Abstract
Diffuse reflectance infrared spectroscopy and static secondary ion mass spectrometry (SIMS) were employed to study the surface species formed during the adsorption and reaction of propylene on a copper-exchanged ZSM-5 catalyst. Propylene showed characteristics of chemisorption on Cu-ZSM-5 at room temperature and total decomposition to CO, CO2 and CH 4 at 350°C. The ir bands of =C–H stretching at 3101 cm -1, =C–C stretching at 916 cm -1 and C=CH 2 twisting at 575 cm -1 for propylene disappeared upon adsorption, indicating the breaking of the C=C double bond, while the decrease in the signal intensity of zeolite isolated and vicinal SiOH groups at 3700 and 3592 cm -1 implied that the adsorbed di-σ species was bound to zeolite SiO–. Static SIMS showed two distinguished peaks at 73 and 147 amu, which were assigned to the adsorbed species H2OSi2(C3H5O2) due to the interaction of propylene with ZSM-5 and Cu-ZSM-5. The adsorption and reaction of propylene were enhanced by the presence of Cu+ in ZSM-5. The mechanism for these processes was discussed.
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