Catalytic Materials for High-Temperature Combustion

Metal-substituted hexaaluminates for high-temperature N2O abatement

Metal-substituted hexaaluminates are highly active, selective, stable, and inexpensive catalytic materials for high-temperature N2O abatement in the chemical industry, such as in nitric acid and caprolactam plants, and in combustion processes.

Influence of the Preparation Method on the Surface Characteristics and Activity of Boron-Nitride-Supported Noble Metal Catalysts

In this article, we report how variations in the preparation method of boron-nitride-supported noble metal catalysts may influence the surface characteristics of the active phase and consequently the potential applications as catalysts for oxidation reactions. The deposition and the dispersion of the active phase are strongly influenced by the preparation process and in particular by the protic or aprotic solvent used as the dispersing phase; in this study, benzene, glyme, water, tetrahydrofuran, diglyme, 2-propanol, and glycol have been investigated. Characterization techniques, such as Brunauer-Emmett-Teller, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, have been used to study the influence of the choice of a solvent phase on the particle size and dispersion of the metal deposited on the BN support. The modifications undergone by the support during the deposition of palladium in different solvents have also been studied. Through the use of the same deposition procedure, different noble metal coatings (Pt, Pd, Au, and Ag) have been prepared. The acidic and redox characteristics of the resulting samples were characterized by temperature-programmed reduction and adsorption microcalorimetry. The catalytic performances of these materials were tested in the total oxidation of methane in lean conditions (excess oxygen and presence of water).

Evolution of electronic structure and spectral evaluation in single-crystal Mn3O4 nanorods

Single-crystal Mn3O4 nanorods with tetragonal structure have been successfully prepared by a chemical reaction route. Transmission electron microscopy (TEM) and high-resolution TEM studies prove that the single-crystal Mn3O4 nanorod is smooth and straight, and that the geometrical shape is structurally perfect. We investigated the electronic characteristics of Mn3O4 nanorods by various spectral evaluations. The present study confirms that the hybridization between oxygen 2p and manganese 3d orbits plays an important role when considering electronic structures of Mn3O4 nanorods.

Adsorption/Desorption Studies of NOx on Well-Mixed Oxides Derived from Co−Mg/Al Hydrotalcite-like Compounds

CoxMg3-x/Al hydrotalcite-like compounds (where x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by the coprecipitation method and characterized by the XRD and TGA techniques. Incorporation of Co for x=0.0-3.0 gradually decreased the transformation temperature of the hydrotalcites to the corresponding oxides from 444 to 246 degrees C and also decreased the surface area from 162.7 to 21.6 m2/g upon calcination at 800 degrees C for 4 h in air. The resultant oxide was generally composed of a poor MgO phase and a spinel phase, with more spinel phase at higher Co incorporation. The derived oxides were tested as the storage/reduction catalysts for NOx adsorption/desorption. The storage capacity for NOx was highly dependent on the catalyst composition and storage temperature. In general, more NOx was stored at lower temperature (100 degrees C) than that at higher temperature (300 degrees C), and tertiary catalysts (x=0.5-2.5) stored more NOx than binary catalyst (x=0.0 or 3.0). The catalytic conversion of NO to NO2 and the catalytic decomposition of NOx were observed on the tertiary catalysts during NOx adsorption at 300 degrees C, which was highly related to the loading of cobalt. The reducibility of catalysts was determined by TPR experiments, and the reduction of cobalt cations started at 150-200 degrees C in H2. In situ IR spectra of catalysts adsorbing NOx revealed that the major NOx species formed on the catalysts were various kinds of nitrites and nitrates, together with some forms of dimers, such as N2O2(2-) and N2O4 (or NO+NO3-). The storage/reduction mechanism and the function of Co in the mixed oxides are proposed and discussed on the basis of these observations.

Preparation and Characterization of Novel Mesoporous Ceria−Titania

Synthesis of a novel thermally stable mesoporous ceria-titania phase using a neutral templating route is reported. The as-made inorganic-template hybrid mesostructured matrix showed a broad low-angle XRD peak characteristic of mesoporous materials. Careful thermal treatment of the matrix allowed the subsequent densification (of the pore walls) of the inorganic component and removal of the organic component so that a high-quality mesoporous ceria-titania was formed as observed by TEM analysis. The calcined material showed the formation of fluorite type structure of CeO(2) but no crystalline titania phase was observed. The mesoporous structure remained even after high-temperature treatment. The material had high surface area after calcination up to the temperature of 973 K, with well-dispersed ceria and titania components and negligible bulk oxide formation (from XRD, UV-vis, and XPS analysis). These novel mesoporous ceria-titania materials showed high performance for the removal of volatile organic compound (toluene). The toluene removal performance was further enhanced for Pt impregnated mesoporous ceria-titania.