Alumina Pillars Research Articles

Observation of nontrivial Zak phase induced topological states in glow discharge plasma

Plasma blackout, which contains ablative impurities, strongly attenuates the signal of the reentry spacecraft. Traditional methods focus on mitigating electron densities and impurities around the antenna, and metamaterial-based electromagnetic methods have yet to be proven experimentally. We simulate the plasma blackout problem using laboratory plasma supported by gas discharge technology. Alumina pillars are embedded in the plasma background to form plasma photonic crystals, while topological phase transitions are achieved by shrinking and expanding pillars within a unit cell. The topological edge states (TESs) that are insensitive to weak impurities in the transport path are verified theoretically and experimentally. We introduce the glide-reflection (GR) symmetry in the nontrivial lattices to obtain the gapless edge states, which are exclusively observed in the acoustic systems. Meanwhile, the Δω of the gapless TES increases with the electron densities, ensuring a wide communication bandwidth. Furthermore, the strong coupling of heterostructure with GR symmetry in plasma photonic crystals is elucidated. Our work not only provides a new approach to the blackout communication problem but can also serve as a nascent experimental platform to investigate topological electromagnetic phenomena.

Modified vermiculites as effective catalysts for dehydration of methanol and ethanol

Abstract Two series of catalysts for the reactions of methanol and ethanol dehydration were obtained from vermiculite. The first series of the catalysts were obtained by treatment of raw clay with nitric acid solution. Such modification of vermiculite resulted in a significant increase of its specific surface area and also partial leaching of Al3+ and Fe3+ cations from clay layers. Acid treatment of vermiculite resulted in its activation in the processes of methanol and ethanol dehydration. The second series of the catalysts were obtained by intercalation of vermiculite with alumina pillars. Prior to the pillaring process, raw vermiculite was treated with nitric acid solution followed by complexation of Al3+ and Fe3+ cations, leached from clay layers, with oxalic acid or citric acid. Alumina pillared vermiculites, characterized by increased specific surface area, porosity and acidity, were found to be very active catalysts of alcohols dehydration. Catalytic performance of modified vermiculites was related mainly to the concentration and strength of acid sites present in the samples.

Preparation of Alumina Pillared Montmorillonite Clays Employing Ultrasonics and Their Catalytic Properties

<p>An accelerated diffusion of alumina precursor species in-between the gallery region of montmorillonite clays by the use of ultrasonic technique is described. This method offers a faster, efficient and attractive route for the synthesis of alumina-pillared clay catalysts. Out of the several preparative parameters studied, the role of pre-exchanged cations influenced the optimum duration of ultrasonic agitation and treatment for the pillaring process. By comparing ultrasonic route and conventional preparation procedure, it is revealed that uniform spacing of alumina pillars in the clay means homogeneously distributed acid centers. The influence of calcination temperature on the acidity and hence the catalytic activity is described. The choice of three different montmorillonite clays with different cation exchange capacities enables one to tune the pore dimensions of the pillared clays. The catalytic applications include studies on cumene cracking, dehydration of propan-2-ol and alkylation of benzene with linear olefins. </p>

Synthesis of stable Cu-supported pillared clays for wet tyrosol oxidation with H2O2

In the present paper the synthesis of stable Cu-containing pillared clays catalysts (Cu-PILCs) is described. These catalysts were prepared by the solid-state reaction of Al-pillared clay with copper nitrate. The resultant materials were then treated with an oxalic acid solution in order to improve the dispersion of metal species on the alumina pillars. Characterization studies were performed by use of X-ray diffraction, nitrogen adsorption at 77K, chemical analysis, temperature-programmed reduction (H2-TPR) and transmission electron microscopy (TEM). The texture of the copper catalysts showed a high specific surface area and microporosity (197m2g−1 and 0.081cm3g−1 respectively for the catalyst Cu5.6Al-PILC), with high loading of copper (up to 4.72Cuwt%). TPRprofiles of catalysts show the presence of isolated copper species with high interaction with the alumina pillars.The properties of copper-based catalysts have been studied in the wet hydrogen peroxide oxidation of an aqueous solution of tyrosol, a molecule which constitutes more than half of the light fraction of the olive mill wastewater. The reaction was conducted in batch and flow reactors. Performance of catalysts remained quite excellent; total removal of tyrosol with high TOC abatement (around 65%) was obtained after 2h reaction. Furthermore, the Cu5.6Al-PILC(t) catalyst showed very high stability and performance in the flow reactor: 90% of tyrosol conversion and 78% of TOC removal are obtained in 192h on stream, without the detection of any change in the activity.

ChemInform Abstract: Synthesis and Characterization of Alumina-Pillared Layered Tetratitanates with Different Interlayer Spacings.

A series of alumina-pillared layered tetratitanates with different Interlayer spacings (d001= 15.2–17.0 A) has been first prepared through a step-wise exchange process and by finely changing the exchange reaction conditions such as reaction time and molar ratio of reactants in the reaction mixture, and hydrolysis conditions such as the pH and aging time used to generate the pillaring agent. Apart from the Interlayer spacing, the pore diameter and specific surface area of the pillared samples can also be changed by varying the preparation conditions. The resulting alumina-pillared layered tetratitanates were porous, with both micro- and meso-pores (average pore diameter = 61.5–95.8 A). The specific surface area (BET, N2, 77 K) of the starting material K2Ti4O9(5 m2 g–1) was increased by pillaring up to 56.6–105.6 m2 g–1. The relatively high surface area is mainly due to the microporous structure of the interlayered spaces formed by stable alumina pillars. The structure of the alumina-pillared layered tetratitanates was thermostable above 500 °C. The results are compared with those previously reported.

Natural Micas Intercalated with Al2O3 and Modified with Transition Metals as Catalysts of the Selective Oxidation of Ammonia to Nitrogen

Natural cationic layered clays—vermiculite and phlogopite—pretreated with acids were intercalated with alumina pillars. In next step, transition metals were deposited on the surface of pillared interlayer clays (PILC) by a liquid ion exchange method. The catalyst samples were characterized with respect to: composition (EPMA), structure (XRD), texture (BET), surface acidity (NH3-TPD) and coordination of deposited transition metals (UV–vis-DRS). The modified clays were tested in the role of catalyst for the selective oxidation of ammonia to nitrogen. In a series of the studied samples the best catalytic performance presented alumina pillared vermiculite modified with copper.

Vermiculites intercalated with Al 2O 3 pillars and modified with transition metals as catalysts of DeNO x process

Vermiculites intercalated with alumina pillars and modified with transition metals (Cu, Fe) were studied as catalysts of selective reduction of NO with ammonia. Prior to the pillaring process, a raw vermiculite was treated with a solution of nitric acid and then citric or oxalic acid in order to reduce the overall charge of layers. This modification was necessary for a successful pillaring of the clay. Transition metals (Fe, Cu) were deposited on the surface of the modified vermiculites by an ion-exchange method. The obtained samples were characterized with respect to composition (EPMA), structure (XRD), texture (BET) and chemical nature of deposited transition metal species (UV–vis–DRS). The vermiculite based materials have been found to be active and selective catalysts of the DeNO x process. The Cu-containing samples were catalytically active at lower temperatures than the pillared clays modified with iron. A side reaction of ammonia oxidation by oxygen decreased the effectiveness of the DeNO x process in the high temperature range.

Phlogophites intercalated with Al2O3 pillars and modified with transition metals as catalysts of the DeNOx process

Natural phlogophite, pre-treated with acids and intercalated with alumina pillars, was used as catalytic support. Transition metals (Fe, Cu) were deposited on the surface of the modified clay materials by an ion-exchange method. The obtained samples were characterized with respect to structure (XRD), texture (BET), composition (EPMA) and chemical nature of the deposited transition metals species (UV-vis-DRS). The phlogophite based materials have been found to be active and selective catalysts of the DeNOx process. The Fe-containing samples were catalytically active at lower temperatures than the clays modified with copper. A competitive ammonia oxidation by oxygen decreased the effectiveness of the DeNOx process in the high temperature range.

Chromium–saponite clay catalysts: Preparation, characterization and catalytic performance in propene oxidation

Chromium–saponite catalysts have been prepared by two synthesis procedures. The first method consisted in the intercalation of the saponite with solutions containing aluminium and chromium oligomers with various molar ratios, while the second one consisted in the incipient wetness impregnation of alumina-pillared saponite with several chromium salts, ammonium chromate, Cr(II) acetate and Cr(III) nitrate. Several techniques, X-ray diffraction, nitrogen physisorption at −196 °C, thermogravimetric and differential thermal analysis, infrared and DR-UV–vis spectroscopies, temperature-programmed reduction and electron paramagnetic resonance spectroscopy at −196 °C, have been used to characterize and to compare the properties of the materials synthesized. The results show that the solids obtained combine the layered structure of the clay and the thermal stability given by the alumina pillars. The catalysts have been tested in the oxidation of propene, showing a catalytic behaviour according to the Mars–van Krevelen mechanism, the performance not depending on the method in which chromium was incorporated to the clay.

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.

A comparative UV–vis-diffuse reflectance study on the location and interaction of cerium ions in Al- and Zr-pillared montmorillonite clays

The environment, location and interaction of the Ce 3+ ions in the micropores of Al- and Zr-pillared clays have been studied by UV–vis-diffuse reflectance spectroscopy (UV–vis-DRS). The DRS spectra show that the chemical environment of the Ce 3+ ions in cerium exchanged clay is different from that of the Al- and Zr-pillared clays. The Al–Ce pillared clays (Al–Ce-PM) show four distinct absorption bands at 224, 263, 294 and 342 nm in the UV region which are attributed to 4f → 5d interconfigurational transitions of Ce 3+ ions associated with alumina pillars. The O 2− → Ce 3+ charge transfer band observed at 263 nm for Ce-exchanged and Al–Ce-PM clays is blue shifted by 10 nm for Ce–Zr-pillared clays (Ce–Zr-PM) due to fully hydrated Ce 3+ ions. The Ce 3+ ions are incorporated in the Al- and Zr-pillars possibly as AlCeO 3 and Ce x Zr 1− x O 2 particles upon heat treatment.

Ultrathin Films and Hollow Shells with Pillared Architectures Fabricated via Layer-by-Layer Self-Assembly of Titania Nanosheets and Aluminum Keggin Ions

Inorganic multilayer films and hollow shells with pillared architectures have been fabricated layer-by-layer on spherical poly(methyl methacrylate) (PMMA) templates as well as flat substrates through the electrostatic self-assembly technique. Positively charged polyoxocations of aluminum Keggin ions were employed both as inorganic binder and as pillaring agent in electrostatic self-assembly with exfoliated unilamellar crystallites of Ti0.91O2, yielding new types of ultrathin films and core−shell composites. Ultraviolet−visible absorption spectra revealed progressive enhancement of absorbance with increasing deposition cycles, indicating the regular growth of multilayer assemblies of titania nanosheets and aluminum polyoxocations. Evolution of a Bragg peak with a periodicity of ca. 1.5 nm and its enhancement also supported the formation of nanostructured multilayer films and shells, accommodating aluminum polyoxocations in the nanosheet gallery. Depth X-ray photoelectron spectra confirmed their inorganic nature. Calcination at 400 °C produced ultrathin films and hollow shells with alumina pillars between the titania sheets. N2 adsorption results revealed a high specific surface area of 260 m2 g-1 and nanoporous feature for the pillared hollow spheres.

Al-pillared montmorillonite-based Mo catalysts: effect of the impregnation conditions on their structure and hydrotreating activity

The effects of the pH and medium of the impregnation solution on the surface structure and activity for gas oil hydrodesulfurization (HDS) of molybdenum catalysts supported on an Al-pillared montmorillonite have been studied. Catalysts were characterized by using X-ray diffraction, nitrogen and ammonia sorption measurements, temperature-programmed reduction, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that impregnation at basic pH leads to the incorporation of molybdenum mainly in form of monomeric and polymeric species, with a substantial part of Mo species in the interlayer space of the Al-pillared clay, probably in interaction with the alumina pillars. Whereas, formation of small particles of bulk MoO 3 deposited on the external surface of the Al-pillared clay was favoured by impregnation at acid pH. The impregnation at pH 8.5 in a H 2O 2 solution produced abundant formation of incipient MoO 3 crystallites relatively well dispersed, partially located inside the porous system. The catalysts prepared at basic pH values had slightly higher HDS activity than those prepared at acid pH values.

Mixed Al/Ce oxide pillaring of montmorillonite: XRD and UV-VIS diffuse reflectance study

Ce and Al pillared clays were prepared by (i) pillaring Ce3+-exchanged montmorillonite with Al13 polycation (Ce-Al-PILC) and (ii) by pillaring Na-montmorillonite with an oligomer obtained from cohydrolysis of Ce3+ and Al3+ salts (Al-Ce-PILC). Cohydrolyzed oligomer gives larger intercalating species with Ce3+ incorporated in it. The UV-DRS spectrum of clay sample intercalated with this species shows four distinct absorption bands at 224, 263, 294 and 342 nm, which are attributed to the 4f-5d interconfigurational transitions of Ce3+ ions associated with alumina pillars.

Selective catalytic reduction of NO by propane on copper containing alumina pillared α-zirconium phosphates

Copper containing alumina pillared α-zirconium phosphates with different copper loadings, where copper was incorporated by ion exchange and by impregnation, have been synthesized and characterized by using techniques such as XPS, UV–VIS spectroscopy, H2-TPR and NO-TPD. The catalytic activity of the synthesized materials in the selective catalytic reduction of NO using propane as a reducing agent in the presence of oxygen at 623–823K has been evaluated. In the exchanged sample, copper is mainly present as isolated Cu2+ species, whereas the impregnated materials show copper to be present as small CuO clusters (not detectable by XRD) and a fraction as spinel-like structures within the alumina pillars. NO-TPD displayed a stronger interaction of NO molecules with the copper exchanged materials, because N2O and O2 are detected at temperatures higher than 773K. Under the selected experimental conditions, the most active catalyst in the SCR of NO is the copper exchanged catalyst, attaining conversions of NO close to 30% at 823K. Moreover, the competitiveness factor is high and the TOF number is 1.57×10−4 moleculesNO per second atCu for the copper exchanged catalyst, this being comparable to that obtained with a Cu-ZSM-5 used as a reference.

Solid acid catalysts from clays: Evaluation of surface acidity of mono- and bi-pillared smectites by FT-IR spectroscopy measurements, NH 3-TPD and catalytic tests

Alumina-pillared and double-pillared montmorillonite and saponite samples have been prepared and characterised from the point of view of their thermal stability, porosity and structure. Surface acidity was studied by ammonia TPD, iso-propanol conversion and n-butene skeletal isomerisation catalysis, and by FT-IR spectroscopy of the surface hydroxy-groups, and of adsorbed acetonitrile and pivalonitrile. The data show that the alumina pillars of pillared montmorillonite carry stronger Lewis sites than those of pillared saponite. Additionally, stronger Brønsted sites are carried by the montmorillonite layers with respect to those of saponite. Finally, pillared montmorillonite is more active in converting iso-propanol. However, it is also too active in converting n-butene, so giving rise to faster coking and more extensive cracking. So, pillared saponite has a more selective behavior in converting n-butene into iso-butene.

Microporous Montmorillonites Expanded with Alumina Clusters and M[(&mgr;-OH)Cu(&mgr;-OCH(2)CH(2)NEt(2))](6)(ClO(4))(3), (M = Al, Ga, and Fe), or Cr[(&mgr;-OCH(3))(&mgr;-OCH(2)CH(2)NEt(2))CuCl](3) Complexes.

Expanded clays bipillared with [Al(13)O(4)(OH)(24)(H(2)O)(12)](7+) ions and with hexameric Cu complexes such as M[(&mgr;-OH)Cu(&mgr;-OCH(2)CH(2)NEt(2))](6)(ClO(4))(3), or with M[(&mgr;-OH)Cu(&mgr;-OCH(2)CH(2)NEt(2))](6)(PF(6))(3) where M = Fe, Al, Ga, form microporous materials whose stability and microporosity depend mainly on the identity of the hexamer central metal atom. In fact, a general decrease in thermal stability, interlamellar heights, surface areas, and pore volumes was noted when, in the (Cu,M) hexamer, M changed from gallium to aluminum to iron. Mossbauer results have indicated that only Fe(3+) in octahedral coordination is present in the iron-containing bi-PILC samples (bi-PILC = bipillared interlayered clays). It is believed that metals such as Fe(3+) and Cu(2+) can interact with the interlamellar Keggin ions thereby decreasing the stability of the alumina pillars. In contrast, the intermediate Al(13)-PILC structure is least affected when the more stable Cr complex is used. Bi-PILC materials containing 2.7-3.4% Cr stable to 500 degrees C have been obtained. The low polarity of the chosen solvent (acetonitrile) appears to inhibit the back-exchange of the intermediate PILC's Keggin ions with the hexameric Cu complexes. Elemental analysis together with XRD results suggests that the primary intercalation pathway was diffusion or ion exchange when Cr[(&mgr;-OCH(3))(&mgr;-OCH(2)CH(2)NEt(2))CuCl](3) or M[(&mgr;-OH)Cu(&mgr;-OCH(2)CH(2)NEt(2))](6)(ClO(4))(3), respectively, was used. In all preparations, bi-PILC were produced containing complexes that suffered ligand losses during the synthesis reaction. Molecular scale AFM images have shown that these complexes can be found also outside the clay interlamellar space.

Copper-doped alumina-pillared montmorillonites as catalysts for oxidation of toluene and xylenes with hydrogen peroxide

AbstractCatalytic properties of Cu-doped alumina-pillared montmorillonite samples have been tested in the liquid phase oxidation of toluene, o-, m-, and p-xylene with hydrogen peroxide. The results show that the clay samples possess significant activity for both the oxidation of methyl groups and hydroxylation of the aromatic ring. Physicochemical characterization of the catalysts using XRD, BET, ESR and ICP-AES techniques show that they are porous materials with Cu species located in the interlayer, present either as isolated Cu2+ ions anchored at alumina pillars or as patches of amorphous CuO. The dependence of the overall yields on the amount of Cu dopant is discussed and explained in terms of the catalyst structural properties.

Development of Composite Adsorbents of Carbon and Intercalated Clay for N2and O2Adsorption: A Preliminary Study

Composite adsorbents of carbon and alumina intercalated montmorillonite were prepared and characterized by adsorption of N2and O2at various temperatures. The effects of pyrolysis, temperature, heating rate, subsequent degassing, and doping of cations and anions were investigated. The adsorption capacities of the composite adsorbents developed at higher temperatures (0 and −79°C) are found to be larger than those of normal alumina pillared clays. The experimental results showed that the framework of these adsorbents is made of alumina particles and clay sheets while the pyrolyzed carbon distributes in the space of interlayers and interpillars. The pores between the carbon particles, clay sheets, and alumina pillars are very narrow with very strong adsorption forces, leading to enhanced adsorption capacities at 0 and −79°C. The composite adsorbents exhibit features similar to those of carbonaceous adsorbents. Their pore structures, adsorption capacities, and selectivities to oxygen can be tailored by a controlled degassing procedure. Meanwhile, ions can be doped into the adsorbents to modify their adsorption properties, as usually observed for oxide adsorbents like zeolite and pillared clays. Such flexibility in pore structure tailoring is a potential advantage of the composite adsorbents developed for their adsorption and separation applications.

Acid/base treatment of Al-PILC in KCl solution

Abstract The ion-exchange properties of Na + montmorillonite and its Al-pillared form have been investigated. Electrolyte solutions of (KCl/HCl), (KCl/KOH) and (KCl/NaOH) at two different concentrations of 0.05 M and 0.1 M were used. The results obtained on the original clay are compared with those on the pillared form to see the impact of the ion exchange on the stability of the pillars. The study was performed by using X-ray diffraction (XRD), nitrogen-adsorption measurements, elemental analysis of the solids before and after modification and atomic absorption spectroscopy (AAS) as a tool to analyze the supernatant. The recorded pH curves of the base substrate montmorillonite and the Al-PILC give an indication of the anion and cation uptakes as a function of the pH of the solutions utilized. The results show a significant increase in ion-exchange capacity after intercalation of alumina pillars. However, by X-ray diffraction an appreciable decrease of the interlayer spacing is noticed from about 18.3 A to 14 A at pH 1.73 and to 16 A at pH 12.45 for Al-PILC although no structural breakdown occurs. In contrast, the surface area and the micropore volume decrease significantly in highly acidic or basic medium. For instance, a surface area of 232 m 2 g −1 for the Al-PILC decreases after treatment at pH 2.63 to 215 m 2 g −1 and to 71 m 2 g −1 at pH 1.73. The same observation is made under basic conditions. Moreover, a considerable amount of Al 3+ is leached out from the modified Al-PILC. Therefore, it is reasonable to assume that the alumina pillars are attacked during this treatment, leading to partial destruction or dissolution of the pillars.