CATALYSTS OF SUPPORTED IRON DERIVED FROM MOLECULAR-COMPLEXES CONTAINING ONE, 2, AND 3 IRON ATOMS

The syntheses and characterization of catalysts derived from Fe(CO)5, Fe2(CO)9, and Fe3(CO)12 supported on γ-A12O3 are described. The temperature-programmed decomposition (TPDE) spectra of the Fe(CO)5 and Fe3(CO)12 catalysts are different, suggesting that the nuclearity of the precursor complex can influence the chemistry of supported complexes. Fe2(CO)9 dry mixed with A12O3 probably undergoes some decomposition to Fe(CO)5 and Fe3(CO)12 prior to bonding to the support. Activation at low temperatures (≲150°C) leads primarily to the formation of zerovalent subcarbonyl species, some of which are reversibly formed. Activation at high temperatures (≳300°C) leads to extensive oxidation of the Fe by reaction with the surface hydroxyl groups of the Al2O3 and loss of reversibility. Compared to the TPDE of the bulk unsupported carbonyls, Al2O3 stabilizes subcarbonyl species over a broad range of temperatures and inhibits their migration, preventing the formation of an Fe mirror. Chemisorption of CO indicates that catalyts derived from the iron carbonyls can be more than an order of magnitude more dispersed than catalysts synthesized by the traditional technique of impregnation with salts of Fe3+. © 1979, American Chemical Society. All rights reserved.