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Qing‐Yu Liu Dr. Jia‐Bi Ma Dr. Zi‐Yu Li Chongyang Zhao Prof. Dr. Chuan‐Gang Ning Prof. Dr. Hui Chen Prof. Dr. Sheng‐Gui He 《Angewandte Chemie (International ed. in English)》2016,55(19):5760-5764
Atomic clusters are being actively studied for activation of methane, the most stable alkane molecule. While many cluster cations are very reactive with methane, the cluster anions are usually not very reactive, particularly for noble metal free anions. This study reports that the reactivity of molybdenum carbide cluster anions with methane can be much enhanced by adsorption of CO. The Mo2C2? is inert with CH4 while the CO addition product Mo2C3O? brings about dehydrogenation of CH4 under thermal collision conditions. The cluster structures and reactions are characterized by mass spectrometry, photoelectron spectroscopy, and quantum chemistry calculations, which demonstrate that the Mo2C3O? isomer with dissociated CO is reactive but the one with non‐dissociated CO is unreactive. The enhancement of cluster reactivity promoted by CO adsorption in this study is compared with those of reported systems of a few carbonyl complexes. 相似文献
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Methane Activation Mediated by a Series of Cerium–Vanadium Bimetallic Oxide Cluster Cations: Tuning Reactivity by Doping
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The reactions of cerium–vanadium cluster cations CexVyOz+ with CH4 are investigated by time‐of‐flight mass spectrometry and density functional theory calculations. (CeO2)m(V2O5)n+ clusters (m=1,2, n=1–5; m=3, n=1–4) with dimensions up to nanosize can abstract one hydrogen atom from CH4. The theoretical study indicates that there are two types of active species in (CeO2)m(V2O5)n+, V[(Ot)2]. and [(Ob)2CeOt]. (Ot and Ob represent terminal and bridging oxygen atoms, respectively); the former is less reactive than the latter. The experimentally observed size‐dependent reactivities can be rationalized by considering the different active species and mechanisms. Interestingly, the reactivity of the (CeO2)m(V2O5)n+ clusters falls between those of (CeO2)2–4+ and (V2O5)1–5+ in terms of C?H bond activation, thus the nature of the active species and the cluster reactivity can be effectively tuned by doping. 相似文献
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Li‐Na Wang Zi‐Yu Li Qing‐Yu Liu Jing‐Heng Meng Prof. Sheng‐Gui He Prof. Tong‐Mei Ma 《Angewandte Chemie (International ed. in English)》2015,54(40):11720-11724
Investigations on the reactivity of atomic clusters have led to the identification of the elementary steps involved in catalytic CO oxidation, a prototypical reaction in heterogeneous catalysis. The atomic oxygen species O.? and O2? bonded to early‐transition‐metal oxide clusters have been shown to oxidize CO. This study reports that when an Au2 dimer is incorporated within the cluster, the molecular oxygen species O22? bonded to vanadium can be activated to oxidize CO under thermal collision conditions. The gold dimer was doped into Au2VO4? cluster ions which then reacted with CO in an ion‐trap reactor to produce Au2VO3? and then Au2VO2?. The dynamic nature of gold in terms of electron storage and release promotes CO oxidation and O? O bond reduction. The oxidation of CO by atomic clusters in this study parallels similar behavior reported for the oxidation of CO by supported gold catalysts. 相似文献
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The reactions of Pt+ with CH3X (X=F, Cl) are studied experimentally by employing an inductively coupled plasma/selected‐ion flow tube tandem mass spectrometer and theoretically by density functional theory. Dehydrogenation and HX elimination are found to be the primary reaction channels in the remarkably different ratios of 95:5 and 60:40 in the fast reactions of Pt+ with CH3F and CH3Cl, respectively. The observed kinetics are consistent with quantum chemistry calculations, which indicate that both channels in the reaction with CH3F are exothermic with ground‐state Pt+(2D), but that HF elimination is prohibited kinetically because of a transition state that lies above the reactant entrance. The observed HF‐elimination channel is attributed to a slow reaction of CH3F with excited‐state Pt+(4F) for which calculations predict a small barrier. The calculations also show that both the HCl‐elimination and dehydrogenation channels observed with CH3Cl are thermodynamically and kinetically allowed, although the state‐specific product distributions could not be ascertained experimentally. Further CH3F addition is observed with the primary products to produce PtCH2+(CH3F)1,2 and PtCHF+(CH3F)1,2. With CH3Cl, sequential HCl elimination is observed with PtCH2+ to form PtCnH2n+ with n=2, 3, which then add CH3Cl sequentially to form PtC2H4+(CH3Cl)1–3 and PtC3H6+(CH3Cl)1,2. Also, sequential addition is observed for PtCHCl+ to form PtCHCl+(CH3Cl)1,2. 相似文献
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Jing‐Heng Meng Xiao‐Jiao Deng Zi‐Yu Li Prof. Dr. Sheng‐Gui He Prof. Dr. Wei‐Jun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5580-5583
The first example of a metal oxide cluster anion, La6O10? that can activate methane under ambient conditions is reported. This reaction is facilitated by the oxygen‐centered radical (O??) and follows the hydrogen atom transfer mechanism. The La6O10? has a high vertical electron detachment energy (VDE=4.06 eV) and a high symmetry (C4v). 相似文献
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Dr. Jia‐Bi Ma Lin‐Lin Xu Qing‐Yu Liu Prof. Dr. Sheng‐Gui He 《Angewandte Chemie (International ed. in English)》2016,55(16):4947-4951
Investigations of the intrinsic properties of gas‐phase transition metal nitride (TMN) ions represent one approach to gain a fundamental understanding of the active sites of TMN catalysts, the activities and electronic structures of which are known to be comparable to those of noble metal catalysts. Herein, we investigate the structures and reactivities of the triatomic anions HNbN? by means of mass spectrometry and photoelectron imaging spectroscopy, in conjunction with density functional theory calculations. The HNbN? anions are capable of activating CH4 and C2H6 through oxidative addition, exhibiting similar reactivities to free Pt atoms. The similar electronic structures of HNbN? and Pt, especially the active orbitals, are responsible for this resemblance. Compared to the inert NbN?, the coordination of the H atom in HNbN? is indispensable. New insights into how to replace noble metals with TMNs may be derived from this combined experimental/computational study. 相似文献
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We previously reported that thymine molecules can specifically form a pentameric magic number cluster named as thymine quintet in the presence of K+, Rb+ and Cs+. Actually, thymine decamer and doubly charged thymine 15‐mer metaclusters can be observed along with thymine quintet in the ESI mass spectra of thymine with the addition of K+, Rb+ and Cs+. The product ion spectra of these metaclusters, especially the 15‐mer with hetero central ions, indicate that they are higher order assemblies of thymine quintets. The collision‐induced dissociation experiments show that the gas‐phase stabilities of these metaclusters depend on the size of the central ions, following the order Cs+ > Rb+ > K+, while K+ leads to the highest dissociation energy of a thymine quintet. The optimized structures of thymine quintet and decamer were provided by density functional theory calculations, which showed that thymine quintet is bowl‐shaped and its tilting angle increases with the size of the central ion. Furthermore, the chirality of thymine quintet was defined for the first time and the resulting different diastereoisomers of thymine decamers were also revealed by the calculation study. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Timo Fuchs Valentín Briega-Martos Jakub Drnec Natalie Stubb Isaac Martens Federico Calle-Vallejo Prof. David A. Harrington Serhiy Cherevko Prof. Olaf M. Magnussen 《Angewandte Chemie (International ed. in English)》2023,62(34):e202304293
The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO4 by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO2 and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage. 相似文献
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Dr. Xun‐Lei Ding Xiao‐Nan Wu Dr. Yan‐Xia Zhao Jia‐Bi Ma Prof. Sheng‐Gui He 《Chemphyschem》2011,12(11):2110-2117
Cerium oxide cluster cations (CemOn+, m=2–16; n=2m, 2m±1 and 2m±2) are prepared by laser ablation and reacted with acetylene (C2H2) in a fast‐flow reactor. A time‐of‐flight mass spectrometer is used to detect the cluster distribution before and after the reactions. Reactions of stoichiometric CemO2m+ (m=2–6) with C2H2 produce CemO2m?2+ clusters, which indicates a “double‐oxygen‐atom transfer” reaction CemO2m++C2H2→CemO2m?2++(CHO)2 (ethanedial). A single‐oxygen‐atom transfer reaction channel is also identified as CemO2m++C2H2→CemO2m?1++C2H2O (at least for m=2 and 3). Density functional theory calculations are performed to study reaction mechanisms of Ce2O4++C2H2, and the calculated results confirm that both the single‐ and double‐oxygen‐atom transfer channels are thermodynamically and kinetically favourable. 相似文献
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Thermal Ethane Activation by Bare [V2O5]+ and [Nb2O5]+ Cluster Cations: on the Origin of Their Different Reactivities
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Dr. Xiao‐Nan Wu Dr. Shi‐Ya Tang Dr. Hai‐Tao Zhao Dr. Thomas Weiske Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6672-6677
The gas‐phase reactivity of [V2O5]+ and [Nb2O5]+ towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room‐temperature conversions C2H6→C2H5OH or C2H6→CH3CHO are brought about solely by [V2O5]+. In distinct contrast, for the couple [Nb2O5]+/C2H6, one observes only single and double hydrogen‐atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C?H bond activation together with quite different bond‐dissociation energies of the M?O bonds cause the rather varying reactivities of [V2O5]+ and [Nb2O5]+ towards ethane. The gas‐phase generation of acetaldehyde from ethane by bare [V2O5]+ may provide mechanistic insight in the related vanadium‐catalyzed large‐scale process. 相似文献
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