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.

Aberration-corrected transmission electron microscopy and high-angle annular dark field imaging was used to investigate the surface structures and internal defects of CeO2 nanoparticles (octahedra, rods, and cubes). Further, their catalytic reactivity in the water-gas shift (WGS) reaction and the exposed surface sites by using FTIR spectroscopy were tested. Rods and octahedra expose stable (111) surfaces whereas cubes have primarily (100) facets. Rods also had internal voids and surface steps. The exposed planes are consistent with observed reactivity patterns, and the normalized WGS reactivity of octahedra and rods were similar, but the cubes were more reactive. In situ FTIR spectroscopy showed that rods and octahedra exhibit similar spectra for -OH groups and that carbonates and formates formed upon exposure to CO whereas for cubes clear differences were observed. These results provide definitive information on the nature of the exposed surfaces in these CeO2 nanostructures and their influence on the WGS reactivity.

Ceria nanorods were investigated using in situ Raman and FTIR spectroscopies for CO adsorption and subsequent reaction with water at 200 and 350 °C. The involvement of defects in ceria nanorods during CO adsorption and reaction with H 2 O is dependent on the temperature. At 200 °C, most of the carbonate and formate species formed in CO do not involve the formation of defects, while at 350 °C all of the carbonates and formates formed can be correlated to the formation of defects (15% by formates and 85% by mono/bidentate carbonates). Finally, at 350 °C very stable polydentate carbonates are formed that do not induce defects and cannot be regenerated with water.

2002). N2O decomposition over Fe/ZSM-5: effect of high-temperature calcination and steaming. Catalysis Letters,, 205-212. https://doi.N 2 O decomposition over Fe/ZSM-5 made by the sublimation method was investigated. Further calcination or steaming treatment (700 8C) increased the decomposition rate of N 2 O. FTIR showed that such treatments lead to the disappearance of Brùnsted acid sites. The various catalysts have dierent apparent activation energies, con®rming the presence of dierent active Fe species. The observation that after high-temperature calcination a higher activity is obtained while no dealumination occurs indicates a mechanism where neutral Fe oxide clusters occluded in the zeolite micropores react at high temperature with the zeolite protons to form [FeO]like species.

A FT-IR spectroscopic study of methane, ethane, and propane adsorption on magnesium and calcium forms of zeolite Y reveals different vibrational properties of the adsorbed molecules depending on the exchanged cation. This is attributed to different adsorption conformations of the hydrocarbons. Two-fold eta(2) coordination of light alkanes is realized for MgY, whereas in case of CaY zeolite quite different adsorption modes are found, involving more C-H bonds in the interaction with the cation. The topological analysis of the electron density distribution function of the adsorption complexes shows that when a hydrocarbon coordinates to the exchanged Mg(2+) ions, van der Waals bonds between H atoms of the alkane and basic zeolitic oxygens significantly contribute to the overall adsorption energy, whereas in case of CaY zeolite such interactions play only an indirect role. It is found that, due to the much smaller ionic radius of the Mg(2+) ion as compared to that of Ca(2+), the former ions are significantly shielded with the surrounding oxygens of the zeolitic cation site. This results in a small electrostatic contribution to the stabilization of the adsorbed molecules. In contrast, for CaY zeolite the stabilization of alkanes in the electrostatic field of the partially shielded Ca(2+) cation significantly contributes to the adsorption energy. This is in agreement with the experimentally observed lower overall absorption of C-H stretching vibrations of alkanes loaded to MgY as compared to those for CaY zeolite. The preferred conformation of the adsorbed alkanes is controlled by the bonding within the adsorption complexes that, in turn, strongly depends on the size and location of the cations in the zeolite cavity.