Aerobic oxidation of cyclohexane over metal-organic framework-derived Ce, Ni-modified Co 3 O 4
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Aerobic oxidation of cyclohexane over metal-organic framework-derived Ce, Ni-modified Co3O4 Enxian Yuan†, Mingqing Gu, and Panming Jian† School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, China (Received 23 December 2019 • Revised 3 March 2020 • Accepted 13 March 2020) AbstractThe heterogeneous interface in materials, due to its crucial role in catalytic reactions, has attracted much attention. Herein, we report the facile synthesis of Co3O4 and Ce/Ni-modified Co3O4 catalysts derived from ZIF-67 and their application in the aerobic oxidation of cyclohexane. The catalytic performance of the catalysts was greatly affected by the calcination temperature and molar ratio of the second metal (Ce, Ni) to Co. The catalytic performance of Co3O4 improved with the increase of the calcination temperature and reached a plateau at 400 oC due to the small-sized Co3O4 crystallites and developed pore structures. The introduction of the second metal improved the dispersion of Co3O4 and induced the creation of the oxygen vacancies at Co3O4-CeO2/NiO interface. The highest catalytic activity with 12.8% conversion and 95.5% selectivity were achieved over the Ce-Ni-modified Co3O4 catalyst with the molar ratio of Ce/Ni/Co=0.11/0.21/1.00. The superior catalytic performance of the Ce-Ni-modified catalyst can be ascribed to the highly dispersed Co3O4 crystallites and the activation of the oxygen molecules by the oxygen vacancies. Keywords: Co3O4 Catalyst, Second Metal, Cyclohexane Oxidation, Heterogeneous Interface, Oxygen Vacancy
metal (Fe, Mo and Mn) to Co on the catalytic activity has been investigated and superior catalytic performance was obtained over CoFe2O4, CoMoO4 and Mn2Co3Ox catalysts, respectively [3,15,16]. Liu et al. developed hydrotalcite-derived Co-MgAlO mixed metal oxides as catalysts for cyclohexane oxidation, and 9.1% conversion and 82.0% selectivity towards KA oil were achieved [17]. Until now, it is still challenging for the aerobic oxidation of cyclohexane to increase both the conversion (>10.0%) and selectivity towards KA oil (>90.0%) under the mild condition. Metal-organic frameworks (MOFs) have been demonstrated to be outstanding candidates for the preparation of the novel porous nanomaterials because of their specific pore structures leading to a large surface area and high porosity [18]. In recent years, MOFs acting as precursors to synthesize transition metal based functional nanomaterials have attracted immense interest [19,20]. Moreover, MOFs loaded with various metal species can also be used to prepare the hybrid metal oxides [21,22]. CeO2 is an effective oxide promoter and widely applied in the various oxidation reactions, because the oxygen vacancies derived from the Ce3+/Ce4+ redox pairs increase the mobility and storage capacity of oxygen [23]. Meanwhile, the synergistic effect between Co and Ni can promote the catalytic performance of the cobalt-nickel oxide in the oxidation reactions
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