The Nature of the Pt−H Bonding for Strongly and Weakly Bonded Hydrogen on Platinum. A XAFS Spectroscopy Study of the Pt−H Antibonding Shaperesonance and Pt−H EXAFS

A long-standing problem in the research of H 2 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 L 2 and L 3 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 L 2 and L 3 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.