Although the copper oxide (CuO) nanostructures have been reported to exhibit efficacy as catalyst in various oxidation and reduction reactions, the origin of the catalytic activity still remains ambiguous and debatable. In this study, Zinnia like aggregates made up of nanopetals (S1) and Marigold like aggerates made up of nanocubes (S3); these two types of CuO nanocatalysts were synthesized through simple chemical co-precipitation route using copper acetate as precursor and air calcination of the as-prepared sample at a certain temperature respectively. The catalytic properties of the nanocataltysts were studied in 4-Nitrophenol (4-NP) reduction and aerobic oxidation of benzyl alcohol (BZA). In spite of having low surface area obtained from BET, the calcined CuO nancatalyst (S3) found to possess better catalytic activity in both oxidation and reduction in comparison to the as-prepared CuO nanoflower (S1). Different kinds of surface oxygen species as well as surface oxygen vacancies were discriminated by X-ray photo electron spectroscopy (XPS) and it was found that the efficient surface reduction leads to the formation of more surface oxygen vacancies and thus distinctly enhance the amount of low coordinated surface adsorbed oxygen species, that are responsible for the enhanced catalytic activity of the calcined CuO nanocatalyst. Furthermore, combining UV-Vis, XPS, EPR, Raman, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), the structure−activity relationship between surface oxygen vacancies/species and catalytic performance was systematically investigated. It was observed that the generation of surface oxygen species/oxygen vacancies was depended on the morphology of the nanostructures where exposed reactive facet leads to generate more surface oxygen species enabling high catalytic performance observed in case of calcined CuO nanocatalyst. By quantitively corelating the amount of specific oxygen species and oxygen vacancies with the reaction rates, the catalytic roles of different oxygen species/oxygen vacancies in oxidation and reduction reactions were to be clarified. The present work illuminates one of the unique mechanistic approach of catalytic reactions toward the understanding of the surface phenomena of CuO, a reducible metal oxide attributed to their catalytic effectiveness.

Oxygen vacancy enhanced catalytic oxidation and reduction on the surface of CuO nanostructures: Insights into the structure-activity relationship

ACS Spring Meeting 2021

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