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An integrated dynamic and steady state method and its application on the screening of MoS2 nanosheet-containing adsorbents for Hg0 capture Haitao Zhao, Fan Hua, Gang Yang, Lu Lu, Chenghang Zheng, Xiang Gao, and Tao Wu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00099 • Publication Date (Web): 06 Feb 2018 Downloaded from http://pubs.acs.org on February 7, 2018

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An integrated dynamic and steady state method and its application on the screening of MoS2 nanosheet-containing adsorbents for Hg0 capture Haitao Zhao1, 2, 3, Hua Fan4, Gang Yang2,3, Lu Lu3, Chenghang Zheng1, Xiang Gao1,*, Tao Wu2, 3, * 1

State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, P. R. China.

2

Municipal Key Laboratory of Clean Energy Conversion Technologies, The University of Nottingham

Ningbo China, Ningbo 315100, P. R. China. 3

4

New Materials Institute, The University of Nottingham Ningbo China, Ningbo 315042, P. R. China School of Resources Environmental & Chemical Engineering, Nanchang University, Nanchang,

330031, P. R. China Corresponding author: [email protected], [email protected]

Abstract

In this research, an integrated dynamic and steady state (IDSS) method was developed to accelerate the discovery of new materials for the capture of Hg0, a pollutant that is associated with fossil fuel utilization and has significant impacts on health and the ecosystem. A suite of metal sulphides and MoS2-based binary metal sulphides were evaluated using this method. It was found that the existence of MoS2 nanosheets promoted the Hg0 removal efficiency of these metal sulphides. Among the MoS2-based metal sulphides studied in this research, Co-Mo-S and Cu-Mo-S exhibited excellent performance with an almost complete removal of Hg0 at low temperatures. The results are superior than their corresponding metal oxides and the MoS2-containing adsorbent, and are comparable to that of the commercial carbon-based adsorbent. Moreover, the working temperature windows for Hg0 1

ACS Paragon Plus Environment

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capture were found to be broader for the Mo-based binary metal sulphides than the corresponding metal oxides. The Co-Mo-S and Cu-Mo-S also showed better performance on Hg0 capture than other samples. It is proved that the IDSS approach is an effective and efficient method for the rapid screening of adsorbents for Hg0 capture, which could be applied in the development of adsorption materials for environmental applications. Keywords: MoS2 nanosheet; Hg0 capture; Dynamic state; Steady state; Hg0-TPSR. 1. Introduction Fossil fuel utilization related industries such as coal burning for power generation and industrial heating syngas utilization

6, 7

1-3

, petroleum burning and refining

4, 5

, and natural gas and

, are the major anthropogenic sources of mercury emission8,

which account for more than 25% of the global total 9. Among the three commonly seen forms of mercury, i.e., elemental mercury (Hg0), particulate bound mercury and oxidized mercury (Hg2+), Hg0 is the most dominant form of airborne mercury 10. It is extremely difficult to be captured because it is highly volatile in air, insoluble in water and thermodynamically stable at high temperatures 11. Recently, Minamata Convention on Mercury has officially come into force on 16th August, 2017, which is to control global anthropogenic mercury emissions

12

.

Therefore, there have been considerable interests worldwide in the development of novel adsorbents for Hg0 capture at fossil fuel utilization industries.

2


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Generally, there are two types of technologies for Hg0 capture, i.e. catalytic oxidation and adsorption

13

. It has been reported that Hg0 can be oxidized to Hg2+ over

different types of catalysts including modified selective catalytic reduction (SCR) catalysts

14

and catalysts based on noble metals

earth metals

18, 19

and modified fly ash

20

15, 16

, transition metals

7, 17

, rare

. However, heterogeneous catalytic

oxidation processes are effective only under specific conditions such as suitable operating temperatures, certain types of fuels utilized, the presence of sufficient HCl and the reliance on other air pollution control devices (APCDs) for the removal of oxidized mercury (HgO or HgCl2) 21-23, etc. Significant effort has also been made to develop suitable adsorbents for mercury 8, 13

capture at coal-fired power stations

. Among these adsorption-based

technologies, the activated carbon injection (ACI) system has been commercially deployed for mercury removal since 2005 24. It was found that the mercury removal capacity of activated carbon could be enhanced if it is impregnated with sulfur 25, 26, which is due to the high affinity of sulfur to mercury. However, the use of activated carbon for the adsorption of mercury could potentially compromise fly ash as a saleable by-product 27. It is therefore necessary to develop alternative non-carbonbased adsorbents, such as zeolite, Ag modified zeolites and MgO, for mercury emission control 27-32. Our previous evaluation of metal oxides and Mo-based binary metal oxides for Hg0 capture demonstrated that the presence of Mo species in the metal oxides promotes the capture of Hg0

19

. Recently, two-dimensional transition-metal dichalcogenides 3


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(2D-TMDs), which are of graphene-like structure, have attracted increasing attention due to their unique physical and chemical properties

33-36

. It was found that the

graphene-like MoS2 nanosheets (developed from traditional hydrodesulphurization catalysts) have excellent performance on Hg0 capture at low temperatures

36, 37

.

However, the potential of other metal sulphides and MoS2-based metal sulphides on Hg0 capture remain unexplored. Normally, the development of new materials for environmental applications is remarkably time-consuming. The initial screening method is therefore crucial and considerable efforts have therefore been devoted to develop methods for CO2 capture materials38,

39

, CO hydrogenation catalysts40, Zinc-based desulfurization

sorbents41 and so on. However, not much work has been conducted to develop methods for the screening of novel materials for mercury removal. The temperatureprogrammed desorption method has been applied in the study of activated carbon for mercury capture

44

. In addition, the Hg0-temperature-programmed surface

reaction (Hg0-TPSR) method was also developed to investigate the dynamic Hg0 capture performance under continuously increasing temperatures 19. In this study, the main focus was to develop a novel method for the rapid screening of adsrobents for Hg0 capture. An integrated dynamic and steady state (IDSS) approach was therefore developed based on the Hg0-TPSR method. Six metal sulphides and their respective MoS2-based binary metal sulphides were evaluated using this IDSS approach in terms of their instant Hg0 removal efficiency, working

4


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temperature window, Hg0 recovery capability and steady-state Hg0 capture behaviours. 2. Materials and methods 2.1. Preparation of samples The graphene-like MoS2 nanosheets containing binary metal sulphides over a commercial γ-Al2O3 support (V-SK Co., Ltd., surface area of 188 m²/g, size range: 1.18 mm ≤ x ≤1.70 mm) were prepared using a combination of incipient wetness impregnation (IWI) and sulphur-chemical vapour reaction (S-CVR) method, the detailed procedure was described elsewhere (NH4)6Mo7O24•4H2O,

Cr(NO3)3•9H2O,

36, 45

. The metal salts used were

Mn(NO3)2•4H2O,

Co(NO3)2•6H2O,

Cu(NO3)2•3H2O, Ce(NO3)3•6H2O (analytical grade, Sinopharm Chemical Reagent Co, Ltd.). During the impregnation step, all the metal precursors was impregnated into the pores, the amount of which was determined based on the pore volume of the γAl2O3. The impregnated solid support was then dried in an oven at 120 °C for 24 h and calcined in air at 520 °C for 12 h. The metal oxides therefore prepared were named as “M-O”. To prepare binary metal oxides, further incipient wetness impregnation step was carried out to load another metal element onto the Mo-O sample prepared previously. The binary metal oxides were then named as “X-Mo-O”. To prepare the metal sulphides and Mo-based binary metal sulphides, approximately 18 g of metal oxide was loaded in a fixed-bed reactor that was operated under atmospheric pressure. In order to remove moisture and other adsorbed impurities, 5


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the sample was pre-heated to 500°C for 1 h with nitrogen purge at a flow rate of 100 ml/min. The sample was then in-situ sulphided with a gas mixture of H2S (10 vol.%) and H2 (90%) at a flow rate of 20 ml/min at 400°C for 3 h, followed by cooling down to room temperature in N2 atmosphere to form X-Mo-S. Detailed schematic procedure is described in Figure 1. 2.2. Dynamic-state screening method Firstly, the metal sulphides and MoS2-based binary metal sulphides were studied adopting the dynamic state approach (Hg0-TPSR). The experiment together with the qualitative and quantitative analyses were carried out using a dedicated experimental rig that equipped with a mercury generator (Tekran 3310, USA) and a mercury analysis system (Tekran 3300RS, USA) as described in our previous research 19

.

During the qualitative analysis, the characteristics of Hg0 capture process were extracted from the profiles generated from the Hg0-TPSR experiment. Quantitative analysis of the Hg0-TPSR experimental data was conducted to study the instant Hg0 removal efficiency, the adsorption and desorption of Hg0 on the surface of the adsorbents. The maximum instant Hg0 removal efficiency (∆X max) was calculated using following equation. ∆X =

[ ] [ ] [ ]

× 100

(1)

6


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The areas of adsorption region (Sa) and desorption region (Sd), which correspond to the areas below/above the baseline concentration of Hg0, were obtained via the integration of the change of mercury concentration against time.

S = ()

(2)

where t1 is the starting time of adsorption/desorption, min; t2 is the ending time of adsorption/desorption, min; f(t) is the change of Hg0 concentration against time; S is the area determined using the integration method, min⋅µg⋅m-3. The amount of Hg0 absorbed (Ma) and desorbed (Md) were determined by using Equation (3). =S

!

(3)

"

where M is the amount of mercury being adsorbed/desorbed per unit mass of the Hg0 capture material, µg/g, F is the gas flow rate, L/min; W is the mass of Hg0 capture materials, g. 2.3. Steady-state screening method During the steady-state analysis, a sample was evaluated under the same temperature (50°C) and Hg0 concentration (30 μg/m3) in N2 for at least 180 min after adsorption reached steady state. Moreover, in order to eliminate any experimental error, the metal sulphides and their corresponding MoS2-based binary metal sulphides, each with a weight of approximately 2 g, were tested simultaneously in a dual-reactor system to allow both samples experience the same testing conditions. 3. Results & discussions

7


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3.1. Dynamic study of adsorption behaviour In order to characterise and confirm the targeted MoS2 nanosheet structure in the prepared adsorbents, XPS, SEM, TEM and HRTEM techniques are applied. Firstly, the stable phases of MoS2 in the prepared adsorbents can be found from the Mo 3d and S 2p XPS spectra as shown in Figure 2. The Mo 3d spectrum of all samples exhibits two contributions, 3d5/2 and 3d3/2 (due to spin–orbit splitting), where located at 228.8, 232.8 eV, respectively. It is the evidence of the Mo4+ metal sulphide formed on the surface. Moreover, the peak at the binding energy (BE) of approximately 162.6 eV is assigned to the S 2p3/2 spectrum. These results clearly evidence the presence of MoS2 in the prepared adsorbents. Morphology of the adsorbent was further characterized using SEM, TEM and HRTEM in different scales (2 μm, 50 nm and 2 nm) as shown in Figure 3. SEM imaging shows that the as-deposited films tend to be layered shapes in Figure 3 (a) and (b) for Mo-S and Co-Mo-S (as an example), respectively. The layer structures and characteristic patterns were further identified by TEM and HRTEM in Figure 3 (c) - (f). In the HRTEM images, regular lattice spacings of 0.27 nm can be clearly observed. It is the characteristic feature of (001) basal plane of two-dimensional hexagonal MoS2 crystal structure. Based on this observation, the schematic structure of the MoS2 nanosheet was proposed and illustrated inside the Figure 3 (e) and (f). Therefore, the thin graphene-like MoS2 nanosheet structures are confirmed. The result is consistent with the recent characterization of the un-supported MoS2 ultrathin nanosheets35.

8


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The adsorption mechanism of the MoS2 nanosheet-containing adsorbent for mercury removal has been revealed by both experimental and DFT theoretical studies in our recent publication37, which showed that defects in MoS2 nanosheets play important role in the adsorption of elemental mercury. The dynamic analysis results of the MoS2 nanosheets containing adsorbent and the other six metal sulphides along with the support γ-Al2O3 (after same S-CVR process) were plotted in Figure 4. The characteristic features for each curve were interpreted in Table 1. Figure 4 and Table 1 illustrated that metal sulphides showed better performance in the adsorption of Hg0 at low temperature region (i.e. T

a, peak region)

from 25°C to a higher temperature between 50 and 173°C. Within this temperature

region, the efficiency (µmax) was maintained at above 97 % for all samples except CeS and Al-S. The breadth of the changes in T a, peak region was found to be in the order of Cr-S (25 - 54°C) < Ce-S (25 - 61°C) < Co-S (25 - 137°C) < Mo-S (25 - 141°C) < Cu-S (25 171°C) < Mn-S (25 - 173°C). This suggests that the working temperature window for the samples, such as Co-S, Mo-S, Cu-S and Mn-S, were more than 100°C but less than 50°C for Cr-S and Ce-S. The broader working temperature window could be an additional indicator for the evaluation of the performance of the adsorbents. For these metal sulphides, the calculated absolute adsorption area (S a) and the amount of Hg0 adsorbed (M a) are illustrated in Table 2, which were extracted from Figure 4 by quantitative analysis. These results enable the screening of the samples by identifying Hg0 adsorption ability, which was found to be in the order of Cu-S > Mo-S > Mn-S > Cr-S > Co-S > Ce-S. 9


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It is obvious that the adsorption areas for all of the metal sulphides were greater than those for their corresponding metal oxides that were reported in our recent publication19. The amount of Hg0 captured by Cr-S, Mn-S, Co-S, Cu-S, Mo-S and Ce-S were 1.3, 3.5, 3.6, 8.8, 29.3 and 2.6 times more than those of their corresponding metal oxides19, respectively. It was observed that Hg0 capture capabilities were significantly enhanced when the samples were transformed from oxidised state to sulphided state, especially for Mo-S sample. Based on the screening of individual metal sulphides, the Hg0 capture performance of these six MoS2-based binary metal sulphides was evaluated. Figure 5 illustrated the dynamic behaviour of these binary metal sulphides, while the key parameters extracted from these profiles were summarized in Table 3 and Table 4. It was found that Mo-based binary metal sulphides (Cr-Mo-S, Mn-Mo-S, Co-Mo-S, Cu-Mo-S and Ce-Mo-S) showed excellent performance and achieved almost complete removal of Hg0 with different effective temperature regions (25 – 170°C, 25 – 175°C, 25 – 145°C, 25 – 185°C and 25 - 168°C, respectively). From Table 3, it is clear that the effective temperature regions for these metal sulphides were broader compared with the regions for individual metal sulphides (as shown in Table 1). From Table 4, it can be seen that the absolute area of Hg0 adsorption for all samples was above 5000 min⋅µg⋅m-3 and the amount of Hg0 captured was more than 3.8 µg g-1. This suggested that the existence of MoS2 had significant positive impacts on Hg0 removal efficiency as well as working temperature window for the MoS2-based binary metal sulphides. 10


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Different from carbon-based adsorbents, it was reported that these adsorbents released mercury when temperature was raised above 135°C

46

. Compared with

carbon-based sorbents, the MoS2 nanosheet-containing samples are of working temperature windows that are much broader than that of Mo-based binary metal sulphides, which have good potential to be alternative non-carbon-based adsorbents for Hg0 capture. To further explore the potentials, Hg0 desorption and steady-state adsorption behaviours are further investigated in this study. 3.2. Dynamic desorption behaviour More detailed information was extracted from Figure 4 and summarized in Table 1. it is clear that Ce-S started to release Hg0 (as the concentration of Hg0 at the outlet was greater than its concentration at the inlet) when the temperature reached 100°C, while the other metal sulphides started to release Hg0 at temperatures higher than 160°C. For example, Co-S started to desorb at 160°C, whilst Mn-S desorbed at 230°C. When temperature was raised to a higher level, there was a greater amount of Hg0 desorbed. It is evident that most of the samples showed desorption peaks (T d, peak) at temperatures greater than 275°C except Ce-S and Al-S. However, the T d, peak of Co-S and Cu-S samples had sharp peaks at relative low temperatures around 200°C. This suggested that for Co-S and Cu-S, the release of Hg0 adsorbed was quicker and easier when compared with other samples. This property could be benefit for the recovery of Hg0 from the spent samples. Table 2 also summarized the calculated desorption area (S d) and the amount of Hg0 desorbed (M d) together with the ratio of desorption over adsorption (R d/a). It should 11


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be pointed out that more than 3 µg/g Hg0 was desorbed from Mo-S, Cr-S, Mn-S, Co-S and Cu-S with the R

d/a

above 85%. Among the samples, Mo-S again achieved the

highest desorption-adsorption ratio (98.5%). These results suggested that the metal sulphides not only demonstrated high effectiveness in Hg0 removal, but also had the potential to recover the captured Hg0 efficiently since the ratios of desorption over adsorption were relative high. Furthermore, desorption of Hg0 from adsorbents was further investigated for the five MoS2-based binary metal sulphides, which is shown in Figure 5. It can be seen that all these materials showed similar dynamic behaviour in desorption except CuMo-S. The Td,peak was found to be in the order of Co-Mo-S < Ce-Mo-S < Cu-Mo-S < CrMo-S < Mn-Mo-S. Cu-Mo-S reached the highest peak within a narrow temperature region. Moreover, for Co-Mo-S and Cu-Mo-S, there was almost the same amount of Hg0 being desorbed with an Hg0 removal efficiency greater than 98.5% as shown in Table 4. The Co-Mo-S and Cu-Mo-S also had lower T d,0 (both below 197 °C) and T d, peak (261°C

and 274°C) values and higher R d/a (98.9% and 98.6%, respectively) values,

which suggested that the Co-Mo-S and Cu-Mo-S might have a better performance on Hg0 recovery than other samples. Based on dynamic state study, it can be concluded that the capacity of Hg0 adsorption and desorption for these MoS2-based binary metal sulphides was enhanced by the presence of MoS2 nanosheets when compared with the results of individual metal sulphides, especially for Co-Mo-S and Cu-Mo-S. 3.3. Steady-state adsorption behaviour 12


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After the primary stage screening using dynamic state analysis, these twelve metal sulphides were selected for the secondary screening to find out materials with better potential for Hg0 capture. The samples studied were Mo-S, Al-S, Cr-S, Cr-Mo-S, Mn-S, Mn-Mo-S, Cu-S, Cu-Mo-S, Ce-S, Ce-Mo-S, Co-S and Co-Mo-S. In this study, these samples were further evaluated in terms of their Hg0 capture performance at 50°C in N2 for at least 180 min with a Hg0 concentration of 30 μg/m3. The metal sulphides and their corresponding MoS2-based binary metal sulphides were tested in a dualreactor system to allow both samples experiencing exactly the same conditions. The parallel screening results were illustrated in Figure 6. It can be seen that the average Hg0 removal efficiency of the Al-S sample was below 8% whilst that of Mo-S sample was above 90%. Moreover, the Hg0 removal efficiency decreased for Al-S sample but there was a small increase for Mo-S sample within the 180 min test. These results indicated that the support, γ-Al2O3, had little effect on Hg0 capture even after S-CVR process. The Hg0 capture effectiveness of these sulphides can therefore be attributed to the presence of MoS2. Furthermore, Figure 6 (b) - (f) illustrate the performance of Hg0 capture for the other five elements and their corresponding MoS2-based binary metal sulphides in the 180 min tests. These results provided additional information on Hg0 removal efficiency under steady state rather than dynamic state. It can be seen from Figure 6 (b) - (f) that Ce-S, Mn-S and Cr-S initially reached almost 100% Hg0 removal efficiency. However, the efficiency was only 8, 75 and 90%, respectively, at the end of the 180 min test. This means that the Hg0 uptake capacity 13


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of these three metal sulphides was not high, especially for Ce-S. Among these individual metal sulphides, Co-S, Cu-S and Mo-S maintained a high removal efficiency during the entire test, which suggested that their Hg0 adsorption capacity was greater than that of the others, although all of them had a similar high removal efficiency during the dynamic state analysis. Figure 6 also demonstrated that the efficiency of all the Mo-based binary metal sulphides was above 98%, which was higher than that of the individual metal sulphides. In particular, the Co-Mo-S and Cu-Mo-S exhibited an excellent performance with an almost complete removal of Hg0. The results are superior than the corresponding metal oxides19 and the individual graphene-like MoS2 nanosheet adsorbents37, and are comparable to that of the commercial carbon-based adsorbent46, and other non-carbon-based adsorbents such as modified zeolites30, 31 and manganese oxides

. The high Hg0 capture efficiency was attributed to the

32

presence of the graphene-like MoS2 nanosheets in those Mo-based binary metal sulphides, which require further study to fully understand their potential in mercury removal in different applications. More importantly, it is proved that the screening method could also be applied to accelerate the discovery of candidate materials for Hg0 capture. 4. Conclusions In this paper, an integrated dynamic and steady-state approach was developed to evaluate metal sulphides and MoS2-based binary metal sulphides for Hg0 removal. It is found that the presence of MoS2 nanosheets promoted the performance of metal 14


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sulphides Hg0 capture. Among the MoS2-based metal sulphides studied, Co-Mo-S and Cu-Mo-S exhibited excellent performance with an almost complete removal of Hg0 from the gas mixture, which are superior than the corresponding metal oxides and the individual graphene-like MoS2 nanosheet adsorbents, are comparable to that of the commercial carbon-based adsorbent. Moreover, the working temperature windows of these adsorbents became broader for the Mo-based binary metal sulphides (up to 185°C for Cu-Mo-S sample). The Co-Mo-S and Cu-Mo-S also had lower T d,0 (both at 197 °C) and T d, peak (261°C and 274°C) and higher R d/a (98.9% and 98.6%, respectively), which showed a better performance on Hg0 recovery than any other samples. It can be concluded that this IDSS approach is an effective and efficient method for the rapid screening of candidate materials for Hg0 capture as well as for other environmental applications. Acknowledgement Following funding bodies are acknowledged for partially sponsoring this research: National Key R&D Program of China (2017YFB0603202, 2017YFB0602601 and 2017YFC0210400), Young Scientist Programme of Natural Science Foundation of China (51706114), Ningbo Natural Science Foundation (2017A610060), China Postdoctoral Science Foundation (2016M601942). References 1.

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Oxide/Titania Materials for Removal of NO x and Elemental Mercury from Flue Gas. Energy & Fuels 2008, 22, (4), 2299-2306.

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the catalytic oxidation of elemental mercury. Fuel 2015, 158, 891-897. 16.

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excellent and durable catalyst for catalytic oxidation of elemental mercury. RSC Advances 2015, 5, (39), 30841-30850. 17.

Zhao, B.; Liu, X.; Zhou, Z.; Shao, H.; Xu, M., Catalytic oxidation of elemental mercury by

Mn–Mo/CNT at low temperature. Chemical Engineering Journal 2016, 284, 1233-1241. 18.

Li, H.; Wu, S.; Wu, C.-Y.; Wang, J.; Li, L.; Shih, K., SCR Atmosphere Induced Reduction of

Oxidized Mercury over CuO–CeO2/TiO2 Catalyst. Environmental Science & Technology 2015, 49, (12), 7373-7379. 19.

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programmed surface reaction and its application on the investigation of metal oxides for Hg0 capture. Fuel 2016, 181, 1089-1094. 20.

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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Schematic procedure for sample preparation

20


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Page 21 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 2. XPS spectra (Mo 3d and S 2p) of MoS2-based binary metal sulphides

21


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

Page 22 of 29

0 1 2

2μ

2μ

3 4

(c)

(d)

5 6 7 8 9 10

(e)

(f)

11 12 13 14 15

2 nm

2 nm

16 17

18

Figure 3. SEM, TEM and HRTEM (with the inside schematic structure) morphologies for Mo-S

19

(a, c and e, respectively) and Co-Mo-S (b, d and f, respectively) as an example

20

22


Page 23 of 29

Al-S Mo-S Cr-S Mn-S Co-S Cu-S Ce-S

180

Hg0 concentration(µ µ g/m3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

150 120 90 60 Baseline 30 0 100

21 22

200

300

400

500

Temperature (°°C)

Figure 4. TPSR profiles of metal sulphides

23


Energy & Fuels

120

Cr-Mo-S Mn-Mo-S Co-Mo-S Cu-Mo-S Ce-Mo-S

100 Hg0 concentration (µ µg/m3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 29

80 60 Baseline

40 20 0 0

23 24

100

200 300 Temperature (°°C)

400

500

Figure 5. TPSR profiles of the Mo-based binary metal sulphides

24


25 20 15 10 5

35

Hg 0 concentration (µ µ g/m 3)

0

(c)

30

(e)

Al-S Mo-S

0

50

25 20 15 10 5 0

0

25

50

30

75 100 125 150 175 200 Time (min)

Mn-S Mn-Mo-S

25

Cu-S Cu-Mo-S

20 15 10 5 0

25

50

75 100 125 150 175 200 Time (min)

Cr-S Cr-Mo-S

20 15 10 5 0

35 30

(f )

30

25

(d)

75 100 125 150 175 200 Time (min)

35

0

25 26 27

25

35


30

(b)

Hg 0 concentration (µ µ g/m 3 )

35


(a)

Hg0 concentration (µ µ g/m 3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Hg 0 concentration (µ g/m 3)

Page 25 of 29

0

25

50

75 100 125 150 175 200 Time (min)

25 Co-S Co-Mo-S

20 15 10 5 0

0

25

50

75 100 125 150 175 200 Time (min)

35 30 25

Ce-S Ce-Mo-S

20 15 10 5 0

0

25

50

75 100 125 150 175 200 Time (min)

Figure 6. Performance of metal sulphides vs MoS2-based binary metal sulphides (50°C in N2, Hg0 concentration: 30 μg/m3): (a) Al-S and Mo-S, (b) Cr-S and Cr-Mo-S, (c) Mn-S and Mn-Mo-S, (d) Co-S and Co-Mo-S, (e) Cu-S and Cu-Mo-S and (f) Ce-S and Ce-Mo-S.

25


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

28

Page 26 of 29

Table 1 Characteristic features of metal sulphides Samplea

Ta, peak region

µmax

Td, 0

Trd, peak

Td, peak

°C

%

°C

°C

°C

Al-S

25-55

50.2

74

126

150

Mo-S

25 - 141

100

215

265

309

Cr-S

25 - 54

98.6

194

215

281

Mn-S

25 - 173

97.5

187

225

257

Co-S

25 - 137

99.8

170

182

193

Cu-S

25 - 171

100

197

209

227

Ce-S

25 - 61

52.1

99

138

155

29

26


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30

Energy & Fuels

Table 2 Adsorption-desorption capacity of the individual metal sulphides

Sa

Sd

Ma

Md

R d/a

min⋅µg/m3

min⋅µg/m3

µg/g

µg/g

%

Al-S

1202.75

1181.1

0.90

0.88

98.2

Mo-S

5483.3

5398.6

4.11

4.04

98.5

Cr-S

4941.8

4237.8

3.70

3.17

85.8

Mn-S

5139.8

4939.1

3.85

3.70

96.1

Co-S

4912.6

4333.2

3.68

3.24

88.2

Cu-S

6129.2

5880.7

4.59

4.41

95.9

Ce-S

2485.5

2035.6

1.86

1.52

81.9

Sample

31

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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

32

Page 28 of 29

Table 3 Characteristics of the MoS2-based binary metal sulphides

Ta, peak region

µmax

Td, 0

Trd, peak

Td, peak

°C

%

°C

°C

°C

Cr-Mo-S

25 - 170

99.5

219

235

282

Mn-Mo-S

25 - 175

99.9

228

244

299

Co-Mo-S

25 - 145

99.9

197

204

261

Cu-Mo-S

25 - 185

100

197

245

274

Ce-Mo-S

25 - 168

99.9

213

218

268

Sample

33

28


Page 29 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

34

Energy & Fuels

Table 4 Adsorption-desorption capacity of the MoS2-based binary metal sulphides

Sa

Sd

Ma

Md

R d/a

min⋅µg/m3

min⋅µg/m3

µg/g

µg/g

%

Cr-Mo-S

5113.8

4840.0

3.83

3.63

95.0

Mn-Mo-S

5670.3

5441.1

4.25

4.08

96.0

Co-Mo-S

5068.7

5013.4

3.80

3.76

98.9

Cu-Mo-S

5747.5

5668.7

4.31

4.25

98.6

Ce-Mo-S

5598.0

5361.8

4.19

4.02

95.8

Sample

35

29


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