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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report here, for the first time, synthesis of anchored Pd complexes in mesoporous supports such as MCM-41 and MCM-48 as true heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols to give excellent conversion ( approximately 100%) and regioselectivity ( approximately 99%) for 2-arylpropionic acids. The catalysts were characterized by powder-XRD, 31P CP-MAS NMR, FT-IR, TEM, XPS and ICP-AES. Recycle studies with these anchored Pd mesoporous catalysts were performed to confirm true heterogeneity.
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PMID:Anchored Pd complex in MCM-41 and MCM-48: novel heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols. 1217 12

The copper-tellurolate cluster [(Cu(6)(TePh)(6)(PPh(2)Et)(5)] has been loaded into the pores of MCM-41 by solid-state impregnation techniques. It was found that the best loading conditions are 110 degrees C and 10(-)(3) Torr static vacuum. The resulting material was analyzed by powder X-ray diffraction (PXRD), nitrogen adsorption isotherms, thermogravimetric analysis (TGA), (31)P CP MAS NMR spectroscopy, and TEM. It was observed that loading is accompanied by loss of the phosphine shell, with retention of the copper-tellurium core. Condensation of the impregnated material may proceed thermally or photochemically. Thermal condensation results in the formation of Cu(2)Te nanoparticles as demonstrated by PXRD, and TEM data suggests that the process has taken place inside the pores of MCM-41. Photochemical condensation yields larger metal-chalcogen clusters in the pores as suggested by the result of UV-vis diffuse reflectance spectroscopy and TEM measurements.
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PMID:Preparation, characterization, and condensation of copper tellurolate clusters in the pores of periodic mesoporous silica MCM-41. 1470 65

CpMo(CO)(3)Cl reacts with the hydroxyl (Si-OH or Si-OH-Al) functionalities of mesoporous molecular sieves such as MCM-41, MCM-48 and its aluminium analogues during grafting. XRD, N(2) adsorption-desorption, BET surface area analysis and TEM show the resulting samples as being well ordered and maintaining a uniform pore size. FT-IR spectra, elemental analysis, (13)C and (29)Si CP MAS NMR spectra confirm the successful grafting. In the presence of excess TBHP the materials show high activity in cyclooctene epoxidation and good stability.
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PMID:Heterogenisation of CpMo(CO)3Cl on mesoporous materials and its application as olefin epoxidation catalyst. 1548 19

The distribution of gallium nanocrystals in mesoporous MCM-41 host were analyzed by continuous-flow hyperpolarized 129Xe NMR spectroscopy. In contrast to unclear TEM images for the high metal contents, laser-polarized 129Xe probe can detect the whole distribution of gallium in the MCM-41 host. It is found that gallium nanocrystals are included in the mesochannels of MCM-41; a part of them also remains in the interparticle voids. The distribution of gallium metal in MCM-41 is heterogeneous. Not all the mesochannels host metallic gallium even at a high gallium loading of 65.1 wt %. Variable temperature measurements can provide information on the xenon adsorption parameters. This approach opens a sensitive way to probe the distribution of high content species in porous host materials.
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PMID:Distribution of gallium nanocrystals in Ga/MCM-41 mesocomposites by continuous-flow hyperpolarized 129Xe NMR spectroscopy. 1588 32

Nanosize mesoporous material MCM-48 was synthesized under the hydro-thermal system. The results of TEM and SEM show that the obtained MCM-48 is well organized on a 100 A length scale. Both the Nanosize and the superior organization provide this material with good thermal stability.
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PMID:Synthesis of nanosize mesoporous MCM-48 material. 1624 42

A new class of porous, mixed phase titanosilicate materials containing a microporous TS-1 phase and a mesoporous Ti-MCM-48 phase has been successfully synthesized. A novel, one-pot synthesis method was used in which the organic templates for the mesoporous and microporous phases were added sequentially to the same reaction mixture, followed by crystallization at 150 degrees C. The gemini surfactant 18-12-18 was used to form the Ti-MCM-48 mesophase; subsequent addition of tetrapropylammonium cation (TPA+) led to the formation of TS-1. The relative amounts of the two phases within the final products were controlled by optimizing the crystallization time. Crystallization times between 12 and 50 h gave materials containing both phases, with an increasing amount of microphase formed at longer crystallization times. These materials, called "Ti-MMM-2" (microporous/mesoporous materials) were characterized using powder XRD, N2 physisorption, TEM, FTIR, DR-UV/Vis spectroscopy, and 29Si MAS NMR. In the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP), Ti-MMM-2 samples exhibited higher catalytic activity (approximately 61%) than either TS-1 (16%) or Ti-MCM-48 (42%), with a very high selectivity (97%) for formation of cyclohexene oxide.
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PMID:Synthesis, structure, and reactivity of a new Ti-containing microporous/mesoporous material. 1637 32

A novel route to heterogenize an organorhenium(VII) oxide, derived from the well examined methyltrioxorhenium(VII) (MTO), on the surface of an iodosilane-modified MCM-41 is applied. The successful grafting of the -CH(2)-ReO3 moiety on the surface was evidenced by 1H CP MAS NMR, IR spectroscopy, TG-MS, and elemental analysis. XRD and TEM analyses confirm the retaining of long-range ordering throughout the grafting process. The rhenium loading of the mesoporous material after heterogenization of MTO is found to be 1.25 wt%. Despite containing formally a derivative of the very sensitive benzyltrioxorhenium(VII) the material is stable at room temperature and applicable as a heterogeneous catalyst for aldehyde olefination reactions.
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PMID:Heterogenization of an organorhenium(VII) oxide on a modified mesoporous molecular sieve. 1639 46

An intrachannel surface of host silica was functionalized through the reaction of surface silanol groups with silanes to generate a monolayer of positively charged groups, and together with the strongly adsorbed and negatively charged PtCl6(2-), resulting in nanostructured platinum-mesoporous silica composites. The highly dispersed Pt nanoparticles and nanonetworks are fabricated from (CH3O)3Si(CH2)3N(CH3)3+Cl- functionalized mesoporous silica MCM-48 with H2PtCl6 in ethanol and water solvent, and characterized by PXRD, XAS, TEM, and N2 adsorption. The solvent of H2PtCl6 solution is found to affect the mobility of Pt precursors and the resulting morphology of nanostructured metallic Pt. The effect of the intrachannel surface properties on the incorporation and the morphology of nanostructured Pt on the deposition of Pt(NH3)4Cl2 and H2PtCl6 on Al-doped or C-coated mesoporous silica MCM-41 is also studied relative to that on pure silica MCM-41.
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PMID:Morphology of nanostructured platinum in mesoporous materials-effect of solvent and intrachannel surface. 1647 27

The present study reports a green synthesis method for preparing pure (free of fly ash) and ordered MCM-41 materials from coal fly ash at room temperature (25 degrees C) during 24 h of reaction. It was shown that the impurities in the coal fly ash were not detrimental to the formation of MCM-41 at the tested conditions. The influence of initial synthesis pH on material properties of calcined MCM-41 samples was investigated by various techniques such as XRF, XPS, XRD, FTIR, DR-UV-vis, solid state NMR, N2 physisorption, TG-DTA, SEM and TEM. The experimental results showed that the amount of trace elements such as Al, Na, Ti and Fe incorporated into the sample increased with synthesis pH value. More aluminum species were incorporated with tetrahedral coordination in the framework under a high pH value. The particle size of the sample decreased with the synthesis pH value. Samples synthesized at high pH values had a larger pore size and were more hydrothermally stable than those at low pH values. From thermal analysis, it was observed that the synthesized MCM-41 samples showed a high thermal stability. These properties made the synthesized MCM-41 suitable for further processing into more useful materials in a wide range of applications.
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PMID:Synthesis of MCM-41 from coal fly ash by a green approach: influence of synthesis pH. 1664 13

Mesoporous molecular sieves Si-MCM-41 (purely siliceous) and Ti-MCM-41 (partly covered with a surface layer of TiO2) were functionalized with phosphate groups by treatment with POCl3 (denoted -MCM-41(P)and Ti-MCM-41(P), respectively). With the use of TEM, X-ray diffraction, and N2 adsorption, it was shown that the initial hexagonal structure, the high specific surface area, and porosity are retained in the functionalized materials but are not as good as in the starting materials. 1H MAS NMR and 31P MAS NMR revealed that the surface of Si-MCM-41(P) consists of silicon phosphate and pyrophosphate species. That of Ti-MCM-41(P) additionally contains titanium dihydro-, hydro-, and pyrophosphate species, the latter being predominant. TPD of adsorbed ammonia for Si-MCM-41(P) and Ti-MCM-41(P) showed that functionalization leads to the creation of moderate and strong acid sites. A combination of mesoporous structure with acidic properties makes the MCM-41 functionalized with phosphate groups promising for use as solid acid catalysts.
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PMID:Synthesis, structure, and acidic properties of MCM-41 functionalized with phosphate and titanium phosphate groups. 1685 50


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