Infrared spectroscopic studies on the surface chemistry of bimetallic zeolite systems. Acidity of Pt,Co- and Pt,CuZSM-5 zeolites A. Tama ´si a, * , I. Kiricsi a , Z. Ko ´nya a , J. Hala ´sz a , L. Guczi b a Applied Chemistry Department, Jo ´zsef Attila University, H-6720 Szeged, RerrichB te ´r 1, Hungary b Department of Surface Chemistry and Catalysis, Institute of Isotope and Surface Chemistry, Chemical Research Center, HAS, P.O. Box 77, H-1525 Budapest, Hungary Received 24 August 1998; received in revised form 23 November 1998; accepted 23 November 1998 Abstract Acid sites on Co-, Cu- and PtZSM-5 as well as on Pt,Co- and Pt,CuZSM-5 samples were investigated by means of pyridine adsorption monitored by IR spectroscopy. After reduction in hydrogen a significant amount of acidity was observed on each zeolite sample. The concentration of the Broensted acid centers was substantially diminished after treating these samples in NaCl solution. When NaBH 4 was used as the reducing agent much less, in some cases a negligible amount of Broensted acid sites was detected, which did not significantly increase after reduction with hydrogen. Creation of the Lewis acid sites proved to be more complex indicated by several IR bands of coordinatively bound pyridine. As a result of this study, an applicable procedure is suggested for preparation of bimetallic zeolites of predetermined acidity.  1999 Elsevier Science B.V. All rights reserved. Keywords: Infrared spectroscopy; Surface chemistry; Acidity measurements; Bimetallic zeolites 1. Introduction Knowledge about catalytically active sites is indispensable for explaining reaction mechanisms of different transformations catalyzed by bime- tallic phases supported on, or generated in the cage or channel systems of various zeolites (see e.g. [1]). Further, the nature and creation of acid sites have been a subject of a wide range of studies, in which the key issue was to clarify the chemistry of the creation and structure of bimetallic phases along with the genesis of acidity and their interactions under catalytic circum- stances. This is of particular importance when the nature of the active centers are different, (i.e. metal centers near acid sites [2]) and the reactants or the products may transform on both sites (e.g. hydrocarbon reactions [3]). It is also known that the acidity of these bifunctional catalysts signifi- cantly depends on the preparation method and pretreatment conditions [4]. For bimetallic zeolite catalysts these parameters have an even greater influence. In this article we present some results on the influ- ence of pretreatment on the acidity of bimetallic systems located in ZSM-5 zeolites. Journal of Molecular Structure 482–483 (1999) 1–5 0022-2860/99/$ - see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0022-2860(98)00926-0 * Corresponding author. Tel.: 0036 62 425523; fax: 0036 62 425523. E-mail address: tamasi@chem.u-szeged.hu (A. Tama ´si)