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Catalysis Communications 7 (2006) 875–878

Single pot synthesis of peroxyacetic acid from acetic acid andhydrogen peroxide using various solid acid catalysts

Arudra Palani, Arumugam Pandurangan *

Department of Chemistry, Anna University, Guindy, Chennai 600 025, India

Received 6 June 2005; received in revised form 16 January 2006; accepted 16 January 2006Available online 19 May 2006

Abstract

The efficacy of various solid acid catalysts, such as Hb, HZSM-5, Al-MCM-41 (Si/Al = 25 and 75) and Si-MCM-41 supported PWAwas investigated in the conversion of acetic acid to peroxyacetic acid using hydrogen peroxide at room temperature. Si-MCM-41 sup-ported PWA was more active than other catalysts. The strength of Bronsted acid sites is found to play a decisive role in this reaction.� 2006 Elsevier B.V. All rights reserved.

Keywords: Acetic acid; Peroxyacetic acid; Hydrogen peroxide; PWA/Si-MCM-41

1. Introduction

Peroxyacetic acid (PAA) is used as a disinfectant in thefood and beverage industries, and also it is an as oxidisingagent. In textile and paper industries PAA is used as ableaching agent [1], and is effective against broad rangeof microorganisms, including bacterial spores. PAA is usu-ally prepared by the reaction of conc. H2O2 with acetic acidover mineral acid catalysts [2]. However homogeneouscatalysts like H2SO4, have drawbacks of corrosion andneutralization of the acid after reaction. There has been aglobal effort to replace hazardous and environmentallyharmful catalysts with more benign and less hazardousalternatives [3]. In this contrast, use of solid acid catalystsare advantageous. Sha et al., [4] reported that super acidcatalysts like Nafion-H, Nafion� SAC-13, Dowex� DR-2030 and Amberlyst� were effective for the preparationof PAA. They reported that conversion of acetic acidincreased with increase in the conc. of acetic acid andH2O2. They obtained 16% conversion of acetic acid, and

1566-7367/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.catcom.2006.01.017

* Corresponding author. Address: Visiting Professor, CAER & Centerfor Nano scale science and engineering, 453F, Paul Anderson Tower,University of Kentucky, Lexington, KY 40506-0046, USA. Tel.: +9122203158; fax: +91 22200660.

E-mail address: pandurangan_a@yahoo.com (A. Pandurangan).

Nafion-H was found to be more active than other catalysts.Recently, for the process requiring high acidity than thezeolites, the use of strongly acidic heterpoly acids has beenattracted [5]. Among the heteropoly acids, the 12-phospho-tungstic acid (PWA) is the most acidic [6], this has led mostresearchers to focus on it. However for the PWA to beeffective as a catalyst, it should be supported over a carrierwith a large surface area due to its extremely small surfacearea (<10 m2/g). The M41S family materials [7] are excel-lent supports for preparing bifunctional catalysts due totheir large surface area and uniform large pore size. Thesematerials have relatively small diffusion hindrance andhence, they can aid the easy diffusion of bulky organicmolecules in and out of their mesopores. For these reasons,in the present investigation we carried out synthesis ofperoxyacetic acid from acetic acid and hydrogen peroxideusing PWA/MCM-41 as catalysts. For the comparisonstudy, the reaction was also carried over Hb, HZSM-5,and Al-MCM-41 (Si/Al = 25 and 75) catalysts.

2. Experimental

Acetic acid, PWA and 30% H2O2 were purchased fromSigma–Aldrich were used as such. The catalysts used in thisstudy were prepared as follows. Sodium forms of beta

Fig. 1. XRD pattern of: (a) Si-MCM-41; (b) 10 wt% of PWA/Si-MCM-41; (c) 20 wt% of PWA/Si-MCM-41; (d) 30 wt% of PWA/Si-MCM-41.

Table 1Physico-chemical characterization of Si-MCM-41/ PWA catalysts

Catalysts d(1 0 0)

spacing (A)Surfacearea (m2/g)

Pore volume(cm3/g)

Porediameter (A)

Si-MCM-41 40.11 1114 0.98 31.2Si-MCM-41/

PWA (10%)38.2 982 0.79 29.1

Si-MCM-41/PWA (20%)

35.03 874 0.65 28.8

Si-MCM-41/PWA (30%)

33.24 743 0.51 28.6

Fig. 2. Pyridine adsorption FT-IR study of: (a) Si-MCM-41; (b) 10 wt%of PWA/Si-MCM-41; (c) 20 wt% of PWA/Si-MCM-41; (d) 30 wt% ofPWA/Si-MCM-41.

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(Si/Al = 12) and ZSM-5 (Si/Al = 40) were purchased fromSud. Chemie and converted into corresponding H forms asper the standard procedure [8]. Al-MCM-41 with Si/Alratios 25 and 75 were prepared by the procedure reportedin our earlier studies [9]. PWA (30%) loaded Si-MCM-41was prepared by wet impregnation which involves additionof 3 g of PWA to a methanolic suspension of 10 g of Si-MCM-41 [10]. The catalyst was dried at 120 �C for 5 h.Similar procedure was followed for the preparation of20% and 10% PWA loaded Si-MCM-41 catalysts. Phys-ico-chemical characterization of all the materials was car-ried out systematically. The hexagonal structure of thesynthesized material was confirmed by powder X-ray dif-fraction (XRD, Siemens D5005). Surface area, pore vol-ume, pore size distribution were measured by nitrogenadsorption at 77 K (ASAP 2010 porosimeter). The acidityof the catalyst was measured by TPD of pyridine adsorbedFT-IR spectroscopy (Nicolet 710). The dispersion of thePWA was determined by means of TEM measurements.TEM was performed using a Philips CM 30 ST electronmicroscope operated at 300 kV. Samples for TEM wereprepared by placing droplets of a suspension of the samplein methanol on a polymer micro grid supported on a Cugrid.

All the experiments were conducted in a 100 ml capacitydouble-necked round bottom flask. The catalyst and thereactants were charged and stirred with a magnetic stirrer.The sample was drawn at every 3 h and the acetic acid con-version was determined by HPLC, Perkin Elmer, Modelseries 2000, and SPHERI-5 RP-18 column with UV/VISDetector. Isocratic evolution was carried out using metha-nol–water (75:25) as the mobile phase at a flow rate of1 ml/min and UV detector wavelength of 230 nm.

3. Results and discussion

3.1. Charcterization of the catalysts

The XRD patterns of Si-MCM-41 and PWA loaded Si-MCM-41 catalysts were shown in the Fig. 1. Si-MCM-41materials has an intense peak at 2.26� (2h) due to (10 0)plane and weak peaks at 4.12 and 4.72 due to higher orderreflections (110) and (200) which are indexed to hexagonallattice[10]. The (100) plane reflection has been shifted tohigher values of 2h at 2.41 for PWA loaded Si-MCM-41catalysts shows the maximum use of PWA to constructthe Keggin phase. The XRD patterns revealed at low load-ing of PWA (less than 20% PWA) no distinct diffractionpeaks due to PWA crystallites are observed. Table 1. givesthe physical characteristics of PWA supported catalysts.The decrease of surface area may be due to the decreaseof pore volume as well as pore diameter. The decrease inpore volume suggests that PWA concentrated inside thepore coincide with the results those reported earlier [11].The gradual decrease in pore volume with increase inPWA loading shows the formation of bulk Keggin within the pores. The IR Spectrum of bulk PWA as well as sup-

ported PWA is shown in Fig. 2. The peaks at 1081 and985 cm�1 are due to P–O and W@O vibrations, respec-tively. The corner shared and edge shared vibrations ofW–O–W appeared at 897 and 803 cm�1. A gradualdecrease in the absorbance of corner shared vibrations of

Fig. 4. TEM micrographs of H3PW12O40 loaded with MCM-41: (a)10 wt% PWA/Si-MCM-41; (b) 20 wt% PWA/Si-MCM-41; (c) 30 wt%PWA/Si-MCM-41.

Fig. 3. FT-IR spectra of: (a) HPW; (b) 10 wt% of PWA/Si-MCM-41; (c)20 wt% of PWA/Si-MCM-41; (d) 30 wt% of PWA/Si-MCM-41.

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W–O–W at 897 cm�1 shows the formation of Keggin struc-ture at only above 20% loading of PWA. These results werein good agreement with the reported values [11]. The spec-tra (Fig. 3) showed the expected bands due to Lewis acidbound (1450, 1575 and 1623 cm�1), Bronsted acid bound(1545 and 1640 cm�1) and both Lewis and Bronsted acidbound pyridine (1490 cm�1). The data, therefore, indicatethe presence of both Bronsted and Lewis acid sites in Al-MCM-41 similar to that reported earlier [12]. The existenceof large PWA crystals on the external surface of MCM-41was confirmed by TEM.

3.2. Catalytic activity

The reaction results are presented in Table 2. The dataindicate high conversion over PWA loaded catalysts thaneither zeolites or Al-MCM-41 molecular sieves. As thisreaction requires activation of H2O2 for insertion of oxy-gen across the C–O bond of acetic acid as shown below,

Table 2Preparation of PAA from aqueous solution of acetic acid (0.5 M) andH2O2 (0.378 M) at 25 �C

Catalyst Conversion of acetic acid (%)a

10 wt% PWA/SiMCM-41 88.820 wt% PWA/SiMCM-41 94.1330 wt% PWA/SiMCM-41 69.95Hb 61.00ZSM-5 46.16Al-MCM-41 (25) 41.65Al-MCM-41 (75) 40.44

Selectivity of peroxyacetic acid = 100%.a Reaction time = 15 h, amount of catalyst = 0.1 g.

the acid strength of the catalysts is to play a major role.Since, PWA is a super acid, it can very well protonateH2O2 and activate it suitable enough for oxygeninsertion.

H2O2 þHPW!H2Oþ �O�HþPW�

CH3COOHþH2Oþ �O�H! CH3COOOHþH2OþHPW

The higher conversion over Al-MCM-41 (25) than Al-MCM-41 (75) is due to its more density of acid sites. Be-tween Hb and HZSM-5 it is found that Hb is more activethan HZSM-5. The lower conversion of HZSM-5 is attrib-uted to its small pore dimensions (5.1 · 5.5 A) than Hbcausing lower rate of diffusion of reactants into pores.The density of acid sites of Hb is higher than HZSM-5,which is also a major factor for high conversion of aceticacid over the former. Among the PWA loaded catalysts,10% PWA loaded catalyst gives less activity than 20%loaded catalyst, hence the presence of Keggin structure ofPWA becomes the necessity to give high conversion. Asit is less probable to have Keggin structure with 10% load-ing, the activity of 10% PWA-Si-MCM-41 is less. Thoughboth 20% and 30% PWA loaded catalysts have Keggin

878 A. Palani, A. Pandurangan / Catalysis Communications 7 (2006) 875–878

structure [13,14], the less activity of the latter is due to morediffusion resistance for the reactants into the pore wherethe Keggin phase is present. Such a decrease in the diffu-sion of the reactants into the pores with increase in PWAloading was also reported earlier for other reactions [15].

In order to confirm PWA is not leaching out from thesupport during the reaction, 20% PWA loaded catalystswas recycled for 5 cycles. But the acetic acid conversionwas found to be slightly less for first three cycles (less than5%) under the optimized conditions. After that there is agradual decrease in conversion (14.2% for fourth cycleand 22.3% for fifth cycle) was observed. This can beexplained by formation of cluster by increased mobilityof the HPA units due to dissolution in adsorbed reactantand product and especially in water which is the by-prod-uct formed. It may be assumed that the internal concentra-tions of these compounds are much higher than the bulkliquid [16]. The less conversion was also due to the solubil-ity of Keggin phase in water. Further, it was already shownthat in the liquid phase reactions the leached out PWAwill again be redispersed on the catalyst surface [17]. Theconversion over Hb, HZSM-5, Al-MCM-41 (25) and Al-MCM-41 (75) is less than that over 20% HPW-SiMCM-41due to the less strength of Bronsted acid sites.

4. Conclusion

From the above study, it is concluded that the PWAloaded Si-MCM-41 catalysts can be better exploited forthe transformation of acetic acid to peroxyacetic acid.20% PWA loading is optimum compared to 10% or 30%loading. The requirement of strong acidic sites as thoseof PWA for the title reaction is also evident by this study.

Acknowledgment

The authors gratefully acknowledge the financial sup-port from DRDO, New Delhi for this research work.

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