Influence of CO and H 2 Concentrations on Coal Gas Dechlorination by Supported Manganese Oxide Sorbent

The Mn2O3/SiO2 sorbent prepared by incipient wetness impregnation was investigated for the elimination of chlorine species produced from coal gasification. The experiments were conducted in a fixed-bed reactor at 673 K with the Mn2O3/SiO2 sorbent at various CO and H2 concentrations to evaluate their influences on the dechlorination performance. It was observed that the absence of inlet H2 led to a drastic decrease in the sorbent capacity; i.e., the presence of H2 was essential for achieving dechlorination. Furthermore, the concentration of CO seemed to have no obvious effect on the HCl removal. Through the breakthrough experiments, X-ray powder diffractometer, and Fourier transform infrared spectroscopy analysis, the overall dechlorination mechanism of the Mn2O3/SiO2 sorbent in a chlorine-containing coal gas system was successfully described in this study. The mechanism consisted of three major routes: (a) Mn2O3 reacted with HCl to form MnCl2, (b) Mn2O3 was first reduced into Mn3O4 and then reacted with HCl to produce MnCl2, and (c) without the involvement of HCl in the dechlorination experiments, the Mn2O3 contained in the fresh sorbent was first reduced to Mn3O4 and then to MnO under the strong reducing atmosphere provided by CO and/or H2.


INTRODUCTION
Since the Industrial Age, the balance between energy supply and environmental protection has been confronted with enormous challenges.Therefore, with its abundance and relatively low and constant price, coal is a popular candidate to manage continuous growth of global energy demand.In the coming decades technology of clean energy production from coal becomes critical.
Integrated gasification combined cycle (IGCC), as an advanced coal technology, has recently provided the world incentive to move toward a cleaner and more efficient energy use.However, since IGCC generates electricity through coal gasification, impurities such as sulfur and chlorine contained in coal will be released in the form of H 2 S and HCl, respectively, during the process of gasification (Yang et al., 2006;Lin et al., 2010;Tu et al., 2011).To achieve the goal of a low pollution to the environment, IGCC requires treatments for these deleterious emissions prior to the combustion of coal gas for electricity production.
Considering absorption by sorbents at high temperature as a most frequent, relatively direct and convenient way to remove contaminants from coal gas, options for desulfurization and dechlorination are various.Popular choices for H 2 S removal include the Ca- (Li et al., 2007), Fe- (Ko et al., 2006), Mn- (Bakker et al., 2003;Ko et al., 2005), Zn-based sorbent (Bu et al., 2008), and mixed metal oxide sorbent (Ko et al., 2007;Lou et al., 2009;Chang et al., 2012); those for HCl removal include the Ca- (Yan et al., 2003;Chin et al., 2005), Na-based sorbent (Nunokawa et al., 2008), and industrial catalyst mixed with multiple components (Dou et al., 2005).Due to the fact that a high percentage of the pollution emitted by coal gasification comes from sulfides, research activities focusing on desulfurization have been widely studied; while relatively little attention has been paid to dechlorination.
Nevertheless, HCl was found to be able to exert a negative influence on the capacity of sulfur removal (Kiil et al., 2002); thereby, taking the possibility of simultaneous sulfur removal into consideration, sorbents capable of eliminating both species will be a better option.Previous literatures have reported on sorbent based upon manganese having promising desulfurization potential (Westmoreland and Harrison, 1976;Atimtay, 2001).Laboratory scale experiments were also conducted showing that Mn-based sorbents had high desulfurization performance (Bakker et al., 2003;Ko et al., 2005).On the basis of potentially removing both species, the Mn-based sorbent emerged as the leading candidate for HCl elimination through thermodynamic screening conducted by the calculation of equilibrium constant.Bakker et al. (2003) studied the desulfurization in a fixed-bed reactor at 400 to 1000°C for hot gas cleaning using Mn-based sorbents.The Mn-based sorbents, prepared by wet impregnation consisting of crystalline MnAl 2 O 4 , a small amount of disperse MnO, and an amorphous Mn-Al-O phase, showed high capacity for desulfurization.Furthermore, MnO and MnAl 2 O 4 were also proved to be feasible for HCl removal.
In this study the main focus was directed toward the coexisting gases since the performance of contaminant removal will be affected by the presence of CO and H 2 (Ko et al., 2006;Tseng et al., 2008).The fact that the extent of influence of these species in coal gas on the performance of HCl removal has not been known completely may suggest the need for further study.This study aims to evaluate the effects of CO and H 2 concentrations on the dechlorination experiments, as well as to carry out a further investigation into the dechlorination mechanism of the Mn 2 O 3 /SiO 2 sorbent.

Material
The Mn 2 O 3 /SiO 2 sorbent prepared by incipient wetness impregnation on supported materials at room temperature were employed in this research.The supported materials were pure commercial SiO 2 spherical particles (Alfa Aesar, stock #44740), which were crushed and sieved to 30-50 mesh and dried in an oven at 393 K for 12 hours to remove the impurities and remaining water before impregnation.The impregnation was proceeded by spraying an aqueous manganese nitrate solution (Mn(NO 3 ) 2 •4H 2 O) added with appropriate amounts of de-ionized water evenly on SiO 2 .Followed by 24 hours of dryness in an oven at 393 K, the impregnated materials were kept at room temperature for 12 hours.Finally, the materials were calcined in airflow conditions at 973 K for 8 hours in a fixed-bed quartz reactor.Sorbents were dried in an oven for 2 hours every time before experiments to remove the remaining water vapor, and every experiment was supplied with 1.0 g sorbent (1.0 cm thick).It should be noted that the nominal weight loading of manganese oxide on SiO 2 was initially 20 wt%, and corrected to approximately 23 wt% through Inductivity coupled plasma-mass spectrometer (ICP-MS) analysis.

Equipment
The experimental apparatus was composed of: (a) a simulated coal gas system, (b) a high-temperature reaction system, and (c) a gas analyzing system.
In the simulated coal gas system, HCl, CO, H 2 , and N 2 were supplied from gas cylinders, mixed in a mixer to ensure the gas mixtures were turbulent, and then introduced to the reaction system.The flow rate of HCl were monitored through a mass flow meter (Protec, PC-540), and that of the rest were monitored by IR soap bubble meters (Gilian, Gilibrator-2).
The reaction system consisted of a bench-scale fixed-bed reactor (a 1.5 cm i.d., 1.8 cm o.d., and 85 cm long quartz tube), an electrical furnace, a temperature controller (TTE, TM-4800), and a K-type thermocouple (0.35 cm o.d., 60 cm long).The quartz tube was housed in the electrical furnace, and set with a 200 mesh frit quartz disk 45 cm below the top of the tube to support the sorbents.The Ktype thermocouple was inserted into the quartz tube with its tip set above the position of the sorbent for accurate temperature measurement through temperature controller.The frit quartz disk was well paved with a layer of glass wool between sorbents and itself prior to every experiment to avoid unstable pressure and the leakage of the sorbent.
The gas analyzing system contained a HCl analyzer and a Fourier transform infrared spectroscopy (FTIR).The outlet HCl concentration was recorded every twelve minute as the experiments proceeded by an on-line gas filter correlation HCl analyzer (Thermo Electron Corporation, MODEL 15C).It is noteworthy that in the experiments with 0 vol% H 2 , the HCl concentration was recorded every two minute rather than twelve due to the sudden breakthrough of the HCl concentration.The FTIR spectrum of the outlet gases from the reactor were obtained on a Perkin Elmer Spectrum One B spectrometer by recording the amount of absorbed light as a function of the scanning wavenumber (cm -1 ).The recorded IR spectra were processed at a resolution of 4 cm -1 with the use of Time Base 2.0 software.

Conditions
The actual composition of coal gas produced by coal gasification varies over a wide range, depending on the type of coal, the gasification temperature, and the model of gasifier (Wakker et al., 1993;Krishnan et al., 1994).The dechlorination experiments were carried out in a simulated coal gas system containing 3,000 ppm HCl, 25 vol% CO, 15 vol% H 2 , and N 2 as a balance gas.Hence, in this study various concentrations of CO and H 2 were applied to the fixed-bed reactor to evaluate their effects on the dechlorination performance.The inlet concentrations of CO included 0, 10, 25 vol%, and that of H 2 included 0, 10, and 15 vol%.The experiments with 500, 1,000, and 3,000 ppm HCl were carried out in advance and the best sorbent capacity was achieved when the inlet HCl concentration was 3,000 ppm.Hence in this research the reaction system was fed with 3,000 ppm HCl.
The influence of temperature on the reaction was studied at 573-873 K, and the optimum operating temperature for HCl removal was found at 673 K. Accordingly, in this research the dechlorination experiments were all carried out at 673 K ensuring the best possible outcome.Moreover, the weight hourly space velocity (WHSV) was all set at 6,000 mL/h/g.The nominal compositions of these gas mixtures are shown Table 1.

Characterization
The chlorinated sorbents were characterized after the experiments.The crystalline structures of fresh and chlorinated samples were analyzed by a Rigaku D/Max III-V X-ray powder diffractometer (XRD) employing Cu Kα

Influence of CO and H 2 Concentrations on the Dechlorination
To measure the dechlorination capacity, performance of the Mn 2 O 3 /SiO 2 sorbent can be expressed as sorbent utilization (SU): where C in and C out are the inlet and outlet concentrations of HCl (ppm), respectively; t is the experimental breakthrough time (min), and t * is the theoretical breakthrough time (min) of the dechlorination process.According to Taiwan Stationary Pollution Source Air Pollutant Emissions Standards, the HCl emissions are regulated within 80 ppm, in which case the experimental breakthrough time was defined as the time from the beginning of the experiment to the point when the outlet HCl concentration reached 80 ppm.As for the theoretical breakthrough time (min), its definition is given as below: where W is the weight of the Mn 2 O 3 /SiO 2 sorbent placed in the reactor (g), X is the actual weight loading of manganese oxide supported on SiO 2 (g/g), M is the molecular weight of the manganese oxide (g/mol), A is the moles of HCl that can be absorbed by one mole of manganese oxide (mol/mol), and F is the molar flow rate of the inlet HCl (mol/min).
A number of chemical reactions were expected to take place in the system when Mn 2 O 3 /SiO 2 made contact with HCl and other components containing in the simulated syngas.The possible reactions were examined by a thermodynamic point of view.
Standard thermodynamic values obtained for later calculations are listed in Table 2. Table 2 summarize the thermodynamic results for reactions of sorbent with HCl, CO, and H 2 , respectively and simultaneously, at various temperatures (400, 500, 600, 800, 1000, and 1500 K).Every positive Gibbs free energy and the related equilibrium constant were highlighted in bold.
Reactions of Mn 2 O 3 with CO and H 2 in Reactions (3) has a tendency to form Mn 3 O 4 when reacting with CO or/and H 2 due to the strong reducing atmosphere.In addition, the Mn 3 O 4 formed from the reduction reaction can subsequently be attacked by the presence of HCl.Same as Reactions (4), Mn 3 O 4 can react with HCl and CO to form MnCl 2 , CO 2 , and H 2 O, or with HCl and H 2 to form MnCl 2 and H 2 O. Also, the production of MnCl 2 , CO 2 and H 2 O can be resulted from reaction of Mn 3 O 4 with HCl and both CO and H 2 .To be noticed, Reaction (5) has the highest equilibrium constant among all of the reaction presented in this study.
Research centered on the effects of CO and H 2 on the performance of HCl elimination was carried out by introducing various amounts of CO and H 2 into the absorption system.The breakthrough curves in Fig. 1 are presented as a plot of dimensionless time t/t * (min/min) versus HCl concentration (ppm).Every set of the experiments were conducted over three times, thus the error bars in the following figures can ensure the accuracy of the experimental data.
In Fig. 1(a), the Mn 2 O 3 /SiO 2 sorbent was reacted at 673 K with 3,000 ppm HCl in the presence of 15 vol% H 2 at various CO concentrations.The breakthrough dimensionless time at 0, 10, and 25 vol% CO were approximately 0.13, 0.10, and 0.12, respectively.The Mn 2 O 3 /SiO 2 sorbent reacted at 0 vol% CO showed the best dechlorination performance.However, there was no significant influence of CO concentration observed on the reaction.Though the SU seemed at first glance to be far lower than expectation, these results could still be considered fairly good in comparison with the capacity of CuO/SiO 2 and Fe 2 O 3 /SiO 2 sorbents tested in advance.
Fig. 1(b) presents the breakthrough curves for the removal of HCl at various CO concentrations as the concentration of H 2 was changed to 10 vol%.The breakthrough dimensionless time at 0, 10, 25 vol% CO were around 0.14, 0.14, and 0.07, respectively.At 0 and 10 vol% CO, the difference between their SUs was not clear; while at 25 vol% CO, its SU fairly dropped.However, this observation was not in concord with the above results in Fig. 1(a); that is, no conclusion so far can be drawn from the above findings.
As tabulated in Fig. 1(c), the inlet H 2 concentration was 0 vol%.The breakthrough dimensionless time at 0, 10, 25 vol% CO were approximately 0.004, 0.010, and 0.011, respectively.It is notable that an abrupt breakthrough was discovered regardless of the CO concentrations when there was no inlet H 2 .The capacity of the Mn 2 O 3 /SiO 2 sorbent was drastically diminished to a level as if the dechlorination did not happen at all.Unquestionably, H 2 should be considered essential for dechlorination.
It was concluded that H 2 was a key parameter in achieving dechlorination, though its specific cause still remained unknown.The presence of CO may not be sufficient for the dechlorination reaction to take place.Furthermore, the concentration of CO seemed to have no obvious influence on the HCl removal.It was likely that in the presence of H 2 , the positive influence of H 2 overpowered that of CO on the absorption reaction.In this case, no matter what the CO concentration was, the benefit it provided was not as significant as that from H 2 .However, when there was no H 2 present in the reaction system, the influence of CO started to take over.Though the absence of H 2 led to the great decrease of sorbent capacity, the slightly increasing sorbent performance in Fig. 1(c) with increasing CO concentration may indicate certain positive effect from CO on the absorption.
It was surprising that the above observations were quite different from the previous literatures (Ko et al., 2004;Ko et al., 2007) where contrary effects of H 2 and CO on the desulfurization were found.The increasing concentration of H 2 reduced the SU of desulfurization while that of CO promoted it, and this phenomenon was related to the watergas shift reaction (Ko et al., 2004;Ko et al., 2007).It was concluded that in this research chance of the participation of water-gas shift reaction in the dechlorination could be low, since the concentrations of H 2 and CO showed different influence on the HCl removal.Furthermore, the fact that the involvement of H 2 was indispensable for dechlorination but it also decreased the SU of desulfurization may result in certain challenges in achieving the best removal performance for both dechlorination and desulfurization.To further confirm the strong influence of the absence of H 2 on the reaction, XRD characterization of the fresh and chlorinated sorbents was carried out.Fig. 2 gives the XRD patterns for eleven samples: one pure SiO 2 , one fresh Mn 2 O 3 /SiO 2 sorbent, and nine sets of chlorinated sorbents.The first XRD patterns were from the pure SiO 2 sorbent.According to the PDF database published by ICDD, the patterns displayed a clear view of SiO 2 (42-1401) in favor of the identification of SiO 2 contained in the following patterns.The second XRD result belonging to the fresh sorbent confirmed that the sorbent initially contained mainly Mn 2 O 3 (65-7467) supported by SiO 2 .The rest of the XRD patterns were obtained from the previous experiments (Fig. 1).As presented in Fig. 2, after the dechlorination reaction with 3,000 ppm HCl at 0 vol% H 2 and various CO concentrations the three patterns of the chlorinated samples stayed unchanged; that is, due to the absence of H 2 the dechlorination failed to take place.This result was in conformity with previous observations in Fig. 1(c).In addition, patterns assessed from experiments with the involvement of H 2 displayed the transition from the fresh sorbent (Mn 2 O 3 ) to the reacted sorbent (Mn 3 O 4 , 24-0734).It is worth mentioning that typically in a high-temperature dechlorination process using Mn-based sorbents, the end product was expected to be MnCl 2 which was undetected in this XRD patterns.In-depth discussion regarding the confirmation of the presence of MnCl 2 in the chlorinated sorbents through X-ray photoelectron spectroscopy (XPS) analysis can be found in our previous investigation where the binding energy of Mn 2p3/2 located at 640.6 eV was assigned to Mn 2+ in MnCl 2 and that of Cl 2p centered around 198.0-199.0eV corresponded to Cl -in MnCl 2 .Fig. 3 displays the FTIR spectroscopy obtained from the previous HCl removal experiments (Fig. 1).Due to the high concentration of the inlet CO (at 2,030-2,250 cm -1 ), the spectroscopy was magnified in favor of the observation of other species.In Fig. 3(a) the experiment was implemented with 10 vol% CO and 10 vol% H 2 , and the existence of CO 2 (at 2,230-2,450 and 3,500-3,800 cm -1 ) and H 2 O (at 1,300-2,000 and 3,500-4,000 cm -1 ) confirmed the accuracy of the previous prediction of Reactions (3)-( 5).The decreasing absorbance of CO 2 and H 2 O was assumed to be related to the exhaustion of Mn 2 O 3 contained in the sorbent and the subsequent exhaustion of Mn 3 O 4 reduced from Mn 2 O 3 .Besides, at around 0.15 t/t * the spectrum patterns of HCl (at 2,700-3,100 cm -1 ) was observed, in which case it could be concluded that the breakthrough of HCl took place approximately within a dimensionless time range of 0.10-0.15which was in accordance with the experimental results in Fig. 1(b).Also, the increasing HCl absorbance indicated that the breakthrough of HCl was gradually achieved as the experiment proceeded.
In Fig. 3(b), the FTIR spectroscopy was obtained from the previous dechlorination experiments conducted with 0 vol% CO and 10 vol% H 2 (Fig. 1(b)).The species detected were HCl and H 2 O (H 2 cannot be detected by FTIR), which was in concord with the reaction products in Reactions (3)-(5).There was no inlet CO, therefore no CO 2 absorbance was observed.Clearer absorbance peaks of H 2 O were found, and its progressively decreasing spectrum pattern was probably due to the exhaustion of Mn 2 O 3 and that of Mn 3 O 4 reduced from Mn 2 O 3 as well.Moreover, the absorbance peak of HCl at 0.15 t/t * revealed that the breakthrough of HCl also took place approximately within a dimensionless time range of 0.10-0.15, in agreement with the previous experimental data displayed in Fig. 1(b).
As discussed previously, the presence of H 2 had a great effect on the dechlorination reaction.The participation of H 2 was extremely essential for the HCl removal experiments.Fig. 3(c) shows the FTIR spectrum of the outlet gases in the experiment carried out with 10 vol% CO and 0 vol% H 2 .The absorbance peaks of H 2 O and CO 2 responded to the reaction products in Reactions (3)-( 5).The decreasing absorbance of CO 2 and H 2 O as the experiment proceeded were resulted from the exhaustion of Mn 2 O 3 and Mn 3 O 4 .Additionally, a large amount of HCl was detected at 0.02 t/t * , implying that the breakthrough of HCl was achieved at about 0.01-0.02t/t * in conformity with previous experimental results in Fig. 1(c).

Reaction Mechanism
Taking above experimental results into consideration, the overall performance of the Mn 2 O 3 /SiO 2 sorbent seemed inadequate for a complete removal of HCl.However, research into the reaction mechanism behind this complex system can still be beneficial for the future development of dechlorination technology.In order to further explore the reaction chemistry of the Mn 2 O 3 /SiO 2 sorbent in a chlorine-containing coal gas system, additional information on the XRD patterns for sorbents that had went through experiments without the presence of inlet HCl at various CO and H 2 concentrations was provided in Fig. 4. Different from the previous results, Fig. 4 displays clear patterns of , and the remaining Mn 2 O 3 contained in the Mn 2 O 3 /SiO 2 sorbent along with some Mn 3 O 4 .Interesting inferences can be drawn from the above observations.Firstly, due to the strong XRD patterns of MnO, it can be assumed that the end product of the experiment carried out without the presence of HCl was MnO.It is obvious that Mn 2 O 3 contained in the fresh sorbent (Fig. 2) was reduced into MnO after reacting with CO and/or H 2 Secondly, given the observed Mn 3 O 4 patterns in the XRD results (Fig. 4), it can be concluded that the reduction of Mn 2 O 3 into MnO was inevitably accompanied by the participation of Mn 3 O 4 as a intermediate product.
Thirdly, the existence of HCl was assumed to be able to inhibit Mn 3 O 4 from being further reduced into MnO.The Mn 3 O 4 would be attacked by HCl to form MnCl 2 .In addition, in previous XRD results assessed from the chlorinated sorbent (Fig. 2) strong patterns of Mn 3 O 4 was detected rather than that of MnO.Combining the above findings, the participation of HCl was able to react with Mn 3 O 4 (reduced from Mn 2 O 3 ) to form MnCl 2 , leading to the failure of the production of MnO.The patterns of Mn 3 O 4 in Fig. 2 indicated that in the research conducted with HCl, parts of the Mn 3 O 4 was reacted with HCl to produce MnCl 2 , and the rest of them remained as Mn 3 O 4 ; that is, the existence of HCl could suppress the formation of MnO from the remaining Mn 3 O 4 .In other words, Mn 2 O 3 contained in the fresh sorbent was supposed to be reduced to Mn 3 O 4 and then to MnO under the strong reducing atmosphere provided by CO and/or H 2 ; however, the existence of HCl restrained this tendency.
Fourthly, in Fig. 4 it was found that the coexistence of CO and H 2 in the reaction was not a necessity for the production of MnO.Either CO or H 2 could be the motivation behind the formation of MnO.The only difference was the extent of the reduction of Mn 2 O 3 , since in Fig. 4 when the inlet concentration of CO was 25 vol% and that of H 2 was 15 vol% almost no XRD patterns of Mn 2 O 3 was observed as if its reduction was achieved more completely.
In conclusion, this study has evaluated the effects of CO and H 2 concentrations on the dechlorination experiments, followed by an investigation into the dechlorination mechanism of the Mn 2 O 3 /SiO 2 sorbent.The parts of the dechlorination mechanism of Mn 2 O 3 /SiO 2 sorbent were established and the multiple reactions involved were also identified (Reactions (3)-( 5)); the Mn 2 O 3 /SiO 2 sorbent could either react with HCl in the atmosphere of CO and H 2 to form MnCl 2 , CO 2 , and H 2 O, or be reduced to Mn 3 O 4 and reacted with HCl in the atmosphere of CO and H 2 to produce MnCl 2 , CO 2 , and H 2 O.
In elaborating the reactions between the Mn 2 O 3 /SiO 2 sorbent and HCl accompanied by CO and H 2 , Fig. 5   produce MnCl 2 , and (c) in the absence of inlet HCl, Mn 2 O 3 was firstly reduced to Mn 3 O 4 and then to MnO (Fig. 4).As can be seen from Fig. 5, in route (a), H 2 was found to be essential for the dechlorination (Fig. 1(c)); that is, for the production of MnCl 2 the involvement of HCl and H 2 was critical, and that of CO was relatively insignificant.In route (b), the fact that without the presence of H 2 the Mn 2 O 3 sorbent showed almost no reactivity with inlet HCl after the dechlorination (Fig. 2) implied the formation of Mn 3 O 4 and MnCl 2 required the participation of H 2 .In route (c), the three well-detected patterns of MnO in Fig. 4 inferred the coexistence of CO and H 2 in the simulated gas was not indispensable for the reduction of Mn 2 O 3 into Mn 3 O 4 and MnO.Either the presence of CO or H 2 could benefit the formation of MnO.

CONCLUSIONS
This study aims at the evaluating the influence of CO and H 2 concentrations on the performance of HCl elimination.The experiments were conducted in a fixed-bed reactor at 673 K by supported manganese oxide sorbent, Mn 2 O 3 /SiO 2 , at various CO and H 2 concentrations.The absence of inlet H 2 led to a drastic diminishment of the sorbent capacity.It was concluded that the participation of H 2 was an indispensable requirement in achieving dechlorination by the Mn 2 O 3 /SiO 2 sorbent though its specific cause still remained unknown.Furthermore, the concentration of CO seemed to have no obvious influence on the HCl removal.
Through the breakthrough experiments, XRD and FTIR analysis, this study also reports on a deeper investigation into the chemistry of the Mn 2 O 3 /SiO 2 sorbent in a chlorine-containing coal gas system.Three major routes in the dechlorination mechanism comprising the formation of MnCl 2 from the reaction of Mn 2 O 3 or Mn 3 O 4 with HCl, the reduction of Mn 2 O 3 into Mn 3 O 4 , and the production of MnO were successfully established.
It is worth mentioning that the SU in this study seemed to be far lower than expectation, due to the unknown reactions taking place in this complex chlorine-containing coal gas system.It was concluded that the reactivity between the Mn 2 O 3 /SiO 2 sorbent and the inlet simulated gas environment containing HCl, CO, and H 2 was not as good as expected.In this research the laboratory scale experiment indicated that the dechlorination performance of Mn 2 O 3 /SiO 2 sorbent was not good.Though the dechlorination mechanism of the Mn 2 O 3 /SiO 2 sorbent was successfully built in this study, the reason behind its low capacity still suggested the necessity for further study.
= 1.54056Å).The applied current and voltage were 30 mA and 20 kV, respectively, and the scan rate was 3°/min.The diffraction patterns were recorded and analyzed using MDI Jade 5.0 software and Powder Diffraction File (PDF) database published by International Centre for Diffraction Data (ICDD).

Table 1 .
The gas composition of simulated coal gas mixtures.
Table 2 indicate the possibility of the reduction of Mn 2 O 3 contained in sorbent to form Mn 3 O 4 accompanied by possible production of CO 2 and H 2 O. Mn 2 O 3 can react with CO to form Mn 3 O 4 and CO 2 , or with H 2 to form Mn 3 O 4 and H 2 O. Reaction (3) shows that Mn 2 O 3 can react with both CO and H 2 to form Mn 3 O 4 , CO 2 , and H 2 O.The reactions of Mn 2 O 3 with HCl accompanied by CO and H 2 to produce MnCl 2 , CO 2 and H 2 O. Mn 2 O 3 can react with HCl and CO to form MnCl 2 , CO 2 and H 2 O, or with HCl and H 2 to form MnCl 2 and H 2 O. Reaction (4) reveals that Mn 2 O 3 can react with HCl and both CO and H 2 to produce MnCl 2 , CO 2 , and H 2 O.

Table 2 .
Summary of the thermodynamic calculations for reaction of Mn 2 O 3 with CO and H 2