Adsorption of O2 on Anionic Gold Clusters in the 0–1 nm Size Range

Article Cite This: J. Phys. Chem. A XXXX, XXX, XXX−XXX

pubs.acs.org/JPCA

Adsorption of O2 on Anionic Gold Clusters in the 0−1 nm Size Range: An Insight into the Electron Transfer Dynamics from Kinetic Measurements Tingting Wang, Jun Ma, Baoqi Yin, and Xiaopeng Xing* School of Chemical Science and Engineering, Shanghai Key Lab of Chemical Assessment and Sustainability, Tongji University, 1239 Siping Road, Shanghai 200092, China S Supporting Information *

ABSTRACT: We systematically studied the adsorption of O2 on Aun− in the size range of 0−1 nm at low temperatures and determined new active sizes with n = 22, 24, 34, and 36. The kinetic measurements more clearly showed the correlation between the reactivity of Aun− with O2 and their electronic properties: the sizes with a closed electron shell are always inert, and the sizes with an unpaired electron can chemically adsorb one O2 molecule if their adiabatic detachment energies (ADEs) are lower than a threshold around 3.5 eV. This ADE threshold dividing the active and inert Aun− is independent of the clusters’ sizes, global geometries, and local adsorption sites. According to the widely accepted electron transfer mechanism, this threshold could stand for the case in which the total energy of the Aun− and an O2 roughly equals that of the spin crossover point of the potential surfaces of Aun−O2− and Aun−···O2. some distinct structures, including the planar structures of Aun− (n ≤ 12),17−19 the cages of Aun− (n = 15−17),20−22 the coexisting cage and pyramid structures for Au18− and Au19−,21−23 and the perfect Td pyramid structure of Au20−.24 The large sizes, Aun− (n = 21−75), were determined to be elongated cages, pyramids, and low-symmetrical structures with enclosed atoms.21,25−32 In these works, coexisting isomers were distinguished for Aun− with n = 4, 8, 10, 12, 18, 22, 26, etc. The structures of AunO2− (n ≤ 20) were characterized by combinations of experiments including photoelectron spectroscopy, infrared dissociation spectroscopy, and theoretical calculations.33−39 These studies directly showed the effects of electron transfer from anionic gold to the chemically adsorbed O2. The combination of photoelectron spectroscopy and theoretical calculations showed that the O2 units are either superoxo or peroxo species in AunO2− (n ≤ 20).36 The isomers of Au10− and Au18− were shown to have an apparently different reactivity with O2.23,34,39 The isomers of Au12−, having different adsorption energies with Ar,40 were shown to form only one kind of Au12O2−.36 Recently, many calculations studied the chemical adsorptions and activations of O2 on even larger gold clusters;41−48 nevertheless, no experiments have shown active sizes larger than Au20−. In addition, even though the reaction mechanism involving electron transfer from anionic gold to O2 is widely accepted, there have been very few experiments through which a glimpse of its dynamic process can be caught.

1. INTRODUCTION The adsorption and activation of O2 on small gold species have been long-standing attractive topics since the discovery of the surprising low-temperature catalytic properties of dispersed gold in the oxidation of CO and other small molecules.1,2 Since gas phase atomic clusters in the range of 0−1 nm are ideal models for the active sites of real catalysts,3−6 studies on the structures, the electronic properties, and the reactivity of small gold clusters has attracted great interest in the past two decades.7−9 Their reactivity with O2 provides fundamental insights into the crucial O2 activation step happening on real gold catalysts. It was found very early that the anionic gold clusters are more active than the cationic ones.10 The reactivity of Aun− (n = 1−7) with O2 has an even−odd oscillation trend, in which the even sizes with open electron shells react faster.11 A study on the reactions between Aun− (n = 1−22) and O2 showed that the Aun− with n = 2, 4, 6, 8, 10, 12, 14, 18, and 20 are active, exclusively forming AunO2−.12 The products containing only one O2 molecule and the correlation between clusters’ reactivity and their adiabatic electron detachment energies (ADEs) suggested an empirical electron transfer mechanism, in which the products AunO2− can be considered as a neutral gold moiety plus an adsorbed O2−. Coadsorptions of O2 and electron donating molecules were observed on many small gold clusters,13−16 which provides indirect evidence for the electron transfer figure. With developments of modern experiment techniques and computational methods, structures of many Aun− and AunO2− species were determined. Aun− in the 0−1 nm size range has © XXXX American Chemical Society

Received: January 19, 2018 Revised: March 7, 2018 Published: March 15, 2018 A

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

Figure 1. Mass spectra showing the parent and the product clusters for the reactions between Aun− (n = 1−26) and O2 at the flow of 0.0−3.0 sccm at 150 K. The products AunO2− were indicated using vertical dashed lines.

Figure 2. Mass spectra showing the parent and the product clusters for the reactions between Aun− (n = 21−42) and O2 at the flow of 8.0 sccm at 150 K (the top ones) and at the flow of 6.0 sccm at 120 K (the bottom ones). The products AunO2− were indicated using vertical dashed lines.

spectrometer.49,50 Briefly, Aun− in the size rage of 0−1 nm were generated in the cluster source and entered the flow reactor together with the helium buffer gas (∼120 sccm) and the residual sputter argon (∼14 sccm). The total pressure inside the flow reactor was about 0.5 Torr, and the temperature was maintained at 150 or 120 K. The nascent clusters from the source chamber were thermalized to the set temperature in the thermalization region of the reactor and then reacted with O2 introduced downstream at a set flow around 0−8.0 sccm. After passing through a skimmer at the end of the reactor, the reaction products as well as the remainder parent gold clusters were analyzed using the TOF mass spectrometer. The intensities of individual Aun− clusters were recorded under the conditions without O2 (I0) or with O2 at various flow rates (I). The depletion processes of Aun− were fitted using eq 1 if the reaction has a constant rate or using eq 2 if the size has isomers with two apparently different reaction rates. In these two equations, the t stands for the reaction time, which is a

In this work, we reported systematic kinetic measurements on the adsorption of O2 on Aun− with n ranging from 1 to larger than 70. In addition to previously reported active sizes with n ≤ 20, the Aun− with n = 22, 24, 34, and 36 were first shown to be reactive with O2. Comparing the variations of the reactivity of Aun− (n = 1−70) and their adiabatic electron detachment energies (ADEs), we found an ADE threshold around 3.5 eV dividing the inert (with higher ADEs) and the active (with lower ADEs) even-sized anionic gold clusters. This structurally independent ADE threshold enables us to evaluate the energy level of the spin crossover point between the potential surfaces of Aun−O2− and Aun−···O2, which is closely correlated with the electron transfer dynamics.

2. EXPERIMENTAL METHODS The kinetic measurements were carried out on an instrument composed of a magnetron sputtering cluster source, a continuous flow reactor, and a time-of-flight (TOF) mass B

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

Figure 3. Fittings of the depletion processes of (a) Au2− and (c) Au12− using eq 1 and those of (b) Au10− and (d) Au22− using eq 2, which were introduced in the Experimental Methods section.

observed. The kinetic rates for the depletion of most Aun− or the generation of corresponding AunO2− seemed to be constant. Howbeit, there were three exceptive sizes, Au10−, Au18−, and Au22−. When the O2 flow was 0.12 sccm, about 65% of parent Au10− did not convert to Au10O2−, and this proportion kept unchanged even though the O2 flow increased to 3.0 sccm. The depletion proportions of Au18− and Au22− were larger than that of Au14− when the O2 flow was 0.12 sccm, while they were smaller than that of Au14− when the O2 flow was increased to 0.30 or 3.0 sccm. We lowered the temperature to 120 K, and all reaction processes seemed to be faster. However, about 65% of Au10− and about 30% of Au18− always remained, even though the O2 flow was increased to 6.0 sccm (as shown in Figure S1). The unusual depletion processes of Au10−, Au18−, and Au22− implied the coexistence of highly reactive and inert or lowly reactive isomers of these sizes. Figure 2 shows the mass spectra of Aun− (n = 21−42) and their reaction products with O2 flow at 8.0 sccm at 150 K and 6.0 sccm at 120 K. In these spectra, the reactions of Au22− and Au24− were more evident than what are shown in Figure 1. The reaction products Au34O2− and Au36O2− were also observed. The reactions of these sizes seem to be accelerated as well at the lower temperature. The TOF mass spectrum of Aun− with n = 35−81 was shown in Figure S2, and no reactive sizes were observed for Aun− (n ≥ 37).

constant determined by the flow condition in the reactor and merges into the obtained relative reaction rate; [O2] indicates the O2 concentration, which is in proportion to the O2 flow rate. The k in eq 1 stands for the reaction rate of the considered Aun−. The k1 and k2 in eq 2 indicate two different reaction rates of various isomers of Aun−, and x1 stands for the proportion of the isomer(s) with the reaction rate k1. Even though some sizes like Au10− have more than two coexisting isomers, their reaction data can still be reasonably fitted using either (1) or (2). That is because some of the isomers have too close of rates to be distinguished by the present measurements.

I /I0 = e−k[O2]t

(1)

I /I0 = x1e−k1[O2]t + (1 − x1)e−k 2[O2]t

(2)

3. RESULTS AND DISCUSSION 3.1. Kinetic Measurements on O2 Adsorption on Aun− in the Size Range of 0−1 nm. Figure 1 shows the TOF mass spectra of the reaction products of Aun− (n = 1−26) and 0.00− 3.00 sccm O2 at 150 K. All active sizes exclusively formed AunO2−, which were indicated using vertical dashed lines. In addition to previously reported active Aun− with n = 2, 4, 6, 8, 10, 12, 14, 18, 20,12,37 the products from Au22− and Au24− were C

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

Figure 4. Relative kinetic rates of the reactions between Aun− (n = 1−70) and O2 at 150 K (a) and the adiabatic electron detachment energies (ADEs) of Aun− determined using the thresholds of their photoelectron spectra (b). In panel (a), the red data points showed the rates of the lower active or inert isomers of Au10−, Au18−, and Au22−; the percentages showed the proportions of their active isomers. In the panel (b), the black data points showed the ADEs of Aun− from ref 51; the red data points and the listed structures were from refs 20, 23−25, 27−30, 32, and 52. Among the red data points, the solid triangle ones indicated the dominant structure for each size, and the red empty cycles indicated the coexisting isomers. The horizontal dashed line indicated the ADE of 3.5 eV, which was found to be a threshold to shut down the O2 adsorption reactions.

We deduced the relative kinetic rates of Aun− (n = 1−70) according to the experiment data at 150 K. Figure 3a−d showed the data fitting for the representative Au2−, Au10−, Au12−, and Au22−, respectively. For the sizes with n = 2, 4, 6, 8, 12, 14, 20, 24, 34, and 36, the depletion processes were nicely fitted using eq 1, even though some of the sizes were known to have coexisting isomers. As an example, Au12−, which contained coexisting two-dimensional and three-dimensional isomers, can still be fitted using eq 1, which is similar to the fitting of Au2−. Meanwhile, the depletion processes of Aun− with n = 10, 18, and 22 were nicely fitted using eq 2, and the example Au10− and Au22− are shown in Figure 3b and d, respectively. For both Au10− and Au18−, the data fittings indicated that one item in eq 2 is constant, which implies that both of the sizes have an isomer being completely inert. For Au22−, the depletion was nicely fitted by a sum of two exponential items, indicating that all its isomers are active, with two apparently different reaction rates. The relative rates of all sizes were normalized to that of Au2−. Figure 4 showed the determined relative rates and the adiabatic electron detachment energies (ADEs) of Aun− from previous works.20,23−25,27−30,32,51,52 The rates of Au4−, Au6−, Au8−, Au10− (the active isomer), Au12−, Au14−, Au18− (the active isomer), Au20−, and Au22− (the active isomer) are nearly two orders higher than that of Au2−, and those of Au22− (the less active isomer), Au24−, Au34−, and Au36− are roughly of the same order. The correlation between the rates in Figure 4a and the ADEs in Figure 4b was discussed in the following section.

3.2. ADE Threshold Dividing the Active and the Inert Even-Sized Aun−. In the whole size range shown in Figure 4, all odd-sized Aun− are inert even though some of them have low ADE values. For example, the ADE of Au5− is lower than those of the reactive Au12−, Au18−, Au22−, Au24−, Au34−, and Au36−, and the ADE of Au7− is close to those of the reactive Au22−, Au24−, Au34−, and Au36−. Nevertheless, both Au5− and Au7− were shown to be inert in the reactions with O2 by the present work and all previous studies.12,35,37 Among all even-sized Aun−, Au2− has the lowest ADE value, and previous experiments and theoretical calculations showed that the adsorption energy of O2 in Au2O2− is the strongest one among all AunO2−.53,54 The slow kinetic rates of Au2− in the reactions with small molecules were attributed to the fact that clusters that are too small lack internal degrees of freedom to stabilize the energetically excited ion−molecule intermediates in the adsorption dynamics.55 The even-sized Aun− with n = 4, 6, 8, 12, 14, and 20 have ADEs apparently lower than 3.5 eV, and their reaction rates are about two orders higher than that of Au2−. For Au10−, the photoelectron spectroscopy determined four isomers with ADEs at 2.86, 3.09, 3.45, and 3.88 eV, respectively; the one with the ADE of 3.88 eV is a triangular structure (shown in Figure 4b) and was shown to be inert to O2.34 Our results consistently showed that about 35% of Au10− was unreactive even at high O2 flow and low temperatures. The Au16− has a VDE of 3.93 eV20 and was shown to be inert in all previous and present experiments.12,37 The Au18− has two isomers.23 Its D

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A ground state has a VDE of 3.27 eV, being reactive with O2, and the other isomer has a VDE of 3.53 eV, being completely inert.36 The present work consistently showed that only part of Au18− was reactive, and about 70% of Au18− was inert. For Au22−, two isomers were distinguished in the photoelectron spectroscopy experiment, the ADEs of which were determined to be 3.25 and 3.41 eV, respectively.25 Our experiments showed that both of these isomers reacted with O2, one of which has a rate as low as that of Au2−, and the other one has a rate two orders higher. The Au24− was shown to be dominated by one structure with an ADE of 3.38 eV.25 The present experiments showed that the Au24− was reactive with O2, and the rate is comparable to that of Au2−. The cluster Au26− from the laser vaporization source was a mixture of three isomers with ADEs of 3.40, 3.70, and 4.00 eV, and the isomer of 3.40 eV is the highest one and makes up a very small proportion.32 Our experiment did not see the reactions between Au26− and O2. For even larger Aun−, only Au34− and Au36− were reactive. The ADEs of these two sizes were 3.33 and 3.45 eV, respectively.28,29,56 Their reaction rates were also the same order as that of Au2−, and that of Au34− is slightly higher. A theoretical work predicted that Au34− is an electronic “magicnumber” cluster, having a relatively stronger O2 adsorption capability than its neighbors.46 Our experiment observation to some extent confirmed this prediction. The ADEs of Au58− and Au60− are local minima in the ADE plot in Figure 4b, which are 3.70 and 3.65 eV, respectively.27,51 The present experiments showed that both Au58− and Au60− were inert even at high O2 flows and low temperatures. In summary of the reactivity and the ADEs of Aun− listed in Figure 4, we found that there is an ADE threshold around 3.5 eV (indicated by the dashed line in Figure 4b) strictly dividing the active and the inert even-sized Aun−. Only the sizes with the ADEs lower than this threshold were active in the reactions with O2. Structures of Aun− change dramatically in the 0−1 nm size range, and those of some typical sizes are shown in Figure 4b. We did not see any correlations between structural variations and kinetic rates. For example, Au6− is a triangular structure with a D3h symmetry,18,52 whose reaction rate is the fastest among all sizes. For Au10−, the isomer with the ADE of 3.88 eV is also a triangular structure with the same D3h symmetry,34 while it is the only inert structure among the four isomers. For Au12−, the two isomers are a 2D plate and a 3D flat cage.18,19,21,52 However, the fitting of the kinetic data indicated that their reaction rates are too close to be distinguished. The Au16− cage20 is the only even size that is completely inert, and the pyramid Au20−24 is among the most active sizes. On the contrary, the cage isomer of Au18−, similar to that of Au16−, is reactive, while the pyramid structure of Au18− related to that of Au20− is completely inert.23,36 For Aun− (n > 20), their structures include pyramids, elongated cages, and low symmetries with enclosed atoms.21,25−30,32 For all these sizes, the structural effects on the reactivity with O2 seems to be negligible compared with those of the spins and the ADEs. 3.3. Insight into the Dynamics of the Electron Transfer Process. The electron transfer from even-sized Aun− to O2 was verified by characterizing AunO2− using photoelectron spectroscopy and infrared photodissociation spectroscopy.35,36,38,39 The AunO2− complexes can be viewed as an O2− chemically bonded to Aun. Similar to a previous work,12 the O2 adsorption on Aun− is schematically shown by Figure 5 including the potential surfaces of Aun−O2− and Aun−···O2 along the approaching direction of the gold and

Figure 5. Schematic illustration of the potential surfaces of Aun−···O2 and Aun−O2− along the approaching reaction coordinate between the gold and the oxygen moieties.

oxygen moieties. The long-range part of the surfaces of Aun− O2− is determined by the electrostatic attractions between O2− and the polarized Aun and tends to be independent of the structural details of the gold moiety. The potential curves of Aun−···O2 stand for physisorption interaction and should be likewise insensitive to the structural details. According to this scheme, a higher ADE of Aun− implies a lower energy level of Aun− + O2 and therefore a smaller adsorption energy from Aun− + O2 to Aun−O2−. If the energy difference between Aun− + O2 and Aun−O2− cannot compensate for the entropy loss accompanying the adsorption process, the Aun−O2− will not be observed. The reactivity of Aun− (n ≤ 10) with O2 can be theoretically interpreted using these thermodynamic analyses.57−61 Meanwhile, a structurally independent ADE threshold dividing the active and inert even-sized Aun− in the whole 0−1 nm size range could also originate from some dynamic reasons. According to the scheme shown in Figure 5, there is a barrier from Aun− + O2 to Au−O2− at their spin crossover point if the ADE of Aun− is large enough. In this scheme, all spin crossover points of Aun−O2− and Aun−···O2 tend to be distributed in a very small area. The ADE threshold observed around 3.5 eV could correspond to the case in which the energy level of Aun− + O2 roughly equals that of the spin crossover point. For Aun− with ADEs lower than this threshold, the reactions from Aun− + O2 to Aun−O2− are barrierless; otherwise, there will be a barrier accompanying the electron transfer process. It is worth noting that an ADE threshold around 3.0 eV was observed in the reactions between Agn− and O2,49 which could be interpreted using the same scheme. A deep understanding of the difference between the ADE thresholds for gold and silver clusters needs further theoretical explorations.

4. CONCLUSIONS In summary, we found that O2 can be adsorbed on anionic gold clusters larger than Au20−, including Au22−, Au24−, Au34−, and Au36−. In the whole size range of 0−1 nm, gold clusters’ global electronic properties dominate the reactivity, and a threshold around 3.5 eV divides the active and the inert Aun−, containing an even number of gold atoms. The apparent variations of clusters’ geometries, adsorption sites, and adsorption patterns have negligible effects on this ADE threshold. From this ADE threshold, we can roughly evaluate the energy level of the spin crossover point involved in the electron transfer processes in O2 adsorption on anionic gold. E

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

■

Stoichiometric Process Correlated to Electron Affinity. Chem. Phys. 2000, 262, 131−141. (13) Hagen, J.; Socaciu, L. D.; Elijazyfer, M.; Heiz, U.; Bernhardt, T. M.; Woste, L. Coadsorption of CO and O2 on Small Free Gold Cluster Anions at Cryogenic Temperatures: Model Complexes for Catalytic CO Oxidation. Phys. Chem. Chem. Phys. 2002, 4, 1707−1709. (14) Wallace, W. T.; Whetten, R. L. Coadsorption of CO and O2 on Selected Gold Clusters: Evidence for Efficient Room-Temperature CO2 Generation. J. Am. Chem. Soc. 2002, 124, 7499−7505. (15) Lang, S. M.; Bernhardt, T. M. Cooperative and Competitive Coadsorption of H2, O2, and N2 on Aux+ (x = 3, 5). J. Chem. Phys. 2009, 131, 024310. (16) Lyalin, A.; Taketsugu, T. Cooperative Adsorption of O2 and C2H4 on Small Gold Clusters. J. Phys. Chem. C 2009, 113, 12930− 12934. (17) Hakkinen, H.; Moseler, M.; Landman, U. Bonding in Cu, Ag, and Au Clusters: Relativistic Effects, Trends, and Surprises. Phys. Rev. Lett. 2002, 89, 033401. (18) Furche, F.; Ahlrichs, R.; Weis, P.; Jacob, C.; Gilb, S.; Bierweiler, T.; Kappes, M. M. The Structures of Small Gold Cluster Anions as Determined by a Combination of Ion Mobility Measurements and Density Functional Calculations. J. Chem. Phys. 2002, 117, 6982− 6990. (19) Johansson, M. P.; Lechtken, A.; Schooss, D.; Kappes, M. M.; Furche, F. 2d-3d Transition of Gold Cluster Anions Resolved. Phys. Rev. A: At., Mol., Opt. Phys. 2008, 77, 053202. (20) Bulusu, S.; Li, X.; Wang, L. S.; Zeng, X. C. Evidence of Hollow Golden Cages. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 8326−8330. (21) Xing, X. P.; Yoon, B.; Landman, U.; Parks, J. H. Structural Evolution of Au Nanoclusters: From Planar to Cage to Tubular Motifs. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 165423. (22) Lechtken, A.; Neiss, C.; Kappes, M. M.; Schooss, D. Structure Determination of Gold Clusters by Trapped Ion Electron Diffraction: Au14− - Au19−. Phys. Chem. Chem. Phys. 2009, 11, 4344−4350. (23) Huang, W.; Bulusu, S.; Pal, R.; Zeng, X. C.; Wang, L. S. Structural Transition of Gold Nanoclusters: From the Golden Cage to the Golden Pyramid. ACS Nano 2009, 3, 1225−1230. (24) Li, J.; Li, X.; Zhai, H. J.; Wang, L. S. Au20: A Tetrahedral Cluster. Science 2003, 299, 864−867. (25) Bulusu, S.; Li, X.; Wang, L.-S.; Zeng, X. C. Structural Transitions from Pyramidal to Fused Planar to Tubular to Core/Shell Compact in Gold Clusters: Aun− (n = 21−25). J. Phys. Chem. C 2007, 111, 4190− 4198. (26) Lechtken, A.; Schooss, D.; Stairs, J. R.; Blom, M. N.; Furche, F.; Morgner, N.; Kostko, O.; von Issendorff, B.; Kappes, M. M. Au34−: A Chiral Gold Cluster? Angew. Chem., Int. Ed. 2007, 46, 2944−2948. (27) Huang, W.; Ji, M.; Dong, C. D.; Gu, X.; Wang, L. M.; Gong, X. G.; Wang, L. S. Relativistic Effects and the Unique Low-Symmetry Structures of Gold Nanoclusters. ACS Nano 2008, 2, 897−904. (28) Shao, N.; Huang, W.; Gao, Y.; Wang, L.-M.; Li, X.; Wang, L.-S.; Zeng, X. C. Probing the Structural Evolution of Medium-Sized Gold Clusters: Aun− (n = 27−35). J. Am. Chem. Soc. 2010, 132, 6596−6605. (29) Shao, N.; Huang, W.; Mei, W.-N.; Wang, L. S.; Wu, Q.; Zeng, X. C. Structural Evolution of Medium-Sized Gold Clusters Aun− (n = 36, 37, 38): Appearance of Bulk-Like Face Centered Cubic Fragment. J. Phys. Chem. C 2014, 118, 6887−6892. (30) Pande, S.; Huang, W.; Shao, N.; Wang, L.-M.; Khetrapal, N.; Mei, W.-N.; Jian, T.; Wang, L.-S.; Zeng, X. C. Structural Evolution of Core-Shell Gold Nanoclusters: Aun− (n = 42−50). ACS Nano 2016, 10, 10013−10022. (31) Yoon, B.; Koskinen, P.; Huber, B.; Kostko, O.; von Issendorff, B.; Hakkinen, H.; Moseler, M.; Landman, U. Size-Dependent Structural Evolution and Chemical Reactivity of Gold Clusters. ChemPhysChem 2007, 8, 157−161. (32) Schaefer, B.; Pal, R.; Khetrapal, N. S.; Amsler, M.; Sadeghi, A.; Blum, V.; Zeng, X. C.; Goedecker, S.; Wang, L.-S. Isomerism and Structural Fluxionality in the Au26 and Au26− Nanoclusters. ACS Nano 2014, 8, 7413−7422.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.8b00629. Mass spectra showing the reactions of Aun− (n = 10−26) and Aun− (n = 35−81) with O2 at the flow of 6.0 sccm and 120 K (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-021-65981097; Fax: +86-021-65981097; E-mail: [email protected]. ORCID

Xiaopeng Xing: 0000-0001-7323-1705 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 21673158 and 21273278), the Ministry of Science and Technology of China (Grant No. 2012YQ22011307), and the Science & Technology Commission of Shanghai Municipality (Grant No. 14DZ2261100). The authors are very thankful to Dr. Joel H. Parks of the Rowland Institute at Harvard for giving us most of the experimental facilities and acknowledge helpful discussions with Prof. XueFeng Wang of Tongji University.

■

REFERENCES

(1) Haruta, M.; Kobayashi, T.; Sano, H.; Yamada, N. Novel Gold Catalysts for the Oxidation of Carbon-Monoxide at a Temperature Far Below 0 °C. Chem. Lett. 1987, 16, 405−408. (2) Haruta, M.; Yamada, N.; Kobayashi, T.; Iijima, S. Gold Catalysts Prepared by Coprecipitation for Low-Temperature Oxidation of Hydrogen and of Carbon-Monoxide. J. Catal. 1989, 115, 301−309. (3) Bohme, D. K.; Schwarz, H. Gas-Phase Catalysis by Atomic and Cluster Metal Ions: The Ultimate Single-Site Catalysts. Angew. Chem., Int. Ed. 2005, 44, 2336−2354. (4) Castleman, A. W. Cluster Structure and Reactions: Gaining Insights into Catalytic Processes. Catal. Lett. 2011, 141, 1243−1253. (5) Ding, X.-L.; Wu, X.-N.; Zhao, Y.-X.; He, S.-G. C-H Bond Activation by Oxygen-Centered Radicals over Atomic Clusters. Acc. Chem. Res. 2012, 45, 382−390. (6) Lang, S. M.; Bernhardt, T. M. Gas Phase Metal Cluster Model Systems for Heterogeneous Catalysis. Phys. Chem. Chem. Phys. 2012, 14, 9255−9269. (7) Wang, L. M.; Wang, L. S. Probing the Electronic Properties and Structural Evolution of Anionic Gold Clusters in the Gas Phase. Nanoscale 2012, 4, 4038−4053. (8) Bernhardt, T. M. Gas-Phase Kinetics and Catalytic Reactions of Small Silver and Gold Clusters. Int. J. Mass Spectrom. 2005, 243, 1−29. (9) Burgel, C.; Reilly, N. M.; Johnson, G. E.; Mitric, R.; Kimble, M. L.; Castleman, A. W.; Bonacic-Koutecky, V. Influence of Charge State on the Mechanism of CO Oxidation on Gold Clusters. J. Am. Chem. Soc. 2008, 130, 1694−1698. (10) Cox, D. M.; Brickman, R.; Creegan, K.; Kaldor, A. Gold Clusters: Reactions and Deuterium Uptake. Z. Phys. D: At., Mol. Clusters 1991, 19, 353−355. (11) Lee, T. H.; Ervin, K. M. Reactions of Copper Group Cluster Anions with Oxygen and Carbon Monoxide. J. Phys. Chem. 1994, 98, 10023−10031. (12) Salisbury, B. E.; Wallace, W. T.; Whetten, R. L. LowTemperature Activation of Molecular Oxygen by Gold Clusters: A F

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

Temperature Dependent Reaction Kinetics Measurements. J. Phys. Chem. A 2009, 113, 2724−2733. (54) Yamaguchi, M.; Miyajima, K.; Mafune, F. Desorption Energy of Oxygen Molecule from Anionic Gold Oxide Clusters, AunO2−, Using Thermal Desorption Spectrometry. J. Phys. Chem. C 2016, 120, 23069−23073. (55) Hagen, J.; Socaciu, L. D.; Heiz, U.; Bernhardt, T. M.; Woste, L. Size Dependent Reaction Kinetics of Small Gold Clusters with Carbon Monoxide: Influence of Internal Degrees of Freedom and Carbonyl Complex Stability. Eur. Phys. J. D 2003, 24, 327−330. (56) Gu, X.; Bulusu, S.; Li, X.; Zeng, X. C.; Li, J.; Gong, X. G.; Wang, L.-S. Au34−: A Fluxional Core-Shell Cluster. J. Phys. Chem. C 2007, 111, 8228−8232. (57) Mills, G.; Gordon, M. S.; Metiu, H. The Adsorption of Molecular Oxygen on Neutral and Negative Aun Clusters (n = 2−5). Chem. Phys. Lett. 2002, 359, 493−499. (58) Zhao, Y.; Khetrapal, N. S.; Li, H.; Gao, Y.; Zeng, X. C. Interaction between O2 and Neutral/Charged Aun (n = 1−3) Clusters: A Comparative Study between Density-Functional Theory and Coupled Cluster Calculations. Chem. Phys. Lett. 2014, 592, 127−131. (59) Ding, X. L.; Dai, B.; Yang, J. L.; Hou, J. G.; Zhu, Q. S. Assignment of Photoelectron Spectra of AunO2− (n = 2, 4, 6) Clusters. J. Chem. Phys. 2004, 121, 621−623. (60) Ding, X. L.; Li, Z. Y.; Yang, J. L.; Hou, J. G.; Zhu, Q. S. Adsorption Energies of Molecular Oxygen on Au Clusters. J. Chem. Phys. 2004, 120, 9594−9600. (61) Yoon, B.; Hakkinen, H.; Landman, U. Interaction of O2 with Gold Clusters: Molecular and Dissociative Adsorption. J. Phys. Chem. A 2003, 107, 4066−4071.

(33) Gao, Y.; Huang, W.; Woodford, J.; Wang, L. S.; Zeng, X. C. Detecting Weak Interactions between Au- and Gas Molecules: A Photoelectron Spectroscopic and ab Initio Study. J. Am. Chem. Soc. 2009, 131, 9484−9485. (34) Huang, W.; Wang, L. S. Au10−: Isomerism and StructureDependent O2 Reactivity. Phys. Chem. Chem. Phys. 2009, 11, 2663− 2667. (35) Huang, W.; Zhai, H. J.; Wang, L. S. Probing the Interactions of O2 with Small Gold Cluster Anions (Aun−, n = 1−7): Chemisorption vs Physisorption. J. Am. Chem. Soc. 2010, 132, 4344−4351. (36) Pal, R.; Wang, L. M.; Pei, Y.; Wang, L. S.; Zeng, X. C. Unraveling the Mechanisms of O2 Activation by Size-Selected Gold Clusters: Transition from Superoxo to Peroxo Chemisorption. J. Am. Chem. Soc. 2012, 134, 9438−9445. (37) Kim, Y. D.; Fischer, M.; Gantefor, G. Origin of Unusual Catalytic Activities of Au-Based Catalysts. Chem. Phys. Lett. 2003, 377, 170−176. (38) Stolcic, D.; Fischer, M.; Gantefor, G.; Kim, Y. D.; Sun, Q.; Jena, P. Direct Observation of Key Reaction Intermediates on Gold Clusters. J. Am. Chem. Soc. 2003, 125, 2848−2849. (39) Woodham, A. P.; Meijer, G.; Fielicke, A. Activation of Molecular Oxygen by Anionic Gold Clusters. Angew. Chem., Int. Ed. 2012, 51, 4444−4447. (40) Huang, W.; Wang, L. S. Probing the 2d to 3d Structural Transition in Gold Cluster Anions Using Argon Tagging. Phys. Rev. Lett. 2009, 102, 153401. (41) Roldan, A.; Ricart, J. M.; Illas, F.; Pacchioni, G. O2 Adsorption and Dissociation on Neutral, Positively and Negatively Charged Aun (n = 5−79) Clusters. Phys. Chem. Chem. Phys. 2010, 12, 10723− 10729. (42) Gao, W.; Chen, X. F.; Li, J. C.; Jiang, Q. Is Au55 or Au38 Cluster a Threshold Catalyst for Styrene Epoxidation? J. Phys. Chem. C 2010, 114, 1148−1153. (43) Liao, M. S.; Watts, J. D.; Huang, M. J. Theoretical Comparative Study of Oxygen Adsorption on Neutral and Anionic Agn and Aun Clusters (n = 2−25). J. Phys. Chem. C 2014, 118, 21911−21927. (44) Boronat, M.; Corma, A. Oxygen Activation on Gold Nanoparticles: Separating the Influence of Particle Size, Particle Shape and Support Interaction. Dalton Trans. 2010, 39, 8538−8546. (45) Xie, Y. P.; Gong, X. G. First-Principles Studies for CO and O2 on Gold Nanocluster. J. Chem. Phys. 2010, 132, 244302. (46) Gao, Y.; Shao, N.; Pei, Y.; Chen, Z.; Zeng, X. C. Catalytic Activities of Subnanometer Gold Clusters (Au16-Au18, Au20, and Au27Au35) for CO Oxidation. ACS Nano 2011, 5, 7818−7829. (47) Tang, D.; Hu, C. DFT Insight into CO Oxidation Catalyzed by Gold Nanoclusters: Charge Effect and Multi-State Reactivity. J. Phys. Chem. Lett. 2011, 2, 2972−2977. (48) Liu, C.; Tan, Y.; Lin, S.; Li, H.; Wu, X.; Li, L.; Pei, Y.; Zeng, X. C. CO Self-Promoting Oxidation on Nanosized Gold Clusters: Triangular Au3 Active Site and CO Induced O-O Scission. J. Am. Chem. Soc. 2013, 135, 2583−2595. (49) Ma, J.; Cao, X.; Xing, X.; Wang, X.; Parks, J. H. Adsorption of O2 on Anionic Silver Clusters: Spins and Electron Binding Energies Dominate in the Range up to Nano Sizes. Phys. Chem. Chem. Phys. 2016, 18, 743−748. (50) Ma, J.; Cao, X.; Liu, H.; Yin, B.; Xing, X. Adsorption and Activation of NO on Silver Clusters with Sizes up to One Nanometer: Interactions Dominated by Electron Transfer from Silver to NO. Phys. Chem. Chem. Phys. 2016, 18, 12819−12827. (51) Taylor, K. J.; Pettiettehall, C. L.; Cheshnovsky, O.; Smalley, R. E. Ultraviolet Photoelectron-Spectra of Coinage Metal-Clusters. J. Chem. Phys. 1992, 96, 3319−3329. (52) Hakkinen, H.; Yoon, B.; Landman, U.; Li, X.; Zhai, H. J.; Wang, L. S. On the Electronic and Atomic Structures of Small Aun− (n = 4− 14) Clusters: A Photoelectron Spectroscopy and Density-Functional Study. J. Phys. Chem. A 2003, 107, 6168−6175. (53) Bernhardt, T. M.; Hagen, J.; Lang, S. M.; Popolan, D. M.; Socaciu-Siebert, L. D.; Woste, L. Binding Energies of O2 and CO to Small Gold, Silver, and Binary Silver-Gold Cluster Anions from G

DOI: 10.1021/acs.jpca.8b00629 J. Phys. Chem. A XXXX, XXX, XXX−XXX