XAFS spectroscopy in catalysis research: AXAFS and shape resonances

Two new techniques in X-ray absorption spectroscopy (XAS) have recently been developed which provide previously unobtainable information on supported noble metal catalysts. Atomic X-ray absorption fine structure (AXAFS) provides direct information on the average changes in interatomic potential of the metal particles induced by metal-support effects. Changes in the interatomic potential can now be directly related to changes in catalytic reactivity. Analysis of shape resonances near the X-ray absorption edge provides information on the changes in the nature of the bonding of adsorbates (like hydrogen) to the metal cluster as induced by the properties of the support. The strong decrease in activity of supported platinum clusters for neo-pentane hydrogenolysis with increasing alkalinity of the support can be ascribed to a decrease in ionization potential of the metal particles directly influenced by the alkalinity of the support.