Synthesis and characterization of Ag/CeO 2 nanocomposites
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1256-N16-31
Synthesis and characterization of Ag/CeO2 nanocomposites Antonella Glisenti,a* Andrea Frasson,a Alessandro Galenda,a Matteo Ferroni,c Isabella Concina,c Marta Maria Natilea,b a
Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy;,bISTM-CNR, Via Marzolo 1, 35131 Padova, Italy; cCNR-IDASC, SENSOR Laboratory, Dipartimento di Chimica e Fisica, Via Valotti 9, 25133 Brescia, Italy ABSTRACT Two Ag/CeO2 nanocomposite samples were prepared by deposition-precipitation (Ag/Ce nominal atomic ratio = 0.03 and 0.12). XPS data suggest the possible presence of traces of Ce(III). Beside Ag (0), oxidized silver species are also revealed in the Ag/CeO2 sample with lower metal content. The deposition of metal increases surface hydroxylation and carbonation. Methanol interacts molecularly and dissociatively with the samples; oxidation products are observed from low temperature and depend on Ag content. Both the samples reveal a high activity in methanol complete oxidation; traces of partial oxidation products are observed in the sample with lower Ag content. INTRODUCTION Ceria is an important material in several fields of applied technology. Thanks to its high oxygen storage capacity and to the ability of cerium to move between Ce(IV) and Ce(III), CeO2 is an excellent catalyst in redox processes and it is used as an additive in three way catalysts. Moreover, the addition of metals was observed to increase the reactivity in oxidation and reduction reactions; silver deposition, in particular, was observed to favor methane oxidation [12], nitrogen oxide reduction [3-4] and oxygen reduction [5]. In the present paper two Ag/CeO2 powders with different compositions (Ag/Ce atomic ratios = 0.03 and 0.12) were prepared by deposition-precipitation and carefully characterized. The effect of the Ag/Ce atomic ratio on the reactivity with respect to methanol was investigated. In particular, the interaction between the alcohol and the samples was studied by means of DRIFT spectroscopy whereas for the activity in methanol oxidation both IR spectroscopy and QMS were used. Methanol oxidation is considered as a test reaction: methanol, in fact, is an important probe molecule as well as an interesting combustible for fuel cells. [6-7] Although silver promoted oxides are considered promising catalysts in several oxidation and reduction reactions, [1-5] further investigations are necessary to understand the reaction mechanisms and the influence of the active sites on reactivity. In formaldehyde oxidation, as an example, it seems that a significant role can be played by the Ag2O species present on the catalyst surface as well as by the ability of the supporting oxide to exchange oxygen [8]. EXPERIMENTAL CeO2 was prepared by precipitation from a basic solution of Ce(NO3)3·6H2O (Strem Chemicals – 99.9%). At this solution (kept at 273 K), H2O2 was added (Aldrich, 35 % wt) under vigorous stirring and then NH3 (AnalaR 25%) until pH = 10. The precipitate was dried at 353 K for 5 h in air. The supporting ceria was
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