No abstract

Publication costs assisted by Monsanto CompanyInfrared spectroscopy has been used to observe intermediates formed in the interaction of NO and CO on the surface of a Pt/A^Os catalyst. The general procedure was to dose a clean surface at elevated temperature with the desired gas or gas mixture, cool to room temperature, and observe the infrared spectrum of the adsorbed species in the 4000-1200-cm"1 region. When mixtures of CO and NO containing excess or stoichiometric amounts of CO were used, the infrared spectrum contained strong bands at 2267 and 2148 cm"1 which were not observed when the sample was treated similarly with known reactants or products or when treated with the reactant mixture below 200°. Labeling experiments and consideration of other factors lead to the assignment of the 2267-cm"1 band to a Pt-NCO species and the 2148-cm"1 band to an (NCO)" anion. The discovery of these intermediates provides a new mechanistic pathway and possible alternative to previous explanations of NHs formation in the catalytic treatment of automobile exhaust.

Isocyanate species have been detected on the surface of noble metal catalysts during the reactions of carbon monoxide with nitric oxide. The intensity of the surface isocyanate infrared band correlates with the known ammonia-forming tendencies among the noble metals. The discovery of this isocyanate species suggests a new mechanistic pathway to the ammonia formed during catalytic reduction of nitrogen oxides in automobile exhaust.

Publication costs assisted by Monsanto CompanyAn infrared spectroscopic study of surface species resulting from the decomposition of 0.5 Torr of methanol on Na, K, Rb, and Cs forms of type X zeolite at 400 °C has been conducted. Methoxide, carbonate, and formate species were observed in varying amounts and types on the different samples. Formation of formaldehyde during methanol decomposition is indicated by control experiments involving room temperature adsorption of formaldehyde. The relative intensities of formate and carbonate bands on these samples correlates with the reported selectivity of these materials for the alkylation of toluene to styrene with methanol or formaldehyde.

Publication costs assisted by the Monsanto Company In order to study changes in the electron structure of benzene as it interacts with the walls of a zeolite supercage, a diffuse reflectance UV study of the -* transition at various benzene loadings has been carried out. In general, red shifts are observed as the benzene loading on a particular zeolite increases. Red shifts are also observed with an increase in the electrostatic field within the supercage whether the increase is accomplished by changing the cation or the Si/Al ratio of the faujasite lattice. Various simple approaches at quantitatively explaining these results fail, but there is some evidence that a full accounting of dispersion, polarization, and quadrupole interactions would be successful.