“Hard” vs. “Soft” Templating Synthesis of Mesoporous Nb2O5 Catalysts for Oxidation Reactions

Nowak, Izabela; Jaroniec, Mietek

doi:10.1007/s11244-008-9084-1

Cited by 21 publications

(14 citation statements)

References 55 publications

(64 reference statements)

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“…As pure Nb 2 O 5 catalysts for the same reaction, mesoporous silica-templated crystalline Nb 2 O 5 catalysts were found to be active and efficiency of H 2 O 2 at more than 98% was reported [26], which is different from the present study. While crystallization occurs in pores of mesoporous silica to expose stable surfaces with less numbers of defect sites in the reported study [26], the surfaces of the presently prepared crystalline mesoporous Nb 2 O 5 appearing after silica removal would probably rich in defect. Such defect-rich surfaces are considered, at present, to work as decomposition sites for H 2 O 2 .…”

Section: Surface Properties Of Mesoporous Nb 2 O 5 Catalystscontrasting

confidence: 99%

“…On the other hand, Nb 2 O 5 -coated mesoporous silica resulted in forming 1, 2-cyclohexanediol as a major product [26] because of the exposure of amorphous Nb 2 O 5 as in the case of present study. As pure Nb 2 O 5 catalysts for the same reaction, mesoporous silica-templated crystalline Nb 2 O 5 catalysts were found to be active and efficiency of H 2 O 2 at more than 98% was reported [26], which is different from the present study.…”

Section: Surface Properties Of Mesoporous Nb 2 O 5 Catalystssupporting

confidence: 48%

“…Briefly, 7 mmol NbCl 5 was added to 10 wt% P-85 (a block copolymer; HO(CH 2 CH 2 O) 26 (CH 2 CH(CH 3 )) 39 (CH 2 CH 2 O) 26 H) propanol solution and stirred for 1 h. After the addition of 70 mmol of water with stirring, the solution was kept at 40 8C in air for 10 days to obtain template-containing niobium oxide or hydroxide gel. The surfactant was removed by calcination at 400 8C for 10 h.…”

Section: Sample Preparationmentioning

confidence: 99%

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Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

et al. 2010

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The amorphous inorganic phase of an ordered amorphous mesoporous Nb 2 O 5 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 Nb 2 O 5 with similar ordered mesoporous structure was compared. It was found from water adsorptiondesorption 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 Nb 2 O 5 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 H 2 O 2 . The high (95%) selectivity for 1,2-epoxycyclohexane was obtained at 40°C for 2 h in methanol solvent over crystalline mesoporous Nb 2 O 5 at 12% conversion, while amorphous mesoporous Nb 2 O 5 showed high (68%) selectivity for 1,2-cyclohexanediol in acetonitrile solvent at 60°C for 2 h 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 Nb 2 O 5 , much higher conversion over crystalline mesoporous Nb 2 O 5 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.

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Section: Surface Properties Of Mesoporous Nb 2 O 5 Catalystscontrasting

confidence: 99%

Section: Surface Properties Of Mesoporous Nb 2 O 5 Catalystssupporting

confidence: 48%

Section: Sample Preparationmentioning

confidence: 99%

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Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

et al. 2010

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“…A sol–gel process, carried out in combination with a templating method and spin-coating deposition, is the easiest and the most versatile way for preparing well-organized, mesoporous, thin films. Among all the different templating approaches, the most widely used for the synthesis of nanostructured porous and high surface area oxides are soft templating (endotemplating) and hard templating (exotemplating) [6–7]. …”

Section: Introductionmentioning

confidence: 99%

Polystyrene-block-poly(ethylene oxide) copolymers as templates for stacked, spherical large-mesopore silica coatings: dependence of silica pore size on the PS/PEO ratio

Nisticò

Magnacca

Jadhav

et al. 2016

Beilstein J. Nanotechnol.

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SummaryLarge-mesopore silica films with a narrow pore size distribution and high porosity have been obtained by a sol–gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers as templates in an acidic environment. PS-b-PEO copolymers with different molecular weight and composition have been studied in order to assess the effects of the block length on the pore size of the templated silica films. The changes in the morphology of the porous systems have been investigated by transmission electron microscopy and a systematic analysis has been carried out, evidencing the dependence between the hydrophilic/hydrophobic ratio of the two polymer blocks and the size of the final silica pores. The obtained results prove that by tuning the PS/PEO ratio, the pore size of the templated silica films can be easily and finely predicted.

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“…29), 30) For the preparation of mesoporous Nb 2 O 5 , we utilized a solvent evaporation method, which is very useful for controlling the morphology, using PC or PAA membranes, 25)27) although a hard templating method using mesoporous silica has been reported. 31) We prepared various types of mesoporous Nb 2 O 5 by using two types of surfactants while changing the amount of surfactants by applying various calcination temperatures. The effect of these parameters in the framework on the mesostructural ordering and crystallinity was carefully examined.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of mesoporous Nb2O5 with crystalline walls and investigation of their photocatalytic activity

Suzuki

Athar

Huang

et al. 2011

J. Ceram. Soc. Japan

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We synthesize various kinds of mesoporous Nb 2 O 5 samples by changing surfactants (P123 and Brij 56), followed by calcination (from 400 to 500 and 600°C). The effect of these parameters helps to produce a well-defined mesoporous framework with crystallinity. The mesoporous Nb 2 O 5 samples are well characterized by using small-angle X-ray scattering (SAXS) measurements, N 2 adsorptiondesorption isotherms, and wide-angle XRD measurements. In a P123 system, the frameworks are well crystallized to the TT-phase (pseudo-hexagonal) by calcination at 500°C with retention of the mesoporous structures. In the Brij 56 system, after calcination at 500°C, the framework is well retained in an amorphous state. It is proved that the thick walls prepared with P123 are easily crystallized in comparison to thin walls prepared with Brij 56. Furthermore, we investigate the photocatalytic activity by using several types of mesoporous Nb 2 O 5 prepared with P123. All these mesoporous Nb 2 O 5 samples show photocatalytic activity with their decomposition reaction of methylene blue (MB) molecules. It is concluded that the reaction rates depend on their crystallinities in the frameworks, surface areas, and average mesopore sizes.

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“Hard” vs. “Soft” Templating Synthesis of Mesoporous Nb2O5 Catalysts for Oxidation Reactions

Cited by 21 publications

References 55 publications

Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

Polystyrene-block-poly(ethylene oxide) copolymers as templates for stacked, spherical large-mesopore silica coatings: dependence of silica pore size on the PS/PEO ratio

Synthesis of mesoporous Nb2O5 with crystalline walls and investigation of their photocatalytic activity

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