A. C. Iñigo

Dissolution of salts crystallised in building materials using ultrasound: an alternative to NORMAL (1983) standard methodology.

Our aim in the present work is to extract salts from ornamental stone using a faster and less tedious method than the customarily used NORMAL method [NORMAL, Dosaggio dei Sali Solubili, CNR-ICR, Roma, Italy (1983) 13/83]. For extraction in aqueous medium, the latter method requires shaking for 72 h at a temperature of 60 degrees C. Our aim is to attempt to shorten this time to less than 1 h using ultrasound. The results of the present study indicate that there is a good correlation between the amount of salts extracted applying the method described in the NORMAL (1983) normative and the amounts extracted with the method proposed here, subjecting the material to ultrasound (50 KHz) for 45 min.

Hydrogenolysis of n-butane on low-loaded Rh/TiO2, I. Catalysts obtained by ion exchange

The activity in n-butane hydrogenolysis of Rh/TiO2 (0.6 wt.% Rh) catalysts prepared by ion exchange and reduced at different heating rates is reported. The heating rate has no major effect on the properties of the catalysts (similar dispersions and activities are achieved). Carbonaceous residues formed at high temperature are removed by hydrogen at room temperature, thus leading to recovery of the activity.AbstractОписывают активность катализатора Rh/TiO2 (0,6 вес.% Rh), приготовленного ионным обменом и восстановленного при различных скоростях нагрева, в гидрогенолизе н-бутана. Скорость нагрева не влияет на свойства катализатора: получены одинаковые дисперсности и активности. Углекислые остатки, образующиеся при высоких температурах, удаляют водородом при комнатной температуре, регенерируя, таким образом, активностя.

Hydrogenolysis of n-butane on low-loaded Rh/TiO2. II. Catalysts obtained by impregnation

The activity in n-butane hydrogenolysis of Rh/TiO2 (0.6 wt. % Rh) catalysts propared by impregnation and reduced at different heating rates is reported. The catalyst reduced at 5 K/min is ten times more active than that reduced at 20 K/min, despite the fact that the dispersion values are similar in both cases.AbstractОписывают активность Rh/TiO2 (0,6 вес. % Rh), приготовленного импрегнированием и qvосстановлением при различных скоростях нагрева, в гидрогенолизе н-бутана. Катализатор, восстановленныи при скорости 5 К/мин, в десять раз активнее катализатора, восстановленного при скорости нагрева 20 К/мин, несмотря на то, что величины дисперсности не отличаются в обоих случаях.

DISPERSION OF RHODIUM ON RUTILE: COMPARISON OF SAMPLES PREPARED BY ION EXCHANGE AND IMPREGNATION

Rh/TiO2 (rutile) samples have been prepared by impregnation (series I) and ion exchange (series C). Upon reduction at low temperature (473 K) the metal dispersity is larger for samples C than for samples I. Removal of surface OH groups in series C cancels the strong Metal-Support Interaction, thus increasing the metal dispersity measured upon reduction at 773 K.AbstractОбразцы Rh/TiO2 (рутила) приготовляии импрегнированием (серия Ї) и ионным обменом (серия С). При восстановлении при низких температурах (473 K) дисперсия металла в случае образца С намного выше, чем для образцов Й. Удаление рорерхностных ОН-групо в серии С уничтожает SMSI-состояине тем самым повышая металлическую дисперсню при восстановлении при 773 K.

Hydrogenolysis of n-butane on low-loaded Rh/TiO2, III. Selectivity studies

A study has been carried out on the selectivity of titania-supported rhodium catalysts in n-butane hydrogenolysis. It is concluded that incorporation of the rhodium precursor onto the titania surface via ion exchange leads to a less pronounced development of Strong Metal-Support Interactions and thus to an homogeneous distribution of active sites on the catalyst surface.

Surface texture properties of TiO2 (rutile) pigments

Titanium dioxide, known in three different crystallographic forms (anatase, rutile and brookite) is one of the transition metal oxides that has received increasing interest in recent years, for various reasons (mainly, because of its role as a pigment), in order to improve its properties and to avoid its decay (due mainly to its ability to catalyse photoreactions under exposure to sunlight). It has also been the subject of research because of its role as a catalyst support for metallic oxides, as well as for oxide catalysts, due to its easy (and reversible) partial reduction to the TiO2n_l form. Rutile is the most stable form of titanium dioxide, and is commercially prepared [1] from titanium(IV) chloride. The pigmentary properties of calcined particles are known to be strongly influenced by the amounts of additives [2]. The presence of chloride as an impurity is difficult to avoid, because of the starting materials for manufacture, and it has been shown that the presence of this species strongly modifies other properties of the solid [3-6]. Garbassi et al. [7] have reported the effect of hightemperature treatments on the surface properties of doped rutile and anatase, but these authors have studied only the effects of several metallic cations (K +, Zn 2+ and A13+) and of P205. Removal of impurities in rutile has been explained on the basis of diffusion of the cations through the structure channels by an interstitial mechanism [8]. In this letter we report the changes (mainly surface properties) observed in commercial rutile when submitted to calcination under a humid atmosphere, a method that has been shown to be valid for removal of chloride species. Commercial rutile containing 9 wt % of chloride was kindly supplied by Tioxide Ltd (UK). It had been obtained by flame hydrolysis of titanium(IV) chloride, dried at 393 K and calcined at 673 K. In addition to chloride, all other impurities (P205, K20, CaO, A1203, SiO2, Fe, Pb, Nb2Os) were less than 100 ppm, except SO3 (220 ppm). X-ray diffraction (XRD) diagrams were recorded in a Siemens D-500 diffractometer equipped with a Difract-AT system and a DACO-MP microprocessor, using CuKo~ radiation. Specific surface area and texture measurements were carried out from nitrogen adsorption isotherms at 77 K. The samples were calcined at 773 K under an oxygen flow, saturated with water vapour at 308 K.

Effect Of The Preparation Method On The Dispersion Of Metallic Particles In Rh/Tio2 Systems

In Rh/TiO2 systems, the dispersion of Rh particles depends on the reduction temperature and on the preparation method. The capacity for H2 adsorption is larger for those samples reduced at low than at high temperature.