L.J. Alemany

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.

Photodegradation of phenol in water using silica-supported titania catalysts

Titania-coated silica microspheres containing 0.5-3.0 theoretical layers of TiOZ have been prepared by homogeneous precipitation of Tit&. All these x Ti02-SiOz materials were characterized by X-ray diffraction and FT-Raman spectroscopy. TiOz species are distributed on the surface as small anatase crystals and possess a titania-like behavior with a performance equivalent to that of bulk TiOz for the photodegradation of phenol. The fraction of used titania is higher than that on bulk catalysts and the absorption of the irradiation by excess titania is prevented. The crystal size of titania particles is critical for optimum performance of the catalyst, since it determines the appropriate surface exposure of titanium sites. A minimum size appears to be required to efficiently mineralize phenol. 0 1997 Elsevier Science B.V.

Morphological and structural characterization of a titanium dioxide system

TiO 2 was prepared by the homogeneous hydrolysis precipitation method from titanium tetraisopropoxide. The decrease of surface area observed with the thermal treatment can be related to the growth of crystallites, and there is good correlation between the surface area and the mean crystallite dimension. The coexistence of the three different crystalline TiO 2 phases is clearly evidenced by the XRD and FT-Raman measurements.

WO3/TiO2 catalysts: Morphological and structural properties

Titania-supported tungsten oxide catalysts with different W loadings up to 9 wt. % and calcined at different temperatures have been prepared and characterized. It is found that W hinders the initial sintering of anatase, providing thermal stability. The interaction of W with TiO2 and the amount of hydroxy groups present on the surface can limit diffusion, thus reducing the sintering rate.

Preparation and characterization of silicon hydride oxide: a fully hydrophobic solid

Silicon hydride oxide, a white solid with composition Si2H2O3, has been prepared by hydrolysis and condensation of triethoxysilane HSi(OC2H5)3. This material is amorphous to XRD. The surface area is 195 m2 g−1. It is stable from the point of view of its chemical composition up to 550 K, as shown by TG-DTA analysis. IR spectra show that the amount of silanol groups at its surface is negligible. The interaction with polar organic compounds such as acetone is very weak and shows no significant hydrogen bonding. Its adsorption capacity towards hexane is definitely higher, while its adsorption capacity for water is smaller than for typical silica. This material appears as a highly hydrophobic silica-like solid. At temperatures higher than 673 K Si–H bonds progressively disappear and SiOH groups appear, in parallel to a significant decrease in surface area.

Nanofiber Alumina Supported Lean NOx Trap: Improved Sulfur Tolerance and NOx Reduction

NOx uptake and S resistance performance was studied over Pt–Ba and Pt–K lean NOx trap (LNT) catalysts, supported on “standard” Al2O3 and a nanofibrous Al2O3. The activity study was accompanied by TEM, XRD and H2 chemisorption characterization. The nanofibrous Al2O3-supported catalysts resulted in better performance. This included improved storage capacity, reduction efficiency during the regeneration phase, thermal stability and S-tolerance.

A new use of boiler ash: recovery of vanadium as a catalytic VPO system

Abstract A VPO system was prepared from boiler-ash. VO(H2PO4)2 phase has been obtained at low temperature and characterized through a combination of techniques including TG-DTA analysis, X-ray powder diffraction and FT-Raman spectroscopy. The thermal decomposition of the precursor material gives a VO(PO3)2 and V(PO3)3 phase mixture. Supported and unsupported catalysts prepared were compared and contrasted in the partial oxidation of methane (POM). The catalysts were more selective to C2-hydrocarbons than a VPO catalyst prepared by the conventional method and studied in similar conditions. Thus, the selectivity to C1-oxygenates was similar, however, the selectivity to COx products was hindered. The observation that the precursor VO(H2PO4)2 obtained from boiler ash as recovery and precipitation of the vanadium can generate catalysts of low selectivity to total oxidation products might provide a useful insight into the design of a new series of high activity and high selectivity partial oxidation catalysts.

Reassessment of fuel‐oil‐ash: Synthesis and characterization of a vanadium‐phosphorus‐oxygen system

Bottom ashes from the combustion of fossil fuels contain a high amount of vanadium. The recovery and the precipitation might be an attractive route for the synthesis of a catalytic system (VPO). The morphology and structure of the precursor and the final systems, calcined at different temperatures, obtained using bottom ash as raw material, have been assessed using a combination of scanning electron microscopy (SEM), thermal analysis (TG‐DTA), X‐ray diffraction (DRX) and Laser Raman Spectroscopy (LRS).

Vanadia-titania catalyst: II. Qualitative kinetic behavior

An improvement of catalytic properties has been observed at low vanadium loading in liquid-phase cumene oxidation, which is due to modification of the chemical nature of the surface as a result of active phase-support interaction.