PREPARATION AND EXAFS STUDIES OF HIGHLY DISPERSED IRON CATALYST DERIVED FROM FE3(CO)12 PRECIPITATED ON ALUMINA

Supported tri-iron dodecacarbonyl has been prepared by a novel method, precipitating the cluster on alumina without any pretreatment. The precipitated Fe3(CO)12/Al2O3 retains a molecular structure similar to that of its parent compound as demonstrated by Fe K-edge XANES (X-ray absorption near-edge structure) and infrared results. After decarbonylation under very mild conditions (310 K in vacuum), the Fe/Al2O3 obtained exhibits a good catalytic selectivity for lower olefins in the hydrogenation of carbon monoxide. K-edge EXAFS (extended X-ray absorption fine structure) analyses of the fresh catalyst and the used catalyst suggest that the active site on the surface is an ensemble of three iron atoms with one short FeFe bond of 2.52 ± 0.05 Å and two longer FeFe bonds of 2.74 ± 0.04 Å. However, the aggregation of these Fe3 groups to particles over 10 Å in size brings about a short lifetime and poor selectivity for the catalyst. The aggregated particles are still two-dimensional, consisting of at least three iron trimers in which the interatomic distance for each trimer of iron on the average is 2.48 ± 0.08 Å, and the nearest interatomic distance between two trimers is 2.83 ± 0.03 Å. © 1993 Academic Press, Inc.