Sub-nanometer Transition Metal Clusters for Dehydrogenation Catalysis: Is the d-band Model Valid?

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The d-band model of Hammer and N{\o}rskovsuccessfully rationalizes the catalytic properties of transition metal (TM) surfaces and nanoparticles. The model predicts a linear relationship between the d-band center energy of a TM or TM alloy (Ed) and its binding energy with a reactant molecule. Many studies have shown that the d-band center with respect to the Fermi energy (Ed-EF) is a useful descriptor of the catalytic properties of TM systems. Originally established for TM surfaces, the d-band model has also been validated for particles with diameters of roughly 10 nm. However, the model has not yet been tested for sub-nanometer clusters and cluster alloys, in which the discrete nature of the energy-level spectrum becomes more prominent. We have calculated binding energies of four atom homogeneous TM clusters (M4) and binary cluster alloys (M4−xNx, x=1,2,3) with propane and propene, for the purpose of a detailed study of propane dehydrogenation. We find that binding energy varies approximately linearly with d-band center for many M4−xNx cluster alloys, in agreement with the d-band model. However, the agreement is much worse when the M4 clusters formed by different TMs are compared. We will discuss possible reasons for these results, along with implications for dehydrogenation catalysis.


Presentation at the 2015 Annual Fall Meeting of the APS Prairie Section