Highly dispersed Co nanoparticles with proper interaction with mesoporous support are benefit for the suppression of self-aggregation, which enhances its Fischer-Tropsch synthesis (FTs) activity. However, construct such Co based supported catalysts with high activity and stability in FTs by conventional mesoporous support, especially the common used mesoporous SiO2, has proven challenging due to their undesirable hydrothermal stability and poor reducibility. Herein, we developed a unique core@double-shell Co@SiO2@C structure with optimized interface of the mesoporous catalyst by introducing graphitic carbon layer which can weaken the interaction between metallic Co and silica. Transmission electron microscopy (TEM) images, together with Nitrogen adsorption-desorption characterization result, proved the well-defined core@double-shell structure of graphitic carbon modified catalyst. The Co@SiO2@C-2 material produced after optimizing the calcination temperature to 600 °C process large surface area and pore volume, and show higher CO conversion (62.2%) and C5+ selectivity (62.2%) than Co3O4@SiO2 in a period of 100 h. The significant improvement in the FTS performance of Co@SiO2@C is not only attributed to a good synergistic effect by a combination of the Co dispersion and reducibility. The unique core@double-shell structure with graphitic carbon modified interior pore-walls also contributes to the formation of heavy hydrocarbon, as well as the protecting with the metallic Co particles away from oxidation and aggregation.Download high-res image (88KB)Download full-size image

Biorenewable lignin has been used as a precursor to produce varieties of carbon materials. However, up to now, it has not been easy to obtain graphitic carbon-encapsulated metal materials without a high-temperature process. Here, we demonstrate an antiprogrammed temperature pyrolysis route for the fabrication of iron encapsulated in thin-walled graphitic layers with a low temperature. The industrially available lignin was used as a biorenewable carbon source, and ferric nitrates were used as metal sources. We found that the pyrolysis process during carbonization is a critical factor to obtain thin-walled graphitic carbon-encapsulated iron materials. When the pyrolysis process is adjusted, the size of iron particles is readily tunable, and more importantly, the iron particles are wrapped in one to four layers of graphitic carbon. The thin-walled graphitic carbon-encapsulated iron material from biorenewable lignin sources is a good candidate for Fischer–Tropsch synthesis to lower olefins catalyst.Keywords: Fischer−Tropsch; Graphitic carbon; Lignin; Lower olefins; Nanomaterials;

Novel Co@C core–shell nanoparticles were prepared by a straightforward low-temperature carbonization process. The industrially available lignin was used as a low-cost biorenewable carbon source for the first time. The products were characterized by X-ray diffraction, energy-dispersive X-ray spectrometry, transmission electron microscopy, nitrogen adsorption–desorption, and Raman spectrum. The results showed that the synthesized Co@C catalysts had a well-defined core–shell structure with a moderate degree of graphitization, and the metal Co nanoparticles with the sizes of 20–150 nm were wrapped by several layers of graphitic carbon. This unique core–shell structure is useful in a Fischer–Tropsch reaction since it can provide high adsorption space and the graphite carbon layer defects are beneficial for H2 dissociative adsorption. Furthermore, the shell of graphitic carbon layers could restrict the aggregation of the cobalt nanoparticles during the activation and reaction processes. Fischer–Tropsch synthesis results showed that the Co@C core–shell catalysts had a high catalytic performance with the highest C5+ selectivity up to 56.8%, which is much higher compared with the traditional Co/AC catalyst (46.2%).Keywords: Carbon materials; Core−shell structure; Fischer−Tropsch synthesis; Nanoparticles

•Saturated adsorption of CO on Aun+ measured by mass spectrometry.•Abrupt changes in CO adsorption after coadsorption of single H2O is observed.•CO adsorption rate on Au6+ increases ten fold in the presence of water vapor.•DFT calculations reveal the presence of dynamic fluxionality that explains data.•Binding energy calculations explain absence of adsorbed H2O in final CO complex.This paper presents mass spectrometry measurements of the saturated adsorption of CO in the presence of coadsorbed H2O on gas phase gold cluster cations, Aun+, n = 3–20, stored in a quadrupole ion trap. Initial mass spectra obtained at 150 K for specific cluster ion sizes as a function of CO pressure and reaction time, indicate increased CO saturation levels correlated with the coadsorption of background H2O vapor. Subsequent to these low temperature experiments, measurements were made of CO and H2O coadsorbed on Au6+ as a function of reaction time at 300 K. These mass spectra indicate that the reaction rate at constant CO pressure increases by an order of magnitude for a constant H2O pressure. First-principles density-functional theory calculations in conjunction with the above measurements allowed identification of energy barriers that control dynamic structural fluxionality between adsorption complexes that depends strongly on preadsorbed water. The calculations revealed that in the presence of H2O the energy barrier for the transition state between ground-state triangular and the incomplete hexagonal isomers of the [Au6(CO)3(H2O)2]+ complex is reduced to ∼0 eV and the exothermicity is increased by 0.43 eV. The theoretical results also identified kinetic pathways exhibiting a transition of the incomplete hexagonal isomer of [Au6(ih)(CO)3(H2O)2]+ to the final saturated complex, Au6(ih)(CO)4+. The energetics and kinetic pathway calculations are consistent with increased formation rates of Au6(CO)4+ as observed in mass spectra. The insights gained from these theoretical results not only explain measurements of the CO saturated adsorption on Au6+ in the presence of water, but also assist in rationalizing coadsorption results obtained over the broader range of cluster size at 150 K.

Hierarchically porous titanium dioxide/graphitic carbon microspheres (xTiO2/GCM, x = 0, 10.0, 20.0, 30.0 and 40.0) are synthesized for the first time by a simple colloidal crystal templating method. The properties of the samples are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis techniques. SEM images show that all the samples have similar particulate morphologies and that the particle sizes are about 1 μm. It is observed that the amount of acetone solvent used greatly influenced the morphology of the composites. The obtained TiO2/GCM composite microspheres possess hierarchical porosity with a large specific surface area, high metallic compound content, and graphitic carbon frameworks. Employing these characteristics and advantages, the as-prepared hierarchical porous TiO2/graphitic carbon microsphere samples were used to fabricate lithium ion batteries (LIBs) as the active anode materials and their corresponding lithium ion insertion/extraction performance is evaluated. The resultant LIBs of the TiO2/GCM composites possess a more stable cyclic performance, larger reversible capacity, and better rate capability, compared with that of the graphitic carbon microspheres. Sample 20TiO2/GCM exhibited a higher specific capacity and better cycling performance and rate capability than other samples.

•Y-doped Li[Li0.20Mn0.534Ni0.133Co0.133]O2 samples were prepared through partially substitute cobalt with yttrium by coprecipitation method.•The high cycling and rate performance of Li[Li0.20Mn0.534 Ni0.133Co0.133-x Yx]O2 (0 ≤x ≤ 0.0665) cathode was first reported.•Li[Li0.20Mn0.534 Ni0.133Co0.1265 Y0.0065]O2 shows the best cycling performance.To improve the cycling performance and rate capability of the promising layered lithium-rich cathode materials, we substitute Co3+ in Li[Li0.20Mn0.534Ni0.133 Co0.133]O2 with unusually large Y3+ during coprecipitation and synthesize Li[Li0.20Mn0.534 Ni0.133Co0.133-x Yx]O2 (0 ≤ x ≤ 0.0665). The influences of yttrium content on the electrochemical properties of the lithium-rich materials are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS) techniques. The charge–discharge cycling tests suggest that after heating at 1223 K in air for 10 h, the material with x = 0.00665 deliver a high discharge capacity of 349.7 mAhg−1 after 1 cycle and 225.2 mAhg−1 after 80 cycles with a current rate of 0.1 C between 2.0 and 4.6 V vs. Li/Li+. Electrochemical impedance spectroscopy indicates that Li[Li0.20Mn0.534Ni0.133Co0.133-xYx]O2 electrode has lower impedance during cycling. The higher capacity retention and high-rate capability of yttrium-substituted materials can be ascribed to the expanded Li+ diffusing channels in the layered structure, lower surface film resistance and lower charge transfer resistance of the electrode during cycling.

Highlights•Ca-doped Li4Ti5O12 samples were prepared by a simple solid-state method.•The high-rate performance of Li4−xCaxTi5O12 (0 ≤ x ≤ 0.2) anode was first reported.•Li3.9Ca0.1Ti5O12 shows the best high-rate performance.Ca-doped lithium titanates with the formula of Li4−xCaxTi5O12 (x = 0, 0.05, 0.1, 0.15, 0.2) were synthesized as anode materials by a simple solid-state reaction in an air atmosphere. The phase structure, morphologies and electrochemical properties of the prepared powders were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV), respectively. XRD revealed that the Ca-doping caused no change on the phase structure and highly crystalline Li4−xCaxTi5O12 (0 ≤ x ≤ 0.2) powders without any impurity were obtained. SEM images showed that all samples had similar particulate morphologies and the particle size distribution was in the range of 1–2 μm. It was observed that Ca-doped lithium titanates employed as the anode materials of lithium-ion batteries delivered excellent electrochemical performances, and sample Li3.9Ca0.1Ti5O12 exhibited a higher specific capacity, better cycling performance and rate capability than other samples. The Li3.9Ca0.1Ti5O12 material showed discharge capacities of 162.4 mAh g−1, 148.8 mAh g−1 and 138.7 mAh g−1 after 100 cycles at 1 C, 5 C and 10 C charge–discharge rates, respectively. Electrochemical impedance spectroscopy (EIS) revealed that the Li3.9Ca0.1Ti5O12 electrode exhibited the highest electronic conductivity and fastest lithium-ion diffusivity, which indicated that this novel Li3.9Ca0.1Ti5O12 material was promising as a high-rate anode material for the lithium-ion batteries.Graphical abstract

•W-doped Li4Ti5O12 samples were prepared by a sol–gel method.•The high-rate performance of Li4Ti5−xWxO12 (0 ≤ x ≤ 0.2) anode was fully investigated.•Li4Ti4.9W0.1O12 shows the best high-rate performance.W-doped Li4Ti5O12 (LTO) in the form of Li4Ti5−xWxO12 (x = 0.05, 0.1, 0.15 and 0.2) is prepared by sol–gel method and following two-step calcinations in the air and argon atmosphere, respectively. The as-prepared samples are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD analysis demonstrates that W6+ can successfully enter the structure of cubic spinel-type LTO, increase the lattice parameter and no impurities appear. XPS results further identify the existence of W6+ ion. SEM images show that all samples had similar particulate morphologies and the particle size distribution was in the range of 0.5–1 μm. The results of electrochemical measurement reveal that W-doping can improve the rate capability of LTO. However, heavy W substitution causes a discharge capability loss. The electronic conductivity of Li4Ti4.9W0.1O12 powder is as high as 1.5 × 10−1 S cm−1, which is much higher than 10−13 S cm−1 of the pristine LTO. The Li4Ti4.9W0.1O12 electrode exhibits the best rate capability and cycling stability, and its discharge capacity at 10 C is 128.1 mAh g−1 after 100 cycles. The Li4Ti4.9W0.1O12 sample stands as a promising potentially high rate anode material for lithium-ion batteries.

To study the mechanism of metal- and nonmetal-ion-doped TiO2, TiO2 codoped with carbon and molybdenum prepared by a hydrothermal method following calcination post-treatment is chosen as the study object. The prepared samples are characterized by X-ray diffractmeter, Raman spectroscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurement. It is found that the doped carbon exists in the form of deposited carbonaceous species on the surface of TiO2, and molybdenum substitutes for titanium in the lattice and exists as the Mo6+ state. All the prepared samples have comparable large surface areas. The photocatalytic activities are tested by degradation of rhodamine-B and acetone under visible light irradiation. The results show that the codoped sample has the best performance in the degradation of both RhB and acetone. Briefly, the enhanced photocatalytic activity of codoped TiO2 is the synergistic effect of C and Mo. Mo substitutes in the Ti site in the lattice for the formation of the doping energy level, and C exists as carbonaceous species on the surface of the TiO2, which can absorb visible light. The synergetic effects of C and Mo not only enhance the adsorption of visible light but also promote the separation of photogenerated electrons and holes, which consequently contribute to the best photodegradation efficiency of organic pollutants under visible-light irradiation. UV–vis diffuse reflectance spectra and photoluminescence spectra of the prepared samples and fluorescence of terephthalic acid for the detection of hydroxide radical are employed to verify the proposed mechanism.Keywords: C and Mo; mechanism; metal and nonmetal codoping; TiO2;

New Sn–C nanocomposite with metallic tin nanocrystals embedded into graphitic mesoporous carbon walls has been synthesized via a simple one-step solid–liquid grinding/templating route. X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy and thermogravimetric analysis techniques are used to characterize the samples. It is observed that high content of metallic tin nanocrystals with the sizes of 3–5 nm are well dispersed into the highly conductive graphitic carbon walls, and synthesized tin–graphitic mesoporous carbon (Sn–GMC) nanocomposite possesses ordered 2D hexagonal mesostructures with moderate surface area, large pore volume and hierarchical porosity. Due to its novel structures, the Sn–GMC nanocomposite exhibits high initial coulombic efficiency, excellent cyclability and rate performance when employed as an anode material in lithium ion batteries.Graphical abstractA simple one-step solid–liquid grinding/templating method has been used for the synthesis of metallic Sn nanocrystals with the sizes of 3–5 nm embedded in graphitic ordered mesoporous carbon walls. The resultant nanocomposite exhibits high initial coulombic efficiency, excellent cyclability and rate performance when employed as an anode material in lithium ion batteries.Highlights► A simple solid–liquid grinding/templating method is used for the synthesis of Sn–C nanocomposite. ► Sn nanocrystals with the sizes of 3–5 nm are embedded in graphitic ordered mesoporous carbon walls. ► The new Sn–C nanocomposite as an anode material exhibits excellent electrochemical performance.

A simple one-step solid–liquid grinding/templating route was firstly proposed to synthesize graphitic ordered mesoporous carbons by using natural seed fat as a carbon precursor, and the prepared carbon materials were used as novel supports for TiO2 catalysts and showed a superior photocatalytic performance in the photoreduction of CO2 with H2O.

A simple one-step solid–liquid grinding/templating route was firstly proposed to synthesize graphitic ordered mesoporous carbons by using natural seed fat as a carbon precursor, and the prepared carbon materials were used as novel supports for TiO2 catalysts and showed a superior photocatalytic performance in the photoreduction of CO2 with H2O.

Hierarchically porous titanium dioxide/graphitic carbon microspheres (xTiO2/GCM, x = 0, 10.0, 20.0, 30.0 and 40.0) are synthesized for the first time by a simple colloidal crystal templating method. The properties of the samples are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis techniques. SEM images show that all the samples have similar particulate morphologies and that the particle sizes are about 1 μm. It is observed that the amount of acetone solvent used greatly influenced the morphology of the composites. The obtained TiO2/GCM composite microspheres possess hierarchical porosity with a large specific surface area, high metallic compound content, and graphitic carbon frameworks. Employing these characteristics and advantages, the as-prepared hierarchical porous TiO2/graphitic carbon microsphere samples were used to fabricate lithium ion batteries (LIBs) as the active anode materials and their corresponding lithium ion insertion/extraction performance is evaluated. The resultant LIBs of the TiO2/GCM composites possess a more stable cyclic performance, larger reversible capacity, and better rate capability, compared with that of the graphitic carbon microspheres. Sample 20TiO2/GCM exhibited a higher specific capacity and better cycling performance and rate capability than other samples.