Structure-Sensitive Reactions Over Ceria-Based Nanocatalysts: The Catalytic Oxidation of Soot and Carbon Monoxide

Paper #:
  • 2017-24-0145

Published:
  • 2017-09-04
Abstract:
A set of CeO2 nanocatalysts with different structural properties (nanocubes, nanorods, high-surface area CeO2) was prepared to investigate the shape-dependency activity for two oxidation reactions: the soot combustion under different soot-catalyst contact conditions (namely, in “loose” and “tight” conditions) and the CO oxidation. The physico-chemical properties of the prepared materials were investigated by complementary techniques (XRD, N2-physisorption at -196 °C, H2-TPR, FESEM, TEM, micro-Raman, FT-IR, XPS). As a whole, the best performances in terms of soot combustion have been achieved for the CeO2-nanocubes (SBET = 4 m2g-1), due to the abundance of highly reactive (100) and (110) exposed surfaces. On the other hand, better results in terms of the onset of soot oxidation (T10%) have been obtained for high-surface-area materials (SBET = 75 m2g-1), thus reflecting the key role of the surface area at low reaction temperature. Activity tests have confirmed the structure-sensitivity for the soot oxidation above 410 °C or 370 °C (in “loose” or “tight” conditions, respectively). On the other hand, the reaction has appeared surface-insensitive at lower temperatures. Thus, soot oxidation over ceria can be considered a reaction that displays both surface-sensitive and surface-insensitive behavior, depending on the operating conditions. The highest CO oxidation activity has been achieved for ceria nanocubes, thus confirming the structure-sensitivity for the CO oxidation reaction over CeO2-based systems. On the other hand, high-surface CeO2 was unable to outdo the activity of nanocubes and nanorods due to the abundant presence of more stable (111) planes. In conclusion, both the oxidation reactions, kinetically described via a Mars-van Krevelen type mechanism, may exhibit a structure-sensitive behavior over Ceria-based catalysts.
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