Preparation of novel Fe-ZSM-5 zeolite membrane catalysts for catalytic wet peroxide oxidation of phenol in a membrane reactor

Preparation of novel Fe-ZSM-5 zeolite membrane catalysts for catalytic wet peroxide oxidation of phenol in a membrane reactor

Accepted Manuscript Preparation of novel Fe-ZSM-5 zeolite membrane catalysts for catalytic wet peroxide oxidation of phenol in a membrane reactor Ying...

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Accepted Manuscript Preparation of novel Fe-ZSM-5 zeolite membrane catalysts for catalytic wet peroxide oxidation of phenol in a membrane reactor Ying Yan, Songshan Jiang, Huiping Zhang, Xinya Zhang PII: DOI: Reference:

S1385-8947(14)01072-9 http://dx.doi.org/10.1016/j.cej.2014.08.018 CEJ 12525

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

3 July 2014 5 August 2014 6 August 2014

Please cite this article as: Y. Yan, S. Jiang, H. Zhang, X. Zhang, Preparation of novel Fe-ZSM-5 zeolite membrane catalysts for catalytic wet peroxide oxidation of phenol in a membrane reactor, Chemical Engineering Journal (2014), doi: http://dx.doi.org/10.1016/j.cej.2014.08.018

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Preparation of Novel Fe-ZSM-5 Zeolite Membrane Catalysts for Catalytic Wet Peroxide Oxidation of Phenol in a Membrane Reactor Ying Yan, Songshan Jiang, Huiping Zhang,Xinya Zhang∗ *School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, PR China Abstract Novel Fe-ZSM-5 zeolite membrane catalysts were prepared for catalytic wet peroxide oxidation (CWPO) of phenol in a membrane reactor. Firstly, the ZSM-5 zeolite membrane with a Si/Al ratio of 80 was fabricated by using secondary growth process on the surfaces of paper-like sintered stainless steel fibers (PSSFs) which was prepared by wet lay-up papermaking process and sintering process. Then, Fe-ZSM-5 zeolite membrane catalysts with Fe loading of 15%, 25% and 35% were prepared and systematically characterized by using X-ray diffraction (XRD), N2 adsorption-desorption, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectra (XPS), respectively. Finally, catalytic activity of Fe-ZSM-5 zeolite membrane catalysts was evaluated by investigating the conversion of phenol, H2O2 and TOC as well as the Fe leaching concentration in the treated effluent based on the CWPO processes in a membrane reactor. The characterization results showed that ZSM-5 zeolite membrane with a thickness of 6 µm was fabricated on the surface of PSSFs and Fe element with a form of Fe2 O3 was uniformly dispersed on the surface of ZSM-5 zeolite membrane support. The results of CWPO of phenol showed that the catalyst with Fe loading around 25% achieved the highest activity (phenol conversion about 95% and TOC conversion about 45%, respectively) after continuously ran for 7 hours. Meanwhile, low loss of Fe species was observed on all of the catalysts (Fe leaching concentration lower than 7 mg/L).

Key words: Fe-ZSM-5 zeolite membrane catalyst; catalytic wet peroxide oxidation; phenol; membrane reactor

*

Corresponding author: Tel: +86 2087112047; fax: +86 2087112047. E-mail address: [email protected] (X.Y. Zhang). 1 / 33

1. Introduction Phenol wastewater discharged from various industrial processes such as refineries, petrochemical, pharmaceutical, coal and other industries has become a great concern as the organic contaminants in the wastewater are resistant to biodegradation and toxic to animals and human beings [1]. Many reports have been published on the removal of phenol or phenolic derivatives in wastewater using physical separation [2], biodegradation [3, 4] and Advanced Oxidation Processes (AOPs) [5]. In the last decades, many researchers have focused on the catalytic wet peroxide oxidation (CWPO) progresses which take advantage of employing H2O2 as the liquid oxidant, enable perform oxidation at ambient conditions, which can not only avoid gas-liquid mass transfer limitations, but decrease the investment costs [6]. Traditionally, the catalysts used for the CWPO processes include homogeneous catalysts and heterogeneous catalysts involved in Fenton reaction which is a powerful source of oxidative hydroxyl radicals generated from H2O2 [7]. Heterogeneous catalysts can be easily recovered, regenerated and reused and can overcome the conventional drawbacks of homogeneous catalysts such as difficulties in separation, regeneration and secondary contamination. Therefore, the CWPO processes of phenol over heterogeneous catalysts using H2O2 as oxidant attracted much attention. The introduction of transition metals and their complexes such as Fe [8-10], Cu [11, 12] and Mn [13] and other metals such as Al [14-16] and Ce [17], into various supports can greatly improve the catalytic performance for CWPO of phenol. Among these transition metal oxides, Fe oxides as active component are frequently chosen because of its widely available trait and non-toxic characteristic. The support materials of catalyst have been always considered as a key factor to influence the catalytic activity. Numerous micro/mesoporous materials such as ZSM-5 [18], MCM-41 [19], SBA-15 [20], pillared clays [21] and activated carbon [22, 23] were used as catalyst support for the CWPO of phenol aqueous solution. Zeolite membranes as new catalyst supports have attracted more and more attention due to their uniform porous structures, unique surface properties, good mechanical strength, as well as good chemical and hydrothermal stabilities [24] in recent years. A series of zeolite membranes have been successfully fabricated on the surface of porous α-alumina supports [25], stainless steel substrates [26], sintered metal fibers [27, 28] and silicon substrates [29]. Recently, ZSM-5 zeolite membrane with a Si/Al ratio of 62.5 was successfully fabricated on

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the surface of PSSFs by a secondary growth method and used for toluene adsorption as reported in the previous literature in our group [30]. However,there is no literature focused on its application for liquid adsorption or catalysis, and the three dimension structure and unique surface properties of the ZSM-5 zeolite membrane make it to be a promising support candidate used for oxidation of phenol in aqueous solution by means of CWPO process. Most of the researches about CWPO processes of phenol were carried out in batch operations [21-23]. And there were many shortcomings existed in the batch reactor such as high concentration of complicated intermediate products and long contact time which results in the decrease of longevity of the catalyst [31] and these drawbacks may be overcome by using a fixed bed reactor. Only Fernando et al. [32, 33] reported a remarkable catalytic performance of iron oxide over different silica supports (meso-structured SBA-15 and non-ordered meso-porous silica), used for the CWPO of phenolic aqueous solution in a fixed bed reactor. Their experimental results showed that complete phenol degradation and 66.0% TOC conversion were achieved and iron leaching concentration above 10 mg/L was detected. Besides, there is no other literature described the CWPO of phenol process in fixed bed reactor, especially in membrane reactor. The aim of present work is to (a) prepare a novel Fe-ZSM-5 zeolite membrane catalyst with iron oxide supported onto the gradient porous ZSM-5 zeolite membrane, (b) study the crystallographic structures and morphological information etc. of the ZSM-5 zeolite membrane and Fe-ZSM-5 zeolite membrane catalysts by using modern instrument analytical techniques and (c) investigate the catalytic activity of Fe-ZSM-5 zeolite membrane catalysts for CWPO of phenol in a membrane reactor.

2. Experimental 2.1 Materials Stainless steel fibers with diameter about 6.5 µm were purchased from Huitong advanced material company (China). Tetrapropylammonium hydroxide (TPAOH, 25 wt% aqueous) was purchased from Sigma-Aldrich. Tetraethoxysilane (TEOS, >99%) and phenol were purchased from Guangzhou Chemical Reagent Factory. Ethanol (C2H5OH, >99.8%), sodium hydroxide (NaOH, 99%), sulfuric acid (H2SO4, 95-98%), ammonia water (NH3, 25-28 wt% aqueous) and sodium aluminate (NaAlO2, Anhydrous) were all purchased from Sinopharm Chemical reagent

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Co., Ltd. Hydrogen peroxide (H2O2, 30 wt% aqueous) was purchased from Jiangsu Qiangsheng Chemical Co., Ltd. Iron nitrate nonahydrate (Fe(NO3 )3·9H2O) was purchased from Tianjin Damao Chemical Reagent Factory. Manganese dioxide was purchased from Shanghai Qiangshun Chemical Reagent Factory. Sodium thiosulfate and potassium iodide were purchased from Tianjin Bodi chemical Co., Ltd. Deionized water was used in all synthesis process. All of the chemical reagents used in this study were analytical grade. 2.2 Preparation of Fe-ZSM-5 zeolite membrane catalysts The novel gradient porous Fe-ZSM-5 zeolite membrane/PSSFs (paper-like stainless sintered steel fibers) catalysts were prepared by three steps. Firstly, fabrication of PSSF by wet lay-up papermaking process. The paper-like sintered steel fibers support was prepared according to our previous research [30]and then pretreated with a 0.5% aqueous solution of the cationic polymer (poly(dimethylamine-co-epiclorohydrin), 50%) for 30 min, washed two times with a 0.1 mol/L NH3 aqueous solution and dried in air. Secondly, synthesis of ZSM-5 zeolite membranes on the PSSF support by secondary growth process. The silicalite-1 seeds were prepared first by hydrothermal synthesis method using the synthesis solution with a molar ration 9TPAOH: 25TEOS: 500H2O: 100C2H5OH. Then, the pretreated PSSFs support was dipped in a silicalite-1 seed solution (approximately 2 wt% aq.) with a pH of 10 adjusted by adding NH3 aqueous solution to adsorb silicate-1 seeds on the surface and air dried. The secondary synthesis solution with a molar composition 1 TEOS: 0.112 TPAOH: 0.0125 NaAlO2: 111H2O was prepared by vigorously stirring TPAOH, NaAlO2 mixed solution with the TEOS dropwise added at room temperature. The seeded PSSF support was dipped vertically in a 200 mL Teflon lined autoclave with secondary synthesis solution and put in an oven at 150 ℃ for 48 h. The synthesized samples were washed, air dried and calcined at 500 ℃ for 4h to remove the TPAOH. Finally, Fe active component was loaded on the ZSM-5 membrane by means of incipient wetness impregnation. To study the effect of Fe loading, three samples were prepared by incipient wetness impregnation of Fe(NO3)3 solutions in ZSM-5 zeolite membrane support. Fe ions concentrations were adjusted to obtain 15, 25 and 35 wt% Fe loading on the catalysts. These catalysts are referred to as Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%). The

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samples were air dried at 100 ℃ for 12 h and calcined in air until 550 ℃ (6h) using a slow ramp of temperature (1 ℃/min). 2.3 Characterizations of Fe-ZSM-5 zeolite membrane catalysts The crystallographic structures of the ZSM-5 zeolite membrane support and Fe-ZSM-5 zeolite membrane catalyst samples were studied by X-ray diffraction (XRD) patterns carried out on a PANalytical X’Pert Pro X-ray diffractometer using Cu Kα radiation, with a fixed power source (40 kV, 40 mA) and 2θ range from 5 to 60°. The textural and morphological information of the samples were characterized using field emission scanning electronic microscopy (FE-SEM) on a Zeiss Merlin FE-SEM. The energy dispersive spectroscopy (EDS) and element mapping were applied to analyze the dispersion of Fe in the catalyst samples. N2 adsorption-desorption isotherms of catalyst sample were tested using a Micromeritics Tristar Ⅱ Surface Area and Porosity (Micromeritics Instrument Co., USA) at 77K. All of the samples were out-gassed on a Micromeritics Vacrep O61 Sample Degas System at 523K for 6 hours before measurement. The X-ray photoelectron spectra (XPS) results were obtained by a Kratos Axis Ultra (DLD) spectrometer with an Al Kα (1486.6 eV) radiation source operated at 15kV and 10mA. The binding energy (B.E.) of C1s peak at 284.6 eV was taken as a reference. Temperature-programmed hydrogen reduction (TPR-H2) experiments were done in a Micromeritics AutoChem Ⅱ Chemisorption Analyzer. Approximately 50 mg of each freshly calcined catalyst sample was placed into a U-tube and attached to the unit. Catalyst samples were pre-treated at 300 ℃ under a flow of helium (30 mL/min) to eliminate contaminants and then cool down to room temperature. For the temperature-programmed reduction, a gas mixture of H2 (10 vol%)/Ar flow (30 mL/min) was passed over the sample, followed by a temperature ramp of 10 ℃/min from room temperature to 700 ℃. The effluent gas was measured using a thermal conductivity detector (TCD). 2.4 Catalyst activity tests Catalytic wet peroxide oxidation of phenol was carried out in a membrane reactor made of a stainless steel tube (20 mm i.d., 100 mm length), operating at constant 80 ℃ of temperature under atmospheric pressure. The experimental set-up used for the oxidation of phenol aqueous solution by means of CWPO is shown in Fig. 1. The prepared Fe-ZSM-5 zeolite membrane catalysts were packed between glassy beads (d=2-3 mm) to obtain a better distribution of the phenol aqueous

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solution and to keep the Fe-ZSM-5 zeolite membrane catalysts at the middle of the membrane reactor. The concentration of reactants in the feed tank was a mixture of phenol solution, 1 g/L of phenol and 5.1 g/L of H2O2 (stoichiometric amount for the total phenol oxidation according to reaction 1). The phenol aqueous solution was fed to the reactor in up-flow operation by a peristaltic pump. The fixed bed reactor was heated by a thermal bath which kept the water at the needed temperature for the control of temperature.

C 6 H 5OH + 14H 2O 2 → 6CO 2 + 17H 2O

(1)

Samples were hourly withdrawn from the treated effluent to test pH immediately and then diluted 10 times to obtain H2O2 concentration. H2O2 concentration was determined by iodometric titration using a 0.02 mol/L sodium thiosulfate solution. And H2O2 conversion (XH2O2, %) was calculated as follows:

C H O (in ) − C H O (out ) × 100% C H O (in )

XH O =

2 2

2 2

2 2

(2)

2 2

Where CH2O2(in) (mg/L) and CH2O2(out) (mg/L) are the concentrations of H2O2 in the inlet and outlet solution, respectively. For the purpose of eliminating residual H2O2 from the samples, all the sample solutions were well mixed with 0.1 g manganese at least 15 min before measuring the phenol concentration, TOC concentration, and iron leaching concentration in the treated effluent. Phenol concentration was measured by means of an HPLC Chromatograph (Agilent 1100) equipped with a Agilent HC-C18(2) column and a UV detector adjusted at 210 nm, employing the methanol and ultrapure water (v/v= 40:60) as mobile phase. And phenol conversion (Xphenol , %) was calculated as follows:

X phenol =

C phenol(in ) − C phenol(out ) × 100% C phenol(in )

(3)

Where Cphenol(in) (mg/L) and Cphenol(out) (mg/L) are the concentrations of phenol in the inlet and outlet solution, respectively. TOC concentration of the samples was measured using a Liqui TOC (Elementar, Germany). And TOC conversion (XTOC, %) was calculated as follows:

X TOC =

C TOC (in ) − C TOC (out ) × 100 % C TOC (in ) 6 / 33

(4)

Where CTOC(in) (mg/L) and CTOC(out) (mg/L) are the concentrations of TOC in the inlet and outlet solution, respectively. Iron leaching concentration in the treated effluent was tested by atomic absorption spectrophotometer (AA240FS, Varian Co., USA).

3. Results and discussion 3.1 Characterizations 3.1.1 XRD The crystallographic structures of the ZSM-5 zeolite membrane support and Fe-ZSM-5 zeolite membrane catalyst samples were studied by X-ray diffraction (XRD) patterns, as shown in Fig. 2. All of the XRD patterns show the diffraction peaks at the ranges of 2θ=7-9° and 2θ=23-25°, matching well with the standard phase of ZSM-5 zeolite [34], indicating that the ZSM-5 zeolite was successfully fabricated on the PSSF support and well crystallized. For Fe loaded ZSM-5 membrane catalyst samples, two peaks of iron oxide at 2θ=33.0° and 2θ=35.6° are detected and its peaks intensity increased with the increasing Fe loading. The structure of the ZSM-5 zeolite remained intact after the modification treatment, whereas decreasing of the intensity of ZSM-5 zeolite diffraction peaks was observed for Fe-ZSM-5 (15%), Fe-ZSM-5 (25%), and Fe-ZSM-5 (35%) compared with the ZSM-5 zeolite membrane, which could result from the higher X-ray absorption coefficient of iron compounds [35]. The diffraction peaks of ZSM-5 zeolite can’t be clearly detected when the Fe loading reached 35%, which could be attributed to the agglomeration of high concentration of Fe2O3 component and wrapped the ZSM-5 zeolite support. 3.1.2 SEM Morphology and structure of the synthesized materials were investigated by FE-SEM. Fig. 3 shows the FE-SEM images of ZSM-5 zeolite membrane support and Fe-ZSM-5 zeolite membrane catalyst. Fig. 3 (a) clearly shows that the junctures of stainless steel fibers are sintered together to form a three-dimension network structure. Fig. 3 (b) shows that the continuous ZSM-5 zeolite membrane with a good crystal form is covered on the surface of stainless steel fiber, which indicates that the ZSM-5 crystals can grow well together to form a dense, polycrystalline and continuous membrane. The thickness of the ZSM-5 zeolite membrane is about 6 µm which can be detected in the cross-sectional SEM image as shown in Fig. 3 (c). Microstructure of the Fe-ZSM-5

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(15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%) are shown in Fig. 3 (d), (e) and (f), respectively. And morphological information of Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%) are shown in Fig. 3 (g), (h) and (i), respectively. As can be seen in Fig. 3 (d), (e) and (f), Fe2 O3 particles were loaded on the surface of the ZSM-5 zeolite membrane and stocked part of the space of PSSFs and the blocks of the pores become severe gradually with the increase of Fe loading. And the space of ZSM-5 zeolite membrane was totally blocked and embedded by the Fe2 O3 particles and thus results in the loss of three dimension structure of the PSSFs when the Fe loading increased to 35% as shown in Fig. 3 (f). As can be seen in Fig. 3 (g) and (h), Fe2O3 particles can be well-distributed on the surface of the ZSM-5 zeolite and loaded into the textures of the PSSFs. However, it can be seen in Fig. 3 (i), the Fe2O3 component could not be well-distributed on the surface of the ZSM-5 zeolite membrane because of the agglomeration of high concentration of Fe2O3 component. This can be used to explain the XRD pattern of Fe-ZSM-5 (35%) with low peaks intensity of ZSM-5 zeolite but high peaks intensity of Fe2 O3 component as discussed before. 3.1.3 EDS The EDS elemental analysis spectrum results of ZSM-5 zeolite membrane, Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%) are shown in Fig. 4(a), (b), (c) and (d) respectively. The results indicate the existence of Fe, Si, Al and O elements in the catalysts. The relative intensity of Fe element increases with the increasing Fe loading. The distribution information of the elements on the surface of catalysts can be obtained in the EDS elemental mapping images depicted in Fig. 5. As can be clearly seen in the figures, the filiform distributions of Si and O elements indicate the well dispersion of the elements on the surface of stainless steel fibers, whereas the O element existed outside of the stainless steel fibers was observed because of the existence form of Fe2O3. Fe element is well distributed on the surface of the catalyst with a uniform dispersion and the color of the Fe EDS mapping darkens with the increasing Fe loading. These results confirm the presence of Fe2O3 active component and its well dispersion on the surface of ZSM-5 zeolite membrane catalyst which could be contributed to the catalytic activity of phenol oxidation. 3.1.4 N2 adsorption-desorption isotherms Specific surface areas and porosity properties of ZSM-5 zeolite membrane and ready-to-use catalysts are determined by N2 adsorption-desorption. Fig. 6 displays the N2 adsorption-desorption

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isotherms of the samples, and their BET surface area and pore properties are summarized in Table 1. The specific surface areas (SBET) are calculated from adsorption branches in the relative pressure range of 0.06-0.3 using the BET (Brunauer-Emmett-Teller) method. The total pore volume (Vtotal) was estimated by analysis the N2 adsorption-desorption isotherms, the micropore volume (Vmicropore) and mesopore volume (Vmesopore) were calculated using the t-plot method and the Barrett-Joyner-Halenda (BJH) method, respectively. Fig. 6 shows that the volume adsorbed increases with increasing relative pressures for all isotherms which is due to the volume filling of micropores in ZSM-5 zeolite membrane. The volume adsorbed increases continually when the relative pressures increase, which should be caused by the multilayer adsorption. The N2 adsorption-desorption isotherms of the ZSM-5 zeolite membrane fit for a typical microporous feature of such material (type Ⅰ adsorption isotherm) and each catalyst samples shows a hysteresis loop at a high relative pressure fit for type Ⅳ of adsorption isotherms [36]. The hysteresis loops of Fe loading catalysts, namely, Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%) shown in Fig. 6 (b), (c) and (d) respectively, are much larger than the ZSM-5 zeolite membrane support shown in Fig. 6 (a), which could be due to the existence of mesopores between the Fe2O3 particles. As can be seen the results listed in Table 1, BET specific surface area and total pore volume of the PSSFs are 12.00 m2/g and 0.0050 cm3/g, respectively. The ZSM-5 zeolite membrane shows much higher BET specific area (215.7 m2/g) and total pore volume (0.1059 cm3 /g) than PSSFs. The BET specific surface of the three catalyst samples is lower than the ZSM-5 zeolite membrane support because of the extra existence of Fe2O3 particles on the surface of the ZSM-5 zeolite. The volume of micropores decreases with the increasing Fe loading that could be attributed to the block of pore canal by the increased Fe2O3 particles. However, the volumes of total pores and mesopores increase from 0.1059 cm3/g to 0.1280 cm3/g and from 0.01676 cm3/g to 0.06309 cm3/g, respectively, with the Fe loading increasing to 25%. These increases of volume may result from the increase of porous Fe2O3 particles. However, the volumes of the catalyst decrease to the lowest values (Vtotal =0.09193 cm3/g and Vmesopore= 0.04408 cm3/g) when the Fe loading increase to 35%, which may result from the blocks of the ZSM-5 zeolite membrane and the agglomeration of high concentration of Fe2O3 component as SEM and EDS mapping confirmed before. It can be concluded that high concentration of Fe2O3 has adverse

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influence to the BET specific surface area and pore distribution of the catalysts [37]. 3.1.5 H2-TPR H2 temperature-programmed reduction (TPR) experiments were conducted on ZSM-5 zeolite membrane support and the catalyst samples following a He pretreatment. The results are shown in Fig. 7. As can be seen in the figure, no obvious reduction peaks are observed in the TPR spectrum of ZSM-5 zeolite membrane support, indicating that the ZSM-5 zeolite membrane support shows no oxidation ability. And all the TPR spectrums of the catalyst samples are similar, charactering by the presence of two reduction peaks with maximum around 320 ℃ and 500 ℃ . Two mechanisms may be referred to explain the reduction of the Fe2O3 as follows, (a) 1 2 1  +  →   +   3 3 3 2 8 8   + → 2  +   3  3  3 (b)   +  → 2  +   2  + 2  → 2  + 2   . The ratios of H2 consumption are 8:1and 2:1 according to the reduction mechanism of equations (a) and (b), respectively. It can be found that the area ratios by integration of the same H2-TPR peaks are higher than 8:1, indicating that reduction mechanism of the Fe2O3 on the catalysts is more likely according to equations (a) [38]. Thus, the first peak may be assigned to reduction of Fe2 O3 to Fe3O4 and the second peak may be assigned to subsequent reduction of Fe4O3 to Fe. As the Fe loading increases, the shape of the TPR profile changes. The reduction areas increase with the increasing of Fe loading and the reduction temperature of Fe3O4 increase from 475.5 to 540.2 ℃. Generally, small particles are expected to get reduced at lower temperatures and the bulk Fe2O3 is expected to get reduced at higher temperature. H2-TPR results confirm the existence phase of Fe active component and the high catalytic ability of the ZSM-5 zeolite membrane catalysts [39-41]. 3.1.6 XPS The X-ray photoelectron spectra (XPS) were performed first by using an aluminum anode, and the XPS results of Fe 2p and O 1s are shown in Fig. 8 (A) and (B), respectively. All spectra were

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first calibrated using the C 1s peak at 284.6 eV and subtracted by linear-type background. As can be seen in Fig. 8 (A), the binding energies of Fe 2p3/2 and Fe 2p1/2 are located around 711.2 and 725.5 eV, indicating that Fe is directly bonded to O [42]. Both 2p3/2 and 2p1/2 peaks are accompanied by a small satellite structures on the high binding energy side. The satellite line is the characteristic of Fe3+ in Fe2O3 and the results are consistent with XRD characterization [43, 44]. According to Jin’s report [42], the Fe valances have some correlation with the calcined temperature, when the calcined temperature was upon 500 ℃, Fe (Ⅲ) species can be obtained. The peak intensities of Fe 2p are increasing with the increase of Fe loading, meanwhile, the 2p3/2 and 2p1/2 peaks were shifted to higher binding energy. This phenomenon may result from the increasing thickness of the Fe2O3 active component. The XPS results of O 1s of the catalyst samples were displayed in Fig. 8 (B), asymmetric two-band structures were observed for all the catalyst samples. The O 1s peak at 530.3 eV observed on all of the three samples could be assigned to the Fe-O bond. The O 1s binding energy of 533.0 eV could be assigned to chemisorbed or dissociated oxygen in SiO2 impurity or hydroxyl species according to literatures [42, 45]. The peaks intensity of Fe-ZSM-5 (25%) at 533.0 eV is the highest of all the catalyst samples, indicating that the absorbed oxygen is the most. This could be attributed to the uniform distribution of active component on the surface of the ZSM-5 zeolite support and result in the storage enhancement of oxide species. 3.2 Catalytic wet peroxide oxidation of phenol over Fe-ZSM-5 zeolite membrane catalysts in the membrane reactor Catalytic wet peroxide oxidation of phenol was carried out in a membrane reactor over Fe-ZSM-5 zeolite membrane catalysts with a 2 cm catalyst bed height while other operation parameters were kept as constants (namely, feed flow rate of 2.0 mL/min, temperature of 80 ℃). The conversion of phenol, H2O2, TOC and the iron leaching concentration in the treated solution as the main parameters monitored during the course of reaction were measured. The experimental results were depicted in Fig. 9. Phenol conversion values depicted in Fig. 9 (a) indicated that all the catalysts showed good catalytic activity for the CWPO of phenol and Fe-ZSM-5 (25%) achieved the highest phenol conversion (about 95%), Fe-ZSM-5 (35%) produced lower phenol conversion (about 85%) and the Fe-ZSM-5 (15%) showed the lowest

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catalytic activity, phenol conversion decreased sharply from 80% to 50%. Meanwhile, the H2 O2 conversion shown in Fig. 9 (b) has the same variation trend as phenol conversion, i.e., the Fe-ZSM-5 (25%) showed the highest H2O2 conversion (about 65%) and the Fe-ZSM-5 (15%) showed the lowest H2O2 conversion (about 35%). These results indicate that the catalytic reaction was not according to the stoichiometric amount for the total phenol oxidation. Phenol was oxidized partially and produced many intermediate products and by-products [46]. On the other hand, the residual TOC is contributed to the low-molecular-weight organic acids (which are more resistant to oxidation) evolved by the primary products from phenol ring opening and oxidation of the aromatics intermediates [31]. TOC conversion described in Fig. 9 (c) showed that Fe-ZSM-5 (25%) presented the best TOC conversion with relative higher values (about 40%), meanwhile the Fe-ZSM-5 (35%) showed lower values (about 30%) and Fe-ZSM-5 (15%) showed a decreasing values (decreased from 42% to 20% rapidly). All of above showed that the best Fe loading was 25%. Lower Fe loading (namely 15%) may produce insufficient OH·, and higher Fe loading (namely 35%) will lead to the agglomeration of active component (as characterization certificated before). As can be seen in Fig. 9 (d), low Fe leaching concentration in the treated solution (lower than 7 mg/L) was observed, the Fe leaching concentrations of Fe-ZSM-5 (25%) showed the highest values (about 5 mg/L), the Fe leaching concentrations of Fe-ZSM-5 (15%) were about 2 mg/L and the Fe leaching concentrations of Fe-ZSM-5 (35%) were lower than 2 mg/L. This novel Fe-ZSM-5 zeolite membrane catalyst showed a good catalytic activity in the CWPO process of phenol. Further researches should focus on the kinetics studies of the oxidation reaction of phenol over this zeolite membrane catalyst. The stability of the Fe-ZSM-5 zeolite membrane catalyst used in the CWPO process of phenol should also be further considered.

4. Conclusions Novel Fe-ZSM-5 zeolite membrane catalysts were synthesized for catalytic wet peroxide oxidation of phenol aqueous solution in a membrane reactor. The characterization results showed that ZSM-5 zeolite membrane with a thickness of 6 µm was successfully fabricated on the surface of the PSSFs and Fe element with a form of Fe2O3 was uniformly dispersed on the surface of ZSM-5 zeolite membrane support. However, blocking and agglomeration of Fe2O3 component was observed on the Fe-ZSM-5 (35%) catalyst and it was adverse to the catalytic activity. The CWPO

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of phenol results showed that Fe-ZSM-5 zeolite membrane catalyst with a Fe loading of 25% achieved the highest activity (phenol conversion about 95% and TOC conversion about 45%, respectively) at the temperature of 80 ℃, feed flow rate of 2 mL/min and catalyst bed height of 2.0 cm after continuously ran for 7 hours. Meanwhile, low loss of Fe species was observed on all of the zeolite membrane catalysts (Fe leaching lower than 7 mg/L).

Acknowledgement We gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant No. 21176086 and 21376101).

References [1] G. Busca, S. Berardinelli, C. Resini, L. Arrighi, Technologies for the removal of phenol from fluid streams: A short review of recent developments, J. Hazard. Mater. 160(2008)265-288. [2] M. Khalid, G. Joly, A. Renaud, P. Magnoux, Removal of phenol from water by adsorption using zeolites, Ind. Eng. Chem. Res. 43(2004)5275-5280. [3] K. Kryst, D.G. Karamanev, Aerobic phenol biodegradation in an inverse fluidized-bed biofilm reactor, Ind. Eng. Chem. Res. 40(2001)5436-5439. [4] X. Jia, J. Wen, X. Wang, W. Feng, Y. Jiang, CFD modeling of immobilized phenol biodegradation in three-phase airlift loop reactor, Ind. Eng. Chem. Res. 48(2009)4514-4529. [5] M. Pera-Titus, V. Garcıá -Molina, M.A. Banos, J. Giménez, S. Esplugas, Degradation of chlorophenols by means of advanced oxidation processes: a general review, Appl. Catal. B: Environ. 47(2004)219-256. [6] E. Guélou, J. Barrault, J. Fournier, J. Tatibouët, Active iron species in the catalytic wet peroxide oxidation of phenol over pillared clays containing iron, Appl. Catal. B: Environ. 44(2003)1-8. [7] C. Walling, Fenton's reagent revisited, Accounts Chem. Res. 8(1975)125-131. [8] J.A. Zazo, A.F. Fraile, A. Rey, A. Bahamonde, J.A. Casas, J.J. Rodriguez, Optimizing calcination temperature of Fe/activated carbon catalysts for CWPO, Catal. Today 143(2009)341-346. [9] L.A. Galeano, A. Gil, M.A. Vicente, Effect of the atomic active metal ratio in Al/Fe-, Al/Cuand Al/(Fe-Cu)-intercalating solutions on the physicochemical properties and catalytic

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activity of pillared clays in the CWPO of methyl orange, Appl. Catal. B: Environ. 100(2010)271-281. [10] K. Fajerwerg, H. Debellefontaine, Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst, Appl. Catal. B: Environ. 10(1996)L229-L235. [11] K.M. Valkaj, A. Katovic, S. Zrnčević, Investigation of the catalytic wet peroxide oxidation of phenol over different types of Cu/ZSM-5 catalyst, J. Hazard. Mater. 144(2007)663-667. [12] N.S. Inchaurrondo, P. Massa, R. Fenoglio, J. Font, P. Haure, Efficient catalytic wet peroxide oxidation of phenol at moderate temperature using a high-load supported copper catalyst, Chem. Eng. J. 198–199(2012)426-434. [13] R.J. Lopes, M. Perdigoto, R.M. Quinta-Ferreira, Tailored investigation and characterization of heterogeneous {Mn, Cu}/TiO2 catalysts embedded within a ceria-based framework for the wet peroxide oxidation of hazardous pollutants, Appl. Catal. B: Environ. 117(2012)292-301. [14] S. Zhou, Z. Qian, T. Sun, J. Xu, C. Xia, Catalytic wet peroxide oxidation of phenol over Cu-Ni-Al hydrotalcite, Appl. Clay Sci. 53(2011)627-633. [15] J.G. Carriazo, E. Guelou, J. Barrault, J.M. Tatibouët, S. Moreno, Catalytic wet peroxide oxidation of phenol over Al-Cu or Al-Fe modified clays, Appl. Clay Sci. 22(2003)303-308. [16] M.N. Timofeeva, S.T. Khankhasaeva, E.P. Talsi, V.N. Panchenko, A.V. Golovin, E.T. Dashinamzhilova, S.V. Tsybulya, The effect of Fe/Cu ratio in the synthesis of mixed Fe, Cu, Al-clays used as catalysts in phenol peroxide oxidation, Appl. Catal. B: Environ. 90(2009)618-627. [17] J. Carriazo, E. Guélou, J. Barrault, J.M. Tatibouët, R. Molina, S. Moreno, Catalytic wet peroxide oxidation of phenol by pillared clays containing Al–Ce–Fe, Water Res. 39(2005)3891-3899. [18] N.H. Phu, T.T.K. Hoa, N.V. Tan, H.V. Thang, P.L. Ha, Characterization and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous solutions, Appl. Catal. B: Environ. 34(2001)267-275. [19] S. Chaliha, K.G. Bhattacharyya, Catalytic wet oxidation of 2-chlorophenol, 2, 4-dichlorophenol and 2, 4, 6-trichlorophenol in water with Mn (II)-MCM41, Chem. Eng. J.

14 / 33

139(2008)575-588. [20] X. Zhong, J. Barbier Jr, D. Duprez, H. Zhang, S. Royer, Modulating the copper oxide morphology and accessibility by using micro-/mesoporous SBA-15 structures as host support: Effect on the activity for the CWPO of phenol reaction, Appl. Catal. B: Environ. 121(2012)123-134. [21] J. Guo, M. Al-Dahhan, Catalytic wet oxidation of phenol by hydrogen peroxide over pillared clay catalyst, Ind. Eng. Chem. Res. 42(2003)2450-2460. [22] A. Quintanilla, A.F. Fraile, J.A. Casas, J.J. Rodríguez, Phenol oxidation by a sequential CWPO–CWAO treatment with a Fe/AC catalyst, J. Hazard. Mater. 146(2007)582-588. [23] A. Rey, M. Faraldos, J.A. Casas, J.A. Zazo, A. Bahamonde, J.J. Rodríguez, Catalytic wet peroxide oxidation of phenol over Fe/AC catalysts: Influence of iron precursor and activated carbon surface, Appl. Catal. B: Environ. 86(2009)69-77. [24] A. Tavolaro, E. Drioli, Zeolite Membranes, Adv. Mater. 11(1999)975-996. [25] Y. Cheng, J. Li, L. Wang, X. Sun, X. Liu, Synthesis and characterization of Ce-ZSM-5 zeolite membranes, Sep. Purif. Technol. 51(2006)210-218. [26] X. Zou, G. Zhu, H. Guo, X. Jing, D. Xu, S. Qiu, Effective heavy metal removal through porous stainless-steel-net supported low siliceous zeolite ZSM-5 membrane, Micropor. Mesopor. Mater. 124(2009)70-75. [27] E.R. Geus, H. van Bekkum, W.J.W. Bakker, J.A. Moulijn, High-temperature stainless steel supported zeolite (MFI) membranes: Preparation, module construction, and permeation experiments, Micropor. Mater. 1(1993)131-147. [28] I. Yuranov, A. Renken, L. Kiwi-Minsker, Zeolite/sintered metal fibers composites as effective structured catalysts, Appl. Catal. A: Gen. 281(2005)55-60. [29] A. Zampieri, A. Dubbe, W. Schwieger, A. Avhale, R. Moos, ZSM-5 zeolite films on Si substrates grown by in situ seeding and secondary crystal growth and application in an electrochemical hydrocarbon gas sensor, Micropor. Mesopor. Mater. 111(2008)530-535. [30] H. Chen, H. Zhang, Y. Yan, Preparation and characterization of a novel gradient porous ZSM-5 zeolite membrane/PSSF composite and its application for toluene adsorption, Chem. Eng. J. 209(2012)372-378.

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[31] G. Centi, S. Perathoner, T. Torre, M.G. Verduna, Catalytic wet oxidation with H2O2 of carboxylic acids on homogeneous and heterogeneous Fenton-type catalysts, Catal. Today 55(2000)61-69. [32] F. Martínez, J.A. Melero, J.Á. Botas, M.I. Pariente, R. Molina, Treatment of phenolic effluents by catalytic wet hydrogen peroxide oxidation over Fe2 O3/SBA-15 extruded catalyst in a fixed-bed reactor, Ind. Eng. Chem. Res. 46(2007)4396-4405. [33] J.A. Botas, J.A. Melero, F. Martínez, M.I. Pariente, Assessment of Fe2O3/SiO2 catalysts for the continuous treatment of phenol aqueous solutions in a fixed bed reactor, Catal. Today 149(2010)334-340. [34] M.M. Treacy, J.B. Higgins, R. von Ballmoos, I.Z. Association, S. Commission, Collection of simulated XRD powder patterns for zeolites, Elsevier, New York, 1996. [35] M. Rauscher, K. Kesore, R. Mönnig, W. Schwieger, A. Tißler, T. Turek, Preparation of a highly active Fe-ZSM-5 catalyst through solid-state ion exchange for the catalytic decomposition of N2 O, Appl. Catal. A: Gen. 184(1999)249-256. [36] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L. Moscou, R.A. Pierotti, J. Rouquérol, T. Siemieniewska, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984), Pure Applied Chemistry, 57(1985)603-619. [37] F. Adam, J. Andas, I.A. Rahman, A study on the oxidation of phenol by heterogeneous iron silica catalyst, Chem. Eng. J. 165(2010)658-667. [38] R.Q. Long, R.T. Yang, Characterization of Fe-ZSM-5 catalyst for selective catalytic reduction of nitric oxide by ammonia, J. Catal. 194(2000)80-90. [39] H. Chen, W.M. Sachtler, Promoted Fe/ZSM-5 catalysts prepared by sublimation: de-NOx activity and durability in H2O-rich streams, Catal. Lett. 50(1998)125-130. [40] L.J. Lobree, I. Hwang, J.A. Reimer, A.T. Bell, Investigations of the state of Fe in H–ZSM-5, J. Catal. 186(1999)242-253. [41] K. Krishna, M. Makkee, Preparation and pretreatment temperature influence on iron species distribution and N2O decomposition in Fe-ZSM-5, Catal. Lett. 106(2006)183-193. [42] M. Jin, R. Yang, M. Zhao, G. Li, C. Hu, Application of Fe/Activated carbon catalysts in the

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hydroxylation of phenol to dihydroxybenzenes, Ind. Eng. Chem. Res. 53(2014)2932-2939. [43] É.G. Bajnóczi, N. Balázs, K. Mogyorósi, D.F. Srankó, Z. Pap, Z. Ambrus, S.E. Canton, K. Norén, E. Kuzmann, A. Vértes, Z. Homonnay, A. Oszkó, I. Pálinkó, P. Sipos, The influence of the local structure of Fe(III) on the photocatalytic activity of doped TiO2 photocatalysts-An EXAFS, XPS and Mössbauer spectroscopic study, Appl. Catal. B: Environ. 103(2011)232-239. [44] T. Fujii, D. Alders, F.C. Voogt, T. Hibma, B.T. Thole, G.A. Sawatzky, In situ RHEED and XPS studies of epitaxial thin α-Fe2O3(0001) films on sapphire, Surf. Sci. 366(1996)579-586. [45] Z. Tian, P.H. Tchoua Ngamou, V. Vannier, K. Kohse-Höinghaus, N. Bahlawane, Catalytic oxidation

of

VOCs

over

mixed

Co-Mn

oxides,

Appl.

Catal.

B:

Environ.

117–118(2012)125-134. [46] J.A. Zazo, J.A. Casas, A.F. Mohedano, J.J. Rodriguez, Catalytic wet peroxide oxidation of phenol with a Fe/active carbon catalyst, Appl. Catal. B: Environ. 65(2006)261-268.

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Figure contents: Fig. 1. Flowchart of the experimental set-up. Fig. 2. XRD patterns of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%). Fig. 3. FE-SEM images of the support and catalyst samples: (a)-(b) ZSM-5 zeolite membrane support, (c) cross-sectional SEM image of ZSM-5 zeolite membranes, (d)-(f) microstructure of Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%), respectively, (g)-(i) morphological images of Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%), respectively. Fig. 4. EDS elemental analysis spectrum of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%). Fig. 5. EDS elemental mapping images of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%). Fig. 6. N2 adsorption-desorption isotherms of the samples at 77 K: (a) ZSM-5 zeolite membrane; (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%). Fig. 7. H2 temperature-programmed reduction profiles observed for (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%) catalysts. Fig. 8. A. Fe 2p XPS spectra for catalyst samples: (a) Fe-ZSM-5 (15%), (b) Fe-ZSM-5 (25%) and (c) Fe-ZSM-5 (35%); B. O 1s XPS spectra for catalyst samples: (a) Fe-ZSM-5 (15%), (b) Fe-ZSM-5 (25%) and (c) Fe-ZSM-5 (35%). Fig. 9. Catalytic wet peroxide oxidation performance of phenol over Fe-ZSM-5 zeolite membrane catalysts: (a) phenol conversion (Xphenol ), (b) H2O2 conversion (XH2O2), (c) TOC conversion (XTOC) and (d) Fe leaching concentration (CFe).

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Fig. 1. Flowchart of the experimental set-up.

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Fig. 2. XRD patterns of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%).

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Fig. 3. FE-SEM images of the support and catalyst samples: (a)-(b) ZSM-5 zeolite membrane support, (c) cross-sectional SEM image of ZSM-5 zeolite membranes, (d)-(f) microstructure of Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%), respectively, (g)-(i) morphological iamges of Fe-ZSM-5 (15%), Fe-ZSM-5 (25%) and Fe-ZSM-5 (35%), respectively.

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Fig. 4. EDS elemental analysis spectrum of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%).

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Fig. 5. EDS elemental mapping images of the samples: (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%).

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Fig. 6. N2 adsorption-desorption isotherms of the samples at 77 K: (a) ZSM-5 zeolite membrane; (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%).

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Fig. 7. H2 temperature-programmed reduction profiles observed for (a) ZSM-5 zeolite membrane, (b) Fe-ZSM-5 (15%), (c) Fe-ZSM-5 (25%) and (d) Fe-ZSM-5 (35%) catalysts.

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Fig. 8. A. Fe 2p XPS spectra for catalyst samples: (a) Fe-ZSM-5 (15%), (b) Fe-ZSM-5 (25%) and (c) Fe-ZSM-5 (35%); B. O 1s XPS spectra for catalyst samples: (a) Fe-ZSM-5 (15%), (b) Fe-ZSM-5 (25%) and (c) Fe-ZSM-5 (35%).

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Fig. 9. Catalytic wet peroxide oxidation performance of phenol over Fe-ZSM-5 zeolite membrane catalysts: (a) phenol conversion (Xphenol), (b) H2O2 conversion (XH2O2), (c) TOC conversion (XTOC) and (d) Fe leaching concentration (CFe).

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Table list: Table 1. Physiochemical properties of the samples.

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Table 1. Physiochemical properties of the samples. Samples

VMicro-pore (cm3/g)

VMeso-pore (cm3/g)

Vtotal (cm3/g)

SBET (m2/g)

PSSFsa

-

-

0.0050

12.00

ZSM-5 membraneb

0.08319

0.01676

0.1059

215.7

Fe-ZSM-5 (15%)c

0.06708

0.03311

0.1102

183.1

Fe-ZSM-5 (25%)d

0.05651

0.06309

0.1280

177.4

Fe-ZSM-5 (35%)e

0.04981

0.04408

0.09193

138.1

a

Relative to paper-like sintered stainless steel fibers support. b

Relative to ZSM-5 zeolite membrane support.

c

Relative to Fe-ZSM-5 zeolite membrane catalyst with a Fe loading of 15%.

d

Relative to Fe-ZSM-5 zeolite membrane catalyst with a Fe loading of 25%.

e

Relative to Fe-ZSM-5 zeolite membrane catalyst with a Fe loading of 35%.

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Graphical abstract: :

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Highlights: 1. Novel Fe-ZSM-5 zeolite membrane catalysts were prepared for catalytic wet peroxide oxidation of phenol in a membrane reactor. 2. The Fe-ZSM-5 zeolite membrane catalyst presented a good catalytic activity (phenol conversion reached 95%). 3. Fe leaching concentration values lower than 7.0 mg/L were observed.

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