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γ-Al2O3 catalysts for removing toluene in indoor air
Materials Letters xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
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Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air Minchan Jeong, Naoyoshi Nunotani, Naoki Moriyama, Nobuhito Imanaka ⇑ Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 Suita, Osaka 565-0871, Japan
a r t i c l e
i n f o
Article history: Received 16 February 2017 Received in revised form 19 April 2017 Accepted 10 May 2017 Available online xxxx Keywords: Catalyst Toluene VOC Rare earths
a b s t r a c t Pt/CeO2-ZrO2-NiO/c-Al2O3 catalysts were prepared by the coprecipitation and impregnation methods. The introduction of a small amount of NiO into the cubic fluorite-type CeO2-ZrO2 structure was considerably effective to enhance the oxygen release and storage abilities due to the formation of oxygen vacancies and the redox feature of Ni2+/3+. For the Pt(10 wt%)/Ce0.64Zr0.16Ni0.2O1.9(16 wt%)/c-Al2O3 catalyst, the complete toluene oxidation was realized at the temperature as low as 100 °C. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Toluene has been widely used as a solvent for paint thinners, printing inks, floor wax, adhesives, and antiseptic, because it dissolves various organic compounds and is easily produced from the oxidation of hydrocarbons or commercial fuels [1]. However, toluene is one of the volatile organic compounds and has harmful effects for human health. Even at low concentration of toluene, it is released from floor wax and wall paint in the individual houses, and causes irritation of the eyes, respiratory tract, and skin, which are cumulatively referred to as symptoms of sick building syndrome [2]. In order to protect our health, it is necessary to remove toluene vaporized into the indoor air. Among the several removal methods [3–7], catalytic combustion is one of competitive technologies of toluene abatement from air streams, due to its low operating cost, high decomposition efficiencies, and environmentally friendliness [7]. Various kinds of catalysts have been widely studied for catalytic combustion of toluene, such as noble metal based catalysts, metal oxide based catalysts, and perovskite catalysts [8–13]. In particular, platinum (Pt) catalysts have been paid attention due to its high efficiency in the oxidation process for toluene [8]. However, it is difficult to realize complete oxidation of toluene at moderate temperatures, and the catalysts need to be heated at least up to 170 °C [9,10]. Although previous attention was primarily directed to the investigation on the Pt-loaded on support material, promoters have been ⇑ Corresponding author. E-mail address: [email protected] (N. Imanaka).
also expected to be an important component of the catalyst. They supply the active oxygen species from inside the lattice to facilitate the oxidation on the platinum. CeO2-ZrO2 (CZ) is one of the most important commercial promoter due to its high oxygen release and storage abilities [14–16]. In our previous studies, we reported that Bi2O3 or SnO2 doping into the CeO2-ZrO2 lattice enhanced the ability to release and store oxygen, because the formation of oxygen vacancy through the low-valent Bi3+ substitution facilitated the supply of oxygen species [17] or the valence change of Sn4+/2+ improved the redox property [18]. Furthermore, we demonstrated that Pt/CeO2-ZrO2-MOx/c-Al2O3 (M = Bi, Sn) oxidized toluene completely at the lower temperatures of 120 °C [19] and 110 °C [18], respectively, compared to the case of Pt/CeO2-ZrO2/c -Al2O3 (140 °C). Recently, we focused on the introduction of NiO as the substitute for Bi2O3 and SnO2 into CeO2-ZrO2, where nickel is expected to show two kinds of lower valent Ni2+ and Ni3+, relative to Ce4+ and Zr4+, and the palladium oxide supported on CeO2-ZrO2-NiO/c-Al2O3 catalysts showed high activity for methane combustion [20]. In order to realize a complete toluene oxidation at temperatures as low as possible for the practical application, we selected CeO2-ZrO2-NiO as a promoter, and the catalytic activities for toluene combustion of Pt-supported on CeO2-ZrO2-NiO/c-Al2O3 catalysts were investigated. 2. Experimental Ce0.64Zr0.18Ni0.2O1.9(16 wt%)/c-Al2O3 (CZN/Al2O3) was synthesized using the coprecipitation method. Then, Pt was supported
http://dx.doi.org/10.1016/j.matlet.2017.05.048 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048
M. Jeong et al. / Materials Letters xxx (2017) xxx–xxx
on CZN/Al2O3 by the impregnation method. Here, the amount of Pt was adjusted in the ranges 7.0–12.0 wt%. For comparison, the Ce0.8Zr0.2O2.0(16 wt%)/c-Al2O3 (CZ/Al2O3) and Pt loaded on CZ/ Al2O3 sample was prepared by the same methods without using Ni(NO3)2. Raman spectra were obtained using a 532 nm laser as an excitation source. The toluene oxidation was carried out using a conventional fixed-bed flow reactor with a feed gas mixture of toluene (900 ppm) and air (balance). The catalytic activity was evaluated in terms of toluene conversion, and the gas composition was analyzed using gas chromatograph. The experimental details are given in the Supplementary Material. 3. Results and discussion
Intensity / a.u.
From the X-ray powder diffraction (XRD) measurements of CZN/Al2O3 and CZ/Al2O3 (Fig. S1), only a cubic fluorite-type structure and c-Al2O3 were observed, and it was found that Ce4+ and Zr4+ sites in CeO2-ZrO2 were partially replaced with Ni2+ ion. Fig. 1 shows the Raman spectra of CZN/Al2O3 and CZ/Al2O3. The spectrum of CZ/Al2O3 consists of the intense peak at 460 cm 1, which is indexed as F2g mode of fluorite-type structure [21]. For CZN/Al2O3, an additional mode positioned at 525 cm 1 was observed, besides the F2g mode. This Raman band could be assigned to be oxygen vacancies [22], formed by the charge compensation due to the replacement of Ce4+ and Zr4+ by low-valent Ni2+/3+ ion. These vacancies are essential for the catalytic performance, because they facilitate the activation and transport of active oxygen species [23]. To investigate the oxygen release behavior of CZN/Al2O3, H2-TPR measurement was carried out, and the results are shown in Fig. 2, with the result for CZ/Al2O3 for comparison. The reduction peak for CZN/Al2O3 was observed at 298 °C, while there was no peak below 400 °C for CZ/Al2O3. This easier reduction for CZN/Al2O3 was related to the enhancement of oxygen species mobility and the improvement of the redox property. In other words, one of the reasons is that the active oxygen was easy to sup-
CZN/Al2O3
CZ/Al2O3
200 300 400 500 600 700 800
Raman shift / cm-1 Fig. 1. Raman spectra of CZN/Al2O3 and CZ/Al2O3.
Oxygen release / a.u.
2
150
CZN/Al2O3
CZ/Al2O3
200
250
300
Temperature / °C
350
400
Fig. 2. H2-TPR profiles of CZN/Al2O3 and CZ/Al2O3.
ply via the oxygen vacancy. The other reason is that the redox property for CZN/Al2O3 was increased by the valence change of Ni2+/3+. Therefore, the introduction of NiO into CeO2-ZrO2 was considerably effective to enhance the oxygen release capability at low temperatures. In addition, the oxygen storage capacity of CZN/Al2O3 (169 lmol O2 g 1) was larger than that of CZ/Al2O3 (76 lmol O2 g 1), indicating that CZN/Al2O3 possesses the high oxygen release and storage abilities compared to CZ/Al2O3. For the Pt(7–12 wt%) supported on CZN/Al2O3 catalysts, the compositions measured by X-ray fluorescence analysis were in good agreement with their stoichiometric values within experimental error, and the insertion of Pt was confirmed from the results of Brunauer-Emmett-Teller (BET) surface area (Table S1). In addition, the existence of metallic platinum was identified by XRD patterns (Fig. S2). The temperature dependences for toluene conversion over the Pt(7-12 wt%)/CZN/Al2O3 catalysts are shown in Fig. 3. For comparison, the data of Pt(10 wt%)/CZ/Al2O3 is also plotted. Among the Pt(7–12 wt%)/CZN/Al2O3 catalysts, the highest activity was observed for Pt(10 wt%)/CZN/Al2O3. Here, the Pt (12 wt%)/CZN/Al2O3 catalyst showed low activity due to the aggregation of Pt, confirmed by the Pt dispersion measurement (Table S2). For Pt(10 wt%)/CZN/Al2O3, toluene conversion began at 60 °C, and complete toluene oxidation was achieved at the temperature as low as 100 °C. This value is 40 °C lower than that for Pt/(10 wt%)CZ/Al2O3 (140 °C), regardless of the low surface area of Pt(10 wt%)/CZN/Al2O3 (162 m2 g 1) compared to the case of Pt (10 wt%)/CZ/Al2O3 (183 m2 g 1). This enhancement of catalytic activity is attributed to the toluene oxidation caused by the synergistic reaction between Pt and CZN. In fact, the oxygen release ability of Pt/CZN/Al2O3 was increased compared to the Pt/CZN/Al2O3 case (Fig. S3) due to the effective supply of oxygen species from the CZN promoter. Furthermore, the complete oxidation temperature for Pt(10 wt%)/CZN/Al2O3 was also lower than those for Pt/CeO2-ZrO2-Bi2O3/Al2O3 (120 °C) [19] and Pt/CeO2-ZrO2-SnO2/ Al2O3 (110 °C) [18], reported previously. For the practical uses of the toluene oxidation catalysts, water vapor, contained in air and generated by toluene oxidation, usually acts as a catalytic poisoning due to the competition of water molecules with toluene molecules for adsorption on the active sites of the catalyst. From the results of the catalytic activity under moist conditions (Fig. S4), it is clear that Pt(10 wt%)/CZN/Al2O3 has high
Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048
M. Jeong et al. / Materials Letters xxx (2017) xxx–xxx
3
Acknowledgement This study was supported by Toyota Physical and Chemical Research Institute Scholars. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.05. 048. References
Fig. 3. Temperature dependencies of toluene oxidation over the Pt(7-12 wt%)/CZN/ Al2O3 and Pt(10 wt%)/CZ/Al2O3 catalysts.
water durability to realize practical application for individual houses. 4. Conclusion Novel Pt/CeO2-ZrO2-NiO/c-Al2O3 catalysts were prepared by coprecipitation and impregnation methods. Introduction of NiO into the cubic fluorite CeO2-ZrO2 lattice as a promoter was significantly effective in enhancing the oxygen release and storage abilities due to the formation of oxygen vacancy and the redox of Ni2+/3+ ions. Pt(10 wt%)/Ce0.64Zr0.16Ni0.2O1.9(16 wt%)/c-Al2O3 catalyst exhibited the highest catalytic activity, and toluene was completely oxidized at the temperature as low as 100 °C. Since it has also the high water durability, it is expected that the catalyst can be employed for the potential practical applications to remove toluene in indoor air.
[1] H. Knöppel, H. Schauenburg, Environ. Int. 15 (1989) 413–418. [2] H.B. Elkins, G.W. McCarl, H.G. Brugsch, J.P. Fahy, Am. Ind. Hyg. Assoc. J. 23 (1962) 265–272. [3] A. Hamins, K. Seshadri, Combust. Flame 68 (1987) 295–307. [4] A.M. Harling, D.J. Glover, J.C. Whitehead, K. Zhang, Appl. Catal. B: Environ. 90 (2009) 157–161. [5] H. Einaga, S. Futamura, T. Ibusuki, Appl. Catal. B: Environ. 38 (2002) 215–225. [6] F. Hauxwell, R.H. Ottewill, J. Colloid, Interface Sci. 28 (1968) 514–521. [7] J.J. Spivey, Ind. Eng. Chem. Res. 26 (1987) 2165–2180. [8] F.J. Maldonado-Hódar, C. Moreno-Castilla, A.F. Pérez-Cadenas, Appl. Catal. B: Environ. 54 (2004) 217–224. [9] A. O’malley, B.K. Hodnett, Catal. Today 54 (1999) 31–38. [10] S.M. Saqer, D.I. Kondarides, X.E. Verykios, Top. Catal. 52 (2009) 517–527. [11] V.P. Santos, S.A. Carabineiro, P.B. Tavares, M.F. Pereira, J.J. Órfão, J.L. Figueiredo, Appl. Catal. B: Environ. 99 (2010) 198–205. [12] W.B. Li, W.B. Chu, M. Zhuang, J. Hua, Catal. Today 93 (2004) 205–209. [13] C.C. Chang, H.S. Weng, Ind. Eng. Chem. Res. 32 (1993) 2930–2933. [14] T. Montini, M. Melchionna, M. Monai, P. Fornasiero, Chem. Rev. 116 (2016) 5987–6041. [15] C. Force, E. Roman, J.M. Guil, J. Sanz, Langmuir 23 (2007) 4569–4574. [16] C.E. Hori, H. Permana, K.S. Ng, A. Brenner, K. More, K.M. Rahmoeller, D. Belton, Appl. Catal. B: Environ. 16 (1998) 105–117. [17] N. Imanaka, T. Masui, K. Minami, K. Koyabu, T. Egawa, Adv. Mater. 19 (2007) 1608–1611. [18] K. Yasuda, A. Yoshimura, A. Katsuma, T. Masui, N. Imanaka, Bull. Chem. Soc. Jpn. 85 (2012) 522–526. [19] T. Masui, H. Imadzu, N. Matsuyama, N. Imanaka, J. Hazard. Mater. 176 (2010) 1106–1109. [20] M. Jeong, N. Nunotani, N. Moriyama, N. Imanaka, J. Asian Ceram. Soc. 4 (2016) 259–262. [21] M. Guo, J. Lu, Y. Wu, Y. Wang, M. Luo, Langmuir 27 (2011) 3872–3877. [22] T. Vinodkumar, D.N. Durgasri, B.M. Reddy, I. Alxneit, Catal. Lett. 114 (2014) 2033–2042. [23] X. Liu, K. Zhou, L. Wang, B. Wang, Y. Li, J. Am. Chem. Soc. 131 (2009) 3140– 3141.
Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air Minchan Jeong, Naoyoshi Nunotani, Naoki Moriyama, Nobuhito Imanaka ⇑ Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 Suita, Osaka 565-0871, Japan
a r t i c l e
i n f o
Article history: Received 16 February 2017 Received in revised form 19 April 2017 Accepted 10 May 2017 Available online xxxx Keywords: Catalyst Toluene VOC Rare earths
a b s t r a c t Pt/CeO2-ZrO2-NiO/c-Al2O3 catalysts were prepared by the coprecipitation and impregnation methods. The introduction of a small amount of NiO into the cubic fluorite-type CeO2-ZrO2 structure was considerably effective to enhance the oxygen release and storage abilities due to the formation of oxygen vacancies and the redox feature of Ni2+/3+. For the Pt(10 wt%)/Ce0.64Zr0.16Ni0.2O1.9(16 wt%)/c-Al2O3 catalyst, the complete toluene oxidation was realized at the temperature as low as 100 °C. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Toluene has been widely used as a solvent for paint thinners, printing inks, floor wax, adhesives, and antiseptic, because it dissolves various organic compounds and is easily produced from the oxidation of hydrocarbons or commercial fuels [1]. However, toluene is one of the volatile organic compounds and has harmful effects for human health. Even at low concentration of toluene, it is released from floor wax and wall paint in the individual houses, and causes irritation of the eyes, respiratory tract, and skin, which are cumulatively referred to as symptoms of sick building syndrome [2]. In order to protect our health, it is necessary to remove toluene vaporized into the indoor air. Among the several removal methods [3–7], catalytic combustion is one of competitive technologies of toluene abatement from air streams, due to its low operating cost, high decomposition efficiencies, and environmentally friendliness [7]. Various kinds of catalysts have been widely studied for catalytic combustion of toluene, such as noble metal based catalysts, metal oxide based catalysts, and perovskite catalysts [8–13]. In particular, platinum (Pt) catalysts have been paid attention due to its high efficiency in the oxidation process for toluene [8]. However, it is difficult to realize complete oxidation of toluene at moderate temperatures, and the catalysts need to be heated at least up to 170 °C [9,10]. Although previous attention was primarily directed to the investigation on the Pt-loaded on support material, promoters have been ⇑ Corresponding author. E-mail address: [email protected] (N. Imanaka).
also expected to be an important component of the catalyst. They supply the active oxygen species from inside the lattice to facilitate the oxidation on the platinum. CeO2-ZrO2 (CZ) is one of the most important commercial promoter due to its high oxygen release and storage abilities [14–16]. In our previous studies, we reported that Bi2O3 or SnO2 doping into the CeO2-ZrO2 lattice enhanced the ability to release and store oxygen, because the formation of oxygen vacancy through the low-valent Bi3+ substitution facilitated the supply of oxygen species [17] or the valence change of Sn4+/2+ improved the redox property [18]. Furthermore, we demonstrated that Pt/CeO2-ZrO2-MOx/c-Al2O3 (M = Bi, Sn) oxidized toluene completely at the lower temperatures of 120 °C [19] and 110 °C [18], respectively, compared to the case of Pt/CeO2-ZrO2/c -Al2O3 (140 °C). Recently, we focused on the introduction of NiO as the substitute for Bi2O3 and SnO2 into CeO2-ZrO2, where nickel is expected to show two kinds of lower valent Ni2+ and Ni3+, relative to Ce4+ and Zr4+, and the palladium oxide supported on CeO2-ZrO2-NiO/c-Al2O3 catalysts showed high activity for methane combustion [20]. In order to realize a complete toluene oxidation at temperatures as low as possible for the practical application, we selected CeO2-ZrO2-NiO as a promoter, and the catalytic activities for toluene combustion of Pt-supported on CeO2-ZrO2-NiO/c-Al2O3 catalysts were investigated. 2. Experimental Ce0.64Zr0.18Ni0.2O1.9(16 wt%)/c-Al2O3 (CZN/Al2O3) was synthesized using the coprecipitation method. Then, Pt was supported
http://dx.doi.org/10.1016/j.matlet.2017.05.048 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048
M. Jeong et al. / Materials Letters xxx (2017) xxx–xxx
on CZN/Al2O3 by the impregnation method. Here, the amount of Pt was adjusted in the ranges 7.0–12.0 wt%. For comparison, the Ce0.8Zr0.2O2.0(16 wt%)/c-Al2O3 (CZ/Al2O3) and Pt loaded on CZ/ Al2O3 sample was prepared by the same methods without using Ni(NO3)2. Raman spectra were obtained using a 532 nm laser as an excitation source. The toluene oxidation was carried out using a conventional fixed-bed flow reactor with a feed gas mixture of toluene (900 ppm) and air (balance). The catalytic activity was evaluated in terms of toluene conversion, and the gas composition was analyzed using gas chromatograph. The experimental details are given in the Supplementary Material. 3. Results and discussion
Intensity / a.u.
From the X-ray powder diffraction (XRD) measurements of CZN/Al2O3 and CZ/Al2O3 (Fig. S1), only a cubic fluorite-type structure and c-Al2O3 were observed, and it was found that Ce4+ and Zr4+ sites in CeO2-ZrO2 were partially replaced with Ni2+ ion. Fig. 1 shows the Raman spectra of CZN/Al2O3 and CZ/Al2O3. The spectrum of CZ/Al2O3 consists of the intense peak at 460 cm 1, which is indexed as F2g mode of fluorite-type structure [21]. For CZN/Al2O3, an additional mode positioned at 525 cm 1 was observed, besides the F2g mode. This Raman band could be assigned to be oxygen vacancies [22], formed by the charge compensation due to the replacement of Ce4+ and Zr4+ by low-valent Ni2+/3+ ion. These vacancies are essential for the catalytic performance, because they facilitate the activation and transport of active oxygen species [23]. To investigate the oxygen release behavior of CZN/Al2O3, H2-TPR measurement was carried out, and the results are shown in Fig. 2, with the result for CZ/Al2O3 for comparison. The reduction peak for CZN/Al2O3 was observed at 298 °C, while there was no peak below 400 °C for CZ/Al2O3. This easier reduction for CZN/Al2O3 was related to the enhancement of oxygen species mobility and the improvement of the redox property. In other words, one of the reasons is that the active oxygen was easy to sup-
CZN/Al2O3
CZ/Al2O3
200 300 400 500 600 700 800
Raman shift / cm-1 Fig. 1. Raman spectra of CZN/Al2O3 and CZ/Al2O3.
Oxygen release / a.u.
2
150
CZN/Al2O3
CZ/Al2O3
200
250
300
Temperature / °C
350
400
Fig. 2. H2-TPR profiles of CZN/Al2O3 and CZ/Al2O3.
ply via the oxygen vacancy. The other reason is that the redox property for CZN/Al2O3 was increased by the valence change of Ni2+/3+. Therefore, the introduction of NiO into CeO2-ZrO2 was considerably effective to enhance the oxygen release capability at low temperatures. In addition, the oxygen storage capacity of CZN/Al2O3 (169 lmol O2 g 1) was larger than that of CZ/Al2O3 (76 lmol O2 g 1), indicating that CZN/Al2O3 possesses the high oxygen release and storage abilities compared to CZ/Al2O3. For the Pt(7–12 wt%) supported on CZN/Al2O3 catalysts, the compositions measured by X-ray fluorescence analysis were in good agreement with their stoichiometric values within experimental error, and the insertion of Pt was confirmed from the results of Brunauer-Emmett-Teller (BET) surface area (Table S1). In addition, the existence of metallic platinum was identified by XRD patterns (Fig. S2). The temperature dependences for toluene conversion over the Pt(7-12 wt%)/CZN/Al2O3 catalysts are shown in Fig. 3. For comparison, the data of Pt(10 wt%)/CZ/Al2O3 is also plotted. Among the Pt(7–12 wt%)/CZN/Al2O3 catalysts, the highest activity was observed for Pt(10 wt%)/CZN/Al2O3. Here, the Pt (12 wt%)/CZN/Al2O3 catalyst showed low activity due to the aggregation of Pt, confirmed by the Pt dispersion measurement (Table S2). For Pt(10 wt%)/CZN/Al2O3, toluene conversion began at 60 °C, and complete toluene oxidation was achieved at the temperature as low as 100 °C. This value is 40 °C lower than that for Pt/(10 wt%)CZ/Al2O3 (140 °C), regardless of the low surface area of Pt(10 wt%)/CZN/Al2O3 (162 m2 g 1) compared to the case of Pt (10 wt%)/CZ/Al2O3 (183 m2 g 1). This enhancement of catalytic activity is attributed to the toluene oxidation caused by the synergistic reaction between Pt and CZN. In fact, the oxygen release ability of Pt/CZN/Al2O3 was increased compared to the Pt/CZN/Al2O3 case (Fig. S3) due to the effective supply of oxygen species from the CZN promoter. Furthermore, the complete oxidation temperature for Pt(10 wt%)/CZN/Al2O3 was also lower than those for Pt/CeO2-ZrO2-Bi2O3/Al2O3 (120 °C) [19] and Pt/CeO2-ZrO2-SnO2/ Al2O3 (110 °C) [18], reported previously. For the practical uses of the toluene oxidation catalysts, water vapor, contained in air and generated by toluene oxidation, usually acts as a catalytic poisoning due to the competition of water molecules with toluene molecules for adsorption on the active sites of the catalyst. From the results of the catalytic activity under moist conditions (Fig. S4), it is clear that Pt(10 wt%)/CZN/Al2O3 has high
Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048
M. Jeong et al. / Materials Letters xxx (2017) xxx–xxx
3
Acknowledgement This study was supported by Toyota Physical and Chemical Research Institute Scholars. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.05. 048. References
Fig. 3. Temperature dependencies of toluene oxidation over the Pt(7-12 wt%)/CZN/ Al2O3 and Pt(10 wt%)/CZ/Al2O3 catalysts.
water durability to realize practical application for individual houses. 4. Conclusion Novel Pt/CeO2-ZrO2-NiO/c-Al2O3 catalysts were prepared by coprecipitation and impregnation methods. Introduction of NiO into the cubic fluorite CeO2-ZrO2 lattice as a promoter was significantly effective in enhancing the oxygen release and storage abilities due to the formation of oxygen vacancy and the redox of Ni2+/3+ ions. Pt(10 wt%)/Ce0.64Zr0.16Ni0.2O1.9(16 wt%)/c-Al2O3 catalyst exhibited the highest catalytic activity, and toluene was completely oxidized at the temperature as low as 100 °C. Since it has also the high water durability, it is expected that the catalyst can be employed for the potential practical applications to remove toluene in indoor air.
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Please cite this article in press as: M. Jeong et al., Introduction of NiO in Pt/CeO2-ZrO2/c-Al2O3 catalysts for removing toluene in indoor air, Materials Letters (2017), http://dx.doi.org/10.1016/j.matlet.2017.05.048