Shape-Dependent Activity of Ceria in Soot Combustion

Abstract

In this study, a series of conventional polycrystalline ceria and single-crystalline ceria nanorods and nanocubes were prepared by hydrothermal methods, and their structural, redox, and morphological properties were investigated using XRD, SEM, HRTEM, BET, temperature-programmed reduction, and oxygen storage capacity measurements. According to HRTEM, they are characterized by exposure of different surfaces: {100} surface for nanocubes; {100}, {110}, and in part {111} for nanorods; and mainly {111} for conventional polycrystalline ceria, with a morphology dominated by {111}-enclosed octahedral particles. The presence of more-reactive exposed surfaces affects the reaction of soot oxidation positively, with an increase in activity in nanoshaped materials compared with conventional ceria. Thermal aging, although detrimental for surface area, is shown to affect morphology by promoting irregular truncation of edges and corners and development of more reactive surface combinations in all crystal shapes. It is likely that thermal treatment, starting from either cubes or octahedral particles, induces the formation of a similar particle geometry whose activity is dependent on the type of plane exposed and by the number an extension of edge and corners, thus linking reactivity of octahedral particles in conventional ceria powders with that of cubes in nanoshaped materials. The results indicate that soot oxidation is also a surface-dependent reaction, and catalyst design for this purpose should allow for surface structure morphology and its evolution against temperature.

Unraveling the structure sensitivity in methanol conversion on CeO2: A DFT+U study

“…The low energy difference and activation energy between both A2 and A3 indicate that these two intermediates may be in thermodynamic equilibrium. Therefore, the low activation energies found for this process on the different CeO 2 surfaces prove that no oxygen vacancies are needed to desorb HCH 18 O upon HCH 16 O adsorption or CH 3 16 OH dehydrogenation. …”

“…Thus, while hydrogenation takes place preferentially on (111) facet orientations, oxidation reactions are favored on the more open (110) and (100) facets exposed in rods and cubes, respectively. Ceria nanoparticles have also been found to exhibit different activity in soot combustion depending on the exposed facet [16].…”

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

“…Two types of shape-controlled nanoceria supports (nanocubes and nanorods) were prepared according to previously reported methodologies [18,[29][30][31]. For ceria nanocubes (CeO 2 -C) a NaOH solution (57.60 g NaOH dissolved in 210 mL of distilled water) was added dropwise into a Ce(NO 3 ) 3 ·6H 2 O solution (5.21 g of Ce(NO 3 ) 3 ·6H 2 O in 30 mL of distilled water) under vigorous stirring.…”

“…In fact, shapedependent activity of ceria has already been recognized in catalytic CO oxidation [11][12][13][14], NO reduction [15], water-gas shift reaction [16,17] and soot combustion [18]. The energy required to form oxygen vacancies on the {1 1 1} surface of CeO 2 is higher than those on {1 1 0} and {1 0 0} surfaces, so the concentration of oxygen vacancies on differents planes of ceria is different [19].…”

The Effect of Sr Addition in Cu- and Fe-Modified CeO2 and ZrO2 Soot Combustion Catalysts

“…Several catalytic materials were developed in the last decade [12] and the most promising are based on transition metals (Ag, Co, Cu, Mn, Fe) [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], ceria-doped materials [28][29][30][31][32][33][34][35][36], alkaline or alkaline-earth metals [37][38][39][40][41], and perovskites [42,43]. The redox capacity of transition metals, cycling between more oxidation states, can efficiently enhanced soot oxidation activity.…”