The nature of the pt-H bonding for strongly andweakly bonded hydrogen on platinum.A SAFS spectroscopy study of the Pt-H antibonding shaperesonance and Pt-H EXAFS

摘要

A long-standing problem in the research of H_2 chemisorption on supported Pt catalysts is theunclarity aobut the difference in nature of the Pt-H bonding for weakly and strongly bonded hydrogen.On the basis of PtPt EXAFS and a newly developed XANES analysis of the Pt L_2 and L_3 deges,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 ewakly or strongly bound hydrogen,indicating a similar nature for bothinteractions.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.