Catalytic activity of maghemite supported palladium catalyst in nitrobenzene hydrogenation

Viktória Hajdu,Gábor Muránszky,Ádám Prekob,Béla Fiser,István Kocserha,Zoltán Kónya,Béla Viskolcz,László Vanyorek

doi:10.1007/s11144-019-01719-1

Abstract

A maghemite supported palladium catalyst was prepared and tested in nitrobenzene hydrogenation. The catalyst support was made by a newly developed combined technique, where sonochemical treatment and combustion have been used. As a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated in polyethylene glycol by high-intensity ultrasound cavitation to get a homogeneous dispersion, then the product was combusted. The produced powder contained maghemite nanoparticles with 21.8 nm average particle size. In the second step of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+ ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active palladium was formed. The prepared maghemite supported Pd catalyst have been tested in nitrobenzene hydrogenation at three different temperatures (283 K, 293 K and 303 K) and constant pressure (20 bar). At 293 K and 303 K, the conversion and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the selectivity was only 73% at 273 K because the intermediate species (azoxybenzene and nitrosobenzene) have not been transformed to aniline. All in all, the prepared catalyst is successfully applied in nitrobenzene hydrogenation and easily separable from the reaction media.

Highlights

Several different complex catalysts have been successfully applied in the hydrogenation of nitro groups, such as carbon (C), silica (SiO2) or alumina (Al2O3) supported Pd, Pt, Ru, Rh, Ni, Fe or bimetallic systems [1,2,3,4,5,6,7,8,9,10,11,12,13]
The reduction of palladium ions to elemental Pd have been confirmed by X-ray diffraction (XRD) measurements (Fig. 1a)
The catalyst is in an active form immediately after the production of the Pd/maghemite nanocomposite, as the sonochemical treatment initiated the involvement of the dispersion media in the reduction of palladium ions to elemental palladium particles (Pd0)

Summary

Introduction

Several different complex catalysts have been successfully applied in the hydrogenation of nitro groups, such as carbon (C), silica (SiO2) or alumina (Al2O3) supported Pd, Pt, Ru, Rh, Ni, Fe or bimetallic systems [1,2,3,4,5,6,7,8,9,10,11,12,13]. Magnetic iron oxides can be combined with different layered double hydroxides (Fe3O4-LDH), complex magnesium silicates (Fe3O4-sepiolite) and hydroxyapatite (γ-Fe2O3-HAP) to use as a support for Pd and these catalytic systems can be applied to catalyze the Heck reaction between iodobenzene and styrene, and the reduction of nitroarenes and nitrobenzene [22,23,24]. In the case of Pd ions, the activation (reduction) can be done on the supports in aqueous solution by molecular hydrogen (6 atm, 75 °C) or by using NaBH4 in ethanol but the ethylene glycol is efficient [21, 24, 29]. Owing to the magnetic properties of the maghemite, this is a remarkable catalyst support in liquid phase hydrogenation because the catalyst separated from the reaction media by magnetic field.

Results and discussion

Conclusion

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