Catalysis

Pt L₂₃ edge X-ray absorption (XAS) studies of dispersed metal catalyst has resulted in the development of two new techniques:

"Atomic" EXAFS (AXAFS) produces long wavelength oscillations in the absorption cross-section similar to normal EXAFS, but coming from scattering off of the interatomic potential involving the absorber atom itself rather then from the neighboring atoms as in EXAFS. The AXAFS is very sensitive to the polarization and charge on the absorber atom.

Differential isolation involves isolating the scattering coming from an adsorber atom by taking the difference between the adsorbate-covered surface and the "clean" surface. Comparison of this experimental c function with similar results from theoretical self-consistent field, multiple-scattering calculations (FEFF8) on clusters representing the clean and adsorbate covered cluster allow a determination of the absorber site. Particularly interesting here has been the ability to determine the adsorption sites for H on the Pt surface.

Read about AXAFS in Chemical and Engineering News article

Collaborators:

Prof. Diek Koningsberger, his research group at the University of Utrecht, NL
Jeff Miller at BP-Amoco Labs

Papers in preparation or submitted:

a) D.C. Koningsberger, M.K. Oudenhuijzen, J. de Graaf, J.A. van Bokhoven, and D.E. Ramaker, "Towards an Understanding of the Compensation Relation and Change of Order in Hydrogen with Support Properties for Pt Catalyzed Alkane Hydrogenolysis", J Catalysis (in press)
b) G. E. van Dorssen, D. C. Koningsberger, and D.E. Ramaker, "Separation of Double Electron and Atomic XAFS Contributions in X-ray Absorption Spectra of Pt Foil and Na₂Pt(OH)₆", J. Phys Condensed Matter ( in press) 
c) D. E. Ramaker and D.C. Koningsberger, Comment on "The Effect of Hydrogen Adsorption on the X-ray Absorption Spectra of Small Pt Clusters",  Phys. Rev. Letters, 89,139701 (2002)
d) M. Oudenhuizen, D.C. Koningsberger, D.E. Ramaker, "Influence of Support Alkalinity on Pt Particle Adsorbate Bonding", to be submitted
e) M. Oudenhuizen, D.C. Koningsberger, D.E. Ramaker, "Evidence for Strongly Bonded Low-Coordinated H on supported Pt clusters in Active Catalysts", to be submitted.