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Oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiFe0.65NixMo oxide catalysts: Effect of nickel content
Catalysis Communications 31 (2013) 76–80
Contents lists available at SciVerse ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Short Communication
Oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiFe0.65NixMo oxide catalysts: Effect of nickel content Jung-Hyun Park a, Kyoungho Row b, Chae-Ho Shin a,⁎ a b
Department of Chemical Engineering, Chungbuk National University, Chungbuk 361-763, Republic of Korea Process Solution Team, Kumho Petrochemical R&BD Center, Daejeon 305-348, Republic of Korea
a r t i c l e
i n f o
Article history: Received 27 August 2012 Received in revised form 14 November 2012 Accepted 16 November 2012 Available online 23 November 2012 Keywords: Oxidative dehydrogenation BiFe0.65NixMo oxide catalyst 1,3-Butadiene Temperature programmed reoxidation
a b s t r a c t BiFe0.65NixMo oxide catalysts (x = 0–0.2) were prepared and applied for the oxidative dehydrogenation of butenes to 1,3-butadiene. Temperature programmed reoxidation (TPRO) measurements revealed that the catalytic activity was closely related to the oxygen mobility. The surface modification by small amounts of nickel addition is favorable in this reaction. Among the catalysts studied here, BiFe0.65Ni0.05Mo oxide catalyst showed the highest conversion and BD yield (X = 86% and YBD = 72%) due to the high oxygen mobility. The BiFe0.65Ni0.05Mo oxide catalyst is very stable and no deactivation during the 100 h reaction was shown. © 2012 Elsevier B.V. All rights reserved.
1. Introduction 1,3-Butadiene (BD) has been usually produced by ODH of n-butenes in C4 raffinate produced by steam naphtha cracking, which is an essential feedstock for the production of styrene butadiene rubber (SBR), acrylonitrile–butadiene–styrene (ABS) resin, and poly-butadiene rubber (BR) [1,2]. The catalysts used in the ODH reaction are usually mixed oxides such as various ferrites, bismuth-molybdate or multicomponent oxides containing iron [3–7]. In particular, bismuth-molybdate based catalysts are exclusively studied the most. However, the catalytic activity over pure bismuth-molybdate catalysts was low in the ODH reaction. In this regard, multicomponent bismuth molybdate catalysts have been widely investigated to improve the catalytic activity of pure bismuth molybdate catalyst [4,5]. It is generally known that multicomponent bismuth-molybdate catalysts can be formed as a Mo–Bi–M(II)–M(III)–O catalyst containing divalent metal (M(II)), trivalent metal (M(III)), bismuth, and molybdenum [6,7]. To make an excellent bismuth-molybdate based catalyst, it is important to activate bismuth by both divalent and trivalent metal cations. The increases in the activity of the Mo–Bi–M(II)–M(III)–O catalyst compared to the pure bismuth molybdates come in part from the increase in the surface area and the remaining increase arises from the increase in the specific activity [6]. In our previous results [8], it was found that the catalytic activity showed a volcano-shaped curve with respect to the Fe content. Among the catalysts tested, the BiFe0.65Mo catalyst showed the highest catalytic ⁎ Corresponding author. Tel.: +82 43 261 2376; fax: +82 43 269 2370. E-mail address: [email protected] (C.-H. Shin). 1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catcom.2012.11.019
activity for the ODH of 1-butene. Considering the possible effect of divalent metal on the properties of the BiFe0.65Mo catalyst, we planned to prepare the BiFe0.65NixMo oxide catalyst with different molar ratios of nickel, and investigated the effect of the nickel content on the catalytic activity. The correlation between the catalytic activity and the nickel content of the BiFe0.65NixMo oxide catalysts was examined by using TPRO analysis. 2. Experimental 2.1. Catalyst preparation BiFe0.65NixMo oxide catalysts (x= 0.0–0.2) were prepared by a co-precipitation method. Bi(NO3)3∙5H2O (Junsei, 98%), Fe(NO3)3∙9H2O (Samchun, 98%), and Ni(NO3)2∙ 6H2O (Samchun, 98%) were dissolved in deionized water that had been acidified with 10% nitric acid (solution A). Solution A was added dropwise to a solution containing (NH4)6Mo7O24∙ 4H2O (Junsei, 99%) under vigorous stirring at 60 °C, and the pH was then adjusted to 5 using NH4OH (Samchun, 28–30 vol.%). The mixed solution was vigorously stirred at 60 °C for 3 h, and the solution was removed by using a rotary evaporator (EYELA N-1000). The solid product was dried at 100 °C for 12 h and calcined at 550 °C for 2 h in airflow. The catalysts are designated by BiFe0.65NixMo, where x is the molar ratio of nickel in the catalyst. 2.2. Characterization Product phase identification of the BiFe0.65NixMo oxide catalysts was carried out by powder X-ray diffraction (XRD) on a Siemens D5005 using Cu Kα radiation with a scan rate of 1.2° min−1. The BET surface
J.-H. Park et al. / Catalysis Communications 31 (2013) 76–80
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area and pore volume of the catalysts were determined from multipoint BET isotherms using N2 adsorption (Micromeritics ASAP 2020). Elemental analysis was performed by inductively coupled plasma and atomic emission spectroscopy (ICP-AES), using a Jarrell-Ash Polyscan 61E spectrometer, in combination with a Perkin-Elmer 5000 atomic absorption spectrophotometer. X-ray photoelectron spectroscopic (XPS) measurements were carried out on a VG Scientific ESCALAB 210 spectrometer with a Mg Kα X-ray source (1253.6 eV). All the binding energies were referenced to the C 1s peak at 284.6 eV from adventitious carbon. In order to investigate the redox property of the catalyst, temperature programmed re-oxidation (TPRO) measurements were carried out by using Omnistar QMS apparatus. The catalysts were pretreated at 420 °C for 1 h in flowing 50% 1-C4H8/He (50 cm3 min−1) and then cooled to room temperature in flowing He (50 cm3 min−1). Subsequently, the flow of 5% O2/N2 (10 cm3 min−1) was then switched into the reactor and heated from room temperature to 600 °C with a heating rate of 10 °C min−1. 2.3. ODH of 1-butene The ODH reaction was investigated in a fixed-bed reactor at atmospheric pressure at 420 °C. The feed composition was fixed at a ratio of 1-butene/air/steam = 1/3.75/5 with a total flow rate of 78 cm 3 min −1. Products were analyzed by an on-line gas chromatograph (Varian 3800) equipped with a flam ionization detector (FID) and thermal conductivity detector (TCD). The conversion, selectivity and yield in BD were calculated following reported procedures previously [8]. 3. Results and discussion The XRD patterns of BiFeNixMo oxide catalysts with different nickel contents were shown in Fig. 1. The solid phase consisted of the Bi3Mo2Fe1O12 phase with a minor amount of the Fe2(MoO4)3 phase. Single oxide phases such as MoO3, NiO, Fe2O3, and Bi2O3 were not observed. It has been reported that Bi–Mo based catalysts are located on the surface of the catalyst particles and act as active phases in the multicomponent Bi–Mo catalyst systems [9]. On the other hand, the M(II)MoO4 and M(III)(MoO4)3 phases are located in the bulk of the catalyst and act as support for the active components as well as oxygen donors to the Bi–Mo based catalyst. Therefore, it can be expected that the Bi3Mo2Fe1O12 phase plays a role of the active phase and the Fe2(MoO4)3 phase acts as an oxygen donor, which is transformed to FeMoO4 after ODH reaction [8,10]. The atomic ratios, BET surface areas and pore volume of BiFe0.65NixMo oxide catalysts are listed in Table 1. The catalyst composition, which calculated as the molar ratio of each metal component based on Bi, is in good agreement with the theoretical values, indicating that the BiFe0.65NixMo oxide catalysts are well prepared. The BET surface areas and pore volume of the BiFeNixMo oxide catalysts were much higher than that of the nickel-free BiFe0.65Mo oxide catalyst, and they gradually increased with increasing nickel content [5]. Table 2 shows the catalytic activity of BiFeNixMo oxide catalysts with different nickel contents (x=0–0.2). The values were obtained after 14 h ODH reaction (see Fig. S1). BD and CO2 were observed as the main products and negligible amounts of cracking products such as CH4, C2H4, C2H6 C3H6, and C3H8 were also observed. For all catalysts studied here, the deactivation was not observed during the 14 h reaction. The conversion and yield in BD are maximized over BiFe0.65Ni0.05Mo oxide catalyst and then decrease with the increase of nickel content (see Fig. S2). The maximum conversion and yield in BD over BiFeNi0.05Mo catalyst are 85.7% and 71.8%, respectively. The addition of nickel provokes the decrease of selectivity to BD due to the increase of combustion activity of hydrocarbons to form CO2 and the formation of C1–C3 hydrocarbons by the cracking of C4 compounds. Increase of nickel content led to the promotion of the complete oxidation reaction. The surface area of the catalyst is one of the important factors that affect the catalytic activity. The BET
Fig 1. (A) XRD patterns of BiFe0.65NixMo oxide catalysts: (a) BiFe0.65Mo, (b) x = 0.05, (b′) after a 100 h reaction, (c) 0.10, (d) 0.15, and (e) 0.20 and (B) detailed in the region 2θ = 24–30°.
surface area of the BiFe0.65Ni0.05Mo catalyst which has shown the highest yield for ODH reaction in our operating conditions (Table 2) is smaller than that of the high amount of Ni-containing catalysts. This result suggests that the surface area is not the main factor that affects the activity of BiFe0.65Ni0.05Mo catalysts for ODH reaction. The catalytic activity of the BiFeNixMo oxide catalysts was correlated by TPRO experiments. Fig. 2 shows the TPRO profiles of BiFeNixMo oxide Table 1 Surface area, pore volume and molar composition of BiFe0.65NixMo oxide catalysts. Catalyst
BiFe0.65Mo BiFe0.65Ni0.05Mo BiFe0.65Ni0.10Mo BiFe0.65Ni0.15Mo BiFe0.65Ni0.20Mo a
SBET (m2 g−1)
3.5 5.2 6.8 7.0 8.1
Determined from ICP-AES.
Pore volume (cm3 g−1)
0.008 0.023 0.026 0.029 0.033
Catalyst composition (mol ratio)a Bi
Fe
Ni
Mo
1.00 1.00 1.00 1.00 1.00
0.63 0.65 0.60 0.61 0.62
0.00 0.04 0.09 0.14 0.19
1.05 1.03 1.03 1.02 1.03
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J.-H. Park et al. / Catalysis Communications 31 (2013) 76–80
Table 2 Catalytic activity for ODH of 1-butene on BiFe0.65NixMo oxide. Catalyst
Catalytic activitya Conv. (%)
BiFe0.65Mo BiFe0.65Ni0.05Mo BiFe0.65Ni0.10Mo BiFe0.65Ni0.15Mo BiFe0.65Ni0.20Mo
79.8 85.7 81.9 79.7 73.3
Selectivity (wt.%)
Yield (wt.%)
BD
CO2
BD
84.4 83.8 81.0 80.3 76.6
15.4 14.7 17.1 18.0 21.7
67.4 71.8 66.3 64.0 56.1
a Obtained after 14 h reaction. 1-Butene/air/steam = 1/3.75/5, T= 420 °C, F/W = 42.9 mmol/gcat h−1.
catalysts. Two kinds of oxidation peaks were observed for all catalysts. The first peak of the TPRO profile in the 100–250 °C range is assigned to the oxidation of the partially reduced bismuth oxide and the second peak of the TPRO profile in the 280–450 °C range is from the oxidation of the molybdenum oxide [11]. In addition, the second peak is partially
Fig. 2. (A) TPRO profiles of BiFe0.65NixMo oxide catalysts: (a) BiFe0.65Mo, (b) x = 0.05, (c) 0.10, (d) 0.15, and (e) 0.20 and (B) the correlation curve between the oxygen mobility and the yield in BD.
related to the 1-butene species and is observed along with a reduction of 1-butene species and a formation of CO2 (see Fig. S3). In particular, the first peak temperature in TPRO profile indicates the degree of oxygen mobility on multicomponent oxide catalysts in selective oxidations [12]. As shown in Fig. 2, the peak temperature of the BiFe0.65Ni0.05Mo oxide catalysts was lower than that of the nickel-free BiFe0.65Mo oxide catalyst, and shifted to high temperatures with increasing the nickel contents. Fig. 2(B) shows a correlation curve between BD yield and TPRO peak temperature which means the degree of oxygen mobility in BiFe0.65NixMo oxide catalysts. The correlation clearly shows that the yield in BD increased with decreasing TPRO peak temperature. Among the catalysts studied here, the BiFe0.65Ni0.05Mo oxide catalyst, which showed the lowest TPRO peak temperature, exhibited the best catalytic activity. From what has been shown with the TPRO curve, we can suggest that the catalytic activity was closely related to the oxygen mobility of the catalyst. To assess the stability of the catalyst, a long term test of the BiFe0.65Ni0.05Mo oxide catalyst was carried out and the results are
Fig. 3. Long-term stability of BiFe0.65Ni0.05Mo oxide catalyst in the ODH reaction: (A) conversion and yield in BD and (B) selectivity to BD and CO2.
J.-H. Park et al. / Catalysis Communications 31 (2013) 76–80
shown in Fig. 3. The conversion and the selectivity to BD are gradually increased, whereas the selectivity to CO2 decreased during the reaction. The conversion and the yield in BD after 100 h reaction were found to be 86.4%, and 77.1%, respectively. The BiFeNi0.05Mo oxide catalyst is very stable and no deactivation for 100 h on stream was shown. To investigate the structural change of BiFe0.65Ni0.05Mo oxide catalyst before and after 100 h ODH reaction, we also conducted XRD analysis (Fig. 1(b′)). XRD patterns before and after 100 h reaction are almost the same except that the Fe2(MoO4)3 phase is reduced to the FeMoO4 phase, which indicates the reduction of Fe3+ to Fe2+ during the ODH reaction [13]. In addition, the crystallinity after ODH reaction is significantly increased. The BET surface area decreased from 5.6 to 2.6 m2 g−1. Despite of the decrease of surface area, the gradual increase of conversion and selectivity to BD was observed. This means the surface area is not one of the important factors for the ODH of 1-butene to produce BD. For a more detailed investigation of the catalyst change before and after reaction, XPS analysis was performed and the results are shown in Fig. 4. All the elements were reasonably detected on the catalyst surface, but the Ni was detected with a small intensity due to its very small concentration. According to the literatures [14,15], the values of the binding energy (BE) indicate that Mo is present as Mo6+, Bi as Bi3+, Fe as Fe3+ or Fe2+ and Ni as Ni2+. The BEs for Bi, Mo, Ni, and O of the used catalyst are equal to those of the fresh catalyst. In the case of the Fe 2p3/2 metal, the BE of the used catalyst (710.3 eV) is slightly shifted to a lower BE compared to that of the fresh catalyst (710.6 eV). This indicates that Fe 2p3/2 of the fresh catalyst is present as Fe3+, and that of the used catalyst as Fe2+. This result is good agreement with the results obtained from XRD analysis. The BE of the used catalyst was similar to those of the fresh catalyst except Fe, but the surface composition of each element changed significantly. The surface concentration of the used catalyst is enriched with Mo and O and has decreased for the elements of Bi, Fe, and Ni. The decrease may be attributed to the result
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that these elements are buried as the relatively rich Mo migrates from the interior to the surface of the catalyst [16,17]. The decrease of surface concentration of Ni species after 100 h ODH reaction could be related to the gradual decrease of CO2 selectivity and increase of BD selectivity at almost constant 1-butene conversion and finally the promotional effect to produce BD in a high yield. 4. Conclusions BiFe0.65NixMo (Ni = 0–0.20) oxide catalysts with different nickel contents were prepared by co-precipitation method and applied for the ODH of 1-butene to BD. Adding a small amount of nickel content in BiFe0.65Mo oxide catalyst improved the catalytic activity showing a maximum yield in BD on BiFe0.65Ni0.05Mo oxide catalyst. However, the addition of nickel element resulted in the decrease of selectivity to BD and then led to total oxidation to CO2. The oxygen mobility of the catalysts was well correlated with the catalytic activity. No significant deactivation of the BiFe0.65Ni0.05Mo catalyst for a 100 h reaction was shown. The detailed characterization of oxygen species by the addition of transition metals would be further studied. Acknowledgment The authors wish to acknowledge the financial support from Korea Institute of Energy Evaluation and Planning (KETEP). This work is part of the Energy Technology Innovation Project (ETI) under the Energy Resources Technology Development Program. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.catcom.2012.11.019.
Fig. 4. XP spectra of fresh and used BiFe0.65Ni0.05Mo oxide catalysts: (A) Bi 4f, (B) Mo 3d, (C) Fe 2p, (D) Ni 2p, and (E) O 1s.
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References [1] G. Ertl, H. Knozinger, J. Weitkamp, in: Handbook of Heterogeneous Catalysis, VCH, Weinheim, 1997, pp. 2253–2263. [2] W.C. White, Chemico-Biological Interactions 166 (2007) 10–14. [3] J.-H. Park, H.R. Noh, J.W. Park, K.H. Row, K.D. Jung, C.-H. Shin, Research on Chemical Intermediates 37 (2011) 1125–1134. [4] J.C. Jung, H.W. Lee, H.S. Kim, Y.M. Chung, T.J. Kim, S.J. Lee, S.H. Oh, Y.S. Kim, I.K. Song, Catalysis Communications 9 (2008) 1676–1680. [5] Y. Moro-Oka, W. Ueda, Advances in Catalysis 40 (1994) 233–273. [6] J.M.M. Millet, H. Ponceblanc, G. Coudurier, J.M. Herrmann, Journal of Catalysis 142 (1993) 381–391. [7] J.C. Jung, H.W. Lee, S.Y. Park, Y.-M. Chung, T.J. Kim, S.J. Lee, S.-H. Oh, Y.S. Kim, I.K. Song, Korean Journal of Chemical Engineering 25 (2008) 1316–1321.
[8] J.-H. Park, H.R. Noh, J.W. Park, K.H. Row, K.D. Jung, C.-H. Shin, Applied Catalysis A: General 431–432 (2012) 137–143. [9] J.F. Brazdil, D.D. Suresh, R.K. Grasselli, Journal of Catalysis 66 (1980) 347–367. [10] M.W.J. Wolfs, P.H.A. Batist, Journal of Catalysis 32 (1974) 25–36. [11] H. Miura, Y. Morikawa, T. Shirasaki, Journal of Catalysis 39 (1975) 22–28. [12] L.T. Weng, B. Delmon, Applied Catalysis A: General 81 (1992) 141–213. [13] T.S.R. Prasada Rao, K.R. Krishnamurthy, Journal of Catalysis 95 (1985) 209–219. [14] I. Matsuura, M.W.J. Wolfs, Journal of Catalysis 37 (1975) 174–178. [15] A.P.V. Soares, L.D. Dimitrov, M.C.R.A. Oliveira, L. Hilaire, M.F. Portela, R.K. Grasselli, Applied Catalysis A: General 253 (2003) 191–200. [16] T.S.R. Prasada Rao, P.G. Menon, Journal of Catalysis 51 (1978) 64–71. [17] W.C. Conner, J.L. Falconer, Chemical Reviews 95 (1995) 759–788.
Contents lists available at SciVerse ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Short Communication
Oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiFe0.65NixMo oxide catalysts: Effect of nickel content Jung-Hyun Park a, Kyoungho Row b, Chae-Ho Shin a,⁎ a b
Department of Chemical Engineering, Chungbuk National University, Chungbuk 361-763, Republic of Korea Process Solution Team, Kumho Petrochemical R&BD Center, Daejeon 305-348, Republic of Korea
a r t i c l e
i n f o
Article history: Received 27 August 2012 Received in revised form 14 November 2012 Accepted 16 November 2012 Available online 23 November 2012 Keywords: Oxidative dehydrogenation BiFe0.65NixMo oxide catalyst 1,3-Butadiene Temperature programmed reoxidation
a b s t r a c t BiFe0.65NixMo oxide catalysts (x = 0–0.2) were prepared and applied for the oxidative dehydrogenation of butenes to 1,3-butadiene. Temperature programmed reoxidation (TPRO) measurements revealed that the catalytic activity was closely related to the oxygen mobility. The surface modification by small amounts of nickel addition is favorable in this reaction. Among the catalysts studied here, BiFe0.65Ni0.05Mo oxide catalyst showed the highest conversion and BD yield (X = 86% and YBD = 72%) due to the high oxygen mobility. The BiFe0.65Ni0.05Mo oxide catalyst is very stable and no deactivation during the 100 h reaction was shown. © 2012 Elsevier B.V. All rights reserved.
1. Introduction 1,3-Butadiene (BD) has been usually produced by ODH of n-butenes in C4 raffinate produced by steam naphtha cracking, which is an essential feedstock for the production of styrene butadiene rubber (SBR), acrylonitrile–butadiene–styrene (ABS) resin, and poly-butadiene rubber (BR) [1,2]. The catalysts used in the ODH reaction are usually mixed oxides such as various ferrites, bismuth-molybdate or multicomponent oxides containing iron [3–7]. In particular, bismuth-molybdate based catalysts are exclusively studied the most. However, the catalytic activity over pure bismuth-molybdate catalysts was low in the ODH reaction. In this regard, multicomponent bismuth molybdate catalysts have been widely investigated to improve the catalytic activity of pure bismuth molybdate catalyst [4,5]. It is generally known that multicomponent bismuth-molybdate catalysts can be formed as a Mo–Bi–M(II)–M(III)–O catalyst containing divalent metal (M(II)), trivalent metal (M(III)), bismuth, and molybdenum [6,7]. To make an excellent bismuth-molybdate based catalyst, it is important to activate bismuth by both divalent and trivalent metal cations. The increases in the activity of the Mo–Bi–M(II)–M(III)–O catalyst compared to the pure bismuth molybdates come in part from the increase in the surface area and the remaining increase arises from the increase in the specific activity [6]. In our previous results [8], it was found that the catalytic activity showed a volcano-shaped curve with respect to the Fe content. Among the catalysts tested, the BiFe0.65Mo catalyst showed the highest catalytic ⁎ Corresponding author. Tel.: +82 43 261 2376; fax: +82 43 269 2370. E-mail address: [email protected] (C.-H. Shin). 1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catcom.2012.11.019
activity for the ODH of 1-butene. Considering the possible effect of divalent metal on the properties of the BiFe0.65Mo catalyst, we planned to prepare the BiFe0.65NixMo oxide catalyst with different molar ratios of nickel, and investigated the effect of the nickel content on the catalytic activity. The correlation between the catalytic activity and the nickel content of the BiFe0.65NixMo oxide catalysts was examined by using TPRO analysis. 2. Experimental 2.1. Catalyst preparation BiFe0.65NixMo oxide catalysts (x= 0.0–0.2) were prepared by a co-precipitation method. Bi(NO3)3∙5H2O (Junsei, 98%), Fe(NO3)3∙9H2O (Samchun, 98%), and Ni(NO3)2∙ 6H2O (Samchun, 98%) were dissolved in deionized water that had been acidified with 10% nitric acid (solution A). Solution A was added dropwise to a solution containing (NH4)6Mo7O24∙ 4H2O (Junsei, 99%) under vigorous stirring at 60 °C, and the pH was then adjusted to 5 using NH4OH (Samchun, 28–30 vol.%). The mixed solution was vigorously stirred at 60 °C for 3 h, and the solution was removed by using a rotary evaporator (EYELA N-1000). The solid product was dried at 100 °C for 12 h and calcined at 550 °C for 2 h in airflow. The catalysts are designated by BiFe0.65NixMo, where x is the molar ratio of nickel in the catalyst. 2.2. Characterization Product phase identification of the BiFe0.65NixMo oxide catalysts was carried out by powder X-ray diffraction (XRD) on a Siemens D5005 using Cu Kα radiation with a scan rate of 1.2° min−1. The BET surface
J.-H. Park et al. / Catalysis Communications 31 (2013) 76–80
77
area and pore volume of the catalysts were determined from multipoint BET isotherms using N2 adsorption (Micromeritics ASAP 2020). Elemental analysis was performed by inductively coupled plasma and atomic emission spectroscopy (ICP-AES), using a Jarrell-Ash Polyscan 61E spectrometer, in combination with a Perkin-Elmer 5000 atomic absorption spectrophotometer. X-ray photoelectron spectroscopic (XPS) measurements were carried out on a VG Scientific ESCALAB 210 spectrometer with a Mg Kα X-ray source (1253.6 eV). All the binding energies were referenced to the C 1s peak at 284.6 eV from adventitious carbon. In order to investigate the redox property of the catalyst, temperature programmed re-oxidation (TPRO) measurements were carried out by using Omnistar QMS apparatus. The catalysts were pretreated at 420 °C for 1 h in flowing 50% 1-C4H8/He (50 cm3 min−1) and then cooled to room temperature in flowing He (50 cm3 min−1). Subsequently, the flow of 5% O2/N2 (10 cm3 min−1) was then switched into the reactor and heated from room temperature to 600 °C with a heating rate of 10 °C min−1. 2.3. ODH of 1-butene The ODH reaction was investigated in a fixed-bed reactor at atmospheric pressure at 420 °C. The feed composition was fixed at a ratio of 1-butene/air/steam = 1/3.75/5 with a total flow rate of 78 cm 3 min −1. Products were analyzed by an on-line gas chromatograph (Varian 3800) equipped with a flam ionization detector (FID) and thermal conductivity detector (TCD). The conversion, selectivity and yield in BD were calculated following reported procedures previously [8]. 3. Results and discussion The XRD patterns of BiFeNixMo oxide catalysts with different nickel contents were shown in Fig. 1. The solid phase consisted of the Bi3Mo2Fe1O12 phase with a minor amount of the Fe2(MoO4)3 phase. Single oxide phases such as MoO3, NiO, Fe2O3, and Bi2O3 were not observed. It has been reported that Bi–Mo based catalysts are located on the surface of the catalyst particles and act as active phases in the multicomponent Bi–Mo catalyst systems [9]. On the other hand, the M(II)MoO4 and M(III)(MoO4)3 phases are located in the bulk of the catalyst and act as support for the active components as well as oxygen donors to the Bi–Mo based catalyst. Therefore, it can be expected that the Bi3Mo2Fe1O12 phase plays a role of the active phase and the Fe2(MoO4)3 phase acts as an oxygen donor, which is transformed to FeMoO4 after ODH reaction [8,10]. The atomic ratios, BET surface areas and pore volume of BiFe0.65NixMo oxide catalysts are listed in Table 1. The catalyst composition, which calculated as the molar ratio of each metal component based on Bi, is in good agreement with the theoretical values, indicating that the BiFe0.65NixMo oxide catalysts are well prepared. The BET surface areas and pore volume of the BiFeNixMo oxide catalysts were much higher than that of the nickel-free BiFe0.65Mo oxide catalyst, and they gradually increased with increasing nickel content [5]. Table 2 shows the catalytic activity of BiFeNixMo oxide catalysts with different nickel contents (x=0–0.2). The values were obtained after 14 h ODH reaction (see Fig. S1). BD and CO2 were observed as the main products and negligible amounts of cracking products such as CH4, C2H4, C2H6 C3H6, and C3H8 were also observed. For all catalysts studied here, the deactivation was not observed during the 14 h reaction. The conversion and yield in BD are maximized over BiFe0.65Ni0.05Mo oxide catalyst and then decrease with the increase of nickel content (see Fig. S2). The maximum conversion and yield in BD over BiFeNi0.05Mo catalyst are 85.7% and 71.8%, respectively. The addition of nickel provokes the decrease of selectivity to BD due to the increase of combustion activity of hydrocarbons to form CO2 and the formation of C1–C3 hydrocarbons by the cracking of C4 compounds. Increase of nickel content led to the promotion of the complete oxidation reaction. The surface area of the catalyst is one of the important factors that affect the catalytic activity. The BET
Fig 1. (A) XRD patterns of BiFe0.65NixMo oxide catalysts: (a) BiFe0.65Mo, (b) x = 0.05, (b′) after a 100 h reaction, (c) 0.10, (d) 0.15, and (e) 0.20 and (B) detailed in the region 2θ = 24–30°.
surface area of the BiFe0.65Ni0.05Mo catalyst which has shown the highest yield for ODH reaction in our operating conditions (Table 2) is smaller than that of the high amount of Ni-containing catalysts. This result suggests that the surface area is not the main factor that affects the activity of BiFe0.65Ni0.05Mo catalysts for ODH reaction. The catalytic activity of the BiFeNixMo oxide catalysts was correlated by TPRO experiments. Fig. 2 shows the TPRO profiles of BiFeNixMo oxide Table 1 Surface area, pore volume and molar composition of BiFe0.65NixMo oxide catalysts. Catalyst
BiFe0.65Mo BiFe0.65Ni0.05Mo BiFe0.65Ni0.10Mo BiFe0.65Ni0.15Mo BiFe0.65Ni0.20Mo a
SBET (m2 g−1)
3.5 5.2 6.8 7.0 8.1
Determined from ICP-AES.
Pore volume (cm3 g−1)
0.008 0.023 0.026 0.029 0.033
Catalyst composition (mol ratio)a Bi
Fe
Ni
Mo
1.00 1.00 1.00 1.00 1.00
0.63 0.65 0.60 0.61 0.62
0.00 0.04 0.09 0.14 0.19
1.05 1.03 1.03 1.02 1.03
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Table 2 Catalytic activity for ODH of 1-butene on BiFe0.65NixMo oxide. Catalyst
Catalytic activitya Conv. (%)
BiFe0.65Mo BiFe0.65Ni0.05Mo BiFe0.65Ni0.10Mo BiFe0.65Ni0.15Mo BiFe0.65Ni0.20Mo
79.8 85.7 81.9 79.7 73.3
Selectivity (wt.%)
Yield (wt.%)
BD
CO2
BD
84.4 83.8 81.0 80.3 76.6
15.4 14.7 17.1 18.0 21.7
67.4 71.8 66.3 64.0 56.1
a Obtained after 14 h reaction. 1-Butene/air/steam = 1/3.75/5, T= 420 °C, F/W = 42.9 mmol/gcat h−1.
catalysts. Two kinds of oxidation peaks were observed for all catalysts. The first peak of the TPRO profile in the 100–250 °C range is assigned to the oxidation of the partially reduced bismuth oxide and the second peak of the TPRO profile in the 280–450 °C range is from the oxidation of the molybdenum oxide [11]. In addition, the second peak is partially
Fig. 2. (A) TPRO profiles of BiFe0.65NixMo oxide catalysts: (a) BiFe0.65Mo, (b) x = 0.05, (c) 0.10, (d) 0.15, and (e) 0.20 and (B) the correlation curve between the oxygen mobility and the yield in BD.
related to the 1-butene species and is observed along with a reduction of 1-butene species and a formation of CO2 (see Fig. S3). In particular, the first peak temperature in TPRO profile indicates the degree of oxygen mobility on multicomponent oxide catalysts in selective oxidations [12]. As shown in Fig. 2, the peak temperature of the BiFe0.65Ni0.05Mo oxide catalysts was lower than that of the nickel-free BiFe0.65Mo oxide catalyst, and shifted to high temperatures with increasing the nickel contents. Fig. 2(B) shows a correlation curve between BD yield and TPRO peak temperature which means the degree of oxygen mobility in BiFe0.65NixMo oxide catalysts. The correlation clearly shows that the yield in BD increased with decreasing TPRO peak temperature. Among the catalysts studied here, the BiFe0.65Ni0.05Mo oxide catalyst, which showed the lowest TPRO peak temperature, exhibited the best catalytic activity. From what has been shown with the TPRO curve, we can suggest that the catalytic activity was closely related to the oxygen mobility of the catalyst. To assess the stability of the catalyst, a long term test of the BiFe0.65Ni0.05Mo oxide catalyst was carried out and the results are
Fig. 3. Long-term stability of BiFe0.65Ni0.05Mo oxide catalyst in the ODH reaction: (A) conversion and yield in BD and (B) selectivity to BD and CO2.
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shown in Fig. 3. The conversion and the selectivity to BD are gradually increased, whereas the selectivity to CO2 decreased during the reaction. The conversion and the yield in BD after 100 h reaction were found to be 86.4%, and 77.1%, respectively. The BiFeNi0.05Mo oxide catalyst is very stable and no deactivation for 100 h on stream was shown. To investigate the structural change of BiFe0.65Ni0.05Mo oxide catalyst before and after 100 h ODH reaction, we also conducted XRD analysis (Fig. 1(b′)). XRD patterns before and after 100 h reaction are almost the same except that the Fe2(MoO4)3 phase is reduced to the FeMoO4 phase, which indicates the reduction of Fe3+ to Fe2+ during the ODH reaction [13]. In addition, the crystallinity after ODH reaction is significantly increased. The BET surface area decreased from 5.6 to 2.6 m2 g−1. Despite of the decrease of surface area, the gradual increase of conversion and selectivity to BD was observed. This means the surface area is not one of the important factors for the ODH of 1-butene to produce BD. For a more detailed investigation of the catalyst change before and after reaction, XPS analysis was performed and the results are shown in Fig. 4. All the elements were reasonably detected on the catalyst surface, but the Ni was detected with a small intensity due to its very small concentration. According to the literatures [14,15], the values of the binding energy (BE) indicate that Mo is present as Mo6+, Bi as Bi3+, Fe as Fe3+ or Fe2+ and Ni as Ni2+. The BEs for Bi, Mo, Ni, and O of the used catalyst are equal to those of the fresh catalyst. In the case of the Fe 2p3/2 metal, the BE of the used catalyst (710.3 eV) is slightly shifted to a lower BE compared to that of the fresh catalyst (710.6 eV). This indicates that Fe 2p3/2 of the fresh catalyst is present as Fe3+, and that of the used catalyst as Fe2+. This result is good agreement with the results obtained from XRD analysis. The BE of the used catalyst was similar to those of the fresh catalyst except Fe, but the surface composition of each element changed significantly. The surface concentration of the used catalyst is enriched with Mo and O and has decreased for the elements of Bi, Fe, and Ni. The decrease may be attributed to the result
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that these elements are buried as the relatively rich Mo migrates from the interior to the surface of the catalyst [16,17]. The decrease of surface concentration of Ni species after 100 h ODH reaction could be related to the gradual decrease of CO2 selectivity and increase of BD selectivity at almost constant 1-butene conversion and finally the promotional effect to produce BD in a high yield. 4. Conclusions BiFe0.65NixMo (Ni = 0–0.20) oxide catalysts with different nickel contents were prepared by co-precipitation method and applied for the ODH of 1-butene to BD. Adding a small amount of nickel content in BiFe0.65Mo oxide catalyst improved the catalytic activity showing a maximum yield in BD on BiFe0.65Ni0.05Mo oxide catalyst. However, the addition of nickel element resulted in the decrease of selectivity to BD and then led to total oxidation to CO2. The oxygen mobility of the catalysts was well correlated with the catalytic activity. No significant deactivation of the BiFe0.65Ni0.05Mo catalyst for a 100 h reaction was shown. The detailed characterization of oxygen species by the addition of transition metals would be further studied. Acknowledgment The authors wish to acknowledge the financial support from Korea Institute of Energy Evaluation and Planning (KETEP). This work is part of the Energy Technology Innovation Project (ETI) under the Energy Resources Technology Development Program. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.catcom.2012.11.019.
Fig. 4. XP spectra of fresh and used BiFe0.65Ni0.05Mo oxide catalysts: (A) Bi 4f, (B) Mo 3d, (C) Fe 2p, (D) Ni 2p, and (E) O 1s.
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