THE ROLE OF PROPANAL IN THE REACTION OF 2-PROPEN-1-OL IN H-ZSM-5

The adsorption of 2-propen-1-ol and propanal has been studied in H-ZSM-5 using simultaneous temperature programmed desorption (TPD) and thermogravimetric analysis (TGA) measurements and C-13 NMR. For both adsorbates, the TPD-TGA results are shown to be a strong function of the initial exposure. Following a saturation exposure of either adsorbate, TPD-TGA results for both molecules farm a large number of complex products. However, for low exposures, less than one molecule/Bronsted site, the initial products can be observed. For 2-propen-1-ol, the initial reaction product, formed between 400 and 425 K, is propanal, formed through either a secondary cation or an epoxide intermediate. The intact desorption of propanal at low coverages was also observed in this temperature range. C-13 NMR spectra of 2-propen-1-ol confirm the formation of propanal and condensation products of propanal. Finally, a potential energy model based on gas-phase proton affinities of the various conjugate bases along possible reaction coordinates for the reaction of 2-propen-1-ol explain the observed chemistry well. (C) 1995 Academic Press, Inc.