DECARBONYLATION AND CO ADSORPTION ON CLUSTER-DERIVED IRON CATALYST - SURFACE FORMATION AND COORDINATE GEOMETRY OF FE-3(CO)(6)(MU(3)-CO)/AL2O3

A surface species has been formed on the cluster-derived catalyst Fe/Al2O3 by saturation with CO. Fe K-edge extended X-ray absorption fine structure (EXAFS) analysis reveals a contribution from the colinear Fe-C-O array as well as a formula of Fe-3(CO)(6)(mu(3)- CO)/Al2O3 with C-3v symmetry for the species. The bond lengths of Fe-C-t (C-t = terminal carbon), Fe-mu(3)-C, Fe-O, and Fe-Fe are 1.84(3), 1.96(1), 1.96(1), and 2.48(6) Angstrom, respectively. The angle Fe-mu(3)-C-Fe is about 80 degrees and that between the Fe-mu(3)-C bond and the Fe-3 plane is about 42 degrees. The geometric consideration reveals that the species is inlaid into the surface and stabilized by the Fe(mu(3)-C)(mu(3)-O) core. Introducing the basic concept of coordination chemistry to the surface approach, the species can be described as [Fe-3(CO)(6)(mu(3)-CO)(O)(6)(mu(3)-O)](3-), a molecular anion with C-3v symmetry ionically bound to the Al+ cationic site. The results suggest that formation of an active intermediate with a mu(3) carbide ligand from the mu(3)-CO is geometrically allowed, but it is unlikely that it can give high activity in CO hydrogenation because of the stability of the Fe(mu(3)-C)(mu(3)-O) core. (C) 1994 Academic Press, Inc.