Broccoli-like CeO2 with Hierarchical/Porous Structures, and promoted oxygen vacancy as an enhanced catalyst for catalytic diesel soot elimination

Abstract

• Ce-MOFs is adopted for fabricating broccoli-like CeO 2 (BCL-CeO 2 ). • BCL-CeO 2 shows a higher activity than commercial CeO 2 (com-CeO 2 ). • BCL-CeO 2 fully converts soot to CO 2 while com-CeO 2 produced CO. • The tight contact modeenables BCL-CeO 2 to exhibit a low T ig of 295 °C. • The mechanism of NO-assisted soot oxidation is examined by DRIFTS. • BCL-CeO 2 is recyclable with high catalytic activity for soot oxidation. While CeO 2 is a promising catalyst for soot elimination, it is essential to develop CeO 2 with higher contact areas, and reactivity for effective soot oxidation as catalytic soot oxidation is dominantly controlled by structures, and surficial properties of catalysts. In this study, a Ce-Metal organic frameworks (MOFs) consisting of Ce and trimesic acid (TA) is employed as the precursor as CeTA exhibits a unique broccoli-like hierachitecture which is transformed into CeO 2 with a hierarchical structure consisting of nanofibers of CeO 2 bundled together, forming a broccoli-like CeO 2 nanostructure. More importantly, these CeO 2 nanofibers in this broccoli-like CeO 2 (BCL-CeO 2 ) possesses porous structures, and also more oxygen vacancies, enabling BCL-CeO 2 to become a promising catalyst for soot oxidation. Thus, BCL-CeO 2 shows a much higher catalytic activity than commercial CeO 2 nanoparticle (com-CeO 2 ) for soot oxidation with a significantly lower ignition temperature (T ig ). More importantly, while soot oxidation by com-CeO 2 leads to production of CO together with CO 2 , BCL-CeO 2 can completely convert soot to CO 2 . The tight contact mode also enables BCL-CeO 2 to exhibit a very low T ig of 295 °C, whereas the existence of NO and H 2 O also enhances the soot oxidation by BCL-CeO 2 to reduce the T ig . The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the presence and transformation of nitrogen-containing intermediates. BCL-CeO 2 is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that BCL-CeO 2 is a promising and easily-prepared hierarchitectured Ce-based catalyst for soot oxidation.