Hierarchical zeolite FeZSM-5 as a heterogeneous Fenton-type catalyst K.A. Sashkina a , V.S. Labko b , N.A. Rudina c , V.N. Parmon a,c , E.V. Parkhomchuk a,c,⇑ a Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090, Russia b State Scientific Institution ‘‘The Joint Institute for Power and Nuclear Research – Sosny’’, 99 Academician A.K. Krasin Str., Minsk BY-220109, Belarus c Boreskov Institute of Catalysis SB RAS, 5 Lavrentieva St., Novosibirsk 630090, Russia article info Article history: Received 25 September 2012 Revised 20 November 2012 Accepted 20 November 2012 Available online 11 January 2013 Keywords: Hierarchical zeolites FeZSM-5 Fenton reaction Oxidation Phenol Lignin abstract Series of hierarchical zeolites ZSM-5 and FeZSM-5 were prepared by hydrothermal treatment using poly- styrene spheres template and characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, scanning and high-resolution transmission electron microscopies, and N 2 sorption techniques. Walls of the macroporous structure consisted of ZSM-5 nanocrystals with a size of 20–300 nm and amorphous globules of SiO 2 . Hierarchical FeZSM-5 contained iron in the form of iron oxide particles with a size of 2–3 nm. Hierarchical zeolites had high values of surface area (437–613 m 2 /g), external surface area (131–462 m 2 /g), and pore volume (0.36–0.76 cm 3 /g). Iron-containing zeolites were tested in the H 2 O 2 decomposition reactions in the absence and presence of iron-complexing agent, as well as in oxidation of low and high molecular weight organic compounds by H 2 O 2 at 25 °C and compared with homogeneous Fe(NO 3 ) 3 solution. Hierarchy of the zeolite porosity resulted in a significant improvement of the catalyst properties. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction The Fenton reaction is known to be one of the most important processes for water decontamination by means of the pollutant oxidation by hydrogen peroxide in the presence of iron-containing catalysts. Compared to homogeneous analogs, solid Fenton-type catalysts are more attractive due to the ease of handling, the pos- sibility to overcome pH limitations, the absence of iron complexing by oxidation intermediates [1,2]. Fe-containing MFI-type zeolite (FeZSM-5) has been proposed as a promising solid Fenton-type catalyst for treating aqueous solutions containing organics [3,4], but some properties of this zeolite limit its use in water decontamination. Previously, we have shown that the oxidation rate and the sub- strate mineralization degree for the organic substrates of low molecular weight (MW), such as 1,1-dimethylhydrazine and etha- nol, were higher in the heterogeneous Fenton system FeZSM-5/ H 2 O 2 compared with the homogeneous one [5,6]. This was possibly due to the adsorption of organic substrates on the zeolite surface enhancing the adsorbed substrate interaction with OH radicals formed on the iron-containing catalytic sites also at zeolite surface. Principally different behavior of the Fenton oxidation systems was observed in aqueous solutions of high MW lignin, and the mineral- ization degree was much lower in the FeZSM-5/H 2 O 2 system compared with homogeneous ones, such as Fe(NO 3 ) 3 /H 2 O 2 and H 2 O 2 /UV [7]. Probably, low mineralization degree of lignin in het- erogeneous system FeZSM-5/H 2 O 2 was connected with too exces- sive spacing from the catalytic sites, where the hydroxyl radicals were formed, to adsorbed organic molecules, resulting in preva- lence of oxygen release reaction over the organics oxidation pro- cesses. Indeed, despite of high surface area of ZSM-5 zeolite (350–450 m 2 /g), the predominant presence of micropores of 0.55 nm complicates transport and access of active surface for high MW organics [8]. This fact limits the use of zeolites in water puri- fication from high molecular pollutants, such as drugs, hormones, pesticides, which concentration in some natural water sources is low, but higher than safe level [9,10]. To expand zeolite use for these types of processes, the accessibility of catalytic sites for large molecules should be significantly increased in zeolites. Different methods for producing the hierarchical zeolites, con- taining additional meso/macroporous system, have been devel- oped in order to increase the catalyst surface accessibility [8,11,12]. One of them was the using of polymeric nanospheres as templates during hydrothermal crystallization of zeolites [13–15]. The superiority of the hierarchical MFI-type zeolite over the conventional zeolite has been shown for several reactions such as alkylation of phenol with tert-butanol [16] and conversion of methanol to olefins [17]. However, so far, there was no any data on the catalytic activity of hierarchical FeZSM-5 in wet peroxide oxidation of organics. The present study reports the synthesis and performance of hierarchical zeolites h-ZSM-5 and h-FeZSM-5 prepared using 0021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcat.2012.11.028 ⇑ Corresponding author at: Boreskov Institute of Catalysis SB RAS, 5 Lavrentieva St., Novosibirsk 630090, Russia. Fax: +7 (383) 333 16 17. E-mail address: ekaterina@catalysis.ru (E.V. Parkhomchuk). Journal of Catalysis 299 (2013) 44–52 Contents lists available at SciVerse ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat