Nanocomposites and nanomaterials
 
Development of nanosized oxide composites
for catalytic CO oxidation
Lutsenko L.V., Oleksenko L.P., Ripko O.P., Fedorenko G.V.
Chemical Department, Taras Shevchenko National University of Kyiv
64 Volodymyrska str.,  Kyiv 01061, Ukraine. 
E-mail: larisa_lutsenko@ukr.net

Well dispersed nanomaterials find wide applications as sorbents, catalysts, gas sensors in many fields of industry and human life. Composite nanomaterials containing oxides of transition and rare-earth metals are attractive catalysts of many oxidation reactions substituting noble metals. Development of preparation methods of highly dispersed materials and establishment of their optimal forming conditions are important to obtain nanosized functional materials with definite properties. In particular, methods where hydroxy carboxylic acids are used as complex-forming agents allow to obtain homogeneous well-dispersed oxide nanomaterials.
In this work, Co-,Mn-,Cu,-Ce-containing oxide nanozised materials were prepared by citrate method and influence of the composition and morphology on their catalytic activities in CO oxidation have been investigated.
The oxide materials were prepared by mixing of solutions of citric acid and metal nitrates in molar ratio metal (or metals) : citric acid = 1 : 2 and following thermal treatment to remove nitrogen oxide (110 – 120 °C ) and organic precursors 2 h at 360 °C). Finally, individual metals oxides MxOy (M = Co, Mn, Cu, Ce), binary oxides and composites containing ternary Co–Mn–Ce-oxides and Co–Cu–Ce-oxides were synthesized.
Study of catalytic activity showed that among individual oxides Со3O4 is the most active (T100 = 160 °C). In the case of mixed composites the samples enriched with Co exhibited better catalytic performance. The activities of more active catalysts varied in the order: 
Co:Mn:Ce(10:1:1)> Co:Mn:Ce(10:1:2) > Co:Cu:Ce(10:1:1)>Co:Ce(10:1). 
It is shown that the doping of cobalt-containing catalysts with manganese, copper and cerium results in the well-dispersed state of Со3O4 (according to XRD, crystallite sizes are 13–17 nm) and the formation of greater amount of oxygen vacancies at oxide interfaces. The presence of the active oxygen species formed on the interfaces facilitates high catalytic activity of the oxide composites.