Composites of palladium nanoparticles and graphene oxide as a highly active and reusable catalyst for the hydrogenation of nitroarenes
Graphical abstract
Introduction
Aniline and its derivatives are very common in not only the production of paints but also in the chemical industry as organic intermediates, in polymer production, the pharmaceutical industry, and agricultural chemicals [1]. When aromatic nitro compounds become reduced, anilines formation occurs [2]. Hydrogen gas is usually the reactive of choice for hydrogenation of nitroarenes [[3], [4], [5], [6]]. However, some difficulties in the utilization such as the need for special equipment, transport of hydrogen gas, storage, and group tolerance are the main problems.
The transfer hydrogenation reaction is the process of adding hydrogen to a hydrogen accepting molecule from a source other than H2. This method is used under standard conditions without the need for hydrogen gas [7]. Hydrogen donors, such as N2H4·H2O [8], NaBH4 [9], HCOOH (FA) [10], NH3.BH3 [10,11] and C2H5OH [12] are used in the transfer hydrogenation hydrogen process. These hydrogen donors have many properties, such as nontoxicity, high energy density, and regeneration of CO2 (carbon dioxide) by hydrogenation. As a result of these characteristics, these materials are preferred as promising, sustainable, and safe hydrogen storage material [13]. In order to use these hydrogen storage materials, the scientist needs some heterogeneous or homogeneous catalysts. Generally, these types of catalysts provide a wide array of application areas in industrial and organic chemistry [14,15]. In chemical processes, hydrogenation reactions deliver the most essential transformations, thus, these reactions are considered remarkable applications [7,16,17]. In previous studies, hydrogenation of vegetable oils [18], hydrogenation of alkenes [19], and nitro reduction with different catalytic systems were reported [20,21].
In this study, a novel monodisperse composite of palladium and graphene oxide (CPG) was used as a catalyst in the transfer hydrogenation of nitro compounds. For this reason, CPG was evaluated for the reduction of nitro groups in the presence of sodium borohydride (NaBH4) and hydrazine monohydrate (N2H4.H2O).
Section snippets
General
All chemical substances were purchased from commercial suppliers (Merck, Sigma-Aldrich, and Fluka) and used as received. The 1H and 13C NMR spectra were obtained on VARIAN Infinityplus 300 and at 75 Hz, respectively and tetramethylsilane (TMS) was used as the internal standard. Thin-layer chromatography (TLC) plates Cell-300-25 were provided from Macherey-Nagel and visualized under UV-light (254 or 360 nm). Centrifugation was performed with Nüve NF 200 Bench top Centrifuge. The details of the
The characterization of CPG
TEM images of CPG were examined in order to see the morphology of the prepared catalyst. As can be seen in Fig. 1, the palladium nanoparticles are homogeneously distributed over graphene oxide. Furthermore, the mean particle size of the Pd nanoparticles was found to be 3.86 ± 0.72. HR-TEM image also indicated that the atomic lattice fringe of CPG was 0.22 nm which is in good agreement with the nominal value of Pd (Fig. 1) [22].
The X-ray diffraction pattern of CPG is shown in Fig. 2. The pattern
Conclusion
The composites of graphene oxide and palladium nanoparticles were synthesized by a facile route and characterized by several analytical techniques such as XRD, XPS, TEM, Raman, etc. These techniques showed most of the properties of the prepared nanocatalyst such as the crystalline structure, morphology, oxidation state of the metals, etc. The fully characterized nanocatalysts were utilized for the nitro reduction reaction by using NaBH4 or N2H4. Catalytic transfer hydrogenation of the
CRediT authorship contribution statement
Hayriye Genc Bilgicli: Writing - original draft, Writing - review & editing. Kemal Cellat: Writing - original draft, Writing - review & editing. Fatih Sen: Supervision, Writing - original draft, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The author(s) declare no competing interests. One of the authors would like to thank to Dumlupinar University BAP grant (2014-05).
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