55,470 research outputs found
High-Quartz solid solution phases from xerogels with conposition 2MgO·2Al2O3·5SiO2 (cordierite) and Li2O·Al2O3·nSiO2 (n=2 to 4) (β-eucriptite) characterization by XRD, FTIR and surface measurements
No full text[100714.EG "beta". SAPERI.ALTRE_INFORMAZIONI:] Si riferisce sulla preparazione di xerogeli amorfi di composizioni pari a quella della cordierite (Mg2Al4Si5O18) e della eucriptite (Li2O·Al2O3·n SiO2 dove n= da2 a 4). Questi interessanti materiali, ad elevatissimo sviluppo superficiale (fino a 900 m²/g) furono caratterizzati mediante diffrazione RX, FTIR e misure di superficie. Caratteristica peculiare di questi materiali è anche lo distribuzione monomodale del diametro dei pori, centrata attorno a 40
Surface and Structure Characterization of Some Perovskite-type Powders To Be Used As Combustion Catalysts
No full textSome perovskite-type transition-metal mixed oxide powders active in the combustion catalysis, with formulas LaMO(3) (M = Fe, Cr, Co, and Mn), have been prepared by different methods. Similarly, potential supports for combustion catalysts nearly isostructural with the above ones have been prepared, with compositions SrZrO3 and LaAlO3. Mixed phases with formulas Sr1-xLaxZr1-xMnxO3 have also been investigated. The bulk properties have been studied by XRD, far-IR spectroscopy, and DTA-TG analyses. Morphological properties have been determined by XRD, SEM, and surface area measurements. These phases crystallize after heating at 970 K (except LaFeO3, which is already crystalline after calcination at 770 K) with surface area ranging 10-20 m(2)/g. The solubility of LaMnO3 into SrZrO3 is limited to near 10%. Their surface properties have been investigated by IR spectroscopy that showed a predominantly basic surface character of all these solids
Mullite-type structures in the systems Al2O3-Me2O (Me=Na,K) and Al2O3-B2O3
No full textAmorphous solids belonging to the systems Al2O3-Me2O (Me = Na,K) and Al2O3-B2O3 were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850-degrees to 900-degrees-C for the compositions Al6MexO(9+0.5x) (x almost-equal-to 1; Me = Na, K) and Al(6-x)BxO9 (1 less-than-or-equal-to x less-than-or-equal-to 3). The resultant solids were stable only within a definite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na+,K+) or (2) substitution of B for Al in some of the tetrahedral positions
FT-IR study of the acid sites on the surface of silica supported ruthenium oxide
No full textFT-IR spectra of adsorbed CO, pyridine and acetone indicate that on the surface of RuO2/SiO2 are present Brønsted and Lewis acid sites and different reduced metal sites. © 1984
An ultraviolet–visible–near infrared study of the electronic structure of oxide-supported vanadia–tungsta and vanadia–molybdena
No full textThe ultraviolet-visible-near IR spectra of a series of catalysts have been recorded and discussed. In particular bulk and alumina-, titania- and silica-supported V, W, and Mo oxides have been considered. Additionally mixed V-W and V-Mo-supported oxides have been investigated. The data show that, in agreement with vibrational data and other literature data, the oxides supported on silica are similar to the corresponding bulk oxides. In contrast, the spectra of the oxides supported on alumina and titania correspond to surface oxide species where the metal stays in a lower overall coordination with respect to the bulk oxides. Finally, the spectra show that only in the case of titania-supported oxides an electronic interaction between the supported metal oxide centers through the support conduction band is possible. This allows to justify on electronic bases the activating effect of titania for vanadia, vanadia-tungsta and vanadia-molybdena catalysts used in the hydrocarbon selective oxidation catalysis and for the selective catalytic reduction of nitrogen oxide by ammonia. (C) 2001 Elsevier Science B.V. All rights reserved
Infrared Characterization of the Hydrocarbon Intermediates In the Oxidation of Toluene and Xylenes Over Vanadia Titania Catalysts
No full textThe IR spectra of adsorbed species arising from the interaction of toluene, o-xylene, m-xylene and p-xylene vapours with the surface of a vanadia-titania selective oxidation catalyst are discussed. It is concluded that they are due to benzyl- and methylbenzyl-vanadium species arising from hydrogen abstraction from the hydrocarbon molecule. These species are thought to play a key role in the oxidation mechanism
Islamic Practices, Traditions and Beliefs in Egypt and the Eastern Mediterranean in the Early 16th Century: Georgius Gemnicensis’ Ephemeris
No full textThis article reports several excerpts of Georgius Gemnicensis’ Ephemeris, a travel journal in which the author recounted his experiences in Mamluk Egypt and the Eastern Mediterranean, and provided a number of details about customs, beliefs and Islamic practices in such territories at the beginning of the 16th century
An FT-IR study of the conversion of 2-chloropropane, o-dichlorobenzene and dibenzofuran on V(2)O(5)-MoO(3)-TiO(2)SCR-DeNO(x) catalysts
No full textSpectra of the adsorbed species arising from contact of a V(2)O(5)-MoO(3)-TiO(2) model SCR catalyst with ortho-dichlorobenzene (o-DCB) and dibenzofuran (DBF) and their evolution with the temperature are presented and discussed. Dichlorobenzene adsorbs weakly probably on Lewis acid sites through the chlorine atom. A very fast nucleophilic substitution on dichlorobenzene to a chlorophenate species occurs already at RT. On the contrary, adsorption of dibenzofuran is molecular, probably through the oxygen atom on Lewis sites. The aromatic rings of both molecules tend to be later oxidized to give carboxylate species. Parallel experiments with chloropropane show that dehydrochlorination occurs readily, hydrochloric acid is adsorbed quite weakly and that propene can be further oxidized. However, heavier oxidized species like cyclic anhydrides are also formed from chloropropane. The data suggest that the dechloration step of the phenyl ring could be not critical. On the contrary, the building-up of aromatic compounds from smaller molecules is possible and the oxidation of phenyl ring can be slow near reaction conditions. The possibility that the reaction between phenate species and chlorobenzenes give the "de novo" synthesis of dioxins is envisaged. (C) 2002 Elsevier Science B.V. All rights reserved
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