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TiO2
Powder Technology 217 (2012) 388–393
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Effect of the support material (TiO2) synthesis conditions in chemical vapor condensation on the catalytic oxidation for 1,2-dichlorobenzene over V2O5/TiO2 Sungmin Chin, Eunseuk Park, Minsu Kim, Gwi-Nam Bae, Jongsoo Jurng ⁎ Environment Division, Korea Institute of Science and Technology (KIST), 39–1, Hawolgok, Seongbuk, Seoul 136–791, Republic of Korea
a r t i c l e
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Article history: Received 30 September 2011 Accepted 26 October 2011 Available online 29 October 2011 Keywords: Chemical vapor condensation 1,2-dichlorobenzene V2O5/TiO2 Thermal decomposition Catalytic oxidation
a b s t r a c t The catalytic oxidation of 1,2-dichlorobenzene (1,2-DCB) on vanadium oxide supported on titanium oxides (V2O5/TiO2) was investigated. The TiO2 particles used as a support material on the V2O5/TiO2 catalysts were synthesized by chemical vapor condensation (CVC) using a tubular electric furnace at various synthesis temperatures (700–1100 °C) and titanium tetraisopropoxide (TTIP) heating temperatures (80–110 °C). V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate. Brunauer–Emmett–Teller (BET) measurements indicated no change in the specific surface area (SSA) of the V2O5/TiO2, whose support material was commercial TiO2 (P25, Degussa), after vanadium impregnation. The SSAs of the V2O5/TiO2 catalysts, whose support material was prepared using the CVC method, increased drastically after vanadium impregnation. XPS showed that the surface vanadium oxide was composed of V2O4 and V2O5. In particular, V5 + species were dominant on the CVCprepared V2O5/TiO2 catalysts. The catalytic oxidation of 1,2-DCB on the CVC-prepared V2O5/TiO2 catalysts showed good performance at lower temperatures. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Polychlorodibenzo-p-dioxins (PCDDs) and polychloro dibenzofurans (PCDFs) are harmful, persistent organic pollutants. Many countries have imposed stringent regulations on the emissions of PCDDs/ PCDFs due to their toxicity and potential human health effects. V2O5/ TiO2-based catalysts, which are designed for the control of NOx emissions by selective catalytic reductions (SCR), have been considered active catalysts for the decomposition of dioxin. Some experiments have been performed to obtain data on the optimal catalytic activities [1–6]. Corella et al. [7] compared the catalytic activities of eight different commercial V2O5–WO3–TiO2 catalysts for the conversion of several chlorinated hydrocarbons, and concluded that such catalysts were ten times more active than noble metal-based catalysts. Graham et al. [8] examined the effect of the V/Ti atomic ratio on the activity of oxide catalysts for the conversion of 265 ppmv of monochlorobenzene. They reported that crystalline vanadia would be needed to convert chlorobenzene at temperatures below 300 °C; total conversion was achieved at 260 °C in a 29,000 h − 1 space velocity. Jones and Ross [9] reported that ethylchloride and mono-chlorobenzene may be totally destroyed at 300–400 °C over vanadia supported on different oxides with a 0–2% water in the feed. Webber [10] examined the activity of two different commercial V2O5–WO3–TiO2 catalysts in the conversion of PCDD/PCDF, chlorobenzenes and polycyclic aromatic
⁎ Corresponding author. Tel.: + 82 2 958 5597; fax: + 82 2 958 6711. E-mail address: [email protected] (J. Jurng). 0032-5910/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2011.10.055
hydrocarbons. PCDD and PCDF are strongly adsorbed but unchanged on the catalyst at temperatures below 200 °C. Above this temperature, 98% conversion of dioxins was observed. The conversion of 1 ppm chlorobenzenes was almost total at 300 °C with 10% oxygen, 20% water and a 5000 h − 1 space velocity. The decomposition of polyaromatic hydrocarbons occurred already at 150 °C while higher temperatures were needed for mono-aromatic compounds. Many researchers [11–19] reported that vanadium oxide supported over titanium oxide could be an important example of a transition metal oxide catalyst with practical relevance in various industrial applications. TiO2 is one of the most widely used supports with significant effects on the activity for oxidation compared to zirconia, alumina, and silica due to the lowered activation energy, stronger vanadia-support interaction, and higher oxygen uptake [11–13]. Bertinchamps et al. [17] have investigated the catalytic activity of 40 different formulations, based on 10 different transition metal oxides (CrOx, MnOx, VOx, SnOx, WOx, NbOx, TaOx, MoOx, ZrOx and BiOx) supported on 4 different supports (2 kinds of TiO2, Al2O3 and SiO2), in the course of the total oxidation of benzene as a model molecule for dioxin. They demonstrated that the best catalysts for the total oxidation of benzene, taken as model molecule for dioxin, are CrOx and VOx welldispersed as monolayers at the surface of titania and Mn3O4 crystallites poorly dispersed at the surface of SiO2. Extensive studies on such catalysts focused on the dispersion, surface structure, oxidation states and reducibility of the supported vanadia species under a variety of conditions, and these properties have been correlated with the performance in selective oxidation reactions. In addition to the nature of the support, the preparation method used to synthesize
S. Chin et al. / Powder Technology 217 (2012) 388–393
A
V2 O5 /P25TiO
R
Relative intensity (a.u.)
the supported vanadia catalysts affects the structure of the active phase. A chemical vapor condensation (CVC) method is an alternative method for the direct synthesis of nanoparticles. The particle morphology, crystalline phase and surface chemistry of thermally decomposed particles can be controlled by regulating the precursor composition, reaction temperature, pressure, solvent property and aging time [20–22]. In a typical CVC method, the precursor solution is atomized into an aerosol reactor, where the droplets undergo solvent evaporation and solute precipitation within the droplets. The droplets are then dried, followed by thermolysis of the precipitates at higher temperatures, and finally sintering to form the final particles. In a recent study [23], the catalytic destruction of 1,2-dichlorobenzene (1,2-DCB) was carried out to compare the catalytic activity of a thermally decomposed catalyst with that of a commercial catalyst. The V2O5/TiO2 catalysts synthesized using the CVC method showed good performance for 1,2-DCB decomposition at lower temperatures. The additional important synthesis parameters affecting the particle size and crystallinity were not described in the earlier study, and are the primary goals of the present paper. This study examined the effect of the support material characteristics on the catalytic oxidation of 1,2-DCB, which is structurally similar to the more toxic 2,4,7,8-tetrachlorodibenzodioxin. TiO2 nanoparticles, which were used as the support materials, were prepared using the CVC method at different synthesis temperatures and various precursor heating temperatures. V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate. The textural properties and crystalline structure of the materials were examined from BET measurements and X-ray diffraction (XRD). The molecular and electronic structures of the catalytic surface vanadia species were determined by X-ray photoelectron spectroscopy (XPS).
389
2
V2 O5 /95TiO 2 1100 V2 O5 /95TiO 2 700 V2 O5 /110TiO 2 900 V2 O5 /95TiO 2 900 V2 O5 /80TiO 2 900 20
30
40 Degrees (2 theta)
50
60
Fig. 1. X-ray diffraction patterns for the samples. The symbols ‘A’ and ‘R’ indicate anatase and rutile, respectively.
powder specific surface area (SSA, m 2 g− 1) was determined by nitrogen adsorption (> 99.999%) at 77 K on a Micromeritics Tristar 3000 apparatus using the Brunauer-Emmett-Teller (BET) method. Prior to analysis, the sample was heated (150 °C, 1 h) with flowing N2 (>99.999%) to remove the adsorbed water. Assuming monodisperse, spherical primary particles, the BET-equivalent particle diameter (dBET) was calculated using the formula, dBET = 6/(ρ × SSA), where ρ is the particle density. XPS measurements were made on a VG scientific ESCA Lab II Spectrometer (resolution 0.1 eV) with Mg Kα (1253.6 eV) radiation as the excitation source. All binding energies were referenced to the C 1 s peak at 285.0 eV for adventitious carbon.
2. Experimental 2.1. Catalyst preparation
2.3. Catalytic activity
The CVC method was used to synthesize the TiO2 particles, which were used as the support material for the V2O5/TiO2 catalysts. The detailed experimental apparatus for the TiO2 nanoparticles synthesis was described in a previous study [22]. Titanium tetraisopropoxide ([(CH3)2CHO]4Ti, TTIP, Aldrich, >97%) was used as the TiO2 precursor. The TTIP heating temperature was 80, 95 and 110 °C. The TiO2 synthesis temperature was varied from 700 to 1100 °C at 200 °C intervals. V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate (NH4VO3, Aldrich, >98%). The V2O5/TiO2 samples were labeled, “V2O5/[TTIP heating temperature] TiO2 [synthesis temperature].” For example, the sample produced from TTIP heated to 95 °C and a synthesis temperature of 900 °C was labeled V2O5/95TiO2900. For comparison of the catalytic activity, vanadia– TiO2 impregnated catalysts were also prepared by impregnating the TiO2 support (Degussa P25, 52 m 2 g − 1) with an aqueous solution of ammonium metavanadate. The vanadium loading on the TiO2-supported catalysts was 5.0 wt.%. The catalyst samples (V2O5/TiO2) were dried overnight at 110 °C and calcined at 500 °C for 2 h in static air.
A gas generator (KIN-TEK, 491 M-B) was used to generate 1800 ppm of 1,2-DCB. Air was introduced into the gas generator at a flow rate of 0.018 m 3 h− 1 (corresponding a space velocity of 18000 h− 1), which was adjusted with a mass flow controller (MKS). The catalytic experiments were carried out in a fixed bed glass reactor at atmospheric pressure, and a K-type thermocouple was placed into the catalyst bed to monitor the reaction temperature [23]. 100 mg of the V2O5/TiO2 was placed into the catalyst bed with commercial glass wool as a support. The noncatalytic oxidation of 1,2-DCB was also performed in the absence of a catalyst to compensate for catalytic degradation. The residual 1,2-DCB in the outlet gas was treated using three adsorbent (activated carbon) cylinders. The reactor effluent gas was analyzed using two gas chromatographs (HP6890, Younglin M600D) equipped with flame ionization detectors employing a capillary column (30 m × 0.32 mm DB-5, 0.25 mm) for 1,2-DCB and a packed column (6 in. × 1/8 ft × 0.085 ft SS, Carbosphere 80/100) with a methanator containing a commercial
2.2. Catalyst characterization XRD was carried out using a high resolution x-ray diffractometer (focal spot size: 5 mm2, Cu rotating anode). The crystallite size and shapes were observed by transmission electron microscopy (TEM) (Philips; operated at 300 kV, image resolution b0.23 nm). For highresolution transmission electron microscopy (HR-TEM) and energydispersive X-ray (EDX), analyses were carried out using a F-20 microscope (Philips; operated at 200 kV, image resolution b0.25 nm). The
Table 1 BET surface area and particle diameter (dBET). Sample
SBET (m2 g− 1), before/aftera
dBET (nm), Before/aftera
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100 V2O5/80TiO2900 V2O5/110TiO2900 V2O5/P25TiO2
142/181 134/270 110/150 149/191 105/113 52/53
10.8/8.5 11.5/5.7 14.0/10.3 10.3/8.1 14.7/13.6 29.6/29.1
a
Before and after impregnation of vanadia.
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S. Chin et al. / Powder Technology 217 (2012) 388–393
a
b
10 nm
10 nm
d
c
10 nm
10 nm
Fig. 2. TEM images of (a) P25TiO2, (b) V2O5/P25TiO2, (c) 95TiO2900 and (d) V2O5/95TiO2900.
nickel catalyst for CO and CO2. The concentration of the vaporized sample was measured quantitatively using a standard solution. The residual 1,2-DCB of the outlet gas was treated using three adsorbent (activated carbon) cylinders. The CO and CO2 selectivity were calculated from the measured concentrations according to the following equation:
SCOx ð−Þ ¼
C COx 6ðC in −C out
where, SCOx are the CO and CO2 selectivity, CCOx are the CO and CO2 concentrations in the product stream, and Cin and Cout are the inlet and outlet concentrations of 1,2-DCB, respectively.
a
b
3. Results and discussion 3.1. Catalyst characterization Fig. 1 shows the XRD patterns of all samples. The typical diffraction peaks characteristic of anatase TiO2 were observed for all samples except for V2O5/P25TiO2, indicating that the CVC method produces anatase TiO2. In addition, there was no change in the diffraction peaks due to the 5 wt.% loading of vanadia. The entrapping and/or diffusion of vanadium ions into the TiO2 structure would probably cause a change in the crystallite phase [1,24]. Djerad et al. [25] reported that vanadium enhanced the phase transformation of TiO2 from anatase to rutile. Since the vanadia loading was fixed to 5 wt.%, the crystalline phase of TiO2 did not transform to rutile.
c
50 nm Fig. 3. Energy-dispersive X-ray images of the V2O5/95TiO2900 samples. (a) High-angle annular dark field image of V2O5/95TiO2900; (b) titanium elemental spots; (c) vanadium elemental spots.
S. Chin et al. / Powder Technology 217 (2012) 388–393
In a recent publication [22], the increased TTIP heating temperature enhanced the collision and coalescence rate of the particles, resulting in an increase in the size of the TiO2 nanoparticles and a reduced SSA. In addition, the peak intensities for anatase increased with increasing synthesis temperature, indicating enhanced crystallization and a reduced SSA. In this study, there was no difference in the SSA of V2O5/P25TiO2 due to vanadium impregnation (see Table 1). On the
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other hand, the SSAs of the V2O5/TiO2 catalysts, in which the vanadium were impregnated on the CVC-TiO2, increased drastically. In particular, the SSA of V2O5/95TiO2900 was increased greatly from 134 to 270 m 2 g − 1 after vanadium impregnation. Table 1 present the specific surface areas for the prepared V2O5/TiO2 samples. As shown in Table 1, there was no difference in the SSA of the V2O5/P25TiO2 catalyst before and after the impregnation of vanadium.
b
a V2 O5 /95TiO 2 700
V2 O5 /95TiO 2 900
5+
V
528
524
520 Binding energy (eV)
516
4+
5+
Intensity (a.u.)
V
Intensity (a.u.)
V
V
528
512
524
520 Binding energy (eV)
4+
516
512
d
c
V2 O5 /80TiO 2 900
V2 O5 /95TiO 2 1100
528
5+
V
524
520 Binding energy (eV)
4+
516
V
Intensity (a.u.)
Intensity (a.u.)
V
528
512
e
5+
V
524
520 Binding energy (eV)
516
4+
512
f V2 O5 /110TiO 2 900
5+
V
524
2
520 Binding energy (eV)
516
Intensity (a.u.)
V
Intensity (a.u.) 528
V2 O5 /P25TiO
4+
512
528
V
5+
V
524
Fig. 4. XPS spectra of the V 2p region for each sample.
520 Binding energy (eV)
516
4+
512
392
S. Chin et al. / Powder Technology 217 (2012) 388–393
Table 2 Binding energies of the samples. Sample
Binding energy (eV) V 2p3/2
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100 V2O5/80TiO2900 V2O5/110TiO2900 V2O5/P25TiO2 a b
516.0 515.6 516.5 515.8 516.4 516.3
Ti 2p3/2 a
(25%) (18%)a (24%)a (21%)a (23%)a (29%)a
517.0 516.9 517.3 517.1 517.1 517.3
b
(75%) (82%)b (76%)b (79%)b (77%)b (71%)b
458.8 458.6 458.7 458.8 458.7 458.7
Binding energies between 515.6 and 516.5 eV correspond to V4 + in V2O4. Binding energies between 516.9 and 517.3 eV correspond to V5 + in V2O5.
However, the V2O5/TiO2 catalysts prepared by the CVC method had a larger surface area, which possibly provided more accessible active sites and enhanced the catalyst activity. Before vanadium impregnation, the SSAs of the prepared TiO2 samples were in the order of 80TiO2900 > 95TiO2700 > 95TiO2900 > 95TiO21100 > 110TiO2900 > P25TiO2, with 80TiO2900 showing the highest SSA. After vanadium impregnation, the SSAs of the prepared V2O5/TiO2 samples were in the order of V2O5/95TiO2900>V2O5/80TiO2900>V2O5/95TiO2700>V2O5/ 95TiO21100>V2O5/110TiO2900>V2O5/P25TiO2900 with V2O5/95TiO2 900 having the highest SSA. The SSA of V2O5/95TiO2900 was >2 times higher after vanadium impregnation. The catalyst SSA is one of the important factors for the catalytic activity [26]. Fig. 2 shows TEM images of P25TiO2 (a), 95TiO2900 (b), V2O5/ P25TiO2 (c), and V2O5/95TiO2900 (d). The morphology and size of P25TiO2 and V2O5/P25TiO2 were similar before and after vanadium impregnation. In addition, the particles size ranged from 20 to 30 nm (see Table 1). After the vanadium impregnation, the V2O5/95TiO2900 particles sizes decreased drastically from 11.5 to 5.7 (see Table 1), indicating enhanced SSA. Tian et al. [27] suggests that the TiO2 nanopowders synthesized by a hydrothermal process in the presence of cetyltrimethylammonium bromide and a post-treatment with ammonia can increase the SSA. The catalyst SSA decreased with increasing loading of the active component [28]. However, the SSA of V2O5/TiO2 catalysts, in which the supported TiO2 was synthesized using the CVC method increased drastically. This varied behavior suggests that the transition metal oxides were dispersed onto the surface of the TiO2 catalysts. EDX mapping images of the V2O5/95TiO2900 catalysts were obtained to investigate this further (Fig. 3). The V elements of the V2O5/95TiO2900 catalyst were more scattered over the TiO2 support than the V2O5/P25TiO2. Accordingly, the V2O5/95TiO2900 fine particle
catalysts may have large surface areas and enhanced dispersion of the active component. XPS is a highly sensitive surface analysis technique that is effective for examining the surface composition and chemical states of solid samples. Fig. 4 shows the V 2p3/2 spectra for each sample. The C 1 s peak at 285.0 eV was used as an internal standard to calibrate the binding energies. The binding energy references of the V 2p3/2 line used to identify the vanadium oxide phases in the catalysts were calculated based on the data [29,30]. The V 2p3/2 XPS spectra were wide and asymmetric, demonstrating at least two V chemical states according to the binding energy range from 512.0 to 528.0 eV. The main contribution was attributed to V2O5. The other minor peak for the V2O5/TiO2 catalyst surface was assigned to V2O4[31]. Therefore, the V 2p3/2 XPS spectra were fitted to the two chemical states using Origin software with a Gaussian rule. Two peaks related to the presence of V 5 + and V4 + could be detected for V2O5/P25TiO2 and V2O5/95TiO2900. No differences were detected among the samples for the Ti XPS peaks. V5 + groups are more powerful oxidants leading to enhanced catalytic reactions, and are a significant factor in catalytic oxidation. As shown in Fig. 4, V5 + in V2O5/ 95TiO2900 was larger than that of V2O5/P25TiO2. Therefore, the V5 + content on the V2O5/95TiO2900 sample surface was higher than that on the V2O5/P25TiO2 sample, resulting in increased catalytic oxidation. Table 2 lists the binding energies of the V 2p3/2 and Ti 2p3/2 lines from the XPS measurements. The V2O5/95TiO2900 sample contained approximately 82% V5 + species, whereas the V2O5/P25TiO2 sample was reduced slightly, 71% V 5 +. Fig. 5 shows the 1,2-DCB conversion on the different V2O5/TiO2 catalysts as a functions of temperature. 1,2-DCB was selected to examine the catalytic activity of V2O5/TiO2 because its structure is similar to the more toxic 2,4,7,8-tetrachlorodibenzodioxin [32]. Noncatalytic oxidation of 1,2-DCB was performed in the absence of a catalysts because 1,2-DCB could be decomposed to other components at high temperatures. Indeed, 2% of 1,2-DCB were actually decomposed to other components at 300 °C and 3% at 400 °C. Therefore, noncatalytic oxidation at high temperature must be considered. As shown in Fig. 5, 1,2-DCB conversion was considered only in the catalytic oxidation except for noncatalytic oxidation. The 1,2-DCB conversions were in the order of V2O5/95TiO2900>V2O5/80TiO2900>V2O5/ 110TiO2900>V2O5/95TiO2700>V2O5/95TiO21100>V2O5/P25TiO2, with V2O5/P25TiO2 having the lowest conversion. In particular, V2O5/ 95TiO2900 had the highest conversion, resulting from its larger SSA value and higher V5 + content, as shown in Tables 1 and 2, and Fig. 5. In addition, the 1,2-DCB conversion order of the prepared V2O5/TiO2 samples is strongly related to the SSA and the V5 + content. With increasing 1.0 V2O5/P25TiO2
1.0
0.8
COx yield (-)
Conversion (-)
0.8
0.6 V2O5/P25TiO2 V2O5/95TiO2700
0.4
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100
0.6
V2O5/80TiO2900 V2O5/110TiO2900
0.4
V2O5/95TiO2900
0.2
V2O5/95TiO21100
0.2
V2O5/80TiO2900 V2O5/110TiO2900
0.0 150
200
250
300
350
400
450
0.0 0.0 500
0.2
0.4 0.6 1,2-DCB conversion (-)
0.8
1.0
Temperature (oC) Fig. 5. 1,2-DCB conversion as a function of temperature for the prepared V2O5/TiO2 samples.
Fig. 6. Catalytic selectivity calculated carbon balance of 1,2-DCB destruction and carbon oxide formation: conversion and selectivity obtained from the various reaction temperatures are plotted.
S. Chin et al. / Powder Technology 217 (2012) 388–393
reaction temperature, the 1,2-DCB conversion became saturated, which agrees with the traditional catalytic curve [1,2,6,32]. The conversion of the V2O5/P25TiO2 catalyst was only 0.280 and 0.582 at a catalytic reaction temperature of 250 and 300 °C, respectively. On the other hand, the conversion of the V2O5/95TiO2900 catalyst prepared by the CVC method was 0.579 and 0.805 at the same reaction temperature, respectively. As a result, the V2O5/TiO2 catalysts synthesized by the CVC method showed good performance for 1,2-DCB decomposition at low temperatures. Fig. 6 presents the relationship between 1,2-DCB conversion and the carbon oxide yields for the prepared V2O5/TiO2 samples. The effluent consists mainly of CO (42–51%) and CO2 (54–61%) the composition did not change much for all catalysts. Overall the carbon balances were closed in all cases within 2%. The carbon balance was well matched at 1,2-DCB conversions > 0.6, indicating most of the 1,2-DCB decomposed to CO and CO2. On the other hand, the carbon balance did not match at lower 1,2-DCB conversions resulting from the low reaction temperature. The remainder of the effluent except for carbon oxides at low reaction temperatures was assumed to be organic byproducts. Choi et al. [1] suggested that carboxylates, carbonates, maleates and phenolates were by-products from the oxidative destruction of 1,2-DCB on the V2O5/TiO2 catalysts. 4. Conclusions V2O5/TiO2 catalysts were prepared by the vanadium impregnation on the TiO2. In particular, the supported TiO2 was prepared using the CVC method at various synthesis temperatures and precursor concentrations, which were varied by the precursor temperatures. This study demonstrated that the characteristics of the support material deeply affect the resulting catalyst activity for 1,2-DCB despite the same support material (TiO2). There was no difference in the SSA of V2O5/TiO2 after vanadium impregnation when commercial TiO2 (P25) was used. However, the SSAs of the V2O5/TiO2 catalysts, in which the vanadium had been impregnated on CVC-TiO2, increased drastically. The SSA of V2O5/95TiO2900 was >2 times higher after vanadium impregnation. XPS suggests that the surface V species were mainly 75–82% V 5 + and 18–25% V 4 +. The higher V 5 + species were related to the higher catalytic oxidation, resulting in greater 1,2-DCB destruction. As a result, the catalytic oxidation of the CVC-made V2O5/TiO2 catalysts showed good performance for 1,2-DCB at a lower temperatures. Future studies should examine the optimum synthesis conditions for the support material in the CVC method to accelerate the V2O5/TiO2 catalytic oxidation for 1,2-DCB. Acknowledgments This work has been supported by the Ministry of Environment (192-091-001), the Ministry of Education, Science and Technology (2011K000750) and the Korea Institute of Science and Technology (KIST) Institutional Program (2E22181). References [1] J.S. Choi, C.B. Sin, T.J. Park, D.J. Suh, Characteristics of vanadia–titania aerogel catalysts for oxidative destruction of 1,2-dichlorobenzene, Applied Catalysis A: General 311 (2006) 105–111. [2] J. Lichtenberger, M.D. Amiridis, Catalytic oxidation of chlorinated benzenes over V2O5/TiO2 catalysts, Journal of Catalysis 223 (2004) 296–308. [3] C.H. Cho, S.K. Ihm, Development of new vanadium-based oxide catalysts for decomposition of chlorinated aromatic pollutants, Environmental Science and Technology 36 (2002) 1600–1606. [4] K.S. Chung, Z. Jiang, B.S. Gill, J.S. Chung, Oxidative decomposition of odichlorobenzene over V2O5/TiO2 catalyst washcoated onto wire-mesh honeycombs, Applied Catalysis A: General 237 (2002) 81–89. [5] P. Liljelind, J. Unsworth, O. Maaskant, S. Marklund, Removal of dioxins and related aromatic hydrocarbons from flue gas streams by adsorption and catalytic destruction, Chemosphere 42 (2001) 615–623.
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Powder Technology journal homepage: www.elsevier.com/locate/powtec
Effect of the support material (TiO2) synthesis conditions in chemical vapor condensation on the catalytic oxidation for 1,2-dichlorobenzene over V2O5/TiO2 Sungmin Chin, Eunseuk Park, Minsu Kim, Gwi-Nam Bae, Jongsoo Jurng ⁎ Environment Division, Korea Institute of Science and Technology (KIST), 39–1, Hawolgok, Seongbuk, Seoul 136–791, Republic of Korea
a r t i c l e
i n f o
Article history: Received 30 September 2011 Accepted 26 October 2011 Available online 29 October 2011 Keywords: Chemical vapor condensation 1,2-dichlorobenzene V2O5/TiO2 Thermal decomposition Catalytic oxidation
a b s t r a c t The catalytic oxidation of 1,2-dichlorobenzene (1,2-DCB) on vanadium oxide supported on titanium oxides (V2O5/TiO2) was investigated. The TiO2 particles used as a support material on the V2O5/TiO2 catalysts were synthesized by chemical vapor condensation (CVC) using a tubular electric furnace at various synthesis temperatures (700–1100 °C) and titanium tetraisopropoxide (TTIP) heating temperatures (80–110 °C). V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate. Brunauer–Emmett–Teller (BET) measurements indicated no change in the specific surface area (SSA) of the V2O5/TiO2, whose support material was commercial TiO2 (P25, Degussa), after vanadium impregnation. The SSAs of the V2O5/TiO2 catalysts, whose support material was prepared using the CVC method, increased drastically after vanadium impregnation. XPS showed that the surface vanadium oxide was composed of V2O4 and V2O5. In particular, V5 + species were dominant on the CVCprepared V2O5/TiO2 catalysts. The catalytic oxidation of 1,2-DCB on the CVC-prepared V2O5/TiO2 catalysts showed good performance at lower temperatures. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Polychlorodibenzo-p-dioxins (PCDDs) and polychloro dibenzofurans (PCDFs) are harmful, persistent organic pollutants. Many countries have imposed stringent regulations on the emissions of PCDDs/ PCDFs due to their toxicity and potential human health effects. V2O5/ TiO2-based catalysts, which are designed for the control of NOx emissions by selective catalytic reductions (SCR), have been considered active catalysts for the decomposition of dioxin. Some experiments have been performed to obtain data on the optimal catalytic activities [1–6]. Corella et al. [7] compared the catalytic activities of eight different commercial V2O5–WO3–TiO2 catalysts for the conversion of several chlorinated hydrocarbons, and concluded that such catalysts were ten times more active than noble metal-based catalysts. Graham et al. [8] examined the effect of the V/Ti atomic ratio on the activity of oxide catalysts for the conversion of 265 ppmv of monochlorobenzene. They reported that crystalline vanadia would be needed to convert chlorobenzene at temperatures below 300 °C; total conversion was achieved at 260 °C in a 29,000 h − 1 space velocity. Jones and Ross [9] reported that ethylchloride and mono-chlorobenzene may be totally destroyed at 300–400 °C over vanadia supported on different oxides with a 0–2% water in the feed. Webber [10] examined the activity of two different commercial V2O5–WO3–TiO2 catalysts in the conversion of PCDD/PCDF, chlorobenzenes and polycyclic aromatic
⁎ Corresponding author. Tel.: + 82 2 958 5597; fax: + 82 2 958 6711. E-mail address: [email protected] (J. Jurng). 0032-5910/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2011.10.055
hydrocarbons. PCDD and PCDF are strongly adsorbed but unchanged on the catalyst at temperatures below 200 °C. Above this temperature, 98% conversion of dioxins was observed. The conversion of 1 ppm chlorobenzenes was almost total at 300 °C with 10% oxygen, 20% water and a 5000 h − 1 space velocity. The decomposition of polyaromatic hydrocarbons occurred already at 150 °C while higher temperatures were needed for mono-aromatic compounds. Many researchers [11–19] reported that vanadium oxide supported over titanium oxide could be an important example of a transition metal oxide catalyst with practical relevance in various industrial applications. TiO2 is one of the most widely used supports with significant effects on the activity for oxidation compared to zirconia, alumina, and silica due to the lowered activation energy, stronger vanadia-support interaction, and higher oxygen uptake [11–13]. Bertinchamps et al. [17] have investigated the catalytic activity of 40 different formulations, based on 10 different transition metal oxides (CrOx, MnOx, VOx, SnOx, WOx, NbOx, TaOx, MoOx, ZrOx and BiOx) supported on 4 different supports (2 kinds of TiO2, Al2O3 and SiO2), in the course of the total oxidation of benzene as a model molecule for dioxin. They demonstrated that the best catalysts for the total oxidation of benzene, taken as model molecule for dioxin, are CrOx and VOx welldispersed as monolayers at the surface of titania and Mn3O4 crystallites poorly dispersed at the surface of SiO2. Extensive studies on such catalysts focused on the dispersion, surface structure, oxidation states and reducibility of the supported vanadia species under a variety of conditions, and these properties have been correlated with the performance in selective oxidation reactions. In addition to the nature of the support, the preparation method used to synthesize
S. Chin et al. / Powder Technology 217 (2012) 388–393
A
V2 O5 /P25TiO
R
Relative intensity (a.u.)
the supported vanadia catalysts affects the structure of the active phase. A chemical vapor condensation (CVC) method is an alternative method for the direct synthesis of nanoparticles. The particle morphology, crystalline phase and surface chemistry of thermally decomposed particles can be controlled by regulating the precursor composition, reaction temperature, pressure, solvent property and aging time [20–22]. In a typical CVC method, the precursor solution is atomized into an aerosol reactor, where the droplets undergo solvent evaporation and solute precipitation within the droplets. The droplets are then dried, followed by thermolysis of the precipitates at higher temperatures, and finally sintering to form the final particles. In a recent study [23], the catalytic destruction of 1,2-dichlorobenzene (1,2-DCB) was carried out to compare the catalytic activity of a thermally decomposed catalyst with that of a commercial catalyst. The V2O5/TiO2 catalysts synthesized using the CVC method showed good performance for 1,2-DCB decomposition at lower temperatures. The additional important synthesis parameters affecting the particle size and crystallinity were not described in the earlier study, and are the primary goals of the present paper. This study examined the effect of the support material characteristics on the catalytic oxidation of 1,2-DCB, which is structurally similar to the more toxic 2,4,7,8-tetrachlorodibenzodioxin. TiO2 nanoparticles, which were used as the support materials, were prepared using the CVC method at different synthesis temperatures and various precursor heating temperatures. V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate. The textural properties and crystalline structure of the materials were examined from BET measurements and X-ray diffraction (XRD). The molecular and electronic structures of the catalytic surface vanadia species were determined by X-ray photoelectron spectroscopy (XPS).
389
2
V2 O5 /95TiO 2 1100 V2 O5 /95TiO 2 700 V2 O5 /110TiO 2 900 V2 O5 /95TiO 2 900 V2 O5 /80TiO 2 900 20
30
40 Degrees (2 theta)
50
60
Fig. 1. X-ray diffraction patterns for the samples. The symbols ‘A’ and ‘R’ indicate anatase and rutile, respectively.
powder specific surface area (SSA, m 2 g− 1) was determined by nitrogen adsorption (> 99.999%) at 77 K on a Micromeritics Tristar 3000 apparatus using the Brunauer-Emmett-Teller (BET) method. Prior to analysis, the sample was heated (150 °C, 1 h) with flowing N2 (>99.999%) to remove the adsorbed water. Assuming monodisperse, spherical primary particles, the BET-equivalent particle diameter (dBET) was calculated using the formula, dBET = 6/(ρ × SSA), where ρ is the particle density. XPS measurements were made on a VG scientific ESCA Lab II Spectrometer (resolution 0.1 eV) with Mg Kα (1253.6 eV) radiation as the excitation source. All binding energies were referenced to the C 1 s peak at 285.0 eV for adventitious carbon.
2. Experimental 2.1. Catalyst preparation
2.3. Catalytic activity
The CVC method was used to synthesize the TiO2 particles, which were used as the support material for the V2O5/TiO2 catalysts. The detailed experimental apparatus for the TiO2 nanoparticles synthesis was described in a previous study [22]. Titanium tetraisopropoxide ([(CH3)2CHO]4Ti, TTIP, Aldrich, >97%) was used as the TiO2 precursor. The TTIP heating temperature was 80, 95 and 110 °C. The TiO2 synthesis temperature was varied from 700 to 1100 °C at 200 °C intervals. V2O5 containing samples were prepared by impregnating TiO2 with an aqueous solution containing an appropriate amount of ammonium metavanadate (NH4VO3, Aldrich, >98%). The V2O5/TiO2 samples were labeled, “V2O5/[TTIP heating temperature] TiO2 [synthesis temperature].” For example, the sample produced from TTIP heated to 95 °C and a synthesis temperature of 900 °C was labeled V2O5/95TiO2900. For comparison of the catalytic activity, vanadia– TiO2 impregnated catalysts were also prepared by impregnating the TiO2 support (Degussa P25, 52 m 2 g − 1) with an aqueous solution of ammonium metavanadate. The vanadium loading on the TiO2-supported catalysts was 5.0 wt.%. The catalyst samples (V2O5/TiO2) were dried overnight at 110 °C and calcined at 500 °C for 2 h in static air.
A gas generator (KIN-TEK, 491 M-B) was used to generate 1800 ppm of 1,2-DCB. Air was introduced into the gas generator at a flow rate of 0.018 m 3 h− 1 (corresponding a space velocity of 18000 h− 1), which was adjusted with a mass flow controller (MKS). The catalytic experiments were carried out in a fixed bed glass reactor at atmospheric pressure, and a K-type thermocouple was placed into the catalyst bed to monitor the reaction temperature [23]. 100 mg of the V2O5/TiO2 was placed into the catalyst bed with commercial glass wool as a support. The noncatalytic oxidation of 1,2-DCB was also performed in the absence of a catalyst to compensate for catalytic degradation. The residual 1,2-DCB in the outlet gas was treated using three adsorbent (activated carbon) cylinders. The reactor effluent gas was analyzed using two gas chromatographs (HP6890, Younglin M600D) equipped with flame ionization detectors employing a capillary column (30 m × 0.32 mm DB-5, 0.25 mm) for 1,2-DCB and a packed column (6 in. × 1/8 ft × 0.085 ft SS, Carbosphere 80/100) with a methanator containing a commercial
2.2. Catalyst characterization XRD was carried out using a high resolution x-ray diffractometer (focal spot size: 5 mm2, Cu rotating anode). The crystallite size and shapes were observed by transmission electron microscopy (TEM) (Philips; operated at 300 kV, image resolution b0.23 nm). For highresolution transmission electron microscopy (HR-TEM) and energydispersive X-ray (EDX), analyses were carried out using a F-20 microscope (Philips; operated at 200 kV, image resolution b0.25 nm). The
Table 1 BET surface area and particle diameter (dBET). Sample
SBET (m2 g− 1), before/aftera
dBET (nm), Before/aftera
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100 V2O5/80TiO2900 V2O5/110TiO2900 V2O5/P25TiO2
142/181 134/270 110/150 149/191 105/113 52/53
10.8/8.5 11.5/5.7 14.0/10.3 10.3/8.1 14.7/13.6 29.6/29.1
a
Before and after impregnation of vanadia.
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a
b
10 nm
10 nm
d
c
10 nm
10 nm
Fig. 2. TEM images of (a) P25TiO2, (b) V2O5/P25TiO2, (c) 95TiO2900 and (d) V2O5/95TiO2900.
nickel catalyst for CO and CO2. The concentration of the vaporized sample was measured quantitatively using a standard solution. The residual 1,2-DCB of the outlet gas was treated using three adsorbent (activated carbon) cylinders. The CO and CO2 selectivity were calculated from the measured concentrations according to the following equation:
SCOx ð−Þ ¼
C COx 6ðC in −C out
where, SCOx are the CO and CO2 selectivity, CCOx are the CO and CO2 concentrations in the product stream, and Cin and Cout are the inlet and outlet concentrations of 1,2-DCB, respectively.
a
b
3. Results and discussion 3.1. Catalyst characterization Fig. 1 shows the XRD patterns of all samples. The typical diffraction peaks characteristic of anatase TiO2 were observed for all samples except for V2O5/P25TiO2, indicating that the CVC method produces anatase TiO2. In addition, there was no change in the diffraction peaks due to the 5 wt.% loading of vanadia. The entrapping and/or diffusion of vanadium ions into the TiO2 structure would probably cause a change in the crystallite phase [1,24]. Djerad et al. [25] reported that vanadium enhanced the phase transformation of TiO2 from anatase to rutile. Since the vanadia loading was fixed to 5 wt.%, the crystalline phase of TiO2 did not transform to rutile.
c
50 nm Fig. 3. Energy-dispersive X-ray images of the V2O5/95TiO2900 samples. (a) High-angle annular dark field image of V2O5/95TiO2900; (b) titanium elemental spots; (c) vanadium elemental spots.
S. Chin et al. / Powder Technology 217 (2012) 388–393
In a recent publication [22], the increased TTIP heating temperature enhanced the collision and coalescence rate of the particles, resulting in an increase in the size of the TiO2 nanoparticles and a reduced SSA. In addition, the peak intensities for anatase increased with increasing synthesis temperature, indicating enhanced crystallization and a reduced SSA. In this study, there was no difference in the SSA of V2O5/P25TiO2 due to vanadium impregnation (see Table 1). On the
391
other hand, the SSAs of the V2O5/TiO2 catalysts, in which the vanadium were impregnated on the CVC-TiO2, increased drastically. In particular, the SSA of V2O5/95TiO2900 was increased greatly from 134 to 270 m 2 g − 1 after vanadium impregnation. Table 1 present the specific surface areas for the prepared V2O5/TiO2 samples. As shown in Table 1, there was no difference in the SSA of the V2O5/P25TiO2 catalyst before and after the impregnation of vanadium.
b
a V2 O5 /95TiO 2 700
V2 O5 /95TiO 2 900
5+
V
528
524
520 Binding energy (eV)
516
4+
5+
Intensity (a.u.)
V
Intensity (a.u.)
V
V
528
512
524
520 Binding energy (eV)
4+
516
512
d
c
V2 O5 /80TiO 2 900
V2 O5 /95TiO 2 1100
528
5+
V
524
520 Binding energy (eV)
4+
516
V
Intensity (a.u.)
Intensity (a.u.)
V
528
512
e
5+
V
524
520 Binding energy (eV)
516
4+
512
f V2 O5 /110TiO 2 900
5+
V
524
2
520 Binding energy (eV)
516
Intensity (a.u.)
V
Intensity (a.u.) 528
V2 O5 /P25TiO
4+
512
528
V
5+
V
524
Fig. 4. XPS spectra of the V 2p region for each sample.
520 Binding energy (eV)
516
4+
512
392
S. Chin et al. / Powder Technology 217 (2012) 388–393
Table 2 Binding energies of the samples. Sample
Binding energy (eV) V 2p3/2
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100 V2O5/80TiO2900 V2O5/110TiO2900 V2O5/P25TiO2 a b
516.0 515.6 516.5 515.8 516.4 516.3
Ti 2p3/2 a
(25%) (18%)a (24%)a (21%)a (23%)a (29%)a
517.0 516.9 517.3 517.1 517.1 517.3
b
(75%) (82%)b (76%)b (79%)b (77%)b (71%)b
458.8 458.6 458.7 458.8 458.7 458.7
Binding energies between 515.6 and 516.5 eV correspond to V4 + in V2O4. Binding energies between 516.9 and 517.3 eV correspond to V5 + in V2O5.
However, the V2O5/TiO2 catalysts prepared by the CVC method had a larger surface area, which possibly provided more accessible active sites and enhanced the catalyst activity. Before vanadium impregnation, the SSAs of the prepared TiO2 samples were in the order of 80TiO2900 > 95TiO2700 > 95TiO2900 > 95TiO21100 > 110TiO2900 > P25TiO2, with 80TiO2900 showing the highest SSA. After vanadium impregnation, the SSAs of the prepared V2O5/TiO2 samples were in the order of V2O5/95TiO2900>V2O5/80TiO2900>V2O5/95TiO2700>V2O5/ 95TiO21100>V2O5/110TiO2900>V2O5/P25TiO2900 with V2O5/95TiO2 900 having the highest SSA. The SSA of V2O5/95TiO2900 was >2 times higher after vanadium impregnation. The catalyst SSA is one of the important factors for the catalytic activity [26]. Fig. 2 shows TEM images of P25TiO2 (a), 95TiO2900 (b), V2O5/ P25TiO2 (c), and V2O5/95TiO2900 (d). The morphology and size of P25TiO2 and V2O5/P25TiO2 were similar before and after vanadium impregnation. In addition, the particles size ranged from 20 to 30 nm (see Table 1). After the vanadium impregnation, the V2O5/95TiO2900 particles sizes decreased drastically from 11.5 to 5.7 (see Table 1), indicating enhanced SSA. Tian et al. [27] suggests that the TiO2 nanopowders synthesized by a hydrothermal process in the presence of cetyltrimethylammonium bromide and a post-treatment with ammonia can increase the SSA. The catalyst SSA decreased with increasing loading of the active component [28]. However, the SSA of V2O5/TiO2 catalysts, in which the supported TiO2 was synthesized using the CVC method increased drastically. This varied behavior suggests that the transition metal oxides were dispersed onto the surface of the TiO2 catalysts. EDX mapping images of the V2O5/95TiO2900 catalysts were obtained to investigate this further (Fig. 3). The V elements of the V2O5/95TiO2900 catalyst were more scattered over the TiO2 support than the V2O5/P25TiO2. Accordingly, the V2O5/95TiO2900 fine particle
catalysts may have large surface areas and enhanced dispersion of the active component. XPS is a highly sensitive surface analysis technique that is effective for examining the surface composition and chemical states of solid samples. Fig. 4 shows the V 2p3/2 spectra for each sample. The C 1 s peak at 285.0 eV was used as an internal standard to calibrate the binding energies. The binding energy references of the V 2p3/2 line used to identify the vanadium oxide phases in the catalysts were calculated based on the data [29,30]. The V 2p3/2 XPS spectra were wide and asymmetric, demonstrating at least two V chemical states according to the binding energy range from 512.0 to 528.0 eV. The main contribution was attributed to V2O5. The other minor peak for the V2O5/TiO2 catalyst surface was assigned to V2O4[31]. Therefore, the V 2p3/2 XPS spectra were fitted to the two chemical states using Origin software with a Gaussian rule. Two peaks related to the presence of V 5 + and V4 + could be detected for V2O5/P25TiO2 and V2O5/95TiO2900. No differences were detected among the samples for the Ti XPS peaks. V5 + groups are more powerful oxidants leading to enhanced catalytic reactions, and are a significant factor in catalytic oxidation. As shown in Fig. 4, V5 + in V2O5/ 95TiO2900 was larger than that of V2O5/P25TiO2. Therefore, the V5 + content on the V2O5/95TiO2900 sample surface was higher than that on the V2O5/P25TiO2 sample, resulting in increased catalytic oxidation. Table 2 lists the binding energies of the V 2p3/2 and Ti 2p3/2 lines from the XPS measurements. The V2O5/95TiO2900 sample contained approximately 82% V5 + species, whereas the V2O5/P25TiO2 sample was reduced slightly, 71% V 5 +. Fig. 5 shows the 1,2-DCB conversion on the different V2O5/TiO2 catalysts as a functions of temperature. 1,2-DCB was selected to examine the catalytic activity of V2O5/TiO2 because its structure is similar to the more toxic 2,4,7,8-tetrachlorodibenzodioxin [32]. Noncatalytic oxidation of 1,2-DCB was performed in the absence of a catalysts because 1,2-DCB could be decomposed to other components at high temperatures. Indeed, 2% of 1,2-DCB were actually decomposed to other components at 300 °C and 3% at 400 °C. Therefore, noncatalytic oxidation at high temperature must be considered. As shown in Fig. 5, 1,2-DCB conversion was considered only in the catalytic oxidation except for noncatalytic oxidation. The 1,2-DCB conversions were in the order of V2O5/95TiO2900>V2O5/80TiO2900>V2O5/ 110TiO2900>V2O5/95TiO2700>V2O5/95TiO21100>V2O5/P25TiO2, with V2O5/P25TiO2 having the lowest conversion. In particular, V2O5/ 95TiO2900 had the highest conversion, resulting from its larger SSA value and higher V5 + content, as shown in Tables 1 and 2, and Fig. 5. In addition, the 1,2-DCB conversion order of the prepared V2O5/TiO2 samples is strongly related to the SSA and the V5 + content. With increasing 1.0 V2O5/P25TiO2
1.0
0.8
COx yield (-)
Conversion (-)
0.8
0.6 V2O5/P25TiO2 V2O5/95TiO2700
0.4
V2O5/95TiO2700 V2O5/95TiO2900 V2O5/95TiO21100
0.6
V2O5/80TiO2900 V2O5/110TiO2900
0.4
V2O5/95TiO2900
0.2
V2O5/95TiO21100
0.2
V2O5/80TiO2900 V2O5/110TiO2900
0.0 150
200
250
300
350
400
450
0.0 0.0 500
0.2
0.4 0.6 1,2-DCB conversion (-)
0.8
1.0
Temperature (oC) Fig. 5. 1,2-DCB conversion as a function of temperature for the prepared V2O5/TiO2 samples.
Fig. 6. Catalytic selectivity calculated carbon balance of 1,2-DCB destruction and carbon oxide formation: conversion and selectivity obtained from the various reaction temperatures are plotted.
S. Chin et al. / Powder Technology 217 (2012) 388–393
reaction temperature, the 1,2-DCB conversion became saturated, which agrees with the traditional catalytic curve [1,2,6,32]. The conversion of the V2O5/P25TiO2 catalyst was only 0.280 and 0.582 at a catalytic reaction temperature of 250 and 300 °C, respectively. On the other hand, the conversion of the V2O5/95TiO2900 catalyst prepared by the CVC method was 0.579 and 0.805 at the same reaction temperature, respectively. As a result, the V2O5/TiO2 catalysts synthesized by the CVC method showed good performance for 1,2-DCB decomposition at low temperatures. Fig. 6 presents the relationship between 1,2-DCB conversion and the carbon oxide yields for the prepared V2O5/TiO2 samples. The effluent consists mainly of CO (42–51%) and CO2 (54–61%) the composition did not change much for all catalysts. Overall the carbon balances were closed in all cases within 2%. The carbon balance was well matched at 1,2-DCB conversions > 0.6, indicating most of the 1,2-DCB decomposed to CO and CO2. On the other hand, the carbon balance did not match at lower 1,2-DCB conversions resulting from the low reaction temperature. The remainder of the effluent except for carbon oxides at low reaction temperatures was assumed to be organic byproducts. Choi et al. [1] suggested that carboxylates, carbonates, maleates and phenolates were by-products from the oxidative destruction of 1,2-DCB on the V2O5/TiO2 catalysts. 4. Conclusions V2O5/TiO2 catalysts were prepared by the vanadium impregnation on the TiO2. In particular, the supported TiO2 was prepared using the CVC method at various synthesis temperatures and precursor concentrations, which were varied by the precursor temperatures. This study demonstrated that the characteristics of the support material deeply affect the resulting catalyst activity for 1,2-DCB despite the same support material (TiO2). There was no difference in the SSA of V2O5/TiO2 after vanadium impregnation when commercial TiO2 (P25) was used. However, the SSAs of the V2O5/TiO2 catalysts, in which the vanadium had been impregnated on CVC-TiO2, increased drastically. The SSA of V2O5/95TiO2900 was >2 times higher after vanadium impregnation. XPS suggests that the surface V species were mainly 75–82% V 5 + and 18–25% V 4 +. The higher V 5 + species were related to the higher catalytic oxidation, resulting in greater 1,2-DCB destruction. As a result, the catalytic oxidation of the CVC-made V2O5/TiO2 catalysts showed good performance for 1,2-DCB at a lower temperatures. Future studies should examine the optimum synthesis conditions for the support material in the CVC method to accelerate the V2O5/TiO2 catalytic oxidation for 1,2-DCB. Acknowledgments This work has been supported by the Ministry of Environment (192-091-001), the Ministry of Education, Science and Technology (2011K000750) and the Korea Institute of Science and Technology (KIST) Institutional Program (2E22181). References [1] J.S. Choi, C.B. Sin, T.J. Park, D.J. Suh, Characteristics of vanadia–titania aerogel catalysts for oxidative destruction of 1,2-dichlorobenzene, Applied Catalysis A: General 311 (2006) 105–111. [2] J. Lichtenberger, M.D. Amiridis, Catalytic oxidation of chlorinated benzenes over V2O5/TiO2 catalysts, Journal of Catalysis 223 (2004) 296–308. [3] C.H. Cho, S.K. Ihm, Development of new vanadium-based oxide catalysts for decomposition of chlorinated aromatic pollutants, Environmental Science and Technology 36 (2002) 1600–1606. [4] K.S. Chung, Z. Jiang, B.S. Gill, J.S. Chung, Oxidative decomposition of odichlorobenzene over V2O5/TiO2 catalyst washcoated onto wire-mesh honeycombs, Applied Catalysis A: General 237 (2002) 81–89. [5] P. Liljelind, J. Unsworth, O. Maaskant, S. Marklund, Removal of dioxins and related aromatic hydrocarbons from flue gas streams by adsorption and catalytic destruction, Chemosphere 42 (2001) 615–623.
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