P. Bosch

Preparation, characterization and photocatalytic activity of ZnO, Fe2O3 and ZnFe2O4

ZnO, Fe 2 O 3 and ZnFe 2 O 4 were synthesized by precipitation or coprecipitation at constant pH. After aging, washing and drying, the solids were calcined at 800 C. The samples were characterized by XRD, TGA, N 2 physisorption, UV-Vis and TPR. The photocatalytic degradation of phenol was studied in a batch reactor and TiO 2 (Degussa, P-25) was used as a reference catalyst. Pure ZnO and Fe 2 O 3 were obtained at 800 C, whereas ZnFe 2 O 4 and α-Fe 2 O 3 (segregated) were detected in the zinc ferrite sample. TPR experiments showed the reduction peaks in the range of 350-800 C only with Fe 2 O 3 and ZnFe 2 O 4 , attributed to Fe 3+ to Fe 2+ reduction and complete dehydroxylation. The photodegradation of phenol (samples calcined at 800 C) showed small but significant variations that decreased in the order: TiO 2 > ZnFe 2 O 4 > ZnO > Fe 2 O 3 . Subproducts such as hydroquinone, catechol and benzoquinone were mainly detected. In particular, attention was focused on our prepared materials because after 24 h they did not dissolve as happened with TiO 2 .

A catalytic application of Cu2O and CuO films deposited over fiberglass

Abstract With the purpose of utilizing copper oxides over fiberglass as a novel catalyst material in oxidation reactions, we have used the chemical vapor deposition of 2,4-pentanedionate copper(II) as a precursor and fiberglass as substrate. The deposition of copper oxides was achieved in a horizontal-flow reactor using O2 as carrier-reactant gas at several deposition temperatures. Copper species deposited on fiberglass were characterized by X-ray diffraction (XRD), UV–visible spectrophotometry (UV–VIs) and scanning electronic microscopy (SEM) techniques. The fiberglass coated with copper oxides showed a catalytic activity for the oxidation of ethanol into a stream of air at different temperatures in a pulse microreactor.

FTIR and UV-Vis (diffuse reflectance) spectroscopic characterization of TiO2 sol-gel

Abstract The semiconductive properties of titania are determined by the density of point defects in the crystalline structure. The synthesis method (sol-gel) provides pure and reproducible solids. This technique is very sensitive to hydrolysis catalysts, pH and calcination temperature. In this work, each one of these parameters is systematically varied and correlations with the structures of the obtained solids are established. It is shown that very acidic or basic catalysts are selective to rutile (900 °C). Acid catalysts favour an hydrolysis reaction, but pH does not change the shape or the size of the particles. The reaction mechanism is a nucleophilic substitution SN 2 in the basic medium and most intermediates in the sol-gel reaction are Ti-OH. The characterization techniques are FTIR, UV-Vis (diffuse reflectance), X-ray diffraction, DTA-TGA and scanning electron microscopy.

Synthesis of lithium silicates

Abstract Lithium silicates were synthesized by three techniques: (1) solid state reaction, (2) the precipitation method and finally, (3) the sol–gel method. Reactions were performed with different Li:Si molar ratios: 0.5, 1, 2 and 4. The obtained products were Li2SiO3, Li4SiO4 and Li2Si2O5. According to the synthesis method the composition of the samples changed as well as the morphology of the particles. The sol–gel method using CH3OLi provided the highest content of Li2SiO3 (94%); the solid state and precipitation methods provided pure Li4SiO4.

Ru/SiO2-impregnated and sol-gel-prepared catalysts: synthesis, characterization, and catalytic properties

Impregnation and sol-gel preparation methods are compared. Only when prepared by sol-gel synthesis, ruthenium is incorporated in the silica network; RuO2 particles are observed, but most Ru is occluded in the silica network. The ruthenium migrates to the surface with thermal treatments and small particles are formed. In the case of impregnated catalysts only RuO2 particles are observed. Their diameter is larger when the catalyst is treated at high temperatures, ortho-Xylene hydrogenation was performed on these two kinds of catalysts. The deactivation and selectivity values are attributed to the structural differences of the catalysts.

DTA-TGA and FTIR spectroscopies of sol-gel hydrotalcites: aluminum source effect on physicochemical properties

Hydrotalcites (crystalline mixed oxides of magnesium and aluminum) were synthesized by the sol-gel method at pH 10. The magnesium source was magnesium ethoxide and the aluminum precursors were aluminum nitrate, aluminum chlorate or aluminum sulfate. The resulting solids were characterized by infrared spectroscopy (FTIR) and thermal analysis (DTA-TGA). It was found that thermal stability depended strongly on aluminum precursor in the following sequence: aluminum chloride > aluminum nitrate > aluminum sulfate.

The influence of the preparation method on the surface structure of ZnAl2O4

Abstract The effect of preparation method (sol-gel, wet mixing or coprecipitation) on the surface structure of zinc aluminate is reported. Coprecipitated and sol-gel prepared ZnAl2O4 were found to be present spinel structure. If calcium was added during synthesis, it was found to be deposited on top of the spinel surface while, if tin was added, the surface of ZnAl2O4 was reconstructed. These aluminates were impregnated with platinum and tested in the isobutane dehydrogenation. The characterization techniques used were LEIS and X-ray diffraction.

Comparison of the structural and acid–base properties of Ga- and Al-containing layered double hydroxides obtained by microwave irradiation and conventional ageing of synthesis gels

Structural and acid–base properties of Mg/Al and Mg/Ga layered double hydroxides (LDHs) obtained by microwave irradiation of the co-precipitated gels have been investigated and compared to those of samples conventionally aged by prolonged hydrothermal treatment of the gels. Similar crystallinities and chemical compositions were obtained whatever the synthesis method used. Besides, all samples, and remarkably the Ga-containing LDHs with a molar ratio Mg ∶ Ga = 4.5, exhibited pure lamellar phases. The acid–base properties of the mixed oxides obtained by calcination of the LDHs have been examined by microcalorimetric adsorption of CO2 and by FTIR spectroscopy upon CH3CN interaction. These techniques gave evidence that the number and strength of acid and basic sites were influenced by the nature and amount of the trivalent cation, as well as by the preparation method.

Effect of sulfation methods on TiO2–SiO2 sol–gel catalyst acidity

A series of x TiO2‐SiO2 (xD1.7, 4.0 and 6.7 wt.% TiO2) binary mixed oxides was prepared by a sol‐gel method in acidic and basic conditions. In order to upgrade the acidic properties of the obtained solids, their sulfation was carried out in three different ways: (1) by in situ (H2SO4 was admixed with the gel), (2) impregnating the dried solids with aqueous solutions of H2SO4, and (3) by impregnating as in (2) but with (NH4)2SO4. FTIR-pyridine adsorption and benzene deuteroexchange showed that the acid site strength depends on the sulfation method. The highest values of total acidity, determined by ammonia thermodesorption, correspond to the in situ sulfated samples. The obtained pore size distribution (4.0‐5.0 nm) was narrow and the specific BET areas (250‐350 m 2 /g) were large. X-Ray diffraction, RDF, XPS spectroscopy and catalytic activity in the 2-butanol dehydration show that one step sulfated in situ TiO2‐SiO2 sol‐gel preparations resulted in catalysts with homogeneous and strong acidity.

Spectroscopic characterization and catalytic properties of sol-gel Pd/SiO2 catalysts

The present study reports the results obtained by UV-VIS spectroscopy, FT-IR (Fourier transform infrared) spectroscopy, and BET area measurements of Pd/SiO2 catalysts synthesized by the sol-gel process. This preparation technique results in the hydrolysis and polycondensation of a silicon alkoxide, which contains the metal halide salt PdCl2 in the initial solution. The reaction takes place at pH 9, forming intermediates which correspond most probably to surface species [SiO2]-[PdClxOHy]-OH The interaction between the silica gel and the palladium precursor has important effects on the specific surface area. The products are solids with BET specific areas up to 800 m2/g. Catalytic tests (hydrogenation of 1-hexene and phenylacetylene) show that sol-gel catalysts exhibit high selectivity in the formation of 2-methylpentane and styrene. To explain the high selectivities shown by the Pd sol-gel catalysts a geometric effect induced by the support is proposed on the structure of the ca. 1-nm-size Pd metal particles.