The genesis of carbon-supported Fe-Mn and K-Fe-Mn catalysts from stoichiometric metal carbonyl clusters I. Characterization by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)

Journal Article · Mon May 01 04:00:00 EDT 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90229-7· OSTI ID:6188864

Venter, J J; Chen, A; Vannice, M A ^[1]

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1. Pennsylvania State Univ., University Park (USA)

The thermal decomposition of Fe{sub 3}(CO){sub 12}, NEt{sub 4}(Fe{sub 2}Mn(CO){sub 12}), Mn{sub 2}(CO){sub 10}, K(HFe{sub 3}(CO){sub 11}), and K(Fe{sub 2}Mn(CO){sub 12}) has been studied for the first time by dispersing these clusters on an oxygen-free carbon surface and monitoring their behavior by diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The Fe{sub 3}(CO){sub 12} decomposed to Fe(CO){sub 5} in either He or H{sub 2}, while Mn{sub 2}(CO){sub 10} decarbonylated without the formation of any stable intermediate clusters in either gas. The NEt{sub 4}(Fe{sub 2}Mn(CO){sub 12}) clusters decomposed with no formation of other stable carbonyl products in He, but in H{sub 2} they formed Mn{sub 2}(CO){sub 10} and (HFe{sub 4}(CO){sub 13}){sup {minus}} species. Similarly, the decomposition of K(Fe{sub 2}Mn(CO){sub 12}) in He produced no detectable intermediates, but under H{sub 2} it led to the formation of these same two intermediate clusters, while K(HFe{sub 3}(CO){sub 11}) yielded (HFe{sub 4}(CO){sub 13}){sup {minus}}. First-order rate constants of decomposition were determined for each cluster, compared to literature k{sub 1} values for nucleophilic substitution reactions in solution, and found to be similar to substitution rate constants for Fe{sub 3}(CO){sub 12} and Mn{sub 2}(CO){sub 10} but higher than those for Fe(CO){sub 5}. The rate-determining step in either the substitution or the decomposition reaction appears to be the removal of the first CO ligand in Fe{sub 3}(CO){sub 12}, but with Mn{sub 2}(CO){sub 10} it is Mn-Mn bond scission. The activation energies of decomposition were 18-21 kcal/mol for Fe{sub 3}(CO){sub 12} and 32-40 kcal/mol for Mn{sub 2}(CO){sub 10}, while those for the decomposition products gave intermediate values. This study represents a portion of the first successful application of an IR spectroscopic technique to characterize carbon-supported metal catalysts. 120 refs.

• OSTI ID: 6188864
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 117:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

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