A COMPARATIVE-STUDY OF 1,3-BUTADIENE AND 1-BUTENE CHEMISORBED ON PT(111), AND PD(111)

The adsorption of 1,3-butadiene and 1-butene on Pt(111), and Pd(111) w as studied by near edge X-ray absorption fine structure (NEXAFS), It i s found that at 95 K, 1-butene is pi-bonded to Pd(111), while it is di -sigma bonded to Pt(111), Ar 95 K, 1,3-butadiene is loosely bonded on both Pd(111) and Pt(111). However, at 300 K, 1,3-butadiene adsorption differs, depending on the substrate, A di-pi bonding is observed on Pd (111) while on Pt(111), a di-sigma interaction, keeping one central ca rbon-carbon double bond, is proposed. In the butadiene molecule half o f the carbon atoms undergo a large rehybridization from sp(2) to sp(3) , as evidenced by high resolution electron energy loss spectroscopy (H REELS), These differences between 1,3-butadiene adsorption on Pt(111) and Pd(111) are discussed in terms of differences in catalytic activit ies and selectivities in the 1,3-butadiene hydrogenation reaction.