The selective reduction of acetic acid to acetaldehyde on iron oxides
has been studied in various pressure ranges. A good selectivity toward
s acetaldehyde could be achieved with molecular hydrogen continuously
present in the gas phase and on a prereduced catalyst containing both
a metal phase (zero-valent metal) and an oxidic phase. The pressure of
acetic acid appears to influence the formation and the kind of by-pro
ducts. At low pressures of acetic acid (0.015 mbar) ketene (CH2=C=O) i
s the most important (by-)product, while at high pressures (25 mbar) k
etene has never been observed and acetone is the main (by-) product. R
eaction mechanisms have been proposed for the selective reduction to a
cetaldehyde and for the formation of the (by-)products. Presumably the
reduction to acetaldehyde occurs on the vacancy-rich oxidic layer, wh
ile hydrogen is dissociated on the zero-valent metal sites. The by-pro
ducts are most likely formed via a common ketene-like intermediate. (C
) 1994 Academic Press, Inc.