Francesco Berti

Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review

Abstract The open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

Characterization and composition of commercial V2O5zWO3zTiO2 SCR catalysts

Abstract The surface and bulk structure and composition of a commercial VzWzTi oxide catalyst used for denitrification of waste gases from power plants has been investigated by XRD, XRF, ICP, TG-DTA, FT-IR and SEM-EDS analyses and by comparison with ‘model’ catalysts. The catalyst powder consists of a full ‘monolayer’ of surface complexes, mainly constituted by wolframyl species with the addition of small amounts of vanadyl and sulphate species over high-area TiO2-anatase. The characteristics of the surface vanadyl, wolframyl and sulphate species fully consist with those previously reported for model VzTi, WzTi, VzWzTi and sulphated titania catalysts. The catalyst powder is mixed with glass-like particles, playing the role of mechanical promoters. The possibility of contamination of the catalyst particles by Mg or other alkali or alkali earth cations possibly arising from the glass particles during monolith preparation and during reactor start-up and shut-off procedures as well as during catalyst operation is suggested.

Role of the redox properties in the SCR of NO by NH3 over V2O5-WO3/TiO2 catalysts

The reactivity of ternary V2O5-WO3/TiO2 De-NOx catalysts is investigated by transient and steady-state techniques, and results have been compared with those obtained over binary V2O5/TIO2 samples having the same V2O5 loading. The results indicate that the reactivity of the ternary catalysts in the SCR reaction is higher than that of the vanadia-titania samples, and that at low temperatures the SCR reaction occurs via a redox mechanism that involves at first the participation of the catalyst lattice oxygen and then the reoxidation of the reduced sites by gas-phase oxygen. Accordingly, the higher reactivity of the ternary catalysts has been related to their superior redox properties.

Spectroscopic and diffractometric study of the V2O5/TiO2 system prepared viamechanochemical activation

Materials consisting of a vanadium oxide (VOx) phase dispersed on a TiO2 matrix and obtained by mechanochemical activation of the V2O5 and TiO2 , are compared with materials obtained by high temperature solid state reaction between the same two oxides. As a consequence of grinding, a non-negligible formation of isolated VIV is evidenced by EPR, whose nature is typically vanadylic (VO2+). Diffuse reflectance UV–VIS spectroscopy indicates that the reduction of the dispersed phase also induces the formation of more reduced vanadium species like VIII . Various distinct VO2+ species are stabilized on the surface by thermal treatments, and their coordinative environment has been tested by adsorption of NH3 and H2O. The phase changes brought about in the TiO2 matrix by the grinding process as well as the presence of crystalline V2O5have been monitored by XRD.

High temperature combustion of methane over hexaaluminate-supported Pd catalysts.

The methane combustion properties of barium hexaaluminate supported Pd catalysts are compared with those of an alumina supported one. Combustion tests over catalysts calcined at 1000°C show that hexaaluminate-supported systems posses lower activity than the alumina-supported one. Tests performed upon treatment under reaction conditions show that marked deactivation occurs to the hexaaluminate based materials. XRD characterization indicate that the lower combustion activity of barium hexaaluminate-based catalysts is associated with the lower dispersion of Pd species on these supports.

On the Relations Between the Rheology of Tio2-Based Ceramic Pastes and the Morphological and Mechanical Properties of the Extruded Catalysts.

A rational and quantitative study of extrusion of TiO 2 -based ceramic pastes is attempted. First the analysis of rheological measurements, that are used to investigate and foresee the formability behaviour of the pastes, is illustrated. Then the mixing stage and two of the most relevant preparation parameters, namely liquid content and inorganic additives, are discussed to clarify the correlations between operative parameters, corresponding rheological characteristics of the paste, and morphological, structural and mechanical properties of the final material.