Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 195
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nat Commun ; 12(1): 5814, 2021 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-34608162

RESUMO

Achieving CO oxidation at room temperature is significant for gas purification but still challenging nowadays. Pt promoted by 3d transition metals (TMs) is a promising candidate for this reaction, but TMs are prone to be deeply oxidized in an oxygen-rich atmosphere, leading to low activity. Herein we report a unique structure design of graphene-isolated Pt from CoNi nanoparticles (PtǀCoNi) for efficiently catalytic CO oxidation in an oxygen-rich atmosphere. CoNi alloy is protected by ultrathin graphene shell from oxidation and therefore modulates the electronic property of Pt-graphene interface via electron penetration effect. This catalyst can achieve near 100% CO conversion at room temperature, while there are limited conversions over Pt/C and Pt/CoNiOx catalysts. Experiments and theoretical calculations indicate that CO will saturate Pt sites, but O2 can adsorb at the Pt-graphene interface without competing with CO, which facilitate the O2 activation and the subsequent surface reaction. This graphene-isolated system is distinct from the classical metal-metal oxide interface for catalysis, and it provides a new thought for the design of heterogeneous catalysts.

2.
Artigo em Inglês | MEDLINE | ID: mdl-34651393

RESUMO

Reaction temperature is an important parameter to tune the selectivity and activity of electrochemical CO2 reduction reaction (CO2 RR) due to different thermodynamics of CO2 RR and competitive hydrogen evolution reaction (HER). In this work, temperature-dependent CO2 RR over Fe-N-C and Ni-N-C single-atom catalysts are investigated from 303 to 343 K. Increasing the reaction temperature improves and decreases CO Faradaic efficiency over Fe-N-C and Ni-N-C catalysts at high overpotentials, respectively. CO current density over Fe-N-C catalyst increases with temperature, then gets into a plateau at 323 K, finally reaches the maximum value of 185.8 mA cm-2 at 343 K. While CO current density over Ni-N-C catalyst achieves the maximum value of 252.5 mA cm-2 at 323 K, and then drops significantly to 202.9 mA cm-2 at 343 K. Temperature programmed desorption results and density functional theory calculations reveal that the difference of temperature-dependent variation on CO Faradaic efficiency and current density between Fe-N-C and Ni-N-C catalysts results from the varied adsorption strength of key reaction intermediates during CO2 RR.

3.
Chem Sci ; 12(34): 11554-11564, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34567504

RESUMO

Heteronuclear dipolar coupling is indispensable in revealing vital information related to the molecular structure and dynamics, as well as intermolecular interactions in various solid materials. Although numerous approaches have been developed to selectively reintroduce heteronuclear dipolar coupling under MAS, most of them lack universality and can only be applied to limited spin systems. Herein, we introduce a new and robust technique dubbed phase modulated rotary resonance (PMRR) for reintroducing heteronuclear dipolar couplings while suppressing all other interactions under a broad range of MAS conditions. The standard PMRR requires the radiofrequency (RF) field strength of only twice the MAS frequency, can efficiently recouple the dipolar couplings with a large scaling factor of 0.50, and is robust to experimental imperfections. Moreover, the adjustable window modification of PMRR, dubbed wPMRR, can improve its performance remarkably, making it well suited for the accurate determination of dipolar couplings in various spin systems. The robust performance of such pulse sequences has been verified theoretically and experimentally via model compounds, at different MAS frequencies. The application of the PMRR technique was demonstrated on the H-ZSM-5 zeolite, where the interaction between the Brønsted acidic hydroxyl groups of H-ZSM-5 and the absorbed trimethylphosphine oxide (TMPO) were probed, revealing the detailed configuration of super acid sites.

4.
Nat Commun ; 12(1): 5665, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34580312

RESUMO

Metal nanoparticles anchored on perovskite through in situ exsolution under reducing atmosphere provide catalytically active metal/oxide interfaces for CO2 electrolysis in solid oxide electrolysis cell. However, there are critical challenges to obtain abundant metal/oxide interfaces due to the sluggish diffusion process of dopant cations inside the bulk perovskite. Herein, we propose a strategy to promote exsolution of RuFe alloy nanoparticles on Sr2Fe1.4Ru0.1Mo0.5O6-δ perovskite by enriching the active Ru underneath the perovskite surface via repeated redox manipulations. In situ scanning transmission electron microscopy demonstrates the dynamic structure evolution of Sr2Fe1.4Ru0.1Mo0.5O6-δ perovskite under reducing and oxidizing atmosphere, as well as the facilitated CO2 adsorption at RuFe@Sr2Fe1.4Ru0.1Mo0.5O6-δ interfaces. Solid oxide electrolysis cell with RuFe@Sr2Fe1.4Ru0.1Mo0.5O6-δ interfaces shows over 74.6% enhancement in current density of CO2 electrolysis compared to that with Sr2Fe1.4Ru0.1Mo0.5O6-δ counterpart as well as impressive stability for 1000 h at 1.2 V and 800 °C.

5.
Chem Rev ; 121(11): 6588-6609, 2021 06 09.
Artigo em Inglês | MEDLINE | ID: mdl-34032417

RESUMO

Syngas chemistry has been under study since Fischer-Tropsch synthesis (FTS) was invented in the 1920s. Despite the successful applications of FTS as the core technology of coal-to-liquid and gas-to-liquid processes in industry, the product selectivity control of syngas conversion still remains a great challenge, particularly for value-added chemicals such as light olefins. Recent studies show that the catalyst design concept of OXZEO (oxide-zeolite-based composite) enables direct syngas conversion to mixed light olefins with a selectivity reaching 80% and to ethylene with a selectivity of 83% among hydrocarbons. They both well-surpass the limits predicated by the Anderson-Schultz-Flory model via the conventional FTS route (58% and 30%, respectively). Furthermore, this catalyst concept allows one-step synthesis of gasoline-range isoparaffins and aromatic compounds, which is otherwise not possible in conventional FTS. A rapidly growing number of studies demonstrate the versatility of this concept and may form a technology platform for utilization of carbon resources including coal, natural gas, and biomass via syngas to a variety of basic chemicals and fuels. However, the selectivity control mechanism is far from being understood. Therefore, we focus mainly on the catalytic roles of the bifunctionalities of OXZEO while reviewing the development of bifunctional catalysts for selective syngas conversion by taking syngas-to-light olefins as an example. With this, we intend to provide insights into the selectivity control mechanism of the OXZEO concept in order to understand the challenges and prospects for future development of much more active and more selective catalysts.

6.
Angew Chem Int Ed Engl ; 60(26): 14329-14333, 2021 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-33837619

RESUMO

Electrochemical CO2 reduction reaction (CO2 RR) to multicarbon hydrocarbon and oxygenate (C2+ ) products with high energy density and wide availability is of great importance, as it provides a promising way to achieve the renewable energy storage and close the carbon cycle. Herein we design a Cu-CuI composite catalyst with abundant Cu0 /Cu+ interfaces by physically mixing Cu nanoparticles and CuI powders. The composite catalyst achieves a remarkable C2+ partial current density of 591 mA cm-2 at -1.0 V vs. reversible hydrogen electrode in a flow cell, substantially higher than Cu (329 mA cm-2 ) and CuI (96 mA cm-2 ) counterparts. Induced by alkaline electrolyte and applied potential, the Cu-CuI composite catalyst undergoes significant reconstruction under CO2 RR conditions. The high-rate C2+ production over Cu-CuI is ascribed to the presence of residual Cu+ and adsorbed iodine species which improve CO adsorption and facilitate C-C coupling.

7.
J Phys Chem Lett ; 12(17): 4187-4194, 2021 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-33900088

RESUMO

The strong metal-support interaction (SMSI) is one of the most important concepts in heterogeneous catalysis, which has been widely investigated between metals and active oxides triggered by reductive atmospheres. Here, we report the oxidative strong metal-support interaction (O-SMSI) effect between Pt nanoparticles (NPs) and inert hexagonal boron nitride (h-BN) sheets, in which Pt NPs are encapsulated by oxidized boron (BOx) overlayers derived from the h-BN support under oxidative conditions. De-encapsulation of Pt NPs has been achieved by washing in water, and the residual ultrathin BOx overlayers work synergistically with surface Pt sites for enhancing CO oxidation reaction. The O-SMSI effect is also present in other h-BN-supported metal catalysts such as Au, Rh, Ru, and Ir within different oxidative atmospheres including O2 and CO2, which is determined by metal-boron interaction and O affinity of metals.

8.
J Phys Chem Lett ; 12(9): 2413-2422, 2021 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-33661009

RESUMO

Herein, utilizing acetonitrile as the probe molecule, the acidity and host-guest interactions of H-mordenite (H-MOR) zeolites are investigated comprehensively by solid-state NMR spectroscopy and theoretical calculation. The locations and local configurations of Brønsted acid sites (BASs) in H-MOR are revealed by multinuclear and multidimensional NMR experiments with adsorption/coadsorption of acetonitrile (CD3CN) and trimethylphosphine (TMP). Moreover, the confinement effect of dual pores in MOR has been characterized via the quantitative determination of host-guest interactions between CH3CN and BASs. The 1H-15N dipolar measurement results and DFT calculations demonstrate that there are two kinds of acetonitrile molecules adsorbed in 12-membered ring (12MR) main channels with distinct mobility, where acetonitrile undergoes either partially restricted or highly flexible motion in the time scale of nanoseconds to microseconds. These two types of acetonitrile can exchange with temperature rising. In contrast, the mobility of acetonitrile in 8-membered ring (8MR) channels is very restricted due to the confinement of the framework.

9.
Nat Commun ; 12(1): 1406, 2021 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-33658489

RESUMO

Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions.

10.
ACS Omega ; 6(5): 4090-4099, 2021 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-33585784

RESUMO

Herein, a detailed analysis was carried out using high-field (19.9 T) 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) on three specially prepared aluminum oxide samples where the γ-, δ-, and θ-Al2O3 phases are dominantly expressed through careful control of the synthesis conditions. Specifically, two-dimensional (2D) multiquantum (MQ) MAS 27Al was used to obtain high spectral resolution, which provided a guide for analyzing quantitative 1D 27Al NMR spectra. Six aluminum sites were resolved in the 2D MQ MAS NMR spectra, and seven aluminum sites were required to fit the 1D spectra. A set of octahedral and tetrahedral peaks with well-defined quadrupolar line shapes was observed in the θ-phase dominant sample and was unambiguously assigned to the θ-Al2O3 phase. The distinct line shapes related to the θ-Al2O3 phase provided an opportunity for effectively deconvoluting the more complex spectrum obtained from the δ-Al2O3 dominant sample, allowing the peaks/quadrupolar parameters related to the δ-Al2O3 phase to be extracted. The results show that the δ-Al2O3 phase contains three distinct AlO sites and three distinct AlT sites. This detailed Al site structural information offers a powerful way of analyzing the most complex γ-Al2O3 spectrum. It is found that the γ-Al2O3 phase consists of Al sites with local structures similar to those found in the δ-Al2O3 and θ-Al2O3 phases albeit with less ordering. Spin-lattice relaxation time measurement further confirms the disordering of the lattice. Collectively, this study uniquely assigns 27Al features in transition aluminas, offering a simplified method to quantify complex mixtures of aluminum sites in transition alumina samples.

11.
J Phys Chem Lett ; 12(5): 1443-1452, 2021 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-33523659

RESUMO

The rational design and controlled construction of active centers remain grand challenges in heterogeneous catalysis, in particular for oxide catalysts with complex surface and interface structures. This work describes a facile way in the design of highly active Ni-O Lewis pairs for water activation where Ni and O sites act as Lewis acid and base, respectively. Surface science experiments indicate that dissociative adsorption of water occurs at edges of NiOx nanoislands grown on Au(111) and NiOx-Ni interfaces formed by further depositing metallic Ni layers along the edges of NiOx nanoislands. Enhanced activity of Ni-O Lewis pairs at the NiOx-Ni interface has been demonstrated by theoretical calculations, which are attributed to the higher Lewis acidity of metallic Ni sites and synergy of the metal and oxide components. Moreover, proton can migrate away from the NiOx-Ni interface and refresh the O base sites, leading to further hydroxylation of the neighboring Ni acid sites.

12.
Solid State Nucl Magn Reson ; 112: 101711, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33508579

RESUMO

With the recent advances in NMR hardware and probe design technology, magic-angle spinning (MAS) rates over 100 â€‹kHz are accessible now, even on commercial solid NMR probes. Under such fast MAS conditions, excellent spectral resolution has been achieved by efficient suppression of anisotropic interactions, which also opens an avenue to the proton-detected NMR experiments in solids. Numerous methods have been developed to take full advantage of fast MAS during the last decades. Among them, dipolar recoupling techniques under fast MAS play vital roles in the determination of the molecular structure and dynamics, and are also key elements in multi-dimensional correlation NMR experiments. Herein, we review the dipolar recoupling techniques, especially those developed in the past two decades for fast-to-ultrafast MAS conditions. A major focus for our discussion is the ratio of RF field strength (in frequency) to MAS frequency, ν1/νr, in different pulse sequences, which determines whether these dipolar recoupling techniques are suitable for NMR experiments under fast MAS conditions. Systematic comparisons are made among both heteronuclear and homonuclear dipolar recoupling schemes. In addition, the schemes developed specially for proton-detection NMR experiments under ultrafast MAS conditions are highlighted as well.

13.
Rev Sci Instrum ; 91(11): 113704, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33261460

RESUMO

A newly developed instrument comprising a near ambient pressure (NAP) photoemission electron microscope (PEEM) and a tunable deep ultraviolet (DUV) laser source is described. This NAP-PEEM instrument enables dynamic imaging of solid surfaces in gases at pressures up to 1 mbar. A diode laser (976 nm) can illuminate a sample from the backside for in situ heating in gases up to 1200 K in minutes. The DUV laser with a tunable wavelength between 175 nm and 210 nm is perpendicularly incident onto the sample surface for PEEM imaging of a wide spectrum of solids with different surface work functions. Using this setup, we have first demonstrated spatiotemporal oscillation patterns of CO oxidation reaction on Pt(110) from high vacuum to NAPs and gas-induced restructuring of metal nanostructures in millibar gases. The new facility promises important applications in heterogeneous catalysis, electrochemical devices, and other surface processes under nearly working conditions.

14.
J Am Chem Soc ; 142(40): 17167-17174, 2020 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-32924478

RESUMO

Encapsulation of metal nanocatalysts by support-derived materials is well known as a classical strong metal-support interaction (SMSI) effect that occurs almost exclusively with active oxide supports and often blocks metal-catalyzed surface reactions. In the present work this classical SMSI process has been surprisingly observed between metal nanoparticles, e.g., Ni, Fe, Co, and Ru, and inert hexagonal boron nitride (h-BN) nanosheets. We find that weak oxidizing gases such as CO2 and H2O induce the encapsulation of nickel (Ni) nanoparticles by ultrathin boron oxide (BOx) overlayers derived from the h-BN support (Ni@BOx/h-BN) during the dry reforming of methane (DRM) reaction. In-situ surface characterization and theory calculations reveal that surface B-O and B-OH sites in the formed BOx encapsulation overlayers work synergistically with surface Ni sites to promote the DRM process rather than blocking the surface reactions.

15.
Angew Chem Int Ed Engl ; 59(50): 22408-22413, 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-32886835

RESUMO

Developing copper-free catalysts for CO2 conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO2 reduction reaction (CO2 RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc-nitrogen-carbon (Zn-N-C) tandem catalyst for CO2 RR to CH4 . This tandem catalyst shows a more than 100 times enhancement of the CH4 /CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO2 is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH4 over Zn-N4 site, decoupling complicated CO2 RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N4 , which is the key to achieve the high CH4 production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.

16.
Angew Chem Int Ed Engl ; 59(36): 15294-15297, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32473050

RESUMO

Encapsulating transition-metal nanoparticles inside carbon nanotubes (CNTs) or spheres has emerged as a novel strategy for designing highly durable nonprecious-metal catalysts. The stable carbon layer protects the inner metal core from the destructive reaction environment and thus is described as chain mail for catalysts. Electron transfer from the active metal core to the carbon layer stimulates unique catalytic activity on the carbon surface, which has been utilized extensively in a variety of catalytic reaction systems. Here, we elaborate the underlying working principle of chain mail for catalysts as well as the key factors that determine their catalytic properties, and provide insights into the physicochemical nature of such catalyst architectures for further application of the strategy in rational catalyst design.

17.
Nat Commun ; 11(1): 2312, 2020 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-32385230

RESUMO

Despite tremendous importance in catalysis, the design of oxide-metal interface has been hampered by the limited understanding of the nature of interfacial sites and the oxide-metal interaction (OMI). Through construction of well-defined Cu2O/Pt, Cu2O/Ag and Cu2O/Au interfaces, we find that Cu2O nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same structure. The activities of these interfaces are compared for CO oxidation and follow the order of Cu2O/Pt > Cu2O/Au > Cu2O/Ag. OMI is found to determine the activity and stability of supported Cu2O NSs, which could be described by the formation energy of interfacial oxygen vacancy. Further, electronic interaction between Cu+ and metal substrates is found center to OMI, where the d band center could be used as a key descriptor. Our study provides insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions.

18.
Angew Chem Int Ed Engl ; 59(37): 15968-15973, 2020 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-32452143

RESUMO

In situ exsolution of metal nanoparticles in perovskite under reducing atmosphere is employed to generate a highly active metal-oxide interface for CO2 electrolysis in a solid oxide electrolysis cell. Atomic-scale insight is provided into the exsolution of CoFe alloy nanoparticles in La0.4 Sr0.6 Co0.2 Fe0.7 Mo0.1 O3-δ (LSCFM) by in situ scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy and DFT calculations. The doped Mo atoms occupy B sites of LSCFM, which increases the segregation energy of Co and Fe ions at B sites and improves the structural stability of LSCFM under a reducing atmosphere. In situ STEM measurements visualized sequential exsolution of Co and Fe ions, formation of CoFe alloy nanoparticles, and reversible exsolution and dissolution of CoFe alloy nanoparticles in LSCFM. The metal-oxide interface improves CO2 adsorption and activation, showing a higher CO2 electrolysis performance than the LSCFM counterparts.

19.
ChemSusChem ; 13(23): 6290-6295, 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-32459062

RESUMO

CO2 electroreduction by solid oxide electrolysis cells (SOECs) can not only attenuate the greenhouse effect, but also convert surplus electrical energy into chemical energy. The adsorption and activation of CO2 on the cathode play an important role in the SOEC performance. La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ -Ce0.8 Sm0.2 O2-δ (LSCF-SDC; SDC=samarium-doped ceria) is a promising SOEC cathode. However, its electrocatalytic activity still needs to be improved. In this study, Pt/SDC interfaces are constructed by decorating Pt nanoparticles onto the SDC surface. Electrochemical measurements indicate that the polarization resistance of the SOEC is decreased from 0.308 to 0.120â€…Ω cm2 , and the current density is improved from 0.913 to 1.420 A cm-2 at 1.6 V and 800 °C. Physicochemical characterizations suggest that construction of the Pt/SDC interfaces increases the oxygen vacancy concentration on the cathode and boosts CO2 adsorption and dissociation, which leads to enhanced CO2 electroreduction performance in SOECs.

20.
Angew Chem Int Ed Engl ; 59(26): 10502-10507, 2020 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-32227428

RESUMO

Perturbing the electronic structure of the MoS2 basal plane by confining heteroatoms offers the opportunity to trigger in-plane activity for the hydrogen evolution reaction (HER). The key challenge consists of inducing the optimum HER activity by controlling the type and distribution of confined atoms. A distance synergy of MoS2 -confined single-atom rhodium is presented, leading to an ultra-high HER activity at the in-plane S sites adjacent to the rhodium. By optimizing the distance between the confined Rh atoms, an ultra-low overpotential of 67 mV is achieved at a current density of 10 mA cm-2 in acidic solution. Experiments and first-principles calculations demonstrate a unique distance synergy between the confined rhodium atoms in tuning the reactivity of neighboring in-plane S atoms, which presents a volcanic trend with the inter-rhodium distance. This study provides a new strategy to tailor the activity of MoS2 surface via modulating the distance between confined single atoms.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...