Keggin-Al13 Polycations: Influence of Synthesis and Intercalation Parameters on the Structural Properties of Al-Pillared Clays

Pillared clays are interesting materials with applications in catalysis and adsorption processes. To obtain these materials, several preparation procedures are necessary and must be optimized to tune the final properties of the resulting pillared clay. Therefore, this article reports the influence of synthesis parameters (temperature and concentration) of Keggin-Al13 polycations and different intercalation times (0.5 up to 72 h) on the structural properties of Al-pillared clays. The natural clays are from Brazil, and they are composed mainly of montmorillonite. By XRD, N2 sorption, XRF and 27Al NMR results of the Al-PILCs, we verified that the pillaring solution could be prepared at room temperature with an aging time of 24 h. For the cation exchange process, a period of at least 2 h is necessary to ensure the formation of pillared materials. The concentration of the Keggin-Al13 polycations was evaluated by using diluted pillaring solutions followed by applying re-pillaring procedures. After submitting the pillared clay to another pillaring process, the number of pillars in the interlamellar space increased; however, the micropore volume decreased concomitantly. Thus, by optimizing the synthesis conditions of the Keggin-Al13 polycations, Al-PILCs could be obtained with good values of basal spacing and specific surface area.

Physico-Chemical Properties of Nano ZrO2-Pillared Bentonite with Nickel as Supporting Metal

Bentonite was modified through intercalation and calcination using a ZrOCl2 pillaring solution. To create nano Ni/ZrO2-bentonite catalyst, ZrO2 pillared bentonite was impregnated using Ni(NO3)2•6H2O precursor first, then followed by calcination and reduction. The physical-chemical properties of the catalyst was characterized by XRD (X-ray Diffractometer), FT-IR (Fourier Transform Infrared), surface acidity with NH3 vapor adsorption method, SAA (Surface Area Analyzer) and TEM (Transmission Electron Microscope). The results of characterization with XRD showed specific peaks for montmorillonite minerals with a monoclinic crystalline type and its chemical composition (Ca)(Al,Mg)6(Si4O10)3(OH)6.nH2O and after pillarization showed a shift in basal spacing d001 to the left (angle 2θ <5°). The typical peak indicating basal spacing d001 shift towards a smaller angle of 2θ was not very apparent after impregnation with nickel metal. Qualitative determination of acidity after adsorption of ammonia showed characteristics at 1404-1635 cm-1 wavenumbers with increasingly sharp spectra indicating increased acidity of the catalyst (Brǿnsted and Lewis acids). Surface area showed a significant increase from 27.385 m2/g to 174.208 m2/g after pillarization and impregnation of nickel metal.

Preparation and Photocatalytic Performance of Iron Oxide-Pillared Layered Tantalum–Tungsten Acid

Using trirutile-structure layered tantalum–tungsten acid as the layered host, [Formula: see text]-propylamin as the pre-swelling agent and aqueous solution of [Fe3(CH3COO)7(OH)(H2O)]NO3 as the pillaring solution, oligomeric polyhydroxyacetato-Fe(III) species-intercalated layered HTaWO6 was synthesized by a stepwise ion-exchange way at room temperature. Upon calcining at 673[Formula: see text]K in air atmosphere, iron oxide-pillared layered HTaWO6with nanoscale interlayer distance (denoted as Fe2O3-HTaWO[Formula: see text] was obtained. A series of Fe2O3-HTaWO6 samples with various Fe contents were prepared by using different volume of Fe(III)-pillaring solution. The layered intermediates obtained at each stage of the ions-exchange process and the final layered products were characterized by powder XRD, FT-IR, DR UV-Vis and SEM techniques. The photocatalytic performance of the Fe2O3-pillared layered HTaWO6 samples for degradation of rhodamine B was investigated. Compared with un-pillared layered HTaWO6, the Fe2O3-pillared layered HTaWO6 exhibited a significantly-improved photo-absorption performance and an enhanced photocatalytic activity. The Fe2O3-HTaWO6 sample with 5.8% (wt) iron showed the best catalytic performance in the photodegradation reaction of rhodamine B.

Structural Transformations of Hydrolysates Obtained from Ti-, Zr-, and Ti, Zr-Solutions Used for Clay Pillaring: Towards Understanding of the Mixed Pillars Nature

Structural characteristics of hydrolysates formed from the aqueous Ti-, Zr-, and Ti, Zr-pillaring solutions prepared from inorganic precursors (TiCl4 and ZrOCl2), was investigated and compared with that of precipitates obtained from the same solutions after a slight alkalization of pH to the values reported for the conditions of clay pillaring. The materials were recovered by lyophilization and subsequently subjected to calcination at 500, 800 and 1000 °C. Of special interest was the effect of pH on the possible formation of mixed Ti, Zr-oxide species. Powder X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) analysis showed that even a relatively moderate alteration of pH in Ti-, Zr-, or Ti, Zr-precursor solutions caused substantial changes in the outcome of hydrolytic transformations, manifested by different phase and/or chemical composition of the resulting hydrolysates. Analysis of thermal evolution of hydrolysates showed that alkalization facilitated the transformation of anatase into rutile in materials obtained from Ti-pillaring solution, but retarded tetragonal to monoclinic zirconia conversion in samples derived from Zr-pillaring agent. The most striking effect was observed for the mixed Ti, Zr-pillaring solution, where an increase of pH enabled the formation of zirconium titanate as the only crystalline phase, rather than a multiphase mixture of anatase, monoclinic zirconia and zirconium titanate obtained from the more acidic precursor. The finding supports the model of mixed Ti-O-Zr network in props generated in Ti, Zr-pillared montmorillonites.

Preparation and Characterization of Immobilized Molybdenum Complex on Pillared Montmorillonite K-10

This study was carried out to immobilize molybdenyl (VI) acetylacetonate (MoO2(acac)2) complex on alumina pillared montmorillonite K-10 (MMT K-10). Pillar MMT K-10 was produced by introducing MMT K-10 with a hydrolysis solution of NaOH with AlCl3. Different concentrations of pillaring solution were prepared in terms of OHto Al3+ ratio (0.5, 1.0, 1.5 and 2.0) to observe the structural characteristics of MMT K-10. The pillared materials were then immobilized with 0.1 M MoO2(acac)2 and were characterized using X-ray diffractometry (XRD), scanning electron microscopy coupled in an energy dispersive X-ray spectrometer (SEM-EDX) and Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) techniques. FTIR bands at ca. 890 – 930 cm-1 indicate that the Mo complex was immobilized on the surface of pillared MMT K-10 not in between the layers. This is supported by the SEM and XRD analysis where the SEM micrograph showed deposition of Mo on the surface of MMT K-10 as well as no modification of basal spacing was observed by XRD. Meanwhile, the d(001) spacing of the alumina pillared MMT K10 samples were seen to increase slightly as the concentration of OH/Al3+ increased.

Study on the Reaction Kinetics and Catalytic Stability of Pillared Bentonite in Heterogeneous UV-Fenton Process

An investigate was carried out to evaluate the catalytic performance of Fe, Al-pillared bentonite in heterogeneous UV-Fenton process. The catalysts were prepared by a cation doping technique. X-ray diffiraction and infraed spectroscopy were used to characterize their properties. Results showed that intercalated process could obtained larger interlayer spacing. Some bands of infrared spectroscopy shifted to lower wave length, indicating that FexAly has intercalated into the layers of the bentonite. The higher ratio of Fe to Al was in the pillaring solution, the higher discolouration rate could be obtained. The discoloration rate reached 79.9% at 20 min and 283K when the ratio of Fe to Al in pillaring solution was 9:1. The reaction constants of the heterogeneous UV-Fenton process increased from 0.074 min-1 at 283K to 0.094min-1 at 323K. Its activation energy was 36.7kJ.mol-1, indicating that temperature had little effect on this process. Little Fe-leaching made it possible for Fe, Al-pillared bentonite to remain a high stability during recycling uses.

Influence of Synthesis Conditions on the Physicochemical Properties and Catalytic Activity of Fe/Cr-Pillared Bentonites

The synthesis of Fe/Cr-pillared bentonites starting from a 2% clay suspension and also from dry clay using ultrasound treatment for both the aging and the intercalation steps of the pillaring solution considerably reduces the time and the amount of water required compared with the conventional synthesis method. The catalysts were characterized using scanning electron microscopy with an energy dispersive system (SEM-EDS), powder X-ray diffraction (XRD), N2and CO2-adsorption/desorption, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis and the catalytic activity of selected samples was evaluated for the phenol oxidation reaction. The results of XRD analysis showed that delaminated Fe/Cr-pillared bentonite with d001value 68 Å was observed after intercalation a direct mixture of the pillaring solution and dry clay. The adsorption-desorption isotherm analysis showed that the samples synthesized with the proposed methodology in intercalation stage have similar textural properties and these properties do not change remarkably with synthesis conditions. In addition, the characterisation studies showed that the physicochemical properties of samples synthesized by ultrasound were comparable to those of sample synthesized by conventional method in this study. The sample synthesized by conventional method show 50% phenol conversion. This value was higher than those of samples synthesized by the ultrasound.

Study on Porous Structure and Surface Characteristics of Al-Pillared Montmorillonite

Al-pillared montmorillonite (Al-PILM) prepared with Keggin ions was studied by means of XRD, SEM-EDS and N2 adsorption-desorption isotherms.The rusults show that, compared to unpillared Na-montmorillonite (Na-M), the interlayer spacing d(001) value, BET specific surface area, surface fractal dimension and the proportion of microporous specific surface area of Al-PILM are larger and the surface is relatively rough. The BJH porous volume distribution of Al-PILM is the most probable distribution, and the most probable pore size is about 2 nm, belonging to mesopore. The porous structure of Al-PILM is characterized as parallel plate slit or “house-of-cards” wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. Besides, the results of elemental distribution show that the ions exchange action between Na+ and hydroxy-Al cations in pillaring solution occurs in the formation of Al-PILM.

CWPO of 4-CP and industrial wastewater with Al–Fe pillared clays

Catalysts based on pillared clays with Al–Fe have been synthesised from a commercial bentonite and tested for catalytic wet peroxide oxidation (CWPO) of aqueous 4-Chlorophenol (4-CP) solution and industrial wastewater from cosmetics manufacture. The effect of the synthesis procedure, the iron load and reaction temperature on the catalytic activity was studied using 4-CP as target compound. A lower temperature in the preparation of the pillaring solution, as well as a higher Fe load, gave rise to a higher catalytic activity, but also a higher leaching of the active phase. The best catalyst, in terms of catalytic activity, was also tested for treating cosmetic wastewater by CWPO. Experiments were carried out at 90°C and atmospheric pressure and the influence of Fe load, catalyst concentration and H2O2/COD ratio (between 0.5 and 2 times the stoichiometric ratio) were analysed. Higher values of these parameters favour COD reduction. The Fe leaching in all cases was lower than 1.2 mg/L, indicating that these catalysts have a high stability under these experimental conditions.