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1.
J Phys Chem Lett ; 10(24): 7850-7855, 2019 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-31790248

RESUMO

Fundamental understanding regarding oxygen storage capacity involving how and why an active site can buffer a large number of oxygen atoms in redox processes is vital to the design of advanced oxygen storage materials, while it is challenging because of the complexity of heterogeneous catalysis. Herein, we identified that an eight-atom iridium-aluminum oxide cluster IrAlO6+ can transfer all the oxygen atoms to catalytically oxidize six CO molecules. This finding represents a breakthrough in cluster catalysis where at most three oxygen atoms from a heteronuclear metal oxide cluster can be catalytically involved in CO oxidation. We found that oxygen prefers to be stored on aluminum to form an O3-• radical in the energetically unfavorable IrAlO6+ isomer and generate the low-coordinated iridium that is pivotal to capturing CO and triggering the catalysis. The powerful electron cycling capability of iridium and the cooperative iridium-aluminum interplay are emphasized to drive the oxygen atom-transfer behavior.

2.
Respir Med Case Rep ; 28: 100948, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31720203

RESUMO

Objective: This case report shows that bronchoscopy is an important method to treat severe airway stenosis caused by bronchial amyloidosis. Bronchoscopic forceps were used to incise the intra-tracheal lump repeatedly. The incision was frozen with a cryosurgery probe, argon knife was used to stop the bleeding until the airway lumen stenosis was reduced to approximately 40%, after which, it continued to enter the lumen. We used bronchoscopic biopsy forceps to repeatedly clamp the lumps in the tracheal carina and left and right main bronchial tumors until the lumen was completely unobstructed. Results: The symptoms of severe dyspnea and wheezing were significantly improved after two interventions with the bronchoscope.

3.
Anal Chem ; 91(20): 12688-12695, 2019 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-31538775

RESUMO

Glyoxal (GLY) acts as a key contributor to tropospheric ozone production and secondary organic aerosol (SOA) formation on local to regional scales. The detection of GLY provides useful indicators of fast photochemistry occurring in the lower troposphere. The fast and sensitive detection of GLY is thus important, while traditional chemical ionization such as the proton-transfer reaction (PTR) is extremely limited by the poor detection limit and extensive fragmentation. To address these limitations, electron attachment reaction (EAR) ionization was applied to detect GLY. The generation of parent anions (GLY-) without fragmentation was observed, and cryogenic photoelectron imaging spectroscopy further characterized the structure of GLY-. The detection limit was estimated to be as low as (52 ± 1) pptv (parts per trillion by volume) with 1 min measurements. Other components in ambient air, such as water, carbon dioxide, and trace gases (acetone, propanal, etc.) have no effect on the detection of GLY. The EAR ionization is more promising than PTR ionization in detecting GLY. The detection of GLY in ambient air by the EAR ionization has been demonstrated.

4.
Angew Chem Int Ed Engl ; 58(48): 17287-17292, 2019 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-31553114

RESUMO

Direct conversion of methane with carbon dioxide to value-added chemicals is attractive but extremely challenging because of the thermodynamic stability and kinetic inertness of both molecules. Herein, the first dinuclear cluster species, RhVO3 - , has been designed to mediate the co-conversion of CH4 and CO2 to oxygenated products, CH3 OH and CH2 O, in the temperature range of 393-600 K. The resulting cluster ions RhVO3 CO- after CH3 OH formation can further desorb the [CO] unit to regenerate the RhVO3 - cluster, leading to the successful establishment of a catalytic cycle for methanol production from CH4 and CO2 (CH4 +CO2 →CH3 OH+CO). The exceptional activity of Rh-V dinuclear oxide cluster (RhVO3 - ) identified herein provides a new mechanism for co-conversion of two very stable molecules CH4 and CO2 .

5.
J Am Chem Soc ; 141(5): 2027-2034, 2019 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-30595020

RESUMO

Oxide supported gold catalysts (e.g., Au/TiO2) are of great significance in heterogeneous catalysis owing to their extraordinary catalytic activity. Study of heteronuclear metal oxide clusters (HMOCs, e.g., Au xTi yO z q) is an important way to uncover the molecular-level mechanisms of gold catalysis in the related heterogeneous catalytic systems. However, the current studies of HMOCs are focused on charged clusters with little attention paid to neutral species. The reactivity study of neutral HMOCs is vital to have a comprehensive understanding of heterogeneous catalysis, but it is experimentally challenging because of the difficulty of cluster ionization and detection without fragmentation. Herein, benefiting from a homemade time-of-flight mass spectrometer coupled with a vacuum ultraviolet laser system, the reactivity of neutral Au1-doped titanium oxide clusters AuTi2O3-6 in catalytic CO oxidation by O2 has been successfully identified. The mechanistic details of the catalysis have been elucidated by quantum chemistry calculations. The crucial roles of the mobile AuCO species that can facilitate not only the process of CO oxidation but also the process of O2 activation have been discovered in the cluster catalysis. The fascinating results are of substantial importance to understand the mechanisms of CO oxidation over Au/TiO2, one type of the best studied gold catalysts.

6.
Anal Chem ; 90(22): 13467-13474, 2018 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-30347147

RESUMO

Methylglyoxal (MGLY) plays a significant role in atmospheric chemistry by serving as a key contributor to the formation of active free radicals, ozone, and secondary organic aerosol. Detection of MGLY by traditional chemical ionization such as proton-transfer reaction has several shortcomings such as parent molecule fragmentation. In this study, an electron attachment reaction (EAR) ionization method has been developed for the effective detection of MGLY. Almost no fragmentation was observed during the EAR. The generation of MGLY- anion in the EAR was further confirmed by cryogenic photoelectron imaging spectroscopy. The concentration of MGLY can be calibrated by using dibromomethane (CH2Br2) as reference gas. The detection sensitivity of MGLY was estimated to be (100 ± 2) mV/ppbv (parts per billion by volume). The O2, H2O, CO2, and trace gases in ambient air have no obvious effects on the detection of MGLY- anion by the EAR ionization method.

7.
Chemistry ; 24(66): 17506-17512, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30191620

RESUMO

Cationic gold has been frequently identified as a suitable reactive species for activating methane in condensed-phase studies. However, it is far from clear how the coordination site manipulates the activity of such species. Herein, by anchoring AuI on silicon oxide cluster supports of variable sizes, the site-specific methane activation by AuI -Ox has been clarified by mass spectrometry in conjunction with quantum chemistry calculations. An unexpected mechanistic switch in C-H activation was identified for the cluster anions Au(SiO2 )n O- (n=1-3) that selectively activate one of the four C-H bonds of methane with different reaction efficiencies: a low efficiency was observed for the two-fold-coordinated gold ion (AuI, 2f ), which was anchored on an AuSiO3 - or AuSi2 O5 - cluster, through an oxidative addition mechanism (a homolytic process), and high efficiency was observed for the one-fold-coordinated gold ion (AuI, 1f ), which was supported on an AuSi3 O7 - cluster, through Lewis acid/base pairs mechanism (AuI, 1f ⋅⋅⋅O2- , a heterolytic process). Fine regulation of the 5d orbital level of the Au atom by the oxygen ligands accounted for the mechanistic difference between AuI, 2f and AuI, 1f species. The mechanistic understanding of the reactivity of AuI -Ox at a strictly molecular level can be used to clarify the dissimilar activity of gold anchored on different oxide supports.

8.
Dalton Trans ; 47(41): 14540-14548, 2018 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-30252007

RESUMO

With the depletion of fossil energy and rapid development of electronic equipment, the commercial lithium-ion batteries (LIBs) do not meet the current energy demand. There is an urgent need to develop novel LIBs with high capacity, long life, and low cost. In this work, we design and synthesize a MnCo2O4@NC@MnO2 three-layered core-shell octahedron with good electrochemical performance using binary transition metal oxide (MnCo2O4), N-doped carbon (NC), and high-capacity manganese oxide (MnO2). The three-layered structure is effective in relieving the volume expansion, improving the electronic conductivity, and strengthening the structural stability. The MnCo2O4@NC@MnO2 three-layered core-shell octahedron displays a high discharge capacity of 894 mA h g-1 at a current density of 500 mA g-1 after 120 cycles. Even at a high current density of 1000 mA g-1, the discharge capacity remains at 839 mA h g-1 after 600 cycles. Furthermore, this material possesses pretty good rate performance. All the results show that this ternary composite is a good anode alternative for lithium storage.

9.
Angew Chem Int Ed Engl ; 57(43): 14134-14138, 2018 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-30203446

RESUMO

The use of CH4 and CO2 to produce value-added chemicals via direct C-C coupling is a challenging chemistry problem because of the inertness of these two molecules. Herein, mass spectrometric experiments and high-level quantum-chemical calculations have identified the first diatomic species (CuB+ ) that can couple CH4 with CO2 under thermal collision conditions to produce ketene (H2 C=C=O), an important intermediate in synthetic chemistry. The order to feed the reactants (CH4 and CO2 ) is important and CH4 should be firstly fed to produce the C2 product. Molecular-level mechanisms including control of product selectivity have been revealed for coupling of CH4 with CO2 under mild conditions.

10.
Adv Mater ; 30(28): e1801171, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29782677

RESUMO

The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2 ). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D-MoS2 /Co(OH)2 hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm-2 in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.

11.
R Soc Open Sci ; 5(2): 171988, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29515897

RESUMO

Triphenylphosphine oxide (TPPO) and oxalyl chloride ((COCl)2) are used as novel and high-efficiency coupling reagents for the esterification of alcohols with carboxylic acids via the TPPO/(COCl)2 system at room temperature for 1 h. The reaction represents the first TPPO-promoted esterification under mild and neutral conditions with excellent yields. Furthermore, we proposed a plausible mechanism with the help of 31P NMR spectroscopy.

12.
Angew Chem Int Ed Engl ; 57(10): 2662-2666, 2018 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-29359384

RESUMO

The underlying mechanism for non-oxidative methane aromatization remains controversial owing to the lack of experimental evidence for the formation of the first C-C bond. For the first time, the elementary reaction of methane with atomic clusters (FeC3- ) under high-temperature conditions to produce C-C coupling products has been characterized by mass spectrometry. With the elevation of temperature from 300 K to 610 K, the production of acetylene, the important intermediate proposed in a monofunctional mechanism of methane aromatization, was significantly enhanced, which can be well-rationalized by quantum chemistry calculations. This study narrows the gap between gas-phase and condensed-phase studies on methane conversion and suggests that the monofunctional mechanism probably operates in non-oxidative methane aromatization.

13.
Angew Chem Int Ed Engl ; 57(13): 3349-3353, 2018 03 19.
Artigo em Inglês | MEDLINE | ID: mdl-29377393

RESUMO

Catalytic CO oxidation by molecular O2 is an important model reaction in both the condensed phase and gas-phase studies. Available gas-phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O2 under thermal collision conditions. Herein, we identified the first example of noble-metal-free heteronuclear oxide cluster catalysts, the copper-vanadium bimetallic oxide clusters Cu2 VO3-5- for CO oxidation by O2 . The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu-Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O2 activation during the catalysis.

14.
Phys Chem Chem Phys ; 20(7): 4641-4645, 2018 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-29379936

RESUMO

Investigation on the reactivity of atomic clusters represents an important approach to discover new species to activate and transform methane, the most stable alkane molecule. While a few types of transition metal species have been found to be capable of cleaving the C-H bond of methane, methane activation by the transition metal boride species has not been explored yet. This study reports that vanadium boride cluster cations VBn+ (n = 3-6) can dehydrogenate methane under thermal collision conditions. The mechanistic details of the efficient reactions have been elucidated by quantum chemistry calculations on the VB3+ reaction system. Compared to the non-polar bare B3 cluster, the B3 moiety in VB3+ can be polarized by the V+ cation and thus its reactivity toward methane can be much enhanced. This study provides new insights into the rational design of boron-based catalysts for methane activation.

15.
J Am Soc Mass Spectrom ; 29(1): 78-84, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29080205

RESUMO

A high-temperature linear ion trap reactor with hexapole design was homemade to study ion-molecule reactions at variable temperatures. The highest temperature for the trapped ions is up to 773 K, which is much higher than those in available reports. The reaction between V2O6- cluster anions and CO at different temperatures was investigated to evaluate the performance of this reactor. The apparent activation energy was determined to be 0.10 ± 0.02 eV, which is consistent with the barrier of 0.12 eV calculated by density functional theory. This indicates that the current experimental apparatus is prospective to study ion-molecule reactions at variable temperatures, and more kinetic details can be obtained to have a better understanding of chemical reactions that have overall barriers. Graphical Abstract.

16.
Angew Chem Int Ed Engl ; 56(15): 4187-4191, 2017 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-28240413

RESUMO

The hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO2 and formation of a C-H bond. Herein, we report that HCO2- and CO can be formed in the thermal reaction of CO2 with a diatomic metal hydride species, FeH- . The FeH- anions were produced by laser ablation, and the reaction with CO2 was analyzed by mass spectrometry and quantum-chemical calculations. Gas-phase HCO2- was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO2 hydrogenation in this gas-phase study parallels similar behavior of a condensed-phase iron catalyst.

17.
Chem Asian J ; 11(19): 2730-2734, 2016 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-27017581

RESUMO

A molecular-level insight into the nature of reactive oxygen species involved in dihydrogen (H2 ) dissociation is of great importance to understand gold catalysis. In this study, laser ablation generated and mass-selected AuNbO4+ oxide cluster cations could dissociate H2 in an ion-trap reactor. The reaction has been characterized by time-of-flight mass spectrometric experiments and density functional calculations. The lowest energy isomer of AuNbO4+ contains two lattice oxygen (O2- ) and one superoxide (O2.- ) species. The gold atom anchors the H2 molecule in the first step and then delivers one hydrogen atom to the O2- ion in H2 dissociation. At the same time, O2.- is reduced into a peroxide unit that can accept the second hydrogen atom of H2 with the generation of a hydroxyl radical as the main product. In this study, the important roles of the O2.- unit in the dissociation of H2 have been identified.

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