Effects of metal loading on activated carbon on its adsorption and desorption characteristics

Accepted Manuscript Title: Effects of metal loading on activated carbon on its adsorption and desorption characteristics Authors: Ji Hye Park, Ra Hyun Hwang, Hyung Chul Yoon, Kwang Bok Yi PII: DOI: Reference:

S1226-086X(18)30915-8 https://doi.org/10.1016/j.jiec.2019.03.004 JIEC 4423

To appear in: Received date: Revised date: Accepted date:

5 October 2018 2 March 2019 4 March 2019

Please cite this article as: Park JH, Hwang RH, Yoon HC, Yi KB, Effects of metal loading on activated carbon on its adsorption and desorption characteristics, Journal of Industrial and Engineering Chemistry (2019), https://doi.org/10.1016/j.jiec.2019.03.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effects of metal loading on activated carbon on its adsorption and desorption characteristics

Ji Hye Parka, Ra Hyun Hwanga, Hyung Chul Yoonb, and Kwang Bok Yic,* Graduate School of Energy Science and Technology, Chungnam National University

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a

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99 Daehak-ro, Yuseong-gu, Daejeon 34134, South Korea b

Korea Institute of Energy Research, 140, Yuseong-daero 1312beon-gil, Yuseong-gu, Daejeon, 34101,

South Korea

Department of Chemical Engineering Education, Chungnam National University

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99 Daehak-ro, Yuseong-gu, Daejeon 34134, South Korea

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Abstract

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Metal loaded activated carbons (AC) were synthesized for an application in NH3 enrichment through repeated adsorption and desorption. The metal loaded activated carbons possesses higher NH3

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adsorption capacity than the raw AC at room temperature. Mg loaded AC (AC-Mg) showed about 10 times (6.34 mg NH3/g) higher adsorption capacity than raw AC and its adsorption capacity was maintained even in repeated breakthrough tests. Metal loading on activated carbon increased the

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concentration of surface oxygen, which provides relatively weak adsorption sites for NH 3 so that the adsorbed NH3 can be released relatively easier compared to the case of raw AC. Keywords: activated carbon, metal, ammonia, adsorption, desorption, breakthrough test *

Corresponding

authors:

[email protected] (K. B. Yi)

Tel:

+82-42-821-8583,

Fax:

+82-42-821-8864,

E-mail:

1. Introduction Ammonia (NH3) has been used for fertilizer production to support the World’s growing population [1]. The industrial-scale synthesis of NH3 is certainly the single biggest scientific discovery of the 20th

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century [1, 2]. According to the U.S. Geographic Survey, it is reported that the total output of worldwide NH3 exceeded 1.4 million tons and the demand has continued to grow [3]. Industrially, the Haber-Bosch

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process is the main technology to produce NH3 exclusively. This process reacts highly pure streams of

N2 and H2 together at high pressures and temperatures (200 – 300 atm and 300 – 500 °C) under Fe or Ru-based catalysts. This process requires energy intensive operating conditions and causes large amount

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of carbon emissions. Therefore, development of energy efficient and environmentally safe processes

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for ammonia production that can substitute the Harbor–Bosch method is required [4]. The

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electrochemical synthesis of ammonia, which is considered as an eco-friendly process for NH3

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production, has been investigated in recent years and several cases of ammonia synthesis using water and air at ambient pressure and relatively low temperature (<100 °C) have been reported [5-8]. However,

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electrochemical synthesis of NH3 is still in a research level and considered as a future technology because of its low yield of ammonia. In addition, even with successful development of the technology,

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ammonia concentration in the product stream is expected to be very low compared to the conventional ammonia production technologies. At current state, further research is required for increasing the yield

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and the concentration of ammonia in the product stream. Nevertheless, it might be possible to enrich ammonia concentration using adsorption technique if an adsorbent with substantial ammonia capacity and durability is available. Ammonia is classified as a hazardous material that is mainly produced in

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semiconductor plants, printing, and livestock facilities [9]. For this reason, adsorption of ammonia has been applied for only removal of trace ammonia as an impurity [9-16] and enrichment of ammonia has never been attempted. Most of adsorbents for ammonia are mainly composed of mesoporous materials such as MOF [16-18], zeolite [18] and activated carbon [10-14, 19]. Among those materials, because of its low price and abundance, activated carbon has been widely used for purification of various gases

such as NH3 [10-14], CO2 [20], H2 [21], CH4 [22], sulfur [23] and phenolic compounds [24]. Generally, activated carbon is functionalized according to its use by introducing acidic or basic functional groups [14]. It has been reported that acidic surface oxides increase the adsorption capacity for polar alkaline molecules such as NH3 [13, 14, 25, 26]. Guo et al. [13] introduced functional groups to a palm shells based activated carbon using H2SO4 and correlated the amount of oxygen on the surface of the activated

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carbon and amount of ammonia adsorption. Huang et al. [14] compared ammonia adsorption capacities of activated carbons with different acids including nitric, sulfuric, hydrochloric, phosphoric, and acetic

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acid. Activated carbon with nitric acid showed the largest capacity of NH3 adsorption and a linear

relationship between the NH3 adsorption capacity and the amount of acidic functional groups of the adsorbent surface.

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There are a number of studies that reported the relationship between adsorption performance and the

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surface treatment of the activated carbon [12]. The introduction of the functional group through acid

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treatment on the surface of activated carbon greatly increases the NH3 adsorption capacity, but this

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functional groups can be lost when elevated temperature (> 200 °C) is applied for regeneration of the adsorbent. With this reason, other researchers introduced inorganic metals on the surface of activated

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carbon instead of acid treatment [10]. Bandosz and Petit [10] prepared ammonia adsorbents using activated carbons with different origins (coal, wood, coconut-shell based carbon) by introducing various

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inorganic metals. They claimed that ammonia adsorption capacities of the adsorbents depend on types

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of origins, the loaded inorganic metal and other experimental conditions. More specifically, the proper combination of the surface pH, the strength, type and amount of functional groups that present on the adsorbents’ surface can be a key point to increase NH3 capacity [10]. Even with these attractive features

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of metal loaded activated carbons, there are only limited number of publications available in the related field. Also, the relation between the metal or metal oxide of the adsorbent surface and NH3 adsorption capacity has not been clearly explained. In this study, metal loaded activated carbons were prepared with varying metal precursor for application in ammonia enrichment from product stream of electrochemical ammonia synthesis process.

The adsorption and desorption performance of ammonia along with thermal stability of the adsorbents were compared and analyzed. It is also attempted to clarify the relationship between the metal loading and the ammonia adsorption capacity.

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2. Experimental 2.1. Preparation of metal loaded activated carbon

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Coal-based activated carbon (BPL® 4*6, granular) were purchased and was washed several times

with distilled water to remove surface impurities and dried at 100 °C overnight. Metal loaded activated

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carbons were synthesized by ultrasonic-assisted impregnation method. Metal amount was fixed as 5 wt% of activated carbon for all adsorbents. For loading of metal on activated carbon, 0.05 M of aqueous

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solutions of Ni(NO3)2∙6H2O, Zn(NO3)2∙6H2O, Fe(NO3)3∙9H2O, Cu(NO3)2∙3H2O, Mg(NO3)2∙6H2O, and

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Cr(NO3)3∙9H2O were prepared, respectively. Then, activated carbon was put into the solution. The

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resulted slurry was placed in an sonication bath (SD-300H, SEONG DONG) at 80 °C with stirring and

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kept until all the solvent evaporates. The samples were cooled down to room temperature, then dried further at 100 °C in an oven overnight. Finally, the dried samples were calcined in N2 at 300 °C for 2 h.

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The prepared adsorbent samples were designated according to the loaded metal as AC, AC-Ni, AC-Zn, AC-Fe, AC-Cu, AC-Mg and AC-Cr. For instance, AC means raw activated carbon and AC-Mg is the

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activated carbon adsorbent loaded with Mg.

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2.2. Breakthrough test NH3 adsorption capacity of the metal loaded activated carbons was measured with the fixed bed

reactor at room temperature. Prior to the breakthrough test, the adsorbents were crushed and sieved to the size of 150 ~ 300 µm. Then, the sieved adsorbent of 0.25 g was loaded and packed into a 1/4 inch quartz reactor. Before the NH3 adsorption tests, the samples were baked at 200 °C for 1 h to remove the moisture. The reactor was cooled down to room temperature and 500 ppm of NH3 gas balanced by N2

was introduced to the reactor at 100 cc/min and passed through the adsorbent bed and the effluent gas was analyzed in a NH3 analyzer (SKT-9300, Korno). Each breakthrough test was terminated when the NH3 concentration at the outlet reached a NH3 concentration of 400 ppm. Desorption process was carried out after each breakthrough test for subsequent adsorption test by purging the reactor with N2 at

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100 cc/min and increasing temperature to 200 °C and maintaining for 1 h.

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2.3. Characterization

In order to confirm the amount of metal loaded of the prepared samples, the metal loaded activated carbons were placed in a TGA (thermogravimetric analyzer, TGA-N1000, Sinco) and weight losses

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were measured with increasing temperature at 10 °C /min to 800 oC in air with flow rate of 100 cc/min.

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The BET surface area of the adsorbents was measured with an ASAP 2010 analyzer (Micromeritics)

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by means of N2 physisorption isotherms at -196 oC. Before N2 adsorption, the samples were thermally

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dried at 200 oC for 4 h under vacuum in order to remove retained gases and adsorbed water.

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The surface physical morphology of samples was examined using a field emission scanning electron microscope (FE-SEM) model Hitachi S-4800. The elemental composition of the sample was determined

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from the SEM/EDX analysis. Energy dispersive analysis by X-ray (EDX) was carried out using X-max 50. X-ray mapping of C, O and metals was performed using energy dispersive X-ray spectroscope

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connected to the SEM.

NH3-TPD (temperature-programmed desorption, BELCAT-M, Bel Japan) was used to measure the

desorption amount of NH3 from adsorbents. The sample cell was heated to 200 °C under a flow of He

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for 1 h and cooled down to 30 °C. 10 vol.% of NH3 gas balanced by N2 flowed through the sample cell for 30 min and the cell was flushed with He to remove remained free NH3. Finally, the sample cell was heated at a rate of 10 °C /min to 800 °C while the desorbed NH3 was measured with a thermal conductivity detector. XPS (X-ray photoelectron spectroscopy, AXIS NOVA (KARTOS)) was used to confirm the

elemental composition and their chemical state near the activated carbon surface. The measurements were performed with Al Kα irradiation as X-ray source. All binding energies were referenced to the C 1s peak at 284.8 eV to compensate for the surface charging effects. The DRIFTS experiments were carried out in a porous ceramic IR reaction cell equipped with ZnSe

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windows and using a PIKE Technologies DiffusIR accessory for diffuse reflectance placed in a NICOLET iS10 (Thermo Scientific) IR spectrometer fitted with an MCT detector working at liquid N2 temperature. A total of 64 scans were recorded per spectrum, which was displayed in absorbance units,

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over the range of 4000 – 650 cm-1 at a resolution of 4 cm-1. Samples were placed in the sample holder. Prior to each test, the background spectrum was recorded against a pure KBr sample at 25 and 200 °C. The samples were pretreated under 50 cc/min of He flow for 20 min at 200 °C and then cooled down

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to room temperature. NH3 gas mixtures were introduced to the reaction chamber to investigate changes

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in the functional groups on the activated carbon surface. In order to observe changes of the functional

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groups during the desorption process, 50 cc/min of He was introduced to the cell and temperature was

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raised to 200 °C.

3. Results and discussion

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3.1. Breakthrough test

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Figure 1 shows the breakthrough test results of the prepared adsorbents at room temperature. As

expected, the breakthrough time of AC was very short as about 4 min. The metal loaded ACs, however, lasted for significantly longer period compared to raw AC. Apparently, the breakthrough time of the

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metal loaded ACs strongly depended on the species of the metal loaded. Among the metal loaded ACs, AC-Mg showed the longest breakthrough time as 40 min, which indicates 10 times higher NH3 adsorption amount can be achieved with Mg loaded activated carbon compared to the raw AC. NH3 adsorption capacity of the adsorbents was in following order: AC < AC-Zn, AC-Fe < AC-Cu < AC-Ni < AC-Cr < AC-Mg. All samples exhibited very sharp breakthrough patterns, indicating that the NH3

adsorption process is not diffusion-controlled. Because the NH3 adsorption was very stable until the depletion of adsorption capacity it seems that all the active sites on the adsorbents for NH3 adsorption are exposed to gas phase and interaction between NH3 and the site are not affected by neighboring sites that are already holding NH3 molecules.

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After the first breakthrough test, each sample was heated to 200 oC in N2 atmosphere and maintained for 1 h for desorption of ammonia. Then, the samples were cooled down to room temperature again for

next breakthrough test. The results of the second breakthrough tests are shown in Figure 2. In the second

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adsorption test, breakthrough time for AC was about 3.5 min that is slightly shorter than that of the first

cycle, whereas the breakthrough time of AC-Mg in the second cycle slightly increased compared to that of the first cycle. However, repeated breakthrough tests of all samples were substantially constant within

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the error range.

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It seems that the metal loading clearly increases the NH3 adsorption capacity of AC, but the degree of increment of the capacity strongly depends on the type of loaded metal. The amounts of adsorbed

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3.2. Characterization

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NH3 for all samples were quantitatively calculated and shown in the Table 1.

The TGA experiment was carried out in the air atmosphere by raising the temperature up to 800 oC

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to determine the amount of metal loading on adsorbent as shown in Figure 3. The weight loss of AC started to appear at around 500 oC at rapid rate and stopped at around 600 oC leaving 6 wt% of the material as residue that is expected to be impurities or ash [27]. In the cases of metal loaded ACs,

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however, the weights of the residues were in the range of 11 to 17 wt%. This result indicates that the metals were successfully loaded on the activated carbons. With counting out the impurities, the metal loading is expected to be at least 5 wt%. The final weight of each adsorbent was slightly different according to the type of metal loaded. The differences in final weight are attributed to the different oxide states of the metals. One should notice that the metal loaded ACs begin to lose their weight at

lower temperatures than the raw AC. Similar results have been reported in literature. Amer et al. [28] were conducted TGA test using the CNTs and CNT-Fe2O3 and confirmed CNT-Fe2O3 samples reduced the initial and final degradation temperature of the CNTs by almost 100 °C. They claimed that lower thermal stability of the CNT-Fe2O3 when compared to the raw CNTs may be due to the attachment of iron oxide particles to the walls of the CNTs. It is believed that the loaded metals behave as catalysts

easily. Nevertheless, all the adsorbents showed good thermal stability up to 300 oC.

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that transfer oxygen ions to inner lattice of the AC so that carbon-carbon bondage can be broken more

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The physical characteristics and BJH pore size distributions of metal loaded ACs are shown in Table

2 and Figure 4. The surface areas and pore volume of raw AC without metal were the highest as 873 m2/g and 0.49 cm3/g respectively. The addition of metals to the raw AC is expected to reduce the surface

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area and pore volume due to the pore filling effect. Indeed, the surface area and pore volume decreased

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as metals was loaded on the raw AC. AC-Mg showed the highest surface area and pore volume among

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the metal loaded ACs. The average pore size was, however, constant for all ACs. Metal loading onto

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the surface of the activated carbon did not affect the pore size. Differences in NH3 capacity of the adsorbents are thought to be originated from differences in its surface area and pore volume but any

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apparent tendency was not recognized.

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SEM and EDX analysis were carried out to examine the surface morphology and the amount of surface oxygen. The analysis results are shown in Figure 5 and Figure 6. The SEM figures shows that

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the metal loaded ACs possess smaller size of particles than bare AC but the difference is insignificant. The elemental mapping analysis reveals that each metal was dispersed uniformly on the surface of

activated carbon. The amount of metals on AC surface were in the range of 4 - 5 wt%. One should

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notice that metal loading significantly increased oxygen amount on the surface of adsorbents. In particular, the amount of oxygen of the AC-Mg was the highest which is matched with the results of breakthrough test on the basis of assumption that larger amount of oxygen on the adsorbent surface results in higher ammonia adsorption capacity. Determination of adsorbed amount of NH3 through breakthrough test was relatively simple but there

were some difficulties using the fixed bed reactor in qualitative determination of desorption amount. Alternatively, NH3-TPD analysis was adopted to estimate the amount of desorption. After the adsorption in the fixed bed at room temperature, the adsorbent was transferred to sample cell in TPD equipment and the desorption was carried out with increasing temperature. The results of desorption test in TPD are shown in Figure 7. The results of the desorption tests were well matched with those of the

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breakthrough tests: the raw AC showed the lowest amount of NH3 desorption and AC-Mg is confirmed

to possess the highest amount of desorption. The desorption amounts were in following order: AC <

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AC-Zn, AC-Fe < AC-Cu < AC-Ni < AC-Cr < AC-Mg, which is very similar to those in adsorption amount. For comparison with adsorption test results, the quantitative analysis for desorption test results was carried out in the range of 30 – 200 °C and the amounts of NH3 desorption per unit weight of the

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adsorbent is shown together in Table 1. It was found that most of the NH3 adsorbed at room temperature

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are desorbed under 200 °C.

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For a more specific characterization, NH3 adsorption and desorption characteristics were analyzed

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through a DRIFTS measurement with raw AC and AC-Mg and the results are shown in Figure 8 and Figure 9. Figure 8(a) compares the band profile changes along with adsorption time under NH3 + He

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atmosphere at room temperature. Figure 8(b) shows the results of AC-Mg under the same conditions. Major band profile changes appeared in the frequency range of 750 – 1300 cm-1. More specifically

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bands in transition during the ammonia adsorption were found to be at 931, 966, 1222, 1243 and 1257

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cm-1. The bands at 931 and 966 cm-1 are associated with free NH3 adsorbed on the adsorbent surface [29-31]. Immediate increase of these two bands after the NH3 injection implies that NH3 is adsorbed directly onto the surface of the AC. On the other hand, in the case of AC-Mg, the bands at the same

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frequencies appeared at about 6 min and the intensities of the bands seemed to be weaker than those of raw AC. Therefore, it might be a reasonable to speculate that Mg inhibits immediate and direct adsorption of ammonia on the surface of adsorbent and helps to transfer ammonia to inner pore region. It was reported that the band at 1222 cm-1 is associated with C-O stretching vibration of epoxide moieties and C-N vibrations. It is also reported that C-N vibration mainly contributes to the changes in the band intensity [32]. As shown in Figure 8(a), the intensity of the band at 1222 cm-1 increased as

NH3 was adsorbed on raw AC. On the other hand, in case of AC-Mg, the increment of the band at 1222 cm-1 with ammonia adsorption was barely noticed as shown in Figure 8(b). This difference on the band intensity implies that the NH3 is bound on each sample in different manner. Presumably, NH3 on AC is chemically bound with functional groups on AC surface forming C-N bondings, whereas NH3 on ACMg is bound on the surface by rather physical attraction. In order to confirm this presumption,

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desorption test was carried out in He atmosphere with increasing temperature in the DRIFT apparatus

and the results are shown in Figure 9. It was found that the band associated with C-N bonding at 1222

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cm-1 for raw AC remain unchanged even in elevated temperature. Despite of its relatively low intensity, the band shape of AC-Mg was also remained unchanged and the original shape of the band was not restored even in the temperature range over 200 °C. Unlikely, the bands associated with direct

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adsorption of NH3 (931 and 966 cm-1) of Ag-Mg decreased drastically with mild increase of temperature.

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These two bands of raw AC, however, remained with relatively high intensities as temperature increased.

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Therefore, it might be reasonable to expect that the AC-Mg is more favorable for regeneration than raw

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AC considering repetitive use of adsorbent in NH3 enrichment. More details are revealed in XPS analysis. Figure 10 shows the XPS peaks of carbon and oxygen in

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raw AC and AC-Mg adsorbent. Because of the shielding effect of loaded Mg in AC-Mg adsorbent, the intensity of C 1s peak of AC-Mg was relatively lower than that of raw AC. It was found that O 1s peak

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of AC-Mg was slightly shifted to the right by 0.3 eV compared to that of raw AC marking peak center

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position at 532.6 eV. The shift of O 1s peak confirms the presence of oxygen on AC-Mg as in a form of MgO or Mg(OH)2. The results of the quantitative analysis of the XPS are shown in Table 3. A comparative mass concentration analysis of AC and AC-Mg showed that the oxygen contained in AC-

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Mg is 4 times greater than in AC. The mass concentrations of adsorbents before and after adsorption did not show any drastic changes. In order to check the chemical state of AC and AC-Mg in more detail, an XPS analysis of the samples was performed as prepared, after adsorption, and after subsequent desorption of NH3. The results are shown in Figure 11. According to the literature, the peaks of O 1s and Mg 2p can be separated into three

peaks, respectively [33]. The O 1s peak of two samples can be deconvoluted into O 1s(I), (II) and(III), and the Mg 2p peak of AC-Mg into Mg 2p(I), (II) and (III) [33]. O 1s(I) is identified as in a O2- and O 1s(II) as in a OH- [33, 34]. O 1s(III) is associated with oxygen in a C-O bond, which is believed to be due to contamination of the surface layer when exposed to the atmosphere during the analysis process [33-35]. The difference between Mg 2p (II) and O 1s (I) is 480.5 eV, and the difference between Mg 2p

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(II) and O 1s (II) is 481.8 eV. Each is expected to correspond to Mg-O and Mg-OH bonds [33-36]. These results suggest that magnesium on the surface of AC-Mg is present in the form of MgO and

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Mg(OH)2. This explanation is also matched with quantitative analysis results in Table 3, which shows

high concentration of oxygen on the surface of AC-Mg. Comparison of the XPS peaks for adsorbent as prepared, after NH3 adsorption and subsequent NH3 desorption revealed more details about adsorption

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mechanism of NH3 on raw AC and AC-Mg adsorbent. In the case of AC, the peak intensity of O 1s

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slightly decreased when NH3 was adsorbed, and the peak intensity was not restored even after

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desorption of NH3 at 200 °C. On the other hand, in the case of AC-Mg, the O 1s peak decreases slightly

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after NH3 adsorption and the peak intensity was restored after desorption. Combining the previous results of the DRIFTS and the XPS analysis, it is concluded that NH3 is

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adsorbed on the surface of AC forming C-N bonding with replacing surface oxygen. The chemical bonding is strong enough to hold NH3 on the adsorbent sorbent even at temperature over 200 °C. On

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the other hand, most of the NH3 on the surface of AC-Mg are desorbed at temperature lower than 200 °C .

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The loaded Mg was confirmed to presents in the forms of MgO and Mg(OH)2 on the adsorbent surface and provides relatively weak adsorption sites for NH3 molecules. It is believed that Mg inhibits direct

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C-N bonding formation by shielding carbon surface.

4. Conclusions

Metal loaded activated carbons were synthesized and their NH3 adsorption-desorption characteristics were investigated. Among the metal loaded activated carbons, AC-Mg (Mg loaded activated carbon) showed the most favorable features for NH3 enrichment including the highest NH3 adsorption capacity,

the largest desorption amount of NH3, and high surface area and pore volume. AC-Mg showed 10 times higher adsorption capacity (6.34 mg NH3/g) than raw AC. The DRIFTS and the XPS analysis indicated that the differences in adsorption-desorption characteristics between raw AC and AC-Mg are mainly attributed to the enriched surface oxygen on the surface of AC-Mg that provide relatively weak adsorption sites for NH3 and the intervention effect of Mg preventing formation of strong C-N bonding.

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These two features of AC-Mg are believed to enable the adsorbent adsorb more NH3 with rather weak attraction force so that the adsorbent can be regenerated in relatively low temperature. Therefore, the

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high potentials of Mg loaded activation carbon was confirmed as a good adsorbent for NH3 enrichment

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process using temperature swing adsorption.

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Acknowledgement

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This work was conducted under the framework of the Research and Development Program of the

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of Chungnam National University.

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Korea Institute of Energy Research (KIER) (B8-2434). This work was also supported by research fund

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[35] C. Chen, S. Splinter, T. Do, N. McIntyre, Surf. Sci., 382 (1997) L652-L657.

A

CC E

PT

ED

M

A

N

U

SC R

[36] L. Yang, B. Luan, J. Electrochem. Soc., 152 (2005) C474-C481.

IP T

[34] H. Yao, Y. Li, A. Wee, Appl. Surf. Sci., 158 (2000) 112-119.

400

1st 350

IP T

250 200

AC AC-Ni AC-Zn AC-Fe AC-Cu AC-Mg AC-Cr

150

SC R

NH3 concentration [ppm]

300

100

0 0

5

10

15

20

25

30

35

40

45

50

55

60

M

A

N

Time (min)

U

50

ED

Figure 1. First breakthrough curves for raw AC and metal loaded ACs with 500 ppm influent NH3 under

A

CC E

PT

ambient pressure.

400

2nd 350

IP T

250 200

AC AC-Ni AC-Zn AC-Fe AC-Cu AC-Mg AC-Cr

150

SC R

NH3 concentration [ppm]

300

100

0 0

5

10

15

20

25

30

35

40

45

50

55

60

M

A

N

Time (min)

U

50

A

CC E

PT

under ambient pressure.

ED

Figure 2. Second breakthrough curves for raw AC and metal loaded ACs with 500 ppm influent NH3

100

Air

90 80

IP T

60 50 40 30 20 10

SC R

AC AC-Ni AC-Zn AC-Fe AC-Cu AC-Mg AC-Cr

0 0

100

200

300

400

U

Weight loss (%)

70

500 o

600

M

A

N

Temperature ( C)

A

CC E

PT

ED

Figure 3. Weight loss profiles of raw AC and metal loaded ACs in TGA.

700

800

0.024

AC AC-Ni AC-Zn AC-Fe AC-Cu AC-Mg AC-Cr

3

Incremental Pore Volume (cm /g)

0.020

IP T

0.016

0.012

SC R

0.008

0.000 10

20

30

40

50

60

70

Å

)

A

N

Pore Diameter (

U

0.004

A

CC E

PT

ED

M

Figure 4. BJH pore size distributions of raw AC and metal loaded ACs.

80

90

100

IP T SC R U N A M ED

A

CC E

AC-Cr .

PT

Figure 5. SEM images of (a)-(b) AC, (c) AC-Ni, (d) AC-Zn, (e) AC-Fe, (f) AC-Cu, (g) AC-Mg and (h)

IP T SC R U N A M

A

CC E

PT

ED

Figure 6. Mapping and EDX results of (a) AC, (b) AC-Cu, (c) AC-Mg and (d) AC-Cr.

50

100

M

IP T

A

N

U

SC R

AC AC-Ni AC-Zn AC-Fe AC-Cu AC-Mg AC-Cr

150

200 o

ED

Temperature ( C)

A

CC E

PT

Figure 7. NH3-TPD profiles of raw AC and metal loaded ACs.

250

300

IP T SC R U N A M ED PT

CC E

Figure 8. DRIFT spectra of the NH3 adsorption on the (a) raw AC and (b) AC-Mg under NH3+He flow at

A

room temperature.

IP T SC R U N A M ED

PT

Figure 9. DRIFT spectra of the NH3 desorption with increasing temperature on the (a) raw AC and (b)

A

CC E

AC-Mg under He flow.

IP T SC R U N A M ED

A

CC E

PT

Figure 10. XPS spectra of the (a) C 1s and (b) O 1s for raw AC and AC-Mg of before NH3 adsorption.

IP T SC R U N A M

Figure 11. XPS spectra of the before NH3 adsorption, after adsorption and after desorption state of (a-c)

A

CC E

PT

ED

O 1s of raw AC, (d-f) O 1s of AC-Mg and (g-i) Mg 2p of AC-Mg.

Table 1. NH3 adsorption and desorptiona capacity of the raw AC and metal loaded ACs (mg NH3/g)

2nd

3rd

desorptiona

AC

0.64

0.54

0.46

0.54

AC-Ni

4.29

3.75

3.69

3.33

AC-Zn

2.06

2.08

1.45

1.77

AC-Fe

2.05

2.45

2.82

AC-Cu

3.73

3.73

2.78

AC-Mg

6.03

6.34

AC-Cr

4.48

3.83

SC R

NH3-TPD test

N A M ED PT CC E A

2.50 3.52

5.84

5.59

3.21

4.01

U

a

IP T

1st

Table 2. Characteristics of the raw AC and metal loaded ACs

Pore volume (cm3/g)

Pore diameter (Å)

AC

873

0.49

22

AC-Ni

812

0.45

22

AC-Zn

775

0.44

22

AC-Fe

740

0.42

AC-Cu

747

0.43

AC-Mg

841

AC-Cr

714

SC R

22 23

0.48

23

0.41

23

U N A M ED PT CC E A

IP T

Surface area (m2/g)

Table 3. Binding energy and mass concentration determined by XPS quantitative analysis of the raw AC

Sample

Component

Binding energy (eV)

Mass conc. (%)

C 1s

284.8

95.86

O 1s

531.6

4.14

C 1s

284.8

96.31

O 1s

531.7

C 1s

284.8

O 1s

531.7

C 1s

284.8

74.35

O 1s

531.9

17.04

Mg 2p

50.2

8.61

U

and AC-Mg

284.8

76.6

532

15.38

50.1

8.02

C 1s

284.8

71.78

O 1s

532.2

18.31

Mg 2p

50.3

9.91

AC

after adsorption

before adsorption

SC R

after desorption

after adsorption

O 1s

A

CC E

PT

M

ED

after desorption

A

Mg 2p

N

C 1s AC-Mg

IP T

before adsorption

3.69

96.16 3.84