e-Journal of Surface Science and Nanotechnology 27 December 2011 Conference - IWAMN2009 - e-J Surf Sci Nanotech Vol (2011) 486-489 Total Oxidation of Toluene on Nano-Perovskites La1−x Bx CoO3 (B: Ag, Sr)∗ Nguyen Thanh Binh† and Luu Thi Thanh Tam Laboratory of Petrochemistry, Faculty of Chemistry, Hanoi University of Science, Vietnam, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam Nguyen Thi Ngoc Quynh Department of Physical Chemistry, Phu Tho College of Chemistry, Lam Thao District, Phu Tho Province, Vietnam (Received December 2009; Accepted May 2010; Published 27 December 2011) A series of nanosized perovskite oxides, LaCoO3 and La1−x Bx CoO3 (x = 0.1; B: Sr, Ag), was synthesized by citrate method The samples were characterized by XRD, IR and SEM The XRD results show that all samples have principal phase with rhombohedra perovskite structure and particles size of 30-50 nm The catalytic performance of these nanoperovskites has been evaluated by the total combustion of 1000 ppm of toluene in air The result obtained shows the highest activity for the sample La0.9 Ag0.1 CoO3 The last one seems to be related with the highest quantity of oxygen released as showed by oxygen temperature program desorption results (O2 -TPD) [DOI: 10.1380/ejssnt.2011.486] Keywords: Nano-perovskite; Total oxidation; Volatile organic compound; Toluene I INTRODUCTION The release of volatile organic compounds (VOCs) are known to cause air pollution such as photochemical smog, ground level ozone, ozone depletion, sick house syndrome, and chemical sensitivity [1-3] A number of catalysts have been used for the complete oxidation of VOCs Generally, they were classified in two groups: supported noble metal and transition metal oxide [4-10] Supported noble metal as Pt and Pd is well estimated as efficient catalysts for the total oxidation of VOC However, they are expensive Therefore, transition metal oxide is attired researcher in recent time Because this one also shows a good activity and, especially, it is much cheaper Among them, mixed oxide of transition metal, as perovskite, has more advantages Since this one not only shows a good activity but also a high thermal and hydrothermal stability In this word, we were prepared a series of perovskites La1−x Bx CoO3 (B: Ag, Sr) and examined their catalytic activity in total oxidation reaction of toluene which has been chosen as VOC probe molecule because aromatics are present in the industrial and automotive emission [11, 12] The partial substitution of Co by Ag or Sr was expected to improve catalytic activity of LaCoO3 which is known as the most active catalyst in perovskite group for total oxidation of VOC II A † B Catalyst preparation This paper was presented at the International Workshop on Advanced Materials and Nanotechnology 2009 (IWAMN2009), Hanoi University of Science, VNU, Hanoi, Vietnam, 24-25 November, 2009 Corresponding author: tbinh76@yahoo.com Catalyst characterization All prepared samples were characterized by different methods: X-ray diffraction, scanning electronic microscopy (SEM), BET surface measurement, and temperature programmed desorption of oxygen (TPD-O2 ) The crystalline phases were examined by X-ray diffraction using D8 Advance Brucke diffractometer with CuKa irradiation source (λ=0.15406 nm) operated at 40 kV and 30 mA The XRD measurement was performed with 0.03◦ step per second, from 20◦ to 70◦ (in 2θ) SEM images of sample were taken by using JEOSJSM5410 LV Scanning Electron Microscope The BET surfaces were determined by using AutochemII The TPD-O2 was performed using Micromeritics Autochem II The samples were activated in O2 (10 vol%)/He at 200◦ C for hour then cooled to ambient temperature and purged in He flow The measurements were carried out from room temperature to 700◦ C EXPERIMENTAL Series of perovskite La1−x Bx CoO3 was prepared by citric method [13] All used chemical compound have analysis purity Firstly, nitrate salt (Co(NO3 )2 , La(NO3 )2 , ∗ AgNO3 ) and citric acid C6 H5 O2 were dissolved each other in an adequate amount of H2 O Then, they were mixed with stirring for 30 minutes before being evaporated in rotary evaporator to obtain a resin This one was dried at 80◦ C in oven and then, calcined at 600◦ C for hour C Catalytic tests Catalytic activity of all samples was estimated by total oxidation of toluene Toluene was mixed in air to obtain a flux at 1000 ppm of toluene concentration The organic products were determined by Chromatography HP 6280 equipped FID detector, and the formation of CO2 was detected by TCD detector III RESULTS AND DISCUSSION X-ray diffraction patterns are presented in Fig.1 Principal phases recognized rhombohedra prerovskite phase c 2011 The Surface Science Society of Japan (http://www.sssj.org/ejssnt) ISSN 1348-0391 ⃝ 486 e-Journal of Surface Science and Nanotechnology Volume (2011) FIG FIG IR spectra of LaCoO3 , La0.8 Sr0.2 CoO3 and La0.9 Ag0.1 CoO FIG 1(a) LaCoO3 La0.8Sr0.2CoO3 La0.9Ag0.1CoO3 FIG 1(b) FIG SEM image of of LaCoO3 , La0.8 Sr0.2 CoO3 and La0.9 Ag0.1 CoO3 (c) 0.25 0.20 Series1 0.8 Series2 LaCoO3 0.8 Series3 La Sr0.2CoO3 TCD signal (a.u) La Ag0.1CoO 0.15 0.10 FIG 1(c) 0.05 FIG XRD patterns of LaCoO3 (a), La0.8 Sr0.2 CoO3 (b) and La0.9 Ag0.1 CoO3 (c) 0.00 100 200 300 400 500 600 700 800 900 Temperature (oC) FIG 4 for all samples In case La0.9 Ag0.1 CoO3 , presence of metallic silver was determined (2θ = 38.1, 48.2 ) Certainly, this one was formed by decomposition of Ag(NO3 ) It is possible that an amount of Ag+ wasn’t substituted or/and incorporated in perovskite phase In order to understand well their structure, these samples were characterized by IR Figure showed results obtained We observed characteristic peaks for perovskite structure such as 593.3 562.7, 417.8 cm−1 [14] In case of sample substituted by Ag and Sr, a shoulder peak was recognized at 642cm−1 This one was characteristic for phase Co3 O4 [15] Thus, it is possible that when a small amount of Ag+ or Sr2+ was incorporated in perovskite structures of LaCoO3 , a small amount of Co2+ ,Co3+ was pushed out of peroskite structure and formed phase Co3 O4 However, this phase may be formed in form of cluster and/or well dispersed on perovskite phase Figure presents the SEM image of all samples It was noted that all samples consisted of nano particles with diameter in range of 30-50 nm The particles were in spherical form and quite uniform Figure presents the results TPD-O2 Generally, it was noted that there were two type of oxygen desorbed [16]: αO2 (oxygen desorbed at temperature below 500◦ C) and FIG TPD-O2 curves of of LaCoO3 , La0.8 Sr0.2 CoO3 and La0.9 Ag0.1 CoO3 αO2 (oxygen desorbed in range of temperature from 500700◦ C) For the sample LaCoO3 , it is obvious that there are three desorption peaks of O2 at 441◦ C, 599◦ C and 713◦ C Among them, the peak at 441◦ C was three times more intense than two others A much more intense peak at 426◦ C was observed for La0.8 Sr0.2 CoO3 In the range of higher temperature, oxygen continued to desorbs but no shape peak was found It seems that there were several peaks but they appeared continuously with a small difference of temperature However, it is seen that the adsorption of O2 is shifted at lower temperature In case of La0.9 Ag0.1 CoO3 , a small peak at 190◦ C appeared more sharply in comparison with the precedent case The second peak was at 471◦ C, but it seems that this one was constituted by different peak, because it was obvious that there were two shoulder-peaks at 420◦ C, and 600◦ C The third peak, most intense, was shifted at 774◦ C This result was quite in accordance to observation of S.Ifrah et al.[17] These curves were not normalized in weight Hence, in order to have a qualitative estimation, it is necessary to http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) 487 Thanh Binh, et al Volume (2011) TABLE I BET surfaces and quantity of mobile oxygen per gram or square meter of sample TPD-O2 Sample SBET (m2 /g) LaCoO3 La0.9 Ag0.1 CoO3 La0.8 Sr0.2 CoO3 73 17 47 nO2 (mmol/g) 100-200◦ C 100-800◦ C 2.81 0.13 0.41 0.12 1.28 100.00 % Conv 80.00 60.00 40.00 LaCoO LaCoO3 20.00 La LaAgCoO3 0.9Ag0.1CoO3 La LaSrCoO3 0.8Sr0.2CoO3 0.00 100 120 140 160 180 200 220 240 260 280 300 o Temperature ( C) FIG nO2 × 10−3 (mmol/m2 ) 100-200◦ C 100-800◦ C 38.5 6.5 24.1 2.5 29.8 our case, basing on TPD-O2 result (Table 1), it seems that the catalytic activity was proportional with the quantity of mobile oxygen in bass temperature range (100◦ C - 200◦ C) The quantity of mobile oxygen released in higher range of temperature not have an important role for total oxidation of toluene if we were noted that, up to 200◦ C, almost of toluene was converted for all catalysts It was obvious that there was a quick diminution of catalytic activity after the beginning of toluene conversion This one is in order of LaCoO3 , La0.8 Sr0.2 CoO3 and La0.9 Ag0.1 CoO3 The diminution was possibly due to deposition of coke which blocked catalytic center on catalyst surface The substitution of Ag or Sr seems to decrease this one FIG Conversion of toluene versus temperature on per7 ovskite samples report the BET surfaces and quantity of mobile oxygen per gram or square meter of sample as showed in Table It is seen that the substituted sample showed a BET surface quite low more than non-substituted sample The result of catalytic test was presented in Fig.5 To compare activity of catalyst, we used two factors, T50 and T90 , which are values of temperature where 50 % or 90 % of reactive is converted respectively For T50 , the diminution of activity was classified as following: La0.8 Sr0.2 CoO3 ≈ La0.9 Ag0.1 CoO3 > LaCoO3 In case of T90 , it is clearly found that La0.9 Ag0.1 CoO3 showed a highest activity: La0.9 Ag0.1 CoO3 > La0.8 Sr0.2 CoO3 > LaCoO3 Generally, La0.9 Ag0.1 CoO3 showed slightly higher activity than La0.8 Sr0.2 CoO3 and activities of substituted samples were clearly higher than pure LaCoO3 This properties of substituted perovskites were observed by the group of S.Kaliaguine in case of La1−x A’x BO3 (A’=Sr, Ce, B=Co, Mn) used for the CH4 oxidation reaction [18] In [1] A Akinson and J Arey, Chem Rev 103, 4605 (2003) [2] B J Finlayson-Pitts and J N Pitts Jr., Science 276, 1045 (1997) [3] Z Meng, D Dabdub, and J H Seinfeld, Science 277, 116 (1997) [4] S Krishnamoorthy, J P Baker, and M D Amiridis, Catal Today 40, 39 (1998) [5] S D Yim, K -H Chang, D J Koh, I -S Nam, and Y G Kim, Catal Today 63, 215 (2000) [6] J I Gutierrez-Ortiz, B De Rivas, R Lopez-Fonseca, and J R Gonzalez-Velasco, Appl Catal A 269, 147, (2004) 488 IV CONCLUSIONS A series of perovskites La1−x Bx Co3 (B: Ag, x = 0.1; Sr, x = 0.2) was synthesized by citrate method They were constituted by nano-particles with the diameter from 30 to 50 nm Perovskite La0.9 Ag0.1 CoO3 showed a highest activity in total oxidation of toluene Based on TPD-O2 measurement, it seems that their activity is proportional with quantity of mobile oxygen on surface in basic range of temperature, from 100◦ C to 200◦ C This result is very potential for the total oxidation of VOC at low temperature ACKNOWLEDGMENTS The authors gratefully acknowledges financial support from the National Foundation for Science and Technology Development of Vietnam (NAFOSTED) [7] N Mizuno, H Fujii, H Igrashi, and M Misono, J Am Chem Soc 114, 7151 (1992) [8] R W Van den Brink, R, Louw, and P Mulder, Appl Catal B 16, 219 (1998) [9] J R Gonzales-Velasco, A Aranzabal, R Lopez-Fonseca, R Ferret, and J A Gonzalez-Marcos, Appl Catal B 24, 33 (2000) [10] H L Tidahy, S Siffert, J.-F Lamonier, R Cousin, E A Zhilinskaya, A Aboukais, B -L Su, X Canet, G De Weireld, M Frere, J.-M Giraudon, and G Leclercq, Appl Catal B 70, 377 (2007) http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) e-Journal of Surface Science and Nanotechnology [11] R G Derwent, M E Jenkin, and S M Saunders, Atmos Environ 30, 181 (1996) [12] R G Derwent, M E Jenkin, S M Saunders, and M J Pilling, Atmos Environ 32, 2429 (1998) [13] H Taguchi, S Matsu-ura, M Nagao, T Choso, and K Tabata, J Sol State Chem 129, 60 (1997) [14] G Sinquin, C Petit, J P Hindermann, and A Kiennemann, Catal Today 70, 183 (2001) Volume (2011) [15] J Jiu, Y Ge, X Li, and L Nie, Mater Lett 54, 260 (2002) [16] T Seiyama, Catal Rev Sci Eng 34, 281 (1992) [17] S Ifrah, A Kaddouri, P Gelin, and D Leonard, C R Chimie 10 1216 (2007) [18] S Royer, H Alamdari, D Duprez, and S Kaliaguine, Appl Catal B 58, 273 (2005) http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) 489 ... of LaCoO3 , La0 .8 Sr0.2 CoO3 and La0 .9 Ag0.1 CoO3 (c) 0.25 0.20 Series1 0.8 Series2 LaCoO3 0.8 Series3 La Sr0.2CoO3 TCD signal (a.u) La Ag0.1CoO 0.15 0.10 FIG 1(c) 0.05 FIG XRD patterns of LaCoO3... for all catalysts It was obvious that there was a quick diminution of catalytic activity after the beginning of toluene conversion This one is in order of LaCoO3 , La0 .8 Sr0.2 CoO3 and La0 .9 Ag0.1... 100.00 % Conv 80.00 60.00 40.00 LaCoO LaCoO3 20.00 La LaAgCoO3 0.9Ag0.1CoO3 La LaSrCoO3 0.8Sr0.2CoO3 0.00 100 120 140 160 180 200 220 240 260 280 30 0 o Temperature ( C) FIG nO2 × 10 3 (mmol/m2