nan Parvulescu

Selective catalytic reduction of NO with NH3 over mesoporous V2O5-TiO2-SiO2 catalysts

Mixed vanadia-titania-silica catalysts (3 or 6 wt% V2O5, and 16-34 wt% TiO2) were one-pot prepared by sol-gel and hydrothermal methods in the presence of surfactants. Sodium silicate (25.5-28.5% silica) or tetraethylorthosilicate was used as a precursor for silica; tetraisopropylorthotitanate or titanyl acetylacetonate, for titania; and vanadyl sulfate or vanadium acetylacetonate, for vanadia. Cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, or dodecylamine was used as a surfactant. The catalysts were characterized by adsorption and desorption curves of N-2 at 77 K, NH3-DRIFTS, H-2-TPR, XRD, in situ Raman spectroscopy, XPS, and TEM. The catalysts were tested in NO reduction with ammonia using a total flow rate of 100 ml/min and a feed composition of nitric oxide 0.1 vol%, ammonia 0.1 vol%, oxygen 3 vol%, in helium. Vanadia was found to be entrapped in these catalysts as V(V) species in which the population of V=O monomeric bonds strongly depended on the dispersion. Titanium also existed in a very oxidated state, and for high dispersions it adopted a tetrahedral coordination. These structures led to surfaces on which mainly Lewis acid sites are effective under reaction conditions. Under such conditions, the dominant route followed an Eley-Rideal mechanism, yielding in such a way very high activity and selectivity. A comparison with a conventional V2O5-TiO2 catalyst led to the conclusion that the intrinsic activity of one-pot prepared polymeric sol-gel catalysts is higher

Preparation, characterisation and catalytic behaviour of cobalt–niobia catalysts

Cobalt-niobia catalysts were prepared using the colloidal sol-gel technique. Niobium chloride or niobia oxide were used as precursor. The differences between the procedures used are due to the methods of preparation of the colloidal suspensions and gelification. The catalysts were characterised using adsorption and desorption curves of Kr and N-2 at 77 K, H-2-Chemisorption, XRD, FT-IR, XPS and electron microscopy investigations. Preparation of these catalysts without experimental precautions led to a very inhomogeneous structural and textural material. In contrast, the colloidal sol-gel technique controls both the structure of the niobia oxide and the tailoring of cobalt. A strong metal support interaction effect (SMSI) was present irrespective of the sample preparation variant. Although the rate of butane hydrogenolysis was low for all catalysts, a correlation between TOF and the catalyst crystallite size was found. Selectivity to methane, ethane, propane or to isomerization also depends on the catalyst crystallite size

Preparation, characterization and catalytic properties of Co-Nb2O5-SiO2 catalysts

Co-Nb(2)Q(5)-SiO2 catalysts were prepared using three different sol-gel procedures: (i) the colloidal sol-gel method using NbCl5 and SiCl4 as precursors; (ii) the polymeric sol-gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol-gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl4. In all procedures, the elimination of the solvent carried out between 80 and 110 degrees C was followed by a reduction in hydrogen flow (30 ml min(-1)) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb2O5) were obtained. The characterization of the catalysts was performed using various techniques: N-2 adsorption and desorption curves at 77 K, NH3- and H-2-chemisorption, TPO, XPS, XRD, and solid state H-1 MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support. (C)2000 Elsevier Science B.V. All rights reserved.

Comparative behavior of silica-embedded tert-butyldimethylsilyltrifluoro-methanesulfonate and lanthanum triflate catalysts

A series of hybrid catalysts containing tert-butyldimethylsilyltrifluoro-methanesulfonate (BDMST) or lanthanum triflate (LaT), hex adecyltrimethylammonium bromide and silica were obtained by sol-gel immobilization. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, TG-DTA, H-1, C-13, and Si-29 solid state MAS-NMR, XRD, TEM, scanning electron microscopy (SEM), XPS and, FT-IR after adsorption of NH3. The catalytic tests were carried out in the reaction of the methyl ester of 1-cyclopentenylacetic acid in various solvents. The results revealed a completely different behavior of the hybrid catalysts compared with catalysts without surfactant or with free tert-butyldimethylsilyltrifluoro-methanesulfonate, or lanthanum triflate, or triflic acid, indicating a behavior for a typical heterogeneous catalyst

TG and DTA investigation of ZrO2-SO42- catalysts exposed to hexane, methylcyclopentane and cyclohexane

AbstractZrO2–

Co-Nb2O5/SiO2 sol-gel catalysts: preparation implications on the texture and acidity of the support and dimension of the metal particle

{\text{SO}}_{\text{4}}^{{\text{2}} - }

Reaction of hexane, cyclohexane, and methylcyclopentane over gallium-, indium-, and thallium-promoted sulfated zirconia catalysts

catalysts with different sulfur contents were analysed with thermal methods coupled with mass spectrometry after exposure to mixtures of hexane, methylcyclopentane, and cyclohexane in argon. The reaction of the hydrocarbons led to carbonaceous deposits, but an important part of hydrocarbon remained chemisorbed as well. Heating these samples in He atmosphere provoked the decomposition of these deposits with evolution of CO2 and CO, and also of SO2 and SO. At the same time, COS was evidenced in the reaction products. The release of these molecules occurred below the activation temperature of the catalysts. The behavior of the catalysts depended both on reactant molecule and sulfur content. The analyses clearly evidenced the oxidation ability of ZrO2–SO