Vibrational Study on the Local Structure of Post‐Synthesis and Hybrid Mesoporous Materials: Are There Fundamental Distinctions?

Vaz, Pedro D.; Nunes, Carla D.; Vasconcellos-Dias, Maria; Nolasco, Mariela M.; Ribeiro‐Claro, Paulo J. A.

doi:10.1002/chem.200700310

Cited by 20 publications

(15 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Other important features comprised the band at ca. 1634 cm −1 due to OH bending modes and an intense broad band at 1240–950 cm −1 associated with asymmetric stretching vibration modes of the mesoporous framework (νSi–O–Si) [25].…”

Section: Resultsmentioning

confidence: 99%

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

et al. 2019

Self Cite

View full text Add to dashboard Cite

Three new complexes [Mo(η3-C3H5)Br(CO)2{iPrN=C(R)C5H4N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)3, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR, 13C- and 29Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.

show abstract

Section: Resultsmentioning

confidence: 99%

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…Another important feature is the band at ca. 1630 cm −1 due to OH bending modes, while the intense broad band at 1239–950 cm −1 is assigned to the asymmetric stretching vibration modes of the mesoporous framework ( ν SiOSi) 20. The immobilization of magnetic iron oxide nanoparticles coated with silica ( MNP‐Si ) on the surface of the mesoporous material was probed by the presence of characteristic bands of this type of nanoparticles, namely, an intense band at 451 cm −1 due to the ν FeO stretching mode and also a broad and intense band that appears at 1082 cm −1 due to the νSiO modes.…”

Section: Resultsmentioning

confidence: 99%

Helical Channel Mesoporous Materials with Embedded Magnetic Iron Nanoparticles: Chiral Recognition and Implications in Asymmetric Olefin Epoxidation

et al. 2015

View full text Add to dashboard Cite

In this workamesoporous nanocomposite material comprising helical chiral channelsa nd with embedded magnetic iron oxide nanoparticles in its Si-basedM CM-41 type framework was synthesized. Afterwards,abipyridine derivativew as grafted to the inner surface used as ligandt oc oordinate am olybdenum(II) precursorc omplex. TheM ol oading was found to be 2.42 wt% Mo,c orresponding to 0.26 mmol Mo g À1 .T he successful preparation of this helicalm esoporous material was evidencedb ya ne xtensivec haracterization process using powder XRD, SEM/TEM analysis,F T-IR and Raman spectroscopies,T GA analysis and also by SQUID measurements.S electivea dsorption of enantiopure d-a nd lphenylalanine shows that the material hasapreference for the d-o ver the l-e nantiomer. This provides evidence that the channels are chiral (although the particles are not)a nd that it is useful for chiral recognition applications.I ta lso sets the explanation to the good results achieved in the selective epoxidation of olefins.T he resulting material was tested as catalytic precursor in the epoxidation of cis-cyclooctene,s tyrene, R-(+ +)-limonene and trans-hex-2-en-1ol, using tert-butyl hydroperoxide (tbhp) as oxygen source.T he catalytic studies show that the synthesized material yields selectively the desired epoxides of the tested substrates with very good results,e specially at higher temperatures andu sing toluene as solvent.T he major achievement of the catalyst was an outstanding stereocontrol of the reactionp roducts imposedb yt he confined space of the helicalc hiral channels.T herefore these materials offer an important contribution to asymmetric catalysis and to fields where chiral recognition is ar elevant concept.

show abstract

“…2935 cm -1 ), this may also be due to the presence of SiO 2 [58] which is very likely to be present on the particles from the soil. Although it may arise from the existence of some organic moieties (confirmed by the presence of −CH stretching modes at ca.…”

Section: Xrd Studiesmentioning

confidence: 99%

Validation of the Steinrath Index Predictions for the Degree of Soil Aggressiveness Toward Copper Corrosion in Soils Contaminated with Chlorides

Fonseca¹,

Niculita²,

Ornelas³

et al. 2015

CORROSION

View full text Add to dashboard Cite

The main goal of this study is to validate the Steinhrath index predictions towards copper corrosion in two different soils (loamy and sandy) non−modified and modified with chlorides, reaching the typical levels of seawater and Steinrath indexes varying between (-3) and (-8). Average corrosion rates between 4.5±0.3 and 124.5±0.5 µm y -1 showed to be in good agreement with the predictions of the Steinrath index.The copper surfaces, covered with corrosion products, were analyzed by visual observation, scanning electron microscopy coupled to energy dispersive spectroscopy (SEM/EDS), powder X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Cuprite (Cu 2 O) has been identified, by XRD, as the main constituent on all the surfaces, with traces of atacamite (Cu 2 (OH) 3 Cl) on top of the Cu 2 O layer. FTIR spectra suggest that, sulfate, silicate and/or hydroxyls are likely to be present. and concluded that, for short time exposures, the mass loss decreases as the amount of water increases.Bech-Nielsen et al. [19] have studied the behavior of copper in moderately acid medium (pH 5.0) and non−deareated chloride aqueous solutions (3% NaCl). Using Auger spectroscopy, the authors identified the presence of a Cu 2 O layer on the surface of copper samples. The layer thickness was found to increase with the exposure time.Soil corrosivity is not a directly measurable parameter and corrosion is largely a random phenomenon, hence no explicit relationship exists between soil properties and soil corrosivity. The soil texture is a parameter that can influence its aggressiveness since the drainage and aeration are texture dependent. Gerwin and Baumhauer [31] have concluded that corrosion of buried iron objects decreased in loamy soils due to oxygen deficiency. On the other hand, a sandy soil results in comparatively good drainage and aeration.Correlation between the corrosion rate of pipeline made of steel and soil parameters has been investigated under both controlled laboratory and natural outdoor conditions by Murray and Moran [33]. They have found a good correlation between corrosion rates of laboratory and outdoor samples. In general, the moisture level appears to control the corrosion rate following a semilog law with water concentration ranging between low (typically 6 wt%) and near saturation (typically 20 to 25 wt%) concentrations. Wang et al. [34] have concluded that the decrease of dissolved oxygen contributes to decrease gradually the corrosion rate of X80 steel in acidic soil solution. In addition, Gardiner and Melchers [35] concluded that oxygen and proton ion (H+) as the most common cathodic depolarizers, both playing its role in the corrosion process of steel in soils.

show abstract

Vibrational Study on the Local Structure of Post‐Synthesis and Hybrid Mesoporous Materials: Are There Fundamental Distinctions?

Cited by 20 publications

References 47 publications

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

Helical Channel Mesoporous Materials with Embedded Magnetic Iron Nanoparticles: Chiral Recognition and Implications in Asymmetric Olefin Epoxidation

Validation of the Steinrath Index Predictions for the Degree of Soil Aggressiveness Toward Copper Corrosion in Soils Contaminated with Chlorides

Contact Info

Product

Resources

About