Search

Optimized porous structure is a prerequisite for high performance Li‒O2 battery cathode. Macroporous-mesoporous carbon (MMC) is fabricated via a nano-replication method using mesoporous SiO2 (KIT-6) containing NiO as the template. By varying the amount of NiO in the KIT-6/NiO composite template, the amount of macropores inside MMC is easily controlled. The as-prepared MMC exhibits a highly porous structure with abundant ordered mesopores along with macropores that are larger than 200 nm in size. When the MMC is applied as the cathode material in a Li‒O2 battery, the cell exhibits greatly improved electrochemical performance in comparison to a cell using conventional ordered mesoporous carbon (OMC) without macropores. Systematic studies indicate that while mesopores in the OMC are clogged with Li2O2 formed during the early stage of discharge, the MMC sufficiently accommodates a large amount of Li2O2 in the pores. In addition, Li2O2 with poor crystallinity forms on the cathode containing MMC during subsequent discharge processes, which can be due to the accumulated side product and the limited size of pores. The formation of amorphous Li2O2 and the expedited mass transport through the interconnected meso- and macropores of MMC can attribute to the improved electrochemical performance of the MMC cathode material.

Mesoporous transition metal dichalcogenides (TMDCs), composed of group VI metals (Mo and W) and chalcogens (S and Se), with 2-D layered crystalline frameworks and 3-D pore structures were successfully prepared via a melting-infiltration assisted nano-replication method using a mesoporous template KIT-6 with cubic Ia3d symmetry. Combined analysis using X-ray diffraction, N2 adsorption–desorption and electron microscopy indicated that the mesoporous TMDCs, thus obtained, exhibited high surface areas (87–105 m2 g−1), large pore volumes (0.21–0.25 cm3 g−1) and well-defined mesopores about 20 nm in diameters. The mesoporous TMDCs showed outstanding rate capabilities up to 2C as well as high reversible lithium storage capacities (MoS2 710 mA h g−1; MoSe2 744 mA h g−1; WS2 501 mA h g−1; WSe2 427 mA h g−1) without a remarkable fading of capacity.

We report on a facile synthesis of the ordered mesoporous carbon (OMC) materials with systematically controlled microporosity and mesoporosity simultaneously through the nano-replication route using phosphoric acid as the acid catalyst and activation agent. The use of phosphoric acid affects the pore structures of OMC materials, such as the formation of numerous micropores by activation of the carbon framework and the enlargement of mesopores by spontaneous phase separation during the carbonization. The mesopore sizes, surface areas, total pore volumes, and micropore volumes of the OMC materials are highly dependent on the phosphoric acid content and can be systematically controlled in the range 3.7–7.5 nm, 1027–2782 m2 g–1, 1.12–3.53 cm3 g–1 and 0.34–0.95 cm3 g–1, respectively. OMC materials with systematically controlled pore structures were successfully synthesized using phosphoric acid as the carbonization catalyst and mesoporous silica materials with cubic Ia3d and 2-D hexagonal mesostructures as the templates. The phosphoric acid in the synthesis of ordered mesoporous carbon materials acts as the chemical activating agent for micropore generation of the carbon framework and pore-expanding agent for controlling of mesopore size, in addition to functioning as the acid catalyst. The present synthesis pathway is very useful for preparing OMC materials with tunable mesopore sizes and well-developed microporosities at the same time.

A thin, uniform carbon coating on Na2/3Fe1/2Mn1/2O2 (NFMO) using 2,3-dihydroxynaphthalene (DN) was prepared. Pristine and DN-coated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An amorphous nanolayer coating of carbon is obtained on the surface of the layered pristine material. The 0.2 wt% DN-coated NFMO exhibits excellent electrochemical performance. An initial discharge capacity of 178 mA h g−1 was obtained at a C-rate of 0.1 C; this capacity is 20% higher than bare NFMO. Capacity retention (77.8% at the 50th cycle) is also maintained comparable to bare NFMO (77.7% at the 50th cycle). The thin and uniform carbon layer leads to improvement of charging and discharging kinetics and protects against direct contact between cathode and electrolyte.

a b s t r a c t Highly ordered mesoporous metal oxides (meso-MOx) such as CeO2, Co3O4, Mn2O3, SnO2, and TiO2 were successfully synthesized by using nano-replication method, and Pd-loaded meso-MOx (Pd/meso- MOx) catalysts for CO oxidation were investigated. The catalysts were characterized by X-ray diffraction, N2 adsorption-desorption, electron microscopy, CO-temperature programmed desorption (CO-TPD), and H2-temperature programmed reduction (H2-TPR). All of the catalysts exhibited highly ordered mesostructure and a high surface area (>100 m 2 g

Highly ordered mesoporous cerium dioxide (meso-CeO2) was successfully synthesized using a facile solvent-free infiltration method from a mesoporous silica template, KIT-6. The meso-CeO2 material, thus obtained, exhibited well-defined mesostructure and high surface area (153 m2 g−1). The physicochemical properties of meso-CeO2 material and Pd-supported on meso-CeO2 (Pd/meso-CeO2) were characterized by electron microscopy, X-ray diffraction, N2 adsorption–desorption, and temperature-programmed experiments. The Pd/meso-CeO2 catalyst exhibited excellent catalytic activity for CO oxidation compared with those of other Pd/CeO2 catalysts which were prepared using nanocrystalline CeO2 and bulk-CeO2 as the supports. Moreover, a hydrogen pretreatment of the Pd/meso-CeO2 catalyst resulted in a remarkable increase of catalytic activity (T100 = 52 °C).

Highly ordered mesoporous silver material was successfully synthesized from a mesoporous silica template (KIT-6) with 3-D channel structure using the nano-replication method. The effects of H 2 or O 2 pretreatments on the catalytic performance of the mesoporous silver were investigated using a temperature programmed CO oxidation technique in a fixed bed reactor. The mesoporous silver material that was pretreated with H 2 exhibited an excellent catalytic activity compared to the as-prepared and 0 2 -pretreated catalysts. Moreover, this present mesoporous silver material showed good catalytic stability. For the CO oxidation, the apparent activation energy of the H 2 -pretreated mesoporous silver catalyst was 61 ± 0.5 kJ mol -1 , which was also much lower than the as-prepared (132 ± 1.5 kJ mol -1 ) and O 2 -pretreated (124 ± 1.4 kJ mol -1 ) catalysts.

Mesoporous tin oxide (SnO 2 ) materials, exhibiting high surface areas, crystalline frameworks and various mesostructures, were successfully obtained by a facile solvent-free infiltration method from mesoporous silica templates. Various kinds of mesoporous silica materials, such as KIT-6 (bicontinuous 3-D cubic, Ia 3 d ), SBA-15 (2-D hexagonal, p 6 mm ), SBA-16 (3-D cubic with cage-like pores, Im 3 m ) and spherical mesoporous silica (disordered), were utilized as the hard templates. Tin precursor (SnCl 2 · 2H 2 O, m.p. 310–311 K) was infiltrated spontaneously within the mesopores of silica templates by melting the precursor at 353 K without using any solvent. The heat-treatment of SnCl 2 -infiltrated composite materials at 973 K under static air conditions and subsequent removal of silica templates by using HF result in the successful preparation of mesoporous SnO 2 materials. The mesostructures as well as the morphologies of mesoporous SnO 2 materials thus obtained were very similar with those of the mesoporous silica templates. The mesoporous SnO 2 materials exhibit high surface areas of 84–121 m 2 /g as well as high pore volumes in the range of 0.22–0.35 cm 3 /g. The present solvent-free infiltration method is believed to be a simple and facile way for the preparation of mesoporous materials via nano-replication from mesoporous silica templates.

E-mail: jimankim@skku.eduReceived July 15, 2008In the present work, Diels-Alder reaction of cyclopentadiene with ethylacrylate has been carried out by usingtwo types of mesoporous solid acid catalysts (Al-MCM-41, Al-MCM-48) with different pore structures. Thespecific topology of Al-MCM-48 (cubic Ia3d structure composed of two independent 3-D channel systems)exhibit higher activity and stereo-control than those of Al-MCM-41 (hexagonal packing of 1-D channels). Thephysical properties of Al-MCM-48 catalyst, such as high accessibility of reactants to the acid sites, spatialconfinement in the nanoscopic reactors, and 3-D channel network structure that are effective adsorption anddiffusion of reactants, play a crucial role in the present study.Key Words : Mesoporous catalyst, Al-MCM-48, Diels-Alder reaction, Cyclopentadiene, Ethylacrylate IntroductionDiels-Alder (DA) reactions have attracted much attentionas a powerful synthesis pathway and widely utilized insynthetic organic chemistry and in the chemical industry,due to the high degree of regio- and stereo-selectivity.

Developing electrode materials with high-energy densities is important for the development of lithium-ion batteries. Here, we demonstrate a mesoporous molybdenum dioxide material with abnormal lithium-storage sites, which exhibits a discharge capacity of 1,814 mAh g−1 for the first cycle, more than twice its theoretical value, and maintains its initial capacity after 50 cycles. Contrary to previous reports, we find that a mechanism for the high and reversible lithium-storage capacity of the mesoporous molybdenum dioxide electrode is not based on a conversion reaction. Insight into the electrochemical results, obtained by in situ X-ray absorption, scanning transmission electron microscopy analysis combined with electron energy loss spectroscopy and computational modelling indicates that the nanoscale pore engineering of this transition metal oxide enables an unexpected electrochemical mass storage reaction mechanism, and may provide a strategy for the design of cation storage materials for battery systems., Electrode materials with high energy density are important for the development of Li-ion batteries. Here, the authors report a molybdenum dioxide anode with abnormal lithium storage sites, exhibiting a discharge capacity twice its theoretical value by utilizing two different storage mechanisms.

A highly selective and active catalyst for the positional isomerisation of 2-butene into 1-butene has been developed by using a mesoporous silica, MCM-41. The yields of 1-butene as well as total conversion decrease when aluminium or lanthanum was added to the MCM-41 even though the amounts of acid sites increase. FT-IR spectra proved that the H site due to the silanol group may act as an active site for the positional isomerisation of 2-butene to 1-butene.

Ordered mesoporous MnO, MnO4, Mn2O3 and MnO2 materials with 3-D pore structure were suc- cessfully synthesized via a nano-replication method by using ordered mesoporous silica, KIT-6 (Cubic Ia3d space group mesostructure) as the template under specific oxidation and reduction conditions. Notably, ordered mesoporous MnO with a crystalline wall (rock salt structure) was syn- thesized for the first time, to the best of our knowledge. The synthesis of the ordered mesoporous MnO was achieved by reducing the ordered mesoporous Mn3O4 under an H2 atmosphere, while preserving the ordered mesostructure and crystalline wall throughout the solid/solid transformation. All of the ordered mesoporous manganese oxides with different crystal structures and oxidation states demonstrated almost the same spherical-like morphology with several hundred nanometers of particles. The synthesized ordered mesoporous manganese oxides had uniform dual mesopores (2-3 nm, and ~20 nm) and crystalline frameworks with large surface areas (86-140 m2/g) and pore volumes (0.27-0.33 cm3/g).

Highly ordered mesoporous α-Mn2O3 with well-defined mesopores, high surface area, and high oxygen vacancy exhibits excellent catalytic activity toward H2O2 decomposition at low temperature.

Highly ordered mesoporous TiO2 materials, exhibiting crystalline frameworks and various mesostructures, have been successfully obtained via nanoreplication using various kinds of mesoporous silicas...

Noble Gemini surfactants containing a siloxane moiety have been designed and successfully synthesized in the present study and are utilized as structure-directing agents for mesoporous metal oxides such as zirconia, titania, and vanadia. The siloxane moiety is believed to play an important nano-propping role during the surfactant removal by direct calcination, yielding thermally stable mesoporous metal oxides. It is also believed that the synthesis strategy described here can be applied to the synthesis of robust nanostructured materials such as nanoparticles and nanorods in addition to mesoporous materials.

Highly ordered mesoporous SnO2 materials with residual silica species were successfully synthesized from a mesoporous silica template (SBA-15) via nano-replication and simple etching processes. A tin precursor, SnCl2·2H2O, was infiltrated spontaneously within the mesopores of the silica templates by melting the precursor at 353 K without using a solvent. After the heat-treatment of composite materials at 973 K under static air conditions, the controlled removal of silica templates using NaOH or HF solutions with different concentrations results in the successful preparation of mesoporous SnO2 materials, where the amounts of residual silica species are in the range 0.9–17.4 wt%. The residual silica species induce a nano-propping effect enabling the mesoporous SnO2 material (containing 6.0 wt% of silica species) to remain stable up to 973 K without any significant structural collapse. More importantly, the optimum amount of residual silica species (3.9–6.0 wt%) results in a dramatic reduction in capacity fading after prolonged charging–discharging cycles in Li-ion battery. The mesoporous SnO2 material with 3.9 wt% of silica species still exhibits a large capacity (about 600 mAh g−1) after the 30th cycle, which is probably because the residual silica species act as a physical barrier to suppress the aggregation of Sn clusters formed in the mesoporous SnO2 materials during the reversible lithium storage.