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1.
Nanoparticles of periodic mesoporous organosilica (PMO) with benzene bridging groups were prepared using a 1,4-bis(triethoxysilyl)benzene organosilica precursor and mixed surfactant templates composed of a poly(ethylene oxide)–poly(dl-lactic acid-co-glycolic acid)–poly(ethylene oxide) (PEO–PLGA–PEO) triblock copolymer and a fluorocarbon surfactant under acidic conditions. Mesoporous organosilica particles clearly exhibited a nanoscale diameter of 50–1000 nm by scanning electron microscopy. Moreover, these particles possessed a mesostructure with uniform pores in the range of 6.3–6.6 nm and core-shell type spherical morphology, which were confirmed by Synchrotron small angle X-ray scattering, transmission electron microscopy, and nitrogen adsorption analysis. Benzene bridging groups linked covalently to Si atoms were analyzed by solid state 13C- and 29Si MAS NMR. 相似文献
2.
Selective hydrogenation of benzene to cyclohexene using a suspended Ru catalyst in a mechanically agitated tetraphase reactor 总被引:4,自引:0,他引:4
The reactivity on unsupported Ru based catalyst in benzene selective hydrogenation to cyclohexene has been studied. The reaction has been carried out in a tetraphase slurry reactor at 423 K, at 5 MPa, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO4 0.6 mol l−1. A detailed study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. No correlation has been found between the characteristic numbers of Weeler–Weisz and of Carberry mass transport at external liquid/solid interface or into the catalyst pores for both benzene and hydrogen and the selectivity of the catalyst. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. In particular the influence of the alkaline or the earth alkaline hydroxide, employed in the precipitation of the Ru precursor, on the selectivity, has been studied. Hydrogen chemisorption measurements indicate that the amount of weakly adsorbed hydrogen depends on the nature of the base employed in the precipitation step. 相似文献
3.
Gold nanoparticles in mesoporous materials showing catalytic selective oxidation cyclohexane using oxygen 总被引:4,自引:0,他引:4
Gaomeng Lü Dong Ji Guang Qian Yanxing Qi Xiaolai Wang Jishuan Suo 《Applied Catalysis A: General》2005,280(2):175-180
The nano-Au supported mesoporous materials were prepared and characterized by XRD, N2 adsorption/desorption, UV–vis, XPS, and ICP-AES. The liquid-phase selective oxidation cyclohexane to cyclohexanol and cyclohexanone over nano-Au in mesoporous materials catalyst was carried out in a solvent-free system, in which oxygen was the only oxidant and the reaction conditions are very moderate. 相似文献
4.
5.
The catalytic hydrogenation of benzene on transition metal surfaces is of fundamental importance in petroleum industry. With the aim to improve its efficiency and particularly the selectivity to cyclohexene, in this contribution we perform periodic density functional theory calculations to determine the potential energy surface in the hydrogenation of benzene on Ru(0 0 0 1). By following the Horiuti–Polanyi mechanism with a step-wise addition of hydrogen adatoms, we investigate the adsorption of all the possible reaction intermediates and identify the most favored adsorption configuration for each intermediate. In particular, the most stable isomer for the same C6Hn (n = 8, 9, 10) species are revealed as the most conjugated isomers, which are consistent with those in the gas phase. The elementary hydrogenation reactions of the most stable intermediates are then investigated under different H coverage conditions: the reaction barriers are calculated to be 0.68–0.97 eV at the low H coverage and 0.32–1.14 eV at the high H coverage. The high H coverage reduces significantly the overall barrier height of hydrogenation. With the determined pathway, we propose that the hydrogenation of benzene on Ru(0 0 0 1) follows the mechanism with the step-wise hydrogenation of neighboring C atoms in the ring, i.e., 1–2–3… hydrogenation. The selectivity to cyclohexene on Ru is also discussed, which highlights the importance of the π mode adsorption of benzene and also the adverse effect of secondary reaction process involving the readsorption and hydrogenation of cyclohexene. 相似文献
6.
Florian Feil Christophe Jung Johanna Kirstein Jens Michaelis Chen Li Fabian Nolde Klaus Müllen Christoph Bruchle 《Microporous and mesoporous materials》2009,125(1-2):70
Mesoporous silica materials are ideally suited as host–guest systems in nanoscience with applications ranging from molecular sieves, catalysts, nanosensors to drug-delivery-systems. For all these applications a thorough understanding of the interactions between the mesoporous host system and the guest molecules is vital. Here, we investigate these interactions using single molecule spectroscopy (SMS) to study the dynamics of three different terylene diimide (TDI) dyes acting as molecular probes in hexagonal and lamellar mesoporous silica films. The diffusion behaviour in the hexagonal phase is represented by the trajectories of the single molecules. These trajectories are highly structured and thus provide information about the underlying host structure, such as domain size or the presence of defects inside the host structure. The three structurally different TDI derivatives allowed studying the influence of the molecular structure of the guest on the translational diffusion behaviour in the hexagonal phase and the lamellar phase. In the lamellar phase, the differences between the three guests are quite dramatic. First, two populations of diffusing molecules – one with parallel orientation of the molecules to the lamellae and the other with perpendicular orientation – could be observed for two of the TDI derivatives. These populations differ drastically in their translational diffusion behaviour. Depending on the TDI derivative, the ratio between the two populations is different. Additionally, switching between the two populations was observed. These data provide new insights into host–guest interactions like the influence of the molecular structure of the guest molecules on their diffusional as well as on their orientational behaviour in structurally confined guest systems. 相似文献
7.
Acidity of mesoporous HZSM-5 prepared using amphiphilic organosilane template molecules was measured. Brønsted acid sites were observed in the prepared sample, and the number and the strength of Brønsted acid sites were determined quantitatively by a method of infrared-mass spectroscopy/temperature-programmed desorption (IRMS-TPD) of ammonia. ΔH for ammonia adsorption as an index of the strength was ca. 150 kJ mol−1 that was almost the same as on usual HZSM-5, but the number was smaller than that of HZSM-5. From the measured acidity, it was concluded that the mesoporous materials contained a smaller concentration of Brønsted acid site notable on the structure of HZSM-5. Measurements of turnover frequency (TOF) in the catalytic cracking of octane supported the conclusion. Density functional calculations showed that the defect sites Al–OH and Si–OH attached to the Brønsted acid site changed the strength of the acid sites to show some possible structures of the weak and strong Brønsted acid sites included in the mesoporous HZSM-5. Acidities of Al-MCM-41 and silica–alumina were also measured, and the difference in the solid acidities of these materials was discussed. 相似文献
8.
Byunghwan Lee Haoguo Zhu Zongtao Zhang Steven H. Overbury Sheng Dai 《Microporous and mesoporous materials》2004,70(1-3):71-80
Catalytic activities of gold strongly depend on its particle size. It is necessary to have homogeneous distributions of small gold nanoparticles with diameters between 2 and 5 nm for excellent catalytic activities. In this study, gold-containing mesoporous silica materials were prepared by a co-synthesis method. The essence of this sol–gel co-synthesis method is to combine together neutral surfactant template synthesis of mesoporous silica materials with the introduction of metal ions via bifunctional silane ligands, so that the formation of mesostructures and metal–ion doping occur simultaneously. The formation of gold nanoparticles with size less than 5 nm inside mesoporous materials (HMS, MSU, and PMO) has been achieved by this co-synthesis sol–gel process. In addition, the effects of post-treatments, such as calcination and reduction, on pore structures and nanoparticle size distributions were also investigated. 相似文献
9.
Marcos J. Jacinto Osvaldo H.C.F. Santos Renato F. Jardim Richard Landers Liane M. Rossi 《Applied Catalysis A: General》2009,360(2):177-182
We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions. 相似文献
10.
Ana C.R. Melo Antonio S. Araujo Edjane F.B. SilvaRicardo M. Oliveira Valter J. Fernandes Jr.Geraldo E. Luz Jr. Antonio G. Souza 《Fuel Processing Technology》2011,92(7):1340-1344
Mesoporous materials type MCM-41 and AlMCM-41 were synthesized by the hydrothermal method and characterized by X-ray diffraction and nitrogen adsorption. Analyses have showed that the hexagonal structures of the materials were preserved and the template completely removed. In this work, the degradation of pure sunflower oil and mixed with mesoporous materials were evaluated. A kinetic study of the oil degradation was performed by thermal analysis under heating rates of 5, 10 and 20 °C min−1 using the model-free kinetic in order to determine the kinetic parameters for this process. From this method, the obtained values of apparent activation energy for sunflower oil/AlMCM-41 was of 167 kJ mol− 1. 相似文献
11.
Qun Guo Zhizhi Zhang Xiwen Zhang Fengxiang Ling Wanfu Sun Ruifeng Li Kechang Xie 《Journal of Porous Materials》2009,16(2):209-213
Mesoporous silica-pillared montmorillonites (SPMs) were prepared based on cation-exchange, gallery-templated synthesis method,
and the post-synthesis treatment using ammonia, and characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis
(TGA), and N2 adsorption–desorption. The results showed that ammonia played a very important role in the formation of the mesoporous materials;
the calcined SPMs indicated a BET surface area of 511 m2/g and average pore size of 3.1 nm by adjusting the ammonia treating temperature at 110 °C. The formation of SPMs was discussed
and its progressing mechanism was suggested. 相似文献
12.
Mesostructured aluminosilicates have been synthesized using gels prepared by reacting colloidal silica (Ludox AS) with Al(OH)3, aluminum isopropoxide (Al(iPrO)3) or NaAlO2 in the presence of a surfactant. The hydrothermal transformation at 110°C of these gels produced solids with the hexagonal structure typical of MCM-41-type materials. These crystals have been characterized by X-ray diffraction, thermal analysis (TG/DTA), N2 sorption and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The type, strength and density of acid sites have been studied using microcalorimetry and infrared (IR) spectroscopy.As a general trend, pore volume and average pore size decreased as the gel SiO2/Al2O3 ratio decreased from 32–8, while the pore wall thickness remained in the 1.0–1.5 nm range. Except for one sample, Al was incorporated in tetrahedral coordination inside the pristine crystals. However, as expected, dealumination occurred upon calcination at 600°C/12 h, yielding materials having both tetrahedral and octahedral Al-species. Fourier transform infrared (FTIR) experiments with pyridine have indicated that these mesostructured aluminosilicates contain both Brönsted and Lewis acid sites and that acidity is strongest in samples prepared with NaAlO2.Microcalorimetry experiments with ammonia as the probe molecule have shown that Al insertion into the mesoporous silicate framework affects acid site strength and distribution in a manner controlled by synthesis condition. Samples prepared with Al(OH)3 contain a wide distribution of acid site strengths, indicating the absence of preferred locations of Si-O-Al groups within the pore walls. In contrast, distinct populations of acid sites with strengths in the 130–140 kJ mol−1 range or near 150 kJ mol−1, appear in materials prepared with Al(iPrO)3 or with NaAlO2, respectively. Al sites may be located at the surface of the pore wall, where they interact directly with the basic probe molecule. They may also be sandwiched between silica layers within the pore wall (3–4 Si layers thick), giving acid sites with a strength comparable with that of smectites. Finally, they may also be present in the pore (or within the pore walls) as extraframework Al(VI)-species. The nature, size, concentration, ease of hydrolysis and condensation of the aluminum precursors during synthesis control aluminum incorporation, distribution and location within the structure and with it the acidity of the resulting mesoporous aluminosilicate. 相似文献
13.
R. Akkari A. Ghorbel N. Essayem F. Figueras 《Microporous and mesoporous materials》2008,111(1-3):62-71
Silica supported sulfated zirconia catalysts were synthesized via a new method by grafting sulfated zirconia on the surface of a silica aerogel previously prepared. The main parameters studied in this work were the S/Zr, Zr/Si molar ratios and the support nature. The synthesized solids were characterized using XRD, N2 physisorption at 77 K, TG-DTA/SM, sulfur chemical analysis and adsorption–desorption of pyridine followed by infrared spectroscopy. These solids were tested in the n-hexane isomerization reaction. Two types of mesopores were observed on the silica aerogel. This mesoporosity was affected depending on the preparation parameters.
The increase of the Zr/Si molar ratio induces the decrease of the size of zirconia particles deposed on the support. In this case, appreciable amounts of sulfur are retained with the presence of a relatively strong Brönsted and Lewis acid sites on the catalyst surface. A high density of Brönsted sites seems to be interesting in the n-hexane isomerization reaction. 相似文献
14.
Ankur Bordoloi Nevin T. Mathew F. Lefebvre S.B. Halligudi 《Microporous and mesoporous materials》2008,115(3):345-355
Inorganic–organic hybrid materials based on functionalized silica and carbon were synthesized by anchoring molybdovanadophosphoric acid (H5[PMo10V2O40] · 32.5H2O) onto amine-functionalized SBA-15, ethane-bridged SBA-15 and mesoporous carbon, respectively. Small angle X-ray diffraction, N2 sorption analysis, HRTEM, SEM, FT-IR, CP-MAS NMR were used to diagnose the mesoporous structure of inorganic–organic hybrid materials. The structural integrity of molybdovanadophosphoric acid has been found to be retained after immobilization over mesoporous materials. These inorganic–organic hybrid materials were tested in the environmentally friendly oxidation of 2-methylnaphthalene (2MN) with 30% aqueous hydrogen peroxide. Molybdovanadophosphoric acid containing mesoporous organosilica hybrid material (ethane-bridged SBA-15) exhibited higher catalytic activities in the oxidation of 2MN to give a clean product 2-methy-1,4-naphthoquinone (menadione vitamin K3 precursor), because of the improved hydrophobicity of the material. The correlation between structural properties and catalytic activities of these hybrid materials has been well addressed in our present studies. 相似文献
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16.
Yunpu Zhai Ying Wan Yan Cheng Yifeng Shi Fuqiang Zhang Bo Tu Dongyuan Zhao 《Journal of Porous Materials》2008,15(5):601-611
A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template
with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization
and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N2 adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted
with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures
were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as
mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors,
but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl
alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs
prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface
areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon
surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors
with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic
walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization
of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high
temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance
carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization.
The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups
and limited graphitizable properties, and in turn medium but almost constant capacitances. 相似文献
17.
Li Zhang Lei Wang Xiao-Yan Ma Rui-Xiang Li Xian-Jun Li 《Catalysis communications》2007,8(12):2238-2242
The influences of pH on the catalytic properties of Ru-η6-C6H6-diphosphine complex [RuCl(η6-C6H6)(BISBI)]Cl (1) (BISBI = 2,2′-bis(diphenylphosphinomethyl)-1,1′-biphenyl), [RuCl(η6-C6H6)(BDPX)]Cl (2) (BDPX = 1,2-bis(diphenylphosphinomethyl)benzene), Ru2Cl4(η6-C6H6)2(μ2-BDNA) (3) (BDNA = 1,8-bis(diphenylphosphinomethyl)naphthalene), [RuCl(η6-C6H6)(BISBI)]BF4 (4), [RuCl(η6-C6H6)(BDPX)]BF4 (5), and [(η6-C6H6)2Ru2Cl2(μ2-Cl)(μ2-BDNA)]BF4 (6) for the hydrogenation of benzene were investigated in aqueous-organic biphasic system. The hydrogenation of benzene catalyzed by all complexes yielded only cyclohexane. The catalytic results revealed that the stabilities of these complexes were not only closely relative with their compositions or molecular structures but also the pH value of aqueous solution. Complexes 1 and 2 were homogeneous catalysts at pH <5, but complexes 3, 4, 5 and 6 were partly decomposed in the same reaction conditions and played simultaneously the roles of homogeneous and heterogeneous catalysts. When the pH was up to 12, all of six complexes were gradually decomposed to Ru(0) particles. The addition of extra phosphine ligand was favorable to prevent these complexes from decomposing in the catalytic process. The experiment of mercury poisoning and the curve of conversion vs time strongly supported above conclusions. 相似文献
18.
《Ceramics International》2021,47(19):27316-27323
CO2 methanation is a significant route to decrease carbon emission as well as realize carbon neutrality and has gained considerable concerns from experts in the environment and energy field currently. Herein, highly dispersed ruthenium nanoparticles entrapped in TiO2 nanotubes, labeled as Ru-in/TNT, were constructed and adopted for photo-thermal driven CO2 methanation. The Ru nanoparticles confined in the nanotube exhibited an enhanced CO2 methanation activity, especially under light irradiation. Multiple characterization techniques (XRD, XPS, UV–vis DRS, HRTEM, Raman, etc.) were conducted to reveal the effect of confinement synergy on photo-thermal catalytic performance. A boosted photo-generated electron-hole separation efficiency is achieved as a result of the confinement effect, yielding more hot electrons to accelerate methanation activity. This photo-assisted confinement synergy can be expected for constructing an efficient photo-thermal catalytic system. 相似文献
19.
通过浸渍法在介孔分子筛上负载亲砷活性组分,制备了介孔分子筛集砷材料。用XRD、SEM、N2吸附和脱附进行了表征,并针对液态烃常温脱砷体系,对该材料的吸附集砷性能进行了进一步的测定。研究结果表明介孔分子筛集砷材料具有比常规脱砷剂更为优良的集砷性能。 相似文献
20.
Preparation and characterisation of chemisorbents based on heteropolyacids supported on synthetic mesoporous carbons and silica 总被引:10,自引:0,他引:10
Alexei Lapkin Bengü Bozkaya Tim Mays Luisa Borello Karen Edler Barry Crittenden 《Catalysis Today》2003,81(4):7892-621
The preparation of chemisorbents based on tungsto- and molybdophosphoric acids supported on two types of synthetic mesoporous carbons and two types of mesoporous silica is described. Strong solid acids with good accessibility to acid sites may potentially be effective adsorbents for the removal of basic molecular impurities, such as amines, from ultrapure manufacturing environments. Prepared materials were characterised by scanning electron microscopy, nitrogen adsorption, Fourier-transform infrared spectroscopy, powder X-ray diffraction, and equilibrium ammonia uptake. Composites of SBA-15 with heteropolyacids were synthesised. It was shown that the inclusion of HPAs into SBA-15 results in the loss of long range order. Adsorbents based on the HPAs impregnated into the supports with the open-pore morphology (Novacarb and SBA-15) were found to be promising materials. A composite of tungstophosphoric acid with sol–gel SiO2 was found to have the highest ammonia uptake. 相似文献