C. Pesquera

Zeolitization of a bentonite and its application to the removal of ammonium ion from waste water

Abstract In this study a bentonite was modified to zeolitic material by alkaline treatment in distilled and seawater media. The alkaline treatment was performed using two different methods: a reflux system and in an autoclave. The structural and textural characteristics of the natural clay were measured and compared to those of the modified clays formed. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDRXA) and cation exchange capacity (CEC). The laminar structure of the starting material was converted into spherical units in the zeolitic nature. The modifications observed were greater in the samples treated in the autoclave than by reflux, and also greater when the treatment medium was distilled water rather than seawater. The capacity of the treated samples to remove ammonium ions from distilled water and seawater was compared with the original samples. It was found that CEC and ammonium removal were increased by alkaline treatment. Ammonium removal was more efficient from distilled water, where there were no competitive ions. The materials generated by alkaline treatment in seawater were more selective for ammonium removal. The samples obtained in seawater were not influenced by the treatment conditions (reflux/autoclave).

Synthesis and characterization of pillared montmorillonite catalysts

Abstract Pillared montmorillonite was synthesized by the direct cation exchange method, varying the hydroxyl/aluminium and aluminium/clay ratios in the preparation in order to find the optimum conditions, within the limits of this study, for obtaining stable products with a microporous structure and high specific surface area, capable of being used as cracking catalysts. The minimum aluminium/clay ratio required was 7.5 meq Al/g clay, independent of the hydroxyl/aluminium molar ratio. The specific surface area of the original sample (61 m2/g) was increased by pillaring up to 366 m2/g. The structure of the aluminium oxide pillared montmorillonite proved to be stable up to 500°C.

Passivation of a montmorillonite by the silica created in acid activation

The evolution of a Spanish montmorillonite with acid treatment has been studied. With a high concentration of acid, 8 mol dm–3 HCl, there is a break in the normal tendency of the observed behaviour. The silica created at the beginning of the reaction protects the clay structure and impedes subsequent attack. This passivation of the material is confirmed by the results obtained from chemical analysis, IR spectroscopy, X-ray diffraction (XRD) and adsorption isotherm experiments. With 5 mol dm–3 acid treatment the specific surface area reaches a maximum value five times that of the starting material, and in the sample treated with 8 mol dm–3 acid it is still 3–4 times the original value.

Differences Between One Aluminic Palygorskite and Another Magnesic by Infrared Spectroscopy

Abstract Two Spanish palygorskites, one from Caceres (Serradilla) and the other from Segovia (Sacramenia) are studied by means of infrared spectroscopy techniques, both in their natural state and after systematic treatment with hydrochloric acid. The first one is identified as aluminic and the second as magnesic. It is found that the magnesic palygorskite is more easily attacked by the acid.

Activated carbon supported Pt catalysts: effect of support texture and metal precursor on activity of acetone hydrogenation

Abstract Four Pt catalysts supported on two commercially available activated carbons supplied by Norit were prepared with H2PtCl6 and (Pt(NH3)4)Cl2 as metal precursors to study the effect of the metal precursor and support texture on catalytic activity. The supports were characterised by chemical analysis, FTIR, volumetric adsorption and TPD. The reduction temperature was determined by TPR. For the catalysts, the metal load was determined by atomic absorption and dispersion measurements were performed by chemisorption. No reference was found in the literature for the application of Pt/active carbon catalysts in the acetone hydrogenation reaction. Our catalysts were used in the reaction of low temperature (between 50 and 130°C) hydrogenation of acetone in the gaseous phase. The catalysts prepared from H2PtCl6 had a metal load closer to that expected, were more dispersed and showed greater catalytic activity than the catalysts prepared from (Pt(NH3)4)Cl2.

Structural and textural evolution of Al- and Mg-rich palygorskites, I. Under acid treatment

Abstract The structural and textural evolution of two Spanish palygorskites, one magnesium-rich and another aluminium-rich, activated with hydrochloric acid of different concentrations, has been studied. The maximum activation is obtained in both cases with a 2 N concentration. The activation is much higher in the magnesium-rich palygorskite, which undergoes a greater dissolution of its octahedral sheet as well as a more extensive alteration of its structure and a greater increased creation of microporosity.

Structural and textural evolution under thermal treatment of natural and acid-activated Al-rich and Mg-rich palygorskites

The structural and textural evolution under thermal treatment of two Spanish palygorskites, one magnesium-rich and the other aluminium-rich, and also of the same palygorskites previously activated with HCl, has been studied. Using IR and X-ray techniques, the structural modification that the samples undergo on heating, is shown. By means of N2 adsorption-desorption isotherms and Hg porosimetry the changes in the texture were followed until 1000°C. The texture of both natural palygorskites is maintained until 600°C, despite the structural changes which they undergo. On heating at 1000°C a great decrease of surface area is observed. In samples previously activated with HCl, a greater evolution of the texture is evident. On heating above 300°C there is a sharp decrease of the surface area, owing to the disappearance of the microporosity created by acid-leaching. This decrease of the surface area is greater in the magnesium-rich sample.

Reversible folding in sepiolite: study by thermal and textural analysis

Abstract The structural changes of sepiolite under thermal treatment, and their reversibility, have been examined by thermogravimetry. These changes have been related to the textural changes, determined by N 2 adsorption under similar conditions. The folding of this material starts at 390°C, from this temperature the microporosity of the material disappears. This folding is reversible, becoming permanent at 570°C. From 390 to 570°C the surface area remains stable, corresponding to the external surface area of the mineral.

Effect of Ce on catalytic properties of pillared montmorillonite with Al- and GaAl-polyoxications

Abstract Montmorillonite pillared with polyoxications of Al and GaAl has been modified with Ce and the effect of the presence of the Ce3+ ion on the activity of catalysts obtained from the PILC products by impregnation with Pt has been investigated. Through acidity studies and catalytic tests the presence of Ce has been found to produce a substantial increase in the conversion of n-heptane and in selectivity towards the cracking products, independently of the greater stability generated in products with mixed AlGa pillars. This also corresponds to the increase in both the number and strength of acid centers produced by the addition of Ce.

High conversion and selectivity for cracking of n-heptane on cerium–aluminium montmorillonite catalysts

The synthesis and catalytic properties of an aluminium pillared clay modified by inclusion of cerium are described; very high catalytic activity and selectivity for the cracking of n-heptane are observed.