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 Một số bài báo về Vật liệu - Xúc tác

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Bài gửiTiêu đề: Một số bài báo về Vật liệu - Xúc tác   Thu Oct 27, 2011 12:57 am

Đã từ lâu, xúc tác đã đóng 1 vai trò rất quan trọng trong các phản ứng hóa học. Nó có thể xúc tiến hay kìm hãm quá trình phản ứng, thay đổi hướng phản ứng theo cơ chế hấp phụ - xúc tác...

Vật liệu mao quản trung bình đang là 1 xu hướng phát triển trong lĩnh vực Hấp phụ-xúc tác. Nhiều loại vật liệu đã ra đời như MCM, SBA,... đã góp phần đáng kể vào nền công nghhiệp hóa, lọc dầu, xúc tác xử lý môi trường... trên toàn thế giới


Sau đây là 1 số bài báo về vật liệu mao quản, xúc tác...:


1. The one-step synthesis of a highly active hierarchical Fe/ZSM-5 zeolite catalyst with a strongly improved lifetime in the selective hydroxylation of benzene to phenol with nitrous oxide; compared to the best Fe/ZSM-5 catalyst, the turnover number after 24 h on stream is almost four times higher.

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Bài gửiTiêu đề: Aluminium-containing mesoporous benzene-silicas with crystal-like pore wall structure   Thu Oct 27, 2011 1:00 am

Mesoporous benzene-silicas with a high content of tetrahedral aluminium in the framework (Si/Al 5 37 and 59) were successfully synthesized, as evidenced by X-ray diffraction, N2 sorption analyses, transmission electron microscopy and solid state 13C CP-MAS, 27Al and 29Si MAS
NMR spectroscopy. These materials have well-ordered 2D hexagonal mesostructure with a molecular scale periodicity in the pore walls. The existence of the phenylene groups in the framework greatly enhances the hydrothermal stability of the aluminium-containing mesoporous
benzene-silicas. The acidity of the mesoporous benzene-silicas arising from the incorporated aluminium was measured by the FT-IR spectra of pyridine adsorption measurements. The organic groups bridged in the mesoporous framework affect significantly the acidity of the
resultant materials although most aluminium atoms are in tetrahedral coordination. These materials are catalytically active for alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol.

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Bài gửiTiêu đề: An Efficient Hybrid, Nanostructured, Epoxidation Catalyst   Thu Oct 27, 2011 1:03 am

A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (> 380 m2/g) and pore volume (^ 0.46 cm3/g)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert-butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites.

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Bài gửiTiêu đề: An efficient solid acid catalyst-Poly-p-styrenesulfonic acid supported on SBA-15 via surface-initiated ATRP   Thu Oct 27, 2011 1:05 am

The sulfonic acid-functionalized mesoporous organic–inorganic hybrid materials were synthesized via atom transfer radical polymerization (ATRP) method. SBA-15 material was first grafted with 4-(chloromethyl) phenyltrimethoxysilane. The surface-initiated polymerization of sodium p-styrenesulfonate inside the pore wall of functionalized SBA-15 results in p-styrenesulfonic acid functionalized SBA-15 (PSS-SBA-15). The results of FT-IR, nitrogen sorption isotherm, XRD, TEM and thermal gravimetric analyses (TGA) confirm that the PSS-SBA-15 materials have ordered mesoporous structure, open channels and styrenesulfonic acid functionalities. The catalytic activity of PSS-SBA-15 was higher than commercial Nafion resin in the esterification of lauric acid with ethanol. The unique catalytic performance of PSS-SBA-15 is probably attributed to the increased accessibility of the active sites to the reactants because of the existence of styrenesulfonic acid on the pore surface of SBA-15.

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Bài gửiTiêu đề: Asymmetric Catalysis with Metal Complexes in Nanoreactors   Thu Oct 27, 2011 1:07 am

Recently, the field of heterogeneous asymmetric catalysis, generally using chiral solid catalysts, has attracted much attention in the production of single enantiomers. Among versatile chiral solid catalysts, chiral metal complexes confined in nanoreactors often exhibit very unique enantioselectivity and catalytic activity compared to homogeneous catalysts. In this Focus Review, we summarize the recent advances in asymmetric reactions on chiral metal complexes confined in nanoreactors with an emphasis on the confinement effect and cooperative activation
effect of the nanoreactor and new strategies for the preparation of chiral solid catalysts, such as the encapsulation of chiral metal complexes in the nanocages of mesoporous silica and incorporation of chiral ligands in the network of mesoporous organosilicas.

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Bài gửiTiêu đề: Asymmetric reactions on chiral catalysts entrapped within a mesoporous cage   Thu Oct 27, 2011 1:10 am

The encapsulation of homogeneous chiral catalysts, e.g. Co(Salen) and Ru-TsDPEN, in the mesoporous cage of SBA-16 is demonstrated; the encapsulated catalysts show performance as good as that of the homogeneous catalysts, and can be recycled for more than 10 times without significant loss of catalytic performance.



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Bài gửiTiêu đề: Biphenylene bridged bifunctional hybrid mesoporous silsesquioxanes with sulfonic acid functionalities and crystalline pore walls   Thu Oct 27, 2011 1:13 am

The first synthesis of highly hydrophobic bifunctional biphenylene bridged hybrid mesoporous silsesquioxane with sulfonic acid functionalities and crystalline pore walls is reported.

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Bài gửiTiêu đề: Catalytic application of sulfonic acid functionalized mesoporous benzene   Fri Oct 28, 2011 7:17 pm

The first catalytic applications of sulfonic acid-functionalized hydrophobic mesoporous benzene–silica with lamellar pore wall structure are reported. The mesoporous benzene–silica attached with propylsulfonic groups to the crystal-like periodic pore walls exhibited the catalytic activity in the esterification of acetic acid with ethanol. The catalytic results show the higher conversion compared to the commercial Nafion-H.

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Bài gửiTiêu đề: Catalytic applications of sulfonic acid functionalized mesoporous organosilicas with different fraction of organic   Fri Oct 28, 2011 7:21 pm


Organosulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall was synthesized in the presence of P123 (EO20PO70EO20) by controlling the molar ratio of tetramethoxysilane (TMOS) to 1,2-bis(trimethoxysilyl)ethane (BTME) in the initial mixture during the co-condensation process of silane precursors in acidic medium. Structural characterizations (X-ray diffraction, nitrogen sorption analysis, and transmission electron microscopy) show that all materials have ordered hexagonal mesoporous structure with large pore diameter (7–9 nm). The existence of ethane and sulfonic acid groups in the material was verified by 29Si MAS and 13C CP MAS NMR and X-ray photoelectron spectroscopy (XPS). The mesoporous solid acids can
adsorb both water and hexane (the adsorption capacity for water and hexane is 240 and 600 mg/g, respectively) due to the existence of surface hydroxyl groups, propyl sulfonic acid group, and the ethane moiety. These mesoporous solid
acids are efficient catalysts for the dehydration of 1-butanol and the hydration of propylene oxide (PO).

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Bài gửiTiêu đề: Chiral mesoporous organosilica spheres-Synthesis and chiral separation capacity   Fri Oct 28, 2011 7:23 pm

New mesoporous organic–inorganic spheres with trans-(1R,2R)-bis-(ureido)-cyclohexane covalently bridged in the pore wall were prepared by co-condensation of N,N0-bis-[(triethoxysilyl)propyl]-trans-(1R,2R)-bis-(ureido)-cyclohexane and 1,2-bis(trimethoxysilyl)ethane through a hierarchical double templating method. The octadecyltrimethylammonium chloride (C18TMACl) and ethanol direct the formation of mono-dispersed hybrid spheres. N,N-dimethyldecylamine, acting as a pore expanding agent, can expand the pore diameter of the hybrid material from less than 1.7–10 nm during the post-synthetic treatment process. The hybrid material was employed as a novel kind of chiral stationary phase for high performance liquid chromatography (HPLC). The column packed with the hybrid material with particle size of 6–9 lm can efficiently separate the R/S-1,10-bi-2-naphthol enantiomers even at high sample loading and high flow rate because of its high chiral ligand loading (0.93 mmol/g) and high surface area (597 m2/g).

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Bài gửiTiêu đề: Chiral mesoporous organosilicas with R-(+)-Binol integrated in the framework   Fri Oct 28, 2011 7:25 pm

Bifunctionalized chiral mesoporous organosilicas with both R-(+)-Binol and ethylene moieties integrated in the framework was synthesized by co-condensation of 1,2-bis(trimethoxysilyl)ethane (BTME) and (R)-2,20-dimethoxy-6,60-di-[(2-trimethoxysilyl)-ethenyl]-1,10-binaphthyl (R-MMB) in acidic medium using P123 as template for the first time. With the molar fraction of R-MMB increasing from10 to 20% in the initial mixture, the mesostructure of the material changes from a well-ordered 2D hexagonal mesostructure to a worm-like structure. The materials have a pore diameter in the range of 4.8–5.2 nm with BET surface areas varying from 356 to 894 m2 g1. The results of FT-IR, 13C and 29Si solid-state NMR shows the integration of the organic groups in the material though some Si–C bond cleavage was observed during the synthesis. The circular dichroism spectrum of the material dissolved in NaOH confirms that the chirality of R-(+)-Binol in the material remains unchanged compared with the molecular precursor. The hydroxyl groups of the R-(+)-Binol units were liberated by treatment of the material with BBr3. The resultant materials were used in Ti-promoted asymmetric addition of diethylzinc to benzaldehyde. High catalytic activity (99%) with moderate enantioselectivity (39.7%) was achieved, which also confirms that R-Binol was incorporated in the PMOs successfully.


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Bài gửiTiêu đề: Chirally functionalized mesoporous organosilicas with built-in BINAP   Fri Oct 28, 2011 7:27 pm

The chirally functionalized periodic mesoporous organosilica (PMO) with C2-symmetric chiral building blocks, BINAP (2,20-bis(diphenylphosphino)-1,10-binaphthyl), in the pore wall was successfully synthesized for the first time using a successive co-condensation and post-synthesis modification method. Chiral BINAPO (2,20-bis(diphenylphosphinooxide)-1,10-binaphthyl) bridging mesoporous organosilica with highly ordered 2-D hexagonal structure was first synthesized by cocondensation of (R)-5,50-bis(3-triethoxysilylpropyl-1-ureyl)-2,20-bis(diphenylphosphinooxide)-1,10-binaphthy with tetramethoxylsilane in the presence of block copolymer P123 as template under weakly
acidic conditions. The BINAPO in the pore wall of PMO was reduced with trichlorosilane to generate BINAP using a post-synthesis modification method. The chiral PMO with built-in BINAP (coordination with [RuCl2-(benzene)]2) is an efficient solid catalyst for the asymmetric hydrogenation
of b-keto esters with ee as high as 99%, which is among the highest ever reported for the chirally functionalized PMOs in asymmetric catalysis.


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Bài gửiTiêu đề: Direct Synthesis of Al-SBA-15 Mesoporous Materials via Hydrolysis-Controlled Approach   Fri Oct 28, 2011 7:29 pm

Aluminum-substituted mesoporous SBA-15 (Al-SBA-15) materials were directly synthesized by a hydrolysiscontrolled approach in which the hydrolysis of the silicon precursor (tetraethyl orthosilicate, TEOS) is accelerated by fluoride or by using tetramethyl orthosilicate (TMOS) as silicon precursor rather than TEOS. These materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms, TEM, 27Al
MAS NMR, IR spectra of pyridine adsorption, and NH3-TPD. It is found that the matched hydrolysis and condensation rates of silicon and aluminum precursors are important factors to achieve highly ordered mesoporous materials. 27Al MAS NMR spectra of Al-SBA-15 show that all aluminum species were incorporated into the silica framework for the samples prepared with the addition of fluoride. A two-step approach (sol-gel reaction at low pH followed by crystallization at high pH) was also employed for the synthesis of Al-SBA-15. Studies show that the two-step approach could efficiently avoid the leaching of aluminum from the framework of the material. The calcined Al-SBA-15 materials show highly ordered hexagonal mesostructure and have both Bro¨nsted and Lewis acid sites with medium acidity.


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Bài gửiTiêu đề: Direct synthesis of hierarchical monolithic silica for high performance liquid chromatography   Fri Oct 28, 2011 7:34 pm

Organosilica porous solids containing chiral organic moieties in the framework with an enantiomeric purity of 95% ee, estimated by eluting organic constituent units from chiral organosilicas, were synthesized from a newly designed chiral (R)-(+)-1,2-bis(trimethoxysilyl)phenylethane precursor via a surfactant-mediated self-assembly approach.

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Bài gửiTiêu đề: Effect of Aluminum on the Nature of the Iron Species in Fe-SBA-15   Fri Oct 28, 2011 7:36 pm

The preparation of highly ordered mesoporous Fe-Al-SBA-15 with isolated extraframework Fe species under acidic conditions. The materials were characterized by means of UV resonance Raman spectroscopy, in conjunction with BET, XRD, TEM, UV-vis, H2-TPR, FT-IR, and 27Al MAS NMR
spectroscopy. The addition of both Fe and Al to the synthesis gel of SBA-15 results in the formation of isolated extraframework Fe species located close to the framework Al ions and the Fe content an order of magnitude higher than that in Fe-SBA-15 synthesized without Al. The existence of anchored extraframework Fe species was confirmed by the presence of a strong absorption band at 270 nm, hydrogen reduction at relatively low temperature, and the presence of a resonance Raman band at 1140 cm-1. The location of Fe in close proximity to framework Al nuclei is further supported by 27Al MAS NMR measurements. Two characteristic UV Raman bands at 510 cm-1 and 1090 cm-1 excited by 244-nm laser are assigned to Fe-O-Si symmetric and asymmetric stretching modes of isolated tetrahedral Fe ions in the silica framework for Fe-SBA-15. The resonance Raman band at 1140 cm-1 excited by 325-nm laser is attributed to the asymmetric stretching mode of the isolated extraframework iron species in Fe-Al-SBA-15. The isolated Fe species close to framework Al species are stable in acidic HCl solution, whereas the majority of Fe species in Fe-SBA-15 can be easily removed.



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Bài gửiTiêu đề: Enhanced Catalytic Oxidation by Hierarchically Structured TS-1 Zeolite   Fri Oct 28, 2011 7:38 pm

A TS-1 zeolite with a disordered network of mesopores penetrating the microporous crystalline zeolite framework was successfully synthesized by a one-pot carbon hard-templating synthesis approach. Besides conventional methods to characterize the mesoporosity, the use of variable-temperature 129Xe NMR spectroscopy was explored. At low temperature, a new resonance of 129Xe adsorbed in the mesopores could be distinguished from the signal of Xe in the micropores. The similarity of UV-vis and UV resonance Raman spectra of this mesoporous TS-1 zeolite with a conventional microporous TS-1 zeolite shows that the local coordination environment of Ti in these samples is identical. Further characterization (TEM, XRD) indicates that phase separation of titanium oxide is absent. The mesoporous TS-1 zeolite exhibits improved catalytic activity in the hydroxylation of phenol and ammoxidation of methyl ethyl ketone. The catalytic activity is substantially improved by introducing mesoporosity in TS-1, whereas the selectivity to the desired products is very similar. The improved catalytic activity of the TS-1 with the hierarchical structure is mainly attributed to the improved mass transfer of reactants and products into and out of the zeolite micropores. The generation of the hierarchical pore structure by the one-pot carbon-templating route becomes a general strategy for the synthesis of hierarchical
zeolite with different compositions.


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Bài gửiTiêu đề: Enhanced Cooperative Activation Effect in the Hydrolytic Kinetic Resolution of Epoxides on [Co(salen)] Catalysts Confined in Nanocages   Fri Oct 28, 2011 7:40 pm

It has been recognized that the cooperative activation by two or more catalytic centers with proper proximity could greatly increase the activity and enantioselectivity of homogeneous chiral catalysts through a specific control of the transition state, like in enzymatic catalysis.[1] If the cooperative activation could be realized in heterogeneous asymmetric catalysis, it may provide new possibilities for the development of highperformance heterogeneous catalysts, especially solid catalysts. This area is of ongoing academic and industrial interest for its potential advantages, such as in the separation and recycling of catalysts, continuous flow operations, and for the easy purification of products.


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Bài gửiTiêu đề: Ethane-bridged hybrid mesoporous functionalized organosilicas with terminal sulfonic groups and their catalytic applications   Fri Oct 28, 2011 7:41 pm

The synthesis of a new class of sulfuric acid-functionalized ethane-bridged, mesoporous hybrid organosilicas is reported where the propylsulfonic groups attached with ethane-bridged silica exhibited reasonable catalytic activity in esterification of acetic acid with ethanol as well as the hydrolysis of cyclohexylacetate. Materials were synthesized by co-condensation of ethane-bridged organosilane (MeO)3SiCH2CH2Si(OMe)3 with 3-mercaptopropyltrimethoxysilane (MeO)3SiCH2CH2CH2SH in the presence of octadecyltrimethylammonium chloride surfactant.
Powder X-ray diffraction patterns and nitrogen sorption analysis reveal the formation of mesoporous material with uniform porosity. The maximum content of incorporated mercaptopropylsilane in the mesoporous framework obtained was 3.45 mmol g21. The thiol (–SH) moieties of mercaptopropyl groups that protrude into the pore channels are readily accessible for further oxidation. The surface moieties functionalized with propylsulfonic groups (–CH2CH2CH2–SO3H) were generated by the controlled oxidation of propylthiol surface groups using concentrated HNO3. A maximum acid exchange capacity (acid–base titration methods) of 1.38 H+ mmol g21 was achieved after oxidation. Further, the materials were
characterized using elemental analysis, FT-IR, 29Si and 13C MAS-NMR, transmission electron microscopy and TGA. Two probe reactions, the esterification of acetic acid with ethanol and its reverse the hydrolysis of cycloacetonate, showed the significance of the material in catalytic
applications. The catalytic results showed the esterification activity is comparable to that of commercial Nafion-H and also the involvement of hydrophobic nature of the material in the hydrolysis reaction.


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Bài gửiTiêu đề: Evolution from hollow nanospheres to highly ordered FDU-12 induced by inorganic salts under weak acidic conditions   Fri Oct 28, 2011 7:44 pm

Sulfates have big influence on the structure and morphology of the mesoporous silicas synthesized under weak acidic conditions. The evolution from silica hollow nanospheres to doughnut-like nanoparticles, and to FDU-12 type mesoporous silicas with Fm 3 m symmetry can be induced by CuSO4 during the condensation of TMOS around Pluronic F127 surfactant in weak acidic solution (pH = 3.25). It is noteworthy that doughnut-like nanoparticles can be obtained in the presence of lower amounts of CuSO4. Similar to CuSO4, other divalent sulfates, such as ZnSO4, NiSO4, and MgSO4 can also induce the formation of Fm 3 m mesostructure. However, the presence of K2SO4 and Na2SO4 specially results in the formation of hollow nanospheres. Plausible mechanisms for the formation of FDU-12 and hollow nanospheres were also proposed.


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Bài gửiTiêu đề: From Hollow Nanosphere to Hollow Microsphere Mild Buffer Provides Easy Access to Tunable Silica Structure   Fri Oct 28, 2011 7:46 pm

A facile synthesis method for producing silica hollow spheres from nano- to microsize level is realized by adjusting the hydrolysis and condensation kinetics of silane precursors in a mild buffer solution (NaH2PO4-Na2HPO4, pH ≈ 7.0) in the presence of F127 (EO106PO70EO106) surfactant. Characterization using transmission electron microscopy, field-emission scanning electron microscopy, and nitrogen sorption techniques
reveals that the silica hollow nanospheres with outer diameter of about 12 nm can be obtained with tetramethoxysilane as silane precursor. Silica hollow nanospheres (∼20 nm) can also be prepared using tetraethoxysilane (TEOS) as silane precursor with the addition of hydrolysis and condensation catalyst NH4F. Using TEOS as the silane precursor without F-, the formation of silica hollow microspheres (0.5∼8 μm) was
observed. Time-resolved in situ UV-Raman results show that TEOS does not hydrolyze at room temperature, and the hydrolysis of TEOS occurs immediately at room temperature when NH4F was added to the buffer solution. The fast hydrolysis and condensation rates of silane precursor favor the formation of hollow nanospheres through the condensation of silicate around a single micelle of F127 in NaH2PO4-Na2HPO4
buffer solution. The construction of hollow microspheres is attributed to the formation of O/W emulsion by the hydrophobic TEOS with the aid of F127 surfactant due to the existence of unhydrolyzed TEOS at room temperature under current synthetic conditions.


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