New Cuprous Adsorbent Prepared by a Bioreduction Method for SO2

Oct 17, 2008 - A new cuprous adsorbent was prepared by bioreduction method with biomass R08 and its desulfurization ability and regenerative property ...
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Ind. Eng. Chem. Res. 2008, 47, 8888–8893

New Cuprous Adsorbent Prepared by a Bioreduction Method for SO2 Removal at Low Temperature Lishan Jia,*,† Hao Song,† Qingbiao Li,† Weiping Fang,‡ Yong Tang,† Jing Gao,† and Peng Zhang† Department of Chemical Engineering and Biochemical Engineering and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen UniVersity, Xiamen 361005, Fujian, China

A new cuprous adsorbent was prepared by bioreduction method with biomass R08 and its desulfurization ability and regenerative property at low temperature were studied. The results indicated that the amount of SO2 adsorbed on the adsorbent was lower than that on Cu/γ-Al2O3 prepared by chemical method at low temperature; however, it can be easily regenerated and the regenerative adsorbent still has a good SO2 adsorption ability, higher than 87% of that in fresh adsorbent after six regenerations. XPS and FTIR analysis showed that biomass can reduce Cu2+ to Cu+ by aldose and keep the valence of copper exposed to O2 and H2O atmosphere. Furthermore, SO2 is adsorbed on the sorbent with chemical complexation bonds so that it can be desorbed by increasing temperature which is different from γ-Al2O3, Cu(II)/γ-Al2O3 and Cu(I)/γ-Al2O3 that sulfate species are formed. 1. Introduction SO2 emission from the combustion of fossil fuels, such as coal and oil, can cause severe environmental pollution, leading not only to environment degradation but also to economic damage and human health hazard as well. Therefore, control of SO2 emissions has become increasingly stringent all over the world and has resulted in national and regional initiatives to reduce its emissions. The technologies developed for the control of emission of SO2 from the flue gas can be categorized into dry and wet processes. Among all the state-of-the-art technologies, wet flue gas desulfurization (FGD) is now the most widely commercially applied process. Although the wet process has a high efficiency in removing SO2, it has a number of disadvantages, mainly the large space required for installation, the large volume of water required, and high capital and operating expenses.1 This deficiency makes the process inapplicable wherever the water reserves are scant, especially when the water resource scarcity is becoming one of increasingly critical issues worldwide. In contrast, dry FGD offers a simpler alternative method to the wet FGD. Some well-proven techniques for SO2 removal are based on the catalytic oxidation of SO2 in the presence of catalysts, or the neutralization of SO2 with alkali and alkaline earth metals to produce the salts of inorganic acids. In the former process, CuO or other metal oxide supported on porous materials2-8 have been frequently used in dry desulfurization processes. Although sorbents have a high capacity for SO2 adsorption, huge and costly heat exchangers are needed to keep the catalysts’ efficiency and the sorbents are difficult to be regenerated. In the latter process, hydrated lime reacting with siliceous materials such as fly ash, diatomaceous earth, and silica9-15 are widely used to remove SO2 at low temperature. However, the removal efficiency of hydrated lime is low, the adsorbents are difficult to be regenerated, and it results in huge waste-product generation. Given this situation, the effort to develop new sorbents of high efficiency, low cost, excellent * To whom correspondence should be addressed. E-mail: Jials@ xmu.edu.cn. Tel.: 086-592-2188283. Fax: 086-592-2184822. † Department of Chemical Engineering and Biochemical Engineering. ‡ Department of Chemistry.

regenerative performance, and for further development of relatively low temperature dry FGD process is of urgent necessity. In the last decades, the technology of adsorption separation via weak chemical bonds such as chemical complexation has been widely studied. For example, the adsorbent CuCl/γ-Al2O316 has been used in the separation and purification of CO in industry; Yang et al.17–19 have developed a π-complexation adsorbent for desulfurization of diesel fuels, etc. As suggested by King,20 chemical complexation bonds are generally stronger than van der Waals interactions, yet weak enough to be reversible by modest changes in temperature or pressure. Therefore, tremendous opportunities exist for developing new sorbents and applications in separations by using weak chemical bonds, including various forms of complexation bonds. So we consider using complexation adsorbent in the DeSOx process. However, complexation adsorbents are not stable21 that copper(I) can be easily oxidized into copper(II) in flue gas atmosphere to make the adsorbent deactivated, and humidity will accelerate the oxidization process. To solve this problem, we try to use a bioreduction method that can reduce metal ions and chelate with metal ions.22,23 In this paper, we prepared a new cuprous adsorbent by bioreduction method, and the possible application of adsorbent in dry desulfurization in the low temperature was investigated. 2. Experimental Section 2.1. Preparation of Adsorbent. The strain biomass R08(Bacillus licheniformis) was cultivated in accordance with ref 24, and then harvested by centrifuging and washed with deionized water. The resulting biomass was dried at 80 °C and ground into powder for use. Stoichiometric amounts of Cu(NO3)2 aqueous solution was impregnated on γ-Al2O3(80-100 meshes) for the preparation of Cu(II)/γ-Al2O3 which loading weight of Cu2+ is 2%. The sample was dried under vacuum at 105 °C for 12 h. Then Cu(II)/γ-Al2O3, R08 biomass and deionized water were mixed with weight ratio of 1:0.6:5. The mixture was kept at pH 6.0 and was incubated at room temperature for 48 h. Finally the sample was dried under vacuum at 105 °C. XRD pattern showed no distinguished characteristic peaks of copper com-

10.1021/ie800059z CCC: $40.75  2008 American Chemical Society Published on Web 10/18/2008

Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008 8889 Table 1. Binding Energies (eV) of Cu

Figure 1. XPS spectrum of Cu 2p3/2 of (a) Cu(II)/γ-Al2O3; (b) bio-Cu.

pounds for the adsorbent except the alumina support. The sample is named bio-Cu in brief. The Cu(I)/γ-Al2O3 was prepared by autoreduction of Cu2+ in Cu/γ-Al2O3 to Cu+ by using a helium atmosphere at 450 °C for 4 h.17-19 2.2. Activity Test. The adsorption experiments were performed in a glass-made jacketed fixed-bed reactor, under isothermal conditions at moderate temperature. Approximately 0.2 g of the adsorbent was placed between two quartz wool plugs held in the reactor. The volume composition of the gas stream was 2% SO2, 5% O2, 10% H2O, and balance N2 at a rate of 15 mL/min (the space velocity was 4500 h-1). The gas mixture flowed to the reactor and the exhaust SO2 is determined by iodine titration method. Other samples such as Cu(II)/γAl2O3, γ-Al2O3, and Cu(I)/γ-Al2O3 were also prepared to make a comparison of the efficiency and activity of the adsorbents at the same experimental conditions. The amount of SO2 adsorption is expressed as milligram SO2 per gram adsorbent. The regenerated adsorbents were performed in the reactor under an N2 flow at 120 °C for at least 0.5 h until SO2 in vent was not determined. 2.3. Characterization of Adsorbents. X-ray photoelectron spectroscopy (XPS) analyses were performed on a PHI Quantum 2000 Scanning ESCA microprobe with a monochromatized microfocused Al X-ray source. The binding energy was calibrated by C1s as reference energy (C1s ) 284.6 eV). The samples for IR analysis were prepared by pressing powered KBr pellets mixed intimately with 0.5% of finely ground powder of the each sample and determined on a Nicolet 740SX FTIR spectrophotometer. The instrument was performed with a MCT-B detector and the spectra were recorded in the region of 4000-400 cm-1 at a resolution of 4 cm-1 with 32 scans. 3. Results and Discussion 3.1. Characterization of bio-Cu. Figure 1 shows X-ray photoelectron spectroscopy spectra for Cu 2p3/2 spectra of Cu(II)/ γ-Al2O3 and bio-Cu. The binding energy (BE) of Cu 2p3/2 of adsorbents and some copper compounds are listed in Table 1. The XPS clearly shows that before contact with R08 biomass the copper component is Cu2+, in which the binding energy of 2p3/2 is 933.4 eV, and an additional shakeup satellite in the

material

BE (2p3/2) (eV)

Cu(II)/γ-Al2O3 Bio-Cu Cu metal25 CuO25 Cu2O25

933.4 932.7 932.6 933.7 932.6

942-944 eV is also observed, which is in good agreement with Cu2+.25 Whereas for bio-Cu, no shakeup peak is observed, and the binding energy of 2p3/2 is shifted to 932.7 eV, which may be attributable to either Cu+ or Cu0 because their binding energy peaks are both at 932.6 ( 0.1 eV. However, the Auger spectrum shows a peak at 915.6 eV in the CuL3MM Auger spectrum, which is a characteristic peak of Cu+ and the Cu0 species does not exist in the adsorbent. The results indicate that the Cu2+ is reduced to Cu+ by biomass R08. FTIR spectra of adsorbents are shown in Figure 2. Compared with Cu(II)/γ-Al2O3(b), some new bands attributed to functional groups of biomass R08 are observed in bio-Cu (a) in the range of 900-1700 cm-1. However, the bands are not obvious and may be overlapped. So to further study the reductive mechanism of the interaction between biomass R08 and Cu2+, FTIR spectra of blank R08 biomass (c) and that exposed to Cu2+ (d) are shown in Figure 2. It has been suggested that the binding of metal ions to microorganisms relates to the oxygenous or nitrogenous functional groups on the cell walls of microbial biomasses.26,27 The bands at 1637 and 1556 cm-1 may be assigned respectively to a CdO stretching vibration band (νCdO) and a coupled vibration involving the N-H bending and the C-N stretching modes (δN-H + νC-N) of the amido bond of the peptidoglycan layer on the cell wall of R08 biomass.28,29 They are shifted to 1651 and 1542 cm-1, respectively, after Cu2+ adsorption. The results imply that copper ions may be adsorbed or chelated by O and N atoms of the amido bond. Bands at 1400 cm-1 belong to an ionized carboxyl group (-COO-) of a remnant amino-acid C-O vibration band (νC-O).29 After R08 biomass reacted with copper ions, most of the carboxyl ions (-COO-) might have complexed or chelated with Cu+, which made the CdO stretching band move to a higher frequency and caused the peak valley between 1637-1542 cm-1 to deepen and the band at 1402 cm-1 to shift to 1384 cm-1. The band at 1072 cm-1 belongs to a coupled vibration band (δO-H+νC-O) of a hydroxyl group (C-O-H) of saccharides.29 After Cu+ biosorption, the band at 1072 cm-1 is shifted to 1054 cm-1. The band at 1726 cm-1 is assigned to νCdO of the nonionized carboxyl group (-COOH) of the remnant amino-acid. The band on curve b is stronger than that on curve a. The reason may be that copper ions are reduced by aldose which is the hydrolysis of polysaccharides on the peptidoglycan layer. 3.2. Desulfurization Activity. The total amount of sulfate/ sulfite species adsorbed on different samples as a function of temperature is shown in Figure 3. It indicates that under the experimental condition the activity of bio-Cu is influenced deeply by temperature. The total amount of SO2 removal on bio-Cu decreases by 50% with increasing temperature, from 33.08 mg SO2/g adsorbent at 30 °C to 14.744 mg SO2/g adsorbent at 120 °C. In contrast, for γ-Al2O3 and Cu(II)/γ-Al2O3, the amount of SO2 removal increases as the reaction temperature increases. It should be noted that the amount of SO2 removal on Cu(II)/γ-Al2O3 at 80 °C reached 90.3 mg SO2/g adsorbent compared with 26.7 mg SO2/g adsorbent at 50 °C. The reason may be that large numbers of sulfates are formed at 80 °C. For Cu(I)/γ-Al2O3, the amount of SO2 removal decreases slowly

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Figure 2. FTIR spectra of (a) bio-Cu, (b) Cu(II)/γ-Al2O3, (c) R08 biomass, (d) Cu2+ adsorbed by R08 biomass.

Figure 3. Comparison of the amounts of SO2 removal at different temperatures on (9) bio-Cu, (b) γ-Al2O3, (2) Cu/γ-Al2O3, and (1) Cu(I)/ γ-Al2O3.

with increasing temperature from 30 to 80 °C, then it increases at 120 °C. The behavior indicates that more cuprous ions may be oxidized into cupric ions and more sulfates may be formed as the temperature increases. Figure 4 shows the amount of desorbed SO2 after an N2 flow at 120 °C and the efficiency of SO2 desorption of the samples as a function of adsorption temperature. As can be seen in the Figure 4, compared with γ-Al2O3 and Cu(II)/γ-Al2O3, although bio-Cu has a low capacity of SO2 adsorption, it has a high efficiency of SO2 desorption. This indicates that nearly all of SO2 can be desorbed at 120 °C in the adsorbent, while for γ-Al2O3 and Cu(II)/γ-Al2O3, more sulfates may be formed with increasing temperature, which is difficult to be desorbed by N2 flow. For Cu(I)/γ-Al2O3, the efficiency of SO2 desorption decreases with increasing temperature, but the amount of desorbed SO2 is higher than that of Cu(II)/γ-Al2O3. Figure 3 and Figure 4 show that the species adsorbed on Cu+ may be desorbed with increasing temperature; however, the valence of copper of Cu(I)/γ-Al2O3 prepared by autoreduction is not stable and Cu+ can be oxidized into Cu2+ exposed to H2O and O2 atmosphere, resulting in copper sulfate being formed which is difficult to regenerate at 120 °C.

Figure 4. The amount of desorbed SO2 at 120 °C on (9) bio-Cu, (b) γ-Al2O3, (2) Cu(II)/γ-Al2O3, and (1) Cu(I)/γ-Al2O3 and the efficiency of SO2 desorption of (0) bio-Cu, (O) γ-Al2O3, (4) Cu(II)/γ-Al2O3, and (3) Cu(I)/γ-Al2O3 at different adsorption temperatures.

To investigate the regenerative performance of the adsorbent, the regenerative experiments for six times at different temperatures, as shown in Figure 5, were carried out. As can be seen in Figure 5, the adsorbent has a good regenerative performance. After six regenerations, the SO2 capacity of bio-Cu at different temperatures is higher than ca. 87% of that in fresh adsorbent. 3.3. Mechanism of Adsorption and Desorption Process. XPS study. Figure 6 shows X-ray photoelectron spectroscopy spectra of S to investigate the species adsorbed on different adsorbents, and we measured the full-width at half-maximum (fwhm) for the S 2p photoelectrons spectra of the samples. The results are recorded in Table 2. The binding energy and fwhm values can determine the nature of sulfur oxide species on the adsorbents. As can be seen from Figure 6 and Table 2, the BE of S 2p on Cu(II)/γ-Al2O3 locates at 169.5 eV and the fwhm value is 2.2 eV, which is a good agreement with SO42-.25 However, the BE of S 2p on bio-Cu is found at 168.4 eV and the fwhm value is 2.3 eV. The results imply that sulfite is the predominant species on bio-Cu after adsorbing SO2 at 80 °C.30,31 After regeneration, the amount of S is very low, nearly all of the SO2 is desorbed, and after six regenerations, some sulfates exist on the adsorbent but the amount is very low. The results

Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008 8891

Figure 5. The amount of SO2 adsorbed on regenerative adsorbent at different temperature: (9) 30, (b) 50, (2) 80 °C.

Figure 6. XPS spectrum of S 2p on different materials (a) Cu(II)/γ-Al2O3 after adsorbing SO2 at 80 °C, (b) bio-Cu after adsorbing SO2 at 80 °C, (c) bio-Cu after one regeneration, (d) bio-Cu after six regenerations. Table 2. The Binding Energy of S 2p materials

BE (eV)

fwhm (eV)

Cu(II)/γ-Al2O3 Bio-Cu Bio-Cu after one regeneration Bio-Cu after six regenerations

169.5 168.4 168.1 168.8

2.2 2.3 2.7 2.5

indicate that SO2 adsorbed on bio-Cu can be easily desorbed which is in good agreement with our experiment results. Figure 7 shows the XPS spectra of Cu 2p3/2 spectra of bioCu, bio-Cu after adsorbing SO2 at 80 °C and bio-Cu after desorbing SO2. As can been seen in Figure 7, after adsorbing SO2 and desorbing SO2, the BE of Cu is all found at 932.6 ( 0.1 eV and the valence of copper does not change. This indicates that R08 biomass can reduce Cu2+ to Cu+ and keep the valence of copper in the process of adsorbing SO2 exposed to an O2 and H2O atmosphere. FTIR Study. Sulfates, sulfites, and adsorbed sulfur oxide species show several vibrational bands in the 1500-600 cm-1 infrared region sensible to the coordination and symmetry of adsorbed species, and thus an infrared characterization of the

Figure 7. XPS spectrum of Cu 2p3/2 of (a) Bio-Cu, (b) bio-Cu after adsorbing SO2 at 80 °C, (c) bio-Cu after desorbing SO2.

Figure 8. IR spectra of (a) γ-Al2O3, (b) Cu(II)/γ-Al2O3, (c) Cu(I)/γ-Al2O3, (d) bio-Cu with adsorbing SO2 at 80 °C.

species formed during the interaction of SO2/O2 with the adsorbent can provide useful information about the reaction mechanism. Due to the strong absorption of skeletal vibrations of the alumina support for frequencies below 900 cm-1, only the 1500-900 cm-1 region was analyzed. Figure 8 shows the FTIR spectra of different materials after adsorbing SO2 at 80 °C. For γ-Al2O3 (a), three bands centered at 1050-1400 cm-1 are observed, the band at 1090 cm-1 can be attributed to aluminum sulfate, and SO2 adsorbed on pure alumina give rise to a band at 1050 cm-1, attributed to the formation of surface sulfite specie. The band at 1384 cm-1 is assigned to the chemisorbed SO3.32,33 For Cu(II)/γ-Al2O3 (b), a new broadband at 1145 cm-1 is observed which is attributed to the bulk sulfate of CuSO4.34 However, different from γ-Al2O3(a) and Cu(II)/ γ-Al2O3(b), a new band at 1077 cm-1 is observed both in the spectra of Cu(I)/γ-Al2O3 prepared by autoreduction and bioCu which may be attributed to chemisorbed SO2 on Cu+ site. For Cu(I)/γ-Al2O3, another broadband appearing at 1145 cm-1 belongs to the bulk sulfate of CuSO4, it indicates that some cuprous ions are oxidized into cupric ions and copper sulfates

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copper; however, it appears that it is a rather complicated process that should require further analysis to explain the reactions. Curve c shows the FTIR spectra of bio-Cu after desorbing SO2. As can be seen in Figure 9, curve c and curve a are nearly the same; the band between 1050 and 1100 cm-1 is weaker than curve b which means nearly all of the SO2 is desorbed and the nonionized carboxyl group is decreased. The result implies that the sulfite species adsorbed on bio-Cu can be easily desorbed and Cu+ chelates with the oxygenous or nitrogenous functional groups again after desorption. Discussion. XPS and FTIR analysis indicate that first copper(II) is reduced to copper(I) by aldose(RCOH), then copper ions are complexed to O and N atoms of the carboxyl group and amido group. In the process of adsorbing SO2, SO2 or SO32species are chemisorbed on the active site of Cu+ where the carboxyl group and amido group are adsorbed with chemical complexation bonds so that it can be desorbed by increasing temperature, and RCOO- and RNH- react with H2O to form RCOOH and RNH2. Figure 9. IR spectra of (a) bio-Cu, (b) bio-Cu with adsorbing SO2 at 80 °C and (c) bio-Cu after desorbing SO2.

are formed which is in good agreement with our experiment results. For bio-Cu, a new absorption peak at 1102 cm-1 is observed in curve d which may be attributed to symmetric stretching sulfite vibrations.35,36 However this band is not observed in the spectra of Cu(I)/γ-Al2O3 prepared by autoreduction; the reason may be that it is a new sulfite species adsorbed on bio-Cu that is influenced by carboxyl groups and amido groups chelated with Cu+. The results imply that sulfate species can be rapidly formed on γ-Al2O3, Cu(II)/γ-Al2O3, and Cu(I)/γ-Al2O3 exposed to an O2 atmosphere at 80 °C, while SO2 cannot be easily oxidized on bio-Cu at the same condition. They also imply that sulfites are the main species on the surface of the bio-Cu, which is in good agreement with our XPS results. However why SO2 is not oxidized on bio-Cu still needs further study. To study the mechanism of interaction of bio-Cu and SO2, the FTIR spectra of bio-Cu (a), bio-Cu with adsorbing SO2 at 80 °C (b), and bio-Cu after desorbing SO2 (c) are shown in Figure 9. The broadband between 1050 and 1080 cm-1 on curve a belongs to a coupled vibration band (δO-H + νC-O) of the hydroxyl group (C-O-H),29 which is not obvious because of the binding of copper to atom O of the hydroxyl group. After adsorbing SO2 the band at 1077 cm-1 is stronger than that on curve a, the reason may be that SO2 is adsorbed on active sites of copper(I) and COO- contacted with Cu+ forms COOH. The band at 1362 cm-1 belongs to the bending vibration of the ionized carboxyl group (-COO-), while after adsorbing SO2, the band is shifted to 1400 cm-1.28 Compared with curve a, some new bands are also observed. The band at 1228 and 990 cm-1 may be assigned respectively to the C-O- stretching vibration band of -COO- group and the δO-H of the nonionized carboxyl group (-COOH).29 The band at 1545 cm-1 belongs to a coupled vibration involving the N-H bending and the C-N stretching modes (δN-H + νC-N).29 These bands on curve b are stronger than those on curves a and c. The reason may be that under the competitive adsorption and vapor atmosphere conditions, SO2/SO32- is adsorbed on Cu+, and the ionized carboxyl group (RCOO-) and amido group (RNH-) is desorbed and forms the nonionized carboxyl group (RCOOH), combining with H+. From FTIR and XPS results, it is thought that the functional groups of biomass can prevent the interaction between SO2 and O2 on the bio-Cu and keep the valence of

4. Conclusion In conclusion, this paper reports a new cuprous adsorbent prepared by a bioreduction method and studies the desulfurization ability and regenerative property of the adsorbent at low temperature. From FTIR and XPS study, it is found that the biomass can keep the valence of Cu(I) which is different from the Cu(I)/γ-Al2O3 prepared by autoreduction where Cu+ can be easily oxidized into Cu2+. Furthermore, only sulfite species are formed on the surface of bio-Cu at low temperature under O2 and H2O atmosphere, which is different from γ-Al2O3, Cu(II)/γ-Al2O3, and Cu(I)/γ-Al2O3 where sulfate species are formed. So it is easily desorbed with increasing temperature, and after regeneration the adsorbent still has a good desulfurization ability. Acknowledgment We would like to thank Professor Chen zhiyang and Professor Wang shuiju for the assistance rendered in using the XPS and FTIR apparatus and Professor Chen in analyzing the FTIR spectra. We would also like to express our gratitude to the anonymous reviewers for their critical comments to enhance the quality of the paper. Literature Cited (1) Srivastava, R. K.; Josewicz, W. Flue Gas Desulfurization: The State of the Art. J. Air Waste Manage. Assoc. 2001, 51, 1676. (2) Centi, G.; Passarini, N.; Perathoner, S. Combined DeSOx/DeNOx Reactions on a Copper on Alumina Sorbent-Catalyst. 2. Kinetics of the DeSOx Reaction. Ind. Eng. Chem. Res. 1992, 31, 1956. (3) Macken, C.; Hodnett, B. K. Reductive Regeneration of Sulfated CuO/ Al2O3 Catalyst-Sorbents in Hydrogen, Methane, and Steam. Ind. Eng. Chem. Res. 1998, 37, 2611. (4) Kijlstra, W. S.; Brands, D. S.; Poels, E. K. Mechanism of the Selective Catalytic Reduction of NO by NH3 over MnOx/Al2O3. I. Adsorption and Desorption of the Single Reaction Components. J. Catal. 1997, 171, 208. (5) Tseng, H. H.; Wey, M. Y.; Fu, C. H. Carbon Materials as Catalyst Supports for SO2 Oxidation: Catalytic Activity of CuO-AC. Carbon 2003, 41, 139. (6) Dunn, J. P.; Koppula, P. R.; Stenger, H. G. Oxidation of Sulfur Dioxide to Sulfur Trioxide over Supported Vanadia Catalysts. Appl. Catal., B 1998, 19, 103. (7) Akyurtlu, J. F.; Akyurtlu, A. Behavior of Ceria-Copper Oxide Sorbents under Sulfation Conditions. Chem. Eng. Sci. 1999, 54, 2991. (8) Zhu, T. L.; Kundakovic, L.; Dreher, A. Redox Chemistry over CeO2Based Catalysts: SO2 Reduction by CO or CH4. Catal. Today. 1999, 50, 381.

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ReceiVed for reView January 14, 2008 ReVised manuscript receiVed August 15, 2008 Accepted September 9, 2008 IE800059Z