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Al 2 O 3 catalysts has been investigated by IR spectroscopy and temperature-programmed desorption. Upon NO interaction, small amounts of nitrites, nitrates, and hyponitrite species were formed on the Ba-containing samples. The NO x storage capacity of the catalysts was highly enhanced upon adsorption of NO/O 2 mixtures and further upon NO 2 admission. Upon adsorption of NO/O 2 on Pt/Al 2 O 3 sample nitrites, nitrates and NO 2 δ+ species were mainly formed, showing a moderate thermal stability. Barium markedly increased the amount and stability of the stored NO x species, which were bidentate and monodentate nitrites and, in minor amounts, nitrates. Nitrites were removed below 750 K and/or transformed into ionic Ba nitrates, stable up to 800-900 K. Upon NO 2 adsorption, huge amounts of nitrates, but no nitrites, were formed on all the samples. Also in this case, Ba increased the amount and stability of the stored NO x species. The nature and the amounts of the stored NO x species formed upon adsorption of NO, NO/O 2 , or NO 2 were similar on Ba/Al 2 O 3 and Pt-Ba/Al 2 O 3 catalysts, whereas Pt slightly decreased their thermal stability. Bulky Ba nitrate was formed during the thermal desorption of NO 2 (and to a less extent of NO/O 2 ), inducing an extensive decomposition of the Ba carbonate or oxycarbonate phase which was detected on the calcined samples.

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The mechanism of the selective oxidation of methanol on two V-Ti oxide catalyst samples, prepared by impregnation and coprecipitation techniques, respectively, is investigated. The interaction of methanol and its oxidation products (i.e., formaldehyde, dimethoxymethane, formic acid, and methyl formate) is studied by FT-IR spectroscopy and compared with the results of flow reactor measurements performed at different temperatures, contact times, and methanol/oxygen molar feed ratios. The data are interpreted on the basis of a reaction mechanism which involves the following steps: (i) condensation of methanol with surface VOH groups; (ii) H abstraction from methoxy groups leading to coordinated formaldehyde; (iii) formation of dioxymethylene species by interaction of adsorbed formaldehyde with nucelophilic sites; (iv) reaction of dioxymethylene species with methanol to give dimethoxymethane; (v) successive oxidation of dioxymethylene groups to formate ions; (vi) reaction of these ions either with methanol to produce methyl formate or with water to give formic acid; (vii) decomposition of formate species to produce carbon monoxide; (viii) parallel oxidation of methanol to carbon dioxide. The behaviors of the surface species are compared with those monitored on other systems and the catalyst requirements for the title reaction are discussed.

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