I. Martin

Surface properties of iron-titania photocatalysts employed for 4-nitrophenol photodegradation in aqueous TiO2 dispersion

Iron(III) doped specimens (0.01–5% atomic Fe ∶ Ti) have been prepared by impregnating polycrystalline “home prepared” TiO2 (mainly anatase) and have been studied for photocatalytic degradation of 4-nitrophenol in aqueous dispersions. Some structural and surface properties have been studied by X-ray diffraction, specific surface area and porosity measurements and FTIR monitoring of pyridine, ammonia and methanoic acid adsorption for surface acidity and basicity. Their surface properties were compared with a corresponding series of photocatalysts prepared by a coprecipitation method. Adsorption of pyridine and ammonia indicates the presence of surface acid Lewis sites, a low concentration of surface Brønsted sites being present only in the samples prepared by impregnation. The photocatalytic experiments indicated that the presence of iron ions does not influence or is detrimental for the occurrence of the 4-nitrophenol photodegradation.

Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of phenol

The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and consequently influences the photocatalytic activity. The addition of Cr ions was found to accelerate the photoreduction reaction, while it is detrimental to the photodegradation of phenol.

An FT-IR study of the adsorption of pyridine, formic acid and acetic acid on magnesia and molybdena-magnesia

Abstract The adsorption of pyridine, formic acid, and acetic acid on MgO, MoO3 and MoO3/MgO (Mo:Mg=1:15) samples calcined at 773 K (where no extensive reaction between the two oxides seems to take place) or 1100 K (where the MgMoO4 species is formed) has been monitored by FT-IR spectroscopy. The adsorption of pyridine indicates the formation of Lewis sites on MgO upon incorporation of molybdena. However, this change in the surface acidity does not modify the adsorption of the two carboxylic acids, which takes place dissociatively, probably because the formation of surface MgMoO4 still leaves exposed Mg2+, where adsorption of the carboxylate ions takes place.

Catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization

A correlation exists between the number of surface acid sites and the catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization. The catalytic activity for thiophene hydrodesulfurization and surface concentration of Brönsted acid sites increase with the titania content in the TiO2−Al2O3 support.

Effect of sulphate removal on the surface texture and acid-base properties of TiO2 (anatase)

Commercial anatase containing an appreciable amount of sulphur has been treated for sulphur removal by calcination at increasing temperatures or soaking with aqueous NaOH solutions. It has been found that both methods are active for sulphur removal, but the first one also leads to a sharp sintering of the titania particles. On the other hand, treatment with NaOHaq leads to incorporation of sodium cations. Both treatments lead also to changes in surface acidity, as measured by Fourier transform infrared (FT-IR) monitoring of pyridine adsorption.

Characterization and Fourier transform infrared spectroscopic study of surface acidity in NiMo/TiO2-Al2O3 catalysts

Abstract Catalysts consisting of Mo and Ni oxides supported on Al 2 O 3 and TiO 2 and on mixtures of both have been prepared by co-impregnation of the supports with aqueous solutions of Mo(VI) and Ni(II) salts, and have been characterized by X-ray diffraction, Fourier transform-infrared (FT-IR) and vis-UV/diffuse reflectance spectroscopies and surface texture by nitrogen adsorption; surface acidity has been measured by FT-IR monitoring of pyridine adsorption. Incorporation of TiO 2 to the support Al 2 O 3 leads to a larger dispersion of molybdena on the catalyst support. The solids (specially those with low TiO 2 content) are not microporous, but have pores open at both ends. The increase in the TiO 2 content leads to a larger concentration of surface Bronsted (Mo-OH) acid sites, associated with an increase in the number of dispersed molybdate species.

Oxidation of Propene on Alkaline Metal-Doped MoO3/TiO2 Catalysts: A FT-IR Study

Abstract The reactivity of MoO 3 /TiO 2 systems (pure or Na- or K-doped) with propene has been studied by FT-IR spectroscopy. Reactivity decreases in the presence of the alkaline cations, and thus reactive adsorption (leading to acrolein formation) is only observed in the doped catalysts above room temperature. This behaviour has been related to the decrease in surface acidity.

AN FT-IR SPECTROSCOPIC ASSESSMENT OF THE SURFACE BASICITY OF CALCIA

Adsorption of formic acid on Ca(OH)2 calcined at increasing temperatures has been monitored by FT-IR spectroscopy. Adsorption takes places dissociatively, forming bidentate formate species, coordinated to surface Ca2+ ions. The basicity decreases as the outgassing temperature increases, due to removal of surface hydroxy groups.