TPD/MS studies of the interaction of simple ketones with ZSM-5 zeolites

Temperature-programmed desorption (TPD) of products formed by the interaction of simple ketones with HZSM-5 zeolites has been studied mass spectrometrically. Acetone (MMK), methyl ethyl ketone (MEK) and diethyl ketone (EEK) were preadsorbed on HZSM-5 and NaZSM-5 zeolites at room temperature in amounts ranging from 0.04 to 2 mmol g⁻¹. It was shown that the qualitative composition of the products did not depend on the amount of preadsorbed ketone; the reactivity of the ketones increased from MMK to EEK. The conversion of MMK on HZSM-5 proceeded via acid intermolecular condensation, which could not take place on NaZSM-5. In the transformation of MEK, intramolecular dehydration played a role in the interaction, along with the above condensation mechanism; in this case NaZSM-5 also exhibited some activity. The mechanism of intramolecular dehydration prevailed in the reaction with EEK where, unlike NaZSM-5, HZSM-5 caused further conversion of the dehydrated products. The experiments with deuterated ketones, MMK-d₆ and MEK-d₅, have shown involvement of zeolitic hydrogen in the reaction complexes.