CHEMPHYSCHEM ARTICLES DOI: 10.1002/cphc.201402347

Gas-Phase Reaction of CeV2O7 + with C2H4 : Activation of CC and CH Bonds Jia-Bi Ma,*[a] Zhen Yuan,[b] Jing-Heng Meng,[b] Qing-Yu Liu,[b] and Sheng-Gui He*[b] Dedicated to Professor Helmut Schwarz on the occasion of his 70th birthday

The reactivity of metal oxide clusters toward hydrocarbon molecules can be changed, tuned, or controlled by doping. Cerium-doped vanadium cluster cations CeV2O7 + are generated by laser ablation, mass-selected by a quadrupole mass filter, and then reacted with C2H4 in a linear ion trap reactor. The reaction is characterized by a reflectron time-of-flight mass spectrometer. Three types of reaction channels are observed:

1) single oxygen-atom transfer , 2) double oxygen-atom transfer , and 3) C=C bond cleavage. This study provides the first bimetallic oxide cluster ion, CeV2O7 + , which gives rise to C=C bond cleavage of ethene. Neither CexOy  nor VxOy  alone possess the necessary topological and electronic properties to bring about such a reaction.

1. Introduction In contemporary chemistry, man-made catalysts are indispensable in the production of almost all manufactured goods. Metal oxides are widely used as catalysts[1] and many of these catalysts are often composed of multiple components that improve catalytic activity, selectivity, stability, and so forth. Substitutional doping of a small fraction of host oxides by different oxides is a typical way of forming oxide catalysts with multiple components. Although great progresses have been made recently in characterization methods, the composition of many active catalytic sites at an atomic level is still ambiguous, thus leading to a scenario in which the effects of doping of binary oxides are far from clear.[2] For instance, it is generally accepted that a new active phase CeVO4 shows up when cerium–vanadium mixed oxide is synthesized,[3] and the activity of the catalyst with VOx clusters supported on ceria (CeO2) is higher than that of either the vanadium oxide (V2O5) or CeO2 in the partial oxidation of propane and in many other reactions.[3b,d, 4] In catalytic processes involving metal oxides, the role of the oxide surface is to provide or form oxygen in activated states.[5] It has been pointed out that an oxygen-centered radi-

[a] Dr. J.-B. Ma The Institute for Chemical Physics Key Laboratory of Cluster Science School of Chemistry Beijing Institute of Technology 100081, Beijing (P.R. China) E-mail: [email protected] [b] Z. Yuan, J.-H. Meng, Q.-Y. Liu, Prof. Dr. S.-G. He State Key Laboratory for Structural Chemistry of Unstable and Stable Species Institute of Chemistry Chinese Academy of Sciences 100190 Beijing (P.R. China) E-mail: [email protected] Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201402347.

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cal (OC) over a transition-metal oxide surface is one important type of reactive oxygen species in the oxidation or oxidative transformation of stable molecules at low temperature.[6] The complexity of condensed-phase systems as well as the “obscure” properties of OC, such as its short lifetime and/or low concentration, make practical investigations challenging, and the nature of the active sites and the mechanisms involving OC remain controversial, despite the considerable resources that have been devoted to understanding these aspects. Thus, it is quite useful and necessary to adopt alternative ways to study the nature of OC radicals so that their reactivity may be tuned or controlled. Gas-phase metal oxide clusters that can be studied under well-controlled and reproducible conditions serve as ideal models that can be used to reveal the nature of active sites and the mechanisms of catalysis at a molecular level. A large body of work on homonuclear metal oxide clusters is available,[7] and these investigations have revealed important details of the elementary steps of many reactions. For example, formation of CH3C through hydrogen atom abstraction is regarded as the decisive step in oxidative dehydrogenation and dimerization of methane,[8] and many studies have indicated that oxide-cluster cations that contain the OC radicals act as active sites to generate CH3C even at room temperature.[9] More recently, evidence that supports the involvement of OC radicals in low-temperature catalytic CO oxidation over titania and zirconia supports has been provided by employing time-offlight (TOF) mass spectrometry and density functional theory (DFT) calculations.[10] Recently, research efforts have focused on the structures and reactivities of heteronuclear oxide clusters such as VxP4xO10 + (x = 1–3),[11] VPO4 + ,[12] AlxVyOz + (x + y = 2–4, z = 3–10),[13] YAlO2,3 + ,[14] AuNbO3 + ,[15] VNbO5 + ,[16] Au(TiO2)xOy (x = 2,3; y = 1,2),[17] neutral VCoO4[18] as well as CeAlO4,[19] among others.[20] It has been demonstrated that changing the substrates on which the ChemPhysChem 0000, 00, 1 – 10

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CHEMPHYSCHEM ARTICLES OC radicals are bonded in cluster systems can affect the distributions of local charge[20c] and spin density (SD),[9i] as well as reaction mechanisms.[14a] Among the heteronuclear oxide clusters mentioned above, vanadium-phosphorus oxo-cluster cations VxP4xO10 + (x = 2,3) and VPO4 + [12] exhibit different, rather intriguing reactivity patterns with small hydrocarbons compared with the homonuclear analogues M4O10 + (M = P or V) and V2O4 + , respectively. Schwarz et al. pointed out that the cooperative effects of V and P atoms in the clusters give rise to the occurrence of oxidative dehydrogenation in the C2H4 oxidation; in distinct contrast, M4O10 + (M = P or V) alone is unable to bring about this reaction. In addition to the VPO cations, CexVyOz + clusters were explored through infrared spectroscopy combined with DFT calculations.[21] The results suggest that, for instance, the CeV2O6 + cluster with a cage-like structure (Ce + 3/ V + 5) is lower in energy by 113 kJ mol1 than the isomer with a bicyclic structure (Ce + 4/V + 4); thus, Ce + 3/V + 5 rather than Ce + 4/V + 4 is predicted to be favored in CexVyOz + clusters.[21] In gas-phase chemistry, the activation of alkenes, for example C2H4, has been widely investigated.[11c, 12, 22] Several types of reactions have been reported (Scheme 1): single oxygen-atom

www.chemphyschem.org oxide cluster ion to bring about this kind reaction in the oxidation of C2H4.

2. Results and Discussion 2.1. Generation and Reaction of the CeV2O7 + Cluster Ions A typical TOF mass spectrum for the distribution of CeV2O57 + clusters generated by laser ablation (see Experimental Section for details) is shown in Figure 1 a. Cerium has four stable iso-

Figure 1. TOF mass spectra for distribution of CexVyOz + clusters in selected mass region (a), and the reactions of mass-selected 14CeV2O7 + (b) with 1.6 mPa (c) and 3.3 mPa C2H4 (d) for approximately 0.62 ms. The numbers x ,y ,z and x, y, z, H denote CexVyOz + and CexVyOzH + clusters, respectively.

Scheme 1. Schematic description of six product channels observed in the reactions of transition-metal-oxide clusters toward C2H4.

transfer (SOAT; Process 1),[12, 22c] double oxygen-atom transfer (DOAT; Process 2),[22g] the rupture of the C=C bond (Process 3),[22a,b,d,e] hydrogen-atom transfer (HAT, Process 4),[11c] association channel (Process 5),[22f] and oxidative dehydrogenation (Process [6]).[11c] Processes 1, 2, and 4–6 are common in the reactions of C2H4 with both homonuclear[12, 22c–g] and heteronuclear oxide clusters.[11c, 12] In contrast, the rupture of the C=C bond (Process 3) has not been reported in reactions of heteronuclear oxide cluster ions with C2H4. In this context, herein, we report on the electronic structure of CeV2O7 + , which is the smallest reactive heteronuclear CexVyOz + cluster, and demonstrate its reactivity toward C2H4 by using mass spectrometry in conjunction with DFT calculations. In the reaction of CeV2O7 + with C2H4, surprisingly, a C=C bond cleavage process occurs, so CeV2O7 + is the first bimetallic  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

topes: 136Ce (0.19 %), 138Ce (0.25 %), 140Ce (88.45 %), and 142Ce (11.11 %) of which the first two have negligible abundances. In addition to the presence of heteronuclear oxide clusters CeV2O57 + , homonuclear oxide clusters V4O8–10 + and Ce2O3–5 + are also present, due to the use of a mixed Ce/V target. Although the molar ratio of cerium and vanadium in the target of laser ablation is 1:10, the intensities of Ce2O3–5 + are still higher than those of V4O8–10 + . This can be a result of higher oxygen-uptake ability of cerium versus vanadium. The CeV2O7 + cluster with a unit oxygen-deficiency[23, 24] was mass-selected (Figure 1 b) by a quadrupole mass filter (QMF), confined in a linear ion trap (LIT) reactor through collisions with He atoms and then reacted therein with C2H4 (Figure 1 b,c). The QMF could be run at unit mass resolution to select the single isotopomer of 140CeV2O7 + (354 amu). However, because of background impurities such as water from the He gas used for confining the cluster ions, a weak peak corresponding to 140CeV2O7H + (355 amu) that does not occur in the cluster source (Figure 1 a) can also be seen in Figure 1 b. ChemPhysChem 0000, 00, 1 – 10

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As shown in Figure 1 c, upon reaction with C2H4, three new product channels are observed; that is, SOAT [c1 channel; Eq. (1)], DOAT [c2 channel; Eq. (2)], and C=C bond cleavage [c3 channel; Eq. (3)]: CeV2 O7 þ þ C2 H4 ! CeV2 O6 þ þ C2 H4 O

ð1Þ

CeV2 O7 þ þ C2 H4 ! CeV2 O5 þ þ C2 H4 O2

ð2Þ

CeV2 O7 þ þ C2 H4 ! CeV2 O6 CH2 Oþ þ CH2 O

ð3Þ

The most abundant product ion is CeV2O6 + , however the generation of other products is also apparent. In Figure 1 c, compared with CeV2O7 + (354 amu), the signal corresponding to a mass loss of 2 amu is CeV2O6CH2 + , which is the product of the c3 channel. Notably, to our knowledge, this is the first observation of rupture of a C=C bond in the reactions of bimetallic oxide cluster ions with alkenes. The above three reaction channels c1–c3 are also confirmed by mass-selection and reaction of both 140CeV2O7 + and 142CeV2O7 + isotopomers, as shown in Figure S1 of the Supporting Information. It is noteworthy that in the interaction with N2 molecules in the ion trap (Figure S1 b), the product peaks of CeV2O6 + , CeV2O5 + , and CeV2O6CH2 + are absent, indicating that they are not due to collision induced dissociation in the reaction with C2H4 (Figure 1 c,d). Figure 2 plots the signal variation of the reactant and product cluster ions in CeV2O7 + +C2H4 with respect to the reactant gas pressure in the reactor. The signal dependence of the SOAT, DOAT and C=C bond cleavage products as well as the

or does not take place in the reactor. Note that the relative intensity decrease of CeV2O7H + can be due to the experimental uncertainties ( 20 %) and (or) a competition between the reaction with C2H4 (the channels c1–c3) and the reaction with impurity molecules (such as CeV2O7 + +H2O!CeV2O7H + +OH) in the reactor. The normalized branching ratios (BRs) of generating CeV2O6 + , CeV2O5 + , and CeV2O6CH2 + are 89:6:5, respectively. The pseudo-first-order rate constant (k1) of the overall reaction (CeV2O7 + +C2H4) was determined to be k1 = (1.0  0.4)  109 cm3 s1 molecule1, corresponding to an efficiency (ø) of (95  38) %.[25] An oxide cluster with the unit oxygen-deficiency (such as CeV2O7 + ) usually contains the oxygen-centered radical OC and does not have structure moieties such as O2 with an unbroken OO bond.[23] To support this point and to verify the CeV2O7 + structure obtained from the DFT calculations (see text below), collision-induced dissociation (CID) experiments were performed with a TOF/TOF tandem mass spectrometer (MS) employing crossed He and Ar beams. The center-of-mass kinetic energies of the CeV2O7 + cluster with He and Ar atoms in the spectrometer were 1560 kJ mol1 (16.2 eV) and 1.4  104 kJ mol1 (145 eV), respectively. Loss of single oxygen atoms rather than the O2 units dominate the CID spectra for the collisions of CeV2O7 + ions with both He (Figure S2b) and Ar atoms (Figure S2 c). In contrast, in the CID experiment with the oxygen-rich cluster V4O11 + , which can have a superoxide unit (O2C),[23, 24] the loss of O2 rather than O dominates the CID spectra (Figure S2 e,f). As a result, the CID experiments indicate that there is no OO unit in CeV2O7 + , although the cluster ions are generated from the reactions of O2 with the metal plasmas in the laser ablation cluster source.

2.2. Structure of CeV2O7 + Cluster

Figure 2. Variation of the relative intensities of the reactant and product cluster ions in the reaction between CeV2O7 + and C2H4 with respect to the experimental reactant gas pressure. The solid lines are fitted to the experimental data points by using the equations derived with the approximation of the pseudo-first-order reaction mechanism.

unreacted CeV2O7 + cluster on the C2H4 pressure can be well fitted with a pseudo-first-order mechanism, which further supports the derived reaction channels c1–c3. In contrast, the relative ion intensity of CeV2O7H + decreases slightly with respect to the increase of the C2H4 pressure, indicating that the HAT channel (CeV2O7 + +C2H4 !CeV2O7H + +C2H3) is either very slow  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The reactivities of clusters show a high dependence on their structures, therefore, it is quite necessary to study the structure of CeV2O7 + before investigating its reactivity. DFT calculations predict several low-lying isomeric structures that are within 105 kJ mol1 in energy, as shown in Figure 3. Both IS1 and IS2 contain the same structure unit (Ot)2V(Ob)2, in which Ot and Ob are terminal and bridging oxygen atoms, respectively. Although it is difficult to confirm whether IS1 or IS2 is the ground state of CeV2O7 + due to the computational accuracy,[26] there is no doubt that the unpaired electron is distributed over the two Ot atoms bound to the same V atom, and [OtOt]C is the active site. The unpaired electron can also be distributed over Ce atom (IS6) or one Ce atom and the adjacent O atoms (IS4, IS5, and IS9); however these structures are disfavored by at least 53 kJ mol1, compared with IS1. Isomer IS6, with an unbroken OO bond is higher in energy by 65 kJ mol1 than IS1, further suggesting the nonexistence of the O2 unit in the cluster. The oxidation states of vanadium and cerium atoms in CeV2O7 + (IS1) and in CeV2O6 + (reported by Asmis and co-workers,[21] IS10 in Figure 3 b), are + 5 and + 4, respectively. ChemPhysChem 0000, 00, 1 – 10

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cage-like structure in 3 is formed via TS2/3, before the release of CH3CHO moiety takes place. Concomitant with the formation of this structure (2!TS2/3!3), the CH3CHO unit migrates to the threefold coordinated Ce atom (3). The structure of CeV2O6 + adopted here is in line with that reported by Jiang et al.[21] To obtain HAc and CeV2O5 + (9 in Figure 4 c), intermediate 2 subsequently undergoes successive HAT steps (2!TS2/5!5! TS5/6!6) to bring about 6 with the co-existence of a hydroxyl group and a COCH3 moiety. The HAc unit in 7 is then generated via TS6/7. With the presence of a HAc moiety, the cage-like CeV2O5 + is formed via 7!TS7/ 8!8. From 8, the weakly bound HAc ligand can easily be liberat+ + Figure 3. DFT calculated structures of a) CeV2O7 and b) CeV2O6 . The point group, electronic state, and relative ed, and the DOAT products 9 energy in kJ mol1 are given under each structure isomer. Some bond lengths (in pm) are given. The unpaired and HAc are generated. Twospin density distributions are shown in the gray isosurfaces, and the values in mB are given in parentheses. The structure of IS10 is adapted from Ref. [21]. state reactivity,[28] which involves the conversion of intermediates from one spin state to another, 2.3. Reaction Mechanisms for the OAT Reactions is a common phenomena for the reactions of transition-metal systems. On the PES of DOAT, the spin conversion from douTo obtain further information on the mechanisms, DFT calculablet to quartet may take place in the step of 5!TS5/6!6. tions were performed for the reaction of CeV2O7 + with C2H4. Due to high computational cost, the details of spin conversion There are several reasonable structures for C2H4O1,2, in which are not considered herein. acetaldehyde (C2H4O) and acetic acid (C2H4O2, denoted as HAc) When looking into the PESs, it is clearly observed that, in are the thermochemically most favored products, respectively, the initial 1!TS1/2!2 step, the SD transfers from Ot bonded in the reactions of metal oxide clusters toward C2H4.[12, 22g, 27] As shown in Figure 4 a, intermediate 1 is generated through with the V atom to the low-coordinated C atom in C2H4, formthe formation of one OC bond, and the CC bond in the ing intermediate 2; the SD then transfers to the Ce atom, acC2H4 unit [r(CC) = 147 pm] is elongated compared with that in companied by large energy release (ca. 400 kJ mol1). The reac+ free C2H4 (133 pm), in the reaction of CeV2O7 with C2H4. The tion mechanisms discussed above also show that the intramonext scenario is that the CH3CHO moiety in 2 is formed by lecular HAT process is important for preparing reaction comovercoming a barrier TS1/2, and CH3CHO coordinates through plexes with structures and energetics that are suitable for the oxygen and hydrogen atoms to the V and Ot atoms, reSOAT and DOAT. spectively. The Ce atom in 2 carries the SD, indicating that the Ce atom is reduced from its highest oxidation state + 4 in 2.4. Reaction Mechanism for C=C Bond Cleavage CeV2O7 + to + 3 in 2. Intrinsic reaction coordinate (IRC) calculations for this step are shown in Figure S3 of the Supporting InStarting from 2, the migration of a H atom from the CH3 formation to illustrate how TS1/2 connects 1 and 2 on the remoiety to C1 results in the formation of 13 with a five-memaction pathway. The energy of TS1/2 (114 kJ mol1) is slightly bered -VOCCO- ring, as shown in Figure 5 . In 13, the CC bond is already strongly elongated compared with that of lower than that of 1 (145 kJ mol1) if zero-point energy (ZPE) free C2H4 ; that is, r(CC) = 154 and 133 pm for 13 and free is taken into consideration. Without ZPE, TS1/2 locates energetically higher than 1. This phenomenon is also found for the C2H4, respectively. By surmounting TS13/14, the CC bond in reaction mechanism of V3PO10 + +CH4 and other theoretical 13 ruptures to give intermediate 14, in which two CH2O units studies.[11a,c] Starting from 2, two different reaction channels, are formed. Subsequently, the interaction between one CH2O SOAT (the formation of CH3CHO, 2!TS2/3!3!4) and DOAT unit and a V atom is weakened via TS14/15, delivering one coordination site on a V atom of 15. With the presence of the (the formation of CH3COOH, Figure 4 c), are accessible. In Figweakly adsorbed CH2O unit, the O2 atom in 15 generates an ure 3 b, the CeV2O6 + cluster with the cage-like structure (IS10) is more stable than IS11 by 100 kJ mol1, and in Figure 4 a the OV bond to form intermediate 16, with the cage-like struc 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Figure 4. DFT calculated potential energy profiles for a) SOAT channel and c) DOAT channel in the reaction of CeV2O7 + with C2H4. Bond lengths are in pm. The zero-point vibration corrected energies (DH0 K in kJ mol1) of the reaction intermediates, transition states, and products with respect to the separated reactants are given. In (c) the superscripts indicate the spin multiplicities for the intermediates and transition states, as well as the products. A doublet-to-quartet conversion point is marked with an asterisk in (c), and the cluster species in (a) are all doublet. Three energies of TS5/6 corresponding to doublet, broken-symmetry (marked with the superscript BS), and quartet states, respectively, are shown. b) The spin density distributions of intermediates 2 and 3 and TS2/3 are shown in the gray isosurfaces; the structure of V3O8C2H4 is adapted from Ref. [22e].

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Figure 5. DFT calculated potential energy profiles for the C=C bond cleavage channel in the reaction of CeV2O7 + with C2H4. Bond lengths are in pm. The zeropoint vibration corrected energies (DH0 K in kJ mol1) of the reaction intermediates, transition states, and products with respect to the separated reactants are given. The superscripts indicate the spin multiplicities for the intermediates and transition states, as well as the products. A doublet-to-quartet conversion point is marked with an asterisk. Three energies of TS14/15 corresponding to doublet, broken-symmetry (marked with a superscript BS), and quartet states are shown.

ture of CeV2O5 + unit. The spin conversion from doublet to quartet may happen in the step of 14!TS14/15!15. In the previous works, C=C bond cleavage processes have been reported in the reactions of homonuclear oxide clusters with ethene, propylene, and butene.[22a,b,e, 29] No such product channel has been obtained in the reactions of heteronuclear oxide cluster ions with alkenes; however, the CeV2O7 + cluster is an exception. Among the reported reaction mechanisms of C=C bond cleavage over oxide clusters, the PESs of VO3(V2O5)n/ C2H4 systems and CeV2O7 + /C2H4 share a common feature: crucial intermediates with five-membered rings are located on the PESs, releasing large energies, and the distance of CC bond (ca. 154 pm) in this type of structure is longer than that of free C2H4, indicating a CC single bond. These ring structures can be formed from V(Ot)2C building blocks, and these types of [3+2] cycloaddition products have been reported in the reactions of V2O6 and V4O11 , which also possess the V(Ot)2C units, with C2H4 and C3H6 ;[22f] however, V2O6 and V4O11 cannot bring about rupture of the C=C bond in alkenes.[22f, 30] In addition to the similarities of the mechanisms mentioned above, three remarkable differences deserve closer examination. First,  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

in the reactions of V2O5 + [31] and V2O6 ,[22f] as well as VO3(V2O5)n[22e, 29a] with alkenes, only the distances between carbon atoms in C2H4 and oxygen atoms in clusters change during the formation of the structures with five-membered rings, and HAT is not involved. In the CeV2O7 + /C2H4 system, to ascertain whether intermediate 13 can be formed directly from a complex of CeV2O7 + with C2H4, the potential energy surfaces are scanned by variation of the OC bond lengths both in 1 and in 13 (Figure S4 of the Supporting Information). No TS that connects 1 and 13 is located, and intermediate 2 is inevitably formed, which suggests that 13 is not directly accessible from 1, and that HAT steps must take place during the formation of the five-membered ring in the C=C bond cleavage channel. Second, in the reactions of neutral VO3(V2O5)n (n = 0,1,2…) cluster with alkenes, intermediates with VOC three-membered ring are indispensable before the product CH2O is released.[22e, 29a] However, this structure is less competitive in the CeV2O7 + /C2H4 system than in the VO3(V2O5)n/C2H4 systems. On the PES of former system, the VO bond rather than the VC bond is formed via 15!TS15/16!16. The intermediate [CeV2O6CH2O] + with VOC three-membered ring (18) is ChemPhysChem 0000, 00, 1 – 10

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CHEMPHYSCHEM ARTICLES 61 kJ mol1 higher in energy compared with the isomer with cage-like structure (17) and is therefore not included in the PES calculations. Third, the rate-determining activation barrier of the CeV2O7 + /C2H4 couple is TS2/13, in which hydrogen atom transfers from C2 to C1, rather than the barrier required to break the five-membered ring to form two CH2O units (13!TS13/14!14); the latter kind of barrier is the rate-determining step in the VO3(V2O5)n/C2H4 systems. Among the reactions of homonuclear cerium and vanadium oxide cluster ions as well as other heteronuclear oxide clusters with alkenes, all general reaction types except for C=C bond cleavage process, shown in Scheme 1, are observed.[9i, 11c, 12, 22c,g, 31, 32] Thus, cooperative effects of Ce and V atoms in the CeV2O7 + cluster operate in the rupture of the C=C bond of C2H4 ; neither CexOy  nor VxOy  alone possess the topological and electronic properties necessary to bring about this reaction. Comparison of the c1, c2, and c3 channels shown in Figure 1 c,d, indicates that DOAT is much less favorable than SOAT, and that the relative rates of DOAT and C=C bond cleavage channels are comparable. Based on the results obtained from the calculations, the products of these three channels, 4+CH3CHO, 9+HAc and 17+CH2O, are close in energy (around 200 kJ mol1). However, two large barriers (TS5/6 and TS2/13 in Figure 4 c and Figure 5, respectively) are involved in the formation of CeV2O5 + /HAc and CeV2O6CH2 + /CH2O, suggesting that DOAT and C=C bond cleavage channels are kinetically unfavorable. This is not consistent with the experimental observations. Attempts to locate a lower TS in the PES of the DOAT channel were unsuccessful. For instance, decreasing the distance between H1 and O1 in 2 to form the OH unit with the presence of CH3 moiety, and decreasing the distances between H1 and C2 as well as C1 and O1 in 5 at the same time by using the multi-coordinate driven method did not reveal a lower TS.[33] Note that IS2 in Figure 3 is only 15 kJ mol1 higher in energy than IS1, and it is probable that IS2 can be populated in the cluster source. Pathways originating from IS2 may explain the remaining reactions. 2.5. The Oxidation States of Ce and V Atoms in the Reactions Cerium oxide is well known for the ability to store, release, and transport oxygen ions,[34] and many investigations employing experimental and theoretical methods have focused on the oxidation states of vanadium and cerium atoms in cerium–vanadium oxide catalysts.[35] In this context, the oxidation states of Ce and V atoms in the cluster reactions are very instructive, and it is convenient to monitor the oxidation states in reactions through the analysis of SD distributions of intermediates and products located on the PESs. The oxidation states of Ce and V atoms in CeV2O7 + are + 4 and + 5, respectively. It was therefore important to establish the oxidation states of the metal atoms when this fully oxidized cluster was reduced. The SD distributions of intermediates 2 and 3 and TS2/3 in the SOAT reaction were investigated, as shown in Figure 4 b. Concomitant with the formation of in 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemphyschem.org termediate 2, the SD is located on the 4 f orbital of Ce atom, and the oxidation state of the Ce atom is reduced to + 3. Both TS2/3 and 3 also contain trivalent cerium atoms. In contrast, the SDs of the analogous intermediates involved in the reaction of V3O8 toward C2H4 are localized on the vanadium atom, as depicted in Figure 4 b, throughout the whole reaction.[22e] Normally, Ce + 3/V + 5 has higher stability than Ce + 4/V + 4,[21] and Jiang et al.[21] pointed out that CeV2O6 + with Ce + 3/V + 5 is lower in energy by 113 kJ mol1 than the isomer with Ce + 4/V + 4. Our results suggest that, compared with the vanadium atom, the cerium atom is more able to accommodate electrons in the localized 4 f orbital.

3. Conclusions The gas-phase reaction of CeV2O7 + cluster toward C2H4 were investigated by mass spectrometry in conjunction with density functional theory calculations. Three types of reactions were observed: single oxygen-atom transfer, double oxygen-atom transfer, and C=C bond cleavage, with first type of reaction predominating as the main reaction channel. The active site of CeV2O7 + cluster was computationally predicted to involve two terminal oxygen atoms carrying the spin density of the cluster. To our knowledge, the CeV2O7 + cluster is the first bimetallic oxide cluster ion to be shown to bring about the rupture of the C=C bond in small alkenes. Neither CexOy  nor VxOy  alone possess the necessary topological and electronic properties to bring about this reaction. The cerium atom shows the ability to easily accommodate electrons in localized 4 f orbital as compared to vanadium atoms in the reaction.

Experimental Section Details of the experimental setup can be found in the previous studies,[36, 37] and only a brief outline of the experiments is given here. The cerium–vanadium oxide clusters were generated by pulsed laser ablation of a rotating and translating disk in the presence of approximately 0.1 % O2 seeded in a He carrier gas (99.999 %) with a backing pressure of 5 atm. To obtain CeV2O7 + with stable and intense signal, several targets with different molar ratios of cerium and vanadium powders were investigated; disks with a Ce/V molar ratio of 1:10 were found to be the most appropriate for studying the reaction of CeV2O7 + with C2H4. A 532 nm (second harmonic of Nd3 + : yttrium aluminum garnet-YAG) laser with an energy of 5–8 mJ pulse1 and a repetition rate of 10 Hz was used. The CeV2O7 + cluster ions were mass-selected by a QMF and channeled into a LIT reactor, where they were thermalized by collisions with a pulse of He gas and then interacted with a pulse of C2H4 for a set time. Assessment of thermalization for the cluster ions in the LIT reactor can be found in the previous studies.[36] The cluster ions ejected from the LIT were detected by a reflectron TOF-MS.[24] The pseudo-first-order rate constant (k1) of the reaction between CeV2O7 + and reactant molecules can be estimated by using Equation (4): ln

IR P ¼ k1 effective tR IT kT

ð4Þ

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in which IR is the signal intensity of the reactant cluster ions (CeV2O7 + ) after the reaction and IT is the total ion intensity including product ion contribution (note that the ion intensity of CeV2O7H + is excluded in IT), Peffective is the effective gas pressure in the trap, k is the Boltzmann constant, T is the temperature of the reactor (298 K), and tR is the reaction time.[36a] The CID experiments were performed in a separated apparatus[36a] of which the resolution has been improved from the one of a previous tandem TOF/TOF-MS.[37a] The setup of the cluster source in the LIT and CID experiments was the same. The clusters of interest (CeV2O7 + and V4O11 + ) were passed through two identical reflectors with a Z-shaped configuration (primary TOF-MS), then they were selected by a mass gate. The selected cluster ions interacted with a crossed gas beam (He or Ar) and the daughter (fragment) and parent ions were passed through a third reflector (secondary TOFMS), then they were detected by a dual micro-channel plate detector. The center-of-mass kinetic energy in the collision can be calculated as Ec = U  m/M, in which U is the average potential applied to the electrodes for accelerating ions in the primary TOF-MS, M is the mass of the cluster, and m is the reduced mass of the cluster with He or Ar atom. All of the DFT calculations were performed with the Gaussian 03 program package[38] employing the hybrid B3LYP exchange-correlation functional.[39] TZVP basis sets[40] were selected for V, C, O, H atoms, and the D95V basis set combined with Stuttgart/Dresden relativistic effective core potential[41] (denoted as SDD in Gaussian 03) was selected for Ce. The same functional and basis sets have been successfully adopted for many reaction systems involving vanadium oxide and cerium oxide clusters.[9d,i, 29a, 31, 42] Geometry optimizations of all reaction intermediates and TSs on the potential energy surfaces were performed with full relaxation of all atoms. Vibrational frequency calculations were performed to check that the reaction intermediates and transition state (TS) species had zero and one imaginary frequency, respectively. Intrinsic reactioncoordinate (IRC) calculations[43] were also performed to connect the TS with local minima. The zero-point vibration corrected energies (DH0 K) are reported in this work. Both doublet and quartet states were tested for the intermediates and TSs, and in most cases the doublet was found to be more stable than the quartet. When spin conversion from doublets to quartets was observed, the spin states of the intermediates and TSs are given. TS5/6 and TS14/15 shown in Figures 4 c and 5, respectively, are structures with broken symmetry states. Unrestricted Kohn–Sham calculations were performed within the broken symmetry approach[44] as an approximation for the multireference treatment. The projected low-spin energy, E(d), was calculated by using Equation (5):[45] 1 E ðdÞ  E ðbsÞ þ ½E ðbsÞ  E ðqÞ 2

ð5Þ

in which E(bs) and E(q) are the energies of broken symmetry states and quartet, respectively.

Acknowledgements This work was supported by the Beijing Natural Science Foundation (Grant No. 2144055), the Basic Research Fund of Beijing Institute of Technology (Grant No. 20121942012), the National Natural Science Foundation of China (Grant No. 21173233), and the Institute of Chemistry, Chinese Academy of Sciences. We thank Professor X.-L. Ding, Dr. M. Schlangen, and Dr. N. Dietl for insight 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ful discussions and are indebted to Professor H. Schwarz for reading and improving the original manuscript. Keywords: cluster compounds · density functional calculations · gas-phase reactions · mass spectrometry · reaction mechanisms [1] a) J. L. G. Fierro, Metal Oxides Chemistry and Applications, CRC, London, 2006; b) G. Ertl, H. Knozinger, J. Weikamp, Handbook of Heterogeneous Catalysis, Wiley-VCH, New York, 1997. [2] E. W. McFarland, H. Metiu, Chem. Rev. 2013, 113, 4391 – 4427. [3] a) J. L. F. Da Silva, M. V. Ganduglia-Pirovano, J. Sauer, Phys. Rev. B 2007, 76, 125117; b) C. A. Chagas, L. C. Dieguez, M. Schmal, Catal. Lett. 2012, 142, 753 – 762; c) W. C. Vining, J. Strunk, A. T. Bell, J. Catal. 2012, 285, 160 – 167; d) A. Mouammine, S. Ojala, L. Pirault-Roy, M. Bensitel, R. Keiski, R. Brahmi, Top. Catal. 2013, 56, 650 – 657. [4] a) W. Daniell, A. Ponchel, S. Kuba, F. Anderle, T. Weingand, D. H. Gregory, H. Knozinger, Top. Catal. 2002, 20, 65 – 74; b) B. M. Weckhuysen, D. E. Keller, Catal. Today 2003, 78, 25 – 46; c) I. E. Wachs, Catal. Today 2005, 100, 79 – 94; d) A. Dinse, B. Frank, C. Hess, D. Habel, R. Schomacker, J. Mol. Catal. A 2008, 289, 28 – 37. [5] M. Che, A. J. Tench, Adv. Catal. 1983, 32, 1 – 148. [6] a) J. H. Lunsford, Catal. Rev. Sci. Eng. 1974, 8, 135 – 157; b) H. F. Liu, R. S. Liu, K. Y. Liew, R. E. Johnson, J. H. Lunsford, J. Am. Chem. Soc. 1984, 106, 4117 – 4121; c) M. S. Palmer, M. Neurock, M. M. Olken, J. Am. Chem. Soc. 2002, 124, 8452 – 8461; d) Q. Fu, H. Saltsburg, M. Flytzani-Stephanopoulos, Science 2003, 301, 935 – 938; e) J. Guzman, S. Carrettin, A. Corma, J. Am. Chem. Soc. 2005, 127, 3286 – 3287; f) H. Launay, S. Loridant, D. L. Nguyen, A. M. Volodin, J. L. Dubois, J. M. M. Millet, Catal. Today 2007, 128, 176 – 182. [7] a) D. K. Bçhme, H. Schwarz, Angew. Chem. 2005, 117, 2388 – 2406; Angew. Chem. Int. Ed. 2005, 44, 2336 – 2354; b) G. E. Johnson, R. Mitric´, V. Bonacˇic´-Koutecky´, A. W. Castleman, Jr., Chem. Phys. Lett. 2009, 475, 1 – 9; c) J. Roithov, D. Schrçder, Chem. Rev. 2010, 110, 1170 – 1211; d) H. Schwarz, Angew. Chem. 2011, 123, 10276 – 10297; Angew. Chem. Int. Ed. 2011, 50, 10096 – 10115; e) Y. X. Zhao, X. N. Wu, J. B. Ma, S. G. He, X. L. Ding, Phys. Chem. Chem. Phys. 2011, 13, 1925 – 1938; f) X.-L. Ding, X.-N. Wu, Y.-X. Zhao, S.-G. He, Acc. Chem. Res. 2012, 45, 382 – 390; g) N. Dietl, M. Schlangen, H. Schwarz, Angew. Chem. 2012, 124, 5638 – 5650; Angew. Chem. Int. Ed. 2012, 51, 5544 – 5555; h) S. Yin, E. R. Bernstein, Int. J. Mass Spectrom. 2012, 321 – 322, 49 – 65; i) Q.-Y. Liu, S.-G. He, Chem. J. Chinese U. 2014, 35, 665 – 688. [8] a) J. H. Lunsford, Catal. Today 2000, 63, 165 – 174; b) A. A. Fokin, P. R. Schreiner, Adv. Synth. Catal. 2003, 345, 1035 – 1052; c) M. Lersch, M. Tilset, Chem. Rev. 2005, 105, 2471 – 2526. [9] a) D. Schrçder, A. Fiedler, J. Hrusˇk, H. Schwarz, J. Am. Chem. Soc. 1992, 114, 1215 – 1222; b) I. Kretzschmar, A. Fiedler, J. N. Harvey, D. Schrçder, H. Schwarz, J. Phys. Chem. A 1997, 101, 6252 – 6264; c) D. Schrçder, J. Roithov, Angew. Chem. 2006, 118, 5835 – 5838; Angew. Chem. Int. Ed. 2006, 45, 5705 – 5708; d) S. Feyel, J. Dobler, D. Schrçder, J. Sauer, H. Schwarz, Angew. Chem. 2006, 118, 4797 – 4801; Angew. Chem. Int. Ed. 2006, 45, 4681 – 4685; e) S. Feyel, J. Dçbler, R. Hçckendorf, M. K. Beyer, J. Sauer, H. Schwarz, Angew. Chem. 2008, 120, 1972 – 1976; Angew. Chem. Int. Ed. 2008, 47, 1946 – 1950; f) N. Dietl, M. Engeser, H. Schwarz, Angew. Chem. 2009, 121, 4955 – 4957; Angew. Chem. Int. Ed. 2009, 48, 4861 – 4863; g) G. de Petris, A. Troiani, M. Rosi, G. Angelini, O. Ursini, Chem. Eur. J. 2009, 15, 4248 – 4252; h) Y. X. Zhao, X. N. Wu, Z. C. Wang, S. G. He, X. L. Ding, Chem. Commun. 2010, 46, 1736 – 1738; i) X.-N. Wu, Y.-X. Zhao, W. Xue, Z.-C. Wang, S.-G. He, X.-L. Ding, Phys. Chem. Chem. Phys. 2010, 12, 3984 – 3997; j) Z.-C. Wang, T. Weiske, R. Kretschmer, M. Schlangen, M. Kaupp, H. Schwarz, J. Am. Chem. Soc. 2011, 133, 16930 – 16937; k) J. H. Meng, Y. X. Zhao, S. G. He, J. Phys. Chem. C 2013, 117, 17548 – 17556. [10] J.-B. Ma, B. Xu, J.-H. Meng, X.-N. Wu, X.-L. Ding, S.-G. He, J. Am. Chem. Soc. 2013, 135, 2991 – 2998. [11] a) J.-B. Ma, X.-N. Wu, Y.-X. Zhao, X.-L. Ding, S.-G. He, Phys. Chem. Chem. Phys. 2010, 12, 12223 – 12228; b) N. Dietl, R. F. Hçckendorf, M. Schlangen, M. Lerch, M. K. Beyer, H. Schwarz, Angew. Chem. 2011, 123, 1466 – 1470; Angew. Chem. Int. Ed. 2011, 50, 1430 – 1434; c) N. Dietl, X. H.

ChemPhysChem 0000, 00, 1 – 10

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These are not the final page numbers! ÞÞ

CHEMPHYSCHEM ARTICLES

[12] [13]

[14]

[15] [16] [17] [18] [19] [20]

[21] [22]

[23]

[24] [25] [26] [27] [28]

[29]

[30]

[31]

Zhang, C. van der Linde, M. K. Beyer, M. Schlangen, H. Schwarz, Chem. Eur. J. 2013, 19, 3017 – 3028. N. Dietl, T. Wende, K. Chen, L. Jiang, M. Schlangen, X. Zhang, K. R. Asmis, H. Schwarz, J. Am. Chem. Soc. 2013, 135, 3711 – 3721. a) Z.-C. Wang, X.-N. Wu, Y.-X. Zhao, J.-B. Ma, X.-L. Ding, S.-G. He, Chem. Phys. Lett. 2010, 489, 25 – 29; b) Z.-C. Wang, N. Dietl, R. Kretschmer, T. Weiske, M. Schlangen, H. Schwarz, Angew. Chem. 2011, 123, 12559 – 12562; Angew. Chem. Int. Ed. 2011, 50, 12351 – 12354; c) Z.-C. Wang, X.N. Wu, Y.-X. Zhao, J.-B. Ma, X.-L. Ding, S.-G. He, Chem. Eur. J. 2011, 17, 3449 – 3457. a) J.-B. Ma, Z.-C. Wang, M. Schlangen, S.-G. He, H. Schwarz, Angew. Chem. 2012, 124, 6093 – 6096; Angew. Chem. Int. Ed. 2012, 51, 5991 – 5994; b) J.-B. Ma, Z.-C. Wang, M. Schlangen, S.-G. He, H. Schwarz, Angew. Chem. 2013, 125, 1264 – 1268; Angew. Chem. Int. Ed. 2013, 52, 1226 – 1230. X.-N. Wu, X.-N. Li, X.-L. Ding, S.-G. He, Angew. Chem. 2013, 125, 2504 – 2508; Angew. Chem. Int. Ed. 2013, 52, 2444 – 2448. Z.-C. Wang, J.-W. Liu, M. Schlangen, T. Weiske, D. Schrçder, J. Sauer, H. Schwarz, Chem. Eur. J. 2013, 19, 11496 – 11501. X.-N. Li, Z. Yuan, S.-G. He, J. Am. Chem. Soc. 2014, 136, 3617 – 3623. Z.-C. Wang, S. Yin, E. R. Bernstein, J. Phys. Chem. Lett. 2012, 3, 2415 – 2419. Z.-C. Wang, S. Yin, E. R. Bernstein, J. Chem. Phys. 2013, 139, 194313. a) Y.-X. Zhao, X.-N. Wu, J.-B. Ma, S.-G. He, X.-L. Ding, J. Phys. Chem. C 2010, 114, 12271 – 12279; b) X.-L. Ding, Y.-X. Zhao, X.-N. Wu, Z.-C. Wang, J.-B. Ma, S.-G. He, Chem. Eur. J. 2010, 16, 11463 – 11470; c) Z.-Y. Li, Y.-X. Zhao, X.-N. Wu, X.-L. Ding, S.-G. He, Chem. Eur. J. 2011, 17, 11728 – 11733; d) X.-N. Li, X.-N. Wu, X.-L. Ding, B. Xu, S.-G. He, Chem. Eur. J. 2012, 18, 10998 – 11006; e) Z. Yuan, X.-N. Li, S.-G. He, J. Phys. Chem. Lett. 2014, 5, 1585 – 1590. L. Jiang, T. Wende, P. Claes, S. Bhattacharyya, M. Sierka, G. Meijer, P. Lievens, J. Sauer, K. R. Asmis, J. Phys. Chem. A 2011, 115, 11187 – 11192. a) A. E. Stevens, J. L. Beauchamp, J. Am. Chem. Soc. 1979, 101, 6449 – 6450; b) H. Kang, J. L. Beauchamp, J. Am. Chem. Soc. 1986, 108, 5663 – 5668; c) K. A. Zemski, D. R. Justes, A. W. Castleman, J. Phys. Chem. A 2001, 105, 10237 – 10245; d) F. Dong, S. Heinbuch, Y. Xie, J. J. Rocca, E. R. Bernstein, Z. C. Wang, K. Deng, S. G. He, J. Am. Chem. Soc. 2008, 130, 1932 – 1943; e) Y. P. Ma, X. L. Ding, Y. X. Zhao, S. G. He, ChemPhysChem 2010, 11, 1718 – 1725; f) J.-B. Ma, X.-N. Wu, Y.-X. Zhao, S.-G. He, X.L. Ding, Acta Phys.-Chim. Sin. 2010, 26, 1761 – 1767; g) Z. Yuan, Y.-X. Zhao, X.-N. Lia, S.-G. He, Int. J. Mass Spectrom. 2013, 354 – 355, 105 – 112. a) Y.-X. Zhao, X.-L. Ding, Y.-P. Ma, Z.-C. Wang, S.-G. He, Theor. Chem. Acc. 2010, 127, 449 – 465; b) Y.-P. Ma, Y.-X. Zhao, Z.-Y. Li, X.-L. Ding, S.-G. He, Chin. J. Chem. Phys. 2011, 24, 586 – 596. X.-N. Wu, B. Xu, J.-H. Meng, S.-G. He, Int. J. Mass Spectrom. 2012, 310, 57 – 64. G. Kummerlçwe, M. K. Beyer, Int. J. Mass Spectrom. 2005, 244, 84 – 90. W. Koch, M. C. Holthausen, A Chemist’s Guide to Density Functional Theory, Wiley-VCH, Weinheim, 2000. G. E. Johnson, R. Mitric´, E. C. Tyo, V. Bonacˇic´-Koutecky´, A. W. Castleman, Jr., J. Am. Chem. Soc. 2008, 130, 13912 – 13920. a) E. R. Fisher, P. B. Armentrout, J. Am. Chem. Soc. 1992, 114, 2039 – 2049; b) D. Schrçder, S. Shaik, H. Schwarz, Acc. Chem. Res. 2000, 33, 139 – 145; c) S. P. de Visser, F. Ogliaro, N. Harris, S. Shaik, J. Am. Chem. Soc. 2001, 123, 3037 – 3047; d) M. D. Michelini, N. Russo, E. Sicilia, J. Am. Chem. Soc. 2007, 129, 4229 – 4239. a) F. Dong, S. Heinbuch, Y. Xie, E. R. Bernstein, J. J. Rocca, Z. C. Wang, X. L. Ding, S. G. He, J. Am. Chem. Soc. 2009, 131, 1057 – 1066; b) Z. C. Wang, W. Xue, Y. P. Ma, X. L. Ding, S. G. He, F. Dong, S. Heinbuch, J. J. Rocca, E. R. Bernstein, J. Phys. Chem. A 2008, 112, 5984 – 5993. a) S. Li, A. Mirabal, J. Demuth, L. Wçste, T. Siebert, J. Am. Chem. Soc. 2008, 130, 16832 – 16833; b) H. B. Li, S. X. Tian, J. L. Yang, Chem. Eur. J. 2009, 15, 10747 – 10751. D. R. Justes, R. Mitric´, N. A. Moore, V. Bonacˇic´-Koutecky´, A. W. Castleman, Jr., J. Am. Chem. Soc. 2003, 125, 6289 – 6299.

 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemphyschem.org [32] a) D. R. Justes, A. W. Castleman, Jr., R. Mitric, V. Bonacˇic´-Koutecky´, Eur. Phys. J. D 2003, 24, 331 – 334; b) S. Feyel, D. Schrçder, X. Rozanska, J. Sauer, H. Schwarz, Angew. Chem. 2006, 118, 4793 – 4797; Angew. Chem. Int. Ed. 2006, 45, 4677 – 4681; c) H. B. Li, S. X. Tian, J. L. Yang, J. Phys. Chem. A 2010, 114, 6542 – 6549. [33] I. Berente, G. Naray-Szabo, J. Phys. Chem. A 2006, 110, 772 – 778. [34] A. Trovarelli, Catalysis by Ceria and Related Materials, Vol. 2, Imperial College Press, London, 2002. [35] a) M. Baron, H. Abbott, O. Bondarchuk, D. Stacchiola, A. Uhl, S. Shaikhutdinov, H. J. Freund, C. Popa, M. V. Ganduglia-Pirovano, J. Sauer, Angew. Chem. 2009, 121, 8150 – 8153; Angew. Chem. Int. Ed. 2009, 48, 8006 – 8009; b) M. V. Ganduglia-Pirovano, C. Popa, J. Sauer, H. Abbott, A. Uhl, M. Baron, D. Stacchiola, O. Bondarchuk, S. Shaikhutdinov, H. J. Freund, J. Am. Chem. Soc. 2010, 132, 2345 – 2349. [36] a) Z. Yuan, Z.-Y. Li, Z.-X. Zhou, Q.-Y. Liu, Y.-X. Zhao, S.-G. He, J. Phys. Chem. C 2014, 118, 14967 – 14976; b) Y.-X. Zhao, Z.-Y. Li, Z. Yuan, X.-N. Li, S.-G. He, Angew. Chem. 2014, DOI: 10.1002/ange.201403953; Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201403953. [37] a) X.-N. Wu, J.-B. Ma, B. Xu, X.-L. Ding, S.-G. He, J. Phys. Chem. A 2011, 115, 5238 – 5246; b) B. Xu, J.-H. Meng, S.-G. He, J. Phys. Chem. C, 2014, 118, 18488 – 18495. [38] Gaussian 03 (Revision E.01), G. W. T. M. J. Frisch, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc., Wallingford CT, 2004. [39] a) C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785 – 789; b) A. D. Becke, Phys. Rev. A 1988, 38, 3098 – 3100; c) A. D. Becke, J. Chem. Phys. 1993, 98, 5648 – 5652. [40] A. Schfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 1994, 100, 5829 – 5835. [41] D. Andrae, U. Hußermann, M. Dolg, H. Stoll, H. Preuß, Theor. Chim. Acta 1990, 77, 123 – 141. [42] a) X.-N. Wu, X.-L. Ding, S.-M. Bai, B. Xu, S.-G. He, Q. Shi, J. Phys. Chem. C 2011, 115, 13329 – 13337; b) X. L. Ding, X. N. Wu, Y. X. Zhao, J. B. Ma, S. G. He, ChemPhysChem 2011, 12, 2110 – 2117; c) K. R. Asmis, T. Wende, M. Brummer, O. Gause, G. Santambrogio, E. C. Stanca-Kaposta, J. Dobler, A. Niedziela, J. Sauer, Phys. Chem. Chem. Phys. 2012, 14, 9377 – 9388; d) J.-B. Ma, Y.-X. Zhao, S.-G. He, X.-L. Ding, J. Phys. Chem. A 2012, 116, 2049 – 2054; e) B. L. Harris, T. Waters, G. N. Khairallah, R. A. J. O’Hair, J. Phys. Chem. A 2013, 117, 1124 – 1135. [43] a) K. Fukui, J. Phys. Chem. 1970, 74, 4161; b) K. Fukui, Acc. Chem. Res. 1981, 14, 363 – 368; c) C. Gonzalez, H. B. Schlegel, J. Chem. Phys. 1989, 90, 2154 – 2161; d) D. G. Truhlar, M. S. Gordon, Science 1990, 249, 491 – 498; e) C. Gonzalez, H. B. Schlegel, J. Phys. Chem. 1990, 94, 5523 – 5527. [44] a) L. Noodleman, J. Chem. Phys. 1981, 74, 5737 – 5743; b) K. Yamaguchi, F. Jensen, A. Dorigo, K. N. Houk, Chem. Phys. Lett. 1988, 149, 537 – 542; c) R. Caballol, O. Castell, F. Illas, P. R. Moreira, J. P. Malrieu, J. Phys. Chem. A 1997, 101, 7860 – 7866. [45] M. Pykavy, C. van Wullen, J. Sauer, J. Chem. Phys. 2004, 120, 4207 – 4215.

Received: May 18, 2014 Revised: June 20, 2014 Published online on && &&, 2014

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ARTICLES J.-B. Ma,* Z. Yuan, J.-H. Meng, Q.-Y. Liu, S.-G. He* && – && Gas-Phase Reaction of CeV2O7 + with C2H4 : Activation of CC and CH Bonds

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Working together: In the reaction of the CeV2O7 + cluster with C2H4, three types of reaction channels are identified. The observation of a C=C bond cleavage product renders CeV2O7 + the first such species to bring about such a reaction.

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Gas-phase reaction of CeV2O7+ with C2H4: activation of C-C and C-H bonds.

The reactivity of metal oxide clusters toward hydrocarbon molecules can be changed, tuned, or controlled by doping. Cerium-doped vanadium cluster cati...
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