Molecular sieve confined noble metal catalyst for CO-SCR denitrification, preparation method and application thereof

Abstract

A molecular sieve confined noble metal catalyst for CO-SCR denitrification, a preparation method and an application thereof are provided. The catalyst includes a molecular sieve carrier and Ir metal nanoclusters loaded in the molecular sieve carrier through confined encapsulation. The preparation method includes the following steps: mixing a first metal precursor solution with a first ligand to obtain a first mixed solution; mixing a second metal precursor solution with a second ligand to obtain a second mixed solution; mixing a silicon source, an aluminum source, an alkali and a solvent to obtain a molecular sieve precursor solution; mixing the molecular sieve precursor solution with the first mixed solution, then adding the second mixed solution for hydrothermal crystallization reaction, and then centrifugally washing, drying and calcining to obtain the catalyst.

Claims

1. A molecular sieve confined noble metal catalyst for CO-SCR denitrification, wherein the molecular sieve confined noble metal catalyst consists of a molecular sieve carrier and Ir metal nanoclusters loaded in the molecular sieve carrier through confined encapsulation; the molecular sieve carrier is an A-type molecular sieve, an X-type molecular sieve or a Y-type molecular sieve; a loading of the Ir metal nanoclusters in the molecular sieve confined noble metal catalyst is 0.1-1 wt. %; and a particle size of the Ir metal nanoclusters is 2 nm, and the Ir metal nanoclusters comprise an oxidized state of Ir.sup.+ and a metallic state of Ir.sup.0, wherein a proportion of the Ir.sup.0 is 10-70 wt. %; wherein the molecular sieve confined noble metal catalyst is prepared by a method comprises the following steps: mixing a first metal precursor solution with a first ligand, and stirring to obtain a first mixed solution; mixing a second metal precursor solution with a second ligand, and stirring to obtain a second mixed solution; mixing silicon source, aluminum source, alkali and solvent, and stirring to obtain molecular sieve precursor solution; mixing the molecular sieve precursor solution with the first mixed solution and stirring, then adding the second mixed solution and stirring to obtain a third mixed solution; carrying out hydrothermal crystallization reaction on the third mixed solution, and after finishing the hydrothermal crystallization reaction, carrying out centrifugal washing, drying and calcining to obtain the molecular sieve confined noble metal catalyst for the CO-SCR denitrification; wherein the first metal precursor solution and the second metal precursor solution are both Ir salt solutions; and the first ligand is a C1-6 linear amine compound; the second ligand is alkoxy silane containing sulfhydryl or amino group.

2. The molecular sieve confined noble metal catalyst for CO-SCR denitrification according to claim 1, wherein a solute of the Ir salt solution comprises at least one of iridium nitrate, iridium acetate or iridium chloride acid, and a solvent of the Ir salt solution is water.

3. The molecular sieve confined noble metal catalyst for CO-SCR denitrification according to claim 1, wherein the aluminum source comprises at least one of sodium metaaluminate, boehmite, pseudo-boehmite, amorphous aluminum hydroxide powder or aluminum isopropoxide; the silicon source comprises at least one of water glass, silica sol, silica gel or amorphous SiO.sub.2 powder; and the alkali is at least one of NaOH or KOH.

4. The molecular sieve confined noble metal catalyst for CO-SCR denitrification according to claim 1, wherein a molar ratio of Ir salt of the Ir salt solution to the first ligand in the first mixed solution is 1:3-8, based on Ir; and a molar ratio of the Ir salt to the second ligand in the second mixed solution is 1:6-12.

5. The molecular sieve confined noble metal catalyst for CO-SCR denitrification according to claim 1, wherein the silicon source is calculated as SiO.sub.2, the aluminum source is calculated as Al.sub.2O.sub.3, the alkali is calculated as at least one of Na.sub.2O or K.sub.2O, Ir salt of the Ir salt solution is calculated as Ir, and a molar ratio of the silicon source, the aluminum source, the alkali, the Ir salt, the first ligand and the second ligand in the third mixed solution is 1-8:1: 1-4:0.003-0 0.020:0.001-0.16:0.001-0.24.

6. The molecular sieve confined noble metal catalyst for CO-SCR denitrification according to claim 1, wherein a temperature of the hydrothermal crystallization reaction is 80-120 C. and a time is 3-48 h; a drying temperature is 80-120 C.; and a calcination temperature is 400-600 C., a time is 4-8 h, and a heating rate is 1-10 C./min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to explain the embodiments of the present disclosure or the technical scheme in the prior art more clearly, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure, and other drawings may be obtained according to these drawings without creative work for ordinary people in the field.

(2) FIG. 1 is an XRD spectrum of catalysts prepared in Embodiment 3 and Comparative Example 1.

(3) FIG. 2 is a TEM image of the catalyst prepared in Embodiment 3.

(4) FIG. 3 is a graph showing the particle size distribution of Ir nanoclusters in the catalysts prepared in Embodiments 1 to 3 and Comparative Examples 2 to 3.

(5) FIG. 4 shows the stability test results of the catalyst prepared in Embodiment 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) A number of exemplary embodiments of the present disclosure will now be described in detail, and this detailed description should not be considered as a limitation of the present disclosure, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present disclosure.

(7) It should be understood that the terminology described in the present disclosure is only for describing specific embodiments and is not used to limit the present disclosure. In addition, for the numerical range in the present disclosure, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Intermediate values within any stated value or stated range, as well as each smaller range between any other stated value or intermediate values within the stated range are also included in the present disclosure. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

(8) Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure relates. Although the present disclosure only describes the preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present disclosure. All documents mentioned in this specification are incorporated by reference to disclose and describe methods and/or materials related to the documents. In case of conflict with any incorporated document, the contents of this specification shall prevail.

(9) It is obvious to those skilled in the art that many improvements and changes may be made to the specific embodiments of the present disclosure without departing from the scope or spirit of the present disclosure. Other embodiments will be apparent to the skilled person from the description of the disclosure. The description and embodiments of the present disclosure are exemplary only.

(10) The terms including, comprising, having and containing used in this disclosure are all open terms, which means including but not limited to.

(11) Where the specific technology or conditions are not specified in the specific embodiment of the present disclosure, it shall be carried out according to the conventional technology or conditions in the field or according to the product specification. The raw materials or instruments used are conventional products that may be purchased through regular channels if the manufacturer is not indicated.

(12) The room temperature referred to in the specific embodiment of the present disclosure specifically refers to 20-30 degrees Celsius ( C.).

(13) The Ir salt (metal precursor), the first ligand, the second ligand, the aluminum source, the silicon source and the alkali involved in the specific embodiment of the present disclosure may be equally substituted within the scope defined by the present disclosure, without affecting the realization of the technical effect.

Embodiment 1

(14) A type A molecular sieve confined noble metal catalyst for CO-SCR denitrification includes the following preparation steps: S1. dissolving 1 gram (g) of chloroiridium hexahydrate (with an Ir content of 39 weight percent (wt. %)) in water to prepare 100 milliliter (mL) of chloroiridium solution (with an Ir concentration of 3.9 grams per liter (g/L)); (as a first metal precursor solution and a second metal precursor solution); S2. mixing 8.50 mL of chloroiridium acid solution (where Ir is 0.033 g, namely, 0.172 millimole (mmol)) (first metal precursor solution) with 0.08 g (1.1 mmol) of 1,3-propanediamine (first ligand), and stirring at 30 C. for 0.5 hours (h) to obtain a first mixed solution; S3. mixing 2.80 mL of chloroiridium acid solution (where Ir is 0.011 g, namely, 0.057 mmol) (second metal precursor solution) with 0.065 g (0.4 mmol) (3-aminopropyl) trimethoxysilane (second ligand), and stirring at 30 C. for 0.5 h to obtain a second mixed solution; S4. dissolving 1.2 g (0.03 mole (mol)) of sodium hydroxide (alkali) and 2.5 g (0.03 mol) of sodium metaaluminate (aluminum source) in 12 mL (0.67 mol) of deionized water, and stirring at 30 C. for 0.5 h to obtain an aluminum alkali solution; mixing 6 g of silica sol (containing 0.03 mol of SiO.sub.2) with 15 mL (0.83 mol) of deionized water, and stirring at 30 C. for 0.5 h to obtain a silica source solution; mixing the aluminum alkali solution and the silicon source solution, and stirring at 30 C. for 0.5 h to obtain a molecular sieve precursor solution; and mixing the molecular sieve precursor solution with the first mixed solution, stirring at 30 C. for 0.5 h, adding the second mixed solution, and continuously stirring at 30 C. for 3 h to obtain a third mixed solution; S5. carrying out hydrothermal crystallization reaction on the third mixed solution at 100 C. for 4 h to obtain a suspension; and S6. using water as a centrifugal washing solvent, centrifugally washing the suspension for 5 times, where the centrifugal rotation speed is 4000 revolutions per minute (rpm), and the centrifugal washing time is 5 minutes (min) each time; then, drying the solid product obtained by centrifugal washing (potential of Hydrogen (pH) 8-10 detected by pH test paper) in the air atmosphere of 100 C., grinding in a mortar for 5 min, and calcining the ground sample in an air atmosphere at 550 C. for 6 h at a heating rate of 2 degrees Celsius per minute ( C./min), to obtain a type A molecular sieve confined noble metal catalyst for CO-SCR denitrification (the Ir loading in the catalyst prepared in this embodiment is 0.83 wt. % by ICP test).

Embodiment 2

(15) Compared with Embodiment 1, the difference is that the amounts of the first metal precursor solution, the second metal precursor solution, the first ligand and the second ligand are 5.6 mL, 5.6 mL, 0.053 g and 0.13 g, respectively (according to ICP test, the Ir loading in the catalyst prepared in this embodiment is 0.81 wt. %).

Embodiment 3

(16) Compared with Embodiment 1, the difference is that the amounts of the first metal precursor solution, the second metal precursor solution, the first ligand and the second ligand are 2.8 mL, 8.5 mL, 0.027 g and 0.194 g, respectively (by ICP test, the Ir loading in the catalyst prepared in this embodiment is 0.79 wt. %).

Comparative Example 1

(17) The preparation of pure A-type molecular sieve includes the following steps:

(18) dissolving 1.2 g of sodium hydroxide and 2.5 g of sodium metaaluminate in 12 mL of deionized water and stirring at 30 C. for 0.5 h to obtain an aluminum alkali solution; mixing 6 g of silica sol with 15 mL of deionized water, and stirring at 30 C. for 0.5 h to obtain a silicon source solution; mixing the Silicon aluminum alkali solution and the silicon source solution, and stirring at 30 C. for 0.5 h to obtain a molecular sieve precursor solution; carrying out hydrothermal crystallization of molecular sieve precursor solution at 100 C. for 4 h, then using water as centrifugal washing solvent, centrifugally washing the products of hydrothermal crystallization reaction for 5 times, with a centrifugal speed of 4000 rpm and a centrifugal washing time of 5 min; subsequently, drying the centrifugal washing product in an air atmosphere of 100 C., then grounding for 5 min, and the ground sample is calcined in an air atmosphere of 550 C. for 6 h, the heating rate is 2 C./min, thus obtaining pure A-type molecular sieve.

Comparative Example 2

(19) The preparation steps of the catalyst are as follows: S1. dissolving 1 g of chloroiridium hexahydrate (with an Ir content of 39 wt. %) in water to prepare 100 mL chloroiridium solution; S2. mixing 11.50 mL of chloroiridium acid solution with 0.10 g of 1,3-propanediamine, and stirring at 30 C. for 0.5 h to obtain a first mixed solution; S3. dissolving 1.2 g of sodium hydroxide (alkali) and 2.5 g of sodium metaaluminate (aluminum source) in 12 mL of deionized water, and stirring at 30 C. for 0.5 h to obtain an aluminum alkali solution; mixing 6 g of silica sol (silicon source) with 15 mL of deionized water and stirring at 30 C. for 0.5 h to obtain a silicon source solution; mixing the aluminum alkali solution and the silicon source solution, and stirring at 30 C. for 0.5 h to obtain a molecular sieve precursor solution; and mixing the molecular sieve precursor solution with the first mixed solution, and stirring at 30 C. for 3 h to obtain a second mixed solution; S4. carrying out hydrothermal crystallization reaction on the second mixed solution at 100 C. for 4 h to obtain a suspension; and S5. using water as a centrifugal washing solvent, centrifugally washing the suspension for 5 times, where the centrifugal rotation speed is 4000 rpm, and the centrifugal washing time is 5 min each time; then, drying the solid product obtained by centrifugal washing (pH 8-10 detected by pH test paper) in the air atmosphere of 100 C., grinding in a mortar for 5 min, and calcining the ground sample in an air atmosphere at 550 C. for 6 h at a heating rate of 2 C./min, to obtain a catalyst (the Ir loading in the catalyst prepared in this embodiment is 0.80 wt. % by ICP test).

Comparative Example 3

(20) S1. dissolving 1 g of chloroiridium hexahydrate (with an Ir content of 39 wt. %) in water to prepare 100 mL chloroiridium solution; S2. mixing 11.50 mL of chloroiridium acid solution with 0.258 g of (3-aminopropyl) trimethoxysilane, and stirring at 30 C. for 0.5 h to obtain a first mixed solution; S3. dissolving 1.2 g of sodium hydroxide (alkali) and 2.5 g of sodium metaaluminate (aluminum source) in 12 mL of deionized water, and stirring at 30 C. for 0.5 h to obtain an aluminum alkali solution; mixing 6 g of silica sol (silicon source) with 15 mL of deionized water and stirring at 30 C. for 0.5 h to obtain a silicon source solution; mixing the aluminum alkali solution and the silicon source solution, and stirring at 30 C. for 0.5 h to obtain a molecular sieve precursor solution; and mixing the molecular sieve precursor solution with the first mixed solution, and stirring at 30 C. for 3 h to obtain a second mixed solution; S4. carrying out hydrothermal crystallization reaction on the second mixed solution at 100 C. for 4 h to obtain a suspension; and S5. using water as a centrifugal washing solvent, centrifugally washing the suspension for 5 times, where the centrifugal rotation speed is 4000 rpm, and the centrifugal washing time is 5 min each time; then, drying the solid product obtained by centrifugal washing (pH 8-10 detected by pH test paper) in the air atmosphere of 100 C., grinding in a mortar for 5 min, and calcining the ground sample in an air atmosphere at 550 C. for 6 h at a heating rate of 2 C./min, to obtain a catalyst (the Ir loading in the catalyst prepared in this embodiment is 0.83 wt. % by ICP test).

Effect Verification

(21) 1. XPS Test

(22) The catalysts prepared in Embodiments 1-3 and Comparative Examples 1-3 are tested by XPS, and the ratio of Ir.sup.+ to Ir.sup.0 (mass ratio, percent (%)) is detected. The results are shown in Table 1.

(23) TABLE-US-00001 TABLE 1 Ir.sup.+/(Ir.sup.+ + Ir.sup.0) Ir.sup.0/(Ir.sup.+ + Ir.sup.0) Sample (%) (%) Embodiment 1 81.77 18.23 Embodiment 2 49.88 50.12 Embodiment 3 31.21 68.79 Comparative Example 1 Comparative Example 2 89.46 10.54 Comparative Example 3 27.64 72.36

(24) According to the relative content ratios of active sites Ir.sup.0 and Ir.sup.+ in the Embodiments and Comparative Examples in Table 1, it may be seen that the ratio of Ir.sup.0 and Ir.sup.+ changes regularly with the changes of the dosage of the first metal precursor solution, the second metal precursor solution, the first ligand and the second ligand. With the decrease of the dosage of the first ligand and the corresponding coordinated first metal precursor solution, the proportion of Ir.sup.0 gradually increased.

(25) 2. CO-SCR Reaction Performance Test

(26) testing 0.25 g of the catalysts prepared in Embodiments 1-3 and Comparative Examples 1-3 respectively, and the methods are as follows: placing the catalyst in a fixed reactor with NO concentration of 400 parts per million (ppm), CO concentration of 8000 ppm, O.sub.2 concentration of 5 volume percentage (vol. %), SO.sub.2 concentration of 100 ppm, N.sub.2 as equilibrium gas and space velocity of 10,000 h-1. The nitrogen oxide conversion rate of the catalyst is tested at different reaction temperatures, and the results are shown in Table 2.

(27) Before the formal performance test, all catalysts are pretreated, and the pretreatment steps are as follows:

(28) The catalyst is pretreated at 200 C. in 5 vol. % H.sub.2 gas flow (N.sub.2 as equilibrium gas) for 30 min to improve its catalytic activity. The calculation method of nitrogen oxide (NO.sub.x) conversion rate (.sub.NOx) in Table 2 is shown in Formula 1-1. In the experiment, the real-time change of gas concentration is measured by Bruker Tensor II infrared spectrum, and the product of complete catalytic reduction is N.sub.2.

(29) $\begin{array}{cc}{}_{{\mathrm{NO}}_x}=\left[\frac{\mathrm{NO}\left(\mathrm{in}\right)-\mathrm{NO}\left(\mathrm{out}\right)-N_{2}O\left(\mathrm{out}\right)-{\mathrm{NO}}_2\left(\mathrm{out}\right)}{\mathrm{NO}\left(\mathrm{in}\right)}\right]100\%& \left(11\right)\end{array}$

(30) TABLE-US-00002 TABLE 2 Conversion rate of nitrogen oxides at different reaction temperatures (%) Sample 150 C. 175 C. 200 C. 225 C. 250 C. 275 C. 300 C. Embodiment 1 3.27 4.48 9.09 41.78 56.46 66.68 39.23 Embodiment 2 3.91 9.43 12.58 77.43 80.06 72.67 45.75 Embodiment 3 8.23 6.60 6.69 46.43 56.69 79.57 44.16 Comparative 0.00 0.00 0.00 0.01 0.05 0.09 0.03 Example 1 Comparative 3.91 4.03 5.53 35.95 41.19 52.54 39.59 Example 2 Comparative 2.22 3.75 3.65 24.69 73.27 45.36 38.44 Example 3

(31) Table 2 shows the conversion rates of nitrogen oxides of the catalysts prepared in Embodiments 1-3 and Comparative Examples 1-3 at different temperatures under the conditions of O.sub.2 concentration of 5 vol. % and SO.sub.2 concentration of 100 ppm. It may be seen that the conversion rate of NO.sub.x in Comparative Example 1 is about 0 in all the reaction processes, indicating that the catalytic activity of the molecular sieve carrier itself for CO-SCR reaction is extremely low, and the main role is the Ir active site. Compared with Comparative Example 1, the catalysts prepared in Embodiments 1-3 of the present disclosure have remarkable catalytic activity, and with the increase of the relative content of Ir.sup.0, the conversion first increases and then decreases, showing a volmayic change. As may be seen from Table 1, the overall catalytic activity is the highest when the ratio of Ir.sup.0 to Ir.sup.+ is about 1:1, and the temperature (T.sub.50) is the lowest when the conversion rate of NO.sub.x reaches 50%. When only the first ligand (Comparative Example 2) or the second ligand (Comparative Example 3) is used to coordinate with metal Ir, the technical effect that may be achieved by the embodiment of this application may not be achieved, which further shows that the appropriate relative content ratio of Ir.sup.0 to Ir.sup.+ may effectively promote the increase of the number of active sites, thus improving the catalytic performance of the catalyst.

(32) 3. XRD Test

(33) FIG. 1 is the XRD spectrum of catalysts prepared in Embodiment 3 and Comparative Example 1 (where Ir@A stands for Embodiment 3 and Azeolite stands for Comparative Example 1). Compared with the standard spectrum, both Embodiment 3 (i.e. Ir@A) and Comparative Example 1 (i.e. Azeolite) have the characteristic peaks of type A molecular sieve, indicating the successful synthesis of the carrier, and the introduction of Ir does not damage the molecular sieve structure. In Embodiment 3 (Ir@A), no obvious Ir characteristic peak is observed, indicating Ir is uniformly dispersed on the carrier. Embodiment 1, Embodiment 2 and Embodiment 3 have the same silicon-aluminum ratio and hydrothermal crystallization reaction time in the preparation process, and the types of the obtained molecular sieve carriers are the same. After testing, the XRD spectra of the catalysts prepared in Embodiment 1 and Embodiment 2 are consistent with those in Embodiment 3, so they are not repeated.

(34) 4. Morphology Characterization of Catalyst

(35) Taking the catalysts prepared in Embodiments 1-3 and Comparative Examples 2-3, carrying out TEM experiments, randomly selecting the sizes of 100 nanoclusters, and making the particle size distribution map.

(36) FIG. 2 is a TEM image of the catalyst prepared in Embodiment 2, and FIG. 4 is a particle size distribution diagram of Ir nanoclusters in the catalysts prepared in Embodiments 1-3 and Comparative Examples 2-3. From the TEM images, it may be seen that Ir nanoclusters are uniformly dispersed on the molecular sieve carrier. It may be seen from the particle size distribution diagram that the size of Ir clusters is mainly in the range of less than 0.8 nm and 1-2 nm. In Embodiments 1-3, the proportion of clusters with particle size of 1-2 nm increased gradually, and the proportion of clusters with particle size less than 0.8 nm decreased in turn. The particle size of Ir clusters in the catalyst of Comparative Example 2 is mainly concentrated in the range of less than 0.8 nm, which shows that its particle distribution is smaller and more concentrated. The Ir clusters of the catalyst in Comparative Example 3 are highly concentrated in the range of 1-2 nm (the proportion is close to 90%), while the proportion of Ir clusters smaller than 0.8 nm is less. And with the different proportion of the two ligands, the proportion of clusters with different sizes is different, and the proportion of clusters with different sizes is basically consistent with the proportion trend of Ir.sup.+ and Ir.sup.0 (XPS results).

(37) 5. Stability Test

(38) 0.25 g of the catalyst prepared in Embodiment 2 is tested under the following conditions: the catalyst is placed in a fixed reactor with NO concentration of 400 ppm, CO concentration of 8000 ppm, O.sub.2 concentration of 5 vol. %, SO.sub.2 concentration of 100 ppm, N.sub.2 as equilibrium gas, and space velocity of 10,000 h.sup.1. The nitrogen oxide conversion rate of the catalyst is tested at 250 C., and the results are shown in FIG. 3.

(39) Before the formal performance test, all catalysts are pretreated, and the pretreatment steps are as follows: the catalyst is pretreated at 200 C. in 5 vol. % H.sub.2 gas flow (N.sub.2 as equilibrium gas) for 30 min to improve its catalytic activity. The calculation method of nitrogen oxide (NO.sub.x) conversion (.sub.NOx) in FIG. 3 is shown in Formula 1-1.

(40) FIG. 4 is the result of the stability experiment of the catalyst prepared in Embodiment 3. As may be seen from FIG. 4, the activity of the catalyst is basically not lost within 18 h, and the catalytic activity is relatively stable.

(41) 6. Activity Test of Catalyst Under Different Concentration Ratios of SO.sub.2 and O.sub.2

(42) 0.25 g of the catalyst prepared in Embodiment 3 is tested under different SO.sub.2 concentrations, as follows: the catalyst is placed in a fixed reactor with NO concentration of 400 ppm, CO concentration of 8000 ppm, O.sub.2 concentration of 5 vol. %, SO.sub.2 concentration of 0, 100, 200, 300 and 400 ppm, N.sub.2 as equilibrium gas, temperature of 250 C. and space velocity of 10,000 h.sup.1. The nitrogen oxide conversion rate of the catalyst is tested at different reaction temperatures, and the results are shown in Table 3.

(43) Before the formal performance test, all catalysts are pretreated, and the pretreatment steps are as follows: the catalyst is pretreated at 200 C. in 5 vol. % H.sub.2 gas flow (N.sub.2 as equilibrium gas) for 30 min to improve its catalytic activity. The calculation method of nitrogen oxide (NO.sub.x) conversion rate (UNOx) in Table 3 is the same as that in Formula 1-1.

(44) TABLE-US-00003 TABLE 3 SO.sub.2 0 100 200 300 400 concentration (ppm) O.sub.2:SO.sub.2 500 250 166.67 125 NO.sub.x 12.54 80.06 75.26 61.25 41.38 Conversion

(45) Table 3 shows the NO.sub.x conversion rate of the catalyst prepared in Embodiment 3 at different concentrations of SO.sub.2. In the presence of SO.sub.2, the activity of the catalyst is better than that without SO.sub.2. With the increase of SO.sub.2 concentration, the conversion of NO.sub.x first increased and then decreased. Among them, when the concentration of SO.sub.2 is 100 ppm, the conversion rate of NO.sub.x is the highest, which shows that the catalyst may maintain good activity at an appropriate O.sub.2:SO.sub.2 ratio.

(46) The above-mentioned embodiments only describe the preferred mode of the disclosure, and do not limit the scope of the disclosure. Under the premise of not departing from the design spirit of the disclosure, various modifications and improvements made by ordinary technicians in the field to the technical scheme of the disclosure shall fall within the protection scope determined by the claims of the disclosure.