Improvement of Water-, Sulfur Dioxide-, and Dust-Resistance in

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Improvement of Water-, Sulfur Dioxide-, and Dust-Resistance in Selective Catalytic Reduction of NOx with NH3 Using a Wire-Mesh Honeycomb Catalyst Yun Shu,† Hong Sun,† Xie Quan,*,† and Shuo Chen† †

Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, China), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China S Supporting Information *

ABSTRACT: A novel V2O5/WO3/TiO2/Al2O3/wire-mesh honeycomb (WMH) catalyst was prepared for selective catalytic reduction (SCR) of NOx with NH3. The resistances to H2O, SO2, and dust were investigated for the WMH catalyst, which were compared with those for ceramic honeycomb (CH) catalysts. The results showed that the WMH catalyst kept above 95% NOx conversion in the broad temperature window (250−425 °C) and provided nearly 92% NOx conversion during H2O and SO2 durability test, which might be attributed to the unique three-dimensional structure. Furthermore, the WMH catalyst could provide nearly 90% NOx conversion during 40 h dust exposure experiment owing to the little dust deposition of 2.9 g/m2, whereas the amount of dust deposited on the CH catalyst with the same cell density reached 6.7 g/m2, which resulted in a decrease of the NOx conversion from 72% to 58%.

1. INTRODUCTION Selective catalytic reduction (SCR) with ammonia is the dominant technology to remove NOx in the exhaust gas from stationary sources. The commercial catalyst for this process is V2O5/WO3/TiO2 operated in 350−400 °C.1 Due to the low pressure-drop even at high flow rate, ceramic honeycomb has been frequently used as a catalytic substrate in practice.2−5 However, ceramic honeycomb catalyst is often deactivated by H2O and SO2 or dust in flue gas due to the plugging of active sites by the deposited sulfate-ammonium salts6 or blocking of support channels by the dust particles.7 Moreover, there are some innate disadvantages for the ceramic honeycomb catalyst, such as the low mechanical strength, interphase mass- and heattransfer rates.8,9 In recent years, metal wire had received much interest as catalytic substrate.10 Ahlströ m-Silversand and Odenbrand reported that wire mesh catalyst showed high mass- and heattransfer numbers, moderate pressure-drop, insignificant effects of pore diffusion and axial dispersion,11,12 which were beneficial to the purification of flue gases. However, the wire mesh catalyst is structured by single gauzes stacked, which is inconvenient for being assembled in the reactor. Wire-mesh honeycomb is a new structured catalytic reactor, which is manufactured by stacking alternatively corrugated and plain wire mesh sheets. This structure can provide the radial mixing of gas flow, enhance the external mass-transfer rate, and give a more uniform distribution of fluids across the entire bed diameter. Furthermore, due to the three-dimensional structure, the wire-mesh honeycomb can provide a low-blocking network, which can improve the resistance to the dust deposition. Recently, wire-mesh honeycomb catalysts have been used in catalytic oxidation of 1,2-dichlorobenzene,13 ethyl acetate,14 and volatile organic compounds in air.15 However, few works have been carried out using wire-mesh honeycomb as catalytic © 2012 American Chemical Society

substrate for selective catalytic reduction of NOx with ammonia in high sulfur and dust conditions. In this study, V2O5/WO3/TiO2/Al2O3/wire-mesh honeycomb (abbreviated as WMH hereafter) catalyst was prepared for the selective catalytic reduction of NOx with NH3. The resistances to H2O, SO2, and dust were also investigated. For comparison purposes, the catalytic activities of ceramic honeycomb (CH) catalysts with the same active composition were investigated under the same working conditions.

2. EXPERIMENTAL SECTION 2.1. Preparation of Al2O3/Wire-Mesh Honeycomb Support. Wire-mesh honeycomb used in this work was 3.5 cm × 3.5 cm in cross-section and 1.0 cm in length, and its cells per square inch (cpsi) were 100. Because the bare surface of metal wire can hardly attach catalyst powder, it is necessary to deposit ceramic oxide coating with a high surface area on the wire-mesh honeycomb substrate. Electrophoretic deposition (EPD) method had been employed to deposit alumina coating on the wire-mesh honeycomb substrate. The alumina suspension was prepared with γ-alumina (γ-Al2O3) powders gritted from γ-alumina pellets. Polycyclic acid and aluminum isopropoxide were used as additives. The detailed preparation procedure was described in our previous work.16 For comparison, three CH catalysts having the same dimensions with the WMH catalyst were prepared. These CH catalysts had different cell densities, i.e. 100, 200, and 400 cpsi. The ceramic honeycombs were first impregnated in an alumina slurry solution for 10 min which consisted of 20.0 g of alumina in 100 mL of water, and then the samples were dried at Received: January 4, 2012 Accepted: May 22, 2012 Published: May 22, 2012 7867

dx.doi.org/10.1021/ie300832d | Ind. Eng. Chem. Res. 2012, 51, 7867−7873

Industrial & Engineering Chemistry Research

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100 °C for 8 h and calcined at 500 °C for 3 h. For the WMH and CH catalysts, the thickness of alumina coating was 20−30 μm (Figure S1 in the Supporting Information). 2.2. Preparation of V2O5/WO3/TiO2/Al2O3/Wire-Mesh Honeycomb Catalyst. WMH catalyst was prepared by a twostep impregnation method. The Al2O3-coated wire-mesh honeycomb was first impregnated in WO3/TiO2 slurry which was composed of WO3/TiO2 commercial powder (Nanjing High Technology of Nano Co.), water, and inorganic binder, and then the impregnated sample was dried at 100 °C for 5 h and calcined at 400 °C for 2 h. Subsequently, the sample was impregnated into an aqueous solution of VO2+ prepared from ammonium metavanadate and oxalic acid, and then the sample was dried at 100 °C for 8 h and calcined at 500 °C for 2 h. Similarly, the above procedures were controlled the same as those of other Al2O3-coated ceramic honeycombs. In order to achieve a uniform and continuous active coating on the catalyst surface, the loadings of active component V2O5/WO3/TiO2 were about 130 g/L for WMH and CH catalysts, and the coating adhesion strengths were almost the same as evidenced by the similar mass loss of coating during the SCR reaction (Figure S2 in the Supporting Information). The compositions of V2O5/WO3/TiO2 as determined by atomic absorption spectrometer (AAS) with graphite furnace (AAnalyst 700, PerkinElmer) were 1.5 wt % V2O5, 8 wt % WO3, and 90.5 wt % TiO2. 2.3. Catalytic Activity. The catalytic studies were carried out in square-shape reactor (4.0 cm × 4.0 cm in width) made of stainless steel with a total bed length of 100 cm. The catalysts were placed inside the reactor in the middle. Free space between the catalyst and the reactor wall was filled with inert material to prevent bypass. The reaction temperature was monitored by K-type thermocouple which connected to a programmable temperature controller. The typical composition of the reactant gas was as follows: 1000 ppm NO, 1000 ppm NH3, 3% O2, 10% water vapor (when needed), 600 ppm SO2 (when needed), and N2 as the balance gas. The total flow rate was 2000 mL/min (refers to 1 atm and 298 K) which corresponded to gas hourly space velocity (GHSV) of 10000 h−1. Before entering the reactor, the feed gases were mixed in a mixing tubing, but NH3 was fed directly into the reactor by passing the mixing tubing to avoid possible reaction between SO2 and NH3 before the catalyst bed. Water vapor was generated by passing N2 through a gas-wash bottle containing deionized water. The tubings of the reactor system were heated to prevent the formation and deposition of ammonium sulfate/ bisulfate and ammonium nitrate. The NO, NO2, and O2 concentrations were measured online by a flue gas analyzer (ecom-J2KN, rbr Messtechnik GmbH Inc.). The N2O was analyzed by a gas chromatograph (Shimadzu GC-14C) with a Porapak Q column. The activities were evaluated in terms of NOx conversion determined according to the following equation [NOx ]conversion =

with the reactant gas until there was no difference between the inlet and the outlet gas. 2.4. Dust Exposure Experiment. The effect of dust on catalytic activity was determined by exposing the catalyst to a dust-containing gas in a lab-scale quartz reactor. Figure 1 shows

Figure 1. Schematic diagram of the dust exposure experimental apparatus.

the schematic diagram of experimental apparatus. At 250 °C, 2000 mL/min N 2 passed through the reactor, which corresponded to gas hourly space velocity (GHSV) of 10000 h−1. In each experiment, about 10 g of dust was placed at the inlet of the reactor in order to generate a stream of dust more easily. The dust was collected from the regional heating boiler plant. The size distribution of the dust particles was 0.1−9 μm, and the average size was 2.39 μm. The deactivating effect of dust deposition was analyzed by comparing the catalytic activity of a given catalyst with that of the same catalyst previously exposed to the dust-containing gas for different periods of time. Initially, the catalytic activity of fresh catalyst was measured at typical conditions (1000 ppm NO, 1000 ppm NH3, 3% O2, 250 °C). Afterward, the catalyst was exposed to the stream of dust for different periods of time, its catalytic activity being measured after each period. The amount of dust deposited on the catalyst could be estimated according to the following equation M = m/S

where m was the weight of dust on the catalyst surface (g), and S was the surface area of the catalyst (m2). The activity recovery of the catalyst used in dust exposure experiment was carried out in sootblowing experiment which had the same experimental apparatus with the dust exposure experiment. During the sootblowing experiment, the dust was removed, and the total flow rate was 10000 mL/min. 2.5. Catalysts Characterization. Scanning electron microscopy (SEM) of the catalyst was measured on a HITACHI S-4800 operating at 3.0 KV. For the specific surface area, V2O5/WO3/TiO2 coating was scraped for being applied. The measurement was carried out by nitrogen adsorption using the Brunauer−Emmett−Teller (BET) method (Quadrasorb SI). The sample was degassed in vacuum at 200 °C for 24 h prior to measurement. The total pore volume was calculated from the amount of nitrogen adsorbed at P/P0 = 0.99. Powder X-ray diffraction (XRD) measurement was carried out on a Rigaku D/MAX-2400 X-ray diffractometer with Cu Kα radiation. Fourier transform infrared spectroscopy (FT-IR) used in this study was performed with a Bruker Vector FTIR spectrometer used a DTGS detector. Before the analyses, about 2 mg of the sample was ground, mixed, and palletized with pure KBr by a weight ratio of 1:100. For the used catalysts after H2O and SO2 durability test, the samples were purged in N2 at 300 °C for 4 h to remove physically adsorbed species and then cooled to room temperature. NH3-TPD experiment was conducted on a ChemBET PULSAR TPR/TPD. Prior to each experiment, about 50 mg

[NOx ]inlet − [NOx ]outlet × 100% [NOx ]inlet

where [NOx] = [NO] + [NO2], and [NOx]inlet and [NOx]outlet were the concentrations of NOx at the inlet and outlet of the reactor, respectively. In order to confirm that the decrease of NOx was not caused by the adsorption of NOx in the catalysts, at the beginning of each experiment, the catalyst was purged 7868



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of sample was placed in a quartz tube and pretreated in flowing N2 at 500 °C for 2 h, then the temperature was lowered to 100 °C, and the sample was exposed to a gaseous mixture of 10% NH3/N2 for 1 h. After NH3 adsorption, the sample was flushed with N2 (50 mL/min) for 100 min at 100 °C. Finally, the TPD operation was carried out by heating the catalyst from 100 to 700 °C (10 °C/min) under a flow of He (25 mL/min).

3. RESULTS AND DISCUSSION 3.1. Physical Properties of Catalysts. The catalytic substrate is an integral part of the catalyst. Its physical properties have significant effects on the performance of a catalyst.17 The physical properties of different catalysts are summarized in Table 1. From Table 1, it could be found that Table 1. Physical Properties of WMH and CH Catalysts WMH catalyst materials cell density (cpsi) GSA (×103 m2/m3) OFA (%) Dh (×10−3 m) (MV2O5−WO3−TiO2)/(Vcatalyst) (g/L)

Figure 2. The geometric structure and surface morphology of WMH and CH catalysts (photograph of WMH catalyst (a) and CH catalyst (b); SEM image of the WMH catalyst surface (a1) and the CH catalyst surface (b1)).

CH catalysts

stainless steel

Cordierite

Cordierite

Cordierite

100 1.62 74.1 2.54 126.8

100 1.28 64.3 2.03 129.5

200 1.60 60.8 1.75 131.7

400 1.92 36.5 0.76 134.3

have a promotional effect on NOx conversion at lower temperatures.19 On the other hand, in a temperature range of 150−225 °C, the difference in the temperatures required to attain the same NOx conversion between WMH and CH catalysts increased with increasing temperature. It was reported by other researchers14,20 that the mass transfer rate had great effect on catalytic activity at higher temperatures. Therefore, for the WMH catalyst, the rapid increase of NOx conversion at 150−225 °C might be ascribed to the high mass transfer rate resulting from the additional effect of free radial mixing across the channel walls of the wire mesh. Furthermore, the WMH catalyst had a broad working temperature window (250−425 °C), where its NOx conversion was around 95%. Figure 3(b) showed that N2O was not observed over WMH catalyst at temperatures below 300 °C but appeared at temperatures above 250 °C on those CH catalysts. Above 300 °C, less N2O was produced on the WMH catalyst than that on the CH catalysts. 3.3. Effect of Gas Hourly Space Velocity. Space velocity is a very important parameter for the practical application. The activities of WMH and CH (200 cpsi) catalysts were measured in a wide range from 5,000 to 20,000 h−1, and the results are shown in Figure 4. The differences in GSA were very small between these two catalysts. For these two catalysts, NOx conversion decreased with increasing of the GHSV, and it should be noted that the NOx conversion of the WMH catalyst decreased more slowly than that of the CH catalyst. This behavior might be attributed to the beneficial increase in radial mixing in the WMH catalyst with increasing space velocity. 3.4. Effect of H2O and SO2. H2O and SO2 are unavoidably existed in flue gas, so it is very important for industrial application to investigate the effects of H2O and SO2 on SCR activity of catalyst. In this work, the impacts of H2O and SO2 on the SCR activities over WMH and CH (400 cpsi) catalysts were studied. As shown in Figure 5(a), when 600 ppm SO2 and 10% H2O were added into the reaction gas, the catalytic activities of both catalysts decreased at temperatures below 250 °C. Nonetheless, the WMH catalyst could provide NOx conversion of about 95% in a temperature range of 250−400 °C.

the WMH catalyst offered higher geometric surface area (GSA) than the CH (100 cpsi) catalyst and had similar GSA with the CH (200 cpsi) catalyst. Furthermore, the GSA of the WMH catalyst was only 15% lower than that of the CH (400 cpsi) catalyst. The high GSA of the ideal substrate was necessary in order to obtain the high conversion efficiency under steady state.18 The pressure-drop characteristic of monolithic catalyst is one of the most important factors to be considered in practice. The high open frontal area (OFA) and large hydraulic diameter (Dh) could help to minimize the backpressure. As shown in Table 1, the OFA and Dh of the WMH catalyst were 74.1% and 2.54 mm, respectively, which were higher than those of the other CH catalysts. Thus it was presumed that the wire-mesh honeycomb catalyst might have a good pressure-drop performance. Figure 2 shows the geometric structure and surface morphology of different catalysts. As shown in Figure 2a and b, the WMH catalyst had a unique three-dimensional structure which was quite different from the CH catalyst. Additionally, it was observed that the accumulation of active coating in the corners of the channels in the WMH catalyst could be avoided. Figure 2a1 and b1 shows the SEM images of both catalysts. It could be seen that there was little difference between both catalysts, and they had a highly rough and porous surface. 3.2. Catalytic Activity Tests. In order to test the effect of the substrate, the activities of selective catalytic reduction of NOx with NH3 over various catalysts were compared, and the results are shown in Figure 3. The active component loading and the experimental conditions were the same. As shown in Figure 3a, the WMH catalyst showed better catalytic activity than the other CH catalysts. It was interesting that there was a large distance between the cures of the WMH catalyst and the CH catalysts below 125 °C, which could be ascribed to the substrate material (Cr25Al5) since the metallic substrate could 7869



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Figure 3. The SCR activities of the various catalysts. Reaction conditions: [NO] = [NH3] = 1000 ppm, [O2] = 3 vol.%, N2 balance and GHSV = 10,000 h−1. (NOx conversion (a) and N2O production (b)).

3.5. XRD of Catalysts. XRD was conducted to determine crystalline structure of V2O5/WO3/TiO2 coating on WMH and CH catalysts used in H2O and SO2 durability test. As shown in Figure 6, the peaks corresponding to TiO2 anatase (PDF#89-

Figure 4. Influence of GHSV on NOx conversion over WMH and CH (200 cpsi) catalysts at different temperatures. Reaction conditions: [NO] = [NH3] = 1000 ppm, [O2] = 3 vol.%, N2 balance.

The H2O and SO2 durability of above catalysts are demonstrated in Figure 5(b) through a 60 h SCR reaction in the presence of 600 ppm SO2 and 10% H2O at 250 °C. As shown in Figure 5(b), WMH and CH catalysts exhibited different catalytic behaviors. The WMH catalyst could keep about 92% NOx conversion during the H2O and SO2 durability test, while the NOx conversion of the CH catalyst decreased from 77% to 54%. The above results clearly indicated that the WMH catalyst exhibited excellent H2O and SO2 durability compared to the CH catalyst.

Figure 6. XRD of the WMH and CH catalyst before and after H2O/ SO2 durability test (fresh CH (a), fresh WMH (b), used WMH (c), and used CH (d)).

4921) could be clearly observed for all catalysts, and no vanadium pentoxide and tungsten trioxide diffractions could be detected, suggesting that the V2O5 and WO3 dispersed well on the catalyst surface. After the H2O and SO2 durability test, several new diffraction peaks were observed at 22.56°, 27.62°,

Figure 5. Effects of H2O and SO2 on NOx conversion over WMH and CH (400 cpsi) catalysts. Reaction conditions: [NO] = [NH3] = 1000 ppm, [O2] = 3 vol.%, [SO2] = 600 ppm, [H2O] = 10%. N2 balance and GHSV = 10,000 h−1. (NOx conversion in the whole temperature range (a), durability test at 250 °C (b)). 7870



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and 29.28° for CH catalyst. The first one peak was ascribed to the formation of (NH4)2SO4 (PDF#84-0130), and the latter two peaks could be assigned to TiOSO4 (PDF#28-1399). Whereas for WMH catalyst, there were no new peaks which appeared, which indicated that no crystal sulfate phase was formed on catalyst surface or the products presented in a scarce amount beyond XRD detection limitation. 3.6. Textural Characterization. The textural characterizations of WMH and CH catalysts used in H2O and SO2 durability test are presented in Table 2. It showed that the two

durability test. For fresh catalysts, the TCD patterns were almost the same. The first weak peak was observed around 330 °C, signifying a distribution of weak acid sites. The second stronger one, centered at about 508 °C, was attributed to NH3 desorbed from moderate acid sites. After the H2O and SO2 durability test, the intensity of desorption bands for the WMH catalyst increased much less than those for the CH catalyst. It was reported22 that the presence of SO2 could promote the formation of sulfate species on catalyst surface during SCR reaction; these sulfate species acted as new acid sites which could improve ammonium adsorption. Thus there was little sulfate species formed on the surface of the WMH catalyst compared to that of the CH catalyst. Furthermore, some literature reported6,23 that the effects of the formed sulfate species were suggested to be two fold: 1) it provided acid sites for ammonium adsorption and thus enhancing the activity and 2) the sulfate species reacted with ammonium and transformed into ammonium sulfate salts, which might plug the catalyst pores resulting in deactivation. Thus it could be concluded that the deposition of sulfateammonium salts was the dominant reason for the catalyst deactivation during the H2O and SO2 durability test. 3.8. FTIR Analysis. Figure 8 shows the FT-IR spectra of WMH and CH catalysts used in H2O and SO2 durability test.

Table 2. Textural Characterizations of WMH and CH (400 cpsi) Catalysts before and after H2O and SO2 Durability Test catalyst fresh WMH fresh CH used WMH used CH

BET surface area (m2/g)

pore volume (cm3/g)

average pore diameter (nm)

74.4

0.22

9.64

85.9 66.2

0.23 0.21

9.56 12.57

32.6

0.09

7.49

fresh catalysts had similar specific surface area, pore volume, and average pore diameter. Generally, the high specific surface area was favorable to catalytic activities. While the WMH catalyst showed much better catalytic activity than the CH catalyst (as shown in Figure 3(a)), although had similar specific surface area. It indicated that the specific surface area was not the main reason for the difference in catalytic activities in this work. After the H2O and SO2 durability test, the specific surface area and pore volume of the WMH catalyst decreased less than those of the CH catalyst. It was reported by other researchers6,21 that the decrease of the BET and pore volume after SCR reaction in the presence of H2O and SO2 was ascribed to the formation of ammonium-sulfate salts such as NH4HSO4 and (NH4)2SO4, which blocked the pores of the catalyst. Thus it was presumed that there was little ammoniumsulfate salts deposited on the surface of WMH catalyst during the H2O and SO2 durability test as compared to that of CH catalyst. This complied with the result in XRD analysis that the sulfates could not be detected on the surface of the WMH catalyst. 3.7. NH3-TPD Analysis. Figure 7 illustrates the NH3-TPD diagrams for WMH and CH catalysts used in H2O and SO2

Figure 8. FT-IR spectra of the WMH and CH catalyst before and after H2O/SO2 durability test (fresh CH (a), fresh WMH (b), used WMH (c), and used CH (d)).

For fresh catalysts, a band in the range of 1000−1100 cm−1 was observed, and the absorption was at 1048 cm−1. Frederickson and Hausen24 reported that V2O5 exhibited two IR bands at 1020 and 825 cm−1, which were assigned to the stretching vibration of V5+=O and V−O−V, respectively, so the peak at 1048 cm−1 could be assigned to the stretching frequency of V5+=O. It was presumed that the shift of the absorptions of 1020−1048 cm−1 might be ascribed to the cooperation of V2O5 and support. After the H2O and SO2 durability test, WMH and CH catalysts showed a new absorption at 1400 cm−1, indicating the presence of NH4+ species, which were chemisorbed on the Brønsted acid sites.25,26 Meanwhile, another new absorption appeared at 1150 cm−1 for the both used catalysts, which might be assigned to the characteristic frequencies of the SO42‑ ion. The free SO42‑ ion has usually two infrared absorptions at 1140 and 626 cm−1.27 The absorption at 626 cm−1 was overlapped by the absorptions of TiO2, which was easily influenced by other metal oxides.28 Furthermore, for the used WMH catalyst, the absorption intensities at 1150 and 1400 cm−1 were lower than

Figure 7. NH3-TPD of the WMH and CH catalysts before and after H2O/SO2 durability test (fresh CH (a), fresh WMH (b), used WMH (c), and used CH (d)). 7871



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provide a low blocking network which made the dust flow through the WMH catalyst with minor inhibition in the dust exposure experiment. In order to evaluate the activity recoveries of the catalysts used in the dust exposure experiment, the sootblowing experiments were carried out as described in section 2. Figure 10 shows the NOx conversion at different sootblowing times

those of the used CH catalyst. These results demonstrated that during the H2O and SO2 durability test, there were little ammonium-sulfate salts deposited on the surface of the WMH catalyst compared to that of the CH catalyst. Above all, due to the less ammonium-sulfate deposition, the WMH catalyst had much better resistance to H2O and SO2 than the CH catalyst. In addition, the enhanced absorption intensities of two catalysts at 1048 cm−1 after 60 h reaction in the presence of H2O and SO2, might result from the vibration absorption of SO (1050 cm−1). 3.9. Resistance to Dust. In order to evaluate the effect of dust on catalytic activity, the catalyst was subjected to a stream of dust at 250 °C as described in section 2. Figure 9 shows the

Figure 10. NOx conversion over various catalysts with the time of sootblowing. Reaction conditions: [NO] = [NH3] = 1000 ppm, [O2] = 3 vol.%, N2 balance and GHSV = 10,000 h−1, temperature = 250 °C.

over various catalysts. As shown in Figure 10, a complete activity recovery happened for all the catalysts after the sootblowing experiments, which indicated that dust particles had deposited on the catalyst surface, not penetrated into the active coating. Furthermore, the activity recovery of the WMH catalyst was much faster than those of the other CH catalysts, which verified further that the unique three-dimensional structure was unfavorable for the high particle material deposition. Thus for the WMH catalyst, the unique threedimensional structure appeared to be the main factor for the excellent resistance to dust.

Figure 9. NOx conversion over various catalysts with the time of dust treatment. Reaction conditions: [NO] = [NH3] = 1000 ppm, [O2] = 3 vol.%, N2 balance and GHSV = 10,000 h−1, temperature = 250 °C.

NOx conversion at different dust exposure times over various catalysts. As shown in Figure 9, the decrease of catalytic activity for the CH (400 cpsi) catalyst was greatly, and the decrease of catalytic activities was subject to an order of WMH < CH (100 cpsi) < CH (200 cpsi) < CH (400 cpsi). The WMH catalyst could keep above 90% NOx conversion during 40 h dust exposure time. The greatly decrease of catalytic activity for the CH (400 cpsi) catalyst might be ascribed to its high cell density that led to the serious dust deposition (as shown in Table 3). However,

4. CONCLUSIONS The WMH catalyst, compared with the other CH catalysts with the same composition, exhibited excellent catalytic activity for selective catalytic reduction of NOx with NH3 and great resistances to H2O, SO2, and dust. The deposition of sulfateammonium salts on catalyst surface was the dominant reason for the catalyst deactivation in H2O- and SO2-containing gases. The unique three-dimensional structure of the WMH catalyst could enhance SCR activity and inhibit the high sulfateammonium deposition on catalyst surface. These results showed that the WMH catalyst could broaden the application prospect of traditional ceramic honeycomb catalysts, especially for the denitrification systems with heavy concentrations of H2O, SO2, and dust.

Table 3. Amount of Dust Deposition on Various Catalysts at Different Dust Exposure Times dust deposition amount at different exposure times (g/m2) catalyst

0h

6h

10 h

18 h

30 h

40 h

WMH (100 cpsi) CH (100 cpsi) CH (200 cpsi) CH (400 cpsi)

-

0.4 0.9 0.9 1.0

0.7 1.7 1.8 1.9

1.2 2.7 3.4 4.1

2.3 4.4 5.2 6.5

2.9 6.7 7.5 8.0

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the decrease of catalytic activity for the CH (100 cpsi) catalyst was still much greater than that for the WMH catalyst. For the WMH catalyst, the amount of dust deposition was only 2.9 g/ m2. These results could be ascribed to the unique threedimensional structure of the WMH catalyst. The wire-mesh honeycomb was composed of metal wire with a high porosity. This cylindrical framed-tube structure was unfavorable to the deposition of powder material. Thus the three-dimensionally connected channels in the wire-mesh honeycomb should

ASSOCIATED CONTENT

* Supporting Information S

The SEM of alumina coating on different substrates and the mass loss of alumina coating over wire-mesh honeycomb and ceramic honeycomb with the time of SCR reaction. This material is available free of charge via the Internet at http:// pubs.acs.org. 7872



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(19) Sun, H.; Zhang, Y. B.; Quan, X. Wire-mesh honeycomb catalyst for selective catalytic reduction of NOx under lean-burn conditions. Catal. Today 2008, 139, 130. (20) Chung, K. S.; Jiang, Z.; Gill, B. S.; Chung, J. S. Oxidative decomposition of o-dichlorobenzene over V2O5/TiO2 catalyst washcoated onto wire-mesh honeycombs. Appl. Catal., A 2002, 237, 81. (21) Bosch, H.; Janssen, F. Formation and control of nitrogen oxides. Catal. Today 1988, 2, 369. (22) Zhu, Z. P.; Liu, Z, Y.; Niu, H. X.; Liu, S. J.; Hu, T. D. Mechanism of SO2 promotion for NO reduction with NH3 over activated carbon-supported vanadium oxide catalyst. J. Catal. 2001, 197, 6. (23) Zhu, Z. P.; Liu, Z. Y.; Liu, S. J.; Z, Y.; Niu, H. X. Catalytic NO reduction with ammonia at low temperatures on V2O5/AC catalysts: Effect of metal oxides addition and SO2. Appl. Catal., B 2001, 30, 267. (24) Frederickson, L. D.; Hausen, D. M. Infrared spectra-structure correlation study of vanadium-oxygen compounds. Anal. Chem. 1963, 35, 818. (25) Topsøe, N. Y. Mechanism of the selective catalytic reduction of nitric oxide by ammonia elucidated by in situ on-line Fourier Transform Infrared spectroscopy. Science 1994, 265, 1217. (26) Takagi, M.; Kawai, T.; Soma, M.; Onishi, T.; Tamaru, K. Mechanism of catalytic reaction between NO and NH3 on V2O5 in the presence of oxygen. J. Phys. Chem. 1976, 80, 430. (27) Nakamoto, K., Infrared and Raman spectra of inorganic and coordination compounds, 4th ed.; Wiley: New York, 1986. (28) Ertl, G.; Knozinger, H.; Weitkamp, J. Handbook of heterogeneous catalysis; Wiley VCH Company: Weinheim, 1997.

AUTHOR INFORMATION

Corresponding Author

*Phone: +86 (411) 84706140. Fax: +86 (411) 84706263. Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (973 Program) (No. 2011CB936002) and Program for Changjiang Scholars and Innovative Research Team in University (IRT0813).

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REFERENCES

(1) Dunn, J. P.; Koppula, P. R.; Stenger, H. G.; Wachs, I. E. Oxidation of sulfur dioxide to sulfur trioxide over supported vanadia catalysts. Appl. Catal., B 1998, 19, 103. (2) Boger, T.; Heibel, A. K.; Sorensen, C. M. Monolithic catalysts for the chemical industry. Ind. Eng. Chem. Res. 2004, 43, 4602. (3) Groppi, G.; Tronconi, E. Design of novel monolith catalyst supports for gas/solid reactions with heat exchange. Chem. Eng. Sci. 2000, 55, 2161. (4) Cybulski, A.; Moulijn, J. A. Monoliths in heterogeneous catalysis. Catal. Rev. Sci. Eng. 1994, 36 (2), 179. (5) Busca, G.; Lietti, L.; Ramis, G.; Berti, F. Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review. Appl. Catal., B 1998, 18, 1. (6) Huang, Z. G.; Zhu, Z. P.; Liu, Z. Y. Combined effect of H2O and SO2 on V2O5/AC catalysts for NO reduction with ammonia at lower temperatures. Appl. Catal., B 2002, 39, 361. (7) Valdés-Solís, T.; Marbán, G.; Fuertes, A. B. Low-temperature SCR of NOx with NH3 over carbon-ceramic supported catalysts. Appl. Catal., B 2003, 46, 261. (8) Beeckman, J. W.; Hegedus, L. L. Design of monolith catalysts for power plant NOx emission control. Ind. Eng. Chem. Res. 1991, 30, 979. (9) Patcas, F. C.; Garrido, G. I.; Kraushaar-Czarnetzki, B. CO oxidation over structured carriers: A comparison of ceramic foams, honeycombs and beads. Chem. Eng. Sci. 2007, 62, 3984. (10) Matatov-Meytal, Y.; Sheintuch, M. Catalytic fibers and cloths. Appl. Catal., A 2002, 231, 1. (11) Ahlström-Silversand, A. F.; Odenbrand, C. U. I. Modelling catalytic combustion of carbon monoxide and hydrocarbons over catalytically active wire meshes. Chem. Eng. J. 1999, 73, 205. (12) Ahlström-Silversand, A. F.; Odenbrand, C. U. I. Thermally sprayed wire-mesh catalysts for the purification of flue gases from small-scale combustion of bio-fuel catalyst preparation and activity studies. Appl. Catal., A 1997, 153, 177. (13) Yang, K. S.; Jiang, Z. D.; Chung, J. S. Electrophoretically Alcoated wire mesh and its application for catalytic oxidation of 1,2dichlorobenzene. Surf. Coat. Technol. 2003, 168, 103. (14) Yang, K. S.; Mul, G.; Choi, J. S.; Moulijn, J. A.; Chung, J. S. Development of TiO2/Ti wire-mesh honeycomb for catalytic combustion of ethyl acetate in air. Appl. Catal., A 2006, 313, 86. (15) Yang, K. S.; Choi, J. S.; Lee, S. H.; Chung, J. S. Development of Al/Al2O3-coated wire-mesh honeycombs for catalytic combustion of volatile organic compounds in Air. Ind. Eng. Chem. Res. 2004, 43, 907. (16) Sun, H.; Quan, X.; Chen, S.; Zhao, H. M.; Zhao, Y. Z. Preparation of well-adhered γ-Al2O3 washcoat on metallic wire mesh monoliths by electrophoretic deposition. Appl. Surf. Sci. 2007, 253, 3303. (17) Roberts, K. L.; Amiridis, M. D. Kinetic investigation of the selective catalytic reduction of nitric oxide by propylene over Pt/ Al2O3. Ind. Eng. Chem. Res. 1997, 36, 3528. (18) Heck, R. M.; Farrauto, R. J.; Gulati, S. T. Catalytic Air Pollution Control, 3rd ed.; Wiley & Sons: New York, 2002. 7873


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