γ-Al2O3 catalyst for degradation dye wastewater

ISSN 1001-0742

Journal of Enuironmentol Sciences Vol. 18, No. 6, pp. 1189- 1192,2006 ~~

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Article ID: 1001-0742(2006)06-1189-04

CN 11--2629/X

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CLC number:X505

Document code: A

Preparation and characterization of Fe203-Ce02-TiO&A1203 catalyst for degradation dye wastewater LIU Yan, SUN De-zhi', CHENG Lin, LI Yan-ping (School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China. E-mail: [email protected])

Abstract: In order to develop a catalyst with high activity for catalytic wet oxidation (CWO) process at room temperature and atmospheric pressure, FezO3-CeO2-TiO~-y-AIzO3 catalyst was prepared by consecutive impregnation method and the prepared parameters were optimized. The structure of the catalyst was characterized by BET, XRF, SEM and XF'S technologies, and the actual wastewater was used to investigate the catalytic activity of FezO3-CeO2-TiO&AlZO3in CWO process. The experimental results showed that the prepared catalyst exhibited good catalytic activity when the doping amount of Ti was 1.O wt% (the weight ratio of Ti to carriers), and the middle product, CeOZ-TiO&Al2O3, was calcined in 450'C for 2 h. The CWO experiment for treating actual dye wastewater indicated that the COD, color and TOC of actual wastewater were decreased by 62.23%, 50.12% and 41.26% in 3 h, respectively, and the ratio of BODJCOD was increased from 0.19 to 0.30. Keywords: catalytic wet oxidation (CWO); Fez03-Ce0z-TiOz/-y-A1zOp catalyst; dye wastewater treatment

Introduction The treatment of organic wastewater is one of the most urgent subjects in pollution control because of the high concentration and refractory degradation (Golka et d.,2004). In recent years, catalytic wet oxidation (CWO), by adding catalysts and oxidants to improve the oxidation rate, has been considered as a promising treatment method to destroy organic pollutants in wastewaters (Gomes et d.,2000; Cao et d.,2003; Hung et al., 2003). However, this process is usually carried out at high temperature and pressure, thus, leading to high equipment and operation costs, which limits a wide application of CWO. More and more attention has been focused on developing new processes to improve the efficiency of CWO, such as the preparation of new type heterogeneous catalysts with high catalytic activity, making the CWO combined with biological methods to treat wastewater. Usually, in a combined CWO-biological treatment system, CWO is used as pre-treatment process to improve the biodegradation of wastewater, and then followed by biological method, to lower the treatment cost and improve the treatment efficiency. Currently, the oxidants used in CWO are air (or 03, H202,O3and so on. The key in CWO process is the preparation of heterogeneous catalysts with high activity and stability (Gould et $., 2001; Neamtu et a!., 2004). In our previous study (Liu and Sun, 2006), Fe203-Ce02/yA1203catalyst was prepared and its catalytic activity was evaluated by using an azo dye, methyl orange, as model pollutant in CWO at room condition. The results show the activity of the catalyst is not satisfactory. Titanium dioxide has received a lot of attention as a promising material for photocatalysis and

degradation of pollutants. Additionally, TiO, also can be used as carrier of catalyst in CWO process because of high specific surface areas (Maugans and Akgerman, 2003; Bang et al., 2003). Based on the so many advantages of Ti02, Ti was chosen as assistant component of catalyst in this study. Fe203-Ce02Ti02/y-A1203was prepared by consecutive impregnation method and the prepared parameters were optimized. BET, XRF, SEM and X P S technologies were employed to characterize the structure of Fe203-Ce02-Ti02/y-A1203, and the catalytic activity of the catalyst was also investigated in CWO process for treating actual dye wastewater.

1 Experimental 1.1 Catalyst preparation Fe203-Ce02-Ti02/y-A1203 catalyst was prepared by consecutive impregnation method. A precursor of tetrabutyl titanate was added dropwise to 50 ml absolute ethanol contained with 0.5 wt% Ce under vigorous stirring, then small amount of distilled water and nitric acid was added to the mixed solution drop by drop. The volume ratio of tetrabutyl titanate and distilled water is 4 :1. Twenty grams y-A1203carrier was added into the above mixed solution for 12 h after the solution was stirred for 1 h under room temperature, then the sample was dried at 809: for 10 h followed by dried at 1 10T for 2 h. The dried samples were calcined in an oven for some hours, so that the intermediate Ce02-Ti02/y-A1203 was obtained. Secondly, Fe was loaded on Ce02-Ti02/y-A1203by impregnation of Ce02-TiOz/y-A1203with 100 ml aqueous solution containing 0.1 m o m Fe(NO& for 12 h under room condition, after the same drylng process, the dried samples were calcined at 350°C for 3 h, thus the Fe203-Ce02-Ti02/y-A1203 catalyst was obtained.

Foundation item: The National Basic Research Program (973) of China (No. 2004CB418505) and the Foundation for Excellent Youth of Heilongjiang Province; *Correspondingauthor

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1.2 Characterization of the catalyst sample The surface area, total pore volume and average pore size of samples were analyzed by using the BET nitrogen adsorption method in surface area and pore size analyzer (Autosorb-1, Quantachrome Com.,

USA). The elementary compositions of samples were determined by a model AXIOS pw4400 XRF analyzer. Rh Ka was used as X-ray source, which operated at 4 kW. The surface morphology of the samples was investigated by means of a Hitachi S-4700 SEM analyzer. XPS spectra were recorded using a model PHI5700 analyzer (Perkin Elmer Co., USA). A Al Ka (hu =1486.60 ev) was used as X-ray source. The source was operated at 250 W and 12.5 kV. Kinetic energies of photoelectrons were measured using a hemispherical electrostatic analyzer working in the constant pass energy mode. The C 1s peak fiom the adventitious carbon-based contaminant, with the bind energy of 284.62 eV, is used as the reference for calibration. 1.3 Operation of CWO process The catalytic activity of FezO3-CeO2-TiOJy-Al2O3 was investigated in CWO process. Methyl orange synthetic wastewater was used as model pollutant in the experiment of optimizing the preparation condition of the catalyst. The concentration of dye is 500 mgL and H202was used as oxidation agent in this process. CWO process was carried out in a cylindrical reactor of 200 ml with constant temperature waterbath. The reaction was conducted at atmospheric pressure and 25°C.3 g catalysts and 33 mg HzOZwere added to 100 ml of an aqueous dye wastewater. Actual dye wastewater was collected fiom the textile industry in Harbin City, China. The main dye in the wastewater is an azo dye, Reactive Black 5. The initial concentrations of COD and BOD, of actual wastewater were 9 15.2 and 171.6 mgL, respectively, pH is 7-8. Air was used as oxidation agent in CWO process for treating actual dye wastewater. The reaction was carried out in a cylindrical reactor of 200 ml with bubbled air at 50°C and normal pressure. 3 g catalysts were added to 100 ml ,of dye wastewater and

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the air flow rate was 400 ml/min. Liquid samples were taken out immediately at regular intervals to analyze absorbance, COD and total organic carbon (TOC). The visible light absorbance at the characteristic wavelength of dye wastewater, 465 nm for the synthetic one and 600 nm for the actual one, was measured by a spectrophotometer (model 721). TOC measurement was carried out with a Shimadzu TOC analyzer model TOC-Vm. The COD and BODSwere measured according to the standard methods of China (State Environmental Protection Administration of China, 2002). For evaluating the catalytic activity of catalysts, color, COD and TOC removal efficiencies were calculated as follows:

X=- co-ct

co

x 100%

where Coand C,are the initial absorbance value and final absorbance value of dye, or the initial and final COD, or the initial and final TOC, respectively.

2 Results and discussion 2.1 Optimization of preparation condition The effects of Ti doping amount, calcination temperature and time of CeO2-TiO2/y-Al2O3on catalytic activity were evaluated by the decolorization efficiency of methyl orange synthetic wastewater in detail, and the preparation parameters were optimized. 2.1.1 Effect of Ti doping amount The decolorization efficiency of dye wastewater is summarized in Fig. 1a. When the doping amount of Ti was 0.5 wt%, 0.75 wt%, 1.0 wt% and 1.25 wt% , respectively. The results show that increasing the doping amount of Ti enhanced the catalytic activity of Fez03-Ce0z-Ti02/y-A1203, whereas, when the doping amount of Ti was higher than 1.0 wt%, the catalytic activity could not be improved any more. So, the best doping amount of Ti is 1.0 wt%. 2.1.2 Effect of calcination temperature of Ce02TiO#y-A1203 Fig. 1b shows the decolorization efficiency of dye wastewater when Ce02-TiOdy-A1203was calcined for the same time at 400, 450, 500 and 550°C , respectively. The catalytic activity of Fe203-Ce02Ti02/y-A1203was declined when the calcinations

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Preparation and characterizationof Fe2O3-CeOrTi0&Al2O3 catalyst for degradation dye wastewater

temperature exceeded 450T. This decline probably occurred because the metal oxides on the support could form larger crystals at calcinations temperature above 450°C, additionally, the agglomeration of metal oxides can be formed on the support, which resulting in a decrease of specific surface area and the amount of active sites, therefore a decline in activity for CWO of dye. So, the optimal calcinations temperature of Ce02-Ti02/y-A1203 is fixed at 450°C. 2.1.3 Effect of calcinations time of Ce02-TiOdyA1203

The effect of calcinations time of Ce02TiO2/y-AI2O3on the catalytic activity of Fe203CeO2-TiOdy-Al2O3was investigated (Fig.1c). When CeO2-TiO2/y-AI2O3 was calcined for 2 h, the catalytic activity of obtained catalyst was slightly higher than that of catalyst calcined for 1 h. When calcination time exceeded 2 h, the activity of the catalyst was decreased greatly, this was probably caused by the agglomeration of metal oxides on the supports which resulted in a decrease in the surface area and amounts of active sites. So, the optimal calcinations time of CeO2-TiO4y-Al2O3 is 2 h. Based on the above results, the Ti doping amount

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was fixed at 1.O wt%, the calcinations temperature and time are 400°C and 2 h, respectively, for preparing Fe203-Ce02-Ti0&A1203catalyst. 2.2 Characterization of Fe203-CeOrTiOdy-Alz03 catalyst 2.2.1 Analysis of BET results A high specific area is good for the catalytic activity of catalysts. The specific surface area, total pore volume and average pore size of the investigated catalysts measured using the BET nitrogen adsorption method show that the catalyst has a specific surface area of 2 13.1 m2/g,and total pore volume and average pore size of 0.4863 mYg and 9.127 nm. 2.2.2 Analysis of XRF results The component contents of Fe203-Ce02-Ti02/yA1203 catalyst were analyzed by XRF technology. According to the results, the contents of FeyCe and Ti in the catalyst were 2.137% , 0.285% and 0.168% , respectively. 2.2.3 SEM images Compared with Fig.2(a), it can be seen from Fig.2 (b) that the Fe203particles are equally dispersed on the surface of Fe203-Ce02-Ti02/y-A1203 catalyst, and the crystal size is very uniform as shown in SEM images.

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Fig.2 SEM image of y-A1203carrier (a) and Fez03-Ce02-TiO~y-A1z00, catalyst (b)

2.2.4 Results of XPS measurements Fe and Ti, without Ce, were found from the survey

XPS pattern of Fe203-Ce02-Ti02/y-A1203 catalyst. Ti and Ce were loaded on the surface of support synchronously according to the preparation procedure of Fe203-Ce02-Ti02/y-A1203, and according to the results of XRF, the content of Ce was higher than that of Ti in the catalyst, which indicates that Ce can not be seen because it was covered by Fe,03 rather than its lower content. As has been known, XPS only can be used to analyze the surface of catalyst with a limited depth (5-10 nm), so Ce could not be detected on the surface of Fe2O3-CeO2-TiO2/y-AI2O3. Fe 2p and Ti 2p XPS patterns of Fe203-Ce02-Ti02/ y-A1203are shown in Fig.3, respectively. The Fe 2p3/2 peak was found at 710.87 eV, which ascribable to Fe203 (Tan et d.,1990). According to the X P S handbook (Wagner et d.,1979), the Ti 2p3/2 peak of

Ti02 should be at 458.8 eV, but for Fig.3bYthe Ti 2p3/2 peak is found at 458.0 eV, so, it is confirmed that Ti does not exist in the from of TiO, only. To investigate the existence state of Ce in Fe2O3-CeOrTiO2/y-Al2O3 catalyst, X P S was employed to analysis the surface of intermediate Ce02-Ti02/yA1203. Fig.3~represents the Ce 3d X P S pattern of Ce02-Ti02/y-A1203.In F i g . 3 ~Ce ~ 3d5/2 peak can be observed at binding energy of 886.75 eV, which can be ascribed that Ce in CeO2-TiO2/y-AI2O3 was exist as the compound oxides form, Ce02and Ti& (Dauscher et al., 1990). 2.3 Practical application of Fe203-Ce02-TiOdy A1203catalyst In order to investigate the applicability of Fe203-Ce02-Ti02/y-A1203,actual wastewater was subjected to CWO process. It can be seen from the Fig.4 that the COD, color and TOC of actual

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wastewater were decreased by 62.23%, 50.12% and 41.26% in 3 h, respectively, and as an important environmental parameter, BODJCOD was increased fiom 0.19 to 0.30. Fez0~-Ce02-Ti0z/y-A1zO~ shows an excellent catalytic activity in the oxidation of nonbiodegradation dye wastewater, and can efficiently improve the biodegradability of wastewater. So, CWO can be used as pretreatment process combined with traditional biological methods for treating dye wastewater without high operating cost and disposal problems.

biodegradability of wastewater improved. As a promising technology, CWO process can be operated as pretreatment process combined with biological methods for treating aqueous solutions containing non-biodegradable organics.

References:

Cao S, Chen G, Hu X et d.,2003. Catalytic wet air oxidation of wastewater containing ammonia and phenol over activated carbon supported h catalysts[JJ Catalysis Today, 8 8 37-47. Dauscher A, Hilaire L, LeNormand F et d.,1990. Characterization by XPS and XAS of supported WTiO,CeO, catalysts[J1. Surface and interface Analysis, 16: 341-346. G o h K, Kopps S, Myslak Z W et d.,2004. Carcinogenicity of aza loo 0.4 colorants: influence of solubility and bioavailability[J]. Toxico- 0.3 logy Letters, 151: 203-210. Gomes H T, Figueiredo J L,Faria J L, 2000. Catalytic wet air oxidation of low molecular weight carboxylic acids using a carbon - 0.2 % supported platinum catalyst[J]. Applied Catalysis B: Environmental, 27: L 2 1 7 4 2 2 3 . - 0.1 Gould D M, Griffith W P, Spiro M, 2001. Polyoxometalate catalysis of dye bleaching by hydrogen peroxide[J]. Journal of Molecular -+COD -A- TOC Catalysis A Chemical, 175: 289-291. 0 Hung C M, Lou J C, Lin C H, 2003. Removal of ammonia solutions 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 used in catalytic wet oxidation processes[JJ Chemospbere, 52: Reaction time, h 989-995. Fig.4 Degradation efficiency for treating actual wastewater by using Liu Y, Sun D Z, 2006. Study on Characterizationand catalytic activity Fe203-Ce0,-TiOdy-A120,catalyst of Fe2OJy-AlD3catalysts modified by Ce[J]. Journal of Functional Materials, 37(6): 915-918. Maugans C B, Akgerman A, 2003. Catalytic wet oxidation of phenol in a trickle bed reactor over a pt/Ti02 catalyst [J]. Water Research, 3 Conclusions 37: 3 19-328. Neamtu M, Catrinescu C, Kettrup A, 2004. Effect of dealumination of Fe203-Ce02-Ti02/y-A1203 catalyst was prepared iron (ID)-exchanged Y zeolites on oxidation of Reactive Yellow by consecutive impregnation method and the 84 a m dye in the presence of hydrogen peroxide[J]. Applied Catpreparation parameters were optimized. The catalyst alysis B: Environmental, 51: 149-157. showed the best activity when the doping amount of State Environmental Protection Administration of China, 2002. Monitoring and analysis methods for water and wastewater [MI. Ti is 1.0 wt% (the amount ratio of Ti to carriers) and 4th ed. Beijing: China Environmental Science Press. 21 1-213; the calcinations temperature of intermediate CeOz227-23 1. Ti02/y-A1203 was at 450T for 2 h. Tan B J, Klabunde K J, Sherwood P M A, 1990. X-ray The characterizations of Fez03-Ce02-TiOz/~-A1203 photoelectron-spectroscopy studied of solvated metal atom dispersed catalysts-monometallic iron and bimetallic iron by BET, XRF, SEM and X P S indicated that the metal cobalt particles on alumina [J]. Chemistry of Materials, 2 (2): oxides was dispersed equably on the surface of 186-191. catalyst, and the content of Fe, Ce and Ti in the Wagner C D. Riggs W M, Davis L E et d.,1979. Handbook of X-ray photoelectron spectroscopy[M]. Minn: Perkin-Elmer Corporacatalyst was 2.137% , 0.285% and 0.168% , tion, Physical Electronics Division, Eden Prairie, 55344. respectively. Fe was located on the surface of catalyst Zhang S H, Tu X Y, Yang Z M et d.,2003. Catalytic wet oxidation of as Fe203,and Ce and Ti existed as compound oxides simulated wastewater succinic acid aqueous solution[J]. Environform, Ce02and TiO,. mental Science, 24(1): 107-1 12.

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Fez03-Ce02-Ti02/y-A1z03 shows viable applicability in treating actual wastewater, and can make the

(Received for review April 25,2006. Accepted July 3 I, 2006)