Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations

Hydrophobic Ti-MCM-41 samples prepared by post-synthesis silylation treatment demonstrate to be highly active and selective catalysts in olefins epoxidation by using organic hydroperoxides as oxidizing agents in liquid phase reaction systems. Epoxide yields show important enhancements with increased silylation degrees of the Ti-mesoporous samples. Catalytic studies are combined and correlated with spectroscopic techniques (e.g. XRD, XANES, UV-Visible, 29Si MAS-NMR) and calorimetric measurements to better understand the changes in the surface chemistry of Ti-MCM-41 samples due to the post-synthesis silylation treatment and to ascertain the role of these trimethylsilyl groups incorporated in olefin epoxidation. In such manner, the effect of the organic moieties on solids, and both water and glycol molecules contents on the catalytic activity and selectivity are analyzed in detail. Results show that the hydrophobicity level of the samples is responsible for the decrease in water adsorption and, consequently, the negligible formation of the non-desired glycol during the catalytic process. Thus, catalyst deactivation by glycol poisoning of Ti active sites is greatly diminished, this increasing catalyst stability and leading to practically quantitative production of the corresponding epoxide. The extended use of these hydrophobic Ti-MCM-41 catalysts together with organic hydroperoxides for the highly efficient and selective epoxidation of natural terpenes is also exemplified.

Paving the way for methane hydrate formation on metal–organic frameworks (MOFs)

The presence of a highly tunable porous structure and surface chemistry makes metal–organic framework (MOF) materials excellent candidates for artificial methane hydrate formation under mild temperature and pressure conditions (2 °C and 3–5 MPa). Experimental results using MOFs with a different pore structure and chemical nature (MIL-100 (Fe) and ZIF-8) clearly show that the water–framework interactions play a crucial role in defining the extent and nature of the gas hydrates formed. Whereas the hydrophobic MOF promotes methane hydrate formation with a high yield, the hydrophilic one does not. The formation of these methane hydrates on MOFs has been identified for the first time using inelastic neutron scattering (INS) and synchrotron X-ray powder diffraction (SXRPD). The results described in this work pave the way towards the design of new MOF structures able to promote artificial methane hydrate formation upon request (confined or non-confined) and under milder conditions than in nature.

Examen de Ingenios, I: Apostillas, Comentarios y glosas al comentario del "Don Quijote",

Mode of access: Internet.

Cantos populares españoles, recogidos,

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El andalucismo y el cordobesismo de Miguel de Cervantes /

Includes bibliographical footnotes.

El apócrifo "Secreto de Cervantes"; juicio emitido acerca de ́ el en dos ocasiones.

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Burla burlando...

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El ingenioso hidalgo Don Quijote de la Mancha,

"Ediciones del ʻQuijote' en castellano": v. 1, leaf following p. xxvii; repeated v. 4, prelim. leaf 3.

La copla : bosquejo de un estudio folk-lórico /

"Conferencia leída en la Fiesta de la Copla que celebró el ateno de Madrid el día 6 de abril de 1910."

Medicina sceptica y Cirugia moderna, con un tratado de operaciones chirurgicas : tomo primero que llaman tentativa medic /

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Noches anatómicas ó Anatomia compendiosa /

Texto con apostillas marginales.

Carta pastoral a los religiosos, y religiosas Carmelitas Descalzos /

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Tratado de fiebres malignas : con su apropiada curacion, acomodada à la mas racional practica /

Palau

Margarita sobre el agua, preciosa perla, que en la divina concha del sagrado texto coge el rocio del cielo, con que evidencia que el agua no es remedio universal /

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