M.A. Bañares-Muñoz

Comparative FT-IR study of the removal of octahedral cations and structural modifications during acid treatment of several silicates

Abstract The acid activation of different silicates of the clay group has been carried out. Sepiolite, palygorskite and two saponites, one having a high iron content, have been studied. Thus, different structures (layered or fibrous) and different chemical compositions (aluminic, magnesic and ferromagnesic) of the clays can be compared. The FT-IR spectra of solids obtained after the acid treatment permit the observation of structural changes occurring during the acid treatment. Thus, the depopulation of the octahedral sheet can be clearly observed from the change in intensity of bands related to octahedral cations. The changes result in the formation of amorphous silica gel, which can be observed from the change in the bands corresponding to the SiO bonds and in new bands corresponding to free silica.

Influence of the Ti precursor on the properties of Ti-pillared smectites

Abstract The pillaring of smectites (two saponites and a montmorillonite) with various Ti precursors was studied. The minerals were intercalated with ‘classical’ Ti precursors, such as titanium tetrachloride and titanium tetraethoxide, and also with new precursors, such as solutions of titanium tetraisopropoxide in acetic acid, or titanium (bis (ethylacetoacetato) diisopropoxide) in acetone. A complete characterization of the intercalated solids was carried out and a comparison of the properties of the solids as a function of the precursors used in the intercalation established. The influence of the severe conditions in which the intercalation with Ti oligomers is usually carried out (low pH and/or high temperature) on the properties of the intercalated solids was analysed. Intercalation with TiCl4 and Ti(EtO)4 strongly affected the structure of the clays, not by acid attack on the octahedral sheet, but mainly by disaggregation of particles. Ti(isop)4 was found to be less aggressive for the clays, while Ti(etacet)2(isop)2 did not form pillared solids but organo-clays, and therefore was of no use as a pillaring agent. The solids were thermally stable up to 300°C, showing a high specific surface area.

Study of the Porous Solids Obtained by Acid Treatment of a High Surface Area Saponite

A new deposit of saponite, Vicálvaro (Madrid, Spain), has recently been described in the Madrid Basin (provinces of Madrid and Toledo, Central Spain). The acid treatment of such material and the characterization of the solids obtained are reported in the present paper. The surface area of the natural saponite is rather high, 197 m2/g, related to the very small size of the clay particles due to the sedimentary origin of the deposit. The treatment of the saponitic material at room temperature with 0.62 wt% HCl for times of between 2 and 48 h or with 1.25 wt% HCl solutions for times of up to 6 h produces a partial dissolution of the saponite structure, resulting in the formation of mixtures of unattacked saponite and free silica, with a high development of the textural properties of the solids. The treatment with 1.25 wt% HCl solutions for times of over 6 h results in an almost total dissolution of the structure of the clay, the obtained solids being mainly formed by some delaminated saponite sheets, free silica and insoluble impurities. Solids with a maximum surface area of 462 m2/g and a maximum number of acid centres of 0.98 mmol H+/g are obtained.

Sonocatalysis and Basic Clays. Michael Addition Between Imidazole and Ethyl Acrylate

Under ultrasound activation, imidazole was condensed with ethyl acrylate using two basic clays (Li+ and Cs+ montmorillonites). The clay catalysts were characterized by chemical analyses, nitrogen adsorption isotherms, and X-ray diffraction. Under sonochemical conditions N-substituted imidazole can be obtained with a high activity and selectivity. The conversion increases with the basicity of the clays and the ultrasonic exposition time. The yield presents a maximum for 0.1 g of Cs+ montmorillonite after 60 min of sonication.

Application of basic clays in microwave activated Michael additions: Preparation of N-substituted imidazoles

Abstract Imidazole (C 3 H 4 N 2 ) was condensed with ethyl acrylate (C 5 H 8 O 2 ) using two basic clays (Li + and Cs + montmorillonites) as catalysts in a microwave oven. The catalysts were characterized by chemical analyses, nitrogen adsorption isotherms and X-ray diffraction. Under these experimental conditions N -substituted heterocycles can be obtained with a high activity and selectivity. The role of alkali promoters (Li + and Cs + ) in the montmorillonite for the Michael addition was studied. It was evidenced that the greater the basicity and the irradiation time and power of irradiation were, the higher were the conversion. The yield of the N -substituted imidazole presents a maximum for 0.1 g of Cs-montmorillonite at 850 W in only 5 min of irradiation.

Dehydrogenation of ethylbenzene on alumina-chromia-pillared saponites

A natural saponite was intercalated and pillared with hydroxy-aluminium–chromium oligomers. The intercalation solutions were characterized by visible spectroscopy and the pillared saponites mainly by chemical analyses, X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and nitrogen adsorption. The catalytic behaviour of these materials in the dehydrogenation of ethylbenzene was investigated. The selectivity to styrene was found to increase as the chromium content of the pillared clays decreased.

Intercalation compounds of trimethylphosphate in graphitic oxide

The intercalation compounds of trimethylphosphate (TMP) in graphite oxide (GO) have been synthezized. Two compounds have been characterized, corresponding to intercalation of one or two molecules of TMP, and have been characterized by gravimetric adsorption, X-ray diffraction and infrared spectroscopy. Bonding between TMP and graphitic oxide takes place through hydrogen bonding with OH groups of the layered material.

INTERCALATION COMPOUNDS BETWEEN ETHYL 2-OXOCYCLOPENTANECARBOXYLATE AND SAPONITE

The retention of ethyl 2-oxocyclopentanecarboxylate by a saponite has been studied. Intercalation compounds were prepared by two different methods: 1) in repose at room temperature and 2) heating at 60 °C under reflux. Contact times between 2 and 12 days were considered for each method. The intercalation compounds obtained were characterized by X-ray diffraction, infrared spectroscopy, chemical analyses and thermal analyses. This characterization indicates that the organic compound is retained both in the interlayer region and at the edge of the clay particles. The amount retained outside of the interlayer space is eliminated by careful washing with benzene and cyclohexane. The results obtained when using acid-activated saponite -obtained by treatment of the clay with dilute HCl solutions- in the intercalation experiments were similar to those obtained when using non-activated saponite.

Adsorption of tetramethylene sulfoxide (TMSO) on graphitic acid

Abstract The interlaminar mono layer and bi layer compounds of TMSO in graphitic acid were obtained by different methods. The quantity of TMSO retained per gram of the adsorbent was determined, together with the surface area of the graphitic acid accesible to the adsorbate. The interlamellar disposition of the organic molecule is also discussed.

Intercalation compounds between a Spanish bentonite (Gador montmorillonite) and ethyl 2-oxocyclopentanecarboxylate (EOCPC)

The process of retention of ethyl 2-oxocyclopentanecarboxylate (EOCPC) by samples of natural bentonite containing Gador montmorillonite has been studied. Firstly, the adsorbent and the adsorbate were studied by different techniques. Intercalation compounds between them were prepared by two different methods: imbibition at room temperature and reflux heating at 60°C. The compounds obtained by both treatments were characterized structurally by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and thermogravimetric analysis (TGA).