Chemical Engineering Journal 247 (2014) 59–65

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Chemical Engineering Journal

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Effect of HCl on V2O5/AC catalyst for NO reduction by NH3 at lowtemperatures

http://dx.doi.org/10.1016/j.cej.2014.01.0361385-8947/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel./fax: +86 351 4043727.E-mail address: zghuang@sxicc.ac.cn (Z. Huang).

Yaqin Hou a, Guoqin Cai a,b, Zhanggen Huang a,⇑, Xiaojin Han a, Shijie Guo a

a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, PR Chinab University of Chinese Academy of Sciences, Beijing 100049, PR China

h i g h l i g h t s

� A promoting effect of HCl on thecatalytic activity of V2O5/AC catalystwas proposed.� Promoting effect depended on the

quantity of NH4Cl formed on thecatalyst surface.� NH4Cl promoted the adsorption of

NH3 and reaction of NHþ4 .

g r a p h i c a l a b s t r a c t

HCl

NH4Cl

AC AC AC V2O5

NO+NH3+O2 N2+H2O

Promotion

Poison

a r t i c l e i n f o

Article history:Received 23 October 2013Received in revised form 13 January 2014Accepted 15 January 2014Available online 24 January 2014

Keywords:V2O5/AC catalystLow-temperature SCRHClNH4Cl

a b s t r a c t

Effect of HCl from municipal solid waste (MSW) on V2O5/AC (activated coke) catalyst for selectivecatalytic reduction (SCR) of NO with NH3 at low temperature is investigated and characterized by TG,elemental analyses and XRD. Results demonstrate that lower concentration HCl is beneficial to theactivity of V2O5/AC catalyst; At the presence of HCl, the catalytic activity increases as the reactiontemperature, and as the volume space velocity increases the catalytic activity decreases gradually. Inthe optimal reaction conditions of temperature above 120 �C and space velocity below 6000 h�1, HClplays a promoting effect on the catalytic activity of V2O5/AC catalyst. The promoting effect of HCl maybe attributed to NH4Cl deposited on the catalyst surface, which can increase the surface acidity of theV2O5/AC catalyst and thus enhance the SCR activity.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

Combustion has been proven to be an attractive technology formunicipal solid waste (MSW)’s disposal due to the primaryadvantages of hygienic control, volume reduction and energyrecovery, however, which also cause some secondary pollutants,such as heavy metals (Pb, Cd, Hg), acid gases (HCl, Cl2, HF, SO2,NOx), particles and dioxins [1,2]. Among these pollutants, nitrogenoxide (NO) has been put on the agenda because of the formation of

photochemical smog and acid rain. With increasingly stringentenvironmental regulations and criteria, NO is supposed to beeliminated before discharge. The average concentration of NOemitted from MSW incineration plants, about 100 ppm, is in thesame range of those from coal-fired plants with wet-desulfuriza-tion devices. As a consequence, selective catalytic reduction (SCR)technique, the most effective means for NO reduction, may alsobe used in MSW combustion [1]. In recent years, the popular com-mercial catalyst for NO removal, V2O5/TiO2 or V2O5–WO3/TiO2,must be used at temperature higher than 350 �C (before dustremoval equipment and desulfurization devices) to avoid catalystdeactivation by SO2. In the MSW incineration system, part of the

60 Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65

exhaust contains significant amounts of heavy metals, alkali metalsand particles, which can easily deactivate the SCR activity of thesecommercial catalysts [3–7]. So the lower temperature SCR technol-ogy is preferable to NO removal in MSW incineration system.

However, even after the dust removal and desulfurizationdevices, there are few amounts of pollutants in the flue gas, suchas SO2 and HCl. In recent years, great attention has been paid tothe influences of SO2 on the performance of catalysts during NOremoval. Several catalysts used for NO reduction at lower temper-ature have been developed, such as CuO/AC [8], MnOx/Al2O3 [9],CuO/Al2O3 [10] and Mn/TiO2 [11]. The results show that thepresence of SO2 can inhibit the SCR activity of these catalysts attemperature of lower than 150 �C, because SO2 can strongly adsorbon the surface of these catalysts and/or react with the active metalsor the supports to form corresponding sulfate or sulfite salts. Theeffects of HCl on the SCR catalysts are mainly studied at tempera-ture above 250 �C. Results showed that the catalysts were deacti-vated by HCl, which is due to the formation of Cu2Cl(OH)3 onCuHM (copper ion exchanged mordenite type zeolite catalyst)and volatile vanadium chlorides and NH4Cl on V2O5/TiO2 catalyst[12–14]. To improve the SCR activity and stability of the catalystsin the presence of HCl, some studies tried to add a second metalto modify the catalysts. For example, Choung et al. stated that add-ing Ce to CuHM catalysts can improve the tolerance of HCl and thestabilization of the mordenite structure of the catalysts [15].Whereas, Chang et al. found that Na modification could not preventthe deactivation of the Rh/Al2O3 catalyst by HCl for NO reduction[16]. Attentively, results of adding a second metal to catalysts arestudied at relatively high temperature; few studies have beendevoted to the effect of HCl on the SCR activity and stability atlow temperature. Therefore, the key to development of the lowertemperature SCR catalysts is to improve the resistance of catalyststo SO2 and HCl poisoning.

Early studies in our laboratory revealed that at temperature150–250 �C, activated coke supported V2O5 (V2O5/AC) showedhigher activity for NO removal with NH3, more importantly, SO2

promoted the catalytic activity, which was attributed to thereactions between the ammonium-sulfate salts formed on thecatalyst surface and NO [17–19]. In this work, the catalytic activityand stability of the V2O5/AC catalyst was investigated in the pres-ence of HCl under different conditions, and the mechanism wasprimarily piloted by means of XRD, element analyses, MS, NH3

adsorption, NH3 transient response and temperature-programmedsurface reaction (TPSR).

Table 2Standard conditions of selective catalytic reduction (SCR) over V2O5/AC.

NO ppm 500NH3 ppm 500HCl ppm 0–1200 (when used)O2 % 5N2 BalanceCatalyst g 2.0Total flow rate ml/min 400Space velocity h�1 6000–12,000Reaction temperature �C 80–150

2. Experimental

2.1. Catalyst preparation

The catalyst support, activated coke (AC), was obtained fromShanxi Xinhua Ltd., Co. Proximate and ultimate analysis of ACwas shown in Table 1.

V2O5/AC catalyst was prepared through conventional pore vol-ume impregnation using an aqueous solution of ammonium meta-vanadate in oxalic acid (m(AC)/V(NH4VO3) = 1.5 g/ml), which wasdescribed in detail elsewhere [20]. The V2O5 loading on the

Table 1Proximate and ultimate analyses of AC (air dry basis).

Proximate analysis (w/%) Ultimate ana

M A V C

1.91 10.74 2.00 82.10

M-moisture, A-ash, V-volatile matter, S-sulfur, C-carbon, H-hydrogen, N-nitrogen, O-oxy

catalysts was determined by the concentration of ammoniummetavanadate and confirmed by ICP. After the impregnation, thecatalyst was dried at 50 �C for 12 h and then at 110 �C for 5 h, sub-sequently calcined in N2 at 500 �C for 8 h and pre-oxidized in air at250 �C for 5 h. The V2O5 loading of the catalyst was named as x wt%V2O5/AC.

2.2. Catalyst tests

Catalytic activity tests were carried out in a fixed-bed glassreactor operating under atmosphere pressure, which are describedin detail in Table 2, including 500 ppm NO, 500 ppm NH3 and 7–8%O2 in a balance of N2. The feed rates of NH3/N2, NO/N2 werecontrolled by mass flow meters and the feed rates of N2 and airwere controlled by rotameters. The mixture of N2, air and NOwas first bubbled into hydrochloric acid to carry gaseous HCl andthen pass through CaCl2 desiccants to avoid the influence of H2O.The concentration of HCl was measured by acid–base titration.To prevent the condensation of hydrochloric acid in the inlet tube,the tube was heated by heating tapes to 50 �C. To avoid the reac-tion of HCl with NH3 before reaching the catalyst surface, HCland NH3 were introduced into the reaction system separately.The inlet and outlet concentration of HCl was measured by acid–base titration. The detail operation was shown in Fig. 1. Using amixture of air and N2 (flow rate of 280 ml/min) through a vesselcontaining different concentrations of hydrochloric acid, a concen-tration of HCl gas was carried into the reactor. HCl concentrationwas calculated theoretically: the inlet and outlet of HCl gas wasadsorbed by NaOH solution, and then determined by acid–basetitration. Difference between the two was retained during thereaction or consumed amount of HCl. The inlet and outlet concen-tration of NO was measured by an on-line flue gas analyzer(KM9106 Quintox, Kane International Limited). The NO conversionon the V2O5/AC catalyst is defined by the equation:

XNO ¼Cin � Cout

Cin� 100% ð1Þ

Cin is the inlet concentration of NO; Cout is the outlet concentrationof NO.

2.3. Catalyst characterization

Elemental analyses of V2O5/AC catalyst before and after SCRreaction were made to confirm the weight percentages of C, H, Non the surface of the catalysts by a Vario EL elemental analyzerof Elementar Enalysensysteme GmbH Co. The content of Cl

lysis (w/%)

H O N S

1.50 4.01 0.94 0.41

gen.

Fig. 1. Schematic diagram of HCl concentration measurement in flue gas.

Fig. 2. Effect of HCl on the catalytic activity of V2O5/AC catalyst with different V2O5

loading. Reaction conditions: 500 ppm NO, 500 ppm NH3, 5% O2, balance N2,1200 ppm HCl, space velocity 6000 h�1, reaction temperature 150 �C.

Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65 61

deposited on the surface of catalyst was examined by the nationalstandard of PR of China GB/T 3558-1996.

Thermo gravimetric analysis (TGA) was carried out on NETZSCHSTA 409PC/PG in an Ar stream of 400 ml/min and a heating rate of10 �C/min.

X-ray diffraction (XRD, Rigaku D/max-2500 diffractometer withCu Ka radiation, k = 0.1542 nm, 40 kV, 100 mA) was used toconfirm the species of substance formed on the catalyst surface.The scanning range of 2h was from 5� to 80� in steps of 0.01�, thescanning speed was 5�/min.

To compare the number of acid sites on V2O5/AC catalyst pre-treated with NH4Cl, isothermal adsorption of NH3 was performedin a fixed bed glass reactor as in Section 2.2. 2.0 g catalystpretreated with NH4Cl was exposed to a stream containing500 ppm NH3 and balance N2. The outlet gas was monitored on-line by a mass spectrometer (Balzers QMS422) during the wholeprocess. To avoid the influence of H2O, m/e = 16 instead of 17was used to monitor NH3.

A transient response experiment of NH3 was carried out tounderstand the effect of NH4Cl on NO conversion. The feed gas con-tains 500 ppm NO, 500 ppm NH3, 1200 ppm HCl, 5% O2 and balanceN2. NH3 was removed from the feed gas at the steady state andthen added again at another steady state. The total flow rate wasmaintained at 400 ml/min in the whole process.

Reaction of NH4Cl pre-deposited on the catalysts with gaseousNO was studied using TPSR. The feed gas, total flow rate of400 ml/min, contains 500 ppm NO, 5% O2 and balance N2. The tem-perature was heated to 150 �C at a rate of 10 �C/min and thenmaintained at 150 �C.

3. Results and discussion

3.1. Effect of HCl on V2O5/AC catalyst with different V2O5 loading

Fig. 2 shows the NO conversion of V2O5/AC catalyst with differ-ent V2O5 loading at the presence or absence of HCl. In the absenceof HCl, NO conversion on AC is only 26% at temperature of 150 �C.However, when V2O5 is loaded on AC, the SCR activity of V2O5/ACcatalyst increases remarkably to above 52% even V2O5 loadingwas only 0.5%. NO conversion increases from 52% to 92% withincreasing V2O5 loading from 0.5% to 5% at temperature of 150 �Cand volume velocity of 6000 h�1. These all indicate that V2O5 pro-motes the SCR activity of AC, which are similar with our beforestudies [18].

In the presence of 1200 ppm HCl gas, under the reactionconditions of 150 �C and volume velocity of 6000 h�1, the catalytic

activity of 0.5%V2O5/AC increases sharply from 52% to 92%, and1%V2O5/AC performs a same trend from 67% to 80%. Meanwhile,high V2O5 loading catalyst (3% and 5%) showed a relatively badperformance compared with low V2O5 loading: NO conversionincreases slightly after adding HCl into the feed gas and after fewminutes decreases to the levels of NO conversion in the absenceof HCl. All these results clearly indicate that under the experimen-tal conditions the effect of HCl on V2O5/AC catalyst was obviouslydifferent from the role on CuHM or Rh/Al2O3 catalysts reported inliterature [15,16]. HCl promotes the SCR activity of V2O5/ACcatalyst while poisoned the SCR activity of CuHM and Rh/Al2O3

catalysts at temperature of 150 �C.According to the experiment results, it can be observed that

0.5%V2O5/AC showed the best performance at the presence ofHCl, which would been taken to further research the HCl concen-tration and reaction temperature and volume velocity, aimed toprovide a optimal operate parameter for the V2O5/AC catalyst atthe presence of HCl.

3.2. Effect of HCl concentration on the SCR reaction

The effect of HCl concentration on the NO conversion of the0.5%V2O5/AC catalyst is illustrated in Fig. 3. NO conversionincreases with HCl concentration, and reaches the highest point

Fig. 3. Effect of HCl concentration on the catalytic activity of 0.5%V2O5/AC catalyst.Reaction conditions: 500 ppm NO, 500 ppm NH3, 5% O2, balance N2, space velocity6000 h�1, reaction temperature 150 �C.

Fig. 5. Effect of HCl on the catalytic activity of 0.5%V2O5/AC catalyst at differenttemperature in the 1200 ppm HCl. Reaction conditions: 500 ppm NO, 500 ppm NH3,5% O2, balance N2, 1200 ppm HCl, space velocity 6000 h�1.

62 Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65

about 92% in 1200 ppm HCl. Interestingly, if the HCl concentrationcontinues increasing, NO conversion decreases sharply. Thisphenomenon shows that high concentration of HCl inhibits theNO reduction activity of 0.5%V2O5/AC catalyst. Although the actualmechanism for the performance at different HCl concentration isunknown at present, it seems to be that the promoting effect ofHCl is limited in a concentration range and high concentration ofHCl is unfavorable to the catalytic activity.

3.3. Effect of space velocity on the SCR reaction

Fig. 4 shows the results of the effect of HCl on NO conversion of0.5%V2O5/AC catalyst at different space velocity. Whether or notHCl in the simulated flue gas, NO conversion of 0.5%V2O5/AC cata-lyst decreases with the increasing of space velocity. At the absenceof HCl, NO conversion decreases from about 52% to 24% as thespace velocity increases from 6000 h�1 to 12,000 h�1; at the pres-ence of HCl, NO conversion decreases from about 92% to 47% as thevolume velocity increases from 6000 h�1 to 12,000 h�1, which isdue to the reduced residence time on the catalyst surface as thespace velocity increases. The results indicated that space velocityis one of the key parameters for the SCR reaction.

Fig. 4. Effect of HCl on the catalytic activity of 0.5%V2O5/AC catalyst at differentspace velocity. Reaction conditions: 500 ppm NO, 500 ppm NH3, 5% O2, balance N2,1200 ppm HCl, space velocity 6000 h�1, reaction temperature 150 �C.

3.4. Effect of reaction temperature on the SCR reaction

Fig. 5 shows the effect of HCl on the NO conversion of 0.5%V2O5/AC catalyst at different temperature. At the absence of HCl,NO conversion changes slightly when the reaction temperatureincreased from 80 �C to 150 �C. After adding HCl into the simulatedflue gas, reaction temperature plays an important role in the cata-lytic activity. The SCR activity of 0.5% V2O5/AC catalyst increasesapparently with the reaction temperature. NO conversion in-creases remarkably from 52% to 92% and 46% to 68% at 150 �Cand 120 �C separately, and the increasing rate at 150 �C is higherthan that of 120 �C. On the contrary, the catalytic activity decreasesat reaction temperature below 100 �C.

3.5. Effect of SO2 and H2O on the SCR reaction

The influence of H2O on the SCR activity over V2O5/AC catalystwas investigated and shown in Fig. 6. In the absence of H2O, theNO conversion over 0.5% V2O5/AC catalyst was above 80%, and anabrupt decrease after introducing 5 vol% H2O. This result showedthat H2O had an obvious inhibition on the SCR activity to thisSCR catalyst, and the inhibition of H2O may be due to thecompetitive adsorption between H2O and NH3 on the active sitesof the catalyst surface. These observations agree well with previousreport [23].

Fig. 6. The effect of H2O on the SCR activity of 0.5%V2O5/AC catalyst.

Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65 63

The influence of SO2 on the SCR activity over V2O5/AC catalystwas investigated and shown in Fig. 7. NO conversion over 0.5%V2O5/AC catalyst exhibited a slight decrease after introducing200 ppm SO2 and then slowly rising again after a certain time,which illustrated that SO2 had an inhibit action for the promotioneffect of HCl on V2O5/AC catalyst, which may be due to excessivedeposition of (NH4)2SO4 or NH4HSO4 on the catalyst surface.

3.6. A possible mechanism of the promotion effect of HCl on V2O5/ACcatalyst

In the course of the experiments, some white crystal substancewas found adhering to the wall of the reactor, and was disappearedat the end of the reaction. By analyzing the catalyst samples withTG, as Fig. 8 shows, DTG curves of b, c, d, e all have a significantweight loss and a similar peak decomposition temperature, whichsuggests that the substance should be NH4Cl. The temperature ofthe weight loss starts at 150 �C and disappears mainly at 270 �Cand the maximum decomposition temperature increases withthe decreasing of the SCR reaction temperature, which indicatesthat the same substance deposited on the catalyst. Comparingthe DTG curves of the catalysts after the reaction and the NH4Clpre-impregnated on V2O5/AC catalyst, the initial temperature is

Fig. 7. The effect of SO2 on the SCR activity of 0.5%V2O5/AC catalyst.

Fig. 8. DTG curves of 0.5%V2O5/AC catalyst. (a) Fresh catalyst. (b–e).0.5%V2O5/ACcatalyst after the SCR reaction in the presence of HCl at 150 �C, 120 �C, 100 �C, 80 �Crespectively. (f) NH4Cl impregnated on 0.5%V2O5/AC catalyst.

almost consistent, while the final temperature and thedecomposition peak temperature become higher as the lower reac-tion temperature, and the quantity of deposited NH4Cl becomemore as the reaction temperature decreases.

In the present study, TG shows that NH4Cl may be deposited onthe catalyst surface. It is important to confirm this conclusion. XRDpatterns of the catalysts are shown in Fig. 9. For the fresh catalystand the catalyst after SCR reaction at temperature of 150 �C in thepresence of HCl, only SiO2 on AC is visible. For the catalyst afterreaction at temperature of 100 �C and 80 �C at the presence ofHCl, NH4Cl is identified on the catalyst surface and the intensityof NH4Cl decreases with the increased temperature. The peak at22.9� (d = 0.388 nm) is the summation of hkl indices of (100).The diffraction at 32.6� (d = 0.274 nm) is the summation of hklindices of (110); the diffraction at 46.8� (d = 0.194 nm) is the sum-mation of hkl indices of (200); and the diffraction at 58.2�(d = 0.158 nm) is the summation of hkl indices of (211). No pres-ence of obvious NH4Cl peaks for the sample used at 150 �C is likelydue to small crystals formed on the catalyst surface and NH4Clcrystals have a well dispersion.

It has been reported that during the SCR reaction NO could reactwith NH4

+ adsorbed on the Brunsted acid site and reaction rate in-creases as the temperature increases [20–22]. Generally speaking,the deposition rate of NH4Cl on the catalyst surface decreases athigh reaction temperature, however, the reaction rate of NHþ4 andNO increases, which is similar to the results from the effect of SO2

on 0.5%V2O5/AC catalyst activity [23]. If the deposition rate exceedsthe reaction rate, HCl poisons the SCR activity; if not, it is promot-ing. To prove the above assumption, the chemical composition ofthe bulk and surface of the catalyst at the different reaction temper-ature is listed in Table 3. The content of N, H, Cl of samples are high-er than that without HCl in the simulated flue gas, and importantlythe calculated content of NH4Cl increases as the decreased reactiontemperature. The curves of NO conversion versus m(NH4Cl)/m(cat.)over 0.5%V2O5/AC catalyst at different reaction temperature(Fig. 10) shows that the highest catalytic activity is about 92% whenlittle NH4Cl deposited on the catalyst surface and the catalyticactivity decreases sharply when the content of NH4Cl increasing.Specifically, if m(NH4Cl)/m(cat.) is above 0.044, HCl poisons theSCR activity; if not, it plays a promoting role.

In the above study, all the analyses of the catalyst sampleproved the formation of NH4Cl on the surface of catalysts, andthere is very little of NH4Cl formed on the 0.5%V2O5/AC catalystsurface at reaction temperature of 150 �C in the presence of HCl.

Fig. 9. XRD curves of 0.5%V2O5/AC catalyst under different reaction temperature.

Table 3Characteristics of 0.5%V2O5/AC catalyst at different temperature.

Temp. (�C) X(NO)% Composition (w/%) m(NH4Cl)/m(cat)

C H N Cl

Fresha 56.600 85.821 1.171 0.500 0b 0150 91.923 82.854 1.250 0.573 0.625 0.019120 68.272 82.668 1.265 1.021 1.475 0.044100 41.670 80.734 1.384 1.095 1.650 0.05080 29.335 79.413 1.582 1.113 1.750 0.053

a The condition of fresh catalyst: reaction temperature of 150 �C, without HCl,space velocity of 6000 h�1.

b The Cl content of fresh catalyst is 0.

Fig. 10. NO conversion (%) versus m(NH4Cl)/m(cat.) over 0.5%V2O5/AC catalyst atdifferent reaction temperature.

Fig. 12. The transient response of NH3 during the SCR reaction over 0.5%V2O5/ACcatalyst. Reaction conditions: 500 ppm NO, 500 ppm NH3, 1200 ppm HCl, 5% O2,balance N2, reaction temperature 150 �C, space velocity 6000 h�1.

64 Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65

3.7. The role of NH4Cl in SCR reaction

It is reported that NH3 adsorption is a key step in the SCRreaction [24]. Fig. 11 shows effluent NH3 profiles measured bythe MS during NH3 adsorption on V2O5/AC and V2O5/AC catalystpre-treated by 3% NH4Cl. The breakthrough time reflects theamount of NH3 adsorption. The results show that the depositionof NH4Cl on V2O5/AC catalyst can significantly enhance the adsorp-tion ability of NH3 and the breakthrough time is 2535 s comparedwith 1800 s on V2O5/AC catalyst, which is possibly concluded that

Fig. 11. Effluent NH3 profile during isothermal of NH3 at 150 �C on fresh and0.5%V2O5/AC pretreated with NH4Cl. Reaction conditions: 2.0 g catalyst, a flow rateof 100 ml/min, 500 ppm NH3 and balance N2.

the promoting effect of HCl can be ascribed to the formation ofNH4Cl on the catalyst surface during the SCR process.

It is well known that a transient response experiment can re-flect the importance of a reactant, so a transient response experi-ment of NH3 was carried out. The results of the transientresponse experiment are plotted in Fig. 12. Before removing NH3

from the feed gas, the stable NO conversion is 92% in the presenceof HCl and 53% in the absence of HCl. When NH3 is removed, NOconversion decreases gradually which is because of the reactionof NH3 adsorbed on the catalyst surface with NO. It takes 80 minfor NO conversion to decrease to 0 in the presence of HCl and10 min in the absence of HCl. After NO conversion decreases to 0,NH3 is added again. NO conversion increases to the previous valuein a short time. The time difference indicates that the deposition ofNH4Cl on V2O5/AC catalyst surface improves the adsorption of NH3

and prolongs the reaction time of the adsorbed NH3 with NO.According to previous studies, the activated form of ammonia

NHþ4 adsorbed on the Brunsted acid site of V2O5/AC catalyst can re-act with NO [17–19], Fig. 13 shows the TPSR result of NH4Cl pre-deposited on V2O5/AC catalyst and AC with NO, the result can alsoprovide some information on the role of V2O5 on the reactivity ofNH4Cl with NO. Because there is no NH3 in the flue gas, the NOconversion is from NO adsorption and/or NO reaction with NH4Cl.

Fig. 13. Reactivity of NH4Cl formed in SCR reaction with NO. Reaction conditions:500 ppm NO, 5% O2, N2 balance, space velocity 6000 h�1.

Y. Hou et al. / Chemical Engineering Journal 247 (2014) 59–65 65

Considering only very little NO adsorbed on the catalyst surface(the breakthrough time of NO is only 420 s, while the breakthroughtime of NH3 is 2535 s), it makes sense to express the reaction ofNH4Cl with NO by the change of NO conversion. From the curvesof 0.5% V2O5/AC catalyst, it is known that the reaction rate reaches100% in a short time and decreases gradually after 60 min anddecreases to 0 about 150 min later. These results indicate thatthe NH4Cl deposited on the 0.5% V2O5/AC can react with NO attemperature below 150 �C, which may be another reason thatHCl promotes SCR activity of V2O5/AC catalyst at low temperature.

4. Conclusions

The effect of HCl on the catalytic activity of V2O5/AC catalyst forlow-temperature SCR reaction depends strongly on the HCl con-centration, V2O5 loading, reaction temperature and space velocity.In the condition of lower HCl concentration (less than 1200 ppm),lower V2O5 loading (0.5%, 1%), higher reaction temperature (120 �C,150 �C) and lower space velocity (6000 h�1, 8000 h�1), HCl plays apromoting effect on the catalytic activity of V2O5/AC catalyst and atthis moment the m(NH4Cl)/m(cat.) is below 0.044, while a poisoneffect with m(NH4Cl)/m(cat.) above 0.044. The promotion effectof HCl is attributed to NH4Cl deposited on catalyst surface duringthe SCR process. On one hand, NH4Cl improved the amount ofNH3 adsorption on the catalyst surface. On the other hand, NH4Clcould react with NO avoiding excessive NH4Cl deposited on thecatalyst surface and made the promotion effect sustainable.

Acknowledgments

We gratefully acknowledge financial support from the NationalNatural Science Foundation of China (21106174, 21103218,21177136), International Cooperation of Shanxi Province(2012081019) and Strategic Priority Research Program of the Chi-nese Academy of Sciences (XDA07030300).

References

[1] J.H. Kuo, H.H. Tseng, P.S. Rao, M.Y. Wey, The prospect and development ofincinerators for municipal solid waste treatment and characteristics of theirpollutants in Taiwan, Appl. Therm. Eng. 28 (2008) 2305–2314.

[2] L.L. Forestior, G. Libourel, Characterization of flue gas residues from municipalsolid waste combustors, Environ. Sci. Technol. 32 (1998) 2250–2256.

[3] F.Y. Chang, J.C. Chen, M.Y. Wey, S.A. Tsai, Effect of particulates, heavy metalsand acid gas on the removals of NO and PAHs by V2O5–WO3 catalysts in wasteincineration system, J. Hazard. Mater. 170 (2009) 239–246.

[4] O. Krocher, M. Elsener, Chemical deactivation of V2O5/WO3–TiO2 SCR catalystsby additives and impurities from fuels, lubrication oils, and urea solution – I.Catalytic studies, Appl. Catal. B 77 (2008) 215–227.

[5] J.P. Chen, R.T. Yang, Mechanism of poisoning of the V2O5/TiO2 catalyst for thereduction of NO by NH3, J. Catal. 125 (1990) 411–420.

[6] X. Zhang, Z. Huang, Z. Liu, Effect of KCl on selective catalytic reduction of NOwith NH3 over a V2O5/AC catalyst, Catal. Commun. 9 (2008) 842–846.

[7] L. Lietti, J.L. Alemany, P. Forzatti, G. Busca, G. Ramis, E. Giamello, F. Bregani,Reactivity of V2O5–WO3/TiO2 catalysts in the selective catalyst reduction ofnitric oxide by ammonia, J. Catal. 29 (1996) 143–148.

[8] Z. Zhu, Z. Liu, S. Liu, H. Niu, Flue gas NOx removal by SCR with NH3 on CuO/ACat low temperature, Stud. Surf. Sci. Catal. 130 (2000) 385–390.

[9] W.S. Kijlstra, M. Biervlet, E.K. Poels, A. Bliek, Deactivation by SO2 of MnOx/Al2O3

catalysts used for the selective catalytic reduction of NO with NH3 at lowtemperature, Appl. Catal., B 16 (1998) 327–337.

[10] G. Xie, Z. Liu, Z. Zhu, Simultaneous removal of SO2 and NOx from flue gas usinga CuO/Al2O3 catalyst sorbent I. Deactivation of SCR activity by SO2 at lowtemperature, J. Catal. 224 (2004) 36–41.

[11] Z. Wu, R. Jin, H. Wang, Y. Liu, Effect of ceria doping on SO2 resistance of Mn/TiO2 for selective catalytic reduction of NO with NH3 at low-temperature,Catal. Commun. 10 (2009) 935–939.

[12] L. Lisi, G. Lasorella, S. Malloggi, G. Russo, Single and combined deactivatingeffect of alkali metals and HCl on commercial SCR catalysts, Appl. Catal. B 50(2004) 251–258.

[13] J.W. Choung, I.S. Nam, Characteristics of copper ion exchanged mordenitecatalyst deactivated by HCl for the reduction of NOx with NH3, Appl. Catal. B 64(2006) 42–50.

[14] J.P. Chen, M.A. Buzanowski, R.T. Yang, J.E. Cichanowicz, Deactivation of theVanadia catalyst in the selective catalytic reduction process, J. Air WasteManage. Assoc. 40 (1990) 1403–1409.

[15] J.W. Choung, I.S. Nam, Role of cerium in promoting the stability of CuHMcatalyst against HCl to reduce NO with NH3, Appl. Catal. A: Gen. 312 (2006)165–174.

[16] F.Y. Chang, J.C. Chen, M.Y. Wey, Catalytic removal of NO in waste incinerationprocesses over Rh/Al2O3 and Rh–Na/Al2O3: effects of particulates, heavy metal,SO2 and HCl, Fuel Process. Technol. 90 (2009) 576–582.

[17] Z. Zhu, Z. Liu, S. Liu, A novel carbon-supported vanadium oxide catalyst for NOreduction with NH3 at low temperature, Appl. Catal. B 23 (1999) 229–233.

[18] Z. Zhu, Z. Liu, H. Niu, S. Liu, NO–NH3–O2 reaction catalyzed by V2O5/AC at lowtemperature: effects of SO2, V2O5 loading and reaction temperature, Sci. ChinaSer. B 43 (2000) 51–57.

[19] Z. Zhu, Z. Liu, H. Niu, S. Liu, Promoting effect of SO2 on activated carbon-supported vanadia catalyst for NO reduction by NH3 at low temperature, J.Catal. 187 (1999) 245–248.

[20] Z. Zhu, Z. Liu, H. Niu, S. Liu, T. Hu, T. Liu, Y. Xie, Mechanism of SO2 promotionfor NO reduction with NH3 over activated carbon-supported vanadium oxidecatalyst, J. Catal. 197 (2001) 6–16.

[21] Z. Zhu, Z. Liu, H. Niu, S. Liu, Decomposition and reactivity of NH4HSO4 on V2O5/AC catalysts used for NO reduction with ammonia, J. Catal. 195 (2000) 268–278.

[22] Z. Huang, Z. Zhu, Z. Liu, Q. Liu, Formation and reaction of ammonium sulfate onV2O5/AC catalyst during selective catalytic reduction of nitric oxide byammonia at low temperature, J. Catal. 214 (2003) 213–219.

[23] Z. Huang, Z. Zhu, Z. Liu, Combined effect of H2O and SO2 on V2O5/AC catalystfor NO reduction with ammonia at lower temperature, Appl. Catal. B 39 (2002)361–368.

[24] X. Zhang, X. Wang, X. Li, X. Wang, Z. Deng, X. Li, C. Jiang, Y. Ren, Oscillatorybehavior of the H2-SCR over Pt/HY, Chem. Eng. J. 232 (2013) 266–272.