Single-Atom Ru Alloyed with Ni Nanoparticles Boosts CO2 Methanation.

Designing catalysts to proceed with catalytic reactions along the desired reaction pathways, e.g., CO2 methanation, has received much attention but remains a huge challenge. This work reports one Ru1Ni single-atom alloy (SAA) catalyst (Ru1Ni/SiO2) prepared via a galvanic replacement reaction between RuCl3 and Ni nanoparticles (NPs) derived from the reduction of Ni phyllosilicate (Ni-ph). Ru1Ni/SiO2 achieved much improved selectivity toward hydrogenation of CO2 to CH4 and catalytic activity (Turnover frequency (TOF) value: 40.00 × 10-3 s-1), much higher than those of Ni/SiO2 (TOF value: 4.40 × 10-3 s-1) and most reported Ni-based catalysts (TOF value: 1.03 × 10-3-11.00 × 10-3 s-1). Experimental studies verify that Ru single atoms are anchored onto the Ni NPs surface via the Ru1-Ni coordination accompanied by electron transfer from Ru1 to Ni. Both in situ experiments and theoretical calculations confirm that the interface sites of Ru1Ni-SAA are the intrinsic active sites, which promote the direct dissociation of CO2 and lower the energy barrier for the hydrogenation of CO* intermediate, thereby directing and enhancing the CO2 hydrogenation to CH4.

High-Index Faceted Cu2 O@CuO Mesocrystals Act as Efficient Catalyst for Si Hydrochlorination to Trichlorosilane.

Mesocrystals (MCs) with high-index facets may have superior catalytic properties to those with low-index facets and their nanocrystal counterparts. However, synthesizing such mesocrystal materials is still very challenging because of the metastability of MCs and energetic high-index crystal facets. This work reports a successful solvothermal method followed by calcination for synthesizing copper oxide-based MCs possessing a core-shell structure (denoted as Cu2 O@CuO HIMCs). Furthermore, these MCs are predominantly bounded by the high-index facets such as {311} or {312} with a high-density of stepped atoms. When used as catalysts in Si hydrochlorination to produce trichlorosilane (TCS, the primary feedstock of high-purity crystalline Si), Cu2 O@CuO HIMCs exhibit significantly enhanced Si conversion and TCS selectivity compared to those with flat surfaces and their nanostructured counterparts. Theoretical calculations reveal that both the core-shell structure and the high-index surface contribute to the increased electron density of Cu sites in Cu2 O@CuO HIMCs, promoting the adsorption and dissociation of HCl and stabilizing the dissociated Cl* intermediate. This work provides a simple method for synthesizing high-index faceted MCs and offers a feasible strategy to enhance the catalytic performance of MCs.

Isolating Single Sn Atoms in CuO Mesocrystal to Form Ordered Atomic Interfaces: An Effective Strategy for Designing Highly Efficient Mesocrystal Catalysts.

Tuning the electronic structures of mesocrystals at the atomic level is an effective approach to obtaining unprecedented properties. Here, a lattice-confined strategy to obtain isolated single-site Sn atoms in CuO mesocrystals to improve catalytic performance is reported. The Sn/CuO mesocrystal composite (Sn/CuO MC) has ordered Sn-O-Cu atomic interfaces originated from the long-range ordering of the CuO mesocrystal itself. X-ray absorption fine structure measurements confirm that the positively charged Sn atoms can tune the electronic structure of the Cu atoms to some extent in Sn/CuO MC, quite different from that in the conventional single-atom Sn-modified CuO nanoparticles and nanoparticulate SnO2 -modified CuO mesocrystal catalysts. When tested for the Si hydrochlorination reaction to produce trichlorosilane, Sn/CuO MC exhibits significantly better performances than the above two catalysts. Theoretical calculations further reveal the electronic modification to the active Cu component and the induced improvement in HCl adsorption, and thus enhance the catalytic performance. This work demonstrates how to design efficient metal oxide mesocrystal catalysts through an electronic structure modification approach.

Structural Design and Synthesis of an SnO2 @C@Co-NC Composite as a High-Performance Anode Material for Lithium-Ion Batteries.

To overcome the drawbacks of the structural instability and poor conductivity of SnO2 -based anode materials, a hollow core-shell-structured SnO2 @C@Co-NC (NC=N-doped carbon) composite was designed and synthesized by employing the heteroatom-doping and multiconfinement strategies. This composite material showed a much-reduced resistance to charge transfer and excellent cycling performance compared to the bare SnO2 nanoparticles and SnO2 @C composites. The doped heteroatoms and heterostructure boost the charge transfer, and the porous structure shortens the Li-ion diffusion pathway. Also, the volume expansion of SnO2 NPs is accommodated by the hollow space and restricted by the multishell heteroatom-doped carbon framework. As a result, this structured anode material delivered a high initial capacity of 1559.1 mA h g-1 at 50 mA g-1 and an initial charge capacity of 627.2 mA h g-1 at 500 mA g-1 . Moreover, the discharge capacity could be maintained at 410.8 mA h g-1 after 500 cycles with an attenuation rate of only 0.069 % per cycle. This multiconfined SnO2 @C@Co-NC structure with superior energy density and durable lifespan is highly promising for the next-generation lithium-ion batteries.

Scalable synthesis of interconnected porous silicon/carbon composites by the Rochow reaction as high-performance anodes of lithium ion batteries.

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible.

Template-free synthesis of mesoporous hollow CuO microspheres as anode materials for Li-ion batteries.

We report the preparation and characterization of mesoporous hollow CuO (MPH-CuO) microspheres by thermal decomposition of hollow copper oxalate microspheres synthesized via the reaction of ammonium oxalate and copper chloride without using any template. The sample was characterized by Nitrogen adsorption, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The electrochemical performance of MPH-CuO microspheres as anode materials in Li-ion batteries was evaluated. It was found that the MPH-CuO microspheres possessed an average diameter of 2.5 microm, a pore size of 17.5 nm, and a BET surface area of 15.2 m2/g. Their shells were composed of CuO nanocrystals with a size of 17.9 nm. Compared with the dense CuO microspheres, the obtained MPH-CuO shows an enhanced electrochemical performance with a higher capacity of 599.4 mAh/g and a better cyclability (484 mAh/g after 15 cycles) because of its mesoporous hollow structure that provides quick intercalation and large accommodation of lithium ions together with short diffusion distance for lithium ions, suggesting a potential application in Li-ion batteries.

Isolating Contiguous Ir Atoms and Forming Ir-W Intermetallics with Negatively Charged Ir for Efficient NO Reduction by CO.

The lack of efficient catalysts with a wide working temperature window and vital O2 and SO2 resistance for selective catalytic reduction of NO by CO (CO-SCR) largely hinders its implementation. Here, a novel Ir-based catalyst with only 1 wt% Ir loading is reported for efficient CO-SCR. In this catalyst, contiguous Ir atoms are isolated into single atoms, and Ir-W intermetallic nanoparticles are formed, which are supported on ordered mesoporous SiO2 (KIT-6). Notably, this catalyst enables complete NO conversion to N2 at 250 °C in the presence of 1% O2 and has a wide temperature window (250-400 °C), outperforming the comparison samples with Ir isolated-single-atomic-sites and Ir nanoparticles, respectively. Also, it possesses a high SO2 tolerance. Both experimental results and theoretical calculations reveal that single Ir atoms are negatively charged, dramatically enhancing the NO dissociation, while the Ir-W intermetallic nanoparticles accelerate the reduction of the N2 O and NO2 intermediates by CO.

Architectural Cu2O@CuO mesocrystals as superior catalyst for trichlorosilane synthesis.

As compared with conventional nanocrystal systems, Cu-based mesocrystals have demonstrated distinct advantages in catalytic applications. Here, we report the preparation of a novel architectural Cu2O@CuO catalyst system integrated with the core/shell and mesocrystal structures (Cu2O@CuO MC) via a facile solvothermal process followed by calcination. The formation mechanism of the Cu2O@CuO MC with hexapod morphology was deciphered based on a series of time-dependent experiments and characterizations. When applied as a Cu-based catalyst to produce trichlorosilane (TCS) via Si hydrochlorination reaction, the Cu2O@CuO MC exhibited a much higher Si conversion, TCS selectivity, and stability than the catalyst-free industrial process and the Cu2O@CuO catalyst with a core-shell nanostructure. The enhanced catalytic efficiency of the former is attributed to the collective effects from its quite rough surface for providing abundant adsorption sites, the ordered nanoparticle arrangement in the core and shell for generating strong synergistic effects, and the micrometer size for the improved structural stability. This work demonstrates a practical route for designing sophisticated architectural structures that combine several structural functions within one catalyst system and their catalysis applications.

Engineering nonspherical hollow structures with complex interiors by template-engaged redox etching.

Despite the significant advancement in making hollow structures, one unsolved challenge in the field is how to engineer hollow structures with specific shapes, tunable compositions, and desirable interior structures. In particular, top-down engineering the interiors inside preformed hollow structures is still a daunting task. In this work, we demonstrate a facile approach for the preparation of a variety of uniform hollow structures, including Cu(2)O@Fe(OH)(x) nanorattles and Fe(OH)(x) cages with various shapes and dimensions by template-engaged redox etching of shape-controlled Cu(2)O crystals. The composition can be readily modulated at different structural levels to generate other interesting structures such as Cu(2)O@Fe(2)O(3) and Cu@Fe(3)O(4) rattles, as well as Fe(2)O(3) and Fe(3)O(4) cages. More remarkably, this strategy enables top-down engineering the interiors of hollow structures as demonstrated by the fabrication of double-walled nanorattles and nanoboxes, and even box-in-box structures. In addition, this approach is also applied to form Au and MnO(x) based hollow structures.

Recycling the CoMo/Al2O3 catalyst for effectively hydro-upgrading shale oil with high sulfur content and viscosity.

Hydrotreatment is an effective upgrading technology for removing contaminants and saturating double bonds. Still, few studies have reported the hydro-upgrading of shale oil, with unusually high sulfur (13200 ppm) content, using the CoMo/Al2O3 catalyst. Here we report an extensive study on the upgrading of shale oil by hydrotreatment in a stirred batch autoclave reactor (500 ml) for sulfur removal and viscosity reduction. From a preliminary optimization of the reaction factors, the best-operating conditions were 400 °C, an initial H2-pressure of 5 MPa, and an agitation rate of 800 rpm, a catalyst-to-oil ratio of 0.1, and a reaction time of 1 h. We could achieve a sulfur removal efficiency of 87.1% and 88.2% viscosity reduction under the optimal conditions. After that, the spent CoMo/Al2O3 was repeatedly used for subsequent upgrading tests without any form of pre-treatment. The results showed an increase in the sulfur removal efficiency with an increase in the number of catalyst runs. Ultimately, 99.5-99.9% sulfur removal from the shale oil was achieved by recycling the spent material. Both the fresh and the spent CoMo/Al2O3 were characterized and analyzed to ascertain their transformation levels by XRD, TEM, TG, XPS, TPD and N2 adsorption analysis. The increasing HDS efficiency is attributed to the continuing rise in the sulfidation degree of the catalyst in the sulfur-rich shale oil. The light fraction component in the liquid products (IBP-180 °C) was 30-37 vol% higher than in the fresh shale oil. The product oil can meet the sulfur content requirement of the national standard marine fuel (GB17411-2015/XG1-2018) of China.

Single-atom Sn-Zn pairs in CuO catalyst promote dimethyldichlorosilane synthesis.

Single-atom catalysts are of great interest because they can maximize the atom-utilization efficiency and generate unique catalytic properties; however, much attention has been paid to single-site active components, rarely to catalyst promoters. Promoters can significantly affect the activity and selectivity of a catalyst, even at their low concentrations in catalysts. In this work, we designed and synthesized CuO catalysts with atomically dispersed co-promoters of Sn and Zn. When used as the catalyst in the Rochow reaction for the synthesis of dimethyldichlorosilane, this catalyst exhibited much-enhanced activity, selectivity and stability compared with the conventional CuO catalysts with promoters in the form of nanoparticles. Density functional theory calculations demonstrate that single-atomic Sn substitution in the CuO surface can enrich surface Cu vacancies and promote dispersion of Zn to its atomic levels. Sn and Zn single sites as the co-promoters cooperatively generate electronic interaction with the CuO support, which further facilitates the adsorption of the reactant molecules on the surface, thereby leading to the superior catalytic performance.

Synthetic control of the pore dimension and surface area in conjugated microporous polymer and copolymer networks.

A series of rigid microporous poly(aryleneethynylene) (PAE) networks was synthesized by Sonogashira-Hagihara coupling chemistry. PAEs with apparent Brunauer-Emmet-Teller surface areas of more than 1000 m(2)/g were produced. The materials were found to have very good chemical and thermal stability and retention of microporosity under a variety of conditions. It was shown that physical properties such as micropore size, surface area, and hydrogen uptake could be controlled in a "quantized" fashion by varying the monomer strut length, as for metal-organic and covalent organic frameworks, even though the networks were amorphous in nature. For the first time, it was demonstrated that these properties can also be fine-tuned in a continuous manner via statistical copolymerization of monomer struts with differing lengths. This provides an unprecedented degree of direct synthetic control over micropore properties in an organic network.

Rapid and reversible hydrogen storage in clathrate hydrates using emulsion-templated polymers.

A method for greatly accelerating the storage of gases such as hydrogen in clathrates by supporting the clathrate phase on a highly macroporous emulsion-templated polymer is presented. The gravimetric penalty is low due to the low bulk density of the support, no mechanical mixing is required, and the system is fully recyclable over multiple charge/ discharge cycles.

Conjugated microporous poly(phenylene butadiynylene)s.

High surface area porous poly(phenylene butadiynylene) networks were obtained (BET surface area up to 842 m(2) g(-1)) by the palladium-catalyzed homocoupling of 1,3,5-triethynylbenzene and 1,4-diethynylbenzene.

Synthesis of graphitic ordered macroporous carbon with a three-dimensional interconnected pore structure for electrochemical applications.

In this study, ordered macroporous carbon with a three-dimensional (3D) interconnected pore structure and a graphitic pore wall was prepared by chemical vapor deposition (CVD) of benzene using inverse silica opal as the template. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectrometry, nitrogen adsorption, and thermogravimetric analysis techniques were used to characterize the carbon samples. The electrochemical properties of the carbon materials as a carbon-based anode for lithium-ion batteries and as a Pt catalyst support for room-temperature methanol electrochemical oxidation were examined. It was observed that the CVD method is a simple route to fabrication of desired carbon nanostructures, affording a carbon with graphitic pore walls and uniform pores. The graphitic nature of the carbon enhances the rate performance and cyclability in lithium-ion batteries. The specific capacity was found to be further improved when SnO(2) nanoparticles were supported on the carbon. The specific activity of Pt catalyst supported on the carbon materials for room-temperature methanol electrochemical oxidation was observed to be higher than that of a commercial Pt catalyst (E-TEK).

Competitive adsorption of Pb2+, Cu2+, and Cd2+ ions on microporous titanosilicate ETS-10.

In the present study, the competitive adsorption characteristics of binary and ternary heavy metal ions Pb2+, Cu2+, and Cd2+ on microporous titanosilicate ETS-10 were investigated in batch systems. Pure microporous titanosilicate ETS-10 was synthesized with P25 as the Ti source and characterized by the techniques of X-ray diffraction (XRD), field emission-scanning electron microscope (FESEM), nitrogen adsorption, and zeta-potential. Equilibrium and kinetic adsorption data showed that ETS-10 displays a high selectivity toward one metal in a two-component or a three-component system with an affinity order of Pb2+ > Cd2+ > Cu2+. The equilibrium behaviors of heavy metals species with stronger affinity toward ETS-10 can be described by the Langmuir equation while the adsorption kinetics of the metals can be well fitted to a pseudo-second-order (PSO) model.

Nanostructured Si-Based Anodes for Lithium-Ion Batteries.

High capacity electrode materials are searched for commercial applications due to the increase in energy density and power density requirements for lithium-ion secondary cells. Silicon has triggered significant research effort because of its low Li-uptake potential and the high theoretical capacity. However, volume changes during cycling cause pulverization and capacity fade, which is an obstacle of the application of silicon as an anode. Here we present a review of research progress on silicon-based anode materials for lithium-ion batteries, focusing on the effects of the morphology and compound on the electrochemical properties. The reasons of poor cycle performance are discussed. It is pointed out that to control the huge volume change and solid electrolyte interface growth during cycling is an effective way to improve the cycle performance. Outlook for the future development of silicon-based composite anode materials for the application of silicon anodes are finally outlined.

Yolk bishell Mn(x)Co(1-x)Fe2O4 hollow microspheres and their embedded form in carbon for highly reversible lithium storage.

The yolk-shell hollow structure of transition metal oxides has many applications in lithium-ion batteries and catalysis. However, it is still a big challenge to fabricate uniform hollow microspheres with the yolk bishell structure for mixed transition metal oxides and their supported or embedded forms in carbon microspheres with superior lithium storage properties. Here we report a new approach to the synthesis of manganese cobalt iron oxides/carbon (MnxCo1-xFe2O4 (0 ≤ x ≤ 1)) microspheres through carbonization of Mn(2+)Co(2+)Fe(3+)/carbonaceous microspheres in N2, which can be directly applied as high-performance anodes with a long cycle life for lithium storage. Furthermore, uniform hollow microspheres with a MnxCo1-xFe2O4 yolk bishell structure are obtained by annealing the above MnxCo1-xFe2O4/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g(-1) even after 500 cycles for Mn0.5Co0.5Fe2O4/carbon microspheres and 774.6 mAh g(-1) over 100 cycles for Mn0.5Co0.5Fe2O4 yolk bishell hollow microspheres at the current density of 200 mA g(-1). The present strategy not only develops a high-performance anode material with long cycle life for lithium-ion batteries but also demonstrates a novel and feasible technique for designed synthesis of transition metal oxides yolk bishell hollow microspheres with various applications.

Growth of linked silicon/carbon nanospheres on copper substrate as integrated electrodes for Li-ion batteries.

We report the growth of linked silicon/carbon (Si/C) nanospheres on Cu substrate as an integrated anode for Li-ion batteries. The Si/C nanospheres were synthesized by a catalytic chemical vapor deposition (CCVD) on Cu substrate as current collector using methyltrichlorosilane as precursor, a cheap by-product of the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry, Raman spectroscopy, nitrogen adsorption, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy. It was found that the linked Si/C nanospheres with a diameter of 400-500 nm contain Si, Cu(x)Si, and Cu nanocrystals, which are highly dispersed in the amorphous carbon nanospheres. A CCVD mechanism was tentatively proposed, in which the evaporated Cu atoms play a critical role to catalytically grown Si nanocrystals embedded within linked Si/C nanospheres. The electrochemical measurement shows that these Si/C nanospheres delivered a capacity of 998.9, 713.1, 320.6, and 817.8 mA h g(-1) at 50, 200, 800, and 50 mA g(-1) respectively after 50 cycles, much higher than that of commercial graphite anode. This is because the amorphous carbon, Cu(x)Si, and Cu in the Si/C nanospheres could buffer the volume change of Si nanocrystals during the Li insertion and extraction reactions, thus hindering the cracking or crumbling of the electrode. Furthermore, the incorporation of conductive Cu(x)Si and Cu nanocrystals and the integration of active electrode materials with Cu substrate may improve the electrical conductivity from the current collector to individual Si active particles, resulting in a remarkably enhanced reversible capacity and cycling stability. The work will be helpful in the fabrication of low cost binder-free Si/C anode materials for Li-ion batteries.