Jinsen Gao

Phosphorus and nitrogen dual-doped few-layered porous graphene: a high-performance anode material for lithium-ion batteries.

Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH4)3PO4 as N and P source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g(-1) at the current density of 50 mA g(-1)), excellent rate capability (750 mA h g(-1) at 1000 mA g(-1)), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs.

Three-dimensionally ordered macroporous Ce0.8Zr0.2O2-supported gold nanoparticles: synthesis with controllable size and super-catalytic performance for soot oxidation

A series of catalysts of three-dimensionally ordered macroporous (3DOM) Ce0.8Zr0.2O2-supported gold nanoparticles with controllable sizes were successfully synthesized by the facile method of gas bubbling-assisted membrane reduction (GBMR). All the catalysts possess well-defined 3DOM structures, which consist of interconnected networks of spherical voids, and the Au nanoparticles are well dispersed and supported on the inner wall of the uniform macropore. The relationship between Au particle sizes and the ability to adsorb and activate oxygen was characterized by means of O2-TPD and XPS. The results show that the active oxygen species (O−) and gold ions with oxidation state of Au+ are essential for soot oxidation reaction. 3DOM Au0.04/Ce0.8Zr0.2O2catalyst with Au particle size of 2–3 nm has the strong capability of adsorption and activation of oxygen. Thus, it exhibits super-catalytic activity for diesel soot oxidation, especially at low temperature. The reaction pathways of catalytic soot oxidation in the presence or absence of NO can be outlined as follows: at low temperature ( 250 °C), the catalytic activity is strongly related to the NO gas, because NO2 derived from NO oxidation is used as intermediate to catalyze soot oxidation.

Solvothermal synthesis of Pt–Pd alloys with selective shapes and their enhanced electrocatalytic activities

Pt-Pd bimetallic alloy nanostructures with highly selective morphologies such as cube, bar, flower, concave cube, and dendrite have been achieved through a facile one-pot solvothermal synthesis. The effects of shape-controllers (sodium dodecyl sulfate (SDS), ethylenediamine-tetraacetic acid disodium salt (EDTA-2Na), NaI) and solvents (water/DMF) on the morphologies were systematically investigated. The electrocatalytic activities of these Pt-Pd alloy nanostructures toward formic acid oxidation were tested. The results indicated that these alloy nanocrystals exhibited enhanced and shape-dependent electrocatalytic activity toward formic acid oxidation compared to commercial Pt black and Pt/C catalysts.

Chemical vapor deposition derived flexible graphene paper and its application as high performance anodes for lithium rechargeable batteries

We present a novel approach to fabricate flexible graphene papers using chemical vapor deposition (CVD) derived graphene. Expanded vermiculite was used as a layered template in the CVD process to produce bulk materials containing graphene sheets of the order of hundreds of microns at a gram scale. Meshes or carbon nanotubes can be introduced into the graphene sheets by template pretreating. Owing to the large sheet size, the as-obtained graphene sheets were easily fabricated into flexible graphene papers with low surface density and good conductivity, which exhibited greatly enhanced reversible capacity (1350 mA h g−1 at 50 mA g−1) and cycling performance as anodes for lithium rechargeable batteries as compared to the graphene papers fabricated using reduced graphene oxide.

High density Co3O4 nanoparticles confined in a porous graphene nanomesh network driven by an electrochemical process: ultra-high capacity and rate performance for lithium ion batteries

Here, we report a novel Co3O4–graphene hybrid electrode material with high density Co3O4 nanoparticles (NPs) in a size range of 2–3 nm confined in a few-layered porous graphene nanomesh (PGN) framework driven by an electrochemical process. Raman spectra indicate that Co species preferentially anchor on the defective sites of the PGN, which results in markedly reduced irreversible Li storage and therefore significantly enhanced coulombic efficiency. The ultra-small Co3O4 NPs provide a large surface area and a short solid-state diffusion length, which is propitious to achieving a high Li ion capacity at high rate. Also, the few-layered graphene network with high electronic conductivity not only permits easy access to the high surface area of the Co3O4 NPs for the electrolyte ions, but also serves as a reservoir for high capacity Li storage. As a result, the Co3O4–PGN composite layers deliver an ultra-high capacity (1543 mA h g−1 at 150 mA g−1) and excellent rate capability (1075 mA h g−1 at 1000 mA g−1) with good cycling stability.

Numerical Simulation of Transfer and Reaction Processes in Ethylene Furnaces

Abstract The complex transfer and reaction processes happened in ethylene furnaces were taken into consideration. A comprehensive mathematical model was developed with CFD technique based on the following knowledge: (1) basic transport equations of hydrodynamics, (2) k – ɛ turbulence model, (3) cracking reaction kinetic model developed by Wang, (4) presumed probability-density-function model for turbulent diffusion combustion, and (5) discrete ordinates method for radiative heat transfer. The simulation results showed detailed information about flow and temperature fields, heat flux distribution, and concentration distribution. They provided thorough understanding on the basic characteristics of hydrodynamic phenomena and reaction behaviour occurring in industrial ethylene furnaces. Parametric studies were carried out to investigate quantitatively the influence of burner staging, tube diameter and spacing on operation performance of ethylene furnaces. The comprehensive mathematical model and computational scheme presented here can be used as a tool for the design of ethylene furnaces.

Hierarchical Macro-meso-microporous ZSM-5 Zeolite Hollow Fibers With Highly Efficient Catalytic Cracking Capability

Zeolite fibers have attracted growing interest for a range of new applications because of their structural particularity while maintaining the intrinsic performances of the building blocks of zeolites. The fabrication of uniform zeolite fibers with tunable hierarchical porosity and further exploration of their catalytic potential are of great importance. Here, we present a versatile and facile method for the fabrication of hierarchical ZSM-5 zeolite fibers with macro-meso-microporosity by coaxial electrospinning. Due to the synergistic integration of the suitable acidity and the hierarchical porosity, high yield of propylene and excellent anti-coking stability were demonstrated on the as-prepared ZSM-5 hollow fibers in the catalytic cracking reaction of iso-butane. This work may also provide good model catalysts with uniform wall thickness and tunable porosity for studying a series of important catalytic reactions.

Enhancing the Li Storage Capacity and Initial Coulombic Efficiency for Porous Carbons by Sulfur Doping

Here, we report a new approach to synthesizing S-doped porous carbons and achieving both a high capacity and a high Coulombic efficiency in the first cycle for carbon nanostructures as anodes for Li ion batteries. S-doped porous carbons (S-PCs) were synthesized by carbonization of pitch using magnesium sulfate whiskers as both templates and S source, and a S doping up to 10.1 atom % (corresponding to 22.5 wt %) was obtained via a S doping reaction. Removal of functional groups or highly active C atoms during the S doping has led to formation of much thinner solid-electrolyte interface layer and hence significantly enhanced the Coulombic efficiency in the first cycle from 39.6% (for the undoped porous carbon) to 81.0%. The Li storage capacity of the S-PCs is up to 1781 mA h g(-1) at the current density of 50 mA g(-1), more than doubling that of the undoped porous carbon. Due to the enhanced conductivity, the hierarchically porous structure and the excellent stability, the S-PC anodes exhibit excellent rate capability and reliable cycling stability. Our results indicate that S doping can efficiently promote the Li storage capacity and reduce the irreversible Li combination for carbon nanostructures.

Pd Cluster Nanowires as Highly Efficient Catalysts for Selective Hydrogenation Reactions

Palladium is a key catalyst invaluable to many industrial processes and fine-chemical synthesis. Although recent progress has allowed the synthesis of Pd nanoparticles with various shapes by using different techniques, the facile synthesis of Pd nanocrystals and turning them into a highly active, selective, and stable catalyst systems still remain challenging. Herein, we report the highly selective one-pot synthesis of monodisperse Pd cluster nanowires in aqueous solution; these consist of interconnected nanoparticles and may serve as highly active catalysts because of the enrichment of high index facets on the surface, including {443}, {331}, and {221} steps. For the first time, carbon nanotube and γ-Al(2)O(3) immobilized Pd cluster nanowires showed highly enhanced catalytic performance in the liquid-phase selective hydrogenation of cinnamaldehyde and gas-phase hydrogenation of 1,3butadiene relative to immobilized Pd icosahedra and nanocubes, as well as commercial Pd catalysts.

Solids contents, properties and molecular structures of asphaltenes from different oilsands

Abstract As the Canadian supply of light crudes has diminished in recent years, refineries have necessarily been required to deal with difficult to process oilsands bitumens and heavy oils. Bitumen in particular exhibits unique behavior during upgrading; nearly 50% (w/w) of the feedstock is an intractable residuum. The fast catalyst deactivation and high coke forming propensity displayed by this feedstock have been attributed to the asphaltene and associated solids contents of extracted bitumen. The variability of these intractable components in bitumens from mined and in-situ Athabasca oilsands were examined and compared with bitumens from Nigerian and Utah oilsands. Except for the in-situ bitumen, all of the samples were found to contain significant amounts of fine solids. Unexpectedly, the in-situ bitumen also contained the least amount of asphaltene and the highest amount of the intractable heteroatoms nickel and vanadium. Solids-free asphaltene samples were characterized by several complementary analytical techniques to determine the relative abundance of different carbon types and to calculate their average three-dimensional molecular conformations. Even though the parent bitumens came from geographically diverse sources the corresponding asphaltene fractions had similar structures. Each sample comprised basic units, or ‘cores’, of condensed aromatic rings connected by bridges. The main differences relate to the number and complexity of the basic units.