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ABSTRACT: AbstractCr/silicalite-1 and Cr/H[B]MFI catalysts were prepared by the impregnation method, and Cr/H[B]MFI were further treated by
steaming. The catalysts were employed for the oxidative dehydrogenation of propane to propylene with CO2 as the oxidant. Cr/H[B]MFI showed significantly higher catalytic activity than Cr/silicalite-1, and steamed Cr/H[B]MFI was
superior in the reaction stability to Cr/H[B]MFI. The nature of the supported chromium species have been characterized by
a number of physicochemical techniques, such as Raman, UV–vis and NMR. It is concluded that the steaming led to the auto-reduction
of some Cr6+ to Cr3+, and resultant Cr3+ species might be located near the boron center in the borosilicate framework to counterbalance the negative charge of the
framework. The transformation of Cr6+ species to Cr3+ species, facilitated by the steaming process and the presence of boron in the catalyst, is responsible for the enhanced stability
of oxidative dehydrogenation of propane to propylene with carbon dioxide as the oxidant.
Graphical AbstractSteaming treatment of Cr/H[B]MFI resulted in enhanced catalytic stability in the dehydrogenation of propane to propylene with
CO2 as oxidant, probably due to the transformation of some Cr6+ species to Cr3+ ones.
KeywordsDehydrogenation–Propane–Cr oxide species–Borosilicate
Catalysis Letters 04/2012; 141(5):670-677. · 2.24 Impact Factor
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ABSTRACT: AbstractThe amorphous inorganic phase of an ordered amorphous mesoporous Nb2O5 with two dimensional hexagonal (2D-hex) structure was crystallized with maintaining the original well arranged porous structure.
The difference in surface property between amorphous and crystalline Nb2O5 with similar ordered mesoporous structure was compared. It was found from water adsorption–desorption isotherms and observation
by infrared (IR) spectroscopy that the amorphous sample was hydrophilic and that the surface OH groups were acidic. On the
other hand, the OH groups on crystalline mesoporous Nb2O5 were non-acidic and inside the pores was less hydrophilic. The surface property was also compared by a catalytic reaction,
oxidation of cyclohexe by an aqueous solution of H2O2. The high (95%) selectivity for 1,2-epoxycyclohexane was obtained at 40°C for 2h in methanol solvent over crystalline mesoporous
Nb2O5 at 12% conversion, while amorphous mesoporous Nb2O5 showed high (68%) selectivity for 1,2-cyclohexanediol in acetonitrile solvent at 60°C for 2h at 22% conversion. The differences
in selectivity and the optimal solvent between amorphous and crystalline samples were interpreted in terms of the acidic feature
of surface OH groups and hydrophilicity. While similar selectivity was observed over non-porous crystalline Nb2O5, much higher conversion over crystalline mesoporous Nb2O5 was attained at the same surface area. Thus, an advantage of mesoporous structure is attributed to the higher contact time
of molecules inside the pores to the catalyst surface than those outside the particles.
Graphical AbstractThe selective epoxidation of cyclohexene using H2O2 has been recognized as an ideal eco-friendly process. The present catalytic performance of crystalline mesoporous Nb2O5 is regarded as one of the best examples to demonstrate the advantage of mesoporous marerials.
KeywordsMesoporous materials–Oxidation–Acidity
Catalysis Letters 04/2012; 141(2):283-292. · 2.24 Impact Factor
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ABSTRACT: Chiral mesoporous silica (CMS) has been successfully synthesized in the presence of basic amino acids; the use of basic amino
acids in combination with the chiral anionic surfactant is advantageous for the formation of CMS in terms of uniformity in
the twisted morphology. We first demonstrate that thus obtained chiral mesoporous silicas can be used for the enantioselective
separation of racemic compounds; the helical rod-shaped CMS is found to be capable of asymmetric separation of racemic N-trifluoroacetylalanine ethyl ester (CF3CO-Ala-OEt). The left handedness-rich CMS shows asymmetric preferential adsorption of the L isomer and vice versa.
KeywordsAMS-Chiral mesoporous silica-Basic amino acid-Handedness-Asymmetric separation
Adsorption 04/2012; 16(6):577-586. · 2.00 Impact Factor
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ABSTRACT: Novel lanthanum borate (LaBO(3)) hollow nanospheres of size 34±2 nm have been reported for the first time by soft-template self-assembly process. Poly(styrene-b-acrylic acid-b-ethylene oxide) (PS-PAA-PEO) micelle with core-shell-corona architecture serves as an efficient soft template for fabrication of LaBO(3) hollow particles using sodium borohydride (NaBH(4)) and LaCl(3)⋅7H(2)O as the precursors. In this template, the PS block (core) acts as a template of the void space of hollow particle, the anionic PAA block (shell) serves as reaction field for metal ion interactions, and the PEO block (corona) stabilizes the polymer/lanthana composite particles. The PS-PAA-PEO micelles and the resulting LaBO(3) hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning-nuclear magnetic resonance ((11)B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO(3) shell domain. The solid state (11)B MAS NMR spectra of LaBO(3) hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO(3) hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge-discharge cycling capacities of up to 100 cycles in the LIBs.
Journal of Colloid and Interface Science 03/2012; 370(1):51-7. · 3.07 Impact Factor
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ABSTRACT: Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.
Nanoscale 11/2011; 3(11):4768-73. · 5.91 Impact Factor
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ABSTRACT: A series of boron- and aluminium-containing MFI zeolites were synthesized and various characterization techniques, such as NMR ((27)Al, (29)Si and (11)B), were employed to study the acidities of zeolites. Moreover, in situ IR was applied to investigate the interaction of methanol and ethene with the acid sites, and those catalytic materials were used for co-reaction of methanol and ethene to produce propene. The production of propene was related to the Al content of the zeolites with Si/Al ratios of higher than 90. It is implied that the presence of boron during the synthesis directed the aluminium to occupy certain tetrahedral sites in the zeolite framework, thus preventing the formation of ethene oligomers, and resulting in increased propene selectivity.
Physical Chemistry Chemical Physics 08/2011; 13(32):14598-605. · 3.57 Impact Factor
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ABSTRACT: A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.
Journal of Colloid and Interface Science 08/2011; 360(1):1-7. · 3.07 Impact Factor
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ABSTRACT: Mesoporous silica containing a large amount of isolated Ti was prepared from an alkoxytitanosiloxane precursor through a hard template method. Isopropoxytris(tris-tert-butoxysiloxy)titanium (((i)PrO)Ti[OSi(O(t)Bu)(3)](3), TS3) was synthesized and TS3 was mixed with mesoporous carbon (CMK-3), a hard template. The mixture was pyrolyzed at 180 °C to form a composite consisting of titanosilica and the hard template. After calcination at 600 °C for the removal of the carbon template, the titanium species were not transformed to anatase TiO(2), proved by DR-UV-Vis, FTIR, XPS, and XRD, while the ESR results indicated the presence of isolated Ti. The mesoporous structure was verified by SEM, TEM, and N(2) adsorption. The Si/Ti ratio of the product was consistent with that of the precursor. All the results show that the material prepared from the precursor is ordered mesoporous silica containing a large amount of isolated Ti in the frameworks. The use of well-defined alkoxytitanosiloxane precursor leads to the formation of mesoporous silica with exactly controlled composition of titanium with neither loss of Ti nor transformation to anatase.
Journal of Colloid and Interface Science 07/2011; 359(1):240-7. · 3.07 Impact Factor
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ABSTRACT: We report a novel protocol to prepare titania hollow nanospheres of size about 28 ± 1 nm with micelles of asymmetric triblock copolymers. The hollow particles exhibit unique electrochemical properties in lithium ion rechargeable batteries such as high capacity, very low irreversible capacity loss, and high cycling performance.
Chemical Communications 06/2011; 47(24):6921-3. · 6.17 Impact Factor
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ABSTRACT: A significant progress has recently been made in the synthesis of monodisperse silica nanoparticles less than 30 nm in diameter by using basic amino acids (e.g., lysine) as a base catalyst for hydrolysis of silicon alkoxide. Alternatively, a more versatile and economical amino acid-free method has been developed to synthesize uniform silica nanospheres (SNSs) with low polydispersity (<12%) in liquid-liquid biphasic systems containing tetraethoxysilane (TEOS), water, and primary amine (or ammonia) under precisely controlled pH conditions (pH 10.8-11.4). The diameter of the SNSs determined from scanning electron microscopy (SEM) can be tuned from ∼12 to ∼36 nm by simply changing the initial pH of the aqueous phase in the reaction mixtures. Furthermore, the as-synthesized sol was taken as the starting material for studying the influences of the type of base catalysts on the solvent evaporation-induced three-dimensional (3D) self-assembly of SNSs. X-ray diffraction (XRD) and nitrogen adsorption-desorption are used to characterize the degree of packing of the resulting 3D arrays. The assembled SNSs with large interparticle mesopores with the diameter of ca. 8.1 nm and low packing fraction of ca. 66.1% are observed upon solvent evaporation of as-synthesized sol in the presence of primary amine. This indicates that SNSs are loosely packed, compared with the packing fraction of 74% for a face-centered cubic array of ideal hard spheres. In contrast, with the aid of an organic buffer or lysine as additives, the assembly of SNSs having smaller mesopores (ca. 3.9 nm) and higher packing fraction of 70.5-71.5% are achieved. It is suggested that the chemical additives with the ability to maintain relatively strong repulsive interaction until the final stage of evaporation play a vital role in the fabrication of well-ordered SNSs arrays.
ACS Applied Materials & Interfaces 05/2011; 3(5):1538-44. · 4.53 Impact Factor
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Angewandte Chemie International Edition 02/2011; 50(8):1853-6. · 13.45 Impact Factor
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ABSTRACT: The confined space synthesis method has been applied to the preparation of sodium tantalate (NaTaO(3)); hydrothermal reaction of NaOH and Ta(2)O(5) was carried out in the pores of a three-dimensional mesoporous carbon, which was replicated by the colloidal array of silica nanospheres (SNSs) 20 nm in size. This approach led to the formation of a colloidal array of NaTaO(3) nanoparticles 20 nm in size with a surface area of 34 m(2) g(-1). The photocatalytic performance of the colloidal array of NaTaO(3) nanoparticles for overall water splitting under UV irradiation (λ > 200 nm) was evaluated after loading a NiO cocatalyst onto NaTaO(3) samples. The NiO-loaded NaTaO(3) nanoparticles showed photocatalytic activity for overall water splitting more than three times as high as non-structured bulk NaTaO(3) particles.
Physical Chemistry Chemical Physics 02/2011; 13(7):2563-70. · 3.57 Impact Factor
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Journal of Colloid and Interface Science 01/2011; · 3.07 Impact Factor
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ABSTRACT: Novel lanthanum borate (LaBO3) hollow nanospheres of size 35±2 nm have been reported for the first time by soft-template self-assembly process. Poly(styrene–b–acrylic acid–b–ethylene oxide) (PS–PAA–PEO) micelle with core-shell-corona architecture serves as an efficient soft template for fabrication of LaBO3 hollow particles using sodium borohydride (NaBH4) and LaCl3.7H2O as the precursors. In this template, the PS block (core) acts as a template of the void space of hollow particle, the anionic PAA block (shell) serves as reaction field for metal ion interactions, and the PEO block (corona) stabilizes the polymer/lanthana composite particles. The PS–PAA–PEO micelles and the resulting LaBO3 hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning–nuclear magnetic resonance (11B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO3 shell domain. The solid state 11B MAS NMR spectra of LaBO3 hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO3 hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge-discharge cycling capacities of up to 100 cycles in the LIBs.
Journal of Colloid and Interface Science 01/2011; · 3.07 Impact Factor
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ABSTRACT: The colloidal dispersion containing the nanosized zeolites with the MFI topology has been successfully prepared. A pre-aging process of the mother gel at 80°C for 24 h before the crystallization was important for the formation of the nanosized zeolites. We have also found that silicalite-1 nanocrystals av. 62 nm in size were formed by the addition of acidic amino acids into the mother gel. The particle size of the zeolites can be controlled ranging from 62 to 530 nm by changing the amount of water, aging process, crystallization time and temperature and the addition of organic molecules. Furthermore, nanosized titanium silicalite-1 (TS-1) with the size of 50-130 nm has been successfully synthesized by the addition of a Ti source into the synthesis gel of the silicalite-1 nanocrystals. The nanosized TS-1 exhibits a higher catalytic activity in the epoxidation of cyclohexene than the microsized ones. Finally, we demonstrate the preparation of thin films of the silicalite-1 and TS-1 nanocrystals onto a silicon substrate by a dip-coating technique.
Journal of Colloid and Interface Science 01/2011; 356(2):434-41. · 3.07 Impact Factor
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ABSTRACT: Using IR spectroscopy, three different surface states of HY zeolite were probed by successive adsorption of CO at 143 K followed by evacuation and pyridine adsorption at 523 K: HY zeolite [1] without strong Lewis acid sites (LAS); [2] after high temperature (873 K) evacuation to convert Brønsted acid sites (BAS) to strong LAS; and [3] after water re-adsorption on HY zeolite [2] to recover BAS from LAS. The original surface of HY zeolite [1] seemed to be recovered on HY zeolite [3] after high temperature evacuation and water treatment by CO adsorption, while a part of generated LAS on HY zeolite [2] seemed irreversible on HY zeolite [3] to HY zeolite [1] by pyridine adsorption. To clarify this discrepancy, re-examination of the IR spectra of adsorbed CO and pyridine on γ-alumina and silica-alumina after similar treatments to those on HY zeolite was conducted. Based on the results of CO adsorption on γ-alumina and silica-alumina, the presence of extra-framework aluminium sites on HY zeolite [1] was confirmed. High temperature evacuation of HY zeolite [1] formed very strong LAS, a part of which was irreversible to BAS by water re-adsorption at room temperature. The irreversible sites on HY zeolite [3] were assigned to non-acidic OH groups attributed to silica-alumina. The non-acidic OH groups on HY zeolite [3], which were BAS on HY zeolite [1], hydrogen-bonded to pyridine to show IR spectra similar to those adsorbed on LAS. Thus, LAS on HY zeolite [3] seemed irreversible by pyridine adsorption after water re-adsorption. On the other hand, CO adsorbed on non-acidic OH groups showed a band at only slightly lower frequency (2160 cm(-1)) than that of BAS (2178 cm(-1)), resulting in overlapps and ignoring their presence. Thus, CO adsorption seemed to show that complete recovery of LAS to BAS occurred.
Physical Chemistry Chemical Physics 10/2010; 12(37):11576-86. · 3.57 Impact Factor
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ABSTRACT: Discrete mesoporous silica nanospheres (MSNSs) with a narrow size distribution were prepared by a newly developed method, which is based on the emulsion system containing Si(OEt)4 (TEOS), water, cationic surfactant, and basic amino acid under weakly basic conditions (pH 9−10). The average 20 nm sized discrete MSNSs have uniform craterlike mesopores about 3 nm in diameter. The size of the discrete spheres can be regulated in the range of 15−200 nm by, for example, changing the stirring rate in the synthesis stage. Furthermore, introduction of tetrahedrally coordinated Ti species onto the pore of MSNSs and their catalytic performance in epoxidation of different-sized alkenes, cyclohexene, cis-stilbene and caryophyllene were also demonstrated.
06/2010;
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ABSTRACT: Liquid-phase catalytic oxidation of cyclohexene by H2O2 (35 wt %) over mesoporous Nb2O5 showed considerable conversion and high selectivity for both cis- and trans-1,2-cyclohexanediols in acetonitrile solvent. The mesoporous structure of the catalyst, in addition to its high surface area, was considered to be advantageous for the reaction due to more frequent interaction of molecules with active sites inside pores. Gradual formation of 1,2-cyclohexanediol from the reaction of adsorbed cyclohexene with diluted (10 wt %) H2O2 was observed at room temperature by an in situ infrared (IR) method. The absence of observation of an IR spectrum of 1,2-epoxycyclohexane confirmed that the hydrolysis of the oxidation product occurred immediately. In addition to the conventional stepwise oxidation and hydrolysis to produce 1,2-cyclohexanediol, a direct hydroxylation of cyclohexene was proposed: the production of cis-1,2-cyclohexanediol with about a half amount of trans-1,2-cyclohexanediol suggests the activation of H2O2 on the acidic OH groups of mesoporous Nb2O5 to directly produce both cis- and trans-1,2-cyclohexanediols from cyclohexene without forming 1,2-epoxycyclohexane. The hydrolysis of adsorbed cyclohexene to cyclohexanol was observed when more diluted (2.5 wt %) H2O2 was used. This indicates that H2O can be also activated for hydrolysis of olefin, but that the preferential activation of H2O2 over H2O occurs during the liquid-phase reaction with 35 wt % H2O2 on mesoporous Nb2O5.
12/2009;
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Angewandte Chemie International Edition 11/2009; 48(52):9884-7. · 13.45 Impact Factor
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ABSTRACT: A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. The SNSs are formed in the emulsion system containing Si(OEt)4 (TEOS), water, and basic amino acids under weakly basic conditions (pH 9−10). Here, we report the formation mechanism of the SNSs; the reasons for the uniform size and the ordered arrangement are described in detail. The formation process is monitored by FE-SEM, SAXS, and liquid-state NMR. The FE-SEM observations reveal that silica nanoparticles ca. 4 nm in size are formed in the water phase at the early stage (0.5 h) of the reaction. The SAXS measurements suggest that the number density of the particles remains unchanged when they are gradually grown. Liquid-state 1H NMR analyses suggest that TEOS are slowly hydrolyzed at the oil−water interface to continuously supply silicate species into the water phase. The silicate species are immediately consumed for the growth of the parent particles without forming new particles. The size of the SNSs can be tuned from 8 to 35 nm by varying the synthesis conditions and/or the amount of TEOS. The zeta potential and pH of the dispersion of SNSs throughout the solvent evaporation process are almost constant approximately at −40 mV and 9−10, respectively; the SNSs have been well-dispersed until the final stage of the evaporation process. The critical roles of basic amino acids in the formation and regular arrangement of SNSs are discussed based on the experimental results.
08/2009;
