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Pd–Fe/SiO2 bimetallic catalysts, prepared by sequential wet impregnation, with a constant 2 wt.% Pd loading and with atomic ratios Fe/Pd = 0.5–2.1, and monometallic samples have been studied by quantitative chemisorption and by FTIR spectroscopy of adsorbed CO and NO. The FTIR results indicate that on the examined bimetallic samples CO is selectively adsorbed on Pdo surface sites and NO is mainly adsorbed on Fe2+ surface sites; furthermore, readsorption and coadsorption experiments reveal that Pd and Fe are interdispersed on an atomic level. The quantitative chemisorption data show that the CO/Pd ratio on all the bimetallic samples is lower than on the pure Pd sample (

The adsorption and the surface reactions of ammonia and nitric oxide on differently pretreated Ru/TiO2 samples have been investigated by means of FTIR spectroscopy. On all the samples, both oxidized and reduced, the ammonia is adsorbed at room temperature in an undissociated form on different Ti4+ surface ions, (at coordinatively unsaturated sites), as on pure TiO2. By heating at 623 K, water and hydroxyls are formed on the oxidized catalyst and some reduction also occurs; on the reduced sample at 623 K, ammonia decomposes with formation of hydrogen atoms. On all the samples NO is adsorbed on Ru atoms or ions, producing bands in the 1750–1900 cm–1 range; at the same time, on the reduced samples, NO is dissociated giving N2O species. Oxidation of ammonia occurs at 573–673 K, producing nitrosylic ruthenium species and nitrates on titania: the latter are transformed to the former by heating at T 473 K. The reduction of NO occurs at 473 K, giving adsorbed ammonia and water on titania. The data suggest a mobility of the adsorbed species between the two phases present in the catalyst.

The infrared spectrum (700–4000 cm–1) of quasi-stoichiometric microcrystalline ZnO has been recorded at various temperatures (97–523 K) and following various redox treatments.A broad band centred at ca. 1500 cm–1, produced on samples cooled down to 97 K in oxygen, is ascribed to the increasing concentration of un-ionized donor centres.The disappearance of all phonon and surface impurity (OH, carbonate-like species) bands, caused by heating the samples to 433 K both in vacuo and in a hydrogen atmosphere, is ascribed to the phonon–plasmon coupling in microcrystals possessing a rather high concentration of electrons in the conduction band.

Several α-Al2O3 specimens were prepared by thermal treatment of pure transition aluminas, already in the form of i.r. pellets. When the starting material is a high external area phase, the resulting sample is still suitable for i.r. work. In particular two preparations are considered, which only differ in the number of hours of treatment at 1150°C. Although the X-ray pattern is the same in both cases, great differences are revealed by the i.r. spectra, especially in the stretching region of the surface hydroxyl groups. It is suggested that the sample treated for the shorter time either maintains or simulates some surface characteristics of the starting transition phase.

Hydrogen adsorption on high-surface-area alkaline-earth oxides has been studied by i.r. spectroscopy at 300 and 78 K. In the former case heterolytic dissociation of H2 molecules produces hydride and hydroxy groups which are partially reversible upon evacuation. Low-temperature hydrogen adsorption appears to be undissociative. The active sites are cation–anion couples in low coordination on the surface.On the basis of i.r. evidence a mechanism is proposed for the interaction of oxygen with preadsorbed hydrogen envisaging an electron-transfer process from H– ions to oxygen molecules to give O–2 paramagnetic species.

Solid solutions of ZnO in MgO with larger surface areas than those previously reported in the literature have been prepared and their formation tested by ultraviolet–visible reflectance spectroscopy. The surface chemistry of CO and H2(or D2) interactions has been studied by infrared spectroscopy. Large differences with respect to the surface chemistry of the pure oxides have been found. CO is mainly adsorbed on MgO couples as oxidized carboxylate-type species, which are stable up to 373 K and then transformed into carbonate-type species. H2 is mainly chemisorbed by heterolytic dissociation on three different Zn—O couples.