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

Abstract

While CeO2 is a promising catalyst for soot elimination, it is essential to develop CeO2 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 CeO2 with a hierarchical structure consisting of nanofibers of CeO2 bundled together, forming a broccoli-like CeO 2 nanostructure. More importantly, these CeO2 nanofibers in this broccoli-like CeO2 (BCL-CeO2) possesses porous structures, and also more oxygen vacancies, enabling BCL-CeO2 to become a promising catalyst for soot oxidation. Thus, BCL-CeO2 shows a much higher catalytic activity than commercial CeO2 nanoparticle (com-CeO2) for soot oxidation with a significantly lower ignition temperature (T-ig). More importantly, while soot oxidation by com-CeO2 leads to production of CO together with CO 2 , BCL-CeO2 can completely convert soot to CO2. The tight contact mode also enables BCL-CeO2 to exhibit a very low T-ig of 295 degrees C, whereas the existence of NO and H2O also enhances the soot oxidation by BCL-CeO2 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 nitrogencontaining intermediates. BCL-CeO2 is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that BCL-CeO2 is a promising and easily-prepared hierarchitectured Ce-based catalyst for soot oxidation.