Mikrochim. Acta [Wien] 1988, II, 101--104 Mikrochimica Acta 9 by Springer-Verlag 1988 Characterization of Alkali Exchanged ZSM5 by IR Spectrosopy Gerhard Warecka, Gerd Rumplmayr, and Johannes A. Lercher* Institute for Physical Chemistry,Technical Universityof Vienna, Getreidemarkt 9, A-1060 Wien, Austria Abstract. The use of time resolved FTIR spectroscopy for characterizing time dependent adsorbate concentrations has been demonstrated with the examples of adsorption/desorption of ammonia and of adsorption and reactions of propan-2-ol. Adsorption sites and adsorbate structures are discussed. Key words: adsorbate spectra, time resolved FTIR spectroscopy, alkali ZSMS. Infrared spectroscopy has been used for several decades to study adsorbate systems. The primary objective for these studies were (i) to elucidate the nature and strength of the bond(s) between the adsorptive and the adsorbent and (ii) to characterize precursors and stable intermediates of surface reactions. Because of experimental constraints in most of the experi- ments reported, only the IR spectra of the most abundant surface species could be obtained, but not if the species observed is part of a specific kinetic event (e.g. a catalytic cycle). To demonstrate a possible circumvention of this shortcoming, temper- ature programmed desorption (t.p.d.) and reaction (t.p.r.) have been used to characterize HZSM5 and a series of alkali exchanged ZSM5, zeolites previ- ously investigated in our lab [1, 2]. The adsorbates and the gas phase tran- sients were characterized simultaneously by time resolved FTIR spec- troscopy and mass spectrometry. By this approach, the kinetics at the surface and of the desorbed products could be followed independently. The kinetics of the adsorption/desorption of ammonia as well as the temper- ature programmed reaction of propan-2-ol will be described. * To whom correspondence should be addressed