The heterogeneous oxidation of C 2H 4 and C 3H 6 was studied over several gold catalysts. The principal products from C 2H 4 were CO 2 and H 2O, but small amounts of acetic acid and acetaldehyde were also found. In addition to these products, up to 3% acetone and 50% acrolein were obtained from C 3H 6. Gold sponge and Au/SiO 2 were much more selective for acrolein formation than Au/α-Al 2O 3. For both olefins, the rate of total oxidation was first order in oxygen pressure and zero order in olefin pressure at low pressures. The apparent activation energies (except for C 2H 4 over Au sponge) ranged from 17 to 22 kcal mol -1. Acrolein formation had a much lower apparent activation energy (9-12 kcal mol -1), was also first order in O 2, but showed a maximum rate for C 3H 6 pressures near 30 Torr. Oxidation of propylene-1- 13C produced acrolein molecules in which the 13C was equally distributed between the end positions. Similarly, CD 3CHCH 2 and CH 3CHCD 2 both yielded CH 2CHCDO and CD 2CHCHO in about equal amounts, although the rate of the reaction with the former olefin was only about 40% that of the latter or that of CH 3CHCH 2. These results indicated that the rate-determining step in acrolein formation was abstraction of a methyl hydrogen (or deuterium) to yield a symmetrical allylic intermediate. The modes of fragmentation of acrolein during mass spectral analysis are discussed on the basis of high-resolution measurements of the labeled acroleins formed in the present work.
|Number of pages||8|
|Journal||Journal of Physical Chemistry|
|Publication status||Published - 1971|