An FTIR and static SIMS study of the adsorption of propylene on Cu-ZSM-5 catalysts

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 CH4 at 350°C. The ir bands of =C-H stretching at 3101 cm-1, =C-C stretching at 916 cm-1 and C=CH2 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.