(541e) DFT and XANES Studies of d-Band Transition Metal Alloys

Carolina Gomez¹, Ruzica Todorovic¹, Tianpin Wu², Neil Schweitzer², Jeff Miller² and Randall Meyer¹

¹Department of Chemical Engineering, University of Illinois at Chicago

²Division of Chemical Sciences and Engineering, Argonne National Lab

Transition metals are characterized by their high catalytic activity in many industrial reactions. This activity has been partially attributed to their unoccupied d-band ⁽¹⁾. Hammer and Norskov have proposed a model in which the adsorption behavior of a transition metal can be predicted by the relative position of its d-band center with respect to the Fermi level ⁽²⁾. Adsorption (and therefore, reactivity) is primarily determined by the location of the d-band center of a metal.

Alloying offers a way to further fine tune the interaction of adsorbates with the catalyst. Alloying alters the shape of the d-band through two primary effects: electronic(charge transfer) and geometric (changes in hybridization).  These changes in the electronic structure of the metal can be partially accessed through X-ray absorption near edge structure spectroscopy.  Recently, we have examined the effect of particle size and adsorbates on the XANES of Pt and Pd metal nanoparticles. We have now expanded this effort to look at a variety of alloys and have performed further density functional theory based calculations to simulate the XANES spectra on a larger group of PdX alloys. We can now further discriminate between two different classes of rehybridization: changes in metal-metal bond distances and changes in orbital extent.

1. X-ray Absorption Edge Studies of the Electronic Structure of Metal Catalyst. Sinfelt, John H. and Meitzner, George D. 1993, Accounts of Chemical Research, Vol. 26.

2. CO Chemisorption at Metal Surfaces and Overlayers. Hammer, B., Morikawa, Y. and Norskov, J. K. 12, March 18, 1996, Physical Review Letters, Vol. 76, pp. 2141-2144.