The influence of the acid sites on the methylamines synthesis with Cu-HZSM-5 zeolite Maria Helena de Oliveira Nunes a , Victor Teixeira da Silva b , and Martin Schmal a, * a NUCAT/PEQ/COPPE/Federal University of Rio de Janeiro (UFRJ), Cidade Universita´ria, Bloco G, sala 128, Ilha do Funda˜o, Rio de Janeiro/RJ, Brasil, CEP: 21945-970 b Instituto Militar de Engenharia, Departamento de Engenharia Quı´mica, Prac¸ a General Tibu´rcio, 80, Praia Vermelha, Rio de Janeiro/RJ, Brasil, CEP: 22290-270 Received 30 January 2004; accepted 11 May 2004 There is a high industrial demand for MMA and DMA, however, the production of TMA is favored with the commercial catalysts. This work tested the methanol amination reaction with HZSM-5 and Cu/HZSM-5 zeolites (%Cu ¼ 1.2, 3.7 and 6.0). Regarding the MMA selectivity, light differences were observed among Cu/HZSM-5 catalysts and pure zeolite, although the catalysts containing 3.7% copper was slightly more selective to MMA than the other metallic catalysts studied. From these results it is suggested that the metal loading present in the catalysts leads to a modification in the nature of the acidic sites, in particular, the selectivity depends on ratio Bro¨ nsted/Lewis acid sites. This modifications would facilitate the amines desorption during the reaction. KEY WORDS: acid sites; methylamines synthesis; Cu-HZSM-5 zeolite. 1. Introduction Methanol conversion in valuable products makes it an important raw material to the wide miscellaneous chemicals. Acetic acid, propionic acid, acetic anhydride, ethylene glycol, ethanol and amines are good examples of products that have already been successfully synthe- sized using methanol as feedstock [1]. Among the materials that can be obtained from methanol, the low molecular weight aliphatic amines occupy an important place in modern society because of their large applica- tion possibilities. Mono-, di- and tri-methylamines (MMA, DMA and TMA) are normally used as corro- sion inhibitors, probe molecules to characterize super- ficial acidity of solid materials, softeners for synthetic fibers, scatters to paints and pigments and like inter- mediates in chemical and pharmaceutical industries (production of pharmaceutical product, pesticides, explosives and animals feed). Methylamines are synthesized industrially, using meth- anol and ammonia and acid catalysts (e.g. alumina or silica–alumina) that approaches the thermodynamic equi- librium molar ratio MMA : DMA : TMA (17 : 21 : 62 at T ¼ 673 K and molar ratio NH 3 /CH 3 OH ¼ 1). Close to the thermodynamic equilibrium the TMA production is favored, and therefore the demanding products MMA and the DMA become more important [2]. For increasing production of MMA and DMA it is necessary to recycle TMA, but it makes the process more expensive. To minimize costs involved for separation of TMA and to increase the production of MMA and DMA, recent research have developed zeolite catalysts [3,4]. According to literature, the product distribution and the enhance- ment of MMA selectivity are related to pore sizes of zeolites in this reaction (shape selectivity). It can be explained either by the retention of TMA in the pores or by the reaction of these molecules inside the pores. The literature did not present new catalysts able to increase the MMA and DMA selectivity to reach the molar ratio 33 : 53 : 14 (MMA : DMA : TMA) re- quired in industrial processes. There are continuously publications in this area [5]. An interesting observation is that there are only few reports concerning the employ- ment of transition metals modified zeolites for this kind of reaction, although copper catalysts on different supports, such as Al 2 O 3 , Cr 2 O 3 and Cr 2 O 3 –SiO 2 , are highly efficient for the catalytic amination of alcohols [6]. The main goal of this paper is to test the Cu/HZSM-5 catalysts and how it affects the molar relation of amines produced in methanol amination reaction. Besides, different characterization techniques were employed to determine the effect of the metal and acidic properties on the selectivity and activity. 2. Experimental 2.1. Catalysts preparation HZSM-5 zeolite from DEGUSSA (SAR ¼ 28.4) was previously calcined at 803 K for 4 h (5 K min )1 ) in a pyrex glass calcinator under continuous air flow *To whom correspondence should be addressed. E-mail: schmal@peq.coppe.ufrj.br Catalysis Letters Vol. 97, Nos. 1–2, August 2004 (Ó 2004) 1 1011-372X/04/0800–0001/0 Ó 2004 Plenum Publishing Corporation