Abstract
A set of ceria, ceria-zirconia (Ce 80 at.%, Zr 20 at.%), ceria-praseodymia (Ce 80 at.%, Pr 20 at.%) and ceria-zirconia-praseodymia (Ce 80 at.%, Zr 10 at.% and Pr 10 at.%) catalysts has been prepared by the solution combustion synthesis (SCS). The effects of Zr and Pr as dopants on ceria have been studied in CO and soot oxidation reactions. All the prepared catalysts have been characterized by complementary techniques, including XRD, FESEM, N2 physisorption at −196 °C, H2-temperature-programmed reduction, and X-ray photoelectron spectroscopy to investigate the relationships between the structure and composition of materials and their catalytic performance. Better results for CO oxidation have been obtained with mixed oxides (performance scale, Ce80Zr10Pr10 > Ce80Zr20 > Ce80Pr20) rather than pure ceria, thus confirming the beneficial role of multicomponent catalysts for this prototypical reaction. Since CO oxidation occurs via a Mars-van Krevelen (MvK)-type mechanism over ceria-based catalysts, it appears that the presence of both Zr and Pr species into the ceria framework improves the oxidation activity, via collective properties, such as electrical conductivity and surface or bulk oxygen anion mobility. On the other hand, this positive effect becomes less prominent in soot oxidation, since the effect of catalyst morphology prevails.
Highlights
Ceria has extensively been investigated in many oxidation reactions, thanks to its unique redox properties that allow rapid oxygen intake-uptake [1,2,3]
A ceria-based catalyst requires a good contact with carbon soot; this is normally attained by tuning ceria morphology at a nanoscale level [7, 8, 11,12,13]
In CO oxidation, on the other hand, the oxygen storage capacity (OSC), which is high in ceria, plays the crucial role since it has been well understood that CO oxidation over ceria conforms to the Mars-van Krevelen (MvK)-type mechanism [3,4,5, 14]
Summary
Ceria has extensively been investigated in many oxidation reactions, thanks to its unique redox properties that allow rapid oxygen intake-uptake [1,2,3]. A ceria-based catalyst requires a good contact with carbon soot; this is normally attained by tuning ceria morphology at a nanoscale level [7, 8, 11,12,13]. Due to the complexity of solidgas interaction in soot oxidation reaction, the ability of ceria-based catalysts to initiate active oxygen species is strictly necessary. In CO oxidation, on the other hand, the oxygen storage capacity (OSC), which is high in ceria, plays the crucial role since it has been well understood that CO oxidation over ceria conforms to the Mars-van Krevelen (MvK)-type mechanism [3,4,5, 14] In this mechanism, oxygen vacancies are formed during the reaction with CO, followed by oxygen refilling from the bulk phase
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