Influence of zirconia addition in TiO2 and TiO2-CeO2 aerogels on the textural, structural and catalytic properties of supported vanadia in chlorobenzene oxidation.

This paper studies the effect of the direct incorporation of ZrO2 in TiO2 and TiO2-CeO2 aerogel supports prepared by sol-gel route on the physico-chemical and catalytic properties of supported vanadia catalysts in the total oxidation of chlorobenzene. The obtained catalysts have been characterized by means of ICP-AES, N2 adsorption-desorption at 77 K, XRD, XPS, H2-TPR and NH3-TPD. The results revealed that Zr-doped V2O5 based catalyst is beneficial for the improvement of catalytic properties in chlorobenzene total oxidation. In particular, in the absence of cerium groups, this beneficial effect is correlated with the better acidic properties or/and the stabilization of the V2O5 active phase in a higher oxidation state. However, in the case of cerium rich catalyst, this positive effect is much stronger thanks to the enhanced redox properties of V2O5/TiO2-CeO2-ZrO2.

Heterogeneous Fenton-like oxidation of p-hydroxybenzoic acid using Fe/CeO2-TiO2 catalyst.

This paper is built on the Fenton-like oxidation of p-hydroxybenzoic acid (p-HBZ) in the presence of H2O2 and 3%Fe supported on CeO2-TiO2 aerogels under mild conditions. These catalysts were deeply characterized by X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). The effect of thermal treatment, pH (2-3, 5, 7), H2O2/p-HBZ molar ratio (5, 15, 20, 25) and reaction temperature (25 °C, 40 °C and 60 °C) on the catalytic properties of supported Fe catalysts are studied. Our results highlight the role of CeO2 and the calcination of the catalyst to obtain the highest catalytic properties after 10 min: 73% of p-HBZ conversion and 52% of total organic carbon (TOC) abatement.

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,ß-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.

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.

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.

Mild photochemical synthesis of the antioxidant hydroxytyrosol via conversion of tyrosol.

Hydroxytyrosol, a naturally occurred orthodiphenolic antioxidant molecule found in olive oil and olive mill wastewaters, was obtained from the wet hydrogen peroxide photocatalytic oxidation of its monophenolic precursor tyrosol. The liquid-phase oxidation of tyrosol to hydroxytyrosol was performed by use of an iron-containing heterogeneous catalyst (Al-Fe)PILC with the assistance of UV irradiation at 254 nm and at room temperature. The spectroscopic and HPLC data of the synthesized compound proved to coincide fully with those of a pure sample obtained by continuous countercurrent extraction. This reaction was found to be light-induced. The hydroxytyrosol synthesis reaction reached its maximum yield of 64.36% under the optimized operating conditions of 3.6 mM tyrosol, 0.5 g L(-1) catalyst, and 10(-2) M H2O2 with the assistance of UV light. Increasing the initial hydrogen peroxide concentration more than 10(-2) M has a diminishing return on the reaction efficiency. Catalyst can be recuperated by means of filtration and then reused in a next run after regeneration since its activity did not significantly decrease (<10%). The reaction synthesis is operationally simple and could find application for industrial purposes.

ESR study of MoY and PdMoY reduction.

This paper deals with the reduction of MoY and PdMoY using ESR in order to study the effect of molybdenum on the reducibility of palladium ions. The evolution of signals of paramagnetic species of palladium (Pd3+ in 4d7 and Pd+ in 4d9) and molybdenum (Mo5+ in 4d1) was followed by EPR spectroscopy. Two paramagnetic species of Mo5+ were observed after reduction under hydrogen, the first with g// = 1.87 and the second with g// = 1.89. However, the Mo5+ ion on the zeolite exhibited various coordination symmetries upon reduction or other treatments, depending on the preparation method. The analysis of the g tensors allowed these signals to be attributed to molybdenyl ions in penta- (Mo5+(5C)) and hexacoordination (Mo5+(6C))symmetries.