SELECTIVE REDUCTION OF ACETIC-ACID TO ACETALDEHYDE ON IRON-OXIDES

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.