Recently, the emergence of photoactive metal–organic frameworks (MOFs) has given great prospects for their applications as photocatalytic materials in visible‐light‐driven hydrogen evolution. Herein, ...a highly photoactive visible‐light‐driven material for H2 evolution was prepared by introducing methylthio terephthalate into a MOF lattice via solvent‐assisted ligand‐exchange method. Accordingly, a first methylthio‐functionalized porous MOF decorated with Pt co‐catalyst for efficient photocatalytic H2 evolution was achieved, which exhibited a high quantum yield (8.90 %) at 420 nm by use sacrificial triethanolamine. This hybrid material exhibited perfect H2 production rate as high as 3814.0 μmol g−1 h−1, which even is one order of magnitude higher than that of the state‐of‐the‐art Pt/MOF photocatalyst derived from aminoterephthalate.
The in visible MOF: A high performance for visible‐light‐driven H2‐evolution is obtained with a new methylthio‐functionalized metal–organic framework (MOF) photocatalyst that is rationally designed and facilely prepared. This approach opens up a new way to achieve photocatalysis based on MOF materials with high quantum efficiency value (up to 8.9 %) and excellent photoactivity.
Methane is an abundant and cheap feedstock to produce valuable chemicals. The catalytic reaction of methane conversion generally requires the participation of multiple molecules (such as two or three ...CH4 molecules, O2, CO2, etc.). Such complex process includes the cleavage of original chemical bonds, formation of new chemical bonds, and desorption of products. The gas phase study provides a unique arena to gain molecular‐level insights into the detailed mechanisms of bond‐breaking and bond‐forming involved in complicated catalytic reactions. In this Review, we introduce the methane conversion catalyzed by gas phase ions containing metals and three topics will be discussed: (1) the direct coupling of methane molecules, (2) the conversion of CH4 with O2, O3 and N2O, and (3) the conversion of CH4 with CO2 and H2O. The obtained mechanistic aspects may provide new clues for rational design of better‐performing catalysts for conversion of methane to value‐added products.
This Review article discusses the significant progress that has been made for catalytic methane conversion in the gas phase, with focus on the coupling reactions of CH4 molecules and of CH4 with other substrates (O2, O3, N2O, CO2, and H2O) catalyzed by ions containing metals. The mechanistic details for generation of C−C coupling and C‐O coupling products from methane have been provided at a strictly molecular level.
Conspectus The increasing supply of natural gas has created a strong demand for developing efficient catalytic processes to upgrade methane, the most stable alkane molecule, into value-added ...chemicals. Currently, methane conversion in laboratory and industry is mostly performed under high-temperature conditions. A lot of effort has been devoted to exploring chemical entities that are able to activate the C–H bond of methane at lower temperatures, preferably room temperature. Gas phase atomic clusters with limited numbers of atoms are ideal models of active sites on heterogeneous catalysts. The cluster systems are being actively studied to activate methane under room-temperature conditions. State-of-the-art mass spectrometry, photoelectron imaging spectroscopy, and quantum chemistry calculations have been combined in our laboratory to reveal the molecular-level mechanisms of methane activation by atomic clusters. In this Account, we summarize our recent progress on thermal methane activation by metal oxide clusters doped with noble-metal atoms (Au, Pt, and Rh) as well as by oxygen-free species including carbides and borides of base metals (V, Ta, Mo, and Fe). In contrast to the generations of CH3 • free radicals in many of the previously reported cluster reactions with methane, the generations of stable products such as formaldehyde, acetylene, and syngas as well as closed-shell species AuCH3 and B3CH3 have been identified for the cluster reaction systems herein. Besides the well recognized mechanisms of methane activation by the O–• radicals through hydrogen atom abstraction and by metal atoms through oxidative addition, the new mechanisms of synergistic methane activation by Lewis acid–base pairs (such as Auδ+–Oδ− and Bδ+–Bδ−) and by dinuclear metal centers (such as Ta–Ta) have been recently revealed. In the reactions between methane and oxide clusters doped with noble-metal atoms, the oxide cluster “supports” can accept the H atoms and the CH x species delivered through the noble-metal atoms and then transform methane into stable oxygenated compounds. The product selectivity (such as formaldehyde versus syngas) can be controlled by different noble-metal atoms (such as Pt versus Rh). The electronic structures of base metal centers can be engineered through carburization so that the low-spin states can be accessible to reduce the C–H bond of methane. Such active base metal centers in low-spin states resemble related noble-metal atoms in methane activation. The boron clusters (such as B3 in VB3 +) can be polarized by the metal cations to form the Lewis acid–base pair Bδ+–Bδ− to cleave the C–H bond of methane very easily. These molecular-level mechanisms may well be operative in related heterogeneous catalysis and can be a fundamental basis to design efficient catalysts for activation and conversion of methane under mild conditions.
Catalytic co‐conversion of methane with carbon dioxide to produce syngas (2 H2+2 CO) involves complicated elementary steps and almost all the elementary reactions are performed at the same high ...temperature conditions in practical thermocatalysis. Here, we demonstrate by mass spectrometric experiments that RhTiO2− promotes the co‐conversion of CH4 and CO2 to free 2 H2+CO and an adsorbed CO (COads) at room temperature; the only elementary step that requires the input of external energy is desorption of COads from the RhTiO2CO− to reform RhTiO2−. This study not only identifies a promising active species for dry (CO2) reforming of methane to syngas, but also emphasizes the importance of temperature control over elementary steps in practical catalysis, which may significantly alleviate the carbon deposition originating from the pyrolysis of methane.
The catalytic co‐conversion of CH4 and CO2 to syngas mediated by single Rh atom‐doped titanium oxide anions (RhTiO2−) has been experimentally identified. The production of free 2 H2+CO and an adsorbed CO (COads) could be achieved at room temperature while the only elementary step that requires the input of external energy is desorption of the COads from RhTiO2CO−.
Photoassisted steam reforming and dry (CO2) reforming of methane (SRM and DRM) at room temperature with high syngas selectivity have been achieved in the gas‐phase catalysis for the first time. The ...catalysts used are bimetallic rhodium–vanadium oxide cluster anions of Rh2VO1–3−. Both the oxidation of methane and reduction of H2O/CO2 can take place efficiently in the dark while the pivotal step to govern syngas selectivity is photo‐excitation of the reaction intermediates Rh2VO2,3CH2− to specific electronically excited states that can selectively produce CO and H2. Electronic excitation over Rh2VO2,3CH2− to control the syngas selectivity is further confirmed from the comparison with the thermal excitation of Rh2VO2,3CH2−, which leads to diversity of products. The atomic‐level mechanism obtained from the well‐controlled cluster reactions provides insight into the process of selective syngas production from the photocatalytic SRM and DRM reactions over supported metal oxide catalysts.
Steam and dry reforming of methane catalyzed by gas‐phase rhodium–vanadium–oxygen cluster anions at room temperature with high syngas selectivity has been identified under photo‐irradiation conditions. The crucial step to govern syngas selectivity is the photo‐excitation of reaction intermediates such as Rh2VO3CH2− to electronically excited states that selectively produce H2 and CO.
The global optimization of metal cluster structures is an important research field. The traditional deep neural network (T-DNN) global optimization method is a good way to find out the global minimum ...(GM) of metal cluster structures, but a large number of samples are required. We developed a new global optimization method which is the combination of the DNN and transfer learning (DNN-TL). The DNN-TL method transfers the DNN parameters of the small-sized cluster to the DNN of the large-sized cluster to greatly reduce the number of samples. For the global optimization of Pt9 and Pt13 clusters in this research, the T-DNN method requires about 3–10 times more samples than the DNN-TL method, and the DNN-TL method saves about 70–80% of time. We also found that the average amplitude of parameter changes in the T-DNN training is about 2 times larger than that in the DNN-TL training, which rationalizes the effectiveness of transfer learning. The average fitting errors of the DNN trained by the DNN-TL method can be even smaller than those by the T-DNN method because of the reliability of transfer learning. Finally, we successfully obtained the GM structures of Pt n (n = 8–14) clusters by the DNN-TL method.
The future of manufacturing applications in three-dimensional (3D) printing depends on the improvement and the development of materials suitable for 3D printing technology. This study aims to develop ...an applicable and convenient protocol for light-curing resin used in 3D industry, which could enhance antibacterial and mechanical properties of polymethyl methacrylate (PMMA) resin through the combination of nano-fillers of surface modified titanium dioxide (TiO2) and micro-fillers of polyetheretherketone (PEEK). PMMA-based composite resins with various additions of TiO2 and PEEK were prepared and submitted to characterizations including mechanical properties, distribution of the fillers (TiO2 or/and PEEK) on the fractured surface, cytotoxicity, antibacterial activity, and blood compatibility assessment. These results indicated that the reinforced composite resins of PMMA (TiO2-1%-PEEK-1%) possessed the most optimized properties compared to the other groups. In addition, we found the addition of 1% of TiO2 would be an effective amount to enhance both mechanical and antibacterial properties for PMMA composite resin. Furthermore, the model printed by PMMA (TiO2-1%-PEEK-1%) composite resin showed a smooth surface and a precise resolution, indicating this functional dental restoration material would be a suitable light-curing resin in 3D industry.
Recently, the emergence of photoactive metal-organic frameworks (MOFs) has given great prospects for their applications as photocatalytic materials in visible-light-driven hydrogen evolution. Herein, ...a highly photoactive visible-light-driven material for H
evolution was prepared by introducing methylthio terephthalate into a MOF lattice via solvent-assisted ligand-exchange method. Accordingly, a first methylthio-functionalized porous MOF decorated with Pt co-catalyst for efficient photocatalytic H
evolution was achieved, which exhibited a high quantum yield (8.90 %) at 420 nm by use sacrificial triethanolamine. This hybrid material exhibited perfect H
production rate as high as 3814.0 μmol g
h
, which even is one order of magnitude higher than that of the state-of-the-art Pt/MOF photocatalyst derived from aminoterephthalate.
Dielectric ceramics are of great potential to be applied in electronic systems due to their fast discharge speed and temperature tolerance. However, the low energy storage density and efficiency ...highly restricts the applications of dielectric ceramics. Here, we propose a strategy of fine grain and highly densified relaxor-antiferroelectric (RE-AFE) ceramics to both increase the energy storage density and efficiency. We fabricated NaNbO3 based relaxor-antiferroelectric (RE-AFE) ceramics by Spark Plasma Sintering (SPS) and obtained an ultra-high recoverable energy storage density of 12.2 J/cm3 and satisfied efficiency of 88%. The present research offers a route for designing dielectric ceramics with enhanced energy storage density and efficiency, which is significant to the application of dielectric ceramics.
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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, CH3OH and CH2O, in the temperature range of 393–600 K. The resulting cluster ions RhVO3CO− after CH3OH 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→CH3OH+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.
Both on board: A dinuclear species (RhVO3−) that can mediate co‐conversion of CH4 and CO2 has been identified. The Rh atom is the active site to activate both of the molecules.
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