On the interpretation of the NH3-TPD patterns of H-ZSM-5 and H-mordenite

The species obtained from adsorption of ammonia over zeolite H-ZSM-5 and H-mordenite were characterized by temperature-programmed desorption (NH3-TPD) and infrared spectroscopy (IR). At ammonia loadings of NH3/Al > 1, the IR spectra indicated the formation of NH4+ . nNH(3) associations, where n greater than or equal to 1. At loadings of NH3/Al < 1 spectra of NH ions and Lewis-bound NH3 were recorded. The decomposition of the NH4+ ions and desorption of NH3 from strong Lewis acid sites gave rise to TPD peaks above about 673 K. The peaks at temperatures lower than about 673 K were assigned to ammonia released from protonated NH3 associations. (C) 2001 Elsevier Science B.V. All rights reserved.