Elsevier

Catalysis Communications

Volume 9, Issue 7, 1 April 2008, Pages 1533-1538
Catalysis Communications

Catalytic wet peroxide oxidation of phenolic solutions over Fe2O3/CeO2 and WO3/CeO2 catalyst systems

https://doi.org/10.1016/j.catcom.2007.12.025Get rights and content

Abstract

Fe2O3/CeO2 and WO3/CeO2 catalysts were synthesized with different metal loading (5–20%), using a simple combustion preparation method. The samples were tested in a batch reactor at atmospheric pressure, in a temperature range of 60–100 °C, for 4 h. Phenol conversion and CO2 production levels were evaluated. Iron-containing samples were comparatively more active, reaching a 100% phenol conversion at 80–100 °C. The systems were considerably stable in the acidic reaction medium: low iron leaching levels (1–5%) were registered. Selectivity towards complete mineralization was high (75–80%) and similar for both types of catalytic systems.

Introduction

Numerous wastewater streams containing organic pollutants are generated by industrial, agricultural and domestic activities, and must be removed to comply with the environmental regulations. Among these compounds, phenol results one of the most representatives due to its high toxicity and poor biodegradability. During the last decades, a variety of technological alternatives have been studied in order to develop cleaner and more effective treatments for refractory pollutants (i.e. wet oxidation, advanced oxidation, membrane processes, adsorption and anaerobic/aerobic biological treatment) [1]. Wet air oxidation (WAO) processes are carried out with oxygen or air, at high temperature and high pressure conditions. Regularly, the oxidation is performed in the presence of a catalyst (CWAO) in order to achieve a highly efficient oxidation [1], [2]. The use of hydrogen peroxide as oxidant has emerged as a viable alternative among other advanced oxidation processes [3], [4]. Hydrogen peroxide does not form any harmful byproducts, it is a non-toxic reactant, improves the oxidation efficiency and reduces the critical reaction conditions. Generally, in the catalytic wet peroxide oxidation (CWPO), the redox properties of metallic cations are used to generate hydroxyl radicals, in mild reaction conditions. The method for phenolic wastewater treatment with hydrogen peroxide is mostly based on homogeneous catalysis by Fe (II) ions in (Fenton-type reaction) [3], [4], [5]. Although their high efficiency, homogeneous CWPO processes require additional separation steps. Thus, the use of “heterogeneous Fenton” is proposed. Transition metals (mainly Fe, but also Cr, Mn, Co, Ni, Ag and Pt) are supported over different materials: silica [6], [7], alumina [8], zeolites [9], [10], mesoporous molecular sieves [11], [12], pillared clays [13], [14], ion-exchange resin [15] and active carbon [16]. However, CeO2-based CWPO systems have not been already investigated. Among stable supports, ceria appeared as a good alternative for the preparation of oxidation catalysts. It has been shown that, when associated with transition metal oxides and noble metals, CeO2 promotes oxygen storage and mobility, and forms surface and bulk vacancies that improve the redox properties of the system [1], [2], [17].

No previous phenol oxidation studies dealing with Fe2O3/CeO2 catalysts have been reported. Recently, Liu et al. [18] presented an investigation of CWPO of azo dyes over Fe2O3/γ-Al2O3 and Fe2O3–CeO2/γ-Al2O3 catalysts. They observed an increase in the mineralization efficiency due to a promoting effect of the ceria in the structural and redox properties of the ferric oxide.

Our purpose is to study the performance of Fe2O3 supported over CeO2 for the catalytic oxidation of phenol with hydrogen peroxide. WO3/CeO2 catalysts were also tested, as an unexplored alternative for this type of reaction systems.

Section snippets

Preparation of the catalysts

Fe2O3/CeO2 and WO3/CeO2 catalysts were synthesized using a simple combustion preparation method [19]. The catalysts were obtained by placing in a ceramic dish a solution of Ce(NO3)3·6H2O, FeC2O4 · 2H2O or H2WO4, pluronic (0.1 g) and ethanol (7 mL). The disk was then introduced into a muffle furnace preheated to 400 °C. After boiling, the solution ignited producing a “cold flame” that yielded a sponge-like solid. At the end of the combustion process, the temperature was kept constant for 3 h at 400 °C.

Results and discussion

According to the characterization results, the catalysts exhibited a sponge-like morphology and a surface area around 30 m2/g for the CeO2 support, with no significant changes for the catalysts. Fig. 1 presents four representative SEM images of the following samples: CeO2 support, 5Fe400, 11W400 and 5Fe800. In all the cases, the similar irregular morphology was observed, as expected for this type of voluminous materials obtained by the combustion method. For the tungsten containing samples, no

Conclusions

  • The Fe2O3/CeO2 and WO3/CeO2 catalysts appeared as a promising alternative in the CWPO of refractory contaminant such as phenol. The catalysts resulted active and selective at moderate temperature conditions (60–100 °C), and atmospheric pressure.

  • At 60 °C, the catalysts with highest metal content (20/22%) exhibited major phenol conversion levels. In the case of the iron based catalyst, the higher metal loading was also associated with higher lixiviation rate.

  • The increase in the reaction temperature

Acknowledgements

This work was supported by funds provided by AECI (A/5188/06), ANPCyT (PICTO No. 14–866), CONICET, Universidad Nacional de Mar del Plata (Argentina), Universitat Rovira I Virgili (Spain) and Fundación Carolina.

References (23)

  • V. Kavitha et al.

    Chemosphere

    (2004)
  • A. Cuzzola et al.

    Appl. Catal. B: Environ.

    (2002)
  • J. Melero et al.

    Catal. Comm.

    (2006)
  • N. Al-Hayek et al.

    Water Res.

    (1990)
  • V. Parvulescu et al.

    Catal. Today

    (2001)
  • X. Hu et al.

    Catal. Today

    (2001)
  • E. Guelou et al.

    Appl. Catal. B: Environ.

    (2003)
  • C. Catrinescu et al.

    Water Res.

    (2003)
  • R.M. Liou et al.

    Chemosphere

    (2005)
  • J. Zazo et al.

    Appl. Catal. B: Environ.

    (2006)
  • P. Massa et al.

    Catal. Comm.

    (2007)
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