Total oxidation of volatile organic compounds on Au/Ce–Ti–O and Au/Ce–Ti–Zr–O mesoporous catalysts

Cerium–titanium mixed oxides and mesoporous cerium-modified titanium and cerium-modified titanium–zirconium mixed oxides were synthesized in order to obtain active support for gold volatile organic compound (VOC) oxidation catalysts. Ce–Ti mixed oxides were synthesized by sol–gel method. Mesoporous TiO₂ and Ti–Zr mixed oxides were prepared through the surfactant templating technique. Gold was loaded on supports by deposition-precipitation method. The catalysts were characterized by thermal analysis, XRD, N₂ analysis, TPR, DR/UV–vis and IR. The results evidenced the beneficial role of ceria modifying additive in decreasing the degree of crystallinity of mesoporous support and its particle size. A high degree of synergistic interaction between ceria and mesoporous oxide was observed. H₂-TPR revealed that the reducibility of the catalysts is greatly enhanced in the presence of gold. Considering the light off temperature, the activity of Au/mesoporous cerium-modified titanium oxide is particularly interesting for VOC oxidation comparatively to the same catalysts with a classical support. The gold particles would be more dispersed and stable. However, the sample Au/mesoporous cerium-modified titanium–zirconium mixed oxide is less interesting for VOC oxidation, particularly for toluene oxidation whose activity depends essentially on the adsorption of toluene molecule.     

Soft mechanochemically assisted synthesis of nano-sized LiCoO<Subscript>2</Subscript> with a layered structure

Soft mechanochemically assisted reaction between CoOOH and LiOH·H₂O at 400 °C yields O3-layered LiCoO₂ with nanometric particle sizes of 20–30 nm. The interaction of CoOOH with LiOH·H₂O is monitored by DTA and TGA analysis. XRD powder and TEM analysis is used for structural and morphological characterization of the precursors and target LiCoO₂. Soft mechanochemical treatment of the CoOOH–LiOH·H₂O mixture leads to amorphization of the lithium salt, while CoOOH remains intact. In addition, a partial exchange of protons from CoOOH with lithium takes place. Thermal treatment at 400 °C of the mechanochemically treated mixture yields layered LiCoO₂ with a small amount of a spinel-type Li_2+y Co_2−y O₄ phase (less than 2%). The morphology of LiCoO₂ inherits the morphology of CoOOH in the precursor. Layered LiCoO₂ displays thin nanometric particles with a narrow particle size distribution: more than 50% of particles are distributed between 20 and 30 nm. The electrochemical extraction and insertion of lithium in nano-sized LiCoO₂ is examined in model lithium cells using a galvanostatic mode.     

The effect of preparation method on the activities of Pd–Fe–O<Emphasis Type="Italic">x</Emphasis>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for CO oxidation

The Pd–Fe–Ox/Al₂O₃ catalysts were prepared by co-impregnation (co-Pd–Fe–Ox/Al₂O₃) and sol–gel method (sol–gel–Pd–Fe–Ox/Al₂O₃) and characterized by N₂ adsorption–desorption, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd–Fe–Ox/Al₂O₃ catalysts prepared by different methods. The 100% conversion temperature (T ₁₀₀) over pre-reduced co-Pd–Fe–Ox/Al₂O₃ (co-Pd–Fe–Ox/Al₂O₃–R) and pre-reduced sol–gel–Pd–Fe–Ox/Al₂O₃ (sol–gel–Pd–Fe–Ox/Al₂O₃–R) is 90 and 25 °C when fed with the reaction mixture containing 1 vol.% CO and a balance of air, respectively. XRD results indicate that the sol–gel method is favorable for the high dispersion of PdO particles compared with co-impregnation method. H₂-TPR results suggest that the interaction between Pd and Fe is existent over both sol–gel–Pd–Fe–Ox/Al₂O₃ and co-Pd–Fe–Ox/Al₂O₃ catalysts, while the interaction in former catalyst is stronger than that in the latter. The XPS results show that the Pd species on the surface of both sol–gel–Pd–Fe–Ox/Al₂O₃–R and co-Pd–Fe–Ox/Al₂O₃–R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd²⁺/Pd⁰ ratio may be the reason for the different activity between sol–gel–Pd–Fe–Ox/Al₂O₃–R and reduced co-Pd–Fe–Ox/Al₂O₃–R catalysts.     

Mesoporous Ce<Subscript>0.8</Subscript>Zr<Subscript>0.2</Subscript>O<Subscript>2</Subscript> solid solutions-supported CuO nanocatalysts for CO oxidation: a comparative study of preparation methods

Ce_0.8Zr_0.2O₂ solid solutions were prepared by three different methods, namely, surfactant-assisted, co-precipitation, and sol–gel methods, and were used as supports of CuO nanocatalysts by the deposition-precipitation (DP) method. The prepared supports and catalysts were characterized by using XRD, N₂ adsorption, TEM, and H₂-TPR techniques. The influence of preparation methods on the low-temperature carbon monoxide oxidation activity of these CuO/Ce_0.8Zr_0.2O₂ catalysts was investigated comparatively by using a microreactor-GC system. The catalyst prepared by surfactant-assisted method is more active for low-temperature CO oxidation than the ones prepared by the co-precipitation and sol–gel methods. The support and catalysts prepared by surfactant-assisted method possess mesoporous framework, nanoscale particle size, and high surface area, improving the synergistic effect between CuO species and support, which is beneficial for enhancing the catalytic performance of low-temperature CO oxidation.     

Synthesis and electrocatalytic activity of platinum nanoparticle/carbon nanotube composites

Pt/CNT nanocomposite materials with an average platinum particle size of 3–5 nm and platinum content of 13–28 wt % have been prepared by reducing chloroplatinic acid, H₂PtCl₆, in the presence of conical carbon nanotubes. The effect of synthesis conditions on the average platinum particle size, total platinum content, and surface composition of the nanocomposites has been studied using X-ray photoelectron spectroscopy, IR spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. Their performance has been assessed by cyclic and steady-state voltammetric techniques. The structure and composition effects on the electrocatalytic properties of the nanocomposites are discussed.     

Meso-macroporous monolithic CuO–CeO2/γ-Al2O3 catalysts and their catalytic performance for preferential oxidation of CO

Meso-macroporous monolithic CuO–CeO₂/γ-Al₂O₃ catalysts were prepared and tested for preferential oxidation of carbon monoxide in hydrogen-rich gases. The catalysts were characterized with photographs, SEM, N₂ adsorption–desorption, XRD, HRTEM, and TPR techniques. CuO–CeO₂ catalysts were evenly coated onto the walls of γ-Al₂O₃ monolith macropores with ceria and copper oxide highly dispersed. The prepared meso-macroporous monolithic CuO–CeO₂/γ-Al₂O₃ catalysts can remove CO from H₂-rich gases to ppm level at high space velocity, indicating that they are a kind of promising structured catalyst.     

Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 °C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.     

Calibration of reaction parameters for the improvement of thermal stability and crystalline quality of multi-walled carbon nanotubes

The results of Raman analysis on multi-walled carbon nanotubes, prepared by catalysed chemical vapour deposition, are used as a guide for the calibration of the growth parameters, directed to improve crystalline quality and resulting thermal stability of nanotubes. Under selective growth conditions, the resistance to oxidation in air, as assessed by thermogravimetry measurements, is found to increase with the establishment of the long-range graphitic order in radial tube direction, as signalled by the Raman G′/G intensity ratio enhancement. In the range of parameters explored (synthesis temperature: 500–700 °C; growth atmosphere: 120 cc/min i-C₄H₁₀–H₂–He mixture with He at 0–25%; i-C₄H₁₀/H₂ flow ratio: 1–3; metal load and reduction temperature of Fe/Al₂O₃ catalysts: 17–40 wt%, and 500 and 700 °C, respectively), the best crystalline quality and the highest oxidative resistance are achieved by carrying out the synthesis reaction at 700 °C in 1:1:0 i-C₄H₁₀–H₂–He atmosphere over 29 wt% Fe catalysts reduced at 700 °C. An additional relevant finding is the strong correlation evidenced between results of thermogravimetry and Raman analyses, suggesting the use of Raman spectroscopy for non-destructively evaluating the thermal stability of any graphitically ordered carbon species.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Fabrication of nanocomposites based on carbon nanotubes containing Pt nanoparticles and TiO<Subscript>2</Subscript>

Using conical multiwalled carbon nanotubes (CNTs), we have prepared Pt/CNT and Pt/TiO₂/CNT nanocomposites with an average platinum particle size of 3–5 nm, Pt/Ti molar ratio on the surface in the range 3.5–4, and C/Pt = 21–22. Titania was deposited onto the CNTs through titanium tetrachloride (TiCl₄) hydrolysis. Platinum particles were produced by reducing chloroplatinic acid (H₂PtCl₆) with sodium borohydride (NaBH₄) in the presence of CNTs. The composition and structure of the composites have been studied using X-ray photoelectron spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. The results demonstrate that the modification of Pt/CNT with titania enhances the catalytic activity of the material.     

Synthesis of Fe/ZnO composite nanocatalyst and its sonophotocatalytic activity on acid yellow 23 dye and real textile effluent

Nanocatalysts such as ZnO, Fe and Fe/ZnO composite were synthesized for better treatment of dye than the conventional treatment methods. The catalysts were characterized using SEM, EDAX, BET surface area, XRD and DRS. The degradation of acid yellow 23 dye in aqueous solution has been investigated using sonolysis, photolysis and sonophotocatalysis. The effect of different conventional operating parameters such as initial solution pH, gas purging (Argon, Oxygen, Air and Nitrogen) and H₂O₂ addition, under sonolysis (13 and 25 mm probe tip diameter) and photolysis (UV light), showed a maximum of 41 % colour removal for 0.0187 mmol/L dye solution under photolysis with 88.2 mmol/L H₂O₂ addition. Among the catalysts used, 98 % dye colour removal was obtained with 0.2 g/L Fe/ZnO composite under 60 min of sonophotolysis that had been benefitted by the synergistic effects. The HPLC spectrum of the untreated dye and treated dye supports the claim of eradication of the parent dye compound. Sonophotocatalytic treatment of real textile effluent in the presence of 6 g/L Fe/ZnO composite and 264.6 mmol/L H₂O₂ reduced the COD level from 792 to 174.4 mg/L in 240 min to meet the allowable effluent discharge standard into running water streams. The studied treatment methods were found to be effective for the degradation of acid yellow 23 dye and subsequently in real textile effluent too.     

Solid acid catalysts for dehydration of glycerol to acrolein in gas phase

The reaction of glycerol dehydration to acrolein was performed at temperatures 220–300 °C over Keggin-type heteropolyacid (H₃PW₁₂O₄₀·xH₂O), supported on alumina and W-modified SBA-15 (Si/W = 20). The supports and catalysts were characterized by nitrogen adsorption, XRD, IR, UV–Vis DRS, SEM, and TPD of NH₃. The acid sites strength, determined according to data from TPD of ammonia, follows the order: HPW/W-SBA-15 > W-SBA-15 > H₃PW₁₂O₄₀ > HPW/γ-Al₂O₃ > γ-Al₂O₃. It was found that this order well correlates with the catalytic activity of studied samples. The most active and selective sample, HPW/W-SBA-15, showed acrolein selectivity of about 75% at almost 100% conversion of glycerol in all studied temperature interval.     

Early stage reactivity and in vitro behavior of silica-based bioactive glasses and glass-ceramics

The surface reactivity of different sets of glasses and glass-ceramics belonging to the SiO₂–P₂O₅–CaO–MgO–K₂O–Na₂O system have been investigated. The attention was focused on the role of their composition on the bioactivity kinetics, in terms of pH modifications, silica-gel formation and its evolution toward hydroxycarbonatoapatite, after different times of soaking in simulated body fluid. Glasses and glass ceramics have been characterized by thermal analysis, SEM-EDS observations and phase analysis (XRD). XPS measurements have been carried out on the most representative set of sample in order to evaluate the evolution of the surface species during the growth of silica-gel and hydroxycarbonatoapatite. The response of murine fibroblast 3T3 to the material before and after a conditioning pre-treatment (immersion in SBF) has been investigated on the same set of samples in order to point out the role of the bioactivity mechanism on cell viability. The main differences among the various glasses have been related to the modifier oxides ratio and to the MgO content, which seems to have an influence on the glass stability, both in terms of thermal properties and surface reactivity. The surface characterization and in vitro tests revealed few variations in the reactivity of the different glasses and glass-ceramics in their pristine form. On the contrary, the different surface properties before and after the pre-treatment in SBF seem to play a role on the biocompatibility of both glass and glass-ceramics, due to the different ion release and hydrophilicity of the surfaces, affecting both cell viability and protein adsorption.     

Simultaneous removal of acetaldehyde,ammonia and hydrogen sulphide from air by active carbon impregnated with p-aminobenzoic acid,phosphoric acid and metal compounds

Simultaneous removal of acetaldehyde, ammonia, and hydrogen sulphide from air by the impregnated active carbon was studied at 25C. p-Aminobenzoic acid (PABA), phosphoric acid (H₃PO₄), and metal compound such as copper (II) chloride dihydrate (CuCl₂·2H₂O), copper (II) nitrate trihydrate (Cu(NO₃)₂·3H₂O), and potassium iodide (KI) were investigated as impregnation ingredients. Acetaldehyde and ammonia were simultaneously removed from air by the active carbon impregnated with PABA and H₃PO₄. The removal was found to be made mainly through chemical reaction. Acetaldehyde, ammonia, and hydrogen sulphide were simultaneously removed from air by the active carbon impregnated with PABA, H₃PO₄, and metal compound such as CuCl₂·2H₂O, Cu(NO₃)₂·3H₂O, and KI.     

The interphase and interface microstructure and chemistry of isothermal/isobaric chemical vapour infiltration SiC/BN/SiC composites: TEM and electron energy loss studies

The boron nitride interphase and its interfaces in two-dimensional-SiC/BN/SiC composites have been analysed by transmission electron microscopy and electron energy loss spectroscopy. BN was deposited by isothermal/isobaric chemical vapour infiltration from BCl₃–NH₃–H₂ mixture at moderate temperature. BN and the fibre/BN interface exhibit different features depending on the nature of the Nicalon^TM fibre surface, raw or treated prior to the BN deposition. When untreated fibres are used, a carbon-rich layer and silica clusters are formed during the manufacturing of the composite. In that case, the interphase is poorly organized and presents a porous microstructure and a large carbon content. With the treated Nicalon^TM fibre, no formation of a new interlayer is observed at the fibre–BN interface and the interphase exhibits a better organized turbostratic microstructure with no voids. Additionally, in both types of composites, a carbon-rich layer is formed at the BN–matrix interface during the SiC infiltration step at about 1000 °C. This revised version was published online in November 2006 with corrections to the Cover Date.     

New insights into anatase crystallization behavior in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

The anatase crystallization behaviors in ionothermal synthesis (sol–gel method containing ionic liquid) of nanostructured TiO₂ were studied in this paper. It was found that the specific physical chemical characteristics of the water/ionic liquid mixture caused the formation path and crystallinity of anatase TiO₂ to depend on the H₂O/titanium dioxide precursor (titanium tetraisopropoxide, TIP) molar ratio. Hydroxylated titanium compound was a key intermediate for forming anatase TiO₂. It could be directly formed from hydrolysis of titanium dioxide precursor or ionic liquid-induced water dissolution of the condensation product. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) data indicated that a higher hydroxyl group ratio content of hydroxylated titanium compound was obtained at medium H₂O/TIP molar ratio and from the system containing hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BuMIm]⁺[BF₄]⁻). The self organization ability of ionic liquid drove anatase crystallization through dehydration of the Ti–OH group of hydroxylated titanium compound in the thermal annealing process. As for the particle size of TiO₂, TEM results indicated smaller particle size of TiO₂ was obtained at medium H₂O/TIP molar ratio case.     

Preparation of porous spherical ZrO2–SiO2 composite particles using templating and its solid acidity by H2SO4 treatment

Porous ZrO₂–SiO₂ composite sphere particles were prepared by impregnating precursor solutions into organic monolith particles, with subsequent calcination in air. The porous spheres possessed uniformly sized pores of around 10 nm. Addition of SiO₂–ZrO₂ decreased the ZrO₂ crystallinity and increased the specific surface area. The acid amount on the surface of the composite spheres was increased by treatment with H₂SO₄. The acid strength and its amount, including the Lewis/Br?nsted acid ratio, depended on the SiO₂/ZrO₂ ratio and the H₂SO₄ concentration. The powder treated under an optimum condition exhibited higher solid acidity than the reference solid acid catalyst. The prepared porous SO₄ ²⁻/ZrO₂–SiO₂ spheres showed higher saccharization activity than the reference solid acid catalyst did.     

Synthesis of tetracalcium phosphate from mechanochemically activated reactants and assessment as a component of bone cements

The aim of this work was to gain a better understanding about the synthesis of tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O) through a solid-state reaction from mechanochemically activated CaCO₃–(NH₄)₂HPO₄ mixtures. The evolution of the reaction was followed by DTA, XRD, FTIR and SEM techniques. An enhanced reactivity of the mixtures was detected as the mechanochemical treatment times increased. This effect was related to both the loss of crystallinity of the reactants and the production of defects on their surfaces. 6 h of mechanochemical processing at 1190 rpm, followed by 3 h of thermal treatment at 1500°C, were enough to obtain pure TTCP. The crystallinity and purity of the obtained TTCP were checked by XRD and FTIR. The morphologic characteristics were analyzed by SEM and BET analysis. The behavior of synthesized TTCP powder in combination with commercial dicalcium phosphate anhydrous (DCPA, CaHPO₄), as the solid phase of bone cements, was tested. Both the combination of different particle sizes of TTCP and DCPA and the effect of different kinds of accelerator agents (disodium hydrogen phosphate, tartaric acid, citric acid and oxalic acid) on setting time and degree of conversion to hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) were evaluated. The combination of TTCP (0.32 m²/g) with DCPA (1.52 m²/g), in a 1/1 molar ratio, showed the shortest setting times and high conversions to HA when an oxalic acid solution (5% volume fraction) was used as the liquid phase of the formulation. Results obtained from this work demonstrated that synthesized TTCP shows promising behavior as a component of bone cements, exhibiting not only a smaller particle size than that usually reported but also a low degree of crystallinity, all of which increases the reactivity of the obtained TTCP. This study provided a very efficient method for synthesizing pure TTCP through a modified solid-state reaction from mechanochemically activated reactants, employing very short times of thermal treatment in comparison with the conventional processes.     

Metal assisted self-assembled nano sized porous 2-D structures incorporating malonic acid dihydrazide and melamine

The solids Cu(MADH)₂·Cl₂·2TAT·9H₂O and Zn(MADH)₂·Cl₂·2TAT·2H₂O (MADH = malonic acid dihydrazide and TAT = melamine) characterized by spectroscopic and elemental analysis, have been investigated by transmission electron microscope. Microstructure at high magnification revealed the supramolecular assembly of MADH and TAT into a mesh structure in presence of Cu(II) metal ions and tubular structure with intermittent openings on the tube walls and Y- junctions for Zn(II) complex. The mesh structure of the Cu(II) complex has uniformly spaced 40–50 nm long and 20–30 nm wide openings, while the diameter of the tubular structure of the Zn(II) complex is 50–200 nm.The assembly of the supramolecular structure is attributed to H-bonding and the different architectures of the assembly with different metal ions to the difference in waters of crystallization. The potential of the complex for gas adsorption was also investigated.     

Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer

Covalent coupling of sulfonic group (–SO₃H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H₂SO₄) or chlorosulfonic acid (ClSO₃H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated solution of calcium hydroxide (Ca(OH)₂). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)₂ treatments allowed formation of –SO₃H groups binding Ca²⁺ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer on their surfaces in SBF within 7 d. These results indicate that the –SO₃H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment method for preparing biomimetic apatite on their surfaces.