Asymmetric Hydrogenation of Ethyl Pyruvate using Layered Double Hydroxides–Supported Nano Noble Metal Catalysts

Layered double hydroxide (LDH)–supported nano noble metal heterogeneous catalysts are synthesized by ion exchange of K₂PtCl₆, Na₂PdCl₄ and impregnation of RhCl₃ ^.3H₂O followed by reduction with H₂. The LDH–Rh, Pt, and Pd catalysts are tested in the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate with very good yields and enantiomeric excess's (e.e.'s) of up to 72% were obtained with Pt. The catalyst was recovered and reused for several cycles with consistent activity.     

Adsorption Site Regulation to Guide Atomic Design of Ni–Ga Catalysts for Acetylene Semi-Hydrogenation

Atomic regulation of metal catalysts has emerged as an intriguing yet challenging strategy to boost product selectivity. Here, we report a density functional theory-guided atomic design strategy for the fabrication of a NiGa intermetallic catalyst with completely isolated Ni sites to optimize acetylene semi-hydrogenation processes. Such Ni sites show not only preferential acetylene π-adsorption, but also enhanced ethylene desorption. The characteristics of the Ni sites are confirmed by multiple characterization techniques, including aberration-corrected high-resolution scanning transmission electron microscopy and X-ray absorption spectrometry measurements. The superior performance is also confirmed experimentally against a Ni₅Ga₃ intermetallic catalyst with partially isolated Ni sites and against a Ni catalyst with multi-atomic ensemble Ni sites. Accordingly, the NiGa intermetallic catalyst with the completely isolated Ni sites shows significantly enhanced selectivity to ethylene and suppressed coke formation.     

Bayesian Optimization-guided Discovery of High-performance Methane Combustion Catalysts based on Multi-component PtPd@CeZrOx Core–Shell Nanospheres

Formula regulation of multi-component catalysts by manual search is undoubtedly a time-consuming task, which has severely impeded the development efficiency of high-performance catalysts. In this work, PtPd@CeZrO_x core–shell nanospheres, as a successful case study, is explicitly demonstrated how Bayesian optimization (BO) accelerates the discovery of methane combustion catalysts with the optimal formula ratio (the Pt/Pd mole ratio ranges from 1/2.33–1/9.09, and Ce/Zr from 1/0.22–1/0.35), which directly results in a lower conversion temperature (T₅₀ approaching to 330 °C) than ones reported hitherto. Consequently, the best sample obtained could be efficiently developed after two rounds of iterations, containing only 18 experiments in all that is far less than the common human workload via the traditional trial-and-error search for optimal compositions. Further, this BO-based machine learning strategy can be straightforward extended to serve the autonomous discovery in multi-component material systems, for other desired properties, showing promising opportunities to practical applications in future.     

Syngas Production by Methane Reforming with Carbon Dioxide on Noble Metal Catalysts

A series of noble metal catalysts (Ru, Rh, Ir, Pt, and Pd) supported on alumina-stabilized magnesia (Spinel) were used to produce syngas by methane reforming with carbon dioxide. The synthesized catalysts were characterized using BET, TPR, TPO, TPH, and H2S chemisorption techniques. The activity results showed high activity and stability for the Ru and Rh catalysts. The TPO and TPH analyses indicated that the main reason for lower activity and stability of the Pd catalyst was the formation of the less reactive deposited carbon and sintering of the catalyst.     

Photoinduced Electron Transfer from the Inorganic Core to the Organic Shell of Hybrid Core–Shell Nanoparticles: Impedance Spectroscopy

In hybrid core–shell nanoparticles with inorganic nanocrystals in the core and organic molecules in the shell, photoinduced electron transfer occurs from the core to the shell. This leads to exciton dissociation through an ultrafast electron-transfer process that results in charge separation and finally photocurrent in the external circuit in devices based on such core–shell nanoparticles. In this work, we have fabricated and characterized sandwiched devices based on a series of core–shell systems. From impedance spectroscopy, we have observed that photoinduced charge separation in core–shell systems is associated with a decrease in the device resistance and an increase in the dielectric constant of the active material. In the series of core–shell systems, we have observed a one-to-one correlation between the photoinduced electron-transfer process and the changes in resistive and dielectric parameters upon illumination.     

Surface-Deactivated Core–Shell Metal–Organic Framework by Simple Ligand Exchange for Enhanced Size Discrimination in Aerobic Oxidation of Alcohols

Metal–organic frameworks (MOFs) are an attractive catalyst support for stable immobilization of the active sites in their scaffold due to the high tunability of organic ligands. The active site-functionalized ligands can be easily employed to construct MOFs as porous heterogeneous catalysts. However, the existence of active sites on the external surfaces as well as internal pores of MOFs seriously impedes the selective reaction in the pore. Herein, through a simple post-synthetic ligand exchange (PSE) method we synthesized surface-deactivated (only core-active) core–shell-type MOF catalysts, which contain 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) groups on the ligand as active sites for aerobic oxidation of alcohols. The porous but catalytically inactive shell ensured the size-selective permeability by sieving effects and induced all reactions to take place in the pores of the catalytically active core. Because PSE is a facile and universal approach, this can be rapidly applied to a variety of MOF-based catalysts for enhancing reaction selectivity.     

Utility of Core–Shell Nanomaterials in the Catalytic Transformations of Renewable Substrates

In recent years, core–shell nano-catalysts have received increasing attention due to their tunable properties and broad applications in catalysis. Control of the two components of these materials allows their catalytic properties to be tuned to various sustainable processes in synthetic and energy-related applications. This Concept article describes recent state-of-the-art core–shell materials and their application as heterogeneous catalysts for a range of sustainable catalytic transformations, focusing on two important classes of renewable substrates, CO₂ and biomass. In the discussion, emphasis is directed to the role of the constituent parts of the core–shell structure and how they can be manipulated to enhance activity.     

High Carbon-Resistance Ni@CeO<Subscript>2</Subscript> Core–Shell Catalysts for Dry Reforming of Methane

Ni@CeO₂ core–shell catalysts were synthesized via a facile surfactant-assisted hydrothermal method and their catalytic performance in the dry reforming of methane (DRM) reaction was evaluated. A variety of techniques including XRD, N₂ adsorption–desorption, SEM, TEM, TPO, TGA were employed to characterize the prepared or spent catalysts. The encapsulation by the CeO₂ shell, on one side, can restrict the sintering and growth of Ni nanoparticles under harsh reaction conditions. On the other side, compared to the conventional shell material of SiO₂, CeO₂ can provide more lattice oxygens and vacancies, which is helpful to suppress coke deposition. Consequently, the Ni@CeO₂ core–shell catalysts exhibited better catalytic activity and stability in the DRM reaction with respect to the referenced Ni@SiO₂ core–shell catalysts and Ni/CeO₂ supported catalysts.     

Sequential Chemistry Toward Core–Shell Structured Metal Sulfides as Stable and Highly Efficient Visible-Light Photocatalysts

A universal sequential synthesis strategy in aqueous solution is presented for highly uniform core–shell structured photocatalysts, which consist of a metal sulfide light absorber core and a metal sulfide co-catalyst shell. We show that the sequential chemistry can drive the formation of unique core–shell structures controlled by the constant of solubility product of metal sulfides. A variety of metal sulfide core–shell structures have been demonstrated, including CdS@CoS_x, CdS@MnS_x, CdS@NiS_x, CdS@ZnS_x, CuS@CdS, and more complexed CdS@ZnS_x@CoS_x. The obtained strawberry-like CdS@CoS_x core–shell structures exhibit a high photocatalytic H₂ production activity of 3.92 mmol h⁻¹ and an impressive apparent quantum efficiency of 67.3 % at 420 nm, which is much better than that of pure CdS nanoballs (0.28 mmol h⁻¹), CdS/CoS_x composites (0.57 mmol h⁻¹), and 5 %wt Pt-loaded CdS photocatalysts (1.84 mmol h⁻¹).     

Constructions of Noble Metal Nanocrystals with Specific Crystal Facets and High Surface Area北大核心CSCD

Noble metal nanocrystals (NCs) have widespread applications in catalysis.Their catalytic performances are strongly related to the surface structures while the atomic utilization efficiency of noble metal is considerably correlated with the surface area.Thus, advantages of both specific surface structure and large surface area are highly required to show off simultaneously so as to optimize the catalytic performance and decrease the usage of noble metal.However, it seems that the two advantages are incom¬patible with each other in one NC since it is difficult for small NCs to keep their specific facets, while NCs with specific surface structure usually crystallize into the large size leading to small surface area.The construction of noble metal NCs with specific sur¬face area and large surface area is a great challenge.This review introduces the strategies to prepare noble metal NCs integrated with both specific surface facets and high surface area from the controllable synthesis of morphologies.The current researches in this field are summarized by introducing specific cases.Subsequently, typical applications in catalysis are presented to demonstrate the advantages of noble metal NCs with both specific facets and high surface area.Finally, the perspectives concerning about the development tendency in this field are put forward. © 2018 Journal of Electrochemistry. All rights reserved.     

Research Progress in Hydrogen Evolution Low Noble/Non-Precious Metal Catalysts of Water Electrolysis北大核心CSCD

Hydrogen energy technology with hydrogen as an energy carrier is gaining more and more attention due to its cleanliness and high energy density.Hydrogen fuel cell vehicles have been listed as one of the ultimate energy technologies in the 21st century.Among them, sustainable hydrogen production technology is a necessary prerequisite for the future development of hydrogen energy economy.Electrolyzed water technology driven by renewable resources represents an important way to support the sustainable development of hydrogen energy economy.The development and utilization of high activity, low cost hydrogen evolution catalysts is a key factor in improving the efficiency and reducing the cost of water electrolysis technology.This paper mainly introduces the recent research progress of hydrogen evolution catalysts including low platinum catalysts and non-platinum transition metal catalysts such as metal sulfides metal phosphides, metal selenides, etc; catalytic properties, synthesis methods, and structure-catalytic properties.Finally, the advantages and challenges of water electrolysis low platinum and non-platinum transition metal catalysts in the future development are prospected. © 2018 Chinese Chemical Society. All rights reserved.     

Understanding the Activity of Co-N4−xCx in Atomic Metal Catalysts for Oxygen Reduction Catalysis

Atomic metal catalysis (AMC) provides an effective way to enhance activity for the oxygen reduction reaction (ORR). Cobalt anchored on nitrogen-doped carbon materials have been extensively reported. The carbon-hosted Co-N₄ structure was widely considered as the active site; however, it is very rare to investigate the activity of Co partially coordinated with N, for example, Co-N_4−xC_x. Herein, the activity of Co-N_4−xC_x with tunable coordination environment is investigated as the active sites for ORR catalysis. The defect (di-vacancies) on carbon is essential for the formation of Co-N_4−xC_x. N species play two important roles in promoting the intrinsic activity of atomic metal catalyst: N coordinated with Co to manipulate the reactivity by modification of electronic distribution and N helped to trap more Co to increase the number of active sites.     

Preparation and Chromatographic Features of Fibrous Core–Shell HPLC Packing Material

In this study, fibrous core–shell silica particles were successfully synthesized via a one-step oil–water biphase stratification coating strategy. The core–shell silica particles were composed of 3-µm non-pore silica cores and thin shells (50–100 nm), which have radial-like direct channels and a large pore size (19.89 nm). The fibrous core–shell silica particles were further modified by n-octadecyltrichlorosilane and used as stationary-phase media in high-performance liquid chromatography (HPLC). The chromatographic properties of the particles were systematically studied in small-molecule and protein separation processes. The results showed that the back pressure was as low as 8.5 MPa under the 1.0-mL min^?1 flow velocity. Furthermore, fibrous core–shell silica particles with an 80-nm shell were used for separating seven small molecules within 10 min and six proteins within 6 min. This work demonstrates that the fibrous core–shell silica particles could be used as an HPLC stationary phase with good performance and low back pressure, and that they have great potential for application to HPLC separation in the future.     

Core–Shell Composites Based on Partially Oxidized Blend of Detonation Synthesis Nanodiamonds

Russian Journal of Applied Chemistry - The results of a study on the production of graphite–diamond nanocompositions by partial oxidation of a detonation synthesis blend in aqueous solutions...     

Co3O4@Cu-Based Conductive Metal–Organic Framework Core–Shell Nanowire Electrocatalysts Enable Efficient Low-Overall-Potential Water Splitting

In the work reported herein, the electrocatalytic properties of Co₃O₄ in hydrogen and oxygen evolution reactions have been significantly enhanced by coating a shell layer of a copper-based metal–organic framework on Co₃O₄ porous nanowire arrays and using the products as high-performance bifunctional electrocatalysts for overall water splitting. The coating of the copper-based metal–organic framework resulted in the hybridization of the copper-embedded protective carbon shell layer with Co₃O₄ to create a strong Cu−O−Co bonding interaction for efficient hydrogen adsorption. The hybridization also led to electronically induced oxygen defects and nitrogen doping to effectively enhance the electrical conductivity of Co₃O₄. The optimal as-prepared core–shell hybrid material displayed excellent overall-water-splitting catalytic activity that required overall voltages of 1.45 and 1.57 V to reach onset and a current density of 10 mA cm⁻², respectively. This is the first report to highlight the relevance of hybridizing MOF-based co-catalysts to boost the electrocatalytic performance of nonprecious transition-metal oxides.     

Synthesis and Optical Properties of Fe@Au,Ni@Au Bimetallic Core–Shell Nanoparticles

Fe@Au and Ni@Au core–shell nanoparticles (NPs) were synthesized by liquid-phase reduction of iron and nickel compounds by sodium borohydride in an aqueous medium. Transmission electron microscopy, X-ray powder diffraction, and spectrophotometry were used to confirm the structure of the NPs and to determine their shape and the average core and shell size.     

Polymerization of α-Hydroxyacetylenes by Transition Metal Catalysts

Abstract

α-Hydroxyacetylenes (2-propyn-1-ol, DL-3-butyn-2-ol, 1-octyn-3-ol, 2-phenyl-3-butyn-2-ol) with a hydroxy functional group were polymerized by various Mo- and W-based catalysts. In general, the catalytic activities of Mo-based catalysts were greater than those of W-based catalysts for these polymerizations. In the polymerization of 2-propyn-l-ol, MoCl₅ alone and the MoCl₅-EtAlCl₂ catalyst system gave a quantitative yield of polymer. In the polymerization of 2-propyn-l-ol and its homologues by Mo-based catalysts, the polymer yield decreased as the bulkiness of the substituent increased. On the other hand, the polymer yield increased as the bulkiness of the substituent increased in WCl₆-EtAlCl₂-catalyzed polymerization. Polymers with a bulkier substituent showed better solubility in organic solvents than those without a substituent [e.g., poly (2-propyn-l-ol)]. The structures of the resulting polymers were characterized by various instrumental methods such as ¹H- and ¹³C-NMR, IR, and UV-visible spectroscopies. Thermogravimetric analyses and thermal transitions of the resulting polymers were also studied.     

Catalytic Oxidation of Cyclohexene by Dendrimer-bond Metal Catalysts

Since Tomalia and Dovornic discussed the promising outlook of surface-functionalized dendrimer catalysts in 1994, [1] dendritic catalysts have been proposed to many kinds of catalysis. These well-defined macromolecular structures enable the construction of precisely controlled catalyst structures. The large number of the peripheral functionalities enhanced their activity in many processes. [2,3]We report herein a new method of using the dendritic catalysts in the oxidation of cyclohexene. The…     

Microwave-Assisted Synthesis of ZnO–rGO Core–Shell Nanorod Hybrids with Photo- and Electro-Catalytic Activity

The unique two-dimensional structure and surface chemistry of reduced graphene oxide (rGO) along with its high electrical conductivity can be exploited to modify the electrochemical properties of ZnO nanoparticles (NPs). ZnO–rGO nanohybrids can be engineered in a simple new two-step synthesis, which is both fast and energy-efficient. The resulting hybrid materials show excellent electrocatalytic and photocatalytic activity. The structure and composition of the as-prepared bare ZnO nanorods (NRs) and the ZnO–rGO hybrids have been extensively characterised and the optical properties subsequently studied by UV/Vis spectroscopy and photoluminescence (PL) spectroscopy (including decay lifetime measurements). The photocatalytic degradation of Rhodamine B (RhB) dye is enhanced using the ZnO–rGO hybrids as compared to bare ZnO NRs. Furthermore, potentiometry comparing ZnO and ZnO–rGO electrodes reveals a featureless capacitive background for an Ar-saturated solution whereas for an O₂-saturated solution a well-defined redox peak was observed using both electrodes. The change in reduction potential and significant increase in current density demonstrates that the hybrid core–shell NRs possess remarkable electrocatalytic activity for the oxygen reduction reaction (ORR) as compared to NRs of ZnO alone.     

Synthesis of CuInS2@CdS Core‐Shell Nanocrystals

CuInS₂@CdS core‐shell nanocrystals were prepared in a wet chemical process. Transmission electron microscope (TEM), x‐ray energy dispersive spectroscopy (EDAX), x‐ray diffraction (XRD), absorption, and photoluminescence (PL) spectra were used to confirm the formation of the CuInS₂@CdS core‐shell structure. The growth of CdS shell not only increased the PL intensity, but also restrained the transformation of CuInS₂ from nanoparticles to nanorods after annealing, which was attributed to an effective chemical passivation of the CuInS₂ core by the CdS shell.