CuxO/CeO2 Nanocomposites: Synthesis and Reactivity with NO
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1074-I03-39
CuxO/CeO2 Nanocomposites: Synthesis and Reactivity with NO Federico Scopel, Alessandro Galenda, Marta Maria Natile, and Antonella Glisenti Scienze Chimiche, Università di Padova, via Marzolo, 1, Padova, 35131, Italy ABSTRACT CuxO/CeO2 nanocomposite powders were prepared by wet impregnation of nanosized ceria powder (Cu/Ce nominal atomic ratio from 0.05 to 0.5). XP analysis reveals the presence of Cu2O in the samples with lower Cu/Ce atomic ratio whereas CuO is prevalent in the samples richer in copper. The surface Cu/Ce atomic ratio obtained from XPS data is always higher than the nominal one suggesting the surface segregation of copper. A plateau value (0.9-1.0) is reached for the samples with a nominal Cu/Ce atomic ratio 0.2 suggesting an island growing mechanism. The nanocomposite samples and the supporting ceria were exposed to a NO+CO mixture (2% CO, 2% NO, 96% He) and the reactivity was investigated by means of DRIFT spectroscopy and QMS. At 523 K (i.e. the temperature at which the nanocatalysts activity is higher) the capability for NO reduction increases with increasing the Cu/Ce atomic ratio. INTRODUCTION NO reduction can be pursued with different reductants: catalytic reduction with ammonia, CO and/or H2 and with hydrocarbons. The reaction with CO, in particular, is one of the most investigated for the automotive exhaust control. Among the investigated catalysts, oxide based materials and, particularly, copper containing oxides are probably the most promising. In recent years copper promoted ceria has attracted much attention owing to the unique catalytic performance, mainly in oxidation reactions. The high activity in CO oxidation, as an example, is attributed to the Cu2+/Cu+ redox couples of highly dispersed copper species but the role played by the oxygen storage capacity of ceria is also relevant. Herein, we deal with copper oxide/ceria nanocomposite powders obtained by wet impregnation of nanoscale ceria. A series of nanocomposites characterized by increasing values of the Cu/Ce atomic ratio (from 0.05 to 0.5) is prepared and investigated; the activity and selectivity of copper promoted ceria catalysts in the CO oxidation is already claimed but the influence of the presence of NO still needs to be studied. EXPERIMENTAL CeO2 was prepared by precipitation at 273 K from a basic solution of cerium nitrate hexahydrate, (Strem Chemicals – 99.9%) and treated at 473 K for 5 h..[1] Five CuxO/CeO2 nanocomposites were obtained depositing, by wet impregnation different amounts of copper oxide on ceria powders. Ceria was impregnated with aqueous solutions containing increasing quantities of Cu(NO3)2⋅6H2O (Strem Chemicals – 99.9%): [Cu/Ce]nominal = 0.05; 0.1; 0.2; 0.35; 0.5; (nominal atomic ratio were obtained from the precursor weighted quantities). The obtained suspensions were maintained under stirring for two days and then kept in rest for one day. Water was evaporated in air at 338 K and the solids were calcined at 923 K for 4 h (in air). This preparation procedure, repeated several times, resulte
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