Preparation and Characterization of PtRu Nanoparticles Supported on Nitrogen-Doped Porous Carbon for Electrooxidation of Methanol

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt1Ru1/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt1Ru1/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs

Crystalline Carbon Hollow Spheres, Crystalline Carbon−SnO₂ Hollow Spheres, and Crystalline SnO₂ Hollow Spheres: Synthesis and Performance in Reversible Li-Ion Storage

A few types of crystalline hollow structures, crystalline carbon hollow spheres (750 nm), crystalline carbon hollow spheres with encapsulated or decorated 1−3 nm SnO2 nanoparticles, and crystalline SnO2 hollow spheres (200−300 nm) synthesized by various methods, have been evaluated for reversible Li+ storage. The experimental results showed noticeable improvements in a number of performance areas such as specific capacity, rate capability, and cyclability. The improvements could be attributed to a high degree of crystallinity, which increases the electronic conductivity, and the facile transport of Li ions in a hollow shell with nanoscale thickness, which significantly shortens the solid-state diffusion length

Yolk Bishell Mn_<i>x</i>Co_1–<i>x</i>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 (Mn_<i>x</i>Co_1–<i>x</i>Fe₂O₄ (0 ≤ <i>x</i> ≤ 1)) microspheres through carbonization of Mn²⁺Co²⁺Fe³⁺/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 Mn_<i>x</i>Co_1–<i>x</i>Fe₂O₄ yolk bishell structure are obtained by annealing the above Mn_<i>x</i>Co_1–<i>x</i>Fe₂O₄/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g^–1 even after 500 cycles for Mn_0.5Co_0.5Fe₂O₄/carbon microspheres and 774.6 mAh g^–1 over 100 cycles for Mn_0.5Co_0.5Fe₂O₄ 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

Thermally Reduced Ruthenium Nanoparticles as a Highly Active Heterogeneous Catalyst for Hydrogenation of Monoaromatics

We report here a thermal reduction method for preparing Ru catalysts supported on a carbon substrate. Mesoporous SBA-15 silica, surface-carbon-coated SBA-15, templated mesoporous carbon, activated carbon, and carbon black with different pore structures and compositions were employed as catalyst supports to explore the versatility of the thermal reduction method. Nitrogen adsorption, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, thermogravimetric analysis, and X-ray absorption near-edge structure techniques were used to characterize the samples. It was observed that carbon species that could thermally reduce Ru species at high temperatures played a vital role in the reduction process. Ru nanoparticles supported on various carbon-based substrates exhibited good dispersion with an appropriate particle size, high crystallinity, strong resistance against oxidative atmosphere, less leaching, lack of aggregation, and avoidance of pore blocking. As such, these catalysts display a remarkably high catalytic activity and stability in the hydrogenation of benzene and toluene (up to 3−24-fold compared with Ru catalysts prepared by traditional methods). It is believed that the excellent catalytic performance of the thermally reduced Ru nanoparticles is related to the intimate interfacial contact between the Ru nanoparticles and the carbon support

Thermodynamic Analysis of the Key Reactions in Synthesizing Inorganic Silicon Compounds or Products

Inorganic silicon compounds or products, such as silicon oxides (SiO2), metallurgical silicon (m-Si), silicon carbide (SiC), silicon halides (such as SiHnCl4–n, n = 0–4 or SiXn, X = F, n = 2; X = Br, n = 4), silicon hydrides (SiH4 and Si2H6), nitrogen compounds (Si3N4), and the others (Si2Cl6 and Si2OCl6), have been remarkably developed in the past years. Silicon chemistry involves various important reactions, such as the hydrochlorination of silicon to chlorosilanes, hydrogenation of silicon tetrachloride in the presence of silicon to trichlorosilane, reduction of quartz sand by carbon to silicon, silicon carbide, and silicon monoxide (also known as the Acheson process). Understanding the basic thermodynamics of these reactions is essential for optimizing the related reaction conditions and catalyst development (if any). This work comprehensively investigated the thermodynamics of silicon-related reactions by using the Gibbs energy minimization method. The effects of the reaction conditions, including temperature, pressure, and ratio of reactants, on the conversion of reactants and the product selectivity, are quantitatively calculated in detail. Optimal operational conditions for each reaction are suggested. This work provides a comprehensive reference for reaction thermodynamics for silicon-related key industrial reactions

Ni–MnO_<i>x</i> Catalysts Supported on Al₂O₃‑Modified Si Waste with Outstanding CO Methanation Catalytic Performance

A series of MnO_<i>x</i>-promoted Ni catalysts supported on Si waste contact mass (W) modified by Al₂O₃ were successfully prepared by the deposition–precipitation method for CO methanation. Compared with the Ni catalysts directly supported on W, Ni/Al₂O₃–Si and MnO_<i>x</i>-promoted Ni–MnO_<i>x</i>/Al₂O₃–Si catalysts exhibited much better catalytic performance for CO methanation, particularly the latter, which exhibited the least decrease in CO conversion (1%) and lowest carbon deposit (0.3 wt %) in a 110 h lifetime test. The structural characterizations showed the highest Ni dispersion and highest oxygen vacancy concentration in the Ni–MnO_<i>x</i>/Al₂O₃–Si catalyst. The added Al₂O₃ improves the dispersion of Ni, and the MnO_<i>x</i> promoter can restrain the sintering and aggregation of Ni particles during the process of reduction and reaction at high temperatures and provides more oxygen vacancies, which is conducive to the removal of carbonaceous species on the catalyst surface for anticoking

Pt Nanoparticles Supported on Nitrogen-Doped Porous Carbon Nanospheres as an Electrocatalyst for Fuel Cells

Nitrogen-doped porous carbon nanospheres (PCNs) with a high surface area were prepared by chemical activation of nonporous carbon nanospheres (CNs). CNs were obtained via carbonization of polypyrrole nanospheres (PNs) that were synthesized by ultrasonic polymerization of pyrrole. The catalysts Pt/PCN, Pt/CN, and Pt/PN were prepared by depositing Pt nanoparticles on supports PCNs, CNs, and PNs, respectively, using ethylene glycol chemical reduction. Nitrogen adsorption, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy were employed to characterize samples. It was found that after chemical activation using KOH, PCNs containing N functional groups (mainly N-6 and N-Q) possessed a microporous structure with a high surface area of 1010 m2/g and a particle size of less than 100 nm. The electrochemical properties of samples Pt/PCN, Pt/CN, and Pt/PN, together with commercial catalysts E-TEK (40 wt % Pt loading), were comparatively investigated in methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) for fuel cells. The results showed that the catalytic activity of Pt/PN toward both reactions at room temperature is almost negligible possibly due to the poor conductivity of support PNs proven by impedance spectroscopy, in contrast with some literature reports. Compared to Pt/CN and E-TEK catalyst, Pt/PCN revealed an enhanced mass activity in ORR and MOR because of the high dispersion of small Pt nanoparticles, the presence of nitrogen species, and developed microporous structure of support PCNs

Thermodynamic Analysis of the Main Reactions Involved in the Synthesis of Organosilanes

Organosilicon compounds or products, including alkoxysilanes [HSi­(OR)3, Si­(OR)4, RSiH­(OR)2, and RSi­(OR)3, where R is methyl (CH3) or ethyl (C2H5)], organohydrosilanes [e.g., CH3SiHCl2, (CH3)2SiHCl, and CH3SiCl3], organosilicon alcohol [(CH3)3SiOH], and organoacyloxysilane [CH3Si­(OCOCH3)3], have been extensively studied and developed in recent years. Understanding the basic thermodynamics of the synthetic processes of these organosilicon compounds is necessary to optimize the associated reaction conditions and catalyst development, if any. Therefore, we have conducted a comprehensive study of the thermodynamics of organosilicon-related reactions using the Gibbs energy minimization method. The study evaluates the effects of reaction conditions, such as temperature, pressure, and reactant ratios, on the reactant conversion and product selectivity. The results show that the optimum thermodynamic conditions for the preparation of alkoxysilanes were low temperature, atmospheric pressure, and stoichiometric feed ratio. Meanwhile, other organosilicon compounds favor high temperatures and atmospheric pressure. The research proposes the optimum operating conditions for each reaction and provides a comprehensive reference for the thermodynamics of organosilicon synthesis reactions

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 Cu2O@Fe(OH)x nanorattles and Fe(OH)x cages with various shapes and dimensions by template-engaged redox etching of shape-controlled Cu2O crystals. The composition can be readily modulated at different structural levels to generate other interesting structures such as Cu2O@Fe2O3 and Cu@Fe3O4 rattles, as well as Fe2O3 and Fe3O4 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 MnOx based hollow structures

Hierarchically Ordered Macro−Mesoporous TiO₂−Graphene Composite Films: Improved Mass Transfer, Reduced Charge Recombination, and Their Enhanced Photocatalytic Activities

Hierarchically ordered macro−mesoporous titania films have been produced through a confinement self-assembly method within the regular voids of a colloidal crystal with three-dimensional periodicity. Furthermore, graphene as an excellent electron-accepting and electron-transporting material has been incorporated into the hierarchically ordered macro−mesoporous titania frameworks by in situ reduction of graphene oxide added in the self-assembly system. Incorporation of interconnected macropores in mesoporous films improves the mass transport through the film, reduces the length of the mesopore channel, and increases the accessible surface area of the thin film, whereas the introduction of graphene effectively suppresses the charge recombination. Therefore, the significant enhancement of photocatalytic activity for degrading the methyl blue has been achieved. The apparent rate constants for macro−mesoporous titania films without and with graphene are up to 0.045 and 0.071 min−1, respectively, almost 11 and 17 times higher than that for pure mesoporous titania films (0.0041 min−1)