J. Cent. South Univ. (2016) 23: 2139-2145

DOI: 10.1007/s11771-016-3270-2

TiO₂ preparation by improved homogeneous precipitation and application in SCR catalyst

YAO Jie(姚杰)^{1, 2}, ZHONG Zhao-ping(仲兆平)²

1. Guodian Science and Technology Research Institute, Nanjing 210046, China;

2. Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,

Southeast University, Nanjing 210096, China

Central South University Press and Springer-Verlag Berlin Heidelberg 2016

Abstract: Ultrasonic treatment and hydrothermal method were applied in the traditional homogeneous precipitation for nano-TiO₂ preparation, which was used as carrier material for the production of honeycomb selective catalytic reduction (SCR) catalyst. The influence rules of the two improved methods on characterization of TiO₂ samples, denitration activity and mechanical strength of honeycomb SCR catalyst samples were mainly focused on. The results indicate that the specific surface area, particle size and uniformity of TiO₂ samples are significantly improved by both of the ultrasonic and hydrothermal treatments compared with the traditional homogeneous precipitation. Also, the denitration activities of catalyst samples are enhanced by the two improved methods (the NO_x reduction ratio increases from 88.89% to 95.45% by ultrasonic homogeneous precipitation process, and to 94.12% by hydrothermal homogeneous precipitation process). On the other hand, because of good spherical shape and high particle distribution of TiO₂ sample from hydrothermal homogeneous precipitation process, the corresponding honeycomb catalyst samples get the best mechanical strength, which is even higher than that of the reference sample from commercial nano-TiO₂. So, it is concluded that the hydrothermal homogeneous precipitation can be a feasible and effective preparation method of TiO₂ carrier for the honeycomb SCR catalyst production.

Key words: nano-TiO₂; honeycomb SCR catalyst; homogeneous precipitation; ultrasonic treatment; hydrothermal method

1 Introduction

Ammonia selective catalytic reduction (SCR) is the most important industrialized flue gas denitration technology [1-5]. As the mainstream SCR catalyst, V₂O₅-TiO₂ catalyst is widely used in the coal-fired boiler system [1-4]. TiO₂ is the catalyst carrier, which can effectively support and disperse the active components to enhance the DeNO_x efficiency and other properties [1-4, 6-7], so it is critical to the costs and quality of catalyst production.

Liquid method for the synthesis of nano-TiO₂ generally includes direct precipitation, homogeneous precipitation, sol-gel method, hydrothermal method, etc. Among these methods, homogeneous precipitation [7-10] usually uses inorganic titanium salt and urea as raw materials. From the thermal hydrolysis process, urea decomposes and generates NH₃·H₂O, which makes the pH of reaction solution rise homogeneously. Then, H₂TiO₃ precipitates out as the reaction product. Compared to other methods, homogeneous precipitation is easy for application and industrialization. The TiO₂ particles prepared from this method have uniform size, good spherical shape and high distribution, but are generally in micrometer scale, which is too large for the preparation of SCR catalyst. So, the traditional homogeneous precipitation process needs to improve.

In this work, ultrasonic treatment [11-13] and hydrothermal method [14-16] were applied in the traditional homogeneous precipitation for nano-TiO₂ preparation. Moreover, honeycomb SCR catalyst samples were prepared with TiO₂ as carrier material. The characterization of TiO₂ samples, denitration activity and mechanical strength of catalyst samples were measured and compared with samples prepared with a commercial anatase nano-TiO₂. The purpose of the work was to find a feasible and effective preparation method of TiO₂ carrier for the honeycomb SCR catalyst production.

2 Experimental

2.1 Preparation of TiO₂

2.1.1 Homogeneous precipitation

A certain amount of titanyl sulfate (TiOSO₄, A.R.)and urea (CO(NH₂)₂, A.R.) were dissolved in deionized water, respectively. The two solutions were mixed and the dosages of titanyl sulfate and urea were controlled to make the initial concentration of TiOSO₄ and CO(NH₂)₂ in the reaction mixture 0.2 mol/L and 0.8 mol/L, respectively. Then, a certain amount of DBS was added into the mixture as dispersant and its concentration was 0.01 mol/L.

The mixture was rapidly stirred under 80 °C for 2 h in water bath. Then, the generated metatitanic (H₂TiO₃) was separated by vacuum filtration and the filter cake was washed by deionized water for several times to remove soluble impurities. After filtration, the metatitanic was dried at 105 °C for 12 h and calcinated at 450 °C for 2 h. Finally, TiO₂ was obtained after natural cooling and ground as Sample 1.

2.1.2 Ultrasonic homogeneous precipitation

After the mixing of titanyl sulfate solution, urea solution and DBS, ultrasound instrument (XIANOU TECH GL-600SD, China) was used to generate ultrasound with fixed frequency of 25 kHZ. The acoustic power was fixed at 400 W and the end face of ultrasonic generator was Ф 0.01 m, which was immersed under liquid surface for 10 mm. Then, the reaction was kept for 2 h with rapid stirring under 80 °C condition. Other operations were the same as preparation of Sample 1. And TiO₂ was obtained as Sample 2.

2.1.3 Hydrothermal homogeneous precipitation

After the mixing of titanyl sulfate solution, urea solution and DBS, the mixture was put in pressurized water reactor and the reaction system was heated to 140 °C with rapid stirring for 2 h. Other operations were the same as preparation of Sample 1. And TiO₂ was obtained as Sample 3.

2.1.4 Reference sample

A commercial anatase nano-TiO₂ (Ishihara, ITAC- 140-7A, Japan) was selected as Sample 4.

2.2 Preparation of honeycomb SCR catalyst

Ammonium metavanadate (NH₄VO₃, A.R.) and ammonium tungstate ( (NH₄)₅H₅[H₂(WO₄)₆], A.R.) were chosen as the precursors of active component. The active component (V₂O₅ and WO₃) was loaded by equal volume impregnation with TiO₂ powders of Sample 1-4 as carriers, respectively. Considering the original certain WO₃ component in commercial TiO₂ powder, therefore only V₂O₅ was loaded for Sample 4. Then, four catalyst powders with the same ingredients of 1%V₂O₅-7%WO₃/ TiO₂ were obtained.

Afterwards, a certain amount of silica and polyacrylamide powder were added as forming agents, and the honeycomb billets were made by compression molding method [17-20]. Then, those billets were dried at 80 °C for 24 h, and calcinated at 350 °C, 1 h+450 °C, 1 h+550 °C, 3 h. After natural cooling, the honeycomb catalyst samples were obtained (Sample HC-1-HC-4 corresponded to TiO₂ Sample 1-4), as shown in Fig. 1.

3 Analysis methods

3.1 Characterization analysis

X-ray diffractometer (Rigaku, D/max 2500/PC, Japan) was used to analyze the X-ray diffraction patterns. Scanning angle (2θ) was from 10° to 80°. Scanning rate was 2 (°)/min with monochromatized Cu radiation. Laser particle size analyzer (Beckman Coulter, Ls200, America) was used to analyze the particles sizes and distributions. X-ray fluorescence (TA, ARL QUANT'X, America) was used to analyze the element contents. Scanning electron microscopy (JEOL, JSM5610LV, Japan) was used to observe the TiO₂ images. BET method (Micomeritics, ASAP 2020, America) was adopt to test the specific surface areas.

3.2 Mechanical strength

Electronic universal testing machine (Shenzhen SANS, CMT5105, China) was used to analyze the axial and lateral compressive strength of the honeycomb catalyst samples to evaluate the mechanical strength.

Fig. 1 Structure of honeycomb catalyst sample (a) and object picture (b) (Height of single honeycomb catalyst sample is 12 mm)

3.3 Denitration performance tests

Denitration activities of honeycomb catalyst samples were tested in self-made DeNO_x activity test bench, which mainly consisted of gas distribution part, reaction part and exhaust gas analysis part. The catalyst samples were filled in reaction tube (The inner diameter of the tube was 37 mm, and single filling height of honeycomb catalyst sample was 72 mm). The simulated flue gas passed into reaction tube when it was heated to the specified temperature. Liquid water was injected into preheating section by micro-flow syringe pump, and then vaporized and mixed with other gases. NH₃/N₂ passed into reaction tube and mixed with the simulated flue gas after preheating. When the mixed gas flowed through the catalyst layer, SCR DeNO_x reaction occurred. Then, NO_x concentrations in outlet exhaust gas with and without reaction were measured by flue gas analyzer (MRU, MGA 5, Germany) to calculate the DeNO_x efficiency of catalyst sample.

4 Results and analysis

4.1 Reaction mechanism and characterization of TiO₂

4.1.1 Reaction mechanism

The main reaction in homogeneous precipitation for TiO₂ preparation includes the hydrolysis of TiOSO₄ and CO(NH₂)₂. For the former, total reaction can be simply described by Eq. (1), but the actual reaction is more complex than that [12, 21]:

TiO²⁺+H₂O→H₂TiO₃+2H⁺                      (1)

In TiOSO₄ solution, the Ti⁴⁺ exists in the form of complex Ti(OH)_p^(4-p)+ mainly in the beginning, which condenses with each other slowly to form the polymer as “≡Ti—O—Ti≡”. In this process, H⁺ is released with the formation of “oxygen bridge” in polymer. So, the titanium salt solution shows acid, and at this moment, the solution still keeps clarity.

When temperature or pH value of the reaction system rises, the equilibrium in Eq. (1) is broken and shifts to the right side. In this homogeneous precipitation process, the hydrolysis of CO(NH₂)₂ can be described by Eqs. (2) and (3) [10]. OH^- generated constantly neutralizes H⁺ generated from the hydrolysis of TiOSO₄, and H₂TiO₃ is generated as precipitate simultaneously. So, the two hydrolysis processes are promoted by each other during the whole reaction:

CO(NH₂)₂+H₂O→2NH₃+CO₂                              (2)

NH₃+H₂O→NH₄⁺+OH^-                           (3)

In the initial reaction period of homogeneous precipitation, plenty of H₂TiO₃ nuclei are generated explosively. Then, the titanium polymer begins to grow and aggregate continuously centering at the nuclei with the same growth rate in all directions, because of the homogeneous rise of pH value in the reaction system. So, the TiO₂ particles prepared from homogeneous precipitation have good spherical shape and uniform size.

In this work, ultrasonic treatment and hydrothermal method were applied in the traditional homogeneous precipitation as the operation improvements, respectively. Ultrasonic treatment can create micro-environment with high temperature and pressure in the liquid reaction system, so the hydrolysis of TiOSO₄ and CO(NH₂)₂ is improved and the generation rate of H₂TiO₃ nuclei is increased in the initial reaction period. On the other hand, ultrasound brings the high-energy cavitation and microjet which can limit the growth of H₂TiO₃ particles effectively. Also, large aggregates formed will be crushed by the microjet. So, the particle size can be maintained at a low level.

The hydrothermal operation can raise the overall temperature and pressure of the reaction system. So, the generation rate of H₂TiO₃ nuclei can be enhanced also, and the increase of particle quantity leads to the decrease of prepared particle size. Moreover, the homogeneous characteristic of homogeneous precipitation reaction ensures the uniformity and sphericity of H₂TiO₃ particles. So, this method can improve the quality of TiO₂ product effectively.

4.1.2 Characterization of TiO₂ samples

The XRD results (Fig. 2) demonstrated that the TiO₂ samples were all in anatase crystal form, which indicated that ultrasonic treatment and hydrothermal method operated in this work would not influence the crystal form of the prepared TiO₂ from homogeneous precipitation. The average grain sizes of Sample 1-4 calculated by Scherrer formula [12] were 5.6 nm, 5.5 nm, 6.2 nm and 15.1 nm, respectively. The results indicated that ultrasound almost had no effect on the TiO₂ grain size during the homogeneous precipitation process. It might be because the instantaneous micro-environment with high temperature and pressure generated by ultrasound could not bring a continuous impact on the growth of H₂TiO₃ crystal grain. However, the hydrothermal operation created a continuous and integrated environment with high temperature and pressure. It changed the overall growth condition for H₂TiO₃ crystal grain, and resulted in a slight increase in the average grain size. In addition, Sample 4 (commercial anatase nano-TiO₂) had the highest degree of crystallinity and the largest crystal grain size. This might be due to the different operation condition during the preparation process.

Fig. 2 XRD patterns of TiO₂ samples

Particles size analysis results (Fig. 3) showed that the average particle sizes of TiO₂ Sample 1-4 were 5.70, 0.65, 0.58 and 1.89 μm, respectively, and the relative standard deviations of particle size distribution were 73.9%, 57.4%, 52.4% and 68.3%, respectively. Combined with the SEM images of the TiO₂ samples (Fig. 4), it could be seen that Sample 1 prepared from the traditional homogeneous precipitation obtained good particle sphericity and larger particle size. But, the obvious crosslinking among the particles resulted in low dispersion of the TiO₂ particles.

However, Sample 2 prepared from ultrasonic homogeneous precipitation presented relatively high dispersion and small particle size, because the random micro-environment with high temperature and pressure generated by ultrasound broke the homogeneous characteristic of reaction system to a certain extent. FromFig. 4(b), it could be seen that the particle sphericity of Sample 2 was low, and the particle shape was irregular. Moreover, it has been reported that ultrasound would cause the fine particles to collide and polymerize in liquid environment, so Sample 2 also showed a certain degree of agglomeration.

Fig. 3 Particles size distribution of TiO₂ samples

TiO₂ Sample 3 made by hydrothermal homogeneous precipitation, by contrast, had the lowest average particle diameter and relative standard deviation of particle size distribution, and also maintained good particle sphericity. It was just because hydrothermal process kept the homogeneous characteristic of reaction system to maintain the growth of spherical particles. In addition, almost all of the H₂TiO₃ nuclei were generated in the initial reaction period, because hydrothermal process enhanced the hydrolysis rate of TiOSO₄. So, the H₂TiO₃ particles had the same growth time which brought them the similar particle size, and avoided the crosslinking and absorption among particles generated in different reaction periods.

Fig. 4 SEM images of TiO₂ samples:

Compared with Sample 4 (commercial anatase nano-TiO₂), Sample 2 and Sample 3 modified by ultrasonic treatment and hydrothermal method presented obvious advantages on the average particle size and distribution.

The BET surface areas of TiO₂ Sample 1-4 are listed in Table 1. Sample 2 prepared from ultrasonic homogeneous precipitation obtained the highest BET surface area (121.4 m²/g), followed by Sample 3 prepared from hydrothermal homogeneous precipitation (113.6 m²/g). Sample 1 without improvement operation, by contrast, had the lower value (88.5 m²/g) than Sample 2 and 3. The results indicated that the two modifications strongly improved the specific surface area of TiO₂ products. Due to the differences between the grain sizes, the specific surface area of Sample 2 was slightly higher than Sample 3.

Table 1 BET surface areas of TiO₂ samples

The specific surface area of TiO₂ carrier material has direct effect on the activity of the final catalyst product, so it is an important quality indicator of TiO₂ materials.

4.2 Mechanical strength of honeycomb catalysts

Compressive strengths of axial and lateral direction were used for mechanical strength assessment of honeycomb catalysts (Sample HC-1-HC-4) [17-19, 22]. The results shown in Fig. 5 presented the average values of four-time measurements for each sample.

The experiment results demonstrated that the mechanical strength of Sample HC-1 was the lowest (compressive strength of axial direction was only 0.1063 MPa), which was loosely structured and friable. While with the ultrasonic treatment, the mechanical strength of sample HC-2 was improved significantly, and its compressive strength of axial direction reached 0.6818 MPa. This was because the small and uniform particles of TiO₂ carrier with high dispersion brought a large contact area among these particles, and the honeycomb catalysts got higher sintering strength during the calcination process. Sample HC-3 was prepared with Sample 3, which was synthesized from hydrothermal homogeneous precipitation. Its mechanical strength wasfurther enhanced and the compressive strength of axial direction reached 0.9873 MPa. Honeycomb catalysts obtained from ultrasonic and hydrothermal homogeneous precipitation (Sample HC-2 and HC-3) had the similar average particle diameter and dispersion. The difference of mechanical strength between them might be due to different degrees of particle sphericity. Irregular particle morphology would hinder the uniformity of contact with each other during the sintering process. The created cracks weakened the connection among carrier particles just as the description in Fig. 6, therefore brought a mechanical strength reduction of honeycomb catalyst Sample HC-2.

Fig. 5 Compressive strength of honeycomb SCR catalyst samples

Compared with Sample HC-4 (compressive strength of axial direction is 0.8924 MPa), Sample HC-3 even had the better mechanical strength than the honeycomb catalyst prepared with commercial nano-TiO₂. Besides, due to the structural features of honeycomb catalyst, the compressive strength of lateral direction was lower than that of axial direction, as shown in Fig. 4.

4.3 Characterization and denitration performance of honeycomb SCR catalysts

The BET surface area and the XRF analysis results of Sample HC-1-HC-4 are given in Table 2 and Table 3.

From Table 1 and Table 2, It could be seen that honeycomb catalyst samples had relatively lower specific surface area than the corresponding TiO₂ samples because of the extrusion and calcination operations, while the order among each other remained unchanged. Data of Table 3 showed that honeycomb catalyst samples had the uniform component of 0.9%V₂O₅-6%WO₃-2%SO₃/TiO₂-SiO₂ basically. It facilitated further comparison of the denitration characteristics among different TiO₂ carriers by catalyst activity tests.

SCR denitration experiments were carried out with honeycomb catalyst samples [1-4]. The testing conditions were set as follows: the catalyst height was 72 mm; volume space velocity (SV) ratio was 3000 h^-1; simulated flue gas was composed of NO 0.05%, O₂ 5%, H₂O 8%, SO₂ 0.3% and balance gas was N₂; NH₃/NO (molar ratio) was 1.05. The reaction temperature range was from 260 to 460 °C, and the test results are shown in Fig. 7.

Fig. 6 Sintering properties of carrier materials with different shapes

Table 2 BET surface areas of catalysts samples

Table 3 XRF results of catalyst samples

From Fig. 7, it could be seen that, all of the four honeycomb catalyst samples presented stable NO_x reduction ratio with the reaction temperature ranging from 320 to 400 °C. It is indicated that the four samples had the same temperature range of denitration activity. The maximum NO_x reduction ratio of Sample HC-1 reached 88.89% at 380 °C nearby. It was higher than the maximum NO_x reduction ratio of Sample HC-4 prepared with commercial nano-TiO₂ (86.28% at 380 °C nearby). The results presented the advantage of homogeneous precipitation process in preparation of SCR catalyst carrier TiO₂. Moreover, Samples HC-2 and HC-3 presented further promotion on their NO_x reduction ratio (95.45% and 94.12% at 380 °C nearby, respectively). These catalyst samples had the uniform component, and their denitration activities showed obvious positive correlation with their specific surface area because high specific surface area would promote the contact of catalytic active sites with the reaction flue gas. It could be concluded that the ultrasonic treatment and hydrothermal method both enhanced the denitration activity of honeycomb SCR catalyst samples by the increase of specific surface area of TiO₂ carrier.

Fig. 7 SCR denitration test results of honeycomb SCR catalyst samples

5 Conclusions

1) Ultrasonic treatment and hydrothermal method applied in traditional homogeneous precipitation could both decrease the product particle size of TiO₂, and increase the dispersity, distribution and the specific surface area. However, ultrasound decreased the sphericity of TiO₂ particles and brought some agglomeration; by contrast, the hydrothermal method made TiO₂ product have the lowest relative standard deviation of particle size distribution, and also maintain good particle sphericity. In addition, both of the two improved methods would not brought obvious influence on the anatase crystal form of prepared TiO₂.

2) Honeycomb SCR catalyst prepared with the TiO₂ which was synthesized by ultrasonic or hydrothermal homogeneous precipitation could obtain higher denitration activity and mechanical strength than the sample prepared with traditional homogeneous precipitation TiO₂ material. Besides, because of the better sphericity and dispersity of TiO₂ particles, hydrothermal homogeneous precipitation brought the higher promotion on mechanical strength of honeycomb catalyst sample than ultrasonic homogeneous precipitation.

3) Compared with the commercial anatase nano- TiO₂, TiO₂ synthesized by hydrothermal homogeneous precipitation made the corresponding honeycomb SCR catalyst obtain the higher denitration activity and mechanical strength. The results indicated the feasibility and advantage of this method on the preparation of SCR catalyst carrier TiO₂ material.

References

[1] ZHENG Yuan-jing, JENSEN A D, JOHNSSON J E. Deactivation of V₂O₅-WO₃-TiO₂ SCR catalyst at a biomass-fired combined heat and power plant [J]. Applied Catalysis B: Environmental, 2005, 60: 253-264.

[2] O, ELSENER M. Chemical deactivation of V₂O₅/WO₃–TiO₂ SCR catalysts by additives and impurities from fuels, lubrication oils, and urea solution I: Catalytic studies [J]. Applied Catalysis B: Environmental, 2008, 75: 215-227.

[3] GUO Xiao-yu, BARTHOLOMEW C, HECKER W, BAXTER L L. Effects of sulfate species on V₂O₅/TiO₂ SCR catalysts in coal and biomass-fired systems [J]. Applied Catalysis B: Environmental, 2009, 92: 30-40.

[4] CASTELLINO F, RASMUSSEN S B, JENSEN A D, JOHNSSON J E, FEHRM A N N R. Deactivation of vanadia-based commercial SCR catalysts by polyphosphoric acids [J]. Applied Catalysis B: Environmental, 2008, 83: 110-122.

[5] THEINNOI K, TSOLAKIS A, SITSHEBO S, CRACKNELL R F, CLARK R H. Fuels combustion effects on a passive mode silver/alumina HC-SCR catalyst activity in reducing NO_X [J]. Chemical Engineering Journal, 2010, 158: 468-473.

[6] MA Zi-ran, WENG Duan, WU Xiao-dong, SI Zhi-chun, WANG Bin. A novel Nb-Ce/WO_X-TiO₂ catalyst with high NH₃-SCR activity and stability [J]. Catalysis Communications, 2012, 27: 97-100.

[7] CHEN Xia, ZHANG Jun-feng, HUANG Yan, TONG Zhi-quan, HUANG Ming. Catalytic reduction of nitric oxide with carbon monoxide on copper-cobalt oxides supported on nano-titanium dioxide [J]. Journal of Environmental Sciences, 2009, 21: 1296-1301.

[8] GINSBERGA T, MODIGELLA M, WILSMANNB W. Thermochemical characterisation of the calcinations process step in the sulphate method for production of titanium dioxide [J]. Chemical Engineering Research and Design, 2011, 89: 990-994.

[9] TIAN Cong-xue, DU Jian-qiao, CHEN Xin-hong, MA Wei-ping, LUO Zhi-qiang, CHENG Xiao-zhe, HU Hong-fei, LIU Dai-jun. Influence of hydrolysis in sulfate process on titania pigment producing [J]. Transactions of Nonferrous Metals Society of China, 2009, 19: 829-833.

[10] V, BAKARDJIEVA S, SZATMARY L. Synthesis of spherical metal oxide particles using homogeneous precipitation of aqueous solutions of metal sulfates with urea [J]. Powder Technology, 2006, 169: 33-40.

[11] LATT K K, KOBAYASHI T. TiO₂ nanosized powders controlling by ultrasound sol–gel reaction [J]. Ultrasonics Sonochemistry, 2008, 15: 484-491.

[12] GHOWS N, ENTEZARI M H. Ultrasound with low intensity assisted the synthesis of nanocrystalline TiO₂ without calcinations [J]. Ultrasonics Sonochemistry, 2010, 17: 878-883.

[13] TIAN Bao-zhu, FENG Che-na, ZHANG Jin-long, MASAKAZU A. Influences of acids and salts on the crystalline phase and morphology of TiO₂ prepared under ultrasound irradiation [J]. Journal of Colloid and Interface Science, 2006, 303: 142-148.

[14] OH S W, PARK S, SUN Y. Hydrothermal synthesis of nano-sized anatase TiO₂ powders for lithium secondary anode materials [J]. Journal of Power Sources, 2006, 161: 1314-1318.

[15] YIN Heng-bo, WADA Y, KITAMURA T, KAMBE S, MURASAWA S, MORI H, SAKATA T, YANAGIDA S. Hydrothermal synthesis of nanosized anatase and rutile TiO₂ using amorphous phase TiO₂ [J]. Journal of Materials Chemistry, 2001, 11: 1694-1703.

[16] PUDDU V, MOKAYA R, PUMA G L. Novel one step hydrothermal synthesis of TiO₂/WO₃ nanocomposites with enhanced photocatalytic activity [J]. Chemical Communications, 2007, 45: 4749-4751.

[17] LIU Qing-ya, LIU Zhen-yu, HUANG Zhang-gen, XIE Guo-yong. A honeycomb catalyst for simultaneous NO and SO₂ removalfrom flue gas: Preparation and evaluation [J]. Catalysis Today, 2004, 93-95: 833-837.

[18] SUN Hong, SHU Yun, QUAN Xie, CHEN Shuo, PANG Bo, LIU Zhao-yang. Experimental and modeling study of selective catalytic reduction of NO_X with NH₃ over wire mesh honeycomb catalysts [J]. Chemical Engineering Journal, 2010, 165: 769-775.

[19] BERETTA A, TRONCONI E, ALEMANY L J, SVACHULA J, FORZATTI P. Effect of morphology of honeycomb SCR catalysts on the reduction of NO_X and the oxidation of SO₂ [J]. Studies in Surface Science and Catalysis, 1994, 82: 869-876.

[20] SHANG Xue-song, HU Gong-ren, HE Chi, ZHAO Jin-ping, ZHANG Fu-wang, XU Ya, ZHANG Yun-feng, LI Jiang-rong, CHEN Jin-sheng. Regeneration of full-scale commercial honeycomb monolith catalyst (V₂O₅– WO₃/TiO₂) used in coal-fired power plant [J]. Journal of Industrial and Engineering Chemistry, 2012, 18: 513-519.

[21] CZEKAJ I, O, PIAZZESI G. DFT calculations, DRIFT spectroscopy and kinetic studies on the hydrolysis of isocyanic acid on the TiO₂-anatase (101) surface [J]. Journal of Molecular Catalysis A: Chemical, 2008, 280: 68-80.

[22] YASHNIK S A, ISMAGILOV Z R, KOPTYUG I V, ANDRIEV SKAYA I P, MATVEEV A A, MOULIJIN J A. Formation of textural and mechanical properties of extruded ceramic honeycomb monoliths: An 1H NMR imaging study [J]. Catalysis Today, 2005, 105: 507-515.

(Edited by YANG Bing)

Foundation item: Project(201031) supported by the Environmental Protection Scientific Research of Jiangsu Province, China; Project(BE2010184) supported by the Technology Support Program of Jiangsu Province— Industrial Parts, China

Received date: 2015-06-08; Accepted date: 2015-12-10

Corresponding author: YAO Jie, PhD; Tel: +86-25-89620838; E-mail: tonglingyaojie@163.com