Centro de Investigación y Desarrollo en Procesos Catalíticos -CINDECA-

UNLP, CONICET, 47 N°257, 1900- La Plata, Argentina.

e-mail: cindeca@dalton.quimica.unlp.edu.ar

The main research lines on clean catalytic processes performed at CINDECA were described below.

L. Pizzio, P. Vázquez, C. Cabello, C. Cáceres, M. Blanco, H. Thomas

e-mail: hds@dalton.quimica.unlp.edu.ar

The acidic and redox properties of heteropolyacids with Keggin structure make them suitable as catalysts for many acid or oxidation catalyzed reactions. Since these compounds are less corrosive and produce lower amount of waste than conventional catalyst. They can be used as replacement in environmentally benign processes, thus contributing to a clean obtainment of compounds of interest for fragance, pharmaceutical or food industries, among others.

Another advantage of the use of the above-mentioned catalysts is to favour the separation between the catalyst and the reactions products as compared with homogeneous systems in which the separation process is much more involved.

The preparation of catalysts based on tungstophosphoric or molybdophosphoric acids supported on a carrier were realiced using different impregnation techniques, as pore filling or equilibrium adsorption. It was observed the stabilizing effect on the Keggin structure of these acids, when different organic solvents (ethanol-water, dimethylformamide) were used to prepare the impregnation solutions. Also the effect of the nature of various supports (alumina, silica, carbon, titania, zirconia) were studied. The catalysts were characterized by different physicochemical techniques, as FTIR, NMR, DRS, and tested in selected reactions. In a first step, the activity on the dehydration of isopropanol was measured as a test of the acidic properties. Promissory results were obtained when the catalysts were proved in acidic reactions, as the esterification of acetic acid and isoamylalcohol, the cyclation of benzilsulfonamides, the dehydration of 1,2 diphenylethanol and the dehydration of cholesterol. In the last two reactions selectivity to one of the diastereoisomers was obtained. The catalysts were also tested in the limonene epoxidation with hydrogen peroxide.

On the other hand, heteropolycompounds with Anderson or Keggin structure may be used as precursors of hydrotreating catalysts. These new catalysts are important due to the more restrictive environmental legislation and the need to use low quality hydrocarbon feedstocks and converting them into clean burning fuels.

Nickel and cobalt Anderson phase based catalysts were prepared by equilibrium impregnation of alumina, at a constant molybdenum amount and variable nickel and/or cobalt concentration. Different Anderson phases and ammonium decamolydocobaltate were also used to obtain new catalysts. With regard to Keggin phases, they were impregnated on alumina, silica, titania, zirconia and different carbons by pore filling or equilibrium techniques, using different solvents in the impregnation solution. The catalysts were physicochemically and thermally characterized. Their activity in hydrodesulfurization, hydrodenitrogenation and/or hydrogenation reactions was measured and compared to the results obtained with commercial catalysts. The performance of the new catalysts was as good or better than the commercial ones.

N.N.Nichio, M.L.Casella, G.Santori, O.A.Ferretti

e-mail: ferretti@dalton.quimica.unlp.edu.ar

It is well-known the importance of the process of reforming of natural gas for the obtention of H₂ and CO. As an alternative to the traditional steam reforming of methane process, partial oxidation (POM), the reforming with CO₂ (R) and mixed reforming (MR, O₂ + CO₂) are advantageous processes from both the energetical and environmental point of view. Ni-alumina catalysts have been reported to be very active catalysts for these reactions. However, they suffer a serious problem of deactivation due to carbon deposition and nickel sintering. Therefore, development of new stable Ni catalysts is of great interest to the practical application of these processes.

In this paper, we studied: i) monometallic nickel catalysts, prepared employing two differents precursors compounds (nickel nitrate and nickel acetylacetonate) and two supports (a-Al₂O₃ and modified a-Al₂O₃); and ii) bimetallic nickel-tin catalysts, in which effect of Sn is added via Surface Organometallic Chemistry on Metals techniques. These catalysts (fresh and used) were characterized by TPR, TEM, TGA, DTA and TPO. The performance of different Ni and Sn-Ni supported catalysts are analyzed in POM, R and MR reactions, with particular emphasis in their activity and resistance to sintering and coke formation.

The results obtained can be summarized in: i)-Nickel catalyzed prepared by using a-Al₂O₃ support modified by aluminium oxide presented good dispersion and stability facing to sintering; ii)-the lower activity of MR reaction compared with POM reaction would be compatible with the ocurrence of two simultaneous (one step and two steps) mechanisms; iii)-MR reaction leads to H₂/CO ratios between 1 and 2, which is attractive for several processes; iv)-Carbon formation rate depends on Ni precursor used (Nickel acetylacetonate leads to the best results); v)- bimetallic catalysts having Sn/Ni atomic ratios higher than 0.005 present a very low activity (X_CH4< 5%), in agreement with those previously published; vi)-when Sn/Ni ratio is lower than 0.005, the behaviour is completely different, being observed that the activity is not affected by the presence of tin (Table 1); vii) stability tests performed on Ni and Sn-Ni samples (Sn/Ni ratios between 0.002 and 0.005), showed an important promoting effect of Sn (high stability), assigned to a strong diminution of coke formation (TGA/TPO analysis).

Table1. Catalytic results measured at 700°C (Ni_a: Ni supported on a-Al₂O₃, Sn-Ni_a: Sn-Ni supported on a-Al₂O₃; Ni_a+Al: Ni supported on modified a-Al₂O₃; Sn-Ni_a+Al: Sn-Ni supported on modified a-Al₂O₃); (for all the samples Ni acetylacetonate was used as Ni precursor).

S.G.Marchetti, A.M.Alvarez, N.Gallegos,F.Bengoa, M.V.Cagnoli, A.A.Yeramian

e-mail: yeram@dalton.quimica.unlp.edu.ar

The preparation, characterization, activity and selectivity determination of zeolitic materials including an heteroatom in their crystaline lattice, in hydrocarbide oxidation is well known in the literature. Actually the synthesis of zeolitic materials including titania atoms in their lattice in tetrahedral position presents difficulties.

The material known as TS-1 which is a zeolitic structure following the MFI pattern, including a titania heteroatom in the lattice in tetrahedral position has been used in clean oxidations using as an oxidizing agent, hydrogen peroxide. The material was synthetized, characterized using diffuse reflectance spectroscopy,submitted to the effect of water and hydrogen peroxide and afterwards to thermal treatments. The final condition of the material, was determined by diffuse reflectance spectroscopy, and the catalytic activity and selectivity, established.

The reaction of benzene oxidation using hydrogen peroxide is studied. The effects of the reactants concentrations on the reaction rate is determined. Different way of addition of the reactants to the reacting solution were tested in order to establish their influence on the reaction rate. Finally the efect of the presence of other solvents was also tested and methanol shows a strong inhibiting effect. p-Benzoquinone appears as a secondary product, which allows to admit the existence of a consecutive reaction scheme.

In order to obtain a mesoporous material which allows the entrance of reactants of major kinetic diametre, MCM-41 was also prepared. The crystalline structure of this material was verified by X ray diffraction and the following step will be the introduction of titania in the crystalline lattice in order to be utilized as a oxidation catalyst.