Abdelhamid Ghorbel

Study of Pd(II) adsorption over titanate nanotubes of different diameters

Hydrogenotitanates (HNTs) nanotubes with different diameters were prepared by hydrothermal treatment of TiO(2) (P25) followed by washing with HCl aqueous solution. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal analysis and N(2) adsorption/desorption. In order to determine the palladium uptake ability of different HNT samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH(+)(4)/NH(3) buffer). Transmission electron microscopy showed that the diameter of the nanotubes depends on the preparation conditions. Chemical analysis of residual sodium and thermal studies showed that the chemical formula of the two prepared HNT was H(x)Na(2-x)Ti(2)O(5)H(2)O with x=1.61 or 1.65. The HNTs are mesoporous materials with a multi-walled nanotubular structure and high specific surface area. In order to determine the capacity of palladium retention of different HNTs samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH(+)(4)/NH(3) buffer). The adsorption kinetics of Pd(II) on the HNTs was very fast. The isotherms of Pd(II) on the HNTs showed that the adsorption occurred (1) initially through cationic exchange and (2) when the concentration of Pd(II) is high by precipitation of different Pd salts. The adsorption capacity of Pd(II) is strongly altered by the morphology of the HNTs samples.

TiO2 nanotubes as solid-phase extraction adsorbent for the determination of polycyclic aromatic hydrocarbons in environmental water samples.

An analytical method based on TiO2 nanotubes solid-phase extraction (SPE) combined with gas chromatography (GC) was established for the analysis of seven polycyclic aromatic hydrocarbons (PAHs): acenaphtylene, acenaphthene, anthracene, fluorene, phenanthrene, fluoranthene and pyrene. Factors affecting the extraction efficiency including the eluent type and its volume, adsorbent amount, sample volume, sample pH and sample flow rate were optimized. The characteristic data of analytical performance were determined to investigate the sensitivity and precision of the method. Under the optimized extraction conditions, the method showed good linearity in the range of 0.01-0.8 microg/mL, repeatability of the extraction (RSD were between 6.7% and 13.5%, n = 5) and satisfactory detection limits (0.017-0.059 ng/mL). The developed method was successfully applied to the analysis of surface water (tap, river and dam) samples. The recoveries of PAHs spiked in environmental water samples ranged from 90% to 100%. All the results indicated the potential application of titanate nanotubes as solid-phase extraction adsorbents to pre-treat water samples.

A compact process for the treatment of olive mill wastewater by combining wet hydrogen peroxide catalytic oxidation and biological techniques

A system based on combined actions of catalytic wet oxidation and microbial technologies for the treatment of highly polluted OMW containing polyphenols was studied. The wet hydrogen peroxide catalytic oxidation (WHPCO) process has been investigated in the semi-batch mode at atmospheric pressure, using aluminium-iron-pillared inter layer clay ((Al-Fe)PILC), under two different catalytic processes: ((Al-Fe)PILC/H(2)O(2)/ultraviolet radiations) at 25°C and ((Al-Fe)PILC/H(2)O(2)) at 50°C. The results show that raw OMW was resistant to the photocatalytic process. However ((Al-Fe)PILC/H(2)O(2)), system operating at 50°C reduced considerably the COD, colour and total phenolic contents, and thus decreased the inhibition of the marine photobacteria Vibrio fischeri luminescence by 70%. This study also examined the feasibility of coupling WHPCO and anaerobic digestion treatment. Biomethanisation experiments performed with raw OMW or pre-treated OMW proved that pre-treatments with ((Al-Fe)PILC/H(2)O(2)) system, for more than 2 h, resulted in higher methane production. Both untreated OMW as well as 2-h pre-treated OMW revealed as toxic to anaerobic bacteria.

Optimisation of the preparation of an Al-pillared clay: thermal stability and surface acidity

The intercalation of montmorillonite by aluminium requires the use of aluminium chloride as a precursor for the intercalation solution. The best samples were obtained with an a pH of 5.6 and an Al/clay ratio = 5 mmol/g. High surface area materials were obtained with good thermal stability after calcination at 773 K. A study of the acidity of surface groups showed that the Al13 polycation is transformed into a specific form of Al oxyhydroxide with amphoteric properties. The data, when treated in the ‘1 site, 2 pK’ model, may be interpreted by the existence of surface species of type AlOH(OH2), having two constants of depronation Ka1 = 10−5 and Ka2 = 0.32 · 10−6. An alternate treatment in terms of the ‘multisite, 1 pK’ model recently developed by Jagiello et al. is also discussed.

EPR and UV-visible spectroscopic studies of alumina-supported chromium oxide catalysts

The oxidation state, the mobility and the molecular structure of chromium species present on CrOx–Al2O3 catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO42− species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al2O3 surface (species B). The CrO42− species show high mobility and are probably responsible for the formation of CrOx clusters.

Comparative study of the sulfur loss in the xerogel and aerogel sulfated zirconia calcined at different temperatures: effect on the n-hexane isomerization

Aerogel and xerogel sulfated zirconia exhibit different structure and texture at various calcination temperatures. At 560°C the aerogel develops only the tetragonal phase, whereas the xerogel contains both the monoclinic and the tetragonal phases. Heating at higher temperature causes the transition of the tetragonal phase into the monoclinic one for all the samples by loss of sulfur, but the tetragonal phase remains significantly more stable in the aerogel. Characterization indicates that the loss of sulfur at higher temperature is easier for the xerogel. The ability of the aerogel to retain sulfur at higher temperature explains its better stability and confers it a good catalytic performance in the n-hexane isomerization reaction.

Acidic properties of a clay prepared from the reaction of zirconyl chloride solution containing sulfate ions with montmorillonite

Sulfated zirconium oxyhydroxide clays were prepared by adding ammonium sulfate to the intercalation solution. The main parameter controlled in this study was the SO4:Zr ratio in solution. The characterization of the catalysts, their acidic properties and catalytic activities were examined by N-2-BET adsorption, chemical analysis, adsorption-desorption of basic molecules and conversion of n-hexane and isopropanol. Two different types of SO4-Zr polycation binding were proposed and related with the acidic properties of these solids. To enhance the acidity of the sulfated zirconium oxyhydroxide clay, the SO4:Zr molar ratio must be higher than 0.125. The higher this ratio, the higher is the activity of these solids. It appears that polymerised entities are more active than individual sulfated polycations. Isopropanol dehydration to propene as well as isomerization of n-hexane seem to be related to the number and strength of Bronsted acid sites

Comparative Study of the Acidity of Sulphated Zirconia Supported on Alumina Prepared by Sol-Gel and Impregnation Methods

Sulphated and unsulphated alumina-zirconia with atomic ratio Zr/Al = 0.5 were prepared by sol-gel and impregnation methods. The solid prepared by the sol-gel method exhibits the higher specific surface area. The Kelvin probe shows that the value of unsulphated sample is around 400 mV. This value grows up to 1100 mV for sample prepared by impregnation of aerogel alumina by sulphated propoxide zirconium and up to 1450 mV for sulphated alumina-zirconia aerogel catalyst. The modification of the work function is probably due to the charge transfer from the zirconium and aluminium to an oxygen species, responsible for the increase of Lewis acidity. XPS results show that the aluminium and zirconium exist in oxide form as Al2O3 and ZrO2. The sulphur is present as sulphate species in the solids bonded to the Al—Zr—O framework. Furthermore, the oxygen species exist in different types created by the introduction of sulphur in the bulk of solids.Compared to the impregnated catalyst the sol-gel sulphated alumina zirconia exhibits higher activity in the isopropanol dehydration reaction in the temperature range 423 K–523 K.

Preparation of Co2+/ZSM5 catalysts by solid-state reaction : Influence of the precursor on cobalt speciation

Abstract Co2+/ZSM5 catalysts (Co/Al = 1, overstoichiometric ratio) have been prepared by solid-state reaction at 500 °C in argon from H-ZSM5 and four Co(II) precursors: formate, nitrate, chloride and acetate. Co3O4 particles supported by the zeolite grains are the only cobalt-containing phases detected when formate is used. When cobalt nitrate is the precursor, Co3O4 particles appear to be independent from the grains. A fraction of cobalt has nevertheless migrated into the zeolite; this is linked with [Co(H2O)6](NO3)2 low melting point and wetting of the zeolite grains by the molten salt at the beginning of the thermal treatment. Catalysts prepared from cobalt chloride contain both nanometric Co3O4 particles on the support grains and cobalt ions inside the zeolitic channels. Ion exchange is possible, at least partly, due to the fact that unlike nitrate and formate, cobalt chloride has not decomposed before reaching the temperature at which the exchange process is activated. This process is chemically driven by the release of HCl in the gas phase. Finally, the major phase detected when cobalt acetate is the precursor is a poorly organized cobalt phyllosilicate surrounding zeolite grains. Acetate ions attack the zeolitic framework from outside during the solid-state reaction; cobalt ions are inserted in the silicate matrix and progressively migrate deeper in the grains upon thermal activation.

One-pot deposition of palladium on hybrid TiO2 nanoparticles and catalytic applications in hydrogenation.

One-pot deposition of Pd onto TiO(2) has been achieved through directly contacting palladium(II) salt with nanosized functionalized TiO(2) support initially obtained by sol-gel process using titanium isopropoxide and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various palladium salts (Na(2)PdCl(4) and Pd(NH(3))(4)Cl(2)·H(2)O) and titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used in order to study the effect of the nature of the precursor and of the citrate content on the final Pd particle size and catalytic properties of the as-obtained Pd/TiO(2) systems. Characterization was performed using N(2) adsorption-desorption isotherms, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained hybrid Pd/TiO(2) catalysts were tested in the selective hydrogenation (HYD) of an α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Citrate-free Pd/TiO(2)-based catalysts present lower selectivity into saturated alcohol. However, citrate-functionalized Pd/TiO(2) catalyst seems to control the selectivity, the particle size and dispersion of Pd NPs leading to high intrinsic activity.