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1.
Chem Commun (Camb) ; 2020 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-31957770

RESUMO

Here we report a new method for controlling photo-deposited metal nanoparticle size by manipulating surface defect structures of TiO2 nanocrystals. Our results demonstrate that the isolated oxygen vacancy could serve as an electron trapper while the oxygen vacancy cluster could act as an electron-hole recombination site in the photo-deposition process.

2.
Chemistry ; 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31696998

RESUMO

Invited for the cover of this issue is Weixin Huang and co-workers at the University of Science and Technology of China. The image depicts the strong influence of electronic metal-support interaction (EMSI) on electronic structures and the catalytic activity of CeOx /Ag inverse catalysts. Read the full text of the article at 10.1002/chem.201904134.

3.
Chemistry ; 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31591759

RESUMO

Electronic metal-support interactions (EMSIs) of oxide-supported metal catalysts strongly modifies the electronic structures of the supported metal nanoparticles. The strong influence of EMSIs on the electronic structures of oxide overlayers on metal nanoparticles employing cerium oxides/Ag inverse catalysts is reported herein. Ce2 O3 overlayers were observed to exclusively form on Ag nanocrystals at low cerium loadings and be resistant to oxidation treatments up to 250 °C, whereas CeO2 overlayers gradually developed as the cerium loading increased. Ag cubes enclosed by {001} facets with a smaller work function exert a stronger EMSI effect on the CeOx overlayers than Ag cubes enclosed by {111} facets. Only the CeO2 overlayers with a fully developed bulk CeO2 electronic structure significantly promote the catalytic activity of Ag nanocrystals in CO oxidation, whereas cerium oxide overlayers with other electronic structures do not. These results successfully extend the concept of EMSIs from oxide-supported metal catalysts to metal-supported oxide catalysts.

4.
Angew Chem Int Ed Engl ; 58(41): 14686-14693, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31403236

RESUMO

The interaction of hydrogen with reduced ceria (CeO2-x ) powders and CeO2-x (111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce3+ species to hydrogen, which results in the formation of Ce4+ , and thus in oxidation of ceria.

5.
Angew Chem Int Ed Engl ; 58(35): 12043-12048, 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31192496

RESUMO

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO2 catalysts with porous Al2 O3 overlayers coated by atomic layer deposition (ALD). 27 Al magic angle spinning NMR analysis showed that Al2 O3 overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al3+ sites capable of strongly interacting with adjacent surface PdOx phases on supported Pd particles. Consequently, Al2 O3 -decorated Pd/SiO2 catalysts exhibit active and stable PdOx and Pd-PdOx structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al2 O3 overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.

6.
Angew Chem Int Ed Engl ; 58(31): 10732-10736, 2019 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-31095821

RESUMO

Ru/TiO2 catalysts exhibit an exceptionally high activity in the selective methanation of CO in CO2 - and H2 -rich reformates, but suffer from continuous deactivation during reaction. This limitation can be overcome through the fabrication of highly active and non-deactivating Ru/TiO2 catalysts by engineering the morphology of the TiO2 support. Using anatase TiO2 nanocrystals with mainly {001}, {100}, or {101} facets exposed, we show that after an initial activation period Ru/TiO2 -{100} and Ru/TiO2 -{101} are very stable, while Ru/TiO2 -{001} deactivates continuously. Employing different operando/in situ spectroscopies and ex situ characterizations, we show that differences in the catalytic stability are related to differences in the metal-support interactions (MSIs). The stronger MSIs on the defect-rich TiO2 -{100} and TiO2 -{101} supports stabilize flat Ru nanoparticles, while on TiO2 -{001} hemispherical particles develop. The former MSIs also lead to electronic modifications of Ru surface atoms, reflected by the stronger bonding of adsorbed CO on those catalysts than on Ru/TiO2 -{001}.

7.
J Am Chem Soc ; 141(11): 4505-4509, 2019 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-30832476

RESUMO

Developing a facile route to access active and well-defined single atom sites catalysts has been a major area of focus for single atoms catalysts (SACs). Herein, we demonstrate a simple approach to generate atomically dispersed platinum via a thermal emitting method using bulk Pt metal as a precursor, significantly simplifying synthesis routes and minimizing synthesis costs. The ammonia produced by pyrolysis of Dicyandiamide can coordinate with platinum atoms by strong coordination effect. Then, the volatile Pt(NH3) x can be anchored onto the surface of defective graphene. The as-prepared Pt SAs/DG exhibits high activity for the electrochemical hydrogen evolution reaction and selective oxidation of various organosilanes. This viable thermal emitting strategy can also be applied to other single metal atoms, for example, gold and palladium. Our findings provide an enabling and versatile platform for facile accessing SACs toward many industrial important reactions.

8.
Angew Chem Int Ed Engl ; 58(13): 4276-4280, 2019 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-30680863

RESUMO

The identification of the contribution of different surface sites to the catalytic activity of a catalyst nanoparticle is one of the most challenging issues in the fundamental studies of heterogeneous catalysis. We herein demonstrate an effective strategy of using a series of uniform cubic Cu2 O nanocrystals with different sizes to identify the intrinsic activity and contributions of face and edge sites in the catalysis of CO oxidation by a combination of reaction kinetics analysis and DFT calculations. Cu2 O nanocrystals undergo in situ surface oxidation forming CuO thin films during CO oxidation. As the average size of the cubic Cu2 O nanocrystals decreases from 1029 nm to 34 nm, the dominant active sites contributing to the catalytic activity switch from face sites to edge sites. These results reveal the interplay between the intrinsic catalytic activity and the density of individual types of surface sites on a catalyst nanoparticle in determining their contributions to the catalytic activity.

9.
Phys Chem Chem Phys ; 21(2): 523-536, 2019 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-30556573

RESUMO

Surface and interface designs are an efficient strategy to fabricate innovative and advanced catalysts. A prerequisite for this is a fundamental understanding of the structure-performance relations of catalyst nanoparticles, which, however, remains a formidable challenge due to the complexity of heterogeneous catalysis. Recent progresses in catalytic nanocrystals with uniform and well-defined structures, in situ characterization techniques, and theoretical calculations have offered opportunities for the fundamental studies of heterogeneous catalysis, and the achieved outputs are turning the innovation of efficient catalysts via surface and interface designs into a reality. Herein, the recent advances in the fundamental-understanding-directed rational surface and interface designs for heterogeneous catalysis, including crystal phase design, morphology/facet design, and size design, are presented. Perspectives are also discussed for the innovation of efficient catalysts via the fundamental-understanding-directed surface and interface designs followed by controlled synthesis.

10.
J Hazard Mater ; 360: 182-192, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30099361

RESUMO

A series of Pt nanoparticles (with size of 3-4 nm) decorated CdS nanorods were prepared via a simple solvothermal method. The samples were then used for photocatalytic selective oxidation (SO) of aromatic alcohols and reduction (SR) of nitroarenes in one reaction system. The platinized samples showed enhanced activity for the conversions than pristine CdS as Pt can serve as e- trapping and reaction sites, by which the recombination of photoinduced charge carriers can be suppressed and the adsorption of reactants and the SR of nitroarenes can be promoted. The sample loaded with only of 0.03% Pt showed the highest performance and, after irradiation for 4 h, the conversions of p-methoxybenzyl alcohol and nitrobenzene are as high as 92.7% and 94.8%, while the yields of p-methoxybenzaldehyde and aniline are 80.5% and 36.0%. The activities are about 2.0 times higher than that of CdS. The coupling reaction mechanism for the SO of aromatic alcohols to aldehydes and SR of nitroarenes to anilines in the reaction system was finally proposed.

11.
Rev Sci Instrum ; 89(6): 064101, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29960580

RESUMO

A pulse chemisorption system combining a Tian-Calvet microcalorimeter (Setaram Sensys EVO 600) and an automated chemisorption apparatus (Micromeritics Autochem II 2920) was established to accurately measure differential adsorption heats of gas molecules' chemisorption on solid surfaces in a flow-pulse mode. Owing to high sensitivity and high degree of automation in a wide range of temperatures from -100 to 600 °C, this coupled system can present adsorption heats as a function of adsorption temperature and adsorbate coverage. The functions of this system were demonstrated by successful measurements of CO adsorption heats on Pd surfaces at various temperatures and also at different CO coverages by varying the CO concentration in the pulse dose. Key parameters, including adsorption amounts, integral adsorption heats, and differential adsorption heats of CO adsorption on a Pd/CeO2 catalyst, were acquired. Our adsorption-microcalorimetry system provides a powerful technique for the investigation of adsorption processes on powder catalysts.

12.
J Phys Chem Lett ; 9(13): 3604-3611, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29902010

RESUMO

We report an investigation of lead halide perovskite CH3NH3PbBr3 nanocrystals and associated ligand molecules by combining several different state-of-the-art experimental techniques, including synchrotron radiation-based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials, we could directly obtain complete band alignment to vacuum of both CH3NH3PbBr3 nanocrystals and the ligands widely used in their preparation. We discuss the possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to those of bulk material. The experimental results were supported by DFT calculations.

13.
ACS Appl Mater Interfaces ; 10(26): 22248-22256, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29900739

RESUMO

Flowerlike NiCo2S4 hollow sub-microspheres are synthesized through Cu2O templates to support Pd nanoparticles as high-efficiency catalysts for the hydrogen evolution reaction (HER). The diameter and shell size of NiCo2S4 hollow sub-microspheres are about 400 and 16 nm, respectively. In addition, the surface of the shells is constructed by petallike nanosheets. About 3 nm Pd particles uniformly incorporate with the flowerlike NiCo2S4 hollow sub-microsphere to form the NiCo2S4/Pd heterostructure. The NiCo2S4/Pd catalysts exhibit significantly lower overpotential of only 87 and 83 mV at 10 mA/cm2 for the HER in both acidic and alkaline conditions, respectively, relative to NiCo2S4 (247, 226 mV) and Pd (175, 385 mV) catalysts. Besides, the NiCo2S4/Pd catalysts also exhibit excellent stability of HER in these two conditions. The superior HER performance of NiCo2S4/Pd might be resulted from the unique architecture of metal nanoparticles anchored on the bimetallic sulfide flowerlike hollow sub-microspheres, which could provide high surface area, lots of active sites, strong synergetic effect, and stable structure.

14.
Nat Commun ; 9(1): 2533, 2018 06 28.
Artigo em Inglês | MEDLINE | ID: mdl-29955067

RESUMO

Transition metal dichalcogenide materials have been explored extensively as catalysts to negotiate the hydrogen evolution reaction, but they often run at a large excess thermodynamic cost. Although activating strategies, such as defects and composition engineering, have led to remarkable activity gains, there remains the requirement for better performance that aims for real device applications. We report here a phosphorus-doping-induced phase transition from cubic to orthorhombic phases in CoSe2. It has been found that the achieved orthorhombic CoSe2 with appropriate phosphorus dopant (8 wt%) needs the lowest overpotential of 104 mV at 10 mA cm-2 in 1 M KOH, with onset potential as small as -31 mV. This catalyst demonstrates negligible activity decay after 20 h of operation. The striking catalysis performance can be attributed to the favorable electronic structure and local coordination environment created by this doping-induced structural phase transition strategy.

15.
Chem Commun (Camb) ; 54(57): 7944-7947, 2018 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-29955750

RESUMO

A facile post-synthesis cation exchange approach has been employed to controllably tune the optical and structural properties of colloidal perovskite nanocrystals (NCs). These optical changes are attributed to the structural transformation of perovskite NCs from three-dimensional (3D) to two-dimensional (2D) layered crystalline forms and vice versa.

16.
Chem Commun (Camb) ; 54(46): 5879-5882, 2018 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-29785421

RESUMO

The optical and structural properties of hybrid perovskites can be tuned by the post-synthetic introduction of new cations. To advance the development of this approach, knowledge of the reaction mechanism is essential, but has not yet been elucidated. Here, the effect of n-octylamine on three-dimensional (3D) methylammonium lead bromide (MAPbBr3) was investigated by in situ X-ray photoelectron spectroscopy. Spectroscopic analysis indicated equimolar substitutions between octylammonium (OcA+) and methylammonium (MA+) cations that cause the formation of two-dimensional (2D) octylammonium lead bromide ((OcA)2PbBr4). The introduction of methylamine reversed these changes, and the cation exchange between MA+ and OcA+ caused the reverse conversion to MAPbBr3.

17.
Nanotoxicology ; 12(6): 571-585, 2018 08.
Artigo em Inglês | MEDLINE | ID: mdl-29732947

RESUMO

Calcium carbonate nanomaterials (nano-CaCO3) are widely used in both manufacturing and consumer products, but their potential health hazards remain unclear. The objective of this study was to survey workplace exposure levels and health effects of workers exposed to nano-CaCO3. Personal and area sampling, as well as real-time and dust monitoring, were performed to characterize mass exposure, particle size distribution, and particle number exposure. A total of 56 workers (28 exposed workers and 28 unexposed controls) were studied in a cross-sectional study. They completed physical examinations, spirometry, and digital radiography. The results showed that the gravimetric nano-CaCO3 concentration was 5.264 ± 6.987 mg/m3 (0.037-22.192 mg/m3) at the workplace, and 3.577 ± 2.065 mg/m3 (2.042-8.161 mg/m3) in the breathing zone of the exposed workers. The particle number concentrations ranged from 8193 to 39 621 particles/cm3 with a size range of 30-150 nm. The process of packing had the highest gravimetric and particle number concentrations. The particle number concentration positively correlated with gravimetric concentrations of nano-CaCO3. The levels of hemoglobin, creatine phosphokinase (CK), lactate dehydrogenase, and high-density lipoprotein cholesterol (HDL-C) in the nano-CaCO3 exposure group increased significantly, but the white blood cell count (WBC), Complement 3 (C3), total protein (TP), uric acid, and creatinine (CREA) all decreased significantly. The prevalence rate of pulmonary hypofunction was significantly higher (p = 0.037), and the levels of vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, peak expiratory flow and forced expiratory flow 25% (FEF 25%), FEF 25-75% were negatively correlated with gravimetric concentrations of nano-CaCO3 (p < 0.05). Logistic analysis showed that nano-CaCO3 exposure level was associated with pulmonary hypofunction (p = 0.005). Meanwhile, a dose-effect relationship was found between the accumulated gravimetric concentrations of nano-CaCO3 and the prevalence rate of pulmonary hypofunction (p = 0.048). In conclusion, long-term and high-level nano-CaCO3 exposure can induce pulmonary hypofunction in workers. Thus, lung function examination is suggested for occupational populations with nano-CaCO3 exposure. Furthermore, future health protection efforts should focus on senior workers with accumulation effects of nano-CaCO3 exposure.


Assuntos
Carbonato de Cálcio/toxicidade , Pulmão/efeitos dos fármacos , Nanoestruturas/toxicidade , Exposição Ocupacional/efeitos adversos , Adulto , Estudos Transversais , Feminino , Humanos , Pulmão/fisiologia , Masculino , Pessoa de Meia-Idade
18.
J Colloid Interface Sci ; 522: 264-271, 2018 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-29604445

RESUMO

Monodisperse hollow mesoporous PdCo alloy nanospheres are prepared via a simple galvanic replacement reaction. The as-prepared PdCo hollow nanospheres have small diameter, such as Pd78Co22 nanospheres of diameter about 25 nm and mesoporous shells about 4-5 nm. The Pd78Co22 hollow mesoporous nanospheres possess the largest electrochemical active surface areas (ECSA, 53.91 m2 g-1), mass activity (1488 mA mg-1) and specific activity (2.76 mA cm-2) towards to methanol oxidation relative to the Pd68Co32, Pd92Co8 hollow mesoporous nanospheres and commercial Pd/C catalysts. Moreover, the activity of Pd78Co22 after long-term stability tests is still the best and even better than those of fresh Pd68Co32 and commercial Pd/C catalysts. The PdCo catalysts not only effectively reduce the Pd usage by forming hollow structure, but also fully realize the Pd-Co alloying effects for enhancing the methanol oxidation catalytic performance.

19.
Phys Chem Chem Phys ; 20(14): 9659-9670, 2018 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-29582032

RESUMO

CeO2-Catalyzed C2H2 semihydrogenation reaction is a newly emerging catalytic reaction, but the reaction mechanism is not established. We herein report a comprehensive mechanistic study by in situ diffuse reflectance infrared Fourier transformed spectroscopy. Various types of surface species were observed to form upon C2H2 and C2H4 adsorption on CeO2 at different temperatures, including molecularly-adsorbed π-bonded and di-σ-bonded species, dissociatively-adsorbed species of C2H and C2H3, carbonates and formate species, and oligomers species, respectively. During the C2H2 semihydrogenation reaction, the CeO2 surface is partially reduced and strongly hydroxylated. Both O and Ce sites on CeO2 are capable of catalyzing C2H2 semihydrogenation reaction to C2H4, and the O site is more active than the Ce site. The reaction mechanism was elucidated with observed molecularly-adsorbed C2H2 species, a C2H3 intermediate and adsorbed C2H4 species on CeO2. The π-bonded C2H2 species at the O site was identified as the dominant active surface species for CeO2-catalyzed C2H2 semihydrogenation reaction. These results greatly advance the fundamental understanding of CeO2-catalyzed C2H2 semihydrogenation reaction.

20.
Adv Mater ; 30(18): e1706617, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29575274

RESUMO

Electrochemical conversion of CO2 to value-added chemicals using renewable electricity provides a promising way to mitigate both global warming and the energy crisis. Here, a facile ion-adsorption strategy is reported to construct highly active graphene-based catalysts for CO2 reduction to CO. The isolated transition metal cyclam-like moieties formed upon ion adsorption are found to contribute to the observed improvements. Free from the conventional harsh pyrolysis and acid-leaching procedures, this solution-chemistry strategy is easy to scale up and of general applicability, thus paving a rational avenue for the design of high-efficiency catalysts for CO2 reduction and beyond.

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