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) was studied by near edge X-ray absorption fine structure (NEXAFS), It is 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 carbon-carbon double bond, is proposed. In the butadiene molecule half of the carbon atoms undergo a large rehybridization from sp(2) to sp(3), as evidenced by high resolution electron energy loss spectroscopy (HREELS), These differences between 1,3-butadiene adsorption on Pt(111) and Pd(111) are discussed in terms of differences in catalytic activities and selectivities in the 1,3-butadiene hydrogenation reaction.