CeO2-based catalysts with engineered morphologies for soot oxidation to enhance soot-catalyst contact

Abstract

As morphology plays a relevant role in solid/solid catalysis, where the number of contact points is a critical feature in this kind of reaction, three different ceria morphologies have been investigated in this work as soot oxidation catalysts: ceria nanofibers, which can become organized as a catalytic network inside diesel particulate filter channels and thus trap soot particles at several contact points but have a very low specific surface area (4 m2/g); solution combustion synthesis ceria, which has an uncontrolled morphology but a specific surface area of 31 m2/g; and three-dimensional self-assembled (SA) ceria stars, which have both high specific surface area (105 m2/g) and a high availability of contact points. A high microporous volume of 0.03 cm3/g and a finer crystallite size compared to the other morphologies suggested that self-assembled stars could improve their redox cycling capability and their soot oxidation properties. In this comparison, self-assembled stars have shown the best tendency towards soot oxidation, and the temperature of non-catalytic soot oxidation has dropped from 614°C to 403°C in tight and to 552°C in loose contact conditions, respectively. As far as the loose contact results are concerned, this condition being the most realistic and hence the most significant, self-assembled stars have exhibited the lowest T10% onset temperature of this trio (even after ageing), thus proving their higher intrinsic activity. Furthermore, the three-dimensional shape of self-assembled stars may involve more of the soot cake layer than the solution combustion synthesis or nanofibers of ceria and thus enhance the total number of contact points. The results obtained through this work have encouraged our efforts to understand soot oxidation and to transpose these results to real diesel particulate filters.

Contact dynamics for a solid–solid reaction mediated by gas-phase oxygen: Study on the soot oxidation over ceria-based catalysts

“…On the other hand, the Ce-SAS sample does not significantly reduce the T 0 value with respect to the uncatalyzed soot oxidation (T 0 = 616 • C), although it affects the onset temperature due to its high BET surface area, as described elsewhere [19,25]. Moreover, several peaks appear in the low-temperature range (<350 • C) as consequence of the high BET surface area of this catalyst.…”

“…500 nm). These micro-aggregates preferentially expose (310), (100), and (110) planes [25]. Finally, TEM images of the Ce-ND sample ( Fig.…”

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

“…Limited diversity of investigated nanocrystals shapes are a direct consequence of the limited possibilities of synthesis protocols. However, we are aware that morphology is an important factor influencing catalysts activity [33,34]. In our case nanoneedle type crystals of cryptomelane exhibit high soot oxidation activity related to the electronic excitation of the potassium promoter at elevated temperatures [35].…”

Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity

“…In this regard, it is known that the morphology of a catalyst plays a relevant role in the degree of contact between the catalyst itself and soot, although this effect is not easy to predict [19] or optimize [37,38]. However, it is interesting to note that when NO is introduced, the slope of the T 10% curve generally increases, although marginally, as the NO oxidation promotes a reduction in T 10% which, as previously mentioned, is influenced by the abundance of defects.…”

“…A set of nine CeO 2 samples was prepared, via a hydrothermal procedure, using different temperatures (150, 170, and 180 • C) and NaOH concentrations (4, 8, and 10 M) [18,37]. During a typical synthesis, appropriate amounts of NaOH and Ce(NO 3 ) 3 ·6H 2 O (99%, Sigma-Aldrich, Steinheim, Germany) were dissolved in 70 mL and 10 mL of bi-distilled water, respectively.…”