The direct influence of the support on the electronic structure of the active sites in supported metal catalysts: evidence from Pt-H anti-bonding shape resonance and Pt-COFTIR data

The catalytic activity and spectroscopic properties of supported noble meta l catalysts are strongly influenced by support properties such as the prese nce of protons, type of charge compensating cations, Si/Al ratio and/or pre sence of extra-framework Al. The metal-support interaction is relatively in dependent of the metal (Pd or Pt) or the type of support (microporous zeoli tes such as LTL and Y or macroporous supports such as SiO2). As the alkalin ity of the support increases (i.e., with increasing electronic charge on th e support oxygen ions), the TOF of the metal particles for neopentane hydro genolysis decreases. At the same time, there is a systematic shift from Lin ear to bridge bonded CO as indicated by the IR spectra. This is a strong in dication of a change in the electronic structure of the catalytically activ e Pt surface atoms. Analysis of the Pt-H anti-bonding shape resonance prese nt in the Pt X-ray absorption spectra of the L-3 edge indicates that the di fference in energy between the Pt-H anti-bonding orbital and the Fermi leve l decreases as the alkalinity of the support increases. The results from th e IR and Pt-H shape resonance data directly show that the support influence s the position in energy of the metal valence orbitals. The ionisation pote ntial of the catalytically active Pt surface atoms decreases with increasin g support alkalinity, i.e., with increasing electron charge on the support oxygen ions. This shift leads to a weakening of the Pt-H bond.