Application of NiCo2O4 as a catalyst in the conversion of p-nitrophenol to p-aminophenol

doi:10.1016/j.matlet.2008.05.028

Materials Letters

Volume 62, Issue 23, 31 August 2008, Pages 3900-3902

https://doi.org/10.1016/j.matlet.2008.05.028 Get rights and content

Abstract

Transition metal containing spinel structure type oxides exhibit characteristic structural, electrical, magnetic and catalytic properties. Present work investigated a novel application of nickel and cobalt containing spinel oxide (NiCo₂O₄) in the conversion of p-nitrophenol to p-aminophenol. The oxide compound was synthesized by citrate gel method and characterized by powder X-ray diffraction method and scanning electron microscopy. The conversion process involved room temperature hydrogenation of p-nitrophenol by aqueous sodium borohydride. Powder nickel cobalt oxide was used as a catalyst. The reduction of p-nitrophenol has been monitored by UV–VIS and IR spectroscopic analysis. Complete conversion of the nitro compound to amino compound was achieved within a minute.

Introduction

Spinel structure type oxides of general formula AB₂O₄ containing 3d metal ions have been studied as catalysts for many organic reactions. Some of the spinel oxides catalyzed reactions are summarized here. Study of decomposition of N₂O to N₂ was reported by Russo et al. [1]. Photocatalytic ability of CuM₂O₄ (M = Al, Cr, Mn, Fe and Co) was evaluated for the evolution of H₂ [2]. Cu_0.5Co_0.5Fe₂O₄ was used as catalyst in the synthesis of orthoalkyl phenols [3].

The role of Cu_xMn_3 − xO₄ in the methylation of phenol was investigated by Sathyanarayana Reddy et al. [4]. Ni, Mn, Fe containing spinel oxides have been reported as catalysts for liquid phase Friedel–Crafts acylation reaction [5]. Various chemical reactions such as dehydrogenation of hydrocarbons [6], decomposition of alcohols and hydrogen peroxide [7], oxidation of various compounds such as CO [8], selective oxidation of styrene [9] etc. involve spinel oxides as catalysts.

p-aminophenol is an important intermediate in the manufacture of pharmaceuticals such as paracetamol, acetanilide, phenacetin etc. The compound finds its application as a photographic developer, corrosion inhibitor and anticorrosion — lubricating agent, as a dyeing agent [10] etc. Due to the significance of p-aminophenol, there is a demand for direct catalytic hydrogenation of p-nitrophenol.

In the hydrogenation of p-nitrophenol, conventional methods involve iron-acid reducing agent [11]. Other reagents containing Zn, Al, Sn etc. [12] have been reported. Such processes associated with the formation of huge amounts of undesirable metal oxide wastes. Hence, various alternative methods have been reported. Precious metals such as Pd, Pt etc. have been used in the catalytic hydrogenation of p-nitrophenol [10]. Goswami et al. [13] reported the reduction of p-nitrophenol using hydrazine as reducing agent and Raney nickel catalyst in ethanol water solvent. Nanosized nickel catalysed synthesis of p-aminophenol was reported by Du et al. [14]. Recently, p-nitrophenol hydrogenation in the presence of TiO₂ supported Ni catalyst was reported [15].

Reduction of aromatic nitro compounds using aq. NaBH₄ in the presence of a catalyst is an alternative route to the conventional reduction processes. Recently resin bound silver nanocomposite [16], bimetallic Pt–Ni nanoparticles [17] etc. have been used as catalysts in such reduction reactions. On the other hand, the reports on the metal oxide catalysts are very limited. Ghorai et al. [18] studied the application of Cu/Co molybdate and chromium phosphate as catalysts. Hence, in view of the simplicity of the reduction process using aq. NaBH₄ against extensive methodologies involving metal/HCl system, H₂ gas etc., current work explores the possibility of using Ni-, Co-containing spinel oxide, NiCo₂O₄ as a catalyst in the reduction of p-nitrophenol.

Section snippets

Synthesis of NiCo₂O₄ by citrate gel method

Chemicals such as Co(NO₃)₂·6H₂O (98%, CDH India), Ni(NO₃)₂·6H₂O (99%, CHD India), citric acid (99%, s. d. Fine. Chem. Ltd, India), and p-nitrophenol (99%, s. d. Fine. Chem. Ltd, India) were used as source materials.

1M solution of nickel nitrate and 1M solution of cobalt nitrate were mixed in 1:2 ratio. To the mixture, 1M solution of citric acid was added. The molar ratio of the metal nitrate and citric acid was maintained as 1:1. The mixed nitrate–citrate solution was stirred at 30°C for 30min

Synthesis and characterization of NiCo₂O₄

In the present study, p-nitrophenol was converted into p-aminophenol rapidly in the presence of NiCo₂O₄ using NaBH₄. The method did not involve any solvent and was carried out at room temperature. Thus, the current route provides an environmentally desirable and rapid method for the hydrogenation of p-nitrophenol.

The oxide was synthesized by citrate gel method [19], [20] due to the possibility of obtaining homogeneous and ultrafine oxide product. The addition of citric acid to the mixed nitrate

Conclusions

Spinel oxide NiCo₂O₄ was found to be an effective catalyst for the reduction of p-nitrophenol at room temperature in the absence of a solvent. The reduction rate has been enhanced substantially in comparison with the reaction carried out in the absence of the catalyst. It is presumed that the activity of the catalyst could be due to the fact that the spinel oxide accelerates the in-situ generation of hydrogen from the aqueous NaBH₄ solution.

Acknowledgement

The authors thank VIT University for providing all required facilities to carry out the experiments.

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Application of NiCo2O4 as a catalyst in the conversion of p-nitrophenol to p-aminophenol

Abstract

Introduction

Section snippets

Synthesis of NiCo2O4 by citrate gel method

Synthesis and characterization of NiCo2O4

Conclusions

Acknowledgement

Catal Today

Renew Energy

Appl Catal, A Gen

J Catal

Appl Catal, A Gen

CatalToday

J Mol Catal A, Chem

Chem Eng Sci

Appl Catal, A Gen

Chin J Chem Eng

Mater Sci Eng, B

Mater Sci Eng, B

Application of NiCo₂O₄ as a catalyst in the conversion of p-nitrophenol to p-aminophenol

Synthesis of NiCo₂O₄ by citrate gel method

Synthesis and characterization of NiCo₂O₄