Enhanced Catalytic Soot Oxidation by Ce-Based MOF-Derived Ceria Nano-Bar with Promoted Oxygen Vacancy

Yu-Chih Tsai,Jechan Lee,Eilhann Kwon,Siming You,Pei-Syuan Hsu,Kun-Yi Andrew Lin,Wen Da Oh,Chao-Wei Huang,Nguyen Nhat Huy

doi:10.3390/catal11091128

Abstract

As CeO2 is a useful catalyst for soot elimination, it is important to develop CeO2 with higher contact areas, and reactivities for efficient soot oxidation and catalytic soot oxidation are basically controlled by structures and surface properties of catalysts. Herein, a Ce-Metal organic framework (MOFs) consisting of Ce and benzene-1,3,5-tricarboxylic acid (H3BTC) is employed as the precursor as CeBTC exhibits a unique bar-like high-aspect-ratio morphology, which is then transformed into CeO2 with a nanoscale bar-like configuration. More importantly, this CeO2 nanobar (CeONB) possesses porou, and even hollow structures, as well as more oxygen vacancies, enabling CeONB to become a promising catalyst for soot oxidation. Thus, CeONB shows a much higher catalytic activity than commercial CeO2 nanoparticle (comCeO) for soot oxidation with a significantly lower ignition temperature (Tig). Moreover, while soot oxidation by comCeO leads to production of CO together with CO2, CeONB can completely convert soot to CO2. The tight contact mode also enables CeONB to exhibit a very low Tig of 310 °C, whereas the existence of NO also enhances the soot oxidation by CeONB to reduce the Tig. The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the formation and transformation of nitrogen-containing intermediates. CeONB is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that CeONB is a promising and easily prepared high-aspect-ratio Ce-based catalyst for soot oxidation.

Highlights

Catalytic decomposition of soot has been regarded as a key step for Catalysts 2021, 11, 1128 emission of diesel engines, and soot collected inside PDFs must be decomposed in order to regenerate PDFs
Characterization of CeO2 nanobar (CeONB) could be still observed with relatively high aspect ratios
Without other noticeable elements, demonstrating that the resultant product from calcina(i.e., CeBTC [30]), indicating that the coordination of Ce3+ and BTC can afford the bar-like tion of Ce-metal oxides ganicdesired frameworks (MOFs) should only consist of Ce, and O

Summary

Introduction

Soot is even considered as a toxic contaminant in view of its carcinogenicity [1]; it is critical to prevent emission of soot into the environment. To this end, diesel particulate filters (PDFs) have been frequently adopted to remove soot particles from the exhaust emission of diesel engines, and soot collected inside PDFs must be decomposed in order to regenerate. Catalytic decomposition of soot has been regarded as a key step for eliminating soot [2,3,4,5], and catalysts for soot oxidation at lower temperatures and higher reaction rates are highly crucial [2]

Methods

Results

Conclusion