Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, S_BET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid.     

Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under redox conditions

A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce_0.6Zr_0.4O₂ homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs.By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic solid solution, prevents any CeAlO₃ formation. On the contrary, such phase due to the interaction between Ce³⁺ and the alumina present in the washcoat is detected when redox cycles are carried out on the ceria–zirconia metal free.Transmission electron microscopy (TEM) investigations of the redox cycled Pt/ceria–zirconia/alumina catalyst detected ceria–zirconia grains with diameter between 10 and 35 nm along with highly dispersed Pt particles (2–3 nm) strongly interacting with ceria.Scanning electron microscopy (SEM) and EDX analyses, recorded on the redox cycled Pt/ceria–zirconia/alumina washcoated monolith evidence a homogeneous distribution of the active components through the channels even after redox aging.Reduction behaviour and CO oxidation activity are in good agreement with the structural modification of the solid solution induced by the redox cycles and reflect the positive effect of Pt/ceria interaction on the catalytic performances.The effect of redox aging on the NO reduction by C₃H₆, in lean conditions, was investigated over the Pt/ceria–zirconia/alumina monolith. The catalyst shows at low temperature (290 °C) good NO removal activity and appreciable selectivity to N₂.     

Synthesis and characterization of polythiophene/titanium dioxide composites

Polythiophene/titanium dioxide (PT/TiO₂) composites were prepared by the in situ chemical oxidative polymerization method. The resulting PT/TiO₂ composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and field emission scanning electron microscopy (SEM). UV–Vis diffuse reflectance spectra measurements show that the PT/TiO₂ composites can adsorb light of wavelengths ranging from 200 nm to 800 nm. The PT/TiO₂ composites showed good adsorption properties and were more efficient in removing dye from solution than pure PT and pure TiO₂. The PT/TiO₂ composites exhibited photocatalytic activities to some extent under UV light illumination.     

Preparation and photocatalytic activity of silver and TiO2 nanoparticles/montmorillonite composites

Ag–TiO₂/montmorillonite (Ag–TiO₂/MMT) was synthesized as photocatalyst using TiCl₄ hydrolysis to introduce nanosized TiO₂ into the interlayer space of the montmorillonite (MMT). Stable pillared TiO₂/MMT was obtained by calcination at 500 °C, then silver was loaded by reduction of silver nitrate. The physico–chemical properties of the photocatalyst were determined by X-ray diffraction (XRD), infrared spectroscopy (IR), atomic absorption spectrophotometer (AAS), nitrogen gas adsorption (BET method) and UV–Visible spectra. The photooxidation activity for methylene blue (M.B.) degradation was as follows: Ag–TiO₂/MMT > TiO₂/MMT > TiO₂(P25). Among them Ag–TiO₂/MMT had the highest photooxidation activity because of its larger specific surface caused by pillaring and loading of silver for improving its light absorption.     

Selective Catalytic Reduction of NO x Over Nano-Sized Gold Catalysts Supported on Alumina and Titania and Over Bimetallic Gold–Silver Catalysts Supported on Alumina

The reduction of NO with octane under lean conditions was examined over gold supported on alumina and titania and over alumina supported bimetallic gold–silver catalysts. The silver loading was either 1.2 or 1.9 wt% whereas 0.3, 1 or 5 wt% gold was used. The catalysts were characterized by means of EDXS, N₂-adsortion, UV–Vis and TEM to correlate recorded results with different preparation methods. UV–Vis measurements indicated that gold was present in the form of fine Au particles, single Au ions and small (Au)_n ^δ+ clusters on the catalysts and silver was mainly present in the form of single Ag ions. The highest NO to N₂ reduction activity was recorded over the 0.3Au–Al₂O₃ catalyst. The Au–TiO₂ catalysts did not result in significant NO to N₂ reduction.     

Simple fabrication and photocatalytic activity of S-doped TiO2 under low power LED visible light irradiation

A series of S-doped TiO₂ with visible-light photocatalytic activity were prepared by a simple hydrolysis method using titanium tetrachloride (TiCl₄) and sodium sulfate (Na₂SO₄) as precursors. The photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectrophotometer (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). With the doping of S, photocatalysts with small crystal size, high content of anatase phase were obtained. The result showed that S-doped TiO₂ demonstrate considerably high photoactivity under low power visible LED light irradiation, while undoped TiO₂ and the Degussa P25 have nearly no activity at all. The possible mechanism of S-doped for the visible-light activity was discussed.     

Preparation of Co–Mo/B2O3/Al2O3 catalysts for hydrodesulfurization: Effect of citric acid addition

The effect of citric acid (CA) addition was studied on the HDS of thiophene over Co–Mo/(B)/Al₂O₃ catalysts. The catalysts were characterized by means of LRS, Mo K-edge EXAFS, NO adsorption capacity measurements, and UV–vis spectra. The catalysts were subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co in order to get deeper insights into the effect of citric acid addition. It was shown that the HDS activity was enhanced by the citric acid addition up to the CA/Mo mole ratio of around 1 and leveled off with further addition. The amount of Co anchored by the CVD was increased by the addition of citric acid, suggesting an increase in the dispersion of MoS₂ particles on the catalyst by the simultaneous presence of Co, Mo and citric acid, in conformity with the increase in the NO adsorption capacity. In contrast to Co–Mo catalysts, the edge dispersion of MoS₂ particles in Mo/B/Al₂O₃ was not affected by the addition of citric acid. The LRS, UV–vis spectra and Mo K-edge EXAFS showed that Co–CA and Mo–CA surface complexes are formed by the addition of citric acid. The Co–CA surface complex is more preferentially formed on CoMo/Al than on CoMo/B/Al, in agreement with a greater promoting effect of citric acid at a lower CA/Mo mole ratio for CoMo/Al than for CoMo/B/Al.     

Nucleophilic addition of water to 1-isoquinolinyl phenyl ketone. The synthesis, spectroscopic investigation, crystal and molecular structure and DFT calculations of [ReOBr2(iquinpk-OH)(PPh3)]

The reaction of [ReOBr₃(PPh₃)₂] with 1-isoquinolinyl phenyl ketone in acetone has been examined and the novel complex [ReOBr₂(iquinpk-OH)(PPh₃)] has been obtained. The complex has been characterised by IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure of [ReOBr₂(iquinpk-OH)(PPh₃)] has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of [ReOBr₂(iquinpk-OH)(PPh₃)] have been calculated with the time-dependent DFT method and the UV–Vis spectrum has been discussed on this basis.     

Sn-containing layered double hydroxides as precursors for nano-sized ZnO/SnO2 photocatalysts

Sn⁴⁺-containing LDH was prepared using the co-precipitation method at constant pH, and characterized using X-ray diffraction, UV–vis diffuse reflectance spectroscopy and TG/DTG methods. The obtained product was further exposed to different thermal treatments in order to obtain nano-sized coupled ZnO/SnO₂ systems with enhanced photocatalytic performances than the ones obtained by mixing the two semiconductor oxides. The formation of a well-defined ZnO/SnO₂ system and the crystallite size, fully investigated using XRD, micro-Raman scattering and UV–vis DR techniques, were found to be influenced by the nature of the precursors and the calcination temperature. The photocatalytic activity of the ZnO/SnO₂ systems, evaluated for the photodegradation of methyl orange (MO) dye, was studied as a function of the initial pH, catalyst loading and the calcination temperature. The metal dispersion supplied by layered structures proved to be an advantage when preparing coupled ZnO/SnO₂ systems, the photocatalytic activity being 2.3 times higher comparing with the physical mixtures performances. The maximum photocatalytic activity of the coupled ZnO/SnO₂ system having a layered precursor was observed when using neutral pH, at a catalyst loading of 1 g/L calcined at 600 °C for 4 h.     

Manganese porphyrin multilayer films assembled on ITO electrodes via zirconium phosphonate chemistry: chemical and electrochemical catalytic oxidation activity

A supported manganese porphyrin-based oxidation catalyst was prepared by zirconium-phosphonate multilayer assembly with [5,15-bis(4-phenylphosphonic acid)porphyrinato] manganese(III) chloride (2) and zirconium(IV) ions on indium–tin oxide electrodes. This assembly technique provided good control over the catalyst loading, which was confirmed by UV–Vis spectroscopy and cyclic voltammetry. Relative to its homogeneous counterpart, [5,15-bis(diethyl-4-phenylphosphonate)porphyrinato]manganese^III chloride (1), the film-based catalyst 2 showed moderately enhanced catalytic activity (up to 550 turnovers) for the oxidation of styrene by a soluble derivative of iodosylbenzene. Electrochemical oxidation of the film-based catalyst at pH 11 generated Mn^V(O)(porphyrin)(H₂O) intermediate at a potential of 1.20 V. The electrochemically generated active intermediate exhibited oxidative catalytic activity toward both the solvent (water) and an olefin substrate (CBZ) affording both hydrogen peroxide and epoxide products.     

Mesoporous aluminophosphates and Fe-aluminophosphates with highly thermal stability and large surface area templated from semi-fluorinated surfactant

A series of mesoporous aluminophosphates (MAP) and Fe-aluminophosphates (Fe-MAP) with highly thermal stability and large surface area have been successfully synthesized by the use of semi-fluorinated surfactant, which were characterized by XRD, TEM, N₂ adsorption, NMR, UV–Vis, and ESR techniques. These results show these samples are thermally stable up to 600 °C. More importantly, these samples give large surface area (BET, ca. 430–580 m²/g), which has an advantage for the use of catalysts or catalyst supports. In contrast, mesoporous aluminophosphates templated from copolymer surfactants such as F127 show relatively low surface area (<260 m²/g). Furthermore, UV–Vis and ESR spectra suggest that Fe species in Fe-MAP are mainly in tetrahedral coordination. Finally, the tests of hydroxylation of phenol with hydrogen peroxide show that Fe-MAPs are catalytically active.     

Preparation and characterization of Cu2O/TiO2 nano–nano heterostructure photocatalysts

Cu₂O/TiO₂ nano–nano heterostructures with different concentrations of Cu₂O were prepared by an alcohol-aqueous based chemical precipitation method, and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV–vis diffuse reflection absorption spectra. The photocatalytic efficiency of the Cu₂O/TiO₂ heterostructures was evaluated by degradation of Acid Orange II in water under UV–vis light and visible light irradiation. The results show that the heterostructures have dramatically improved photocatalytic activity comparing with pure TiO₂ (P25). The prepared Cu₂O/TiO₂ heterostructures with the Cu₂O concentrations of 30% and 70% have the best photocatalytic efficiencies, which are 6 times and 27 times higher than that of pure TiO₂ (P25) under UV–vis light and visible light irradiation, respectively.     

Inclusion Compound of Poly(vinyl alcohol) with Multivalent Molybdenum Coordination Compound

An inclusion compound of Mo(VI,V,IV) complexes and poly(vinyl alcohol) (PVA) that contains some carbonyl groups was prepared by a photoelectron transfer reaction between PVA and 12-molybdophosphoric acid (PMo₁₂). A dark-blue film was obtained when the aqueous solution of PMo₁₂ and PVA was irradiated with UV light. The film exhibited the characteristic electron spin resonance (ESR) signal of Mo(V). The existence of Mo(VI,V,IV) complexes was supported by XPS analysis of the film. Furthermore, the infrared (IR) and ultraviolet–visible (UV–Vis) spectra of the film showed weak absorption bands at 1710 cm^–1 and 300–314 nm that are consistent with carbonyl groups, which presumably are a result of partial oxidation of secondary hydroxyl groups on PVA. Differential scanning calorimetry (DSC) of the dark-blue film exhibited a peak at 220.3°C that is different from PMo₁₂ and PVA. Except for the IR absorption at 1710 cm^–1, the wavelengths and shapes of the other IR bands were similar to those of PVA. The UV–Vis spectrum of the film showed a new absorption band at 742–770 nm. In addition, the XRD spectrum of the film, the diffraction angles, and the crystalline sites were different from that in PMo₁₂ or PVA. However, the peak shape was similar to that of PVA. In summary, the DSC, IR, UV–Vis, and XRD data support a Mo(VI,V,IV) complex that is included into the spiral tube structure of PVA, which contains some carbonyl groups.     

Optical properties of ZnO/BaCO3 nanocomposites in UV and visible regions

Pure zinc oxide and zinc oxide/barium carbonate nanoparticles (ZnO-NPs and ZB-NPs) were synthesized by the sol–gel method. The prepared powders were characterized by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis), Auger spectroscopy, and transmission electron microscopy (TEM). The XRD result showed that the ZnO and BaCO₃ nanocrystals grow independently. The Auger spectroscopy proved the existence of carbon in the composites besides the Zn, Ba, and O elements. The UV–Vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is redshifted by adding barium carbonate. In addition, the optical parameters including the refractive index and permittivity of the prepared samples were calculated using the UV–Vis spectra.

PACS

81.05.Dz; 78.40.Tv; 42.70.-a.     

Synthesis and spectroscopic studies of new adducts of organotin(IV) chlorides with a polydentate N,S ligand

The reaction of a polydentate N,S ligand, 1′-amino-1′-cyclohexyl 2-cyclohexylideneamino-1-cyclohexene-1-dithiocarboxylate (ACCCD), with Ph₂SnCl_2, Ph₃SnCl and Me₂SnCl₂ was investigated. The new adducts have been characterized by UV–Vis, ¹H NMR, IR, mass spectroscopy and elemental analysis. These data are consistent with 1:1 adducts. The ligand behaves as a bidentate and shows both nitrogen and sulfur coordination. There is also evidence that the ligand ACCCD exhibits some interest in forming possible inter-/intra-molecular hydrogen bonds through ClH₂N interactions in Me₂SnCl₂ and Ph₂SnCl₂ adducts. The UV–Vis spectra indicate that the compounds partially dissociate in chloroform.     

Alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) N,N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine complexes: Synthesis, characterization and catalytic oxidation of cyclohexene with tert-butylhydroperoxide and hydrogen peroxide

New square-planar manganese(II), copper(II), nickel(II) and cobalt(II) complexes of a tetradentate Schiff-base ligand “N,N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine, H₂[salpnMe₂]” have been prepared and characterized by elemental analyses, IR, UV–Vis, conductometric and magnetic measurements. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate N₂O₂ donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(salpnMe₂)] for the 1:1 non-electrolytic complexes. Alumina-supported metal complexes (ASMC; [M(salpnMe₂)/Al₂O₃]) catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and hydrogen peroxide. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene whereas, oxidation with H₂O₂ resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(salpnMe₂]–Al₂O₃” shows significantly higher catalytic activity than other catalysts.     

Characterisation by vibrational and electronic spectroscopies

The EUROCAT SCR catalyst has been characterised by IR spectroscopic methods (transmission/absorption and diffuse reflectance techniques) by investigating its spectrum after different outgassing treatments, and the spectra of the surface species arising from adsorption of water (surface hydroxyl groups), carbon monoxide, ammonia, pyridine, nitrogen monoxide, trimethyl borate and NO + NH₃ coadsorptions. Additionally, Raman spectra and DR UV–Vis spectra have been reported after different outgassing treatments. The presence of Lewis and Brønsted acid sites has been discussed, as well as the evidence of different electronic states. A picture for the surface structure of the catalyst has been obtained. This picture is not significantly modified after extensive use of the catalyst in an SCR reactor for denitrifaction of flue gases from an incineration plant.     

NO Oxidation Kinetics on Iron Zeolites: Influence of Framework Type and Iron Speciation

Zeolites having MFI, FER and *BEA topology were loaded with iron using solid state cation exchange method. The Fe:Al atomic ratio was 1:4. The zeolites were characterized using nitrogen adsorption, FTIR and DR UV–Vis–NIR spectroscopy. The catalytic activity in NO oxidation and the occurrence of NO _x adsorption was determined in a fixed-bed mini reactor using gas mixtures containing oxygen and water in addition to NO and NO₂ and temperatures of 200–350 °C. Under these reaction conditions, the NO _x adsorption capacity of these iron zeolites was negligible. The kinetic data could be fitted with a LHHW rate expression assuming a surface reaction between adsorbed NO and adsorbed O₂. The kinetic analysis revealed the occurrence of strong reaction inhibition by adsorbed NO₂. FER and MFI zeolites were more active than *BEA type zeolite. MFI zeolite is most active but suffers most from NO₂ inhibition of the reaction rate. FTIR and UV–Vis spectra suggest that isolated Fe³⁺ cations and binuclear Fe³⁺ complexes are active NO oxidation sites. Compared to the isolated Fe³⁺ species, the binuclear complexes abundantly present in the MFI zeolite seem to be most sensitive to poisoning by NO₂.     

Characterization of silver catalysts for the oxidation of methanol

The selection of a silver catalyst system for further study was determined on a basis of cost and its ability to oxidize formaldehyde selectively. In addition a silver catalyst can provide a low light off temperature for the conversion of methanol to carbon dioxide and water vapor. Silver catalysts were prepared by the deposition of solutions of silver nitrate or silver chloride on gamma alumina washcoat supported on cordierite monolith. These silver catalysts were characterized by a variety of analytical techniques including TEM, SEM, EMP, STEM, XRF, XRD and FTIR.It is concluded that the best silver catalyst is prepared by deposition of silver from a solution of silver ammnonium chloride onto a cordierite supported high surface area gamma alumina washcoat, drying at 100°C in air, followed by reduction in flowing 3% H₂ in N₂ at 500°C for 4 h. This procedure will produce a silver catalyst with highest activity, largest retention and most uniform distribution of silver. The procedure also retains the concentration of silver and the gamma phase of alumina at temperatures as high as 1000°C in air for as long as 6 h.Due to the inability of normal TEM imaqing modes to obtain silver particle size information in the presence of the small gamma alumina washcoat particles a model system was made to test the ability of a dedicated STEM to furnish that information. The model system consisted of silver particles in the range of 1 to 50 nm which had been evaporated onto a uniform thin film of alumina. High resolution X-ray maps obtained from the model system demonstrate the ability to determine location and size of silver particles > 5 nm.A number of catalysts containing noble and base metals supported on gamma alumina washcoat on a cordierite monolith have also been studied. Laboratory flow reactor studies and chassis dynamometer studies using a Mercury Lynx modified to burn neat methanol have shown the following order of activity for conversion of methanol burned in experimental or engine exhaust gas: Pd > Ag > Pt + Rh > CuO + ZnO + Cr₂O₃ > Ni.     

Co/Al2O3 catalysts promoted with noble metals for production of hydrogen by methane steam reforming

The effect of noble metal addition on the catalytic properties of Co/Al₂O₃ was evaluated for the steam reforming of methane. Co/Al₂O₃ catalysts were prepared with addition of different noble metals (Pt, Pd, Ru and Ir 0.3 wt.%) by a wetness impregnation method and characterized by UV–vis spectroscopy, temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) of the reduced catalysts. The UV–vis spectra of the samples indicate that, most likely, large amounts of the supported cobalt form Co species in which cobalt is in octahedral and tetrahedral symmetries. No peaks assigned to cobalt species from aluminate were found for the promoted and unpromoted cobalt catalysts. TPO analyses showed that the addition of the noble metals on the Co/Al₂O₃ catalyst leads to a more stable metallic state and less susceptible to the deactivation process during the reforming reaction. The Co/Al₂O₃ promoted with Pt showed higher stability and selectivity for H₂production during the methane steam reforming.