Mixed Al/Ce oxide pillaring of montmorillonite: XRD and UV-VIS diffuse reflectance study
01 Mar 2002-Reaction Kinetics and Catalysis Letters (Kluwer Academic Publishers)-Vol. 75, Iss: 2, pp 251-258
TL;DR: In this paper, the authors show that the 4f-5d interconfigurational transitions of Ce3+ ions associated with alumina pillars can be attributed to the co-hydrolysis of co-drained Ce3 and Al3+ salts, resulting in four distinct absorption bands at 224, 263, 294 and 342 nm.
Abstract: Ce and Al pillared clays were prepared by (i) pillaring Ce3+-exchanged montmorillonite with Al13 polycation (Ce-Al-PILC) and (ii) by pillaring Na-montmorillonite with an oligomer obtained from cohydrolysis of Ce3+ and Al3+ salts (Al-Ce-PILC). Cohydrolyzed oligomer gives larger intercalating species with Ce3+ incorporated in it. The UV-DRS spectrum of clay sample intercalated with this species shows four distinct absorption bands at 224, 263, 294 and 342 nm, which are attributed to the 4f-5d interconfigurational transitions of Ce3+ ions associated with alumina pillars.
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TL;DR: In this paper, an Ag loaded Bi2O3/montmorillonite nanocomposite has been successfully prepared by a facile thermal and impregnation methods for the first time to study its photocatalytic performance for aqueous pollutant decomposition under the visible light irradiation.
60 citations
TL;DR: In this article, the environment, location and interaction of the Ce 3+ ions in the micropores of Al and Zr-pillared clays have been studied by UV-vis-diffuse reflectance spectroscopy (UVvis-DRS).
48 citations
TL;DR: The defect structure and microstructure of the complex fluorite-like oxides have an effect on the state of the supported active component, favoring the formation of clustered species in the vicinity of extended defects in the support as discussed by the authors.
Abstract: Models of the defect structure and microstructure of the CeO2, ZrO2, Ce-Me1-O (Me1 = La, Sm, Zr), and Zr-Me2-O (Me2 = Ca, Sr, Ba) nanomaterials are discussed. For ceria-based fluorite, the appearance of weakly bound oxygen and the mobility of bulk oxygen are due to distortions in the Ce-O coordination sphere and the appearance of interstitial oxygen atoms. For pure and doped zirconia, the phases forming in the intermediate temperature range are characterized by metastable structural networks differing from those observed in the equilibrium phases. The change in the local environment of the Zr cations (eight-atom coordination sphere) from a square antiprism in the initial salts to a distorted fluorite-like polyhedron in zirconia and the principle of structural conformity between hydrolyzed cations and the terminal hydroxyls of the Zr complexes in solution are the factors determining the genesis and structural features of the metastable phases. The defect structure and microstructure of the complex fluorite-like oxides have an effect on the state of the supported active component, favoring the formation of clustered species in the vicinity of extended defects in the support. Some examples of this effect in different types of reactions are provided.
44 citations
TL;DR: In this article, a heterogeneous catalyst was obtained by the direct immobilization of molybdenum compound on montmorillonite K10 clay, and the resultant solid was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffractometry (XRD), scanning electron microscopy coupled in a energy dispersive x-ray spectrometer (SEM-EDS), transmission electron microscope (TEM), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller and Bar
Abstract: Heterogeneous catalyst was obtained by the direct immobilization of molybdenum compound on montmorillonite K10 clay. The resultant solid was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffractometry (XRD), scanning electron microscopy coupled in a energy dispersive X-ray spectrometer (SEM-EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller and Barret–Joyner–Halenda isotherms (BET/BJH), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis-DRS) and Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR). The catalyst was tested for the epoxidation of both soybean and castor oils, using tert -butyl hydroperoxide (TBHP) as oxidizing agent. After the first use, the immobilized catalyst showed an enhanced activity and also catalytic stability in recycling experiments. The best results for epoxidation reactions concerning castor oil were observed under conditions of 80 °C for 24 h (100% conversion and 75% selectivity) and catalytic reuse.
42 citations
TL;DR: The studies showed that 20 min illumination under visible light can complete degradation of methylene blue (MB), and indicate a high stability of photocatalytic degradation, and the mechanism of separation of photo-generated electrons and holes at the Ag/AgCl-MMT nanocomposite was discussed.
41 citations
References
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TL;DR: The main properties of cationic and anionic clays as well as their role in catalysis are discussed in this paper in light of the versatility and potential of these materials, which may be very useful tools in the move towards establishing environmentally friendly technologies.
686 citations
TL;DR: In this article, a review of the latest results obtained when introducing modifications in the chemical aspects of PILC synthesis are reviewed, including using coordination or organometallic compounds, polymers and surfactants, and acid-activated clays.
Abstract: New methods have been developed in recent years that are now being successfully applied in the preparation of pillared interlayered clays (PILCs). Variations in the procedures concern different parameters involved in the synthesis, such as the starting clay, the intercalating solution, the intercalation process, and the drying and calcination steps of the pillared solids, among others. In the present article, the latest results obtained when introducing modifications in the chemical aspects of PILC synthesis are reviewed. These include (1) pillaring with mixed solutions containing two or more cations, (2) using coordination or organometallic compounds, (3) using polymers and surfactants, (4) pillaring of acid-activated clays, and (5) enhancement of PILC acidity. A separate section is devoted to the specific features of preparing these solids in amounts large enough to make their manufacture on an industrial scale economically feasible. Recent developments in the catalytic applications of PILCs are also re...
491 citations
TL;DR: Silica-supported ceria samples of various cerium content ( 0.008 to 11 % Ce ) were prepared either through anchoring cerium acetylacetonate in organic medium or by capillary aqueous impregnation of cerium nitrate as mentioned in this paper.
Abstract: Silica-supported ceria samples of various cerium content ( 0.008 to 11 % Ce ) were prepared either through anchoring cerium acetylacetonate in organic medium or by capillary aqueous impregnation of cerium nitrate. After calcination, ceria particles as small as 2 nm were obtained by the anchoring process while impregnation leads to larger particles (5–9 nm). These samples show significant spectroscopic differences with pure ceria: (i) increase of the X-ray photoelectron spectroscopy binding energies of the Ce 3d and of the O 1s lines, (ii) blue shift of the band gap measured by diffuse reflectance, (iii) observation of narrow UV bands at low cerium content, (iv) increase of the CO stretching vibration of CO-Ce4+ terminal species. These results are ascribed to the coordinative unsaturation of surface cerium and oxygen ions.
272 citations
TL;DR: A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v. spectroscopy in the elucidation of structural, physical, and chemical properties of such systems as mentioned in this paper.
Abstract: A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v.-visible spectroscopy in the elucidation of structural, physical, and chemical properties of such systems. Spectra, which were obtained in the suspension, film, and single crystal states (where applic- able), are interpreted in terms of iron-associated transitions. Microcrystalline clay minerals typically show Fe(lll) in octahedral oxo-ligand geometry whereas mica-type minerals may show a range of iron species, including octahedral Fe(III), tetrahedral Fe(IlI), and octahedral Fe(I1). Iron affects the local site geometry and in "high iron" minerals may dictate layer geometry and subsequently the crystalline form.
146 citations