SURFACE REACTIVITY OF ZSM-5 ZEOLITES IN INTERACTION WITH KETONES AT AMBIENT-TEMPERATURE (A FT-IR STUDY)

Surface complexes formed at ambient temperature from acetone, acetone-d6, diethyl ketone, diacetone alcohol, and mesityl oxide on HZSM-5, dehydroxylated HZSM-5, and NaZSM-5 zeolites were studied using FTi.r. spectroscopy. It was found that the C=O bond in ketones is perturbed far more by the bridging hydroxyls than by electron-accepting sites, Al and Na ions, and that this effect is greater for the more basic diethyl ketone than for acetone. The bridging hydroxyls cause the formation of protonated ketones. In contrast to diethyl ketone, protonated acetone is aldolized by the reaction with the physisorbed molecule to form diacetone alcohol, which is immediately dehydrated to strongly adsorbed mesityl oxide at room temperature. Acetone does not react in the cavities of NaZSM-5, but dehydration of diacetone alcohol occurs readily, most probably due to the effect of Al Lewis sites present in small concentrations.