SiC Filter for the

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Novel synthesis of a high performance Pt/ ZnO/SiC filter for the oxidation of toluene Linlin Li, Feng Zhang, Zhaoxiang Zhong, Ming Zhu, Chenyang Jiang, Jian Hu, and Weihong Xing Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02793 • Publication Date (Web): 26 Oct 2017 Downloaded from http://pubs.acs.org on October 27, 2017

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Industrial & Engineering Chemistry Research

Novel synthesis of a high performance Pt/ZnO/SiC filter for the oxidation of toluene Linlin Li, Feng Zhang, Zhaoxiang Zhong*, Ming Zhu, Chenyang Jiang, Jian Hu, Weihong Xing* State Key Laboratory of Materials-Oriented Chemical Engineering, National Engineering Research Center for Special Separation Membrane, Nanjing Tech University, Nanjing210009, Jiangsu, China *Corresponding author. Tel: +86-25-83172288; Fax: +86-25-83172292; E-mail address: [email protected], [email protected]

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Abstract: In the work, a novel Pt/ZnO/SiC filter was successfully prepared by first coating ZnO nanoparticles on silicon carbide filter with sol-gel process and then loading Pt nanoparticles on the ZnO layer with impregnation. Microstructure, crystal morphology, composition and elemental valence of the prepared filter were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectronic spectroscopy (XPS). It is found that ZnO coating layer has improved dispersity of Pt nanoparticles and significantly enhanced the catalytic performance. Toluene was used as model volatile organic compound which went through a complete conversion up to 100 % over the porous tubular Pt/ZnO/SiC material with filtration velocity of 0.72 m/min within 240 h at 210 °C. The synthetic ceramic filter presented good capacity of catalytic oxidation on VOCs and accordingly a simple approach is suggested here for preparing catalyst on the support in order to increase the catalytic efficiency. Keywords: Ceramic filter; sol-gel; impregnation method; toluene; catalytic oxidation Introduction A large amount of volatile organic compounds (VOCs) and dust are discharged to the environment in industrial processes at chemical plants, and power plant, and this air pollution has attracted increasing concern due to the potential threat to human health. Therefore, considerable efforts have been performed to eliminate VOCs, by adsorption1, photo-catalysis2, condensation, bio-filtration, and catalytic oxidation3-4. Of these methods, catalytic oxidation is recognized as a potentially efficient and economical technology for the removal of VOCs from industrial waste gas for this 2


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method avoids creating secondary pollution. Supported noble metal catalysts such as Pt and Pd are widely used for the removal of VOCs. Peng et al.5 prepared Pt-CeO2 for toluene removal and achieved a 100% conversion ratio at 180 °C with a mass space velocity (WHSV) of 48000 ml·g-1·min-1. Fu et al.6 used Pt-Pd/MCM-41 for the total catalytic oxidation of toluene (initial concentration of 500 ppm) at 180 °C with a flow rate of 170 ml·min-1. Enhancing the catalytic efficiency of Pt for toluene oxidation reaction is an important perspective for energy consumption. An appropriate selection on the support material and active ingredients is the key point for the effective combination and improved catalytic performance Various materials coated with catalytic active species have been widely used in exhaust gas treatment with extended surface area and high adsorption capacity, such as active carbon fiber7, hollow fiber membrane, mesoporous ZSM-5 zeolite8, and AlOOH nanoflakes9. Among the supports, ceramic filters are widely used in gas purification due to high filtration efficiency and feasibility for upscaling processes10-12. The ceramic material SiC is of good thermal and chemical stability and has large pore interconnectivity with three-dimensional reticular structure and uniform channel distribution13-15, which could possibly replace the traditional materials as a supporting substrate for catalyst, for instance, in the toluene removal application. In our previous work16, 17, photocatalytic and antibacterial ZnO/SiC material was synthesized and coated ZnO has improved the specific surface area by 6 folds. It is also demonstrated that a strong binding force between ZnO and SiC as formed in the form of covalent bond. Many studies point out that metal-metallic oxide could 3



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facilitate catalytic oxidation, meanwhile, the interaction between metal and metal oxide reinforces the coating adhesion18, 19. Moon et al.20 reported that the metal-oxide interface plays and important role on catalytic activity, such as TiO2, Nb2O5, Ta2O5, and CeO2. Metal oxide catalyst ZnO has properties including large specific surface area, good adsorption ability, lattice imperfection and anti-microbial activity16. In this work, Pt/ZnO/SiC filter was designed and prepared by first coating a layer of ZnO on the surface of pore channel in SiC tubular filter via sol-gel method. To follow up, Pt nanoparticles were added on the ZnO coating layer SiC in an impregnation way and the catalytic performance was examined for oxidizing the toluene. The morphology, composition, and microstructure of the prepared catalytic ceramic filter were characterized by SEM, XRD, HRTEM, and XPS. Effect of the ZnO layer on Pt nanoparticle formation, the interaction between Pt and ZnO, and the factors affecting the catalytic oxidation would be discussed in the paper. Catalysis mechanism

of

toluene

oxidation

route

was

proposed

based

on

the

adsorption-desorption test and in-situ infrared absorbance measurement at the reaction temperature. An overall schematic diagram on VOCs oxidation and degradation using the catalytic composite is displayed in Figure 1.

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Figure 1. The schematic diagram of the composite catalytic filter

Experimental Section Materials A microporous SiC filter with an inner diameter of 16 mm and outer diameter of 40 mm was provided by the Institute of Metal Research of Chinese Academy of Sciences. Hydrated zinc acetate (Zn(Ac)2·2H2O; Xilong Chemical Co.), 2-methoxyethanol and ethanolamine (MEA; Shanghai Ling Feng Chemical Reagent Co., Ltd.) were used as the precursors of zinc oxide, solvent and stabilizer, respectively. Chloroplatinic acid (H2PtCl6; Sinopharm chemical reagent co., LTD) was used as the precursor of the Pt nanoparticles. Toluene (0.1 vol. % toluene and 99.9 vol. % N2, Nanjing special gas co., LTD) and air (Nanjing day ze gas co., LTD) were used for the catalytic oxidation of toluene. Preparation of Pt/ZnO/SiC filter First, a layer of ZnO nanoparticles was applied to a SiC filter via sol-gel method. The zinc colloidal sol at a concentration of 1 mol/L was prepared as follow. 5



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Zn(Ac)2·2H2O was dissolved in 2-methoxyethanol and ethanolamine and the molar ratio of ethanolamine to Zn(Ac)2·2H2O was kept at 1:1. The mixed solution was stirred at 60 °C for an hour to obtain the homogeneous colloidal sol. The SiC filter was cleaned in ethanol for 30 min under ultrasonication before use. Then, the SiC filter was dried and subsequently dipped into the zinc sol and suctioned for an hour under vacuum pump. The sample was moved from the sol to a drying oven and dried at 70 °C for 10 min. Finally, a ZnO/SiC filter was obtained after calcination at 600 °C in air with a heating rate of 10 °C /min and holding temperature of 600 °C for 30 min. To obtain the Pt catalyst attached on the ZnO/SiC filter, a simple impregnation method was used. First, a certain amount of chloroplatinic acid hexahydrate was dissolved in distilled water at a mass concentration of 1 g/L. 15 ml of ammonium hydroxide (0.5 mol/L) was added to the platinum solution to adjust the pH to 7. The prepared solution was transferred to a suction flask. The ZnO/SiC filter was dipped into the solution and de-gassed by application of a vacuum pump (SHB-Ⅲ) for 1 hour to ensure adequate coating of the PtCl62- on the ZnO/SiC filter. The Pt/ZnO/SiC filter with 0.03 wt.% Pt was obtained after calcination at 600 °C with a heating rate of 10 °C/min and holding temperature of 600 °C for 30 min. Characterization of the as-prepared sample Morphology of the Pt/ZnO/SiC filter was investigated with Field Emission Scanning Electron Microscope (FESEM, S4800, Hitachi, Tokyo, Japan) at operating voltage of 20 kV and High Resolution Transmission Electron Microscope (HRTEM, JEOL JEM-2010 UHR; JEM- 2100F, JEOL Inc., Japan) at an acceleration voltage of 6


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200 kV. The TEM sample was prepared by addition of the diluted solution in ethanol on a copper grid and then dried in air. The crystal phase of the Pt/ZnO/SiC filter and the sample without Pt nanoparticles were investigated by X-ray diffraction (XRD; Mini Flex 600) using Cu Kα radiation (40 kV, 15 mA) at a step size of 0.05°, and a scanning rate of 2°/ min, from 10° to 80°. The grain size was calculated with the Scherrer equation ௞ఒ

D = ఉ௖௢௦ఏ

(1)

where D represents the average crystallite size, k is the Scherrer constant, λ is x-ray wavelength, and β and θ represent the half peak width of the XRD diffraction patterns and diffraction angle, respectively. X-ray Photoelectronic Spectroscopy (XPS) measurement was performed with a Theta Probe XPS system (Thermo ESCALAB 250, USA) and analyzed by means of the energy analyzer (30eV). The adsorption capacity of the porous materials was characterized by ASAP 2460. In-situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT) measurement was performed to track the reaction of toluene in the reaction route. Loading amount, and gas permeation of the Pt/ZnO/SiC filter In order to determine the loading amount of ZnO and Pt nanoparticles, the SiC filter and ZnO/SiC filter support were weighed before and after coating. The prepared ZnO/SiC filter and Pt/ZnO/SiC filter were dissolved in hydrochloric acid to obtain Zn solution and Pt solution, respectively. The prepared solution was diluted with deionized water to 1 L and measured by inductive coupled plasma emission 7



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spectrometer (ICP, Optima 7000DV, Perkin Elmer). The concentration of Zn and Pt were known. The mass of ZnO and Pt were determined as below:

݉௓௡ை % = ݉௉௧ % =

ిೋ೙ ౒ ∗୑ೋ೙ೀ ಾೋ೙

ெೋ೙ೀ/ೄ೔಴ େು೟ ∗௏

ெು೟/ೋ೙ೀ/ೄ೔಴

∗ 100%

(2)

∗ 100%

(3)

The gas permeation flux was measured using a pore-size distribution analyzer (GaoQ Func. Mater. Co. Ltd., China). Measurement of catalytic activity The catalytic activity of the Pt/ZnO/SiC filter was examined by measuring the conversion of toluene, as a representative VOC, in a laboratory testing unit (Figure 2). The test apparatus was designed to measure the oxidation of VOCs. Five concentrations of toluene from 100 ppm to 500 ppm were used to assess the catalytic performance of Pt/ZnO/SiC filter. The flow rate was controlled using a mass flow controller (Beijing sevenstar huachuang electronics co., LTD). The measurements were performed on catalytically activated element cylinders (40 mm o.d., 16 mm i.d., and 80 mm in length) in the temperature range of 110 to 250℃ using adjusting a constant filtration velocity of 1.2 cm/s at all temperature points. The conversion ratio was measured as shown below: Conversion ratio of toluene (%) = 1 −

஼೚ೠ೟೗೐೟ ஼೔೙೗೐೟

× 100%

(4)

where Cinlet and Coutlet represent the initial concentration and final concentration of toluene, respectively. The concentration of toluene was measured by Gas Chromatograph (GC-2014) analyzer, with hydrogen flame detector. 8


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Figure 2. Flow scheme of the test apparatus for the measurement of toluene conversion in the catalytic activate filter. “T” is temperature; “P1” and “P2” are pressure for the entrance point and exit point, respectively. Result and Discussion Characterization of materials Microstructure and morphology Morphology of the bared SiC and the compositely coated SiC filters are presented in Figure 3. The three-dimensional structure of interconnected voids can be observed in the silicon carbonate framework as in Figure 3(a), which allows the gas molecules to penetrate the filter. In Figure 3 (b) it reveals that the ZnO grains were uniformly distributed on the macroporous surface. After addition of Pt nanoparticles the microstructure of ZnO layer were maintained as in Figure 3 (c). Yet the the loaded Pt nanoparticles could not be directly detected in SEM scanning limited by the very small dimension of the particles. High Resolution Transmission Electron Microscopy (HRTEM) was employed to characterize the adhered Pt nanoparticles. It can be seen from Figure 3 (e) that there was significant agglomeration of Pt nanoparticles when they were directly coated onto 9



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SiC surface. In the contrast, Pt nanoparticles could be more homogeneously distributed on the ZnO/SiC surface as in Figure 3 (f). It reveals that ZnO layer, as a potential second carrier, plays an important role in loading and dispersing the catalyst Pt. Dimension size of Pt nanoparticles is estimated to be 2 – 3 nm as circled and measured in TEM image in Figure 3 (g). The lattice spacing of the crystalline plane (111) is 0.23 nm also marked in the same TEM image which is consistent to the literature report21.

Figure 3. SEM images of (a) SiC filter, (b) ZnO/SiC filter, (c) Pt/SiC filter and (d) Pt/ZnO/SiC filter; TEM images of the (e) Pt/SiC filter and (f) Pt/ZnO/SiC filter, (g) zoomed on Pt/ZnO/SiC filter.

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Figure 4. EDS spectrum of the Pt/ZnO/SiC filter

Elemental composition in the material was analyzed in Energy Dispersive Spectrometry (EDS) (Figure 4) and it founds that C, O, Cu, Zn, Si and Pt were contained. Cu is present due to the copper grid used for TEM. The successful loading of Pt was confirmed by the EDS analysis (at 2.09 keV). X-Ray Diffraction patterns of the SiC filter before and after coating with ZnO and/or Pt are provided in Figure 5. Diffraction peaks of ZnO were found at 2θ 32.08°, 34.74°, and 36.56° representing the planes (100), (002), and (101) which is consistent to the literature report22. The mean particle size of nanoscale grains as calculated by the Scherrer equation is 22 nm (Table S1). No diffraction peak observed for Pt could be due to the very low loaded weight amount (0.030% according to ICP analysis) in the well-dispersed form.

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Figure 5. X-ray diffraction patterns of (a) SiC, (b) ZnO/SiC, (c) Pt/ZnO/SiC and (d) Pt/SiC filters. Loading amount and gas permeation The loading mass of ZnO and Pt were determined with Inductive Coupled Plasma Emission Spectrometer (ICP) and the weight percentage of ZnO was found 4.8% (Table 1). Specific surface area of SiC, ZnO/SiC, Pt/SiC and Pt/ZnO/SiC were measured and also listed in Table 1. The presence of ZnO layer improved the specific surface area of SiC by 8 times, as well as, enhanced the loaded amount of Pt nanoparticles from 0.030% (Pt/ZnO/SiC) to 0.017% (Pt/SiC). The gas permeation flux of N2 through the various filters were measured at different pressure drops whose resulted are also given in Table 1. There is no apparent difference between the original filter and the modified samples in terms of N2 permeation flux indicating that Pt nanoparticles and ZnO thin layer cause only a slight change in the pore structure. The average pore size of the ZnO/SiC filter was slightly reduced to 537 µm compared to 586 µm for the pristine SiC filter due to the ZnO covering layer but without an effect on gas permeation rate. 12


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Table 1. Loading amount, BET, pore diameter and gas permeation of different filters. Loading ZnO

BET

Loading

Mean pore

Gas permeation

(%)

(m2/g)

Pt (%)

diameter (µm)

(m3·m-2·h-1·kPa-1)

SiC

-

0.20

-

586

20.53±1.1%

ZnO/SiC

4.8

1.62

-

537

20.44±0.85%

Pt/ZnO/SiC

4.8

1.93

0.03

529

20.43±0.92%

Pt/SiC

-

0.29

0.017

577

20.49±0.97%

Sample

Chemical composition analysis The chemical composition of the prepared Pt/ZnO/SiC filter was analyzed with X-ray Photoelectronic Spectroscopy (XPS) as displayed in Figure 6 and the percentage of Si, C, Zn, O and Pt were measured as 2.86%, 16.84%, 37.81%, 39.97% and 2.52%, respectively (Table 2). Signals on Si and C were derived from the filter substrate, Zn and O from ZnO transition layer, and Pt from the upmost loaded nanoparticles. The high-resolution spectrum of Zn 2p (Figure 6 (a)) at a binding energy 1019.65 eV is consistent with the reported result for the binding energy of Zn2+ oxidation state. Reaction between ZnO and SiO2 in the filter forming a new phase (Zn2SiO4) on the surface has been described in our previous work16. The O1s core level spectrum could be divided into two peaks after peak-fit processing in Figure 6 (b). The main peak located at 529.9 eV corresponds to lattice oxygen, and the minor peak at 531.3 eV drives from chemisorbed oxygen (C-O, C=O) and hydroxyl groups on ZnO surface. Mass ratio of the lattice oxygen over the chemisorbed oxygen was about 3. Higher amount of lattice oxygen complementarily proves the existence of ZnO layer and possibly also the oxides as PtO and PtO2 on the 13



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support surface23. In the Pt4f core level spectrum, there are three states of Pt0, Pt2+ and Pt4+ each having doublet peaks which have been fitted as in Figure 6 (c). The results indicate that Pt loaded on the surface of ZnO/SiC filter exhibits three valence states: Pt0, Pt2+, and Pt4+ (summarized in Table 3). The binding energy of 71.08 eV and 74.4 eV correspond to the electronic energy level of 4f7/2 and 4f5/2 for Pt0 state; 72.60 eV and 75.9 eV for 4f7/2 and 4f5/2 of Pt2+ sate; and 74.7 eV and 78.00 eV for 4f7/2 and 4f5/2 of Pt4+ state. The ratio of the three valence states of Pt0 : Pt2+ : Pt4+ is 23.6 : 28.30 : 48.07.

Table 2. The percentage of elements on the pore channel surface of the Pt/ZnO/SiC filter Elements

Si

C

Zn

O

Pt

Percentage (%)

2.86

16.84

37.81

39.97

2.52

Table 3. The binding energy and ratio of different Pt valence state. Pt0 (eV)

Valence state

Pt2+ (eV)

Pt4+ (eV)

Ratio

(Pt)

4f7/2

4f5/2

4f7/2

4f5/2

4f7/2

4f5/2

600 ℃

71.08

74.4

72.6

75.9

74.7

78

14


Pt0

/ Pt2+ / Pt0

23.63/28.30/48.07

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Figure 6. XPS analysis of the Pt/ZnO/SiC filter (a) Zn2p3/2 peaks, (b) O1s peaks, and (c) Pt4f peaks.

Catalytic activity and stability Catalytic performance of the Pt/ZnO/SiC filter The effect of reaction temperature, toluene concentration and residence time on the conversion rate were investigated using the catalytic Pt/ZnO/SiC filter in which the mixed gas of toluene and air passed through. The effect of temperature and residence 15



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time on the catalytic conversion ratio of toluene is plotted in Figure 7(a). A 100 % complete conversion rate was achieved with residence time 1 s at 210 °C using the filtration speed 0.72 m/min (the residence time and the filtration speed is reciprocally related). The conversion efficiency could be improved as increasing temperature from 120 °C to 210 °C. And it was easier to completely decompose toluene (300 ppm) at slower filtration rate (that is the longer residence duration 15 s). The optimal temperature was found as 210 °C and filtration velocity 0.72 m/min which is compatible to the conditions in industrial application. The effect of concentration of toluene on the catalytic conversion ratio was investigated. The results conclude that the conversion ratio decreased slightly with higher concentration of toluene (from 100 – 500 ppm) at both reaction temperature 141 °C and 173 °C. However, at the highest reaction temperature 210 °C the conversion ratio kept all above 99.9 % along with various concentration of reactant. It indicates that higher reacting temperature is required for treating more concentrated toluene gas at fixed filtration velocity.

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Figure 7. The conversion rate as a function of (a) reaction temperature with increased residence time and (b) toluene concentration at various temperature. Catalytic activity analysis of the Pt/ZnO/SiC filter In the catalytic oxidation reaction, the conversion ratio of toluene of has been measured using the pristine SiC filter and the catalyst modified filters under the operation conditions (residence time 1 s and toluene 300 ppm) at various temperatures (Figure 8). Toluene could not be degraded when it passed through either the SiC filter or ZnO/SiC filter (without catalyst Pt load), regardless of the reaction temperature. Conversion ratio of toluene on Pt/SiC filter was 50.4% at 210 °C, lower than that of using the Pt/ZnO/SiC filter (100% converted). It could be ascribed to agglomeration 17



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of Pt grains on SiC surface (without ZnO intermediate layer) which reduces the surface area of the catalyst (observed in TEM image in Figure 3 (e)). The interface layer ZnO apparently improved dispersed deposition of Pt nano-grains on the filter surface. The chemisorbed oxygen and oxygen vacancy in the ZnO layer could provide reactive oxygen species and increase the mobility of active oxygen atoms. The combined effect lead to the enhancement on the catalytic efficiency of Pt/ZnO/SiC filter24.

Figure 8. Conversion ratio of toluene using SiC filter, ZnO/SiC filter, Pt/ZnO/SiC filter and Pt/SiC filter (conditions: 210 °C, 0.72 m/min and 300 ppm). In addition, adsorption capacity (using nitrogen) of the bared filter and modified filters were carried out with ASAP 2460 whose results are given in Figure 9. It can be seen that the adsorption capacity of the materials ranks in the order: Pt/ZnO/SiC > Pt/SiC > SiC. Adsorption capacity of Pt/ZnO/SiC was significantly enhanced and its hysteresis loop was narrowed in comparison to that of Pt/SiC. It suggests that the presence of ZnO interlayer has improved the specific surface area for more efficient 18


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reversible adsorption/desorption process. In addition, pore size distribution of the three materials are found generally in the range of 2-10 nm.

Figure 9. (a) Adsorption-desorption isotherms and (b) pore size distribution of Pt/ZnO/SiC, Pt/SiC and SiC In-situ high temperature infrared measurement was made in order to understand the reaction mechanism. In Figure 10 (a) that the amount of absorbed toluene increases over time from 5 min to 30 min in the ZnO/SiC filter at 150 °C as the vibrational bands attributable to carboxylic salt25 (1528 and 1417 cm-1) whose intensity has been enhanced. By introducing the air (ambient oxygen) at the reaction temperature 150 °C, 180 °C and 210°C, no additional molecular vibration peak is observed in the infrared spectra. It demonstrates that adding gas phase oxygen could not effectively initiate oxidation reaction of toluene on the ZnO/SiC surface. In the contrast to ZnO/SiC, oxidation reactions of toluene on Pt/ZnO/SiC above 150 °C could be detected in Figure 10 (b). Absorbance bands around 3700 cm-1 (supposed to be the intermediate products) appeared when the air flow was added at in the system 150 °C and the corresponding absorbance intensity increased with higher reaction temperature from 150 °C to 210 °C. When the reaction temperature reached 210 °C, the two main vibrational absorbance at 1700 cm-1 and 1500 cm-1 19



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(corresponding to carboxylic acid) diminished, whereas, two sharp peaks at 1558 cm-1 and 1473 cm-1 maintained. In a conclusion, with catalytic performance of loaded Pt in the modified filter, oxidation of the maleate26 has been successfully initiated at 210 °C and further decomposed smaller molecules (e.g. carboxylic acid) have produced during the reaction.

Figure 10. In-situ infrared analysis tracing the toluene oxidation route on the filters (a) ZnO/SiC and (b) Pt/ZnO/SiC Proposed reaction mechanism for toluene oxidation over catalytic Pt/ZnO/SiC filter is schematically presented in Figure 11. Modification with both Pt and ZnO on the filter support has greatly improved adsorption capacity for the reactants. Studies reported that Pt-based catalyst performs effective adsorption of toluene and oxygen20. Composite Pt-ZnO catalyst is supposed to accelerate migration of lattice oxygen on the surface and improve formation of reactive oxygen species. Reactive oxygen species could promote the catalytic oxidation of toluene3, 27. In the end, toluene could be completely oxidized into final products CO2 and H2O through a series of intermediates in the presence of catalyst and oxygen28, 29.

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Figure 11. Catalytic diagram for toluene oxidation over the catalytic Pt/ZnO/SiC filter Stability and performance evaluation of the Pt/ZnO/SiC filter To test long-term stability and catalytic function of Pt/ZnO/SiC filter, oxidation reaction of toluene (concentration 300 ppm) was performed under the conditions residence time 1 s, filtration velocity 0.72 m/min at 210 °C (Figure 12). It maintained the steady and complete conversion ratio up 100% through the prepared Pt/ZnO/SiC filter within 240 hours. The result proves that the Pt/ZnO/SiC product has good catalytic lifetime and is compatible for industrial application.

Figure 12. The stability of the catalytic Pt/ZnO/SiC filter in toluene oxidization reaction at 210 °C lasting for 240 hours Catalytic properties of the prepared Pt/ZnO/SiC filter is compared with other catalytic products as listed in Table S2. Fu et.al.30 prepared Pt-Pd/MCM-41 catalyst which 21



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could completely convert toluene at 180 °C with gas flow rate 170 mL/min, whilst, Pt/ZnO/SiC (in the work) performed a complete catalytic conversion of toluene at 173 °C with the filtration rate 200 mL/min. Yang31,32 used 0.27Pt/3DOM 26.9CeO2– Al2O3 and Pt/8.9Co3O4/3DOM Al2O3 to catalytically convert toluene (1000 ppm) completely at flow rate 16.7 ml/min; Peng5 used Pt-CeO2 for catalytic decomposition of toluene (1000 ppm) totally at filtration rate 160 ml/min These works treated toluene at high concentration but under low filtration rate. In our work, the Pt/ZnO/SiC filter exhibited effective performance on toluene oxidation working with fast filtration rate. The improved catalytic efficiency of Pt/ZnO/SiC filter is mainly attributed to the homogenous dispersion of Pt on the substrate. Three dimensional structure in the SiC filter increases the effective interaction area and helps to the collision between the gaseous reactant molecules at active sites. Conclusion SiC filter coated with ZnO layer was used as the support for catalyst Pt loading instead of using the bared SiC filter. ZnO interface layer has effectively enhanced the adhesion, loaded amount and homogeneous dispersion of Pt nanoparticles on the filter surface. The composite Pt/ZnO/SiC filter was successfully fabricated and applied in catalytic oxidation which has obtained remarkable conversion ratio (100%) of toluene (300 ppm) with filtration velocity of 0.72 m/min at reaction temperature 210 °C in the long-term test for 240 hours. The synergetic effect of ZnO and Pt through improved oxygen transfer has significantly increased the catalytic performance of Pt/ZnO/SiC by 43% compared to the Pt/SiC filter. The Pt/ZnO/SiC filter presents promising 22


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properties for the stable catalytic oxidation to VOCs for industrial scale application. Acknowledgement Financial support was provided by the National Key R&D Program (2016YFC0204000), the National Natural Science Foundation of China (U1510202), and the Jiangsu Province Scientific Supporting Project (BK20170046, and BE2015695). Supporting Information Calculated mean size of the nanoscale ZnO crystal grain (Table S1); Comparison of the catalytic performance with other products (Table S2).

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References: (1) Yang, J.; Zhuang, T. T.; Wei, F.; Zhou, Y.; Cao, Y.; Wu, Z. Y.; Zhu, J. H.; Liu, C., Adsorption of nitrogen oxides by the moisture-saturated zeolites in gas stream. J.

Hazard. Mater. 2009, 162, 866-873. (2) Dzinun, H.; Othman, M. H. D.; Ismail, A. F.; Puteh, M. H.; Rahman, M. A.; Jaafar, J., Photocatalytic degradation of nonylphenol by immobilized TiO2 in dual layer hollow fibre membranes. Chem. Eng. J. 2015, 269, 255-261. (3) Maldonado-Hodar, F. J.; Moreno-Castilla, C.; Perez-Cadenas, A. F., Catalytic combustion of toluene on platinum-containing monolithic carbon aerogels. Appl.

Catal. B-Environ. 2004, 54, 217-224; (4) Per-Olof Larsson; Andersson, A.; Wallenberg, L. R.; Svensson, B., Combustion of CO and Toluene; Characterisation of Copper Oxide Supported on Titania and Activity Comparisons with Supported Cobalt, Iron, and Manganese Oxide. J. Catal. 1996, 163, 279–293. (5) Peng, R.; Sun, X.; Li, S.; Chen, L.; Fu, M.; Wu, J.; Ye, D., Shape effect of Pt/CeO2 catalysts on the catalytic oxidation of toluene. Chem. Eng. J. 2016, 306, 1234-1246. (6) Fu, X. R.; Liu, Y.; Yao, W. Y.; Wu, Z. B., One-step synthesis of bimetallic Pt-Pd/MCM-41 mesoporous materials with superior catalytic performance for toluene oxidation. Catal Commun. 2016, 83, 22-26. (7) Lin, C.-L.; Cheng, Y.-H.; Liu, Z.-S.; Chen, J.-Y., Metal catalysts supported on activated carbon fibers for removal of polycyclic aromatic hydrocarbons from incineration flue gas. J. Hazard. Mater. 2011, 197, 254-263. 24


Page 24 of 29

Page 25 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) Chen, C. Y.; Wang, X.; Zhang, J.; Bian, C. Q.; Pan, S. X.; Chen, F.; Meng, X. J.; Zheng, X. M.; Gao, X. H.; Xiao, F. S., Superior performance in catalytic combustion of toluene over mesoporous ZSM-5 zeolite supported platinum catalyst. Catal Today 2015, 258, 190-195. (9) Xu, Z. H.; Yu, J. G.; Jaroniec, M., Efficient catalytic removal of formaldehyde at room temperature using AlOOH nanoflakes with deposited Pt. Appl. Catal. B:

Environ. 2015, 163, 306-312. (10) Heidenreich, S.; Haag, W.; Salinger, M., Next generation of ceramic hot gas filter with safety fuses integrated in venturi ejectors. Fuel 2013, 108, 19-23; (11) Zhong, Z.; Xing, W.; Li, X.; Zhang, F., Removal of Organic Aerosols from Furnace Flue Gas by Ceramic Filters. Ind. Eng. Chem. Res. 2013, 52, 5455-5461; (12) Rys-Matejczuk, M.; Mueller, M., Corrosion behaviour of ceramic filter candle materials for hot gas filtration under biomass gasification conditions at 850 degrees C.

Adv. Appl. Ceram. 2013, 112, 466-470. (13) Parmentier, J.; Patarin, J.; Dentzer, J.; Vix-Guterl, C., Formation of SiC via carbothermal reduction of a carbon-containing mesoporous MCM-48 silica phase: a new route to produce high surface area SiC. Ceram. Int. 2002, 28, 1-7; (14) Pol, V. G.; Pol, S. V.; Gedanken, A., Novel synthesis of high surface area silicon carbide by RAPET (reactions under autogenic pressure at elevated temperature) of organosilanes. Chem. Mat. 2005, 17, 1797-1802; (15) Hao, Y. J.; Jin, G. Q.; Han, X. D.; Guo, X. Y., Synthesis and characterization of bamboo-like SiC nanofibers. Mater Lett. 2006, 60, 1334-1337. 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(16) Hu, J.; Zhong, Z.; Zhang, F.; Xing, W.; Low, Z.-X.; Fan, Y., Coating of ZnO nanoparticles onto the inner pore channel surface of SiC foam to fabricate a novel antibacterial air filter material. Ceram. Int. 2015, 41, 7080-7090; (17) Hu, J.; Zhong, Z.; Zhang, F.; Xing, W.; Jin, W.; Xu, N., High-efficiency, Synergistic ZnO-Coated SiC Photocatalytic Filter with Antibacterial Properties. Ind.

Eng. Chem. Res. 2016, 55, 6661-6670. (18) An, K.; Musselwhite, N.; Kennedy, G.; Pushkarev, V. V.; Baker, L. R.; Somorjai, G. A., Preparation of mesoporous oxides and their support effects on Pt nanoparticle catalysts in catalytic hydrogenation of furfural. J. Colloid Interface Sci. 2013, 392, 122-128; (19) Checa, M.; Auneau, F.; Hidalgo-Carrillo, J.; Marinas, A.; Marinas, J. M.; Pinel, C.; Urbano, F. J., Catalytic transformation of glycerol on several metal systems supported on ZnO. Catal Today 2012, 196, 91-100. (20) Moon, S. Y.; Naik, B.; Jung, C.-H.; Qadir, K.; Park, J. Y., Tailoring metal-oxide interfaces of oxide-encapsulated Pt/silica hybrid nanocatalysts with enhanced thermal stability. Catal Today 2016, 265, 245-253. (21) Shang, N. G.; Papakonstantinou, P.; Wang, P.; Ravi, S.; Silva, P., Platinum Integrated Graphene for Methanol Fuel Cells. J. Phys. Chem. C. 2010, 114, 15837-15841. (22) Giannakopoulou, T.; Todorova, N.; Giannouri, M.; Yu, J.; Trapalis, C., Optical and photocatalytic properties of composite TiO2/ZnO thin films. Catal Today 2014,

230, 174-180. 26


Page 26 of 29

Page 27 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Hong, Y.; Tian, C. G.; Jiang, B. J.; Wu, A. P.; Zhang, Q.; Tian, G. H.; Fu, H. G., Facile synthesis of sheet-like ZnO assembly composed of small ZnO particles for highly efficient photocatalysis. J. Mater. Chem. A. 2013, 1, 5700-5708. (24) Chen, H. Y.; Tang, M. N.; Rui, Z. B.; Wang, X. Y.; Ji, H. B., ZnO modified TiO2 nanotube array supported Pt catalyst for HCHO removal under mild conditions. Catal

Today 2016, 264, 23-30. (25) Hosseini, M.; Siffert, S.; Cousin, R.; Aboukaïs, A.; Hadj-Sadok, Z.; Su, B.-L., Total oxidation of VOCs on Pd and/or Au supported on TiO2/ZrO2 followed by “operando” DRIFT. C. R. Chim. 2009, 12, 654-659. (26) Lichtenberger, J., Catalytic oxidation of chlorinated benzenes over V2O5/TiO2 catalysts. J. Catal. 2004, 223, 296-308. (27) N. Radic, B. Grbic, A. Terlecki-Baricevic, Kinetics of deep oxidation of n-hexane and toluene over Pt/Al2O3 catalysts - Platinum crystallite size effect, Appl. Catal. B:

Environ. 2004, 50, 153-159. (28) Chen, C.; Wang, X.; Zhang, J.; Bian, C.; Pan, S.; Chen, F.; Meng, X.; Zheng, X.; Gao, X.; Xiao, F.-S., Superior performance in catalytic combustion of toluene over mesoporous ZSM-5 zeolite supported platinum catalyst. Catal Today 2015, 258, 190-195; (29) Zhang, Q.; Luan, H.; Li, T.; Wu, Y.; Ni, Y., Study on Pt-structured anodic alumina catalysts for catalytic combustion of toluene: Effects of competitive adsorbents and competitive impregnation methods. Appl. Surface Sci. 2016, 360, 1066-1074. 27



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(30) Fu, X.; Liu, Y.; Yao, W.; Wu, Z., One-step synthesis of bimetallic Pt-Pd/MCM-41 mesoporous materials with superior catalytic performance for toluene oxidation. Catal Commun. 2016, 83, 22-26. (31) Yang, H.; Deng, J.; Liu, Y.; Xie, S.; Xu, P.; Dai, H., Pt/Co3O4/3DOM Al2O3: Highly effective catalysts for toluene combustion. Chinese J. Catal. 2016, 37, 934-946; (32) Yang, H.; Deng, J.; Liu, Y.; Xie, S.; Wu, Z.; Dai, H., Preparation and catalytic performance of Ag, Au, Pd or Pt nanoparticles supported on toluene oxidation. J. of Mol. Catal. A. 2016, 414, 9-18.

For Table of Contents Only

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3DOM CeO2-Al2O3 for

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295x132mm (150 x 150 DPI)


SiC Filter for the

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