Journal of Alloys and Compounds, 180 (1992) 289--294 289 JAL 8037 Determination of catalytic active sites in (Ce ~+, Ca2+)-supported Y zeolite by Fourier transform IR spectroscopy L. B. Zinner Instituto de Quimica, Universidade de Sdo Paulo, C.P. 20.780, CEP 01498, Sd~o Paulo SP (Brazil) A. S. Arat~o Departamento de Qutmica, Universidade Federal do Rio Grande do Notre, CEP 59072, Natal RN (Brazil) Abstract Catalytic active sites in an aluminosilieate matrix Y zeolite were generated by exchange with calcium and cerium chloride solutions, followed by calcination. Acid properties of the (Ce, Ca)e~--NaY zeolite were studied by semi quantitative (Fourier transform) IR spectroscopy of the pyridine adsorption. The molecular probe interacts with BrSnsted active sites (BASs) and bonds coordinatively to Lewis active sites (LASs). The main observed frequencies were 1459 an -1 (BAS) and 1443 em -1 (LAS). It has been found that the BAS:LAS optical density ratio was ca. 1.4. The observed protonic active sites may be due to cerium cation-hydroxyl supported on the Y zeolite matrix under specific ion exchange and thermal conditions. 1. Introduction A zeolite is an aluminosilicate with a framework structure enclosing cavities occupied by large ions and water molecules, both of which have considerable freedom of movement permitting ion exchange and dehydration [ 1 ]. The unit cell composition best representing the structural formula of a zeolite is M~/n[(A1Oe)~"(SiOe)u]" wHuO, where M is a cation metal of valence n, w is the number of water molecules contained in the framework and the ratio y/x has values dependent on the structure. The sum x + y is the total tetrahedral number in the unit cell [2]. Crystalline Y zeolite has a structure corresponding to the mineral faujasite [3]. According to the secondary building units, it is classified in the double- six-ring group. The unit cell chemical composition of a typical Y zeolite is [4] Naso[(A102)5o'(SiO2),3o] .250HuO. This represents aluminium atoms te- trahedrally coordinated in AIO4- forms, resulting in a negative charge density in the lattice. The neutralization of this charge is achieved by the introduction of mono-, di- or trivalent metal cations into the zeolite. In this work we used calcium(II) and cerium0ID cations to neutralize AIOa- species by ion exchange. 0925-8388/92/$5.00 © 1992- Elsevier Sequoia. All rights reserved