Cu Single-Atom

Article pubs.acs.org/JPCC

Dehydrogenation of Propane to Propylene by a Pd/Cu Single-Atom Catalyst: Insight from First-Principles Calculations Xinrui Cao,† Yongfei Ji,† and Yi Luo*,†,‡ †

Department of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden ‡ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China S Supporting Information *

ABSTRACT: The catalytic properties of the single-Pd-doped Cu55 nanoparticle toward propane dehydrogenation have been systemically investigated by first-principles calculations, and the possible reaction mechanisms and effects of the single and multiple Pd doping on the catalytic activity have been discussed. Calculations reveal that the low-energy catalytic conversion of propane to propylene by the Pd/Cu single-atom catalyst comprises the initial crucial C−H bond breaking at either the methyl or methylene group, the facile diffusion of detached H atoms on the Cu surface, and the subsequent C−H bond dissociation activation of the adsorbed propyl species. The single-Pd-doped Cu55 nanoparticle shows remarkable activity toward C−H bond activation, and the presence of relatively inactive Cu surface is beneficial for the coupling and desorption of detached H atoms and can reduce side reactions such as deep dehydrogenation and C−C bond breaking. The single-Pddoped Cu55 cluster bears good balance between the maximum use of the noble metal and the activity, and it may serve as a promising single-atom catalyst toward selective dehydrogenation of propane.

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INTRODUCTION The single-atom catalyst (SAC) is a newly developed heterogeneous catalyst, in which the single metal atoms serve as the catalytically active sites, separately anchored on the support surface or isolated by other metal atoms.1−6 Generally, SACs possess high activity and realize the maximum utilization of the noble metal. Experimentally, the extraordinary performance of SACs has been observed in many catalytic reactions. For example, Kyriakou et al.7 reported that individual, isolated Pd atoms embedded in a Cu surface can significantly promote the H2 dissociation at Pd atom sites and the spillover of resulting hydrogen atoms relatively weakly adsorbed on the Cu support. A similar strategy was introduced to prepare Pd−Cu alloy nanoparticles for selective hydrogenation reactions, and a high selectively catalytic activity was found in the synthesized Pd0.18Cu15 nanoparticles.8 These findings have been interpreted by our recent density functional theory (DFT) calculations that a single Pd atom doping at the edge site can remarkably decrease the activation energy of H2 dissociation on the Cu nanoparticle represented by a 55-atom icosahedral cluster.9 Given the extraordinary catalytical activity toward H 2 dissociation exhibited in such Pd-doped Cu nanoparticles, a question arises here that can such SACs catalyze other chemical reactions? And if this strategy is accessible, how good is its catalytical performance? Here, we investigated the dehydrogenation of propane to propylene catalyzed by the Pd/Cu SAC, one of the most important chemical reactions in industrial processes. The dehydrogenation process, C3H8 → C3H6 + H2, is strongly © XXXX American Chemical Society

endothermic, and it takes place only at a high temperature (525−575 °C),10 requiring a considerable high energy input.11 Accordingly, it is important to design an appropriate catalyst to make the reaction feasible. Up to now, much effort has been put into propane dehydrogenation and various types of catalysts have been developed and evaluated. 12−16 As mentioned above, the Pd-doped Cu nanoparticles can effectively facilitate the dissociation of the H2 molecule. Presumably, the Pd/Cu SAC may also have the ability to activate the C−H bond, and serves as a potential candidate for propane dehydrogenation. In this work, we carried out first-principles calculations to investigate the catalytic activity of the single-Pd-doped Cu55 nanoparticle toward propane dehydrogenation. For comparison and gaining insight into the catalytic role of isolated Pd atoms in dehydrogenation, the pure Cu55 cluster and a multiple-Pddoped “Pd3-E” cluster (one Pd atom at the edge site of surface shell is directly connected by two Pd atoms in the inner layer)9 are also considered here. Plausible reaction pathways and the corresponding reaction intermediates involved in the dehydrogenation process have been investigated. Based on extensive calculations, the rate-determining step for the whole reaction, the catalytic effect of the single Pd atom dispersed on the Cu surface, and the selectivity of initial hydrogen abstraction have been discussed. Received: August 26, 2014 Revised: December 18, 2014

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DOI: 10.1021/jp508625b J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

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METHODS AND MODELS First-Principles Calculations. Herein the spin-polarized DFT calculations were performed by the Vienna ab initio simulation package (VASP).17,18 The negligible effects of spin polarization were found in the models considered here. The projector augmented wave (PAW) pseudopotentials19 were employed to describe the electron−ion interaction. The exchange-correlation interactions were described by GGAPBE.20 A 400 eV cutoff energy for the plane-wave basis set and a three-dimensional (3D) periodic cube supercell with a 25 Å lattice constant were used in the calculations. The interaction between the adjacent clusters was negligible due to the large enough separation spacing. The Γ point was used for Brillouin zone sampling. All the atoms were allowed to relax until the maximum force becomes less than 0.03 eV/Å. The long-range dipole correction is not considered in our calculations due to a negligible energy correction found in the x, y, and z direction for the tested models (configuration c and c-1), respectively. The climbing-image nudged elastic band (CI-NEB) method21 was used to explore the transition states of the propane dehydrogenation process. Construction of SAC Models. Here the SAC nanoparticle computed in our calculations was mimicked by an icosahedral cluster with 55 atoms (shown in Figure 1), the most stable

number in the Cu55 cluster is more active than the top atom toward H2 dissociation, as shown in our previous study.9 Such abnormal phenomenon may arise from the unique configuration of the icosahedral cluster, in which the local structural environment of the edge atom can facilitate the bond activation and stablize the corresponding transition state. Similar to the H2 dissociation catalyzed by the pure Cu nanoparticles, the edge-Pd-doped Cu55 cluster can remarkably promote the H2 dissociation, while doping a single Pd atom at the top site is less effective.9 The thermal stability of the Pd/Cu SAC model was examined by performing ab initio molecular dynamics (AIMD) simulations at several temperatures (400, 500, and 800 K) within a canonical ensemble. The time step was 1 fs, and the total simulation time was 12 ps. Our AIMD simulations indicated that the icosahedral structure was well retained at 400 and 500 K during the simulation. Although a notable deformation might occurred at 800 K, its structural integrity was retained and the coordination number for each atom was also unchanged. Clearly, the SAC model is of relatively high thermal stability. The corresponding snapshots at 12 ps with different temperatures are given in Figure S1 (Supporting Information), labeled as a, b, and c, respectively.

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RESULTS AND DISCUSSION Propane Dehydrogenation on the Single-Pd-Doped Cu55 Nanoparticle. Molecular Adsorption of Propane. Based on the single-Pd-doped Cu55 cluster, the adsorption of propane at the edge Pd site was investigated first. Five possible adsorption states at the Pd atom by varying the conformation of propane are considered, labeled as a, b, c, d, and e, respectively, are given in Figure 2. The corresponding adsorption energies calculated by the PBE functional are given in Table 1. As Table 1 shows, the adsorption energies of

Figure 1. Schematic structure of the icosahedral Cu55 cluster used in our calculations. The two kinds of inequivalent Cu atoms at the shell of the cluster, namely the top atom and the edge atom, are shown in different colors.

Table 1. Adsorption Energies of Propane on the Single-PdDoped Cu55 Cluster (See Figure 2)a configuration Ead(propane) (kcal/mol)

configuration of the Cu55 cluster verified by different experiments.22,23 This cluster is the second Mackay icosahedron,24 enclosed by 20 {111} facets; its diameter is about 1 nm. There are two types of inequivalent atoms on the shell, that is, the edge atom and the top atom (see Figure 1). Generally, the lowcoordinated metal atoms dispersed on the nanoparticle surface can serve as the active sites for many kinds of catalytic reactions. However, the edge atom with a higher coordination

a 1.1

b 1.4

c 1.8

d 1.6

e 2.4

a Here Ead(H) is defined as Ead(propane) = E(NP) + E(propane) − E(NP-propane).

different optimized configurations are very close, ranging from 1.1 to 2.4 kcal/mol, and the distances between the Pd atom and its nearest H atom in these configurations are in the region of

Figure 2. Structures of the possible adsorption patterns of propane on the single-Pd-doped Cu55 cluster and the distances between the Pd atom and its nearest H atom for each configuration are given. B


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distances decrease, suggesting that the adsorption interactions between propane and the cluster surface are enhanced.

2.15−2.64 Å, suggesting that propane is generally physically adsorbed on the SAC surface. From the adsorption energy point of view, the most favorable adsorption of propane on the Pd/Cu SAC is configuration e, which has been extensively taken as the initial state in the propane dehydrogenation catalyzed by different catalysts.11,12,25−27 Considering the unique adsorption structure arising from the terminal methyl group, configuration c was also considered in the present work. In consequence, the adsorbed configurations c and e as two representatively initial states have been utilized to investigate the dehydrogenation process of propane. It was known that the PBE functional has a poor description of the van der Waals interaction, and the vdW-DF functional28 implemented in VASP is used here as a comparison. The predicted adsorption energies for the two representative configurations c and e are 6.3(6.1) and 7.4(7.3) kcal/mol, which are about 4.5(4.3) and 5.0(4.9) kcal/mol higher than the adsorption energies obtained by the PBE functional, respectively. Here the adsorption energies listed in parenthese are from the vdW-DF single point calculations based on the PBE-optimized structures. Apparently, further optimization of the structure with the vdW-DF functional has minor effects on the adsorption energies. Therefore, the vdWDF calculations are all performed on the PBE structures. Additionally, we also studied the adsorption of propane on the pure Cu55 cluster and the “Pd3-E” cluster for comparison. The counterparts of configuration c and e are labled as c′ and e′ on the pure Cu55 cluster, and c′ and e′′ on the “Pd3-E” cluster. The optimized structures for these configurations are given in Figure 3. As shown in Figure 3, the optimized C−C

Table 2. Adsorption Energies of Propane on the Single-PdDoped Cu55, Pure Cu55, and “Pd3-E” Clusters (See Figure 3) configuration Ead(propane) (kcal/mol)

c 1.8

c′ 0.7

c′′ 2.5

e 2.4

e′ 1.1

e′′ 3.3

C−H Bond Activation. The initial C−H bond cleavage from the methyl or the methylene group of propane leads to the 1propyl or 2-propyl species, respectively. On the basis of the initial states of propane adsorbed on the single-Pd-doped Cu55 catalyst, configurations c and e should be responsible for the C−H bond activation in the methyl and methylene groups, respectively. According to the initial C−H bond activation at either the methyl or methylene group, plausible mechanisms for two different dehydrogenation pathways have been proposed. Figures 4 and 5 show the relative energy profiles and the optimized structures of different reactive states calculated for the catalytic conversion of propane to propylene, starting from the initial configurations c and e, respectively. For the dehydrogenation from the methyl group of propane, the reaction starts from configuration c, in which propane is weakly adsorbed over the top of the edge-Pd atom. As Figure 4 shows, the propane-adsorbed configuration c undergoes transition state c-TS1 to form configuration c-1 with the 1-propyl chemisorbed on the Pd/Cu SAC through the dissociation activation of the methyl C−H bond. In the transition state (cTS1), the activated C−H bond is elongated to about 1.8 Å, much longer than the original C−H bond of 1.1 Å in isolated propane. The predicted barrier for the first C−H bond cleavage catalyzed by the Pd/Cu SAC is 24.4 kcal/mol as shown in Figure 4, about 5.8 kcal/mol lower in energy than the corresponding barrier for catalysis by a pure Cu55 cluster (see Figure 6, part a), showing that the doped Pd atom exhibits remarkable catalytic activity toward the C−H activation. With the correction of the vdW-DF functional, the energy barrier for the initial C−H cleavage is increased to 27.0 kcal/mol (see Figure S2, Supporting Information), which is about 2.6 kcal/ mol higher than that predicted by the PBE functional. At configuration c-1, the reaction can proceed through two possible routes. One pathway starts from the direct methylene C−H bond activation in the adsorbed 1-propyl, and the other comprises the weakly adsorbed H atom diffusion on the Cu surface prior to the C−H bond activation. The former is a onestep process and the latter is a multistep process to the product of propylene. As Figure 4 shows, the direct C−H bond cleavage of methylene yields the adsorbed propylene c-3 through transition state c-TS3 with a barrier of 14.2 kcal/mol, and this energy barrier will increase to 16.3 kcal/mol when the van der Waals correction is included. In the multistep process, the H atom diffusion across the Cu−Cu bridge experiences a low barrier of 3.8 kcal/mol, and structure c-1 evolves to an almost isoenergetic configuration c-2. The subsequent methylene C− H bond dissociation activation via transition state c-TS4 produces a product state c-4 with a barrier of 10 kcal/mol. With the correction of the vdW-DF functional, the diffusion barrier is decreased by 1.3 kcal/mol while the energy barrier for the further C−H bond activation is increased to 12.6 kcal/mol. We note that the adsorbed propylene configuration c-4 is more stable than c-3 by 8.5 kcal/mol (8.7 kcal/mol, with the van der Waals correction), and such difference in stability basically

Figure 3. Optimized initial states of molecular propane on the singlePd-doped Cu55, pure Cu55, and “Pd3-E” clusters.

bond lengths of the adsorbed propane in different configurations are almost the same while the optimized C−H bond (the nearest C−H bond to the Pd atom) lengths is in a small region of 1.11−1.13 Å, and the main difference among these configurations is the intermolecular distance between propane and SAC. Accordingly, the physisorption interactions may influence the C−H bond to some extent but not the C−C bond. With the increase of Pd concentration, the adsorption energies (see Table 2) increase while the intermolecular C


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Figure 4. Relative energy profiles for the dehydrogenation of propane to propylene on the single-Pd-doped Cu55 cluster and the equilibrium structures of species involved in the catalytic conversion starting from configuration c.

Figure 5. Relative energy profiles for the dehydrogenation of propane to propylene on the single-Pd-doped Cu55 cluster and the equilibrium structures of species involved in the catalytic conversion starting from configuration e.

Figure 6. Relative energy profiles for propane dehydrogenation to the 1-propyl (c′-1) or 2-propyl (e′-1) species on the pure Cu55 cluster and the equilibrium structures of selected reactive configurations.

arises from the H atom diffusion. Since the H atom adsorption on the Cu surface is relatively weak, its migration on the Pd/Cu SAC surface, leading to a favorable configuration, should be facile. Clearly, the multistep process starting from c-1 is more favorable than the one-step process, both dynamically and thermodynamically. The first C−H bond activation is the ratedetermining step for the whole reaction. These conclusions still hold when van der Waals corrections are included, as shown in Figure S2 in the Supporting Information.

For the catalytic conversion of propane to propylene, triggered by the methylene C−H bond activation, the reaction begins from configuration e. As Figure 5 shows, the barrier for the initial C−H dissociation activation to yield the 2-propyl species is 24.7 kcal/mol, much lower than the corresponding energy barrier of 31.4 kcal/mol on a pure Cu55 cluster (see Figure 6, part b). The further dehydrogenation at configuration e-1 can follow two possible pathways. Similar to the reaction shown in Figure 4, the multistep process composed of the H atom diffusion and C−H bond activation is more favorable than D


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Figure 7. Relative energy profiles for the deep dehydrogenation of propylene on the single-Pd-doped Cu55 cluster. Configurations cluster-C3H6-1 and cluster-C3H6-2 are the adsorption conformation of propylene from a different perspective.

propyl group at the atop site. The diffusion of the H atom on the Cu surface can stabilize the product configuration, as shown in Figures 4 and 5. Presumably, the facile H atom migration can enhance formation and desorption of H2. As can be seen from Figures 4 and 5, here the detached H atoms are transferred to their adjacent sites with small barriers of 3.8 and 4.3 kcal/mol, respectively. Overall, the low-energy catalytic mechanism for the catalytic conversion of propane to propylene by the Pd/Cu SAC, arising from both methyl and methylene C−H bond activations, can be divided into three steps: the initial C−H bond dissociation activation leading to the 1-propyl or 2-propyl group, the diffusion of the detached H atom on the Cu surface, and the dehydrogenation of the adsorbed propyl group to form propylene. Evaluation of Deep Dehydrogenation and C−C Bond Cleavage in Propane Dehydrogenation by the Pd/Cu SAC. The deep dehydrogenation and the cracking of propylene are critical for the selective dehydrogenation of propane to propylene, and they should be considered in our calculations. For the sake of simplification, we assumed that the detached H atoms from previous dehydrogenation steps are far away from the newly formed propylene or desorbed from the cluster as H2, and thus the following C−H and C−C bond activations start from the configuration of one propylene adsorbed at the atop site of the edge-Pd atom. Under this condition, the propylene desorption from the single-Pd-doped Cu55 cluster is predicted to require an energy of about 14 kcal/mol by PBE calculations, which is very close to its adsorption energy. Generally, the coadsorbed atomic H may deactivate the d-states of the surface metal atom, and its bonding ability would be weakened as a consequence.29 This phenomenon is also observed in our calculations. As Figures 4 and 5 show, configurations c-4 and e-4, in which the first detached H atom moves away from the doped Pd, are more stable than configurations c-3 and e-3, with the first detached H atom adjacent to Pd, by 8.5 and 6.8 kcal/mol, respectively. The weakened adsorption would promote the desorption of propylene, which may benefit the selectivity toward propylene. To evaluate selectivity of the SAC catalyst, the deep dehydrogenation from further C−H activations and the propylene cracking from the C−C bond activation are considered here. Deep Dehydrogenation. The further C−H bond activation of propylene can arise from either the methylene or the methine of propylene, and the corresponding deep dehydrogenation product is either 1-propenyl or 2-propenyl species,

the one-step process, both dynamically and thermodynamically. Generally, the catalytic conversions of propane to propylene shown in Figures 4 and 5 may follow similar mechanisms with comparable reaction energetics, and both catalytic mechanisms are competitive and they will be involved in the dehydrogenation of propane by the Pd/Cu SAC. The relative stability and the C−H accessibility of the initial configurations c and e may dominate their significance in the catalytic conversion. Comparison with Other Heterogeneous Catalytic Conversions of Propane to Propylene. The dissociation activation of the initial C−H bond in the conventional oxidative dehydrogenation (ODH) of propane by the single-crystal V2O5 catalyst is generally predicted to experience substantially higher barriers beyond 27 kcal/mol, and the predicted barriers for the subsequent ODH process to propylene are higher than 30 kcal/ mol.25,27 Furthermore, the desorption of the resulting H2O and the O2 addition for the supplement of lattice oxygen atoms may hinder the ODH reaction. Most recent experimental studies, in combination with first-principles calculations based on the hybrid density functional (B3LYP), show that the silicasupported single-site Zn(II) catalyst has high selectivity for propane dehydrogenation to propylene. The predicted barriers for the C−H bond dissociation activation range from 38 to 49 kcal/mol, and the whole reaction is endothermic by about 19 kcal/mol.14 Clearly, the catalytic conversion of propane to propylene by the single-Pd-doped Cu55 is comparable or more feasible than most of the above-mentioned catalysts. It is well-known that the noble metals exhibit high activity toward alkane dehydrogenation. Recent DFT calculations on propane dehydrogenation over Pt and PtSn catalysts reveal that the initial C−H bond dissociation activation on Pt(111) experiences a barrier of ∼25 kcal/mol relative to the adsorbed state of propane, and the introduction of Sn may improve the catalytic selectivity although the PtSn alloyed surfaces have relatively lower activity than the Pt(111) surface.12 High catalytic activity of small clusters and step sites of platinum have also been observed and investigated.11,26 Owing to the strong adsorption of both propylene and H atoms on the Pt-based catalyst, the possible side reactions such as deep dehydrogenation and C−C bond cleavage may easily occur. For the single-Pd-doped Cu55 SAC, the single noble metal atom as the active site is isolated by the inactive Cu atoms, which can reduce the possibility of side reactions. Moreover, previous calculations9 show that the detached H atom can easily migrate to other sites due to a low diffusion barrier or stays at its original detached hollow site upon formation of the E


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Figure 8. Relative energy profiles for the cracking of propylene on the single-Pd-doped Cu55 cluster.

Figure 9. Relative energy profiles for propane dehydrogenation to propylene on “Pd3-E” and the equilibrium structures of species involved in catalytic conversion starting from configuration c′′.

Figure 10. Relative energy profiles for propane dehydrogenation to propylene on “Pd3-E” and the equilibrium structures of species involved in catalytic conversion starting from configuration e′′.

good performance in catalyzing propane dehydrogenation to propylene, it is worth exploring the effect of doping more Pd atoms on the catalytic activity. The catalytic activity of the multiple-Pd doped “Pd3-E” cluster toward H2 dissociation has been investigated in previous calculations.9 The “Pd3-E” nanoparticle contains an edge Pd atom and two directly connected inner layer Pd atoms, which formed a triad embedded in Cu55 with the substitution of three Cu atoms. “Pd3-E” exhibits slightly better activity toward dissociation of H2,9 compared with the single-Pd-doped Cu55 cluster. As shown in Figures 9 and 10, similar effects of multiple Pd doping have been found for the first C−H bond activation from either the methyl or methylene group, and the barriers for the ratedetermining step are reduced by about 4 kcal/mol, showing the cooperation effect of inner-layer Pd atoms on the activity of the edge Pd to a certain extent. In the transition states c′′-TS1 and e′′-TS1, the activated C−H bond is around 1.7 Å, which is slightly shorter than those in c-TS1 and e-TS1. Considering the lower barrier for the detached H atom diffusion as compared with the direct dehydrogenation, the evolution of the Hadsorbed configuration should be dominant upon the formation of the propyl group. We note that the diffusion

respectively. As shown in Figure 7, the energy barriers for the third C−H bond dissociation to yield the 1-propenyl and 2propenyl species are 26.8 and 33.0 kcal/mol, respectively, which are 12.8 and 19 kcal/mol higher than the values for the propylene desorption, indicating that the desorption process is much more favorable dynamically. Propylene Cracking. In propane dehydrogenation, the cracking of the C−C bond will lead to undesired byproducts. The predicted energy barriers for the C−C bond cleavage of C3 derivatives by DFT calculations are in the range of 38.3−55.3 and 31.1−61.1 kcal/mol on the Pt(111) surface26 and the PtSn alloyed surface,12 respectively. The cracking of propylene is relatively more feasible than that of propane according to the previous studies by Yang et al.12,26 Therefore, we only take into account the former cracking here. The cracking of propylene leads to CH3CH- and CH2-adsorbed species, and the predicted energy barrier is as high as 59.0 kcal/mol, as shown in Figure 8. This substantially high energy requirement will kinetically hinder the cracking reaction of propylene, enhancing the selectivity toward propylene. Propane Dehydrogenation on the “Pd3-E” Nanoparticles. Since the single-Pd-doped Cu55 cluster exhibits F



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barrier of the H atom here increases by ∼2 kcal/mol, in comparison with the single-Pd-doped Cu55. Additionally, configuration e′′-2 is less stable than e′′-1 by 3.3 kcal/mol, indicating that such an H atom diffusion process is endothermic. If the H atom diffusion occurs, the energy barriers for the subsequent dehydrogenation steps are 10.7 and 9.5 kcal/mol, respectively, which are comparable with the corresponding steps catalyzed by the single-Pd-doped Cu55 catalyst. On the contrary, the barriers for the direct dehydrogenation processes from the 1-propyl and 2-propyl groups are 2.2 and 0.4 kcal/mol higher than those by the singlePd-doped Cu55 cluster, respectively. Overall, the triad of Pd atoms can facilitate the initial C−H activation, but it makes H atom diffusion on the Cu surface become difficult, which is unfavorable for the formation and desorption of H2 . Accordingly, the single-Pd-doped Cu55 catalyst can achieve good balance between the maximization use of the noble metal and the catalytic activity toward propane dehydrogenation.

ACKNOWLEDGMENTS This work is supported by the Göran Gustafsson Foundation for Research in Natural Sciences and Medicine, the Swedish Research Council (VR), the Major State Basic Research Development Programs (2010CB923300), and the National Natural Science Foundation of China (20925311). The Swedish National Infrastructure for Computing (SNIC) is acknowledged for the supercomputer resources.

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CONCLUSIONS In summary, we have systematically investigated the propane dehydrogenation process catalyzed by the single-Pd-doped Cu55 cluster based on first-principles calculations. The present results show that the single Pd doping at the edge site of the Cu55 cluster can effectively decrease the energy barrier for the rate-determining step, and the facile diffusion of detached H atoms on the Cu surface is beneficial for the subsequent dehydrogenation. Although the multiple Pd doping could further reduce the energy barrier of the first crucial C−H bond cleavage, it might hinder the diffusion of the detached H atom. As a consequence, the subsequent C−H bond cleavage becomes more difficult, compared with that on the single-Pddoped cluster. Overall, the introduction of a single Pd atom to the Cu55 cluster can significantly promote the propane dehydrogenation reaction, and the relatively inactive Cu surface may facilitate recombination and desorption of weakly adsorbed H atoms and reduces the related side reactions. The present results suggest that the single-Pd-doped Cu55 nanoparticle is a promising single-atom catalyst for selective dehydrogenation of propane to propylene. ASSOCIATED CONTENT

S Supporting Information *

Snapshots of the edge-Pd-doped Cu55 cluster at 12 ps of the ab initio molecular dynamics simulation at different temperatures in a canonical ensemble (Figure S1) and relative energy profiles with vdW-DF correction for the dehydrogenation of propane to propylene on the single-Pd-doped Cu55 cluster and the equilibrium structures of species involved in the catalytic conversion starting from configuration c (Figure S2). This material is available free of charge via the Internet at http:// pubs.acs.org.

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*E-mail: [email protected]. Tel: +46-8-55378414. Fax: +46-855378590. Notes

The authors declare no competing financial interest. G


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Cu Single-Atom

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