Three montmorillonite samples, from Wyoming (particle size <0.2 µm, 4.6 wt. % Fe2O3), Greece (<14 µm, 6.5 wt. % Fe2O3), and Poland (0.5 wt. % Fe2O3, two fractions <2 µm and 2–10 µm) were intercalated with hydroxy-Al species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 wt. % Al2O3 for 0.2 µm in size to 22.6 wt. % for >2 µm. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80°C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 Å. The diffusion of the Al cations therefore limited the cation-exchange process. The addition of NH4+ to the pillaring solution decreased the amount of Al fixed by the clay from 31 (no NH4+ to 26 wt. % (NH4+/Al = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4+ and Al-hydroxy cations for ion-exchange sites forced the Al species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Al exchanged was then reduced. After calcination in air at 700°C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4+ was added, compared with 0.11 ml/g for a NH4+/Al ratio of 10. The Fe content of the clay affected the thermal stability of pillared clays at 800°C: for two samples prepared by competitive ion exchange (NH4+/Al = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe2O3 to 0.08 ml/g for 0.5 wt. % Fe2O3. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150°C, on samples calcined at 500°C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.

The surface charges and the zeta potential of a Na-montmorillonite (Na-mont) and two pillared montmorillonite (MP1 and MP2) samples with different aluminum contents were determined by Potentiometric titrations and electrophoretic measurements. At pH >9 the two pillared montmorillonite samples showed zeta potentials similar to those of Na-mont, but at pH <8, the negative zeta potential shifted to lower negative values as the aluminum content increased. Sample MP1, which had a greater Al content, showed an isoelectric point (IEP) of 5.0–5.5. Titration curves obtained by acid-base Potentiometrie titration for sample MP1 showed a well-defined cross-over point at pH = 5.0, whereas this point was not observed for sample MP2 in the pH range studied. The results indicate, in principle, that both techniques can be used to characterize surface charges in this type of material. An attempt was also made to relate the data obtained from electrophoretic mobility and Potentiometrie titrations.

The hydrolysis of 2-(2-trichlorosilylethyl)pyridine (TCSEP) or 3-aminopropyltrimethoxysilane (APTMS) yields a complex mixture of oligomers, the composition of which is a function of time. 29Si NMR measurements show that the same oligosilsesquioxanes can be obtained from both compounds after prolonged hydrolysis. Ion exchange by montmorillonite with the pillaring solution obtained from TCSEP results in partial intercalation, with a noticeable fraction of the clay exchange sites occupied by protons not by the Si cationic species. Calcination of this pillared clay results in a mixture of phases showing 1.86 or 1.56 nm basal spacings. Pillaring of the same montmorillonite by the solution obtained by partial hydrolysis of APTMS results in a homogeneous solid with a basal spacing of 2 nm, which reduces to 1.65 nm upon calcination above 773 K. The microporous volume (pores < 1 nm) of these Si-clays, determined after calcination at 773 K, 0.15 ml/g for the PILC obtained from TCSEP, and 0.186 ml/g for the PILC obtained from APTMS is comparable to that measured for Al or Zr pillared clays. A better thermal stability is observed for the clay pillared by APTMS, which retains a large microporosity (0.167 ml/g) up to 973 K in air. These Si-pillared clays show a small number of weakly acidic sites and some strongly acidic sites retaining ammonia up to 723 K, which are most likely localized on the clay layers.

A commercial bentonite (primarily smectite) from Fischer Scientific Company (F bentonite) and a natural bentonite from Peru (P bentonite) were used in the preparation of pillared clays with polyoxymetal cations of Al that were subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) were used to investigate the effects on the thermal and hydrothermal stability of these synthetic clays. The structure of these materials was studied by X-ray diffraction. Isotherms were determined by N2 adsorption. Thermal stability was determined using thermogravimetric (TG) measurements and ara-monia-TPD (temperature programmed desorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 Å, with surface areas from 239 to 347 m2g−1, with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than those prepared from P bentonite. Pillared clays modified with Ce or La did not show any apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared clays. In contrast, the thermal and hydrothermal stabilities of these materials were greater than Al-pillared clays. However, Ce-pillared clay appears to be more effective than La-pillared clay in delaying the dehydroxylation of pillared clays with increasing temperature. The intercalation of Ce and La into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.

Ce/Al- and La/Al-pillared smectites were prepared by cation exchange of bentonite, saponite and laponite with hydrothermally treated (130–160 °C for 16–136 h) solutions containing mixtures of aluminumchlorohydrate (ACH) and Ce3+-/and La3+-salts. After calcination at 500 °C, the pillared products are characterized by basal spacings between 24.8 and 25.7 Å and surface areas of approximately 430 m2 g−1. The products are hydrothermally stable at 500 °C after 2 h in steam. The large basal spacings are due to the formation of a large Ce/La-bearing Al-polyoxocation, whose formation is favored by initially high Al concentrations ≥3.7 M and an OH/Al molar ratio of approximately 2.5. The Ce/Al or La/Al molar ratios can be as low as 1/30. 27Al nuclear magnetic resonance (NMR) spectroscopy has shown that the polyoxocation has a higher Altetrahedral/Aloctahedral ratio than the Keggin structure Al13, which may partly explain the higher stability compared to normal Al-pillared clays. Hydroconversion of n-heptane indicated that the activity of the Pt-loaded pillared products is higher than that of a conventional Pt-loaded amorphous silica-alumina catalyst. Selectivity is strongly dependent on the type of starting clay and its acidity. In industrial hydrocracking of normal feedstock, a Ni/W-loaded Ce/Al-pillared bentonite catalyst showed rapid deactivation due to coke-formation reducing the surface area and the pore volume. Additionally, coke-formation is facilitated by the relatively high iron content of the pillared bentonite (3.43 wt% Fe2O3).

Two samples, obtained by pillaring a Wyoming montmorillonite with hydroxy aluminium and oligosilsesquioxane cations, were studied by stepwise thermal desorption of ammonia and by highly sensitive diffuse reflectance IR-spectroscopy. For both clays, the adsorption of ammonia shows a total number of acid sites equal to 0.35 meq/g, with acid strengths comparable to that of HY zeolites. By IR reflectance spectroscopy, Brönsted acid sites with an acid strength comparable to that of bridging hydroxyls in zeolites were found in Al samples but not on Si-montmorillonites. These sites were characterized by an overtone band at 7100 cm-1 and an activity for ethylene oligomerization at 300 K.

OH-Cr smectites were prepared with different mmol Cr/g smectite: 0.5, 1.5, 3.5, 5, 10 and 20 by treatment with hydroxy-chromium solution prepared at 60°C and one day of hydrolysis with OH/Cr = 2. The samples were characterized by X-ray diffraction (XRD), differential thermal analyses (DTA) and N2 adsorption-desorption isotherms.

The d(001) spacings of OH-Cr-smectite were different according to Cr added/g smectite. Larger d(001) spacings: 1.95, 2.05 and 2.07 nm were obtained with 5, 10 and 20 mmol Cr per gram of sample. DTA diagrams of smectite treated with OH-Cr solution showed exothermic peak at 420°C corresponding to Cr203 (confirmed by XRD). N2 adsorption-desorption isotherms of smectite treated with different amounts of Cr preserved the same slit-shaped pores than original sample, but with different micropore volume. This behavior was maintained until treatment temperature of 380°C. The specific area of smectite was increased from 36 to 175 m2/g after treatment with OH-Cr solution. The textural characteristics of OH- Cr smectite heated up to 420°C were changed. The specific area decreased and mesopore volume was produced. The different Cr added modified the structural and textural behavior.

Microporous materials, (materials with pore sizes with widths <2 nm) were prepared by pillaring of smectites obtained from different soil deposits. The materials were prepared by intercalation with oligomeric cations of aluminum, which were transformed to aluminum-oxide pillars by calcination. The adsorption of n-hexane in the pillared clays was studied by the determination of heats of adsorption. Heats of adsorption were measured using either a static microcalorimeter or differential scanning calorim-etry coupled with thermogravimetry (TG-DSC). In this latter case, two different procedures were used that differ on the introduction of the (n-hexane) molecules that are to be adsorbed. The results obtained by the (standard) static microcalorimeter method and the TG-DSC method were compared. This comparison showed the heats of adsorption obtained by TG-DSC are differential heats of adsorption, and it showed the range of adsorption. Characterizing the texture of pillared clays, especially microporosity, is important for monitoring the intercalation process and for determining potential applications of these materials. Correlations between the obtained heats of adsorption and the dimensions of micropores suggest that TG-DSC is a semi-quantitative method for characterizing micropores in aluminum-pillared clays.

Pillared clays (PILCs) with magnetic properties have significant potential for application in industry and the environment, but relatively few studies of these types of materials have been carried out. The aim of the present work was to gain insight into the magnetic and structural properties of pillared clays by examining in detail the influence of the calcination temperature and the nature of different pillared clays on these properties.

Magnetic layered systems from different pillared clays were prepared and characterized. Firstly, Ti-, Al-, and Zr-pillared clays (Ti-PILCs, Al-PILCs, and Zr-PILCs, respectively) were produced at different calcination temperatures and then magnetic pillared clays (Ti-M-PILCs, Al-M-PILCs, and Zr-M-PILCs) were prepared at ambient temperature. The synthesis involves a reduction in aqueous solution of the original Fe-exchanged pillared clay using NaBH4. The structural properties of pillared clays and their magnetic forms were investigated using X-ray diffraction, N2 adsorption, cation exchange capacity determination, and X-ray fluorescence (XRF) measurements. The properties of the magnetic pillared clays were investigated by superconducting quantum interference devices and Mössbauer spectroscopy. An evaluation of the data obtained allowed an estimation of the pillared structure in one PILC-model before and after magnetization. The model was determined on the basis of a simple geometric model and experimental data leading to the calculation of a filling factor (FF) which contained information about the number of intercalated pillared layers and the unaffected layers. In the case of Ti precursors, the best calcination temperature was 400°C, which maintained the highest specific surface area and pore volume with magnetic parameters suitable for magnetic application. Similar experiments with Al- and Zr-pillars have been discussed. A correlation between the XRF data, porosity, FF calculation, and magnetic properties led to the conclusion that the sample Al-M-PILC previously calcined at 500°C was the most stable material after the magnetization process. The same examination in the case of Zr materials suggested that the most stable sample had been calcined at 300°C (sample Zr-M-PILC-300).

The surface acidic properties of pillared clays (PILCs) with Al or Zr oxide pillars (prepared from a natural Portuguese smectite and a synthetic Laponite), and of a protonic NaHY zeolite, were studied by two methods: pyridine adsorption followed by infrared (IR) spectroscopy, and the catalytic transformation of 1-butene. The results of the pyridine adsorption revealed that all the pillared clays studied have mainly Lewis-type acidity, the exception being the clay pillared with Zr oxide, obtained from natural smectite, which also presents a significant number of Brönsted acid sites. The results of 1-butene transformation showed that the pillared clays exhibit catalytic properties similar to those of the protonic Y zeolite. The acid character of the solids was confirmed by the values of the cis/trans 2-butene isomers ratio. At short reaction times, product distribution showed that the main reaction is oligomerization, followed by cracking. After 15 min the products are mainly the linear isomers, cis and trans-2-butene, showing that the majority of the catalytic active sites, are already poisoned after 15 min of reaction. The particular behaviour of Laponite intercalated with Al oxide pillars is discussed. The IR spectra of the pyridine adsorbed on the fresh samples and after the catalytic assays, revealed that Lewis acid sites behave as active sites for 1-butene catalytic transformation. The consistency between the results of the two complementary techniques used for the characterization of the acidity of the solids was proved.

Al-hydroxy intercalated clays (ALHICs) obtained from different parent clays were used to investigate the interactions between oligomers and clay surface layers.

The thermal stability of ALHICs obtained from natural, Cs-, Ca-, Ba-, Fe-, Cu- or Ce-montmorillonites has been investigated by studying the relationship between basal spacing and calcination temperature. X-ray diffraction has shown that the basal spacing of ALHICs obtained from Cu-montmorillonite calcined at 550°C is 13.4 Å, different from basal spacings of ALHICs obtained from Fe-montmorillonite (16.0 Å) and other parent clays (16.7 Å). Thermograms for AlHICs obtained from natural, Fe- and Ce-montmorillonites displayed distinct steps at 225 and 650°C, attributed to the dehydration of Al13 oligomers, and the dehydroxylation of the surface layer, respectively. By contrast, thermograms of ALHICs obtained from Cu-montmorillonite displayed one step between 250 and 700°C for both dehydration and dehydroxylation. Mössbauer parameters showed that Fe3+ octahedra in octahedral sheets are distorted in pillared interlayered clay (PILC) obtained from Cu-montmorillonite and undistorted in that obtained from Fe-montmorillonite. The difference in thermal stability for the various ALHICs is attributed to the retention of some of the original cations after intercalation with Al13 oligomers, which induces several interactions between the oligomers and the clay surface layers.

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.

Three raw samples of Fe-rich smectites from Gafsa (Jebels Shemsi and Hammadi, Tunisia) have been characterized by different techniques which indicate that they contain (15 – 20%) illite, probably interstratified and to a lesser extent they also contain kaolinite, calcite, quartz and Fe oxides. These samples present a relatively high Fe content (∼9%) in the <2 μm fraction. From EPR and Mössbauer spectroscopy it is deduced that Fe is mainly present as Fe(III) in the octahedral environment of smectites and also in Fe-oxyhydroxides associated with the clays. Aluminium-pillared clays have been prepared from the Na+-purified samples, and their thermal stability and acidity have been studied.

Porous clay heterostructures were prepared from Al-intercalated clays, and they allowed the insertion of Al into the framework of intercalated silica in porous clay heterostructures (PCHs). This method has led to tuneable Al contents within the resulting porous clay heterostructures. X-ray fluorescence confirmed the presence of Al in the intercalated precursors and their derivatives (porous clay heterostructure materials) in various environments, as indicated by 27Al magic-angle spinning nuclear magnetic resonance. The Al porous clay heterostructures exhibited specific surface areas that varied from 743 to 850 m2/g with total acid concentrations which varied from 0.969 to 1.420 mmol of protons/g of material, values which were deduced from the temperature desorption of cyclohexylamine. These acid sites were sufficiently strong to initiate the hydro-isomerization of n-heptane. The catalytic properties of the porous clay heterostructures depended on the Al contents and reached a maximum conversion rate of 50% and an isomer selectivity of 70% at a test reaction temperature of 350°C.