FTIR Study of the Adsorption of Methanol on Clean and Ca-promoted Pd/SiO2 Catalysts.

The adsorption and decomposition of methanol on a highly dispersed supported Pd/SiO2 catalyst (2% Pd w/w) prepared via ion exchange of [Pd(NH3)4]2+ in alkaline solution, together with two Ca-promoted preparations (Ca/Pd=2 at/at), where calcium was added either to the prereduced Pd crystallites or to the diammine palladium complex, were studied by FTIR at 298–623 K. Methanol adsorbs and reacts at 298 K on Pd/SiO2. The presence of Pd on the silica surface influences slightly the processes occurring on the support, where CH3OH is mostly adsorbed molecularly at room temperature, but readily forms very stable Si–O–CH3 groups upon heating. The dissociation of methanol via both O–H and C–O bond breaking is observed on Pd. The latter scission is only detected at 653 K. At room temperature, adsorbed CH3OH decomposes easily on the Pd crystallites, to give CO multicoordinated to the metal surface. Formyl species were also found at this temperature, but they promptly disappeared, above 393 K, when the catalyst was heated. Calcium promotion, either to the prereduced Pd or to its diammine complex precursor during the preparation steps, enhances methanol decomposition onto the catalyst surface, even at room temperature. With heating, formyl groups are replaced by mono- and bi-dentate formate species, which are chemisorbed on the support and/or the promoter. Bidentate formate is not as stable as the monodentate form and its IR band vanishes above 500 K. The observed features indicate that an excellent Ca–Pd intimacy was achieved with both types of promotion strategies.Fil: Cabilla, Griselda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baltanas, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Infrared Study of the Absorption of Formic Acid on Clean and Ca-promoted Pd/SiO2 Catalysts

The adsorption and decomposition of formic acid on a highly dispersed supported Pd/SiO2 catalyst (2 wt.% Pd) prepared via ion exchange (IE) of [Pd(NH3)4]2+ in alkaline solution, together with two Ca-promoted preparations (Ca/Pd=2 at./at.) where calcium was added either to the prereduced Pd crystallites or to the diammine palladium complex, were studied by FTIR at 298–653 K. On the support, HCOOH is mostly adsorbed molecularly at room temperature, with partial dimerization, condensation and extensive hydrogen bonding, but readily decomposes, on the Pd crystallites of Pd/SiO2, via decarbonylation, to give CO multicoordinated to the metal surface, and water. With heating, formic acid decomposition is accompanied by some water gas shift as well, while CO reacts to give methyl (methane) and methoxy. Calcium promotion to both the prereduced Pd and its diammine complex precursor, enhanced HCOOH decomposition onto the catalyst surface, even at 298 K. Together with sorbed HCOOH and chemisorbed CO, mono- and bidentate formates were observed on these materials, owing to the incorporation of well-dispersed CaOxHy. These formates were readily decomposed by atomic hydrogen produced by decarbonylation/WGS of formic acid on Pd. At increasing temperatures, some carbonates (polydentate and simple) were formed, but hardly any methane was detected. On Ca–Pd/SiO2 with calcium added to prereduced Pd metal particles the extension and/or onset of all these processes was more straightforward than on the promoted Ca–Pd/SiO2 where calcium was added to diammine palladium instead, most likely owing to the combined impact of a higher dispersion of the Pd crystallites on the former preparation, and calcium oxyhydroxide decoration (CaOxHy) of the metal particles on the latter, which hamper H-spillover from them.Fil: Cabilla, Griselda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baltanas, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin