View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Arabian Journal of Chemistry (2014) xxx, xxx–xxx King Saud University Arabian Journal of Chemistry www.ksu.edu.sa www.sciencedirect.com ORIGINAL ARTICLE Selective oxidation of styrene to benzaldehyde using soft BaFe2O4 synthesized by citrate gel combustion method Ravindra Y. Pawar, Satish K. Pardeshi * Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007, India Received 25 February 2013; accepted 20 August 2014 KEYWORDS Abstract BaFe2O4 spinel type catalyst is synthesized by a simple and inexpensive one-step citrate gel combustion method, the only method to synthesize soft ferrite other than the Pechini method Soft BaFe2O4; Sol gel combustion; reported earlier. The precursor and oxide are well characterized by various techniques such as ther- Coralloid morphology; mogravimetry–differential thermal analysis, Fourier transform IR, X-ray diffraction, X-ray flores- Site preference energy cence and scanning electron microscopy. The SEM images confirm coralloid morphology of BaFe2O4 catalyst. BaFe2O4 catalyst shows high activity for styrene oxidation in the presence of H2O2 (30%) as an oxidant in acetone as solvent. Gas chromatography and mass spectroscopy anal- ysis revealed that, conversion of styrene takes place selectively to benzaldehyde up to 88.5 mol% as major product with 39.9% yield. The optimization and effect of various reaction conditions on sty- rene conversion and product distribution were also studied. Ultrasonication exposes active sites on the surface of catalyst and breaks the hydrophobic cluster to make the reagent available. Better cat- alytic activity of BaFe2O4 is due to different site preference energies of individual ions which depend on the ionic size of barium (1.35 A˚) and iron (0.67 A˚), the size of interstices and temperature. The catalyst can be reused with marginal loss in activity. ª 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. 1. Introduction Spinel compounds with the general formula of AB2O4 are one of the most frequently encountered structure types in inorganic * Corresponding author. Tel.: +91 020 25601394x514; fax: +91 020 chemistry (Sawada, 1996). Spinel is often used as catalysts for 25691728. reactions at elevated temperature due to their high temperature E-mail address: [email protected] (S.K. Pardeshi). stability and resistance to sintering (Busca et al., 1997); Peer review under responsibility of King Saud University. MgAl2O4 has been considered as a material for a number of applications in high radiation environments (Clinard et al., 1984) such as electrical insulators and dielectric windows in fission reactors (Nitani et al., 2003) and so on. Production and hosting by Elsevier http://dx.doi.org/10.1016/j.arabjc.2014.08.012 1878-5352 ª 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. Please cite this article in press as: Pawar, R.Y., Pardeshi, S.K. Selective oxidation of styrene to benzaldehyde using soft BaFe2O4 synthesized by citrate gel combustion method. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.08.012 2 R.Y. Pawar, S.K. Pardeshi Alkaline earth metal (AEM) ferrites have attracted a consid- weighed and mixed according to determined proportion. The erable attention due to their potential application as magnetic aqueous solutions of ferric nitrate and barium nitrate were materials in various electronic, magnetic and microwave devices mixed and added slowly with continuous stirring in the aque- (Cabuil, 2000; Horvath, 2000; Viswanathan and Murthy, 1990; ous solution of citric acid for 30 min at 40 °C temperature. Sugimoto, 1999). The wide application of these materials is Then the mixed solution was evaporated slowly at high tem- mainly due to its excellent chemical stability, high mechanical perature, during which the Fe3+ and nitrate ion provided an durability, and resistant to corrosion (Simmons, 1989). They in situ oxidizing environment for carboxylic acids, to form have also been employed as heterogeneous catalysts and elec- homogeneous mixture of metal carboxylates. When the reac- trode materials (Bronoel et al., 1980; Grenier et al., 1981). In tion completed, the obtained solution was heated in oven for order to get high-powered barium ferrite, different synthesis 12 h at 120 °C. The brown fluff mass was obtained which techniques have been developed, such as micro emulsion (Liu was ground into fine powder and turned into a dried precursor. et al., 1998), hydrothermal reaction (Liu et al., 1999), glass crys- Finally, powder of the dried precursor was ignited in a crucible tallization (Rezlescu et al., 1993), and salt-melt technique (Chin and followed by calcination at different temperatures for 2 h et al., 1993). The ultrafine powder of barium ferrite (BaFe12O19) with a heating rate of 10 °C per minute to obtain barium ferrite was synthesized by a sol–gel combustion technique using gly- powders. cine gels, the results showed that the formation of single phase barium ferrite is significantly influenced by Ba/Fe and glycine/ nitrate molar ratio, the phase composition and morphology of 2.2. Physico-chemical characterization the barium ferrite are confirmed by X-ray diffraction, transmis- sion electron microscopy (TEM) and high resolution TEM The thermal transformation associated with heat treatment (Meng et al., 2014). All these methods have many drawbacks was studied by a thermo gravimetric-differential thermal anal- such as small area of deposition, requirement of sophisticated ysis (TG–DTA) performed on a Shimadzu TG–DTA instru- instruments, high working cost of system, and prolonged calci- ment with heating rate of 10 °C minÀ1. XRD pattern was nation time for crystallization. When sol–gel technique (Surig recorded at room temperature by using a D-8 Advance Bru- et al., 1993) is used, we get high-powered ferrite material. The ker AXS, diffractometer with Cu Ka radiation atomic-level blending of the constituent elements in the required (k = 0.15406 nm) operated at 40 kV and 40 mA, employing stoichiometric ratio is attained in the citrate precursor complex, Ni-filter. Data were collected at 0.02° with counting rate of which enables the decomposition of the precursor directly into 5 s per step, in the (2h) range from 20° to 70°. The composi- the final binary oxide at lower temperature, without the forma- tion of BaFe2O4 calcined at 900 °C for 2 h was determined by tion of intermediate oxide phases that delay the formation of the X-ray fluorescence on a pw1400 Philips instrument. The final oxide (Sankaranarayanan et al., 1993). obtained percentage of elements is compared with the calcu- The synthesis of barium ferrite (BaFe2O4) powder by a sol– lated values. gel combustion technique is the focus of the present work, The FTIR spectra of calcined catalysts were recorded on a since it allows the homogeneous mixing of two metal cations Shimadzu FTIR 8400 equipped with KBr beam splitter spec- and it retards particle growth via the formation of surface cit- trometer at a resolution of 4 cmÀ1, finely powdered sample rate complexes, inhibiting the agglomeration of the particles. was mixed with small amount of KBr and pressed under pres- The catalytic activity of the synthesized catalyst is tested by sure. The results were obtained at ambient temperature in using selective oxidation of styrene as a model reaction. Some wavelength range from 4000 to 400 cmÀ1. A model of SEM oxidants such as KMnO4, CrO3, and HNO3 (Sato et al., 1996, JEOL JSM 6360 A was used to record the scanning electron 1997) were applied traditionally to the oxidation of various microscopy (SEM) pattern. substrates, which might result in much serious pollution and some potential risks in the process of operation. In terms of 2.3. Catalytic activity atom efficiency and environment friendly, after oxygen, aque- ous hydrogen peroxide (30% H2O2) is a very attractive oxidant The selective oxidation of styrene was carried out in a three for industrial applications since water is the only by-product, necked round bottom flask (50 ml) equipped with an X- and it is easy to be dealt with after reactions. Selective oxida- crossed Teflon coated magnetic stirrer and a reflux con- tion of styrene is successfully carried out over spinel type denser. 10 mmol styrene [99+%, Aldrich], 10 ml acetone, CaFe2O4 (Pardeshi and Pawar, 2010) and SrFe2O4 (Pardeshi 0.1 g catalyst, 1.0 ml of hydrogen peroxide (30% aq. Merck), and Pawar, 2011) by using 30% H O as oxidizing agent. 2 2 and (Styrene/H2O2)molar = 1 were added successively into the In this paper, we attempt to show how BaFe2O4, of Ba-Fe-O flask. The flask is then immersed in an oil bath at a fixed system synthesized by citrate–nitrate gel combustion route, temperature and time. The reaction was carried out for dif- characterized by various techniques, is better for styrene (one ferent temperatures and times. The reaction products were of the most important pro-chiral alkenes) oxidation reaction in analyzed with a gas chromatograph (Shimadzu QP5050A acetone as solvent using environmentally benign oxidant H2O2. instrument) equipped with a DB-5 capillary column and Quadra pole detector. Helium was used as carrier gas. The 2. Experimental GC injection volume of 2 lL and the split ratio of 25:30 were used. 3-Nitrotoluene (99+%, Aldrich) is used as an internal 2.1. Preparation of catalyst standard. The styrene conversion, product selectivity and the percentage yield of the desirable product are calculated by using the equations given elsewhere (Pardeshi and Pawar, The starting materials were of A.R. grade Fe(NO3)3Æ9H2O 2010). (99.9%), Ba(NO3)2 (P99%) C6H8O7ÆH2O. The chemicals were Please cite this article in press as: Pawar, R.Y., Pardeshi, S.K. Selective oxidation of styrene to benzaldehyde using soft BaFe2O4 synthesized by citrate gel combustion method.