Many commercially important catalysts consist of small metal particles dispersed on inorganic oxide surfaces. Although in most cases there is no significant interaction between the metal and the support, strong bonding can be demonstrated in a recently discovered class of supported-metal catalysts. These cases typically involve group VIII metals dispersed on transition metal oxides whose surfaces can be reduced to form cations with lower valences. Spectroscopic measurements indicate that an electron is transferred from the cation (such as Ti(3+) or Nb(4+)) to the metal particle. This, in turn, leads to profound changes in the catalytic and chemisorption properties and the morphology of the metal particles.

K shell excitation spectra of the aromatic molecules benzene and pyridine in the gas phase are compared to those for the solids (ices) and for monolayers chemisorbed on Pt(111). The gas phase and solid spectra are essentially identical and even the spectra for the chemisorbed molecules exhibit the same resonances. Because of the orientation of the molecules upon chemisorption the latter spectra show a strong polarization dependence as a function of x-ray incidence. This polarization dependence in conjunction with a multiple scattering Xα calculation for the benzene molecule allows us to assign the origin of all K shell resonances. The resonances are found to arise from transitions to π* antibonding orbitals and to σ* shape resonances in the continuum. The shape resonances are characterized by potential barriers in high (l=5 and 6) angular momentum states of the excited photoelectron. The polarization dependence and energy position of the resonances allow the molecular orientation on the surface to be determined and show that the change in the carbon–carbon bond length is less than 0.02 Å.

The X-ray absorption near-edge spectra (XANES) of the L¡ tungsten edge in W03/A1203 samples indicate that the symmetry of the tungsten environment depends on both the surface coverage and the presence of coordinated water. At coverages of less than 1 /3 monolayer, in the absence of coordinated water, the XANES spectrum indicates a distorted tetrahedral structure for the surface tungsten oxide species. Samples exposed to air at room temperature have water molecules coordinated to the surface tungsten oxide species and produce an octahedral site symmetry, but the water is removed by heating to 500 °C. The Raman spectra of the W03/A1203 samples are consistent with a distorted tetrahedral tungsten oxide environment and, in addition, show features due to W=0 and W-O-W bonds. These results suggest that the surface tungsten oxide is present as both isolated and dimeric tetrahedra. At coverages approaching a monolayer, in the absence of coordinated water, a significant fraction of the surface tungsten oxide sites appears to have a distorted octahedral environment in the XANES spectra. At this high coverage the effect of coordinated water molecules is much less evident than at low coverage.The Raman results, however, only provide information about the tetrahedral component because the Raman cross section of the tetrahedral tungsten oxide is much higher than the octahedral tungsten oxide. The Raman spectra show features of W=0 and W-O-W bonds in the tetrahedral fraction of the surface tungsten oxide monolayer on alumina. These observations are consistent with a surface complex where the supported tungsten oxide has formed a polymeric structure on the alumina support composed of W04 and W06 units jointed in infinite chains.

A molecular orbital study of a strong metal-support interaction (SMSI) catalyst, platinum supported on T1O2, has been carried out by the -SW-SC F method using two different cluster models. The calculations favor a model in which platinum atoms are inserted into surface oxygen ion vacancies in the support, with bonding between the titanium cations and the platinum atoms. A possible mechanism for the suppression of FJ2 chemisorption on the supported metal in SMSI catalysts is suggested.