外文翻譯---關(guān)于利用ceo2γ-al2o3來(lái)脫除氣態(tài)汞的實(shí)驗(yàn)研究（英文）

1、Published: May 25, 2011r 2011 American Chemical Society 2939 dx.doi.org/10.1021/ef200144j | Energy Fuels 2011, 25, 2939–2944ARTICLEpubs.acs.org/EFExperimental Study of Gaseous Elemental Mercury Removal with CeO2/γ-Al2O3X

2、iaoyu Wen,?,? Caiting Li,*,?,? Xiaopeng Fan,?,? Hongliang Gao,?,? Wei Zhang,?,? Ling Chen,?,?Guangming Zeng,?,? and Yapei Zhao?,??College of Environmental Science and Engineering, and ?Key Laboratory of Environmental Bio

3、logy and Pollution Control (Ministry of Education), Hunan University, Changsha 410082, People’s Republic of ChinaABSTRACT: The Hg0 removal ability of γ-Al2O3 impregnated with cerium dioxide (CeO2/γ-Al2O3) was tested in t

4、he experimental flue gas of N2 þ O2 þ NO þ SO2 þ H2O. Brunauer?Emmett?Teller (BET), X-ray diffractogram (XRD), and thermogravimetric (TG) analyses were used to characterize the samples. The effects of

5、 CeO2 loading values, reaction temperatures, reaction time, and individual flue gas components, including SO2, NO, O2, and H2O(g), on the Hg0 removal efficiency were investigated. The results show that the Hg0 removal ef

6、ficiency of γ-Al2O3 can be greatly improved by CeO2 and, at a test temperature of 350 ?C, the best suitable loaded mass percentage of CeO2 is 9%. In the temperature range from 150 to 350 ?C, the Hg0 removal efficiency us

7、ing CeO2/γ-Al2O3 increases with the increase of the temperature and then decreases above 350 ?C, except virgin γ-Al2O3. In addition, the presence of O2 and NO have positive effects on the Hg0 removal efficiency, while th

8、e presence of SO2 and H2O inhibited it. Furthermore, prolonging the reaction time had a small negative effect on the Hg0 removal performance, indicating that the catalyst of CeO2/γ-Al2O3 possesses thermostability.1. INTR

9、ODUCTIONMercury has been a well-known environmental pollutant for several decades, because it has detrimental effects on human health and the environment because of its volatility, persistence, bioaccumulation, and toxic

10、ity.1?3 Consequently, mercury emis- sions are receiving more and more attention over recent years. The United Nations Environment Program4 proposed a global legally binding paper on mercury emissions in 2010, and global

11、mercury pollution control is becoming a topic of increasing legislative and scientific focus. According to refs 5?7, there are mainly three forms of mercury in coal-fired flue gas: elemental mercury (Hg0), oxidized mercu

12、ry (Hg2þ), and particle-bound mercury (Hgp). Different forms of mercury have different physical and chemical properties. Specifically, Hg2þ is water-soluble and can be removed by the wet flue gas desulfurizatio

13、n(WFGD) system;Hgp canbecaptured by a dust removal device, e.g., electrostatic precipitators (ESPs). How- ever, in terms of Hg0, it is insufficiently captured because of its high volatility and low solubility in water. H

14、ence, the study on Hg0removal from flue gas is becoming a scientific focus. Several methods, such as the particulate adsorption method, oxidation? reduction method, and chemical sedimentation method, have been proposed f

15、or control of Hg0 emissions and evaluated from bench to pilot scale in the past few decades.8?11 Among those schemes, the major drawbacksof the particulate adsorbent are high costs, poor capacity, narrow temperature rang

16、e of application, and slow regeneration and adsorption rates,12 and therefore, the oxidation?reduction method exhibits a promising future. In this method, the catalyst is the most important element because it plays a dom

17、inant role in the operating costs and Hg0 removal performance. At present, many catalysts, such as V2O5/AC, MnO2/AC, and Fe2O3/TiO2, have been used in the oxidation?reductionmethod and proven to be effective for Hg0 remo

18、val.13?16 However, it was seldom reported that CeO2/γ-Al2O3 was used as a catalyst in the Hg0 oxidation?reduction or capture process. As reported, cerium oxide (CeO2), as a nontoxic, abundant, and inexpensive rare earth

19、material, attracted considerable attention for its potential application as fast ion conductors, oxygen-storage capacitors, catalysts, ultraviolet (UV) blockers, and polishing materials.17?19Most importantly, it was also

20、 reported that CeO2 can enhance the Hg0 removal efficiency of many catalysts.20,21 Nevertheless, pure ceria has poor thermal stability, and it undergoes a rapid sintering at higher temperatures, thereby losing oxygen sto

21、rage capacity (OSC), which would lead to the deactivation of the catalysts. Therefore, many efforts have been devoted to the chemical synthesis of metal oxides impregnated with CeO2. The mixing of two different oxides of

22、fers an opportunity not only to improve the performance of the involved metal oxide but also to form new stable compounds that may lead to totally different physicochem- ical properties and catalytic behavior from the in

23、dividual compo- nents.22 γ-Al2O3 has important applications as an industrial catalyst support, catalyst, adsorbent, or ceramic raw material, because of its low costs, high surface area and porosity, good thermal stabilit

24、y, high mechanical strength, and extensive variability of acid?base properties.23?26 Hence, the major objective of present study is to performanexperimentalstudytoinvestigatethe Hg0removalusing CeO2 supported by γ-Al2O3

25、(CeO2/γ-Al2O3) as the catalyst. Experimental studies were carried out on a lab-scale fixed-bed system. The simulated flue gas system included N2, O2, SO2, NO, H2O, and gaseous Hg0. During the course of the study, differe

26、nt operating conditions, including loading values of CeO2, reactionReceived: January 25, 2011Revised: May 24, 20112941 dx.doi.org/10.1021/ef200144j |Energy Fuels 2011, 25, 2939–2944Energy & Fuels ARTICLEcomponent, Ce

27、O2, is impregnated on the surface of γ-Al2O3 and blocked its pores.28Figure 2 shows the XRD patterns of virgin γ-Al2O3, 6% CeO2/ γ-Al2O3, and 9% CeO2/γ-Al2O3. The peaks at the ranges of 2θ = 36?40?, 44?48?, and 65?70? in

28、 the XRD pattern are corre- sponding to the characteristic peaks of γ-Al2O3, which can be detected in these three samples. Furthermore, there is no CeO2 characteristic peak for 6% CeO2/γ-Al2O3. According to the monolayer

29、 dispersion theory,29 an oxide like CeO2 has a trend of spontaneous dispersion on the carrier surface and forms a monolayer or sub-monolayer. This is because, when the oxide content is in the range of the threshold value

30、, the oxide is in a monolayer dispersion state and, when the content of oxide is more than the threshold value, the oxide is in a crystalline phase. The XRD pattern of 9% CeO2/γ-Al2O3 shows a weak crystal phase of CeO2,

31、powerfully indicating that the surface of γ-Al2O3 is occupied by CeO2. TG analyses of fresh CeO2/γ-Al2O3 and 9% CeO2/γ-Al2O3, which was used at 350 ?C in the presence and absence of Hg0 in the flue gas, are shown in Figu

32、re 3. There is a quick mass loss asthe temperature increases up to 200 ?C for the three curves, which corresponds to the evaporation of adsorbed water. As for the TG curve of used 9% CeO2/γ-Al2O3 in the presence of Hg0in

33、 the flue gas, the small weight loss that occurred at 400 ?C can be ascribed to HgO.30 As the pyrolysis temperature increases to 450 ?C, the weight losses of used 9% CeO2/γ-Al2O3, which was used at 350 ?C in the presence

34、 and absence of Hg0 in the flue gas, can be attributed to the decomposition of Ce(SO4)2 and their weight loss at 750 ?C can be ascribed to the decomposition of Ce2(SO4)3 according to the related research.313.2. Effects o

35、f the Loading Value and Reaction Tempera- ture. Figure 4 presents the relationship between the Hg0 removal efficiency and CeO2 loading value supported on γ-Al2O3 at different reaction temperatures (reaction time = 1 h).

36、As shown in this figure, γ-Al2O3-loaded 9% CeO2 shows significantly higher Hg0 removal efficiency. At the temperature of 350 ?C, with the loading value of CeO2 changing from 0 to 9 wt %, Hg0removal efficiency increases f

37、rom 45.36 to 86.76%, which indicates that CeO2 has an obvious accelerative effect on Hg0removal. Figure 3 illustrates that HgO is the major product of the Hg0 removal reaction over CeO2/γ-Al2O3, indicating that CeO2 can

38、catalyze the oxidation reaction of Hg0.19 The processes can be described as follows: First, Hg0 in the flue gas collides with the catalyst and is adsorbed onto its surface. Then, the adsorbed Hg0is oxidized by the active

39、 constituent on the sample surface, leading to the formation of Hg2þ presented as HgO. Therefore, the more the CeO2 loading value, the higher the Hg0 removal efficiency of CeO2/γ-Al2O3. However, the Hg0 removal effi

40、- ciency does not enhance consistently but decreases when the CeO2 loading value increases above 9 wt %. Especially with a loading value of 15 wt %, the Hg0 removal efficiency decreases to 78.17%. The possible reason can

41、 be ascribed to the fact that the surface area, total pore volume, and pore size of CeO2/γ-Al2O3 decrease with the increase of CeO2, as shown in Table 1. The decrease of the surface area prevents the valid collision betw

42、een Hg0 and CeO2/γ-Al2O3.32 Although CeO2 can promote the Hg0removal, its positive effect is weaker than its side effect when the CeO2 loading is higher than 9 wt %. Therefore, the loading valueFigure 2. XRD comparison b

43、etween samples of virgin γ-Al2O3, 6% CeO2/γ-Al2O3, and 9% CeO2/γ-Al2O3.Figure 3. TG analyses of the samples.Figure 4. Relationship between the Hg0 removal efficiency and CeO2 loading value supported on γ-Al2O3 at differe