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 ther mogravimetric analysis (TGA) measurements and C-13 NMR. For both adsor bates, the TPD-TGA results are shown to be a strong function of the in itial exposure. Following a saturation exposure of either adsorbate, T PD-TGA results for both molecules farm a large number of complex produ cts. 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 th rough either a secondary cation or an epoxide intermediate. The intact desorption of propanal at low coverages was also observed in this tem perature range. C-13 NMR spectra of 2-propen-1-ol confirm the formatio n of propanal and condensation products of propanal. Finally, a potent ial energy model based on gas-phase proton affinities of the various c onjugate bases along possible reaction coordinates for the reaction of 2-propen-1-ol explain the observed chemistry well. (C) 1995 Academic Press, Inc.