Catalytic removal of NO

Chromium-, manganese- and cobalt-doped titanium dioxide photocatalysts containing 0.2, 0.5 or 1 at.% of metal-dopant were investigated by UV–VIS, FT-IR, near-IR and electron paramagnetic resonance (EPR) spectroscopic techniques. The presence of the doping ions in the titania structure caused significant absorption shift to the visible region compared to pure TiO 2 powder (P25 Degussa). The EPR spectra of TiO 2 powders containing chromium showed the superposition of three types of individual paramagnetic species (β-, γ- and δ-signals), whose relative EPR intensity is significantly dependent on the dopant concentration, as well as on the photocatalysts preparation and treatment. The EPR spectra of the chromium-doped photocatalysts heated in H 2 /N 2 atmosphere corresponded to the Cr(III) ions occupying vacated cation sites in the rutile or anatase crystal lattice. The characteristic feature of the EPR spectra of the Mn/TiO 2 samples is a sharp six-line Mn(II) component centered on g eff =1.99, flanked by shoulders with a weak feature, which appeared on g eff =2.66 and 4.32. The photocatalytic activity of the various metal-doped TiO 2 samples was tested in aqueous or dimethylsulfoxide (DMSO) suspensions using EPR spin trapping technique with 5,5-dimethyl-1-pyrroline N -oxide (DMPO) spin trap. The ability of the irradiated photocatalysts to generate reactive oxygen species, namely hydroxyl radicals and super-oxide anion radicals, which were trapped as the corresponding DMPO-adducts was investigated.

Investigations of metal-doped titanium dioxide photocatalysts

Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.

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Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides.

Cr3+-doped anatase titanium dioxide photocatalysts were prepared by the combination of sol–gel process with hydrothermal treatment. The samples were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area (SBET), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was confirmed that Cr substitutes Ti4+ in TiO2 lattice in trivalent ionic state, and the concentrations of dopants Cr3+ decrease from the exterior to the interior of doped TiO2. The photocatalytic activity of Cr-TiO2 was investigated for the photocatalytic degradation of XRG aqueous solution both under UV and visible light irradiation. Due to the excitation of 3d electron of Cr3+ to the conduction band of TiO2, Cr-TiO2 shows a good ability for absorbing the visible light to degrade XRG. Doping of chromium ions effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.15% and 0.2%, respectively. The special distribution of dopants Cr3+ seems having a good effect on enhancing the photocatalytic activity of Cr-TiO2.

A. Vonzelewsky

Papers

Chromia Supported on Titania: I. An EPR Study of the Chemical and Structural Changes Occurring during Catalyst Genesis

Chromia supported on titania. II: Morphological properties and catalytic behavior in the selective reduction of nitric oxide by ammonia