(641e) Active Sites, Kinetics, and Second Sphere Coordination Effects for CO Oxidation on Mixed-Valence Oxo-Bridged Trimers
AIChE Annual Meeting
2021
2021 Annual Meeting
Catalysis and Reaction Engineering Division
Microporous and Mesoporous Materials III: Reaction Pathways and Effects Beyond the Binding Site
Thursday, November 11, 2021 - 4:42pm to 5:00pm
Steady state and transient kinetics experiments evidence steps constituting the oxidation half cycle to be kinetically relevant, with activation energies reflecting standard state free energy differences between Fe(IV)=O intermediates and gas phase nitrogen, and the bare Fe2+ surface and gas phase N2O. We show that CO oxidation turnover frequencies and apparent activation energies can be systematically tuned through manipulation of second sphere coordination environment, with both quantities decreasing monotonically with increasing average trimer electron density (Figure 1). The average electron density of the trimer was varied either by changing the coverage of a specific oxygenate, or by modifying the identity of the oxygenate at constant oxygenate coverage through the use of larger alkyl chain lengths. Overall, the results provide an unprecedented level of kinetic clarity as to the effect of second sphere coordination environment on the rates of redox reactions occurring over multinuclear clusters, and point to the utility of metal organic framework materials in addressing questions hitherto rendered intractable by heterogeneity in active site speciation.