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Magnetic core-shell Fe₃O₄@Cu₂O and Fe₃O₄@Cu₂O-Cu materials as catalysts for aerobic oxidation of benzylic alcohols assisted by TEMPO and N-methylimidazole.

ABSTRACT: In this work, core-shell Fe₃O₄@Cu₂O and Fe₃O₄@Cu₂O-Cu nanomaterials for aerobic oxidation of benzylic alcohols are reported with 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and N-methylimidazole (NMI) as the co-catalysts. To anchor Cu₂O nanoparticles around the magnetic particles under solvothermal conditions, the magnetic material Fe₃O₄ was modified by grafting a layer of l-lysine (l-Lys) to introduce -NH₂ groups at the surface of the magnetic particles. With amine groups as the anchor, Cu(NO₃)₂ was used to co-precipitate the desired Cu₂O by using ethylene glycol as the reducing agent. Prolonging the reaction time would lead to over-reduced forms of the magnetic materials in the presence of copper, Fe₃O₄@Cu₂O-Cu. The nanomaterials and its precursors were fully characterized by a variety of spectroscopic techniques. In combination with both TEMPO and NMI, these materials showed excellent catalytic activities in aerobic oxidation of benzylic alcohols under ambient conditions. For most of the benzylic alcohols, the conversion into aldehydes was nearly quantitative with aldehydes as the sole product. The materials were recyclable and robust. Up to 7 repeat runs, its activity dropped less than 10%. The over-reduced materials, Fe₃O₄@Cu₂O-Cu, exhibited slightly better performance in durability. The magnetic properties allowed easy separation after reaction by simply applying an external magnet.

SUBMITTER: Xu B

PROVIDER: S-EPMC9055318 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Magnetic core-shell Fe3O4@Cu2O and Fe3O4@Cu2O-Cu materials as catalysts for aerobic oxidation of benzylic alcohols assisted by TEMPO and N-methylimidazole.

Xu Binyu B Senthilkumar Samuthirarajan S Zhong Wei W Shen Zhongquan Z Lu Chunxin C Liu Xiaoming X

RSC advances 20200710 44

In this work, core-shell Fe3O4@Cu2O and Fe3O4@Cu2O-Cu nanomaterials for aerobic oxidation of benzylic alcohols are reported with 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and N-methylimidazole (NMI) as the co-catalysts. To anchor Cu2O nanoparticles around the magnetic particles under solvothermal conditions, the magnetic material Fe3O4 was modified by grafting a layer of l-lysine ( ...[more]

PMID: 35519734

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Project description:The development of efficient catalysts is one of the main challenges in CO2 conversion to valuable chemicals and fuels. Herein, inspired by the knowledge of the thermocatalytic (TC) processes, Cu/ZnO and bare Cu catalysts enriched with Cu+1 were studied to convert CO2 via the electrocatalytic (EC) pathway. Integrating Cu with ZnO (a CO-generation catalyst) is a strategy explored in the EC CO2 reduction to reduce the kinetic barrier and enhance C-C coupling to obtain C2+ chemicals and energy carriers. Herein, ethanol was produced with the Cu/ZnO catalyst, reaching a productivity of about 5.27 mmol·gcat-1·h-1 in a liquid-phase configuration at ambient conditions. In contrast, bare copper preferentially produced C1 products like formate and methanol. During CO2 hydrogenation, a methanol selectivity close to 100% was achieved with the Cu/ZnO catalysts at 200 °C, a value that decreased at higher temperatures (i.e., 23% at 300 °C) because of thermodynamic limitations. The methanol productivity increased to approximately 1.4 mmol·gcat-1·h-1 at 300 °C. Ex situ characterizations after testing confirmed the potential of adding ZnO in Cu-based materials to stabilize the Cu1+/Cu0 interface at the electrocatalyst surface because of Zn and O enrichment by an amorphous zinc oxide matrix; while in the TC process, Cu0 and crystalline ZnO prevailed under CO2 hydrogenation conditions. It is envisioned that the lower *CO binding energy at the Cu0 catalyst surface in the TC process than in the Cu1+ present in the EC one leads to preferential CO and methanol production in the TC system. Instead, our EC results revealed that an optimum local CO production at the ZnO surface in tandem with a high amount of superficial Cu1+ + Cu0 species induces ethanol formation by ensuring an appropriate local amount of *CO intermediates and their further dimerization to generate C2+ products. Optimizing the ZnO loading on Cu is proposed to tune the catalyst surface properties and the formation of more reduced CO2 conversion products.

Dataset Information

Magnetic core-shell Fe₃O₄@Cu₂O and Fe₃O₄@Cu₂O-Cu materials as catalysts for aerobic oxidation of benzylic alcohols assisted by TEMPO and N-methylimidazole.

Publications

Magnetic core-shell Fe<sub>3</sub>O<sub>4</sub>@Cu<sub>2</sub>O and Fe<sub>3</sub>O<sub>4</sub>@Cu<sub>2</sub>O-Cu materials as catalysts for aerobic oxidation of benzylic alcohols assisted by TEMPO and <i>N</i>-methylimidazole.

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