Alumina-pillared Clay Research Articles

Adipic ester hydrogenation catalyzed by platinum supported in alumina, titania and pillared clays

Aluminum pillared clay (Al-PILC) and platinum impregnated pillared clay (Pt/Al-PILC) were prepared, characterized and tested as catalysts in adipic ester hydrogenation. Results were compared with those obtained for titania (TiO2) and alumina (γ-Al2O3) as supports. Results indicate that platinum species are partially occupying the inner porous network of the pillared clay, a solid with an amphoteric character, and these crystallites are small enough to occupy the solid inner micropores. Alumina and Al-PILC supports are active as catalyst, allowing an adipate conversion of 26.3% and 83.3%, respectively, and the products distribution is very influenced by the solid surface acidity. When platinum containing catalysts were tested, the products distribution indicates that reactions of cracking and hydroisomerization, attributed to the acidity of the supports and to the presence of platinum, occur preferentially. However, the reduction in the acidity of Pt/Al-PILC, promoted by a barium bath, allowed the preparation of a catalyst more active and selective than the original catalyst, indicating that the acidity control step is crucial to the performance of this catalyst.

Structure Evolution of Co/Alumina-Pillared Clay Catalysts under Thermal Treatment at Increasing Temperatures

The aim of this work is to study the effect of the thermal treatment at 350 and 500 °C on the structure of a Co/alumina-pillared montmorillonite catalyst. For this purpose, the X-ray powder diffraction patterns of the solids, the nitrogen physisorption data at −196 °C, the micropore-size distributions, the UV−vis and NIR spectroscopies of the dried materials, the gravimetric and differential thermal analyses, and the temperature-programmed reduction analyses of the supported cobalt catalysts have been analyzed and compared. The impregnation with cobalt and the temperature has modified the textural properties of the alumina-pillared clay supports, giving rise to a loss of surface area and micropore volume in the final catalysts. Co3O4 is the only cobalt oxide species detected in all the supported catalysts. The oxidation of propene at low concentrations over selected cobalt oxide catalysts shows that the structural characteristics of the support influence on the catalytic performance.

Adsorption of vapor-phase VOCs (benzene and toluene) on modified clays and its relation with surface properties

A mexican bentonite was used to prepare three modified clays: an organoclay (OC–CPC) by intercalating cetylpyridinium chloride (CPC), an aluminum-pillared clay (Al-PILC), and an inorganic–organic clay (IOC–CPC) prepared from Al-PILC intercalating CPC. The infrared and thermogravimetric analyses enabled us to differentiate between the structures obtained. Interlayer distance was assessed through X-ray diffraction; the OC–CPC was the clay that showed the highest value (12.4 Å). The natural clay’s specific area was 43.5 m2/g, increasing to 157.2 m2/g for Al-PILC. The OC–CPC and IOC–CPC specific areas were 13.27 m2/g and 14.5 m2/g, respectively. Al-PILC was a microporous material; whereas natural clays, OC–CPC and IOC–CPC were non-porous materials. Toluene and benzene adsorption on OC–CPC was higher than in IOC–CPC and Al-PILC. Natural clay showed no adsorption capacity for these compounds. Comparison of the GC retention times for non polar and low-polarity compounds (octyne and benzene) in columns packed with OC–CPC and a commercial non polar column (squalene) showed that the OC–CPC possessed a higher organophilic (non polar) nature than squalene. This explains the higher benzene and toluene adsorption capacity of the OC–CPC compared with the other modified clays. The toluene and benzene adsorption isotherm for OC–CPC was well-described by the GAB (Guggenheim–Anderson–De Boer) model for the whole range of relative pressure used in this work (0–0.9) describing multilayer adsorption and capillary condensation.Key words: organoclay, inorgano–organo clay, vapor phase VOC’s adsorption, clay surface properties.

Influence of synthesis condition on pore structure of Al pillared clays and supported Pd catalysts for deep oxidation of benzene

Alumina pillared clays (Al-PILC) were impregnated with Ce and Pd, and then studied as catalysts in the deep oxidation of benzene of low concentration (130–160 ppm). The influence of synthesis conditions on pore structure of Al-PILC was investigated, and also the relationship between structure of the supports and catalytic properties in benzene oxidation of the catalysts was studied. The supports and catalysts were characterized by X-ray powder diffraction, N 2 adsorption, atomic force microscopy, transmission electron microscopy, and temperature programmed reduction techniques. The results showed that pillaring caused a strong increase in basal spacing ( d 001), surface area, micropore volume ( V mic) and mesopore surface area ( A mes). Doping with Ce on Al-PILC yielded a super structure and a reduction in V mic and A mes. Activity tests showed that optimized synthesis conditions of pillaring solution and doping with Ce can obviously improve the activity of Pd/Al-PILC catalysts. The optimized structure of the supports can strengthen the interaction between CeO 2 and Al-PILC, improve the dispersion of Pd particles and increase the active sites, which enhances the catalytic activity of catalysts for the deep oxidation of low concentration of benzene.

A novel method of copper-exchanged aluminum-pillared clay preparation for olive oil mill wastewater treatment

A novel method of preparing copper-exchanged aluminum-pillared montmorillonite has been developed. The process does not use water and is simpler to operate than the conventional method of doping [K. Bahranowski, M. Gasior, A. Kielski, J. Podobinski, E.M. Serwicka, L.A. Vartikian, K. Wodnicka, Clay Miner. 34 (1999) 79–87. [1]; W. Najjar, L. Chirchi, E. Santosb, A. Ghorhel, J. Environ. Monit., 3 (2001) 697–701. [2]]. Here, catalysts containing different ratios of Cu/clay were prepared by solid-state reaction of the Al-pillared clay already synthesized with copper nitrate in controlled atmosphere. The resultant materials are characterized by X-ray diffraction, nitrogen sorption, chemical analysis, temperature-programmed reduction (TPR), and UV–visible diffuse reflectance spectroscopy. The properties of copper-based catalysts have been studied in the wet hydrogen peroxide photocatalytic oxidation (WHPPCO) (H 2O 2 with UV light) of real olive oil milling wastewater (OMW). For solution containing 0.5 g L −1 of catalyst, 2.2% H 2O 2 (V/V), and UV, results showed that after 2 h reaction, important concentration of polyphenols were removed with a significant total organic carbon (TOC) removal.

Direct immobilisation versus covalent attachment of a Mn(III) salen complex onto an Al-pillared clay and influence in the catalytic epoxidation of styrene

A Mn(III) salen complex was immobilised onto an aluminium-pillared clay (Al-WYO) by three different methodologies: method A (catalyst A2), direct immobilisation of the complex into the Al-WYO; method B (catalyst A4), covalent anchoring through cyanuric chloride (CC); and method C (catalyst A7), covalent attachment onto a 3-aminopropyltriethoxysilane (APTES) modified Al-WYO mediated by CC. All the materials were characterised by XPS and FTIR; the Mn content of the materials with the immobilised complex was determined by AAS. FTIR and XPS spectra confirmed the organo-functionalisation of Al-WYO and complex immobilisation in the parent and organo-modified Al-PILCs. Direct immobilisation of the complex into the Al-WYO (method A) leads to the highest immobilisation efficiency ( η = 37.5%) compared with the anchoring procedures using the two spacers, methods B and C, which gave η = 7.4% and 8.7%. Nevertheless, the surface Mn contents are always higher than those obtained by bulk analysis, suggesting that in all materials the complexes are located within the most external pores. The Mn(III) salen-based pillared clays were tested in catalytic epoxidation reaction of styrene using iodosylbenzene as the oxygen source and were reused for several cycles. The catalyst A2 was the best heterogeneous catalyst among the catalysts prepared since it showed similar substrate conversion and styrene epoxide selectivity to the homogeneous counterpart; the heterogeneous catalysts A4 and A7 showed considerably lower values for these parameters. The styrene epoxide yields decrease in the order, A2 ≫ A4 > A7, which might be associated with some pernicious catalytic activity of the organo-modified supports (A3 and A6). Moreover, A2 could be reused for four times with a slight decrease in its catalytic activity and with almost no leaching of the active phase.

Analysis of the Structure of Alumina-Pillared Clays by Nitrogen and Carbon Dioxide Adsorption

Nitrogen and carbon dioxide adsorption methods were used to study the structural properties developed by a series of alumina-pillared clays. The solids were prepared by varying the Al/clay ratio and the calcination temperature of a montmorillonite intercalated with solutions of aluminium. Equilibrium data for CO2 adsorption by these materials were analyzed using the Langmuir, Freundlich and Toth isotherm models. The fitting parameters for these models demonstrated the heterogeneous nature of the materials studied and that CO2 interaction with the surface was influenced by the calcination temperature.

Dehydrogenation of ethylbenzene to styrene catalyzed by Co, Mo and CoMo catalysts supported on natural and aluminum-pillared clays: Effect of the metal reduction

In this work Co, Mo and CoMo catalysts supported on a montmorillonite clay (STx-1, Texas, USA) in its natural and Al-pillared forms were prepared. These catalysts in their unreduced and reduced forms were tested over the dehydrogenation of ethylbenzene to study the effect of the metal reduction. The catalysts were prepared by impregnation with aqueous solutions of CoCl 2·6H 2O and (NH 4) 6Mo 7O 24·4H 2O and characterized by N 2 adsorption, X-ray diffraction, temperature programmed reduction and CO chemisorption. The total metal content of cobalt and/or molybdenum was 4 wt.% in the monometallic and bimetallic catalysts, varying the Co–Mo mass ratio in 1:3, 2:2 and 3:1 (Co:Mo atomic ratios of 0.54, 1.63 and 4.84) in the latter. The surface areas of the natural and Al-pillared clays were 72 and 123 m 2/g, while the areas of the Co, Mo and CoMo catalysts supported on ST and Al-ST were 48–69 and 77–89 m 2/g. The reduction profiles revealed the presence of different Co and Mo species and the existence of metal-support interactions. The use of cobalt chloride formed particles of large sizes and Cl − blocks the active sites. The reduced catalysts showed greater activity than the unreduced catalysts at 400 °C. The most active catalysts were the one that contained 4 wt.% of Mo (in the monometallic) and that with the higher Mo content (in the bimetallic).

Cu (II) Adsorption on Aluminium Pillared Clay in Aqueous-ammoniacal Solutions

Cu (II) Adsorption on Aluminium Pillared Clay in Aqueous-ammoniacal Solutions

PLS versus zeolites as sorbents and catalysts: Part 9. An unexpected reaction of Al-PILC sorbed CCl 4 with benzene

Reactivity of CCl 4 on alumina-pillared clays (PILCs) has been exploited to investigate if benzene activation is possible under both static and dynamic conditions. PILC-encapsulated CCl 4 indeed reacts, giving chlorobenzene (PhCl) and biphenyl as main products (with benzoyl chloride as a side-product). Although overall yields are low (2–4%, calculated on starting benzene) they increase when a transition metal-containing pillar is present (e.g. FAZA, which has Fe 2+/Fe 3+-alumina pillars and activity comparable with the mid-pore zeolite ZSM-5). Yields increase further (e.g. PhCl > 5%) when the PILC is also cation-exchanged, as in Cu-FAZA. Trends in yields on changing reaction parameters show that the reaction giving PhCl occurs via a cation-intermediate, whereas biphenyl is formed via a free-radical mechanism. Finally, chlorohydroxybenzenes can be obtained in both mid-pore zeolites and PILCs, which is rationalised in terms of generation of active oxygen species at the Lewis acid sites. It is suggested that benzoyl chloride forms from interaction between in situ-generated COCl 2 and Lewis acid sites.

Encapsulation of Co phthalocyanine in alumina-pillared clays and their characterization

AbstractAlumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the ‘neat’ complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tertbutyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.

Effect of the Platinum Content on the Microstructure and Micropore Size Distribution of Pt/Alumina-Pillared Clays

The aim of this work is to study the effect of the platinum content (0-1.8 wt % Pt) on the microstructure of an alumina-pillared clay. For this purpose, the nitrogen physisorption data at -196 degrees C, the micropore size distributions of the supported platinum catalysts, and the hydrogen chemisorption results at 30 degrees C have been analyzed and compared. The preparation of the catalysts has modified the textural properties of the Al-pillared clay support, giving rise to a loss of surface area and micropore volume. After reduction at 420 degrees C, the presence of dispersed metallic platinum with mean crystallite size in the 22-55 A range has been found by hydrogen adsorption. Comparison of all results reveals that the platinum species block the micropore entrances by steric hindrance to nitrogen access as the platinum content increases.

PILC-based monolithic catalysts for the selective catalytic reduction of nitrogen oxides by methane in oxygen excess

The aim of this work was the study and development of aluminum-pillared clay (Al-PILC)-based monolithic Pd catalysts for reducing NO x emissions from natural gas-fired power plants using methane as a selective reductant. During preparation of the support, the same raw material used to synthesize the pillared clays was used as a permanent inorganic binder. This confers high surface area and acidity to the extrudates, in addition to high hydrothermal resistance and mechanical strength. The influence of the method used for active phase incorporation on the physico-chemical properties and DeNO x activity and selectivity was studied. Conclusions were drawn from the use of different solution pH values and precursors in relation to the isoelectric point of the solid. Characterization was carried out using X-ray diffraction, inductively coupled plasma-optical emission spectroscopy, X-ray photoelectron spectroscopy, N 2 adsorption, and NH 3 and CO chemisorption.

Pillared layered structures versus zeolites as sorbents and catalysts. Part 8. Catalytic destruction of some chloro- and chlorofluoro-hydrocarbons in alumina-pillared clays

Pillared clays have been monitored for catalytic destruction of halocarbons. In comparison with HZSM-5 zeolites, the catalysts tested give higher chlorohydrocarbons destruction with polymers formation. Fluorochlorohydro-carbons are destroyed as well.

Removal of Vanadium(IV) from Aqueous Solutions by Adsorption Process with Aluminum-Pillared Bentonite

The objective of this research work is to investigate the possibility of using a natural bentonite clay as a precursor to produce aluminum-pillared clay (Al−PILC) for the removal of vanadium(IV) from aqueous solutions. The original bentonite and Al−PILC were characterized with the help of surface area analyzer, X-ray diffraction, scanning electron microscopy, and potentiometric titration. The adsorption of vanadium(IV) onto Al−PILC has been dynamically and thermodynamically investigated. Batch experiments were carried out as a function of solution pH, contact time, vanadium(IV) concentration, adsorbent dose, ionic strength, and temperature. The maximum adsorption capacity was observed in the pH range 4.5−6.0. The maximum adsorption of 99.8 and 88.5% took place at pH 5.0 from an initial concentration of 5 and 10 mg/L, respectively. The external mass-transfer and intraparticular mass-transfer diffusion models were tested to describe the kinetic data. It was shown that the adsorption of vanadium(IV) could be fitted to the intraparticular mass-transfer model. The temperature dependence indicates the endothermic nature of adsorption. The activation energy of sorption was also calculated. The percentage removal of vanadium(IV) decreased with increasing ionic strength. The equilibrium isotherm data were fitted to the Langmuir, Freundlich, and Scatchard isotherm equations to obtain the characteristic parameters of each model. The Freundlich isotherm was found to well represent the measured sorption data. Isotherm experiments conducted at different temperatures allowed the calculation of the isosteric heat of adsorption at different surface loading. The desorption data showed that the spent PILC can be regenerated for further use by 0.1 M HCl.

CHARACTERIZATION OF THE POROUS STRUCTURE OF AN ALUMINA-PILLARED CLAY BY MEANS OF NITROGEN ADSORPTION AND IMMERSION CALORIMETRY

ABSTRACT The characterization of the porous structure developed by the pillaring of a natural clay of the smectite class, a montmorillonite, with aluminum polycations using a relatively concentrated clay suspension (10 wt.%) is presented. Nitrogen adsorption data at 77 K and immersion calorimetry experiments with benzene, cyclohexane, tetraisopropyl o-titanate, and tri-2,4-xylylphosphate at 293 K have been considered for this purpose. Both slit-like and cylindrical pore models have been applied to the nitrogen adsorption results (p/p0 ≤ 0.2) to characterize the micropore region of the alumina-pillared clay. From the measured enthalpies of immersion into the various liquids, the presence of very narrow micropores or constrictions at the entry of the micropores in the alumina-pillared clay is suggested.

Adsorption of hydrogen sulfide on montmorillonites modified with iron

Sodium-rich montmorillonite was modified with iron in order to introduce active centers for hydrogen sulfide adsorption. In the first modification, interlayer sodium cations were exchanged with iron. In another modification, iron oxocations were introduced to the clay surface. The most elaborated modification was based on doping of iron within the interlayer space of aluminum-pillared clay. The modified clay samples were tested as hydrogen sulfide adsorbents. Iron-doped samples showed a significant improvement in the capacity for H 2S removal, despite of a noticeable decrease in microporosity compared to the initial pillared clay. The smallest capacity was obtained for the clay modified with iron oxocations. Variations in adsorption capacity are likely due to differences in the chemistry of iron species, degree of their dispersion on the surface, and accessibility of small pores for H 2S molecule. The results suggest that on the surface of iron-modified clay hydrogen sulfide reacts with Fe +3 forming sulfides or it is catalytically oxidized to SO 2 on iron (hydro)oxides. Subsequent oxidation may lead to sulfate formation.

Pillar effects in MoS 2 catalysts supported on Al and Zr pillared clays in a hydrotreatment reaction : A preliminary study

Molybdenum (Mo) supported on aluminum-pillared clay (Al-PILC) and zirconium-pillared clay (Zr-PILC) with contents of 0.6, 1.4 and 2.8 atoms of Mo/nm 2 were prepared and tested in the hydrogenation (HYD) of naphthalene (NP). It was found that the molybdenum sulfide (MoS 2) catalysts supported on Zr- pillared clays were more active than the samples supported on Al-pillared clays and catalysts supported on alumina. The catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis, nitrogen adsorption and transmission electron microscopy (TEM). Characterization analysis clearly pointed out to a close interaction of MoS 2 with ZrO 2 in the pillared clays. Therefore, the highest hydrogenation activities can be related to the presence of an interaction of MoS 2 with ZrO 2, probably with a different electronic interaction between the active phase and the support, than that reported for the MoS 2/Al 2O 3 system.

Microstructure and quantitative estimation of the micropore-size distribution of an alumina-pillared clay from nitrogen adsorption at [formula omitted] and carbon dioxide adsorption at [formula omitted

Several approaches have been considered and compared in order to characterize the microporous structure of an alumina intercalated clay from nitrogen and carbon dioxide adsorption. The Dubinin–Astakhov (DA) equation, the Horvath–Kawazoe (HK) and the Jaroniec–Gadkaree–Choma (JGC) methods as well as the density functional theory (DFT) have been applied to the adsorption data for both slit-like and cylindrical pore geometries. The effect of the temperature of the thermal treatment on the microstructure of the resulting pillared materials has been investigated by analyzing the micropore-size distributions (MPSDs) of samples calcined at temperatures between 473 and 873 K . The results from nitrogen adsorption at 77 K and carbon dioxide adsorption at 273 K have also been quantitatively compared to characterize these materials. It has been found that the ultramicropores generated by the pillaring process were the most deteriorated at the highest calcination temperatures whereas the mesopores were not significantly affected.

Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays

Supported vanadium-containing catalysts were prepared by impregnation of Al-pillared clays with NaVO 3 precursor aqueous solutions. A montmorillonite and a saponite, both natural as well as previously pillared with Al 13-Keggin polycations, were used as supports, being impregnated with solutions of the precursor by means of the incipient wetness technique. The layered structure of the supports is maintained after impregnation, and even after calcination of the impregnated solids at 500 °C, although with a significant worsening of the textural properties of the solids, in particular, a loss of specific surface area. Three crystalline vanadium-containing phases were identified in the impregnated solids, namely, NaV 3O 8, AlVO 4 and V 2O 5 (shcherbinaite). The reduction of these phases to V 3+ species was observed as wide processes in the 450–750 °C range, all of them centred at ca. 600 °C.