Fathi Kooli

Vibrational modes in layered double hydroxides and their calcined derivatives

Abstract Vibrational modes of layered double hydroxides and their calcined derivatives in the region of 60–4000 cm −1 have been studied using a combination of inelastic neutron scattering (INS), Fourier transform infrared (FTIR) and Raman spectroscopies. The INS spectra recorded at 30 K are dominated by the vibrational contribution of the water contained in the negatively charged layers. Using FTIR and Raman assignments of LDHs and magnesium hydroxide, the lattice modes of the moieties present in the positively charged layers have been identified and assigned. We infer from the results that the vibrational modes of the cationic layer are unaffected by change in the identity of the interlayer anions and that the hydroxyl bonds are strengthened by thermal activation.

Synthesis of highly ordered mesoporous polymer networks

Synthesis of highly ordered three-dimensionally interconnected mesoporous hydrocarbon polymer networks exhibiting Bragg X-ray diffraction is reported by replicating the mesoporous MCM-48 and SBA-15 channel frameworks.

Dependence of the properties of titanium-pillared clays on the host matrix: a comparison of montmorillonite, saponite and rectorite pillared materials

Titanium pillared clays using montmorillonite, saponite and rectorite hosts have been prepared from TiCl 4 –ethanol solutions. The products have been characterised structurally by PXRD and IR studies and for acidity by cyclohexylamine and pyridine adsorption–desorption studies. Catalytic activity data for pentanol dehydration and cumene cracking are also presented. The amount of Ti incorporated is related to the cation-exchange capacity of the host. The thermal stability of the pillared material decreases from rectorite through montmorillonite to saponite. Cyclohexylamine desorption suggests that the saponite sample has the highest acidity, and this is reflected in the highest conversion for cumene cracking. In the case of pentanol dehydration, however, the highest activity is seen for the rectorite sample, despite its apparent lower acidity. Similar effects have been reported previously for this reaction with alumina pillared clays.

Al and Zr pillared acid-activated saponite clays: characterization and properties

An acid-activated saponite has been used in the preparation of Al and Zr pillared acid-activated clays. The properties of this new family of pillared clays (pillared acid-activated saponites, PAASs) have been compared to those of conventional pillared (non-activated) saponites (PILSs). It is found that the acid treated materials incorporate less Al or Zr than the parent saponite, with the most likely cause being the reduced cation exchange capacity of the matrix following acid-activation. Powder X-ray diffraction suggests that Al PAASs are thermally more stable than the corresponding Zr PAASs. The acidity of the pillared materials (as monitored by cyclohexylamine adsorption–desorption thermogravimetry studies) is related to the nature and to the amount of the metal oxides incorporated between the sheets of the host clays. Catalytic data for the Bronsted catalysed dehydration ofpentan-1-ol is reported.

Insertion of electrochemically reduced Keggin anions into layered double hydroxides

A new procedure is described to enable the charge on a Keggin ion to be modified to improve incorporation into layered double hydroxides. The procedure, involving electrochemical reduction, has been tested using the 12-molybdophosphate anion. Chemical analysis and PXRD data confirm that from the otherwise hydrolytically unstable and low charge anions which are unsuitable for intercalation within the basic matrix of MgAl–LDH, a species is obtained in which the stoichiometry is preserved and which yields a pillared LDH structure of 14.8 A basal spacing.

Precursor dependence of the nature and structure of non-stoichiometric magnesium aluminium vanadates

Hydrotalcite-like compounds containing (a) MgII, AlIII and VIII in the layers and carbonate in the interlayers, or (b) MgII and AlIII in the layers and decavanadate in the interlayers, have been synthesized and characterized using powder X-ray diffraction, thermal analysis, FTIR spectroscopy. temperature-programmed reduction, and specific surface-area determination. The crystalline phases formed after calcination in air at 700 °C have been identified using these same experimental techniques. It has been found that the nature of the precursor determines the nature of the Mg–V–O phases formed; thus, when starting from (a), Mg3(VO4)2 containing isolated [VO4] units is formed, while when starting from (b), MgV2O6, containing pairs of edge-sharing [VO6] octahedra, is formed preferentially. Such a reactivity appears to depend on the nature of the support, and not on the stoichiometry (i.e., Mg/V atomic ratio) of the starting materials.

Transformation of kanemite into silicalite1: parameters affecting the cation exchange reaction

The optimum crystallization conditions for the transformation of kanemite into silicalite 1 have been determined by X-ray powder diffraction, thermal analysis and 29Si NMR spectroscopy. The synthesis of silicalite 1 was favored by the use of a TPAOH template, in preference to a TPABr template, highly basic conditions during stirring of the suspension at 70 °C and the adjustment of the pH to 8.5 after stirring. The more the layered structure of kanemite disintegrated after the cation exchange reaction, the higher the amount of incorporated template and the higher the crystallinity of silicalite 1 after the solid-state transformation. The dissolution process that occurs during the cation exchange reaction with short-chain alkylammonium cations was different from that which occurs in the case of long-chain alkylammonium cations which are used for the synthesis of mesoporous materials.

Effect of aluminium source and content on the synthesis of zeolite ZSM-5 from kanemite via solid-state transformation

The effect of the incorporation of aluminium during the synthesis of zeolite ZSM-5 from kanemite via solid-state transformation was studied using X-ray powder diffraction, 29Si and 27Al NMR spectroscopy, thermal analysis and elemental analysis. During cation exchange, which takes place in highly basic media, silicate layers of kanemite give rise to the formation of silica colloids and shorter silicate layers. For Si/Al ratios ≥19, some aluminium is incorporated into the short silicate layers, however, most of the aluminium is incorporated into the Si–O–Si network during the condensation of the silica colloids in silica polymers when the pH is lowered to 8.5, independent of the aluminium source used (NaAlO2, Al2(SO4)3 or Al(NO3)3·9H2O). Mesoporous materials are synthesized from Al-containing kanemite, that is, aluminium is added during the synthesis of kanemite. The formation of silica colloids during cation exchange is the reason why, unlike the synthesis of mesoporous materials, aluminium could be added to the kanemite-template mixture during cation exchange. The highest amount of incorporated aluminium was obtained using NaAlO2 because it is the aluminium source for which the pH is highest during cation exchange and consequently it is the aluminium source which yields the highest amount of silica colloid precipitates during the adjustment of the pH to 8.5.

Novel layered silicate and microporous silica materials in the Na-magadiite–H2O–(TMA)2O system

Novel layered silicate and microporous silica materials have been successfully synthesized in a Na-magadiite–H2O–(TMA)2O system. At appropriate water and TMAOH contents, Na-magadiite was converted into a new layered silicate phase (KLS2) at relatively low temperatures, in the range 130 to 150 °C. However, a microporous silica material (FLS) was formed at higher temperatures, from 160 up to 180 °C. The samples were characterized by powder X-ray diffraction, 29Si magic-angle spinning NMR, infra-red spectroscopy, scanning electron microscopy, thermogravimetric and differential thermal analysis, and adsorption measurements. It was found that the KLS2 phase has lower thermal stability than the FLS phase. An amorphous phase was formed upon heating KLS2 below 300 °C, while FLS was found to be stable up to 600 °C and exhibits a surface area of 300 m2 g−1 and micropore volume of 0.082 mL (liquid nitrogen) g−1. Factors such as the Na-magadiite, TMAOH and water contents, which dominate the conversion of Na-magadiite, are discussed.

Conversion of protonated magadiite to a crystalline microporous silica phase via a new layered silicate.

Organic structure-directing agents are necessary to the formation of defined zeolitic structures; doing without the organic component can simplfy the reaction immensely. Such a transformation, of protonated magadiite to a new layered silicate, is reported herein. The picture shows the XRD patterns of as-prepared protonated magadiite and the product after simple hydrothermal treatment at two different temparatures. After calcination (500 °C) the final material has a surface area of 457 m(2) g(-1).