The Nature of the Pt-H Bonding for Strongly and Weakly Bonded Hydrogen on Platinum : A XAFS Spectroscopy Study of the Pt-H Antibonding Shape Resonance and Pt-H EXAFS

Abstract

A long-standing problem in the research of H2 chemisorption on supported Pt catalysts is the unclarity about the difference in nature of the Pt-H bonding for weakly and strongly bonded hydrogen. On the basis of Pt-Pt EXAFS and a newly developed XANES analysis of the Pt L2 and L3 edges, it will be shown that both types of hydrogen are truly chemisorbed species. The EXAFS analysis shows a similar contraction of the Pt-Pt bond irrespective of the removal of weakly or strongly bound hydrogen, indicating a similar nature for both interactions. Moreover, the analysis of the L2 and L3 X-ray absorption edges shows unambiguously the presence of a Pt-H antibonding state for both the weakly and strongly bonded hydrogen. This is a clear indication for chemisorption of hydrogen for both types of hydrogen. The Pt-H EXAFS shows a smaller Pt-H bond length in the case of strongly adsorbed, which is in correlation with the expected strength of the Pt-H bond.