Ind. Eng. Chem. Res. 2005, 44, 6485-6490
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Parametric Study of Cs/CaO Sorbents with Respect to Simulated Flue Gas at High Temperatures Alexander Roesch, Ettireddy P. Reddy, and Panagiotis G. Smirniotis* Chemical and Material Engineering Department, University of Cincinnati, Cincinnati, Ohio 45221-0012
The development of novel sorbents for reducing the carbon dioxide emissions at high temperature focused on cesium-doped CaO sorbents with respect to other major flue gas compounds in a wide temperature range has been studied in this paper. The sorbent calcined under oxygen atmosphere leads to the formation of cesium superoxide (CsO2) on the sorbent surface. The thermogravimetric analysis of sorbent with 20 wt % cesium loading on CaO demonstrated a CO2 sorption uptake of 66 wt % CO2/g of sorbent. It is remarkable to note that zero adsorption affinity for N2 and O2 at temperatures as high as 600 °C was observed. This is due to the presence of highly oxidized phase of cesium (CsO2) on the sorbent surface and the sorbent being unable to react with nitrogen at the above-mentioned temperatures. In the presence of water vapor, the adsorption of CO2 increased to the highest capacity of 77 wt % CO2/g of sorbent. The reason for this behavior is that the water vapor digs into the bigger particles, thus making the porous type of sorbent material. In the presence of nitrogen oxide, the final CO2 adsorption remained the same, but the rate of adsorption was higher at the initial stages (10%) than the case where no nitrogen oxide was fed. 1. Introduction The carbonation of CaO sorbents has been recently studied for the separation of carbon dioxide at high temperatures using industrial or natural limestone.1-4 The present study is a continuation of our earlier work,4 in which we investigated CaO-supported alkali metal sorbents. It was found that, in the family of sorbents involved with low BET surface area supports, the CO2 sorption increases in the following order: Li < Na < K < Rb < Cs. The optimum adsorption temperature for CO2 is 600 °C. The reason for the enhanced CO2 adsorption affinity was observed as a result of the increase of the basic nature of sorbent with the addition of the alkali metals, particularly with cesium. Moreover, it was found4 that the CaO support doped with 20 wt % cesium synthesized from CsOH precursors reached the highest CO2 adsorption. The carbonation reaction on calcined limestone is well investigated, but most of the studies have been performed under nonpractical conditions such as the absence of poisons or low temperature. Thereby, it is clear that the species such as H2O, NO, and particularly SO2 can influence the CO2 sorption on CaO-based sorbents. Borgwardt5 has investigated the influence of water on CaO sorbent, and he reported increasing sorbent sintering effects. Although several studies have been carried out to investigate the effect of flue gas on pure CaO, to the best of our knowledge no investigation was performed for the direct influence of flue gas for CO2 adsorption on alkali metal doped CaO sorbents. In this work, the sorption performance of Cs/CaO sorbent for the major components of exhaust gases from coal-fired power plants (namely, CO2, N2, O2, NO, and H2O) was studied. We investigated the effects of both the individual compounds and a gas mixture simulating flue gas. * To whom correspondence should be addressed Tel: (513) 556-1474. Fax: (513) 556-3473. E-mail:
[email protected].
2. Experimental Section 2.1. Synthesis Procedure. The alkali metal doped sorbents were prepared by the wet impregnation method using commercial CaO (Aldrich) support. The precursor used for the loading of cesium was CsOH (Aldrich, 50 wt % solution in water) since we found earlier4 that this precursor leads to better sorbent. The sorbent was prepared by mixing the appropriate amount of CsOH and CaO in order to reach cesium of 20 wt % (based on cesium metal and CaO only). Distilled water was added for the formation of the slurry in the proportion of 1 g of CaO:100 g of aqueous solution of the alkali metal precursor. The slurry was heated and stirred until the water was evaporated. The powder was ground to fine powder and dried in an oven at 120 °C overnight. The calcination of sorbent was carried out under oxygen atmosphere at 750 °C for 5 h in order to reach a full oxidation of the cesium. Helium was also used to calcine the sorbent since we found that the state of sorbent can vary with the treatment environment. After the step of calcination, the sorbents were stored in a glovebox under inert atmosphere. 2.2. Particle Size Analysis. The particle size distribution of the sorbent material was obtained with a laser scattering particle distribution analyzer (Malvern Mastersizer S series). The instrument is accurate to within 5% of the median value, as claimed by the manufacturer. Prior to the measurements, the sorbent was dispersed in distilled water using ultrasound. 2.3. BET Surface Area and Pore Size Measurements. BET surface area and pore size distribution measurements were performed using nitrogen adsorption and desorption isotherms at -196 °C on a Micromeritics ASAP 2010 volumetric adsorption analyzer. The sorbent samples were degassed at 300 °C for at least 5 h in the degassing port of the apparatus. The pore size distribution was obtained from the branch of the isotherm using the KJS method.6 An additional BET measurement was carried out in an AutoChem 2910
10.1021/ie040274l CCC: $30.25 © 2005 American Chemical Society Published on Web 04/08/2005
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chemisorption is low but the uptake increased significantly for temperatures above 450 °C. The maximum adsorption uptake was reached at 600 °C and was equal to 66 wt % CO2/g of sorbent. Surprisingly, at 675 °C the CO2 sorption is about 10 wt % lower in comparison with that at 600 °C. The reason is that the thermal stability of the formed Cs2CO3 is limited to ∼610 °C.7 Hence, when the adsorption and/or desorption steps take place at temperature higher than 610 °C, the state of the sorbent significantly changes. Evidently, the ideal temperature for high-temperature CO2 adsorption using cesium-doped sorbents is around 600 °C. Our XPS investigations4 confirmed the reactions of carbonation and desorption in the corresponding range, which are presented in eqs 1-4. Figure 1. Effect of temperature for CO2 adsorption over 20 wt % Cs/CaO. Concentration of CO2 ) 28.6% balanced on helium. Total flow ) 70 mL/min. Temperature ) 600 °C.
analyzer to determine the BET surface area before and after the water vapor injection by avoiding exposure of the sorbents to the ambient atmosphere. The sorbent was pretreated at 750 °C for 5 h in order to get a complete outgassed sorbent. In this manner, the sorbent is free of all pre-adsorbed atmospheric water or carbon dioxide. 2.4. X-ray Photoelectron Spectroscopy (XPS). The XPS analyses were conducted on a Perkin-Elmer model 5300 X-ray photoelectron spectrometer with Mg KR radiation at 300 W. Typically, 89.45 and 35.75 eV pass energies were used for survey and high-resolution spectra, respectively. The effects of sample charging were eliminated by correcting the observed spectra for a C 1s binding energy value of 284.6 eV. The sorbents were mounted onto the sample holder and were degassed overnight at room temperature and pressures on the order of 10-7 Torr. The binding energy values of Cs 3d5/2 for two different samples were measured by using XPS analysis. 2.5. Sorption Experiments. The adsorption and desorption experiments were carried out in a PerkinElmer PYRIS-1 thermogravimetric analyzer (TGA) equipped with thermal analysis gas station (TAGS). For the sorption experiments, the samples were placed in a platinum sample holder. The sample-pan holder was operated batch-wise with a single charge ranging from 5 to 10 mg, depending on the type of experiment. Each experiment started with a pretreatment step to degass the sorbent from the pre-adsorbed gases and water. The temperature profile of these experiments consisted of heating with a ramp of 10 °C/min to 750 °C, holding the sample for 3 h at 750 °C, and a cooling with a rate of 15 °C /min to the adsorption temperature. The pretreatment was carried out under helium atmosphere. The adsorption experiments were carried out at the desired adsorption temperature for 5 h. Prior to the adsorption experiments, the samples were held for 30 min at the adsorption temperature in helium flow in order to get a stable flow profile and baseline. 3. Results and Discussion 3.1. Effect of Temperature on CO2 Adsorption. Characteristic TGA curves of isothermal CO2 adsorption over 20 wt %Cs/CaO sorbent are depicted in Figure 1 within a temperature range of 225-675 °C. A monotonic increase of CO2 sorption was observed by increasing the temperature. At relatively low temperature, the CO2
Chemisorption: CaO + CO2 f CaCO3
(1)
Cs2O + CO2 f Cs2CO3
(2)
CaCO3 f CaO + CO2
(3)
Cs2CO3 f Cs2O + CO2
(4)
Desorption:
The advantage of cesium-doped CaO sorbent is clearly demonstrated in comparison to the CO2 uptake on the commercial pure CaO sorbent support used in this study (Aldrich, 99.9%) at 600 °C (dashed curves in Figure 1). This is due to the fact that cesium oxide leads to higher surface basicity, which favors the chemisorption of a weak acid such as CO2. It is worth noting that the uptake of the sorbent reaches as high as 30 wt % CO2/g of sorbent within the first 2 min, a property of unique importance from a kinetic point of view since it can result in rapid sorption/ desorption cycles. This behavior is different in comparison with our previous experimental observations4 where a lower adsorption rate was observed. However, it can be justified by the use of different gas atmospheres during the calcination step. In our previous work,4 the sorbent was calcined under helium atmosphere, and the CsOH precursor used was dehydrated but not fully oxidized (reaction 5). In the present set of experiments, the calcination was carried out under oxygen and resulted in the complete oxidation of the cesium precursor, thus leading to the fully oxidized (CsO2) form of sorbent (reaction 6). Consequently, the surface characteristics of the present sorbents are completely different in comparison to those in our earlier work.4 Equations 5 and 6 present what is happening during the calcinations under the different atmospheres.
Dehydration: 750 °C
8 Cs2O + H2O 2CsOH 9 He
(5)
Oxidation: 750 °C
4CsOH + 3O2 98 4CsO2 + 2H2O
(6)
During the wet impregnation method, only the excess water of the slurry was evaporated, and the slurry becomes a solid material at ambient temperatures and acquires the uniform dispersion of cesium on the sorbent. Hence, the uncalcined sorbents possess CsOH.
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Figure 4. XPS spectra of Cs3d5/2 core level peak for 20% Cs/CaO sorbent calicned under helium and oxygen. Figure 2. Temperature-programmed oxidation (TPO) and temperature-programmed desorption of 20 wt % Cs/CaO sorbent after calcinations at 750 °C under oxygen atmosphere.
Figure 3. Effect of calcination gases on adsorption of CO2 over 20 wt % Cs/CaO2. Concentration of CO2 ) 28.6% balanced on helium. Total flow ) 70 mL/min. Temperature ) 600 °C.
Typical dehydration of CsOH (reaction 5) is only taking place during the calcinations at 750 °C under helium atmosphere. As shown in reaction 6, CsOH is fully oxidized and forms cesium superoxide8 (CsO2) layers on the sorbent surface when calcined at 750 °C under oxygen atmosphere. Yagi and Hattori9 investigated the oxygen adsorption on cesium-added zeolite X. They reported that Cs2O adsorbs oxygen to form Cs2O3 and Cs2O4. TPO-TPD experiments of the un-calcined sorbent under oxygen atmosphere were carried out in order to find out the temperature and phase of the cesium oxides formed in our sorbent. As shown in Figure 2, only one adsorption peak was found at 643 °C, which corresponds to CsO2 as determined by the total amount of oxygen consumed after integration of the TCD peaks. The CO2 adsorption affinity of sorbents calcined under helium and oxygen (Figure 3) was compared. It was observed that the sorbent calcined under oxygen atmosphere demonstrated significantly high CO2 adsorption as compared to the sorbent calcined under helium. This difference was due to the formation of CsO2 phase in the sorbent during the calcination under oxygen atmosphere. This phase of Cs enforces the rapid and significantly high amount of CO2 adsorption.
XPS analysis of 20% Cs/CaO sorbent calcined under helium and oxygen was undertaken to know the surface species of the sorbent formed after calcination under different environments. The photoelectron peaks of Cs 3d5/2 for these sorbents are shown in Figure 4. The binding energy value of Cs 3d5/2 at 724 eV is observed for the sorbent calcined under helium, which is due to Cs in the Cs2O form. On the other hand, the binding energy value of Cs 3d5/2 for sorbent calined under oxygen was observed at 724.3 eV. The increase in binding energy value for Cs 3d5/2 was mainly due to presence of CsO2 on sorbent surface after calcination under oxygen atmosphere. According to Band et al.,10 who reported the sputtering of oxygen on Cs metal gives microcrystalline particles of cesium oxide (Cs2O), cesium peroxide (CsO) and cesium superoxide (CsO2) are constituents of the reaction products. They also detected CsO2 as the most abundant product as the super oxide ion with the highest percentage. Therefore, the XPS data obtained on the sorbent calcined under oxygen atmosphere are in good agreement with the previous reports.10 The binding energy values of two different types of Cs 3d5/2 peaks can be judged from the difference in the electronegativity of the elements.11 3.2. Effect of N2 and O2 Adsorption. The results of the nitrogen and oxygen adsorption experiments are presented in Figure 1. It is remarkable to note that the sorbent shows zero affinity for both gases. This is the case for the entire range of temperatures we investigated varying from 50 to 600 °C. This demonstrates that sorbent selectively adsorbs CO2. More specifically, the sorbent was calcination at 750 °C under O2 atmosphere formed the fully oxidized phase of cesium (CsO2) on the surface. Therefore, it cannot further react with oxygen at a temperature range of up to 750 °C. On the other hand, our sorbent does not react with N2 in a wide range of temperatures. This is due to the lack of any chemical reaction with Cs species and nitrogen. In contrast, nitrogen reacts with other alkali metals (e.g., Li + N2 f Li3N) and forms alkali nitrides.12 This property is of unique importance for the development of highly selective CO2 sorbents from a stream of flue gas utilizing any fossil fuels and air since the nitrogen and the unused O2 will correspond to at least 70 vol % of the gases depending on the case.
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Figure 5. Effect of temperature for H2O adsorption over 20 wt % Cs/CaO. Concentration of H2O ) 10% balanced on helium. Total flow ) 70 mL/min.
3.3. Effect of H2O Adsorption with Respect to Temperature. The effect of temperature for water adsorption on our sorbent is presented in Figure 5. A rather “complicated” behavior is observed with respect to temperature due to the various reactions occurring. The reaction of water with calcium oxide (eq 7) is a wellknown and keen process at ambient pressures and temperatures. In addition, the cesium oxide also possesses high adsorption affinity toward water since cesium oxide is the strongest known basic oxide, and it readily reacts with water to form CsOH. The reaction is shown in eq 8. 225 °C
CaO + H2O {\ } Ca(OH)2 580 °C
(7)
225 °C
Cs2O + H2O {\ } 2CsOH 580 °C
(8)
Hence, at 225 °C Ca(OH)28 and CsOH layers were formed on the sorbent’s surface due to high water adsorption, namely, 27 wt % H2O/g of sorbent. However, with increasing the sorption temperature a considerable decrease of the water adsorption was observed. This trend continues up to the point where the sorbent exhibits a zero water adsorption affinity at temperatures equal to or higher than 600 °C. The chemical explanation for this monotonic decrease of the adsorbed amount of water with increasing temperature is based on the continuously decreasing extent of reactions 7 and 8 with temperature. Ca(OH)2 and CsOH completely decompose at temperatures higher than 580 °C.7 Furthermore, the sorbent becomes more porous and acquires smaller particle size (Table 1), which explains the significantly larger CO2 adsorption capacity at high temperature in the presence of water. To some extent this phenomenon is somehow similar to the preparation of activated carbons by water treatment. The influence of water for the surface chemistry on CaO was intensively investigated by Borgwardt,5 who studied the rapid decomposition of Ca(OH)2 and CaCO3 with respect to
Figure 6. Effect of temperature for NO adsorption over 20 wt % Cs/CaO. Concentration of NO ) 4000 ppm balanced on helium. Total flow ) 70 mL/min.
temperature and partial pressures of water vapor and other gases. They observed the change in BET surface areas of CaO with respect to temperature and partial pressure of water vapor in the first 10-20 min of the sintering process. In contrast to the Borgwardt5 study, our sorbent acquires low particle size and high BET surface after treatment with water vapor at 750 °C due to the presence of cesium oxide in the sorbent. However, the Borgwardt5 study supports our results only in terms of an increase in CO2 adsorption in the presence of water vapor. 3.4. Effect of NO Adsorption with Respect to Temperature. The results of the performance of adsorption experiments using nitrogen oxide are presented in Figure 6. A monotonic decrease of NO adsorption affinity at high temperatures was found. At relatively low temperatures (225 °C) a slight NO adsorption of 0.8 wt % NO/g of sorbent was obtained. The reason for this behavior is that nitrogen oxide is reacting with trace amounts of undispersed cesium oxide on the sorbent surface and forms CsNO3 (reaction 9). This compound is thermally stable up to 414 °C.
CaO2 + NO f CaNO3
(9)
450 °C
CsNO3 98 Cs2O + NO2v
(10)
At higher temperatures the decomposition of CsNO3 takes place. The decomposition of CsNO3 starts at above 450 °C, which means that the adsorption of NO is not possible beyond this temperature. This might be the reason for the negligible increase of the sorbent’s weight at this temperature. However, in the presence of nitrogen oxide, a loss in sorbent weight was observed at high temperatures (>450 °C). This is due to the decomposition of CsNO3 into porous Cs2O occurring beyond 450 °C (reaction 10). Because of this phenomenon a rapid adsorption of CO2 was observed in the presence of NO (Figure 7). It is further supported from Table 1, which
Table 1. BET Surface Areas, Pore Volume, Average Pore Diameter, and Mean Particle Size of the Sorbent of 20 wt % Cs/CaO Sorbent after Calcinations and Adsorption of Different Gases at 600 °C sorbent name
BET surface area (m2/g)
pore volume (cm3/g)
average pore diameter (Å)
mean particle size (µm)
20 wt %Cs/CaO (after O2 calcination) 20 wt %Cs/CaO (after H2O adsorption) 20 wt %Cs/CaO (after NO adsorption) 20 wt %Cs/CaO (after CO2 adsorption)
9.2 15.5 4.7 2.1
0.021 0.011 0.012 0.006
90.0 93.3 87.2 110.1
19.4 11.2 13.9 20.4
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Figure 7. Effect of different gases on CO2 adsorption. Concentrations: CO2 ) 28,6%; H2O ) 10%; NO ) 500 ppm balanced on helium. Total flow ) 70 mL/min.
shows the decrease in average pore diameter of the sorbent after NO adsorption at 600 °C. 3.5. Effect of Various Gas Mixtures on CO2 Adsorption. Adsorption experiments with different mixtures of CO2 and other flue gas compounds were conducted to investigate the effect of the flue gas composition on the CO2 adsorption at 600 °C. The CO2 + N2 + O2 absorption curves presented in Figure 7 show that the presence of nitrogen and oxygen does not have any effect for the CO2 adsorption. The curve of CO2 alone is coincident with the curve of CO2 + O2 + N2 in Figure 7. This is because the same amount of adsorption was observed with the case of using CO2 alone, where 66 wt % CO2/g of sorbent was reached under identical operating conditions. This finding clearly demonstrates the opportunity for highly selective CO2 separation if one considers that nitrogen is the component flue gas with a highest concentration (≈75 vol %). In addition, it was observed that the nitrogen oxide does not have any negative influence on the final carbon dioxide adsorption. However, the rate of adsorption was higher at the initial stages in the presence of NO. The results in Figure 7 furthermore demonstrate that the water vapors improved significantly the CO2 uptake. In the presence of 10 vol % water, the highest adsorption 77 wt % CO2/g of sorbent after 5 h adsorption time was recorded. The reason behind this is the water vapors “dig” into the bigger sorbent particles, thus making a porous type of sorbent material. This results in the decrease in sorbent particle size (see Table 1) and an increase in porosity of the sorbent in comparison to the sorbent prior to the presence of water vapor. It is possible that the water vapor increases the porosity of the sorbent and acquires bimodal pore diameter (see Figure 8). This character of sorbent enhances the high CO2 adsorption due to the fact that the CO2 can react with the entire cesium and calcium oxide present in the sorbent. In this manner, the diffusion of CO2 is enhanced into the core levels of the sorbent. Gupta and Fan2 also reported that low surface area CaO sorbent demonstrated high CO2 uptake due to larger pore diameters. The BET surface area, pore volume, average pore diameter, and mean paerticle size of our sorbents treated under different environments are depicted in Table 1. The addition of NO and water at high temperatures decreases pore volume and increases the average pore diameter, which causes the more effective sorbent toward CO2 adsorption. In addition, Shimizu and Ina-
Figure 8. Pore diameter diamgram of the sorbent 20 wt %Cs/ CaO after calcination at 750 °C under oxygen and after adsorption of different gases at 600 °C.
Figure 9. Particle size vs distribution volume of the sorbent 20 wt %Cs/CaO after calcinations at 750 °C under oxygen and after adsorption of different gases at 600 °C.
gaki13 reported that water affects the higher mobility of Ca2+ and O2-, and this promoted higher reaction with CO2. The promising adsorption characteristics of the cesiumdoped calcium oxide with its high CO2 adsorption capacity, zero adsorption affinity for water, nitrogen, oxygen, and nitrogen oxide promise an advanced practical use for CO2 separation from flue gas at temperatures as high as 600 °C. The results of the particle size distribution and mean particle size after the calcinations and after the addition of CO2, H2O, and NO are depicted in Figure 9 and Table 1, respectively. As one can observe, the mean particle size of the un-calcined sorbent is the largest after calcination under oxygen atmosphere. The increasing of sorbent particle size was due to the formation CsO2 on the surface of the sorbent during the calcination. The particle size decreased in the presence of NO and water during the calcination. It can be explained due to the formation of a mesoporous type of sobent in the presence of NO and water. The largest particle size was found for the sample after the CO2 adsorption step, which is reasonable, by the formation of CaCO3 and Cs2CO3 particles on the sorbent surface. 4. Conclusions Experiments were performed with 20 wt % Cs/CaO sorbent in a TGA. The objective of these experiments
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was to verify the effect of CO2 adsorption on the sorbent with consideration to flue gas conditions: (1) The carbonation rate of the new sorbent was reasonably improved by a full oxidation of the cesium because of oxygen as a calcination gas. (2) To develop selective adsorbents for carbon dioxide at high temperature, our findings show a zero adsorption affinity for N2, O2, H2O, and NO at 600 °C. (3) At high temperatures, NO and H2O promote shrinking effects by decreasing particle size and simultaneously forming uniform pore sizes. (4) The presence of water vapor significantly promotes the CO2 sorption capacity of the sorbent. (5) In the presence of nitrogen oxide, a rapid CO2 uptake was observed within the first 2 min. Acknowledgment The authors acknowledge the financial support from U.S. Department of Energy (Innovative Phase II Project DE-FG03NT41810). We also acknowledge the cooperation of the Institut fur Energieverfahrenstechnik und Chemieingenieurwesen (Technische Universitat Bergakademie Freiberg, Germany). Literature Cited (1) Salvador, C.; Lu, D.; Anthony, E. J.; Abanades J. C. Enhancement of CaO for CO2 capture in a FBC environment. Chem. Eng. J. 2003, 96, 187-195. (2) Gupta, H.; Fan, L. S. Carbonation-calcination cycle using high reactivity calcium oxide for carbon dioxide separation from flue gas. Ind. Eng. Chem. Res. 2002, 41, 4035-4042. (3) Abanades, J. C.; Alvarez, D. Conversion limits in the reaction of CO2 and lime. Energy Fuels 2003, 17, 308-315.
(4) Reddy, E. P.; Smirniotis, P. G. High-temperature sorbents for CO2 made of alkali metals doped CaO supports. J. Phys. Chem. B 2004, 108, 7794-7800. (5) Borgwardt, R. H. Calcium oxide sintering in atmospheres containing water and carbon dioxide. Ind. Eng. Chem. Res. 1989, 28, 493-500. (6) Kurk, M.; Jaroniec, M.; Sayari, A. Application of large pore MCM-41 molecular sieves to improve pore size analysis using nitrogen adsorption measurements. Langmuir 1997, 13, 62676273. (7) Lide, D. R. CRC Handbook of Physics and Chemistry, 84th ed.; CRC Press: Boca Raton, FL, 2003-2004. (8) West, A. R. Basic Solid-State Chemistry; John Wiley & Sons: New York, 1999. (9) Yagi, F.; Hattori, H. Oxygen exchange between adsorbed oxygen and cesium-added zeolte X. Microporous Mater. 1997, 9, 247-251. (10) Band, A.; Albu-Yaron, A.; Livneh, T.; Kohen, H.; Feldman, Y.; Shimon, L.; Popovitz-Biro, R.; Lyahovitskaya, V.; Tenne, R. Characterization of oxides of cesium. J. Phys. Chem. B 2004, 108, 12360-12367. (11) Imamura, I.; Ishida, S.; Tarumoto, H.; Saito, Y.; Ito, T. Effect of the composition of titania silica on its physical and catalytic properties. J. Chem. Soc., Faraday Trans. 1993, 89, 757762. (12) Cotton, F. A.; Wilkenson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry; John Wiley & Sons: New York, 1999. (13) Shimizu, T.; Inagaki, M. Decomposition of N2O over limestone under fluidized-bed combustion conditions. Energy Fuels 1993, 7, 648-654.
Received for review November 8, 2004 Revised manuscript received February 23, 2005 Accepted February 26, 2005 IE040274L
