The catalytic activity and spectroscopic properties of supported noble metal catalysts are strongly influenced by the acidity/ alkalinity of the support but are relatively independent of the metal (Pd or Pt) or the type of support (zeolite LTL or SiO 2 ). As the alkalinity of the support increases, the TOF of the metal particles for neopentane hydrogenolysis decreases. At the same time, there is a decrease in the XPS binding energy and a shift from linear to bridge bonded CO in the IR spectra. Analysis of the shape resonance in XANES spectra indicates that in the presence of chemisorbed hydrogen the difference in energy between the Pt-H antibonding orbital and the Fermi level decreases as the alkalinity of the support increases. Based on the results from the IR, XPS, and shape resonance data a new model is proposed in which the interaction between the metal and support leads to a shift in the energy of the metal valence orbitals. The EXAFS structural analysis indicates that the small metal particles are in contact only with the oxide ions of the support. Finally, a new spectroscopic characterisation, Atomic XAFS, is presented which provides new insights into the origin of the electronic changes in the metal. As the alkalinity of the support increases, there is decrease in the metal ionisation potential. The primary interaction is a Coulomb attraction between metal particle and support oxygen ions, which affects the metal interatomic potential. This model for the metal-support interaction explicitly excludes the need for electron transfer, and it can account for all observed changes in the catalytic, electronic, and structural properties of the supported metal particles induced by support acidity ranging from acidic to neutral to alkaline.

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The turnover frequency (TOF) for conversion of neo-pentane was determined for Pt in Y zeolite with different numbers of protons and La +3 ions, different Si/Al ratios and with non-framework Al being present. Comparing Pt/NaY to Pt/H-NaY and Pt/K-USY with Pt/H-USY, respectively, shows an increase in the ln (TOF) which is proportional to the number of protons. Compared to NaY, the TOF of Pt in non-acidic NaLaY zeolite is about 25 times higher, which indicates also a strong influence on the charge of the cations on the TOF of Pt. The 20 times increase in the Pt TOF for K-USY compared to NaY is attributed to the effect of a higher Si/Al ratio and non-framework Al in the K-USY.EXAFS data collected on Pt/NaY and Pt/H-USY showed platinum particles consisting of 14-20 atoms on an average. These results were confirmed by HRTEM, which also showed that the Pt particles were dispersed inside the zeolite. The EXAFS data indicate that the metal particles are in contact with the oxygen ions of the support. The peak in the Fourier transform of the atomic XAFS (AXAFS) spectrum of the Pt/H-USY is larger in intensity than the corresponding peak of the Pt/Na-Y data. A detailed analysis of the L 2 and the L 3 X-ray absorption near edge structure revealed a shape resonance due to the Pt-H anti-bonding state (AS) induced by chemisorption of hydrogen on the surface of the platinum metal particles. The difference in energy (E res ) between the AS and the Fermi-level (E F ) is 4.7 eV larger for Pt/H-USY than for Pt/NaY. Both the AXAFS spectra and the shape resonances of the Pt-NaY and the Pt/H-USY catalysts provide direct experimental evidence of how the support properties determine the electronic structure of the platinum metal particles.Previous AXAFS and shape resonance work lead to a model in which the position in energy of the Pt valence orbitals is directly influenced by changes in the potential (i.e. electron charge) of the oxygen ions of the support and how the proton density affects this oxygen charge. This work shows that the potential of the oxygen ions is also a function of the Si/Al ratio of the support and the polarisation power of the charge compensating cations (H + , Na + , La 3+ and extra-framework Al); the metal particles experience an interaction which is determined by several properties of the support. The data further reveal how the change in the Pt electronic structure directly influences the catalytic properties of the catalyst.While the TOF is dependent on the metal-support interaction, the hydrogenolysis selectivity is determined by the Pt particle size, and increases linearly with increasing dispersion, or decreasing particle size.