CENTRO DE INVESTIGACION Y DESARROLLO EN CIENCIAS APLICADAS "DR. JORGE J. RONCO"
Unidad Ejecutora - UE
congresos y reuniones científicas
×-Al2O3 supported complex Heteroplytungstate and its application in limonene epoxidation
M.G. EGUSQUIZA, A. CANEPA, E. HERRERO, M. CRIVELLO, G. EIMER, S. CASUSCELLI, C. I. CABELLO, D. GAZZOLI, H. J. THOMAS.
Porto Alegre, Brasil
Congreso; 15 º Congresso Brasileiro de Catálise, 5º Congresso de Catálise do Mercosul; 2009
Sociedade Brasileira de Catalise
The epoxidation of olefins is an important reaction both in the laboratory and in the chemical industry because they are widely used as raw materials for epoxy resins, paints, surfactants and also as intermediates in organic syntheses. In particular, the production of oxygen derivates from natural terpenes and terpenoids is interesting for later use as food additives and fragrances. Among them, limonene is outstanding as it is relatively inexpensive and capable of being converted to oxygen derivates of high added value (1). One of the objectives of selective oxidation field is the replacement of stoichiometric oxidation processes for catalytic processes. Within the different oxidants, H2O2 is the most attractive because of its low cost and lack of by-products (clean technology). The research is focused on the synthesis of effective and non-toxic catalysts to produce low-cost, non-polluting industrial processes. Generally, the most important prerequisites for these processes are: catalyst stability, high selectivity and operation at room temperature without consumption of the oxidant used. Consequently, one of the preferred solutions is the use of catalysts based on inorganic complexes substituted for transition metals (2) in combination with hydrogen peroxide as an oxygen donor usingbiphasic system. In this sense, these species can be used in small quantities for their subsequent separation (3). The versatility and accessibility of polyoxometalates (POMs) have led to various applications in the area of structural chemistry, analytical chemistry, surface science, medicine, photochemistry and electrochemistry (4). Especially, the catalytic function of POMs has attracted much attention (5), since their redox and acidic properties can be controlled. Recently, several applications of these compounds as catalysts have appeared (2). The structure of various POMs including heteropolitungstates consists of d0 (W) atoms attached to oxo bonds (O2-). These species can function as stable-to-oxidation catalysts, thus being particularly interesting for their use in homogeneous and heterogeneous systems. The substitution of one or more of W (VI) atoms for transition metal cations Co (II), Cu (II), Fe (II), Mn (II), etc. which contain d electrons, produces catalysts resistant to oxidation, therefore these compounds and their application in catalysis are being extensively studied (6). In this context it has been recently analyzed the oxidation of limonene in biphasic conditions, using as catalyst Na8HPW9O34 and K10 [M4 (H2O)2PW9 O34) 2] (M = Co (II), Cu (II)), with good results (7). This article presents the synthesis, characterization and catalytic evaluation of catalysts based on K and Na salts ofheteropolyanion mixed phases: [Cu(II)4(H2O)2(PW9O34)2]10-/[Cu2(H2O)2PW10O38]7-named (PWCu) supported on £^-Al2O3 used in the selective oxidation of limonene with H2O2. Physicochemical characterization of phase PWCu was carried out by different analytical techniques such as diffraction of X-ray powder (XRD), FTIR spectroscopy, scanning electron microscopy (SEM) and Microprobe analysis (EDS) (previously reported results (8)). The supported phase was comparatively characterized by Microprobe Raman and XPS spectroscopies. The content of PWCu metals on the support was determined by Atomic Absorption Analysis (AAS), optical emission spectroscopy by inductively coupled plasma (ICP-OES) and X-ray Fluorescence.