Low-temperature NH3-SCR (selective catalytic reduction) catalyst as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature NH3-SCR catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts. The preparation method comprises the following steps: sulfating praseodymium oxide or praseodymium-cerium composite oxide to prepare the low-temperature NH3-SCR catalyst; wherein the sulfating treatment time is 20-240 minutes, and the sulfating treatment mode is that mixed gas containing SO2 and O2 is in contact with praseodymium oxide or praseodymium-cerium composite oxide. The preparation method disclosed by the invention is simple, rapid and low in energy consumption, a certain amount of SO2 is introduced at a specific temperature, a new acid site is provided for praseodymium oxide and a praseodymium-based catalyst with relatively good oxidation-reduction performance, and the low-temperature NH3-SCR activity of the praseodymium oxide and the praseodymium-based catalyst is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and more specifically, relates to a low-temperature NH3-SCR catalyst and a preparation method and application thereof. Background Art

[0002] Nitrogen oxides (NO x ) will cause many environmental problems including photochemical smog, ozone layer depletion and acid rain, affecting people's production and life. Among the many nitrogen oxide removal technologies currently available, NH3 selective catalytic reduction (NH3-SCR) is considered to be the most effective means. High-performance catalysts are the core of NH3-SCR technology.

[0003] For thermal power plants, the commercial catalysts currently used are mainly V2O5-WO3 / TiO2. However, with the completion of the transformation of nitrogen oxide emissions in the thermal power industry, V2O5-WO3 / TiO2 catalysts are no longer suitable for low reaction temperatures (< 200 °C) due to their high reaction window temperature, poor N2 selectivity and vanadium's own biological toxicity. o C) non-electricity industry, which will cause pollution and energy waste. At the same time, there is still a certain amount of toxic SO2 in the flue gas of non-electricity industry. Therefore, how to prepare a new type of low-temperature NH3-SCR catalyst is the focus of current research.

[0004] Usually, after the flue gas from non-power industries is treated with desulfurization and dust removal, the flue gas temperature reaching the denitrification device is relatively low. Considering that the working window of commercial catalysts is around 200 o C or above, so if you need to get a better denitration efficiency, you need to add an additional preheating / heating device to the denitration device to reheat it, so that the temperature of the reactor reaches the reaction temperature of the catalyst. This will invisibly increase the operating cost of denitration, and at the same time will also generate a lot of energy waste, which is not in line with the current national environmental protection policy. Therefore, seeking a new type of low-temperature NH3-SCR and its preparation method can not only solve the current problems of denitration in the non-electric industry, but also promote the development of NH3-SCR denitration technology. Summary of the invention

[0005] In view of the above problems existing in the prior art, the first technical problem to be solved by the present invention is to provide a method for preparing a low-temperature NH3-SCR catalyst; the second technical problem to be solved by the present invention is to provide a low-temperature NH3-SCR catalyst prepared by the above method; the third technical problem to be solved by the present invention is to provide the application of the above-mentioned low-temperature NH3-SCR catalyst in low-temperature NH3-SCR catalytic denitrification.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a low-temperature NH3-SCR catalyst comprises subjecting praseodymium oxide or praseodymium-cerium composite oxide to sulfation treatment to obtain a low-temperature NH3-SCR catalyst; wherein the sulfation treatment time is 20 to 240 minutes, and the sulfation treatment method is: contacting a mixed gas containing SO2 and O2 with praseodymium oxide or praseodymium-cerium composite oxide.

[0008] Preferably, the SO2 is 100-300 ppm and the O2 is 5 vol%.

[0009] Preferably, the temperature of the sulfation treatment is 200°C.

[0010] Preferably, the preparation process of praseodymium oxide is as follows: praseodymium nitrate and citric acid are dissolved in deionized water and stirred evenly at room temperature, followed by drying and roasting to obtain praseodymium oxide.

[0011] Preferably, the mass ratio of praseodymium nitrate, citric acid and deionized water is 1:1:8.

[0012] Preferably, the calcination temperature is 550° C. and the calcination time is 5 hours.

[0013] Preferably, in the praseodymium-cerium composite oxide, the molar ratio of cerium to praseodymium is 2-8:8-2.

[0014] Preferably, the preparation process of the praseodymium-cerium composite oxide is as follows: praseodymium nitrate, cerium nitrate and citric acid are dissolved in deionized water and stirred evenly at room temperature, followed by drying and calcining to obtain the praseodymium-cerium composite oxide.

[0015] The method for preparing a low-temperature NH3-SCR catalyst prepares a low-temperature NH3-SCR catalyst.

[0016] The low-temperature NH3-SCR catalyst is used in low-temperature NH3-SCR catalytic denitration.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention provides new acid sites for praseodymium oxide and praseodymium-based catalysts with good redox performance by introducing a certain amount of SO2 at a specific temperature, thereby greatly improving the low-temperature NH3-SCR activity of praseodymium oxide and praseodymium-based catalysts;

[0019] (2) The preparation method of the present invention is simple and fast, has low energy consumption, has no special requirements for equipment, is environmentally friendly, and does not produce wastewater or waste gas. The prepared catalyst can be directly placed in a denitration device and treated with the SO2 atmosphere in the flue gas. The current national requirement for SO2 emissions is 35 mg / m 3 This is less than the amount of SO2 (100 ppm) for catalytic sulfation in the present invention, which helps the catalyst to operate for a long time in the denitration device without affecting the catalytic activity, and has good industrial application prospects in the field of flue gas denitration in non-power industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The activity diagram of the NH3-SCR catalyst prepared in Example 1;

[0021] Figure 2 XRD pattern of the NH3-SCR catalyst prepared in Example 1;

[0022] Figure 3 This is the H2-TPR result diagram of the NH3-SCR catalyst prepared in Example 1;

[0023] Figure 4 This is a temperature-programmed desorption (NH3-TPD) diagram of the NH3-SCR catalyst prepared in Example 1;

[0024] Figure 5 This is the activity diagram of the NH3-SCR catalyst prepared in Example 4. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described below in conjunction with specific embodiments. In the following examples, unless otherwise specified, the technical means used are conventional means well known to those skilled in the art. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0026] Example 1

[0027] 1) Weigh 10 g of praseodymium nitrate and 10 g of citric acid, dissolve in 100 mL of deionized water and stir at 300 r / min for 1 h at room temperature, then dry in an oven at 120 °C for 12 h, grind into powder with a mortar, and calcine in a muffle furnace at 550 °C for 5 h in air atmosphere to obtain praseodymium oxide, recorded as PrO x ;

[0028] 2) The praseodymium oxide prepared in step 1) was subjected to sulfation treatment at 200°C by passing 100 ppm SO2 and 5 vol% O2 (2 mL / min of 1% SO2 / Ar, total flow rate of 200 mL / min) under normal pressure. The treatment time was 20 min, 40 min, 60 min, 120 min, and 240 min, respectively. The treatment mass space velocity WHGS = 60000 mL·g -1 ·h -1 , low-temperature NH3-SCR catalysts were obtained and were recorded as Pr-S20, Pr-S40, Pr-S60, Pr-S120 and Pr-S240 respectively.

[0029] Example 2

[0030] The PrO x , Pr-S20, Pr-S40, Pr-S60, Pr-S120, Pr-S240 catalysts were used in low-temperature NH3-SCR reaction. The experimental steps were as follows: the catalytic reaction test was carried out in a fixed-bed continuous flow quartz reactor. The catalyst particle size was 40-60 mesh after sieve screening, and the dosage was 0.2g. The reaction gas composition was: 500 ppm NO, 500 ppm NH3, 5vol% O2, Ar was used as the balance gas, the gas flow rate was 200 mL / min, and the gas space velocity in the reaction was WHGS = 60000 mL·g -1 ·h -1 The catalytic reaction was carried out at 100-300 °C, and the activity data were collected after the catalyst was pre-adsorbed and saturated. The product was detected and analyzed by Thermofisher IS10 FTIR. Figure 1 And as shown in Table 1.

[0031] Table 1 NH3-SCR activity test results of the catalyst prepared in Example 1

[0032]

[0033] Depend on Figure 1 As shown in Table 1, the catalytic activity of the catalyst after sulfation increases with the increase of sulfation time. o C reaches 80%.

[0034] Depend on Figure 2 It can be seen that the Cu target Kα ray filtered by Ni is used as the light source of the X-ray diffractometer to scan the catalyst, and the 2θ range is 10~80 oThe XRD results show that the samples before and after sulfation treatment all show a cubic fluorite structure (JCPDS No. 42-1121), and no crystal phase diffraction peaks belonging to sulfate species are observed, which indicates that the crystal structure of the catalyst does not change significantly before and after sulfation, and the catalyst prepared by the present invention has good stability.

[0035] Depend on Figure 3 It can be seen that the temperature was programmed to reduce the catalyst by purging with N2 gas at 150℃ for one hour and then introducing 7% H2 / Ar at a flow rate of 10 mL / min. The reduction peaks α, which belong to the surface oxygen species, and the surface bulk phase Pr 4+ The reduction peak β and deep bulk phase Pr 4+ After sulfation, as the sulfation time increases, the peak intensities of the reduction peaks α and β gradually decrease, and two reduction peaks δ and ε belonging to sulfate species appear. As the reduction peak intensity of sulfate species increases, the reduction peak of oxygen species on the catalyst surface decreases. This indicates that the amount of active oxygen on the catalyst surface is decreasing. This also shows that pure PrO x The surface acidity of PrO is weak, but the oxidizing ability is too strong. x Making its surface acidity and redox ability reach a suitable state can effectively improve the reaction activity of the catalyst.

[0036] Example 3

[0037] PrO x The Pr-S120 was first saturated with NH3 at room temperature, and then the physical adsorption peak on the catalyst surface was purged by Ar, and then 100 mL / min Ar was introduced for programmed temperature desorption. The programmed temperature was from room temperature to 400 °C, and the heating rate was 10 o C / min. The results are as follows Figure 4 shown.

[0038] Depend on Figure 4 It can be seen that in PrO x On the curve, an obvious NH3 desorption signal can be seen at 110°C, indicating that the surface acidity of praseodymium oxide is less, which is one of the reasons for the low catalytic activity of praseodymium oxide. On the Pr-S120 curve, in addition to an obvious NH3 desorption signal at 110°C, obvious NH3 desorption signals can also be seen near 210°C and 263°C, indicating that the surface acidity of the praseodymium oxide denitrification catalyst has increased after sulfation for different times, and the sulfate species formed on the surface have brought it more acidic sites.

[0039] Example 4

[0040] 1) A certain amount of praseodymium nitrate, cerium nitrate and citric acid (the mass ratio of citric acid to metal is 1:1) were weighed and dissolved in 100 mL of deionized water, wherein the molar ratios of cerium to praseodymium were 2:8, 4:6, 6:4 and 8:2, respectively. The mixture was stirred at 300 r / min at room temperature for 1 h, then dried in an oven at 120 °C for 12 h, ground into powder with a mortar, and calcined at 550 °C for 5 h in an air atmosphere in a muffle furnace to obtain praseodymium-cerium composite oxides with different proportions, which were recorded as C2P8, C4P6, C6P4 and C8P2, respectively.

[0041] The PrO prepared in Example 1 x The C2P8, C4P6, C6P4, and C8P2 catalysts prepared above were treated with sulfation by passing 100 ppm SO2 and 5 vol% O2 (2 mL / min of 1% SO2 / Ar, total flow rate of 200 mL / min) at 200°C for 120 min.

[0042] The PrO before and after the sulfation treatment x , C2P8, C4P6, C6P4, C8P2 catalysts were used in low-temperature NH3-SCR reaction. The experimental steps were as follows: The catalytic reaction test was carried out in a fixed-bed continuous flow quartz reactor. The catalyst particle size was 40-60 mesh after sieve screening, and the dosage was 0.2g. The reaction gas composition was: 500 ppm NO, 500 ppm NH3, 5vol% O2, Ar was used as the balance gas, the gas flow rate was 200 mL / min, and the gas space velocity in the reaction was WHGS = 60000 mL·g -1 ·h -1 The catalytic reaction was carried out at 200 °C, and the activity data were collected after the catalyst was pre-adsorbed and saturated. The product was detected and analyzed by Thermofisher IS10 FTIR. Figure 5 And as shown in Table 2.

[0043] Table 2 NH3-SCR activity test results of catalysts before and after sulfation treatment

[0044]

[0045] Depend on Figure 5 As shown in Table 2, the catalytic activity of the praseodymium-cerium composite oxide catalysts that have not been subjected to sulfation treatment is very low, and the highest catalytic activity does not exceed 45%; the denitrification catalytic activity of different proportions of praseodymium-cerium composite oxides after sulfation treatment is improved to varying degrees, indicating that the preparation method of the present invention has a certain universality.

[0046] Example 5

[0047] The PrO prepared in Example 1x The catalyst was subjected to sulfation treatment at different temperatures. x The catalyst was sulfated by passing 100 ppm SO2 and 5 vol% O2 (2 mL / min of 1% SO2 / Ar, total flow rate of 200 mL / min) at 100°C, 200°C and 300°C for 120 min, respectively. They were recorded as Pr-S120-100°C, Pr-S120-200°C, and Pr-S120-300°C.

[0048] Subsequently, the Pr-S120-100℃, Pr-S120-200℃, and Pr-S120-300℃ catalysts before and after the sulfation treatment were applied to the low-temperature NH3-SCR reaction. The experimental steps were as follows: The catalytic reaction test was carried out in a fixed-bed continuous flow quartz reactor. The catalyst particle size was 40-60 mesh after sieve screening, and the dosage was 0.2g. The reaction gas composition was: 500 ppm NO, 500ppm NH3, 5vol% O2, Ar as the balance gas, the gas flow rate was 200 mL / min, and the gas space velocity in the reaction was WHGS = 60000mL·g -1 ·h -1 The catalytic reaction was carried out at 200 °C. The activity data were collected after the catalyst was pre-adsorbed and saturated. The product was detected and analyzed by Thermofisher IS10 FTIR. The results are shown in Table 3.

[0049] Table 3 NH3-SCR activity test results of catalysts before and after sulfation treatment at different temperatures

[0050]

[0051] It can be seen from Table 3 that different temperatures are used for PrO x The sulfation treatment of the catalyst will have different catalytic effects. x The catalyst has a greater impact, which may be because the large amount of ammonium sulfate species produced at this temperature will cover the active sites of the catalyst, resulting in the x The catalyst is poisoned and deactivated. However, when the sulfation temperature (≥200°C) is high, the PrO x The improvement of the denitrification catalytic activity of the catalyst is quite obvious.

[0052] Example 6

[0053] The PrO prepared in Example 1 x The catalyst was subjected to sulfation treatment at different temperatures. xThe catalyst was treated with sulfation by passing different concentrations of SO2 (100 ppm, 200 ppm, 300 ppm) and 5 vol% O2 at 200°C for 120 min, recorded as Pr-S120-100 ppm, Pr-S120-200 ppm, and Pr-S120-300 ppm.

[0054] Subsequently, the Pr-S120-100 ppm, Pr-S120-200 ppm, and Pr-S120-300 ppm catalysts before and after the sulfation treatment were applied to the low-temperature NH3-SCR reaction. The experimental steps were as follows: the catalytic reaction test was carried out in a fixed-bed continuous flow quartz reactor. The catalyst particle size was 40-60 mesh after sieve screening, and the dosage was 0.2 g. The reaction gas composition was: 500 ppm NO, 500 ppm NH3, 5 vol% O2, Ar as the balance gas, the gas flow rate was 200 mL / min, and the gas space velocity in the reaction was WHGS=60000 mL·g -1 ·h -1 The catalytic reaction was carried out at 200 °C. The activity data were collected after the catalyst was pre-adsorbed and saturated. The product was detected and analyzed by Thermofisher IS10 FTIR. The results are shown in Table 4.

[0055] Table 4 NH3-SCR activity test results of catalysts before and after sulfation treatment at different SO2 concentrations

[0056]

[0057] It can be seen from Table 4 that at the same temperature and the same time, different concentrations of SO2 have an effect on PrO x The catalyst was treated with sulfation. It was found that the concentration of SO2 was x The denitration performance of the catalyst has a certain influence. When the time is the same, the lower the concentration, the worse the denitration performance. x When the catalyst is subjected to sulfation treatment, the concentration of SO2 and the time of SO2 introduction need to be considered.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a low-temperature NH3-SCR catalyst, characterized in that: The praseodymium oxide or praseodymium-cerium composite oxide is subjected to sulfation treatment to obtain a low-temperature NH3-SCR catalyst; wherein the sulfation treatment time is 20 to 240 minutes, and the sulfation treatment method is: a mixed gas containing SO2 and O2 is brought into contact with the praseodymium oxide or praseodymium-cerium composite oxide.

2. The method for preparing a low-temperature NH3-SCR catalyst according to claim 1, characterized in that: The SO2 is 100-300 ppm, and the O2 is 5 vol%.

3. The method for preparing a low-temperature NH3-SCR catalyst according to claim 1, characterized in that: The temperature of the sulfation treatment is 200°C.

4. The method for preparing a low-temperature NH3-SCR catalyst according to claim 1, characterized in that: The preparation process of praseodymium oxide is as follows: praseodymium nitrate and citric acid are dissolved in deionized water and stirred evenly at room temperature, and then dried and roasted to obtain praseodymium oxide.

5. The method for preparing a low-temperature NH3-SCR catalyst according to claim 4, characterized in that: The mass ratio of the praseodymium nitrate, citric acid and deionized water is 1:1:

8.

6. The method for preparing a low-temperature NH3-SCR catalyst according to claim 4, characterized in that: The calcination temperature is 550° C. and the calcination time is 5 hours.

7. The method for preparing a low-temperature NH3-SCR catalyst according to claim 1, characterized in that: In the praseodymium-cerium composite oxide, the molar ratio of cerium to praseodymium is 2-8:8-2.

8. The method for preparing a low-temperature NH3-SCR catalyst according to claim 1, characterized in that: The preparation process of the praseodymium-cerium composite oxide is as follows: dissolving praseodymium nitrate, cerium nitrate and citric acid in deionized water and stirring evenly at room temperature, and then drying and calcining to obtain the praseodymium-cerium composite oxide.

9. The method for preparing a low-temperature NH3-SCR catalyst according to any one of claims 1 to 8 is used to prepare a low-temperature NH3-SCR catalyst.

10. Use of the low-temperature NH3-SCR catalyst according to claim 9 in low-temperature NH3-SCR catalytic denitrification.

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