Antonio Gómez-Cortés

REDUCTION OF NO BY CO OVER NiWO4, NiO, AND WO3 CATALYSTS

We present a comparative study of NiWO4, NiO, and WO3 catalysts for simultaneous conversion of NO and CO. Samples were synthesized by reacting ammonium metatungstate and/or nickel nitrate at high temperature (773 K to 903 K) under an oxygen stream. Catalysts were characterized by X-ray diffraction, surface area measurements, energy dispersive spectroscopy and scanning electron microscopy. The catalytic reduction of NO by CO took place in the temperature range (523 to 973) K under highly reductive conditions (NO:CO= 1:5) over NiWO4NiO, and WO3, respectively. The 100 % NO conversion at GHSV of 11460 h-1 was achieved at 773 K over NiWO4 and at 848 K over NiO. The WO3 was deactivated at 898 K. However, in the range (523 to 723) K NiO was more active than NiWO4 and WO3 catalysts.

Textural, structural and electrical properties of TiO2 nanoparticles using Brij 35 and P123 as surfactants

Abstract The effect of the use of the triblock copolymer Pluronic P123[(PEO)20(PPO)70(PEO)20, Aldrich] and the non-ionic polyoxyethylene-lauryl ether Brij 35 as surfactants on the textural, structural and electrical properties of nanosized TiO2 is analyzed in this work. The as-obtained samples were thermally treated at 400 °C to eliminate the surfactant, promote dehydroxylation and crystallize the sample. The TiO2 samples were characterized by thermal analysis, N2 physisorption, x-ray diffraction analysis, micro-Raman spectroscopy and scanning electron microscopy. To evaluate the TiO2 electrical features, I–V data were obtained. The x-ray diffraction results show that in the chemical synthesis using surfactants, the crystallite size is smaller than that of the commercial sample. The Raman spectroscopy results clearly indicate that, when P123 is used, the anatase phase of TiO2 is obtained, whereas when Brij 35 is used a mixture of the anatase and brookite phases is obtained. The specific surface area and crystallite size of the TiO2 prepared as indicated above are higher and smaller, respectively, than the corresponding properties found in commercial TiO2. The I–V plot showed a nonlinear behavior of the nanosized TiO2. The samples obtained with P123 showed the best electrical conductivity.

NO + H2 reaction on Pt-Ru/SiO2 catalysts: correlation between nanostructure and catalytic activity and selectivity

Nitric oxide reduction by hydrogen has been studied on Pt-Ru/SiO2 catalysts of various Pt/Ru atomic compositions in the temperature range 298–673 K. Physical characterization showed the presence of bimetallic particles which tend to be Pt-rich. The overall activity of the bimetallic catalysts suggests a dilution of the active component (Pt) in the range 373–523 K. The addition of Ru results in a general improvement of the N2 selectivity and significant modifications in the product distribution are observed as a function of the catalyst composition. A bimetallic particle model is proposed in which various types of surfaces are exposed including those with pure Pt atoms and/or Pt-Ru mixture. This model allows to explain the overall activity and selectivity in the whole series of catalysts.

Reactivity of methanol over copper supported on well-shaped CeO2: a TPD-DRIFTS study

TPD-DRIFTS experiments upon methanol adsorption over copper (5 wt%) supported on well-shaped ceria (polyhedra, rods and cubes) have been performed for the first time. Support morphology influences the type of methoxy and formate adsorbed species; in polyhedron and rod-shaped catalysts, linear methoxy and formate are the predominant species, while in cube-shaped catalyst, bridged species dominate. In the catalysts, desorption of H2 and CO2 increases significantly indicating that besides dehydrogenation of adsorbed methoxy, oxidation of adsorbed formate species is taking place. Heterogeneity of surface sites (copper, ceria and copper/ceria interface), surface defects and acid–base properties may account for the differences in the desorption profiles and reactivities of the adsorbed species over the three copper–ceria catalysts.

Effect of La2O3 concentration in La2O3-Al2O3 supports and Pd/La2O3-Al2O3 catalysts in reduction of NO by H2

It was obtained that the selectivity of La 2 O 3 -Al 2 O 3 oxides in the NO reduction by H 2 depends on the La 2 O 3 concentration and reaction temperature. The surface area as well as the structure of the supports is varied with the lanthana concentration. All mixed supports are highly selective to the production of N2 when the catalytic reaction is conducted at 973 K. La 3d 5/2 binding energy measured for mixed supports is higher than that reported for La 2 O 3 and it is comparable with value published for dispersed lanthanum phases in alumina. XRD data also show that lanthanum is highly dispersed in Al 2 O 3 . Lanthana concentration does not influence significantly on NO conversion with temperature neither for Pd catalysts nor for supports with an exception for 50 % La 2 O 3 -Al 2 O 3 support. Its activity is higher than activity of other supports. Application of coprecipitation method for preparation of La 2 O 3 -Al 2 O 3 supports results in: 1) significant enhance of N 2 selectivity (at high temperatures) on La 2 O 3 -Al 2 O 3 supports and Pd/La 2 O 3 -Al 2 O 3 catalysts and 2) increase of NO conversion on La 2 O 3 -Al 2 O 3 supports compared with sol-gel method.