117,420 research outputs found
Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FT-IR, XRD and MAS-NMR study
No full textSamples of beta-zeolite thermally treated at di†erent temperatures and acid leached with diluted hydrochloric
acid solution have been investigated by XRD, 27Al MAS-NMR spectroscopy and FTIR spectroscopy. The
results have been used to interpret the behaviour of the samples as catalysts for the acylation of 2-methoxynaphthalene.
It has been shown that the as prepared sample presents two types of extraframework species.
These are identiÐed as Al hydroxo-ions highly dispersed in the internal zeolite channels and Al oxide
nanoparticles. Calcination causes dealumination of the framework and progressive conversion of the Al
hydroxo-ions into Al oxide nanoparticles that reduce the zeolite channels practicability, modifying the shape
selectivity e†ect. The acid sites present in the sinusoidal channels cm BrÔnsted (l ~1) can be OH \ 3608
distinguished from those located in the larger ones cm (l ~1), due to the inability of the bulky OH \ 3620È3612
probe molecule pivalonitrile to enter the former. However, internal terminal silanols cm (l ~1) also OH \ 3735
apparently display a signiÐcant acidity, deÐnitely higher than the acidity of those absorbing at 3747 BrÔnsted
cm~1, thought to be located at the external crystal surface. The strongest Lewis acidity is displayed by the
aluminum hydroxo-ions, while that of alumina nanoparticles is a little weaker. Acid-leached beta-zeolite also
displays a medium strength Lewis acidity, likely due to framework Al cations. Thus a partial reinterpretation
of the real structure of beta-zeolite and a partial reassignment of the bands due to the surface hydroxy groups
are proposed
Liquid Phase Hydroformylation of 1,1-Diarylethenes catalyzed by rhodium based heterogeneous catalysts
No full textSynthesis, characterization and catalytic activity of ruthenium containing aluminum pillared bentonites
No full textA multinuclear NMR study of [Pt°( PPh3)2(alchene)] compounds containing asymmetric olefins
No full textAcylation of 2-methoxynaphtalene with acetic anhydride catalyzed by modified natural and synthetic clays
No full textVAPOR-PHASE PROPENE HYDROFORMYLATION CATALYZED BY THE RH/AL SYSTEM ON SILICA
No full textA Rh/Al system with rhodium nanocrystals was prepared by reducing rhodium trichloride supported on silica with lithium aluminum hydride at low temperature in THF. After pretreatment in Ar and in CO/H2 the system was found to be an active catalyst of vapour phase propene hydroformylation at atmospheric pressure. The nature and composition of the active surface was studied by X-ray diffraction, X-ray photoemission spectroscopy (XPS) and Fourier transform-IR spectroscopy. Regioselectivity and chemoselectivity data are correlated to the proposed nature and morphology of the active sites of the catalyst derived from spectroscopic data. The Rh/Al system is compared with the Rh/B system we described in preceding papers. © 1993
Solid acid catalysts from clays-Part 3: Benzene alkylation with ethylene catalyzed by aluminum and aluminum gallium pillared bentonites
No full textSynthesis of Aminopropyl-silica Xerogels: Tuning of the Preparation Method for the Optimization of the Catalytic Performance in the Selective Synthesis of (E)-nitrostyrenes
No full textSynthesis of Aminopropyl-Silica Xerogels: Tuning of the Preparation Method for the Optimisation of the Catalytic Performance in the Selective Synthesis of (E)-Nitrostirenes
No full textSTRUCTURAL STUDIES OF AL-BASED POWDERS PREPARED BY CHEMICAL METHODS
No full textFinely dispersed metal powders have been obtained after chemical reduction of Ni and Co acetylacetonate by lithium aluminum hydride in tetrahydrofuran at low temperature. The Al/Ni and Al/Co stoichiometry of the as-reduced powders was 1.1 and 1.2, respectively. The structure and thermal stability of the as-reduced powders were affected by the temperature of reduction. For the NiAl powders it was found that the thermal treatment initially induces a separation of highly unstable Ni(Al) and Al(Ni) solid solutions, which subsequently react to give a single NiAl phase of cubic structure not reported in the equilibrium phase diagram. Conversely, the reduction of cobalt acetylacetonate directly gives a cubic metastable phase, from which precipitates some hexagonal form of Co after treatment at 450-degrees-C
- …
