Alexander Moronta

Two alternative sample mineralization procedures to permit subsequent polarographic determination of total soluble aluminium in haemodialysis water

Two differential pulse polarographic-based methods were developed in order to determine total soluble aluminium in the water used to prepare haemodialysis solutions for chronic renal failure patients. The interference from organic matter was overcome by closed-vessel microwave and high-pressure digestion procedures. The electrochemical results were compared with those obtained by using graphite furnace atomic absorption spectrometry and the correlation was excellent (r = 0.980, p < 0.001). The detection limits for aluminium were 6 and 3 μg 1−1 for microwave and high-pressure mineralizations, respectively. The proposed methods are a reliable alternative to graphite furnace atomic absorption methods to monitor inexpensively the water quality of dialysis units.

Catalyst characterization by a probe reaction: Effect of tin addition in PtSn/Al2O3

Abstract Ethylene hydrogenation as a probe reaction was used to characterize PtSn/Al 2 O 3 catalysts. The effects of the amount of tin and the impregnation order of platinum and tin on the activity for ethylene hydrogenation, the hydrogen number and the hydrogen uptake were studied. Two series of catalysts were prepared by two different successive impregnations of aqueous solutions of platinum and tin compounds. The platinum content was constant at 0.5 wt.-% and the tin content was varied over the range 0.0 to 0.45 wt.-%. The presence of tin caused a decrease in both the ethylene hydrogenation activity and the hydrogen number values in the two series of bimetallic catalysts. Hydrogen uptake decreased on the Pt-Sn catalysts and increased on the Sn-Pt catalysts when the atomic Sn/Pt ratio was increased. As shown in the literature, these results can be related to a chemical change of the platinum due to the presence of tin either by forming Pt-Sn clusters or by interaction between platinum and tin ions on the alumina surface.

Reduction of NO by CO using Pd–CeTb and Pd–CeZr catalysts supported on SiO2 and La2O3–Al2O3

The catalytic activity of Pd catalysts supported on Ce0.73Tb0.27Ox/SiO2, Ce0.6Zr0.4Ox/SiO2, Ce0.73Tb0.27Ox/La2O3-Al2O3 and Ce0.6Zr0.4Ox/La2O3-Al2O3 was studied using the reduction of NO by CO. The catalysts were characterized by X-ray fluorescence, surface area, X-ray diffraction, temperature-programmed reduction, CO chemisorption and oxygen storage capacity. Temperature-programmed reduction results indicated that Tb or Zr incorporation improves the reducibility and oxygen storage capacity. CO chemisorption data suggested the presence of large PdO particles due to the low CO/Pd ratio. No significant differences were obtained in light off temperatures (TLight off) for all Pd catalysts and the most active was 1.5%Pd/Ce0.6Zr0.4Ox/SiO2.

CONDENSATION OF OLEFINS ON CLAYS. GAS-SOLID SYSTEMS. PART I: GRAVIMETRIC METHODS

The adsorption-condensation of olefins was studied on 7 adsorbents: 2 commercial clays, a natural clay and its protonated form, γ-alumina and porous and nonporous silicas. These adsorbents were characterized by X-ray diffraction (XRD), chemical analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and determination of specific surface area measurement by the BET method. The experiments were carried out gravimetrically, in gas- or vapor-solid systems, at 25 °C and on adsorbents dried at 120 °C. Adsorption-condensation of olefins are fast processes, diffusion controlled. Alumina and silicas adsorb olefins and paraffins only reversibly, but are unable to condense olefins. The water polarized by the countercations is the source of Brønsted acid sites. When the gas phase is evacuated or swept with inert gas, the condensation terminates. On clays, paraffins are reversibly adsorbed but no condensation was observed.

Determination of total copper in haemodialysis water by differential-pulse anodic stripping voltammetry

An anodic stripping voltammetric method was developed in order to determine copper in the water used to prepare haemodialysis solutions. The interference from organic matter was overcome by high-pressure bomb mineralization. The electrochemical results were compared with those obtained by using graphite furnace atomic absorption spectrometry and the correlation was excellent (r = 0.983, p < 0.001). The detection limit was 0.2 μg l−1 copper.

ISOMERIZATION OF 1-BUTENE CATALYZED BY SURFACTANT-MODIFIED, Al2O3-PILLARED CLAYS

Recent studies indicate that a template method for creating Al-pillared clays, in which surfactant micelles foster the creation of a homogeneous mesoporous network within the pillar, effectively enhance catalyst performance and adsorbent properties. No studies, however, have described the relative effects of the surfactant concentration and Al content on the textural and acidic properties and on the catalytic activity of the Al-pillared clays. The purpose of the present study was to fill this gap, using the isomerization of 1-butene as the test process for catalytic activity. Modified pillared clays (MPC) were prepared from a synthetic clay, TS-1, using different amounts of a non-ionic surfactant (Igepal CO-720) and a fixed concentration of a solution containing the Al polycation [Al13O4-(OH)24]7+. MPC with a fixed amount of surfactant and different amounts of Al were also prepared. The catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), temperature-programmed desorption of ammonia, 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR), and N2 adsorption/desorption isotherms. Isomerization of 1-butene at 250°C was used to test the catalytic activity. Analyses by XRD and XRF showed that the synthesized solids were amorphous and that the amount of pillaring by Al increased with the amount of Al complex used. Interestingly, the surface area and pore volume were directly proportional to the amount of surfactant employed and decreased with increasing amounts of Al pillaring. All solids showed activity for 1-butene isomerization, with a maximum conversion of ∼75%. Only cis- and trans-2-butene were observed. The absence of isobutene suggested that acid sites of moderate strength were formed, in agreement with the results obtained from the desorption of ammonia.

Condensation of olefins on clays, gas-solid systems; Part II, Spectroscopic methods

The adsorption of olefins at 25 °C in gas- or vapor-solid systems on 4 clays dried at 120 °C was studied by infrared spectroscopy. Products of condensation have the spectra of paraffinic oligomers. Paraffins are adsorbed onto the same structural surface hydroxyls that adsorb olefins, confirming the physical unspecific character of this adsorption. These hydroxyls do not participate in the condensation reaction. The reappearance of these hydroxyl bands after evacuation suggests that product molecules are not adsorbed onto the surface but remain on it because of its low vapor pressure. The reversible adsorption sites participate in feeding the condensation sites. Double-bond isomerization of olefins was not observed, at room temperature, on clays, alumina and silicas dried at 120 °C. When the gas-phase is evacuated or swept with inert gas, reaction does not proceed with a new monomer. Paraffins are only physically adsorbed.