Removal of Greenhouse Gas (N2O) by Catalytic

Removal of Greenhouse Gas (N2O) by Catalytic Decomposition on Natural Clinoptilolite Zeolites Impregnated with Cobalt A. Ghahri, Farideh Golbabaei, L. Vafajoo, S. M. Mireskandari, M. Yaseri & S. J. Shahtaheri International Journal of Environmental Research ISSN 1735-6865 Volume 11 Number 3 Int J Environ Res (2017) 11:327-337 DOI 10.1007/s41742-017-0030-6

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Author's personal copy Int J Environ Res (2017) 11:327–337 DOI 10.1007/s41742-017-0030-6

RESEARCH PAPER

Removal of Greenhouse Gas (N2O) by Catalytic Decomposition on Natural Clinoptilolite Zeolites Impregnated with Cobalt A. Ghahri1 • Farideh Golbabaei1 • L. Vafajoo2 • S. M. Mireskandari3 M. Yaseri4 • S. J. Shahtaheri1

•

Received: 4 January 2017 / Revised: 24 May 2017 / Accepted: 13 June 2017 / Published online: 25 July 2017 Ó University of Tehran 2017

Abstract In this work, natural zeolite, clinoptilolite were treated with acid (0.6 N HCl; code ‘‘Z-AM’’) and alkaline solutions (1.5 N NaOH; code ‘‘Z-BM’’). Thereafter, nonmodified (as parent zeolite; code ‘‘Z-NM’’) and modified zeolites were impregnated with cobalt using wet incipient impregnation method (Codes: ‘‘Z-AM-Co-0.5,1,1.5’’, ‘‘ZBM-Co-0.5,1,1.5’’, ‘‘Z-NM-Co-0.5,1,1.5’’). The prepared zeolites were characterized by XRD, ICP-OES, BET, NH3TPD and H2-TPR. Also, these materials were studied for the catalytic decomposition of nitrous oxide (a greenhouse gas) to nitrogen and oxygen. The obtained results showed that the applied modifications had no significant influence (destruction) on the main structure of the zeolites including clinoptilolite, quartz and cristobalite. In addition results showed that acid modification increases the nitrous oxide decomposition because of surface area increment and the higher amount of CO/Al as well as the strong acid sites of this zeolite compared to other zeolites. Also, experiments showed that the main active species in nitrous oxide decomposition are mono-atomic (Co2? cations) and other species exhibit much lower activity. In conclusion, natural

& Farideh Golbabaei [email protected] 1

Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

2

Department of Chemical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

3

Department of Anesthesiology and Critical Care, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran

4

Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

clinoptilolite zeolites treated with acid and impregnated with Cobalt (Z-AM-CO-1.5) could be a very effective and cost-benefit catalyst for reducing N2O as a greenhouse gas, due to its very low price, high chemical stability and high availability. Keywords Greenhouse gas N2O decomposition Clinoptilolite Cobalt Natural zeolite Acid modification

Introduction In recent decades, one of the most important issues in environment has been climate change, especially global warming and ozone layer destruction. Global warming is intensified by the increased concentrations of greenhouse gases (GHG) such as carbon dioxide, methane, nitrous oxide and halogenated hydrocarbons (Gregg and Sing 1982; Sulbaek et al. 2010; Rajska et al. 2016; Osvaldo et al. 2016; Rowland et al. 1995). Although N2O, among the GHG, is present in low concentrations in the troposphere, it is a potent greenhouse gas with a global warming potential of 310 and 21 times that of CO2 and CH4, respectively (Kannan and Swamy 1999; Labhsetwar et al. 2009; Paschalia Taniou and Savvas 2013; Xie et al. 2014; Xue et al. 2007). It is estimated that the role of nitrous oxide as a greenhouse gas and its effects is approximately 6.5% by volume (Rajska et al. 2016; Osvaldo et al. 2016). In addition, occupational exposure to N2O affects the central nervous system, cardiovascular, hepatic, hematopoietic, and reproductive systems in humans (Marylou Austin 2013; Wronska-Nofer et al. 2012). Microbial activity in the soil is the main source of nitrous oxide (Todd et al. 1995) and secondary sources are exhaust streams of industries include production and

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transportation of N2O, healthcare (use as an anesthetic gas in hospitals and clinics), whipped creams (as a foaming agent), natural gas pipelines (as a leak-detecting agent), production of chemicals such as adipic acid, nitric acid and fertilizer, and fossil fuel combustion (Kapteijn et al. 1997; Marylou Austin 2013; Xie et al. 2014). It should be noted that the concentration of nitrous oxide in the atmosphere of various industries or exhaust streams of industries is different. For example, the range of nitrous oxide concentration is about 50–400 ppm in exhaust streams of operating rooms (hospitals) in Iran (Maroufi et al. 2011; Masoumeh et al. 2014; Mortazavi et al. 2013). Regarding the high number of people exposed to N2O and also its adverse effects on environment as well as the annual increasing rate of 0.2–0.3% in atmosphere, it is important to find economical and feasible reduction methods of nitrous oxide as one of the major challenges in environmental protection and occupational health efforts (Kapteijn et al. 1997; Labhsetwar et al. 2009; Paschalia Taniou and Savvas 2013; Xie et al. 2014). Different methods for N2O removal have been described in the literature, which include thermal decomposition, non-selective catalytic reduction, direct catalytic decomposition and biological process (Labhsetwar et al. 2009; Osvaldo et al. 2016; Xie et al. 2014). The decomposition of nitrous oxide would be a relatively simple, suitable, preferable, most efficient and economic method for stationary sources (Centi et al. 1997; Goto et al. 2000; Xie et al. 2014). Many catalysts have been used in the decomposition of N2O, including supported noble metals, pure and mixed oxides and metal-exchanged zeolites (Kapteijn et al. 1997; Mauvezin et al. 1999; Mul et al. 2001; Labhsetwar et al. 2009; Nobukawa et al. 2002; Xie et al. 2014; Xue et al. 2007). One group of catalysts which has demonstrated high activities for N2O decomposition to harmless product (nitrogen and oxygen) are metal oxides and mixed metal oxides such as Rh, Ru, Pd, Cu, Co, Fe, Pt, Ni, and Mn. Since the surface areas of these materials are very low, the metal oxides are used as supporting materials, e.g., zeolites to form metal-exchanged zeolites (Kapteijn et al. 1996, 1997; Kawi et al. 2001; Miller et al. 1998). The activity of metal zeolites depends on the metal ion and type of zeolite in N2O decomposition. For example, copper and iron-ZSM-5 are not quite active under hydrothermal conditions, while cobalt-ZSM-5, because of its thermostability, is very active under the same condition (Kapteijn et al. 1997). However, cobalt is not very active in Y-zeolite. In general, due to the high redox properties, cobalt has excellent activity in nitrous oxide decomposition as well as on most zeolites such as ZSM-5, Beta, ZSM-11, Ferrierite and Mordenite (MOR) (Ates et al. 2011; Kapteijn et al. 1996, 1997).

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Most of the zeolites used in investigation of N2O decomposition are synthetic and few studies have addressed this issue using natural zeolites (Ates 2015). The main reasons for low application of natural zeolite include low thermal and hydrothermal stability at high temperatures, heterogeneity and high cost of homogenization and purification of this material (Ates 2007, 2015). However, Ayten Ates found that the modification of natural zeolites by ion exchange and acid treatment due to the formation of isolated iron and Fe–O–Al species improves their activity in N2O decomposition (Ates 2015). Other studies have shown that iron exchanged natural zeolites have high activity in selective catalytic reduction of nitrous oxide with NH3 (Ates et al. 2011). One of the most common and most used natural zeolite in the world is clinoptilolite. This natural zeolite has certain characteristics such as high chemical stability, high availability and low extraction cost and owing to these characteristics; it is extensively employed in environmental and industrial applications (Alver and Sakizci 2015; Ates 2007; Garcia-Basabe et al. 2010; Radosavljevic-Mihajlovic et al. 2004). Based on the studies in the literature, despite the excellent response of cobalt synthetic zeolites in the decomposition of nitrous oxide, to date, clinoptilolite and cobalt have not been used in this process. Hence, in this study, the first natural zeolite, clinoptilolite was treated with acid (0.6 N HCl) and alkaline solution (1.5 N NaOH). Thereafter, non-modified (as parent zeolite) and modified zeolites were impregnated with cobalt using wet incipient impregnation method. In the following sections, effects of these modifications on physicochemical properties of zeolites in N2O decomposition are discussed by XRD, ICPOES, BET, NH3-TPD and H2-TPR.

Materials and Methods Preparation of the Catalysts: The natural zeolite, clinoptilolite used in the present study was obtained from deposits in Semnan province in the center of Iran. Preparation of modified and non-modified samples from this raw material was carried out according to the following steps (Fig. 1): 1.

Non-modified zeolite (code ‘‘Z-NM’’): First, samples were grinded and sieved through a diameter of 400–420 lm. Thereafter, this raw material was washed with distilled water (three times) to remove soluble impurities such as dust. Finally, dried samples (for 24 h in an oven at 60 °C) were calcinated at 450 °C in air for 2 h at a heating rate of 10 °C/min and kept in a desiccator for the next stage (modified zeolites).

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Fig. 1 Preparation schema of the natural and modified zeolites

2.

3.

Modified zeolite with acid (code ‘‘Z-AM’’): According to studies (Alver and Sakizci 2015; GarciaBasabe et al. 2010; Radosavljevic-Mihajlovic et al. 2004), to minimize the framework damage of zeolites, acid treatment of zeolites was conducted by placing sufficient amount of zeolite (Z-NM) in a flask containing 0.6 N HCl solution in a ratio of 1:10 w/v. This mixture was shaken at 150 rpm using a shaking incubator at 60 °C for 24 h. Beyond the specified time for shaking, the separated zeolites from solution were washed three times with 0.05 N HCl for 15 min and then rinsed with distilled water several times to obtain a negative reaction for Cl-. Assurance of complete removal of chloride ions was accomplished through volumetric analysis by AgNO3. The samples obtained were dried and calcinated in a similar way to the first stage. Modified zeolite with base (code ‘‘Z-BM’’): Alkaline treatment was carried out at 50 °C using 1.5 M NaOH (30 mg/g of zeolite; Z-NM) for 4 h in the shaking incubator with agitation rate of 150 rpm. Thereafter, samples were washed, dried and calcinated in a similar way to the first stage.

4.

Modified zeolite with cobalt (code ‘‘Z-NM, BM and AM-Co-%’’): In this stage, modified and non-modified zeolites were impregnated with cobalt using wet incipient impregnation method. In each experiment, 20 g of heated zeolite in an oven at 100 °C was added to 200 ml of deionized water containing 1.5, 3 and 4.5 g of Co(NO3)26H2O to obtain Co-zeolites of 0.5, 1 and 1.5 wt.%, respectively (code ‘‘Z-NM,BM,AM-Co0.5,1,1.5’’). Thereafter, mixed solutions were placed in the incubator at 150 rpm and 60 °C for 24 h or more until the solution was completely dried. After impregnation, the samples were re-slurried in hot water (150 °C) for 1 h and then washed, dried and calcinated in a similar way to the first stage.

Catalyst characterization: It should be noted that according to preliminary studies, determination of catalysts characterizations were performed on selected samples. The specific area of modified zeolites and parent zeolites was determined by nitrogen adsorption on a MicrotracBelBelsorp mini II Japanese instrument. The pore size distribution of the sample was obtained according to Horvath–

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Kawazoe equation. In addition, microporous volume was determined using the t-plot method. For determination of the catalysts crystalline phases, X-ray diffraction (XRD) patterns of samples was performed with an X-ray diffractometer, Model (Philips: PW-1830) operating at 40 kV and 30 Ma, using Cu Ka radiation. In addition, determination of sample compositions was investigated by ICP technique, Varian Vista 735 ICP-OES. Hydrogen temperature-programmed reduction (H2-TPR) of samples and NH3 temperature-programmed desorption (NH3-TPD) experiments were performed using (CHEMBET3000) from Quanta Chrome Corporation equipped with thermal conductivity (TCD) equipment for determining H2 consumption and NH3 desorbed. Before the measurements (H2-TPR and NH3-TPD), zeolites (0.05 g) were pretreated at 400 °C for 60 min in helium, and then cooled to room temperature in helium. The H2-TPR runs were performed at a ramping rate of 10 °C/min from 50 to 950 °C with the flow rate on reduction gas at 5% for H2 and 15 cm3/min for He. In NH3-TPD, samples were first saturated with NH3 diluted with He (10%) for 60 min at room temperature. Thereafter, NH3 was desorbed from catalysts using a He flow (10 cm3/min) up to 800 °C at a ramping rate of 10 °C/min. Catalytic test: The catalytic activity of zeolites in N2O decomposition were conducted in a fixed bed stainless steel reactor of 1 cm internal diameter and 10 cm length and a temperature range of 150–600 °C. For each experiment, a 4 g catalyst was packed into the reactor and a gas stream of N2O (350–400 ppm) balanced with N2 was fed into the reactor at a rate of 300 cm3/min to obtain a space velocity (GHSV) of 4500 cm3/(h gcat). The concentrations of N2O in the reactor inlet and outlet were measured according to NIOSH 6600 method (Eller 1994); collection and analysis were done using bag and portable IR spectrophotometer model 3010 Bacharach Company, respectively. Before each measurement, the apparatus was calibrated according to manufacturer’s instructions. The conversion of nitrous oxide to N2 and O2 was calculated using the following equation: ðN2 OÞin ðN2 OÞout X¼ 100; ð1Þ ðN2 OÞin


and NM, BM, AM-Co-0.5, 1, 1.5 were prepared. Figure 2 shows the major phases of all the zeolites, which includes clinoptilolite at 2h = 9.88°,11.19°, 22.46°, 30.38° (Akgu¨l 2014; Alver and Sakizci 2015; Treacy and Higgins 2007), quartz at 2h = 20.86°, 26.65°, 39.49° and cristobalite at 2h = 22.00°, 31.44°, and 36.5° (Treacy and Higgins 2007). In addition, the trace phase in Z-NM is dolomite, which after alkaline and acid treatments disappeared (Ates and Hardacre 2012). A quick survey of the obtained patterns show that HCl and NaOH treatments and cobalt loading on samples did not produce significant effect and the Z-NM zeolites structure were well preserved. However, a decrease and increase in intensity of the diffraction peaks were observed for acid and alkaline treatments, respectively. These results are in perfect agreement with recent studies (Akkoca et al. 2013; Alver and Sakizci 2015; Cheng et al. 2005). For example, Erdogan and Sakizci showed that acid treatment using concentrations up to 0.5 M have no considerable effect on the crystallinity of samples (Alver and Sakizci 2015). However, a slight decrease in the intensity of the main clinoptilolite peaks as observed in the current study, resulted in a loss in crystallinity of the sample due to dealumination and the partial collapse of the structure of the natural zeolite. Diffraction peaks of cobalt spinel structure were at 2h = 31.2°, 36.8° and 59.3° on XRD patterns of zeolites, but they were not clearly distinguishable. This may be due to the high intensity of diffraction peaks of the major phases (clinoptilolite, quartz and cristobalite) and/or weak diffraction peaks of cobalt spinel as Shen et al. have pointed out in their research (Shen et al. 2012). In addition, after impregnation of zeolites, a slight decrease in peak intensities observed, which was similar to the results of the study of Murat Akgu¨l (2014) might be due to the distortion of the mesoporous channels caused by the collapse of pore structure during the modification process.

where X is the conversion percent, (N2O)in and (N2O)out are the nitrous oxide concentration in the reactor inlet at room temperature and the reactor outlet at an elevated temperature, respectively.

Result and Discussion physicochemical properties for zeolites (XRD): To reveal the influence of modifications on the crystal structure of zeolites, the XRD patterns of all the samples NM, BM, AM

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Fig. 2 XRD patterns of non-modified and modified zeolites


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Several surveys on the alkaline treatment of zeolites have shown that the wt.% of samples compositions were changed (Lin et al. 2015). In this study, the results obtained were similar to that reported by other investigators (Akgu¨l and Karabakan 2011; Akkoca et al. 2013); silica and potassium decreased, but other compounds particularly sodium increased. Comparison of the percentage composition of samples impregnated with cobalt and their parent zeolites showed that as the amount of cobalt increased, wt.% of Na, K and Fe decreased, but other elements were significantly unchanged, which is similar to a study conducted in 2007 (Ates 2007). Cobalt to aluminum ratio was one of the important parameters in the catalytic activity of transition metal zeolites (Abu-Zied et al. 2008; Smeets et al. 2008; Xie et al. 2015). The amount of this ratio was higher than 0.5 in most studies (Chen et al. 2004; Jentys et al. 1997; Seyedeyn-Azad and Zhang 2001; Wang et al. 2000) and was between 0.1 and 0.15 in the present study. BET: Nitrogen adsorption and desorption of Z-NM, Z-AM, Z-BM, Z-NM-Co-1.5, Z-BM-Co-1.5, Z-AM-Co0.5, 1.5, 2.5 are shown in Fig. 3 All isotherms were of the type II according to IUPAC (Sing et al. 1985; Gregg and Sing 1982). In these types of isotherms, samples’ structure was composed from microporous and mesoporous materials with multiple layers on zeolites. The isotherm curves in Fig. 3 show that the modified zeolite with acid (Z-AM) is able to absorb more nitrogen. The results of the influence of acid and alkaline treatments and cobalt loading on the specific surface area, total volume, and average pore diameter are summarized in Table 2. As seen from the results, modifying zeolites with HCl and NaOH have opposite effect relative to each other on the specific surface area. Acid treatment of zeolite Z-NM led to an abrupt increase in specific surface area from 25.79 to 103.09 m2/g and total volume from 5.92 to 23.68 cm3/g, non-significant increase of micropore volume from 0.138 to 0.158 cm3/g as well as significant decrease of average pore diameter from 23.55 to 6.143 nm (Table 2).This considerable growth in specific surface area and total volume of Z-AM

Compositions analysis by ICP: Zeolites are crystalline, porous, hydrated aluminosilicates material with the primary building units (PBU) of AlO4 and SiO4 tetrahedra (Alver and Sakizci 2015; Kowalczyk et al. 2006). Clinoptilolite—a natural zeolite—has been diagnosed with exchangeable cations of potassium and calcium of high value, and magnesium and sodium of low values. In addition, compounds such as iron and titanium occur as impurities in their oxides (Alver and Sakizci 2015). According to chemical analysis results of samples (Table 1), the main compounds of zeolites Z-NM are those of silica and aluminum (71.38 and 10.76 wt.%, respectively). Calcium and sodium are the next highest components at 4.49 and 1.77 wt.%, respectively. These results are similar to results of the studies conducted by Ates et al. (2007), Camacho et al. (2011). The only difference was in the low levels of calcium observed in this study compared to that of Ayten study (0.45–1.64% against 0.45–5.74%). This is due to the low dolomite content in zeolite Z-NM. It is well known that acid treatment of natural zeolites causes the exchange of H? ion with exchangeable cations in clinoptilolite and dealumination by hydrolysis of Al–O– Si bonds (Akkoca et al. 2013; Alver and Sakizci 2015; Kowalczyk et al. 2006; Rozˇic´ et al. 2005). Facilitation of its dissolution by chloride ions via the formation of inner sphere complexes with surface groups were also found, as well as increase in the number of acidic sites and secondary porosity (Akkoca et al. 2013; Alver and Sakizci 2015). After HCl treatment of zeolite Z-NM, all elements were reduced with the exception of silica and potassium due to their high resistance to acid. The highest decrease was recorded in calcium (52%). The presence of Ca can be attributed to the dolomite and feldspar phase in the natural zeolites as stated by Ayten Ates (2007). XRD results (Fig. 2) showed that diffraction peaks of dolomite disappeared following treatment with HCl. Thus, it can be adduced as the reason for calcium reduction. In addition, dealumination value was about 8% in this study, which is in consonance with the findings of other researchers (Ates and Hardacre 2012; Segawa and Shimura 2000). Table 1 Chemical compositions (wt.%) and textural properties of natural and modified zeolites

Zeolite name

Si/Al

SiO2

Al2O3

BaO

CaO

F2O3

K2O

Na2O

TiO2

LOI

Co

Co/Al

Z-NM

6.63

71.38

10.76

0.08

0.97

0.74

4.49

1.77

0.19

8.5

NM

–

Z-NM-1.5

6.51

70.68

10.85

0.09

0.82

0.78

4.4

1.08

0.2

8.78

1.2

0.11

Z-BM Z-BM-Co-1.5

5.79 5.62

68.86 67.12

11.89 11.95

0.07 0.16

1.15 1.64

0.82 0.94

3.88 3.82

2.87 1.69

0.22 0.23

9.12 9.8

NM 1.53

– 0.13

Z-AM

7.57

72.86

9.62

0.13

0.49

0.77

5.41

0.97

0.26

8.37

NM

–

Z-AM-Co-0.5

7.77

73.75

9.49

0.12

0.49

0.47

4.38

0.75

0.23

8.75

0.45

0.05

Z-AM-Co-1

7.84

73.71

9.4

0.11

0.47

0.38

4.18

0.81

0.22

8.65

0.95

0.10

Z-AM-Co-1.5

7.91

73.68

9.32

0.12

0.46

0.29

3.98

0.89

0.22

8.42

1.5

0.16

Z-AM-Co-2.5

7.96

73.42

9.22

0.12

0.47

0.27

3.97

0.88

0.23

8.45

1.85

0.20

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Fig. 3 N2 adsorption isotherms of non-modified and modified zeolites

Table 2 Textural properties of natural and modified zeolites Zeolite name

3

Vtotal (cm /g)

Vmicro

2

SBET (m /g)

Dp (nm)

Z-NM

5.92

0.148

25.79

23.55

Z-NM-1.5

6.24

0.154

27.20

22.75

Z-BM Z-BM-Co-1.5

5.80 8.07

0.169 0.176

25.27 35.13

26.76 20.07

Z-AM

23.68

0.158

103.09

Z-AM-Co-0.5

15.78

0.154

68.7

8.773

Z-AM-Co-1

15.2

0.149

67.5

8.976

Z-AM-Co-1.5

14.95

0.146

65.09

8.985

Z-AM-Co-2.5

11.65

0.149

50.72

11.780

6.143

BET specific surface area

compared to Z-NM can be attributed to dissolution of some impurities that block pores in the acids as well as the almost complete replacement of the metal cations by H? and opening of the windows formed from its replacement. These results are in consonance with the results of other researchers (Akkoca et al. 2013; Alver and Sakizci 2015; Garcia-Basabe et al. 2010; Hernandez et al. 2013). In addition, reduction of average pore diameter of Z-AM zeolite was related to forming of secondary micropores by free linkage. Results similar to this study were reported for Clinoptilolites treated with acid solutions by Alver and Sakizci (2015). According to the data in Table 3, modifying Z-NM with NaOH solution had no significant effects on the physical properties of zeolite. The results obtained from this part of the study are in agreement with results from studies by DicleBal Akkoca et al. (2013) and Jeong et al. (2001). Impregnation of Z-NM and Z-BM zeolites with cobalt did induce an increase in total volume, micropore and

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specific surface area and a decrease in average pore diameter. As seen from the data of Table 3, SBET of Z-NMCO-1.5 and Z-BM-CO-1.5 are equal with 27.20 and 35.13 m2/g, respectively, indicating an increase in value compared to their parent zeolites (Z-NM and Z-BM). Similar changes after modifying zeolites with metals to form metal/zeolite were also observed by other authors (Akgu¨l 2014; Liu et al. 2012). This increase in the BET surface area of the modified Clinoptilolites is probably due to the formation of surface cracks and defects as a result of the collapse of pore structure during impregnation with cobalt. Based on the results obtained (Table 2) as well as the % increase in cobalt impregnation with Z-AM zeolites, average pore diameter increased, whereas other parameters including total volume, specific surface area and micropore volume reduced in a similar way to previous studies (Akgu¨l 2014; Rutkowska et al. 2014; Zhang et al. 2007). This reduction in surface area after the modification can be attributed to the occupation of the pores by cobalt oxides or partial conglomeration of the samples crystallites. TPR: The H2-TPR measurements carried out for selected zeolites (Z-NM-CO-1.5 and Z-AM-CO-1.5). According to the H2-TPR profiles obtained in Fig. 4, three broad peaks were characterized around 250–350, 350–450 and 700–900 °C for Z-NM-CO-1.5. In addition, in the case of Z-AM-CO-1.5 addition to these broad peaks, a weak peak was diagnosed around 500–600 °C. Several studies performed on H2-TPR of cobalt-exchanged zeolites (Akkoca et al. 2013; Liu et al. 2012; Xie et al. 2015) have shown that up to 3 reduction regions can be distinguished; (a) 200–400 °C (reduction Co3O4 to CoO and then to metal cobalt in external surfaces of zeolites), (b) 400–700 °C (reduction CoOx in internal surfaces of zeolites) and (c) 700–950 °C (reduction Co2? to Co? or Co0 ion-exchanged sites). In addition, Smeets reported that in


Fig. 4 H2-TPR profiles of selected catalysts

catalysts with low Co loadings (Co/Al \0.3), cobalt is predominantly present as a mono-atomic Co species, and higher Co loadings (Co/Al [0.5) culminate in the formation of different kinds of Co-oxides (Smeets et al. 2008). According to results of Fig. 4 (existence of one main reduction region in both H2-TPR profiles) and Table 1 (Co/ Al ratio is 0.05–0.2), it can be concluded that the main active species in nitrous oxide decomposition are Co2? cations and other species which exhibit much lower activity. This result is in complete agreement with the results of other studies (Boron´ et al. 2015; Smeets et al. 2008; Xie et al. 2015). TPD: The temperature-programmed desorption of ammonia was conducted to obtain the strength and concentration of acid sites. NH3-TPD profiles of adsorbed ammonia on the selected samples (Z-AM-CO-1.5 and

Fig. 5 NH3-TPD profiles of selected catalysts

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Z-NM-CO-1.5) are shown in Fig. 5. These results indicate that zeolite of Z-AM-CO-1.5 is characterized by three ammonia desorption peaks; the first at about 120 °C, the second at about 450 °C and third at about 600 °C. Zeolite of Z-NM-CO-1.5 also has two peaks of ammonia desorption at about 100 and 550 °C. The desorption above 300 °C is related to decomposition of NH4? resulting from NH3 reacting with strong acid sites (Ates et al. 2011; Rutkowska et al. 2014; Shen et al. 2012). The low temperature peak (below 400 °C) has been attributed to NH3 weakly absorbed by acid sites and NH3 linked to Na? or extra framework of Al (Ates 2007; Ates and Hardacre 2012; Rutkowska et al. 2014). Temperature of desorption peak on zeolite of Z-AM-Co-1.5 was slightly higher than that of Z-NM-CO-1.5 (600 vs. 550 °C). For this reason, we can say that the acid sites in Z-ZM-Co-1.5 are slightly stronger than that in Z-NM-CO-1.5. Catalytic activities: The catalytic activities of natural zeolite (Clinoptilolite) modified with 0.6 N HCl and 1.5 N NaOH and impregnated with cobalt (different loading %) as well as the parent zeolites were tested for nitrous oxide (N2O) decomposition. Figure 6a shows that the modified zeolites with HCl are more active than the parent zeolite and the base zeolite in this catalytic process. Across these zeolites including Z-AM, Z- BM and Z-NM, only 39, 34 and 32% N2O reduction occurred at 600 °C. It has been reported that acid leaching of zeolites increases the decomposition activity of N2O in comparison with parent samples because of the formation of isolated iron and Fe– O–Al species. In addition, the data of Table 2 reveal that the specific surface area of Z-AM is higher than that of other zeolites and this can be attributed to the more activity of Z-AM in N2O conversion. These results are in consonance with results obtained by other researchers (Kapteijn et al. 1996; Miller et al. 1998). Figure 6b–d shows that samples impregnated with cobalt are more active than the parent zeolites in N2O decomposition. The results also show that increase in conversion efficiency with increasing amount of cobalt on zeolites was similar to the results of Shen et al. (2012), Rutkowska et al. (2014). As seen from Fig. 6d, an increase in cobalt loading on zeolites above 1.5% resulted in a decrease in activities. The reasons for this phenomenon can be attributed to a smaller specific surface area of samples containing higher metal loading, and subsequently blocking the pores and channels of zeolites, leaving only a small amount of cobalt oxides for reaction and N2O decomposition. These results have also been corroborated by other studies (Miller et al. 1998; Shen et al. 2012). The comparison of catalytic activity of the three zeolites of Z-AM-CO-1.5, Z-BM-CO-1.5 and Z-NM-CO-1.5 (Fig. 6e) shows that samples modified with HCl had the best performance in N2O direct decomposition. It has been

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Fig. 6 Decomposition of N2O over natural and modified zeolites. Experimental conditions: N2O concentration = 350–400 ppm balanced with N2; rate flow = 300 cm3/min and space velocity (GHSV) = 4500 cm3/(h g cat)

reported that metal loading does not affect its activity in N2O direct decomposition (Guzmań-Vargas et al. 2003) and that an increase in the metal to aluminum ratio induces a continuous increase in its activity (Li and Armor 1992; Turek 1998). Co/Al ratio in Z-Am-Co-1.5 was slightly more than that of the two other zeolites and it is responsible for the high activity together with the high surface area according to Table 1. Based on the previous studies, several options has been suggested for removal of N2O from exhaust streams of artificial sources which include thermal decomposition,

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catalytic decomposition, and decomposition by biological process and purification (Vanisudha et al. 2003; Osvaldo et al. 2016; Xie et al. 2014). Criteria for choosing the options are Safety of the treatment, efficiency of the technology, controllability and Investing and operating cost. In following, the selected method (catalytic decomposition) in the present study has been compared with other methods. Since, the molecular size of N2O and O2 are ˚ and O2 1.2 A ˚ ), purification method is similar (N2O 1.6 A very difficult to do and according to the low price of N2O, this method isn’t cost-benefit in comparison with


decomposition. Also, N2O decomposition by biological process for the following reasons is not a feasible or costbenefit method in comparison with catalytic decomposition: (1) decomposition rate of N2O by microbes is low and its efficiency is around 60–85% (Vanisudha et al. 2003), while the method used in this study (catalytic decomposition of nitrous oxide by Zeolites Z-AM-CO-1.5) has high rate in decomposition and efficiency of 100% at temperature of 400 °C (Fig. 6). (2) Some cultured microbes need anaerobic environment for their growth. Absence of oxygen is not possible in this case, as O2 is in the gaseous mixture of exhaust streams of industries and difficult to be separated from N2O, while catalytic decomposition of N2O is feasible with high efficiency in the presence of O2 and other agents such as CO2, humidity, NO, NO2, CO (Chengyun Huang et al. 2017; Runhu Zhang et al. 2016; Dann et al. 1995). Thermal decomposition of N2O, due to the requirement of high energy (temperature of 1500–1800 °C for conversion around 90–95% or more), is not a cost-benefit method in comparison with catalytic decomposition (Vanisudha et al. 2003). In the present study, catalytic decomposition of N2O on Zeolites Z-AM-CO-1.5 with efficiency around 90–95% or more is done at temperature 400–450 °C. It can be concluded that the used method in present study can be more cost-benefit than thermal decomposition.

Conclusion In this study, natural zeolite (Clinoptilolite) treatment with 0.6 N HCl, 1.5 N NaOH and modified with cobalt by impregnation method was used in direct N2O decomposition. From the experiments conducted for the non-modified and modified zeolites by ICP, XRD, BET, TPR, TPD and catalytic activity, it can be concluded that: 1.

2.

3.

The applied modifications had no significant influence (destruction) on the main structure of the zeolites including clinoptilolite, quartz and cristobalite. The alkaline treatment did not change the properties of zeolites significantly, whereas acid leaching induced abrupt increase in surface area and reduction in average diameter of the pores. This could be an excellent characteristic in absorption and consequently in N2O decomposition. Among the zeolites impregnated with cobalt (Z-AMCO-1.5, Z-BM-CO-1.5 and Z-NM-CO-1.5), sample Z-AM-Co-1.5 had the highest CO/Al ratio, which is an indication that it can be an important parameter in nitrous oxide conversion in metal-zeolite catalyst. It also demonstrated that increased cobalt loading is not an indicator of continuous increase of the process.

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4.

5.

6.

7.

TPR analysis showed that the main active species in nitrous oxide decomposition are mono-atomic and other species exhibit much lower activity. Survey of the acid sites of samples showed that the acid sites in Z—ZM-Co-1.5 were slightly stronger than that in Z-NM-CO-1.5. In this work, all samples used as catalyst were active in N2O decomposition; however, zeolite Z-Am-Co-1.5 had the best performance in the process. This effect could be attributed to the higher amount of CO/Al and surface area as well as the strong acid sites of this zeolite compared to other zeolites. In conclusion, natural clinoptilolite zeolites treated with acid and impregnated with Cobalt (Z-AM-CO1.5) could be a very effective and cost-benefit catalyst for reducing N2O as a greenhouse gas, due to its very low price, high chemical stability and high availability.

Acknowledgements The authors gratefully acknowledge the contribution of Tehran University of Medical Sciences, Iran for funding this research (Grant No. 28427).

References Abu-Zied BM, Schwieger W, Unger A (2008) Nitrous oxide decomposition over transition metal exchanged ZSM-5 zeolites prepared by the solid-state ion-exchange method. Appl Catal B 84:277–288 Akgu¨l M (2014) Enhancement of the anionic dye adsorption capacity of clinoptilolite by Fe3?-grafting. J Hazard Mater 267:1–8 Akgu¨l M, Karabakan A (2011) Promoted dye adsorption performance over desilicated natural zeolite. Microporous Mesoporous Mater 145:157–164 Akkoca DB, Yilgin M, Ural M, Akçin H, Mergen A (2013) Hydrothermal and thermal treatment of natural clinoptilolite zeolite from Bigadiç, Turkey: an experimental study. Geochem Int 51:495–504 Alver BE, Sakizci M (2015) Influence of acid treatment on structure of clinoptilolite tuff and its adsorption of methane. Adsorption 21:391–399 Ates A (2007) Characteristics of Fe-exchanged natural zeolites for the decomposition of N2O and its selective catalytic reduction with NH3. Appl Catal B 76:282–290 Ates A (2015) Effect of pre-treatment and modification conditions of natural zeolites on the decomposition and reduction of N2O. React Kinet Mech Catal 114:421–432 Ates A, Hardacre C (2012) The effect of various treatment conditions on natural zeolites: ion exchange, acidic, thermal and steam treatments. J Colloid Interface Sci 372:130–140 Ates A, Reitzmann A, Hardacre C, Yalcin H (2011) Abatement of nitrous oxide over natural and iron modified natural zeolites. Appl Catal A 407:67–75 Boron´ P, Chmielarz L, Casale S, Calers C, Krafft J-M, Dzwigaj S (2015) Effect of Co content on the catalytic activity of CoSiBEA zeolites in N2O decomposition and SCR of NO with ammonia. Catal Today 258:507–517 Camacho LM, Parra RR, Deng S (2011) Arsenic removal from groundwater by MnO2-modified natural clinoptilolite zeolite:

123

Author's personal copy 336 effects of pH and initial feed concentration. J Hazard Mater 189:286–293 Centi G, Galli A, Montanari BEA, Perathoner S, Vaccaria A (1997) Catalytic decomposition of N2O over noble and transition metal containing oxides and zeolites. Role of some variables on reactivity. Catal Today 35:113–120 Chen H-H, Shen S-C, Chen X, Kawi S (2004) Selective catalytic reduction of NO over Co/beta-zeolite: effects of synthesis condition of beta-zeolites, Co precursor, Co loading method and reductant. Appl Catal B 50:37–47 Cheng X-W, Zhong Y, Wang J, Guo J, Huang Q, Long Y-C (2005) Studies on modification and structural ultra-stabilization of natural STI zeolite. Microporous Mesoporous Mater 83:233–243 Chengyun Huang ZM, Miao Changxi, Yue Yinghong, Hua Weiming, Gao Zi (2017) Catalytic decomposition of N2O over Rh/Zn– Al2O3 catalysts. RSC Adv 7:4243–4252 Dann TW, Schulz KH, Mann M, Collings M (1995) Supported rhodium catalysts for nitrous oxide decomposition in the presence of NO, CO2, SO2 and CO. Appl Catal B 6:1–10 Eller PM (1994) NIOSH manual of analytical methods. Diane Publishing, Collingdale Garcia-Basabe Y, Rodriguez-Iznaga I, De Menorval L-C, Llewellyn P, Maurin G, Lewis DW, Binions R, Autie M, Ruiz-Salvador AR (2010) Step-wise dealumination of natural clinoptilolite: structural and physicochemical characterization. Microporous Mesoporous Mater 135:187–196 Goto T, Niimi A, Hirano K, Takahata N, Fujita S-I, Shimokawabe M, Takezawa N (2000) Comparative study of decomposition of N2O over metal oxides and metal ion exchanged ZSM-5 zeolites. React Kinet Catal L 69:375–378 Gregg SJ, Sing KSW (1982) Adsorption, surface area and porosity. Academic Press, london Guzmań-Vargas A, Delahay G, Coq B (2003) Catalytic decomposition of N 2 O and catalytic reduction of N2O and N2O ? NO by NH3 in the presence of O2 over Fe-zeolite. Appl Catal B 42:369–379 Hernandez MA, Rojas F, Portillo R, Salgado MA, Perez G (2013) Porosity on external surface of H-clinoptilolite sorption of CCl4 and n-C6H14. JCCE 7:901 Jentys A, Lugstein A, Vinek H (1997) Co-containing zeolites prepared by solid-state ion exchange. J Chem Soc Faraday Trans 93:4091–4094 Jeong SW, Kim J-H, Seo G (2001) Liquid-phase degradation of HDPE over alkali-treated natural zeolite catalysts. Korean J Chem Eng 18:848–853 Kannan S, Swamy C (1999) Catalytic decomposition of nitrous oxide over calcined cobalt aluminum hydrotalcites. Catal Today 53:725–737 Kapteijn F, Rodriguez-Mirasol J, Moulijn JA (1996) Heterogeneous catalytic decomposition of nitrous oxide. Appl Catal B 9:25–64 Kapteijn F, Marbań G, Rodriguez-Mirasol J, Moulijn JA (1997) Kinetic analysis of the decomposition of nitrous oxide over ZSM-5 catalysts. J Catal 167:256–265 Kawi S, Liu S, Shen S-C (2001) Catalytic decomposition and reduction of N2O on Ru/MCM-41 catalyst. Catal Today 68:237–244 Kowalczyk P, Sprynskyy M, Terzyk AP, Lebedynets M, Namiesńik J, Buszewski B (2006) Porous structure of natural and modified clinoptilolites. J Colloid Interface Sci 297:77–85 Labhsetwar N, Dhakad M, Biniwale R, Mitsuhashi T, Haneda H, Reddy PSS, Bakardjieva S, Subrt J, Kumar S, Kumar V, Saiprasad P, Rayalu S (2009) Metal exchanged zeolites for catalytic decomposition of N2O. Catal Today 141:205–210 Li Y, Armor JN (1992) Catalytic decomposition of nitrous oxide on metal exchanged zeolites. Appl Catal B 1:L21–L29

123

Int J Environ Res (2017) 11:327–337 Lin H, Liu Q-L, Dong Y-B, He Y-H, Wang L (2015) Physicochemical properties and mechanism study of clinoptilolite modified by NaOH. Microporous Mesoporous Mater 218:174–179 Liu N, Zhang R, Chen B, Li Y, Li Y (2012) Comparative study on the direct decomposition of nitrous oxide over M (Fe Co, Cu)—BEA zeolites. J Catal 294:99–112 Maroufi SS, Gharavi M, Behnam M, Samadikuchaksaraei A (2011) Nitrous oxide levels in operating and recovery rooms of Iranian hospitals. Iran J Public Health 40:75 Marylou Austin R (2013) Nitrous oxide sedation: clinical review & workplace safety. Academy of Dental Learning & OSHA Training, Albany Masoumeh A, Abdolkazem N, Mostafa F (2014) Investigation of nitrous oxide concentration in operating rooms of educational hospitals of Ahvaz Jundishapur University in year 2012. IJHSE 1:138–144 Mauvezin M, Delahay G, Kisslich F, Coq B, Kieger S (1999) Catalytic reduction of N2O by NH3 in presence of oxygen using fe-exchanged zeolites. Catal Lett 62:41–44 Miller J, Glusker E, Peddi R, Zheng T, Regalbuto J (1998) The role of acid sites in cobalt zeolite catalysts for selective catalytic reduction of NOx. Catal Lett 51:15–22 Mortazavi Y, Khalilpour A, Amouei A, Tirgar A (2013) Assessment of nitrous oxide concentration in the operating and recovery rooms of Babol University of medical sciences. IJHS 1:95–99 Mul G, Pe´rez-Ramı´rez J, Kapteijn F, Moulijn JA (2001) NO-assisted N2O decomposition over ex-framework FeZSM-5: mechanistic aspects. Catal Lett 77:7–13 Nobukawa T, Tanaka S-I, Ito S-I, Tomishige K, Kameoka S, Kunimori K (2002) Isotopic study of N2O decomposition on an ion-exchanged Fe-zeolite catalyst: mechanism of O2 formation. Catal Lett 83:5–8 Osvaldo D, Frutos IC, Arnaiz E, Lebrero R, Munõz R (2016) Biological nitrous oxide abatement by paracoccus denitrificans in bubble column and airlift reactors. CET 54:289–294 Paschalia Taniou ZZA, Savvas V (2013) Catalytic decomposition of N2O: best achievable methods and processes. Am Trans Eng Appl Sci 2:149–188 Radosavljevic-Mihajlovic A, Dondur V, Dakovic A, Lemic J, Tomasevic-Canovic M (2004) Physicochemical and structural characteristics of HEU-type zeolitic tuff treated by hydrochloric acid. J Serb Chem Soc 69:273–281 Rajska M, Wo´jtowicz B, Klita Ł, Zych Ł, Zybała R (2016) The use of CeO2-Co3O4 oxides as a catalyst for the reduction of N2O emission. E3S Web Conf 10:1–6 Rowland AS, Baird DD, Shore DL, Weinberg CR, Savitz DA, Wilcox AJ (1995) Nitrous oxide and spontaneous abortion in female dental assistants. Am J Epidemiol 141:531–538 Rozˇic´ M, Cerjan-Stefanovic´ Sˇ, Kurajica S, Maeˇefat MR, Margeta K, Farkasˇ A (2005) Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff. J Colloid Interface Sci 284:48–56 Runhu Zhang CH, Wang Bingshuai, Jiang Yan (2016) N2O decomposition over Cu–Zn/–Al2O3 catalysts. Catalysts 6:1–9 Rutkowska M, Chmielarz L, Jabłon´ska M, Van Oers C, Cool P (2014) Iron exchanged ZSM-5 and Y zeolites calcined at different temperatures: activity in N2O decomposition. J Porous Mater 21:91–98 Segawa K, Shimura T (2000) Effect of dealumination of mordenite by acid leaching for selective synthesis of ethylenediamine from ethanolamine. Appl Catal A 194:309–317 Seyedeyn-Azad F, Zhang D-K (2001) Selective catalytic reduction of nitric oxide over Cu and Co ion-exchanged ZSM-5 zeolite: the effect of SiO2/Al2O3 ratio and cation loading. Catal Today 68:161–171

Author's personal copy Int J Environ Res (2017) 11:327–337 Shen Q, Li L, He C, Zhang X, Hao Z, Xu Z (2012) Cobalt zeolites: preparation, characterization and catalytic properties for N2O decomposition. Asia-Pac J Chem Eng 7:502–509 Sing K, Everett D, Haul R, Moscou L, Pierotti R, Rouquerol J, Siemieniewska T (1985) Physical and biophysical chemistry division commission on colloid and surface chemistry including catalysis. Pure Appl Chem 57:603–619 Smeets PJ, Meng Q, Corthals S, Leeman H, Schoonheydt RA (2008) Co-ZSM-5 catalysts in the decomposition of N2O and the SCR of NO with CH4: Influence of preparation method and cobalt loading. Appl Catal B 84:505–513 Sulbaek MP, Andersen SPS, Nielsen OJ, Wagner DS, Sanford TJ Jr, Wallington TJ (2010) Inhalation anaesthetics and climate change. Br J Anaesth 105:760–766 Treacy MM, Higgins JB (2007) Collection of simulated XRD powder patterns for zeolites fifth (5th) revised edition. Elsevier, Amsterdam Turek T (1998) A transient kinetic study of the oscillating N2O decomposition over Cu–ZSM-5. J Catal 174:98–108 Vanisudha C, Yiling L, Chunyu M, Nikhil S, Ying Z, Kisoen D (2003) Removal of N2O and Isoflurane from the exhaust stream of the operation rooms in hospitals. Delft ChemTech - Faculty of Applied Sciences, Delft University of Technology, Delft

337 Wang X, Chen H-Y, Sachtler W (2000) Catalytic reduction of NOx by hydrocarbons over Co/ZSM-5 catalysts prepared with different methods. Appl Catal B 26:L227–L239 Wronska-Nofer T, Nofer J-R, Jajte J, Dziubaltowska E, Szymczak W, Krajewski W, Wasowicz W, Rydzynski K (2012) Oxidative DNA damage and oxidative stress in subjects occupationally exposed to nitrous oxide (N2O). Mutat Res Fundam Mol Mech Mutagen 731:58–63 Xie PF, Ma Z, Zhou HB, Huang CY, Yue YH, Shen W, Xu HL, Hua WM, Gao Z (2014) Catalytic decomposition of N2O over CuZSM-11 catalysts. Microporous Mesoporous Mater 191:112–117 Xie P, Luo Y, Ma Z, Wang L, Huang C, Yue Y, Hua W, Gao Z (2015) CoZSM-11 catalysts for N2O decomposition: effect of preparation methods and nature of active sites. Appl Catal B 170:34–42 Xue L, Zhang C, He H, Teraoka Y (2007) Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst. Appl Catal B 75:167–174 Zhang Y, Zhou Y, Wang Y, Xu Y, Wu P (2007) Effect of calcination temperature on catalytic properties of PtSnNa/ZSM-5 catalyst for propane dehydrogenation. Catal Commun 8:1009–1016

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