Contact dynamics for a solid-solid reaction mediated by gas-phase oxygen

Abstract

Ceria-based catalysts with different topological and textural properties have been prepared to study the role of the soot-catalyst contact on the soot oxidation reaction. The physico-chemical features of the catalysts have been investigated by means of complementary techniques, such as powder XRD, N₂ physisorption at -196 °C, optical microscopy at variable temperature, FESEM, TEM, and thermogravimetric analysis.As a whole, the best catalytic activity has been obtained with the CeO₂-nanocubes (denoted to as "Ce-NC") because of their higher intrinsic reactivity. On the other hand, high-surface area materials prepared by the cerium nitrate decomposition (denoted to as "Ce-ND") or hydrothermal route (CeO₂-stars, referred to as "Ce-SAS") resulted less effective toward the soot combustion, confirming the surface-sensitivity for this reaction.Moreover, it has been proven a higher dependence of the oxidation activity on the catalyst-to-soot ratio (wt./wt.) for the nanostructured catalyst (Ce-NC) exhibiting the lowest BET specific surface area (S_BET = 4 m² g^-1). On the other hand, the accessible (real) surface area, at variance of the BET surface area, seems to play a relevant role for this solid-solid reaction mediated by gas-phase oxygen.