(121f) NO Reduction By CO over CeO2 Supported CoxOy Catalysts

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, the series of CeO₂ supported Co_xO_y 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, and molecular/electronic structure were investigated by FTIR, BET, Raman spectroscopy, X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). No diffraction peaks due to crystalline CoO or Co₃O₄ were observed in XRD patterns under to 10 wt%, while nanocrystaline Co₃O₄ peaks at ~610cm^-1 was observed in the Raman spectra with 6wt% sample. Both Raman and XRD spectroscopy results provided that 5~6wt% Co_xO_y /CeO₂ contains monolayer coverage. It was observed that both Co_xO_y coverage and oxidation state of Co are closely related to the NO reduction by CO. Monolayer and above monolayer coverage catalysts showed 80~90% CO and NO conversion at 300~400^oC with high N₂ and CO₂ selectivity (>90%). Based on the time on stream results, it was also observed that the crystalline Co₃O₄ nanoparticles above monolayer coverage improve the stability of catalyst.

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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