, J. Efficiency of ab initio total energy calculations for metals and semiconductors using plane wave basis set. Comput. Mater. Sci. 1996, 6, 15−50. (74) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (75) Blochl, P. E. Project augmented-wave method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953−17979. (76) Monkhorst, H. J.; Pack, J. D. Special points for Brillouin-zone integrations. Phys. Rev. B 1976, 13, 5188−5192. (77) Henkelman, G.; Jonsson, H. A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives. J. Chem. Phys. 1999, 111, 7010−7022. H


Article

The Journal of Physical Chemistry C (78) Kresch, M.; Delaire, O.; Stevens, R.; Lin, J. Y. Y.; Fultz, B. Neutron scattering measurements of phonons in nickel at elevated temperatures. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 104301. (79) Hu, X.; Hase, W. L.; Pirraglia, T. Vectorization of the general Monte Carlo classical trajectory program VENUS. J. Comput. Chem. 1991, 12, 1014−1024. (80) Nesbitt, D. J.; Field, R. W. Vibrational energy flow in highly excited molecules: role of intramolecular vibrational redistribution. J. Phys. Chem. 1996, 100, 12735. (81) Baer, T.; Hase, W. L. Unimolecular Reaction Dynamics, Theory and Experiments; Oxford University Press: New York, 1996. (82) Kolb, B.; Luo, X.; Zhou, X.; Jiang, B.; Guo, H. HighDimensional Atomistic Neural Network Potentials for Molecule− Surface Interactions: HCl Scattering from Au(111). J. Phys. Chem. Lett. 2017, 8, 666−672. (83) Maurer, R. J.; Askerka, M.; Batista, V. S.; Tully, J. C. Ab initio tensorial electronic friction for molecules on metal surfaces: Nonadiabatic vibrational relaxation. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 94, 115432. (84) Juaristi, J. I.; Alducin, M.; Díez Muiño, R.; Busnengo, H. F.; Salin, A. Role of electron-hole pair excitations in the dissociative adsorption of diatomic molecules on metal surfaces. Phys. Rev. Lett. 2008, 100, 116102. (85) Farjamnia, A.; Jackson, B. The dissociative chemisorption of CO2 on Ni(100): A quantum dynamics study. J. Chem. Phys. 2017, 146, 074704.

■

NOTE ADDED IN PROOF After the submission of this work, Farjamnia and Jackson reported a quantum dynamical study of CO2 dissociation using a reaction path Hamiltonian parameterized using DFT within a rigid surface approximation.85 The dissociation was assumed once CO2 enters the chemisorption well. This model reproduced the experimental data reasonably well.

I


Ab Initio Molecular Dynamics Study of Dissociative Chemisorption and

Recommend Documents