Investigation of a series of CeO2 supported Co3O4 catalysts for NO reduction by CO

Taejin  Kim, Stony Brook University

Abstract

Nitrogen oxides (NO_x) are a main contributor—in addition to hydrocarbons (HC), carbon monoxide (CO), sulfur oxides (SO_x), and particulate matter (PM)—to global air pollution ^[1]. Significant investigations have been performed for catalytic NO_x reduction resulting in technologies such as NH₃-SCR and NO_x storage and reduction ^[2]. In the last several decades, platinum group metals (PGMs) and zeolites have been extensively applied to NO_x abatement ^[3]. Although these catalysts exhibit a high level of catalytic activity, NO_x decomposition over PGMs and zeolites has some practical issues such as high cost and high light-off temperature ^[4]. To resolve these issues, transition metal oxide catalysts have been investigated for low temperature NO_x decomposition reaction by CO with varied O₂ concentrations, which is a primary reaction in three-way catalysis (TWC).

In this study, a series of ceria supported cobalt oxide catalysts were prepared by incipient wetness impregnation method with different metal oxide loadings (0.5 wt%-30 wt%) for NO reduction by CO. Catalytic activity, catalyst physicochemical property, electronic and molecular structure were investigated by XANES, EXAFS, FTIR, BET, X-ray diffraction (XRD) and Raman spectroscopy. Using the Raman spectroscopy, it was observed that the monolayer coverage for CoOx/CeO₂ is 5~6wt% (2.3~2.8 Co/nm²), while XRD shows Co₃O₄ crystalline peak at 10wt% (4.9 Co/nm²). The XAS results obtained on Co-ceria samples with high and low Co loadings show that 10 wt% sample is very close to that of Co₃O₄ in both XANES and EXAFS region, suggesting Co has similar valence state and atomic structure as that in Co₃O₄. Observation found that 6 wt% and 10 wt% Co₃O₄/CeO₂ catalysts show highest NO and CO conversion (~80%) at ~300 ^oC. In this presentation, addition to cobalt oxide loading effect, calcination temperature effect, concentration of O₂ effect, and catalyst stabilities will be shown and discussed.

ACKNOWLEDGMENT: We gratefully acknowledge the financial support for this study from the Department of Materials Science & Chemical Engineering at Stony Brook University through start-up research funding.

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