A facile method for the synthesis of graphene-like 2D metal oxides and their excellent catalytic application in the hydrogenation of nitroarenes

Abstract

Graphene-like two-dimensional (2D) metal oxides in the form of nanosheets (NSs) often exhibit superior performance in many applications in comparison with their bulk counterparts, owing to their unique electronic and physicochemical properties arising from their layered 2D structure; however, it is still a great challenge to produce 2D metal oxides in a facile way, especially for non-layered metal oxides. In the present work, a modified evaporation induced self-assembly (EISA) method was developed to synthesize graphene-like CeO₂ nanosheets (NS-CeO₂). Moreover, the EISA method is proved to be rather universal and a series of other single and mixed metal oxides, including TiO₂, ZrO₂, CoO_x, NiO, Al₂O₃, CuO, CuO–ZrO₂, MnO_x–Al₂O₃, FeO_x–CoO_x, Cr₂O₃–ZnO, CeO₂–ZrO₂, CeO₂–CuO, CeO₂–CoO_x, CeO₂–La₂O₃, CeO₂–FeO_x, CeO₂–MnO_x, CeO₂–ZnO, CeO₂–Al₂O₃, CeO₂–NiO, CeO₂–Cr₂O₃, CeO₂–TiO₂, MnO_x–CeO₂–ZrO₂, and CuO–CeO₂–ZrO₂, can be successfully prepared in the form of nanosheets with tunable pore structure and sheet thickness by using this method. The catalytic application of the graphene-like metal oxides was considered and the results illustrate that the CeO₂ nanosheets decorated with Pd clusters (Pd/NS-CeO₂) exhibit excellent catalytic performance in the hydrogenation of nitroarenes under mild conditions; over them, nitrobenzene can be completely converted to aniline even at room temperature in a short time. A series of characterization results combined with DFT calculations demonstrate that the CeO₂ nanosheets are enriched with surface defects and Ce³⁺ species, which can promote the adsorption and activation of nitroarenes. The present work brings forward a facile and effective approach to synthesize graphene-like metal oxides with superior catalytic performance; besides, the results obtained in this work are also rather helpful to clarify the relationship between the 2D structure and performance of the Pd/NS-CeO₂ catalyst in the hydrogenation of nitroarenes.