Abstract
In the present work, ceria, ceria-zirconia (Ce = 80 at.%, Zr = 20 at.%), ceria praseodymia (Ce = 80 at.%, Pr = 20 at.%) and ceria-zirconia-praseodymia catalysts (Ce = 80 at.%, Zr = 10 at.% and Pr = 10 at.%) have been prepared by the multi-inlet vortex reactor (MIVR). For each set of samples, two inlet flow rates have been used during the synthesis (namely, 2 ml min−1 , and 20 ml min−1) in order to obtain different particle sizes. Catalytic activity of the prepared materials has been investigated for CO and soot oxidation reactions. As a result, when the catalysts exhibit similar crystallite sizes (in the 7.7–8.8 nm range), it is possible to observe a direct correlation between the Ov/F2g vibrational band intensity ratios and the catalytic performance for the CO oxidation. This means that structural (superficial) defects play a key role for this process. The incorporation of Zr and Pr species into the ceria lattice increases the population of structural defects, as measured by Raman spectroscopy, according to the order: CeO2 < Ce80Zr20 < Ce80Zr10Pr10 < Ce80Pr20. On the other hand, the presence of zirconium and praseodymium into the ceria lattice does not have a direct beneficial effect on the soot oxidation activity for these catalysts, in contrast with nanostructured ones (e.g., Ce–Zr–O nanopolyhedra, Ce–Pr–O nanocubes) described elsewhere (Andana et al. Appl. Catal. B 197: 125–137, 2016; Piumetti et al., Appl Catal B 180: 271-282, 2016).
Highlights
During the last few decades, ceria-based catalysts and related materials have extensively been investigated, thanks to their interesting redox properties that allow rapid oxygen intake-uptake [1,2,3]
In soot combustion, whose noncatalytic oxidation occurs at temperatures above 550 °C [11], a good contact between the catalyst and soot particles is necessary to considerably reduce the oxidation temperatures; this is normally attained by tuning ceria morphology at the nanoscale size [7, 8, 12,13,14]
Among the various elements used as dopants for ceria catalysts, zirconium and praseodymium have received a major interest over the last few years [6, 12, 16, 19]
Summary
During the last few decades, ceria-based catalysts and related materials have extensively been investigated, thanks to their interesting redox properties that allow rapid oxygen intake-uptake [1,2,3]. In CO oxidation, the oxygen storage capacity (OSC) plays a key role since this reaction catalyzed by ceria takes place through the Mars-van Krevelen (MvK)-type mechanism [3,4,5, 15]. According to this mechanism, oxygen vacancies (Ov) are created during the CO oxidation at catalyst surface, followed by oxygen refilling from the bulk phase. Zr or Pr species embedded into the ceria lattice promote the formation of crystallographic
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