High-performance cerium-based denitration catalyst, preparation method and application thereof

Abstract

The application discloses a high-performance cerium-based denitration catalyst, which is prepared by using cerous sulfate as raw material and performing gas-phase heating under low-flow ammonia gas; the proportion of N element in the high-performance cerium-based denitration catalyst is 0.02%-0.1%, and the proportion of S element is 1.325%-16.473%. The cerium-based catalyst is prepared by using the gas-phase heating treatment method, the preparation method is simple and easy to implement, no solvent is used in the preparation process, and no grinding is needed, so that the loss of active species can be effectively avoided, and the prepared catalyst has good thermal stability in a low-temperature zone and excellent catalytic performance.

Description

Technical Field

[0001] This invention relates to the technical field of nitrogen oxide pollution control in the atmosphere, and more specifically to a method for preparing a high-performance cerium-based low-temperature denitrification catalyst by heating cerium sulfate in ammonia gas at a low flow rate. Background Technology

[0002] Nitrogen oxides (NO) x Nitrogen oxides (NOx) are among the major air pollutants, causing a series of severe climate problems such as acid rain and the greenhouse effect. They have a significant impact on soil and buildings, posing a serious threat to the entire ecological environment and human health. Ammonia selective catalytic reduction (NH3-SCR) of nitrogen oxides is recognized as the most effective and widely used method for NOx reduction. x This emission reduction technology, characterized by mature processes, high removal efficiency, and stable system operation, is currently the preferred method for NO removal in industrial flue gas treatment. x It is one of the emission control measures. The core of its denitrification efficiency lies in the development of catalysts. Currently, many catalysts require temperatures above 300℃ to maintain good catalytic activity. However, the emission temperature of industrial coal-fired flue gas is generally 150-250℃. Therefore, it is necessary to develop suitable low-temperature denitrification catalysts.

[0003] Cerium-based catalysts have attracted widespread attention in the field of denitrification in recent years. They are among the most promising catalysts for low-temperature NH3-SCR processes, and the core of their research lies in regulating the balance between acidity and redox performance (i.e., acid-oxygen balance). Previous researchers primarily used CeO2, with its excellent redox properties, as a precursor, and then supplemented it with acidity, such as by doping with acidic metals like W and Ti, or acidic non-metals like S and P. While the denitrification activity of the catalyst does improve with increasing acidity, the redox performance often drops sharply, indicating that there is still room for improvement in its activity. Summary of the Invention

[0004] The purpose of this invention is to overcome the deficiencies in the prior art and provide a denitrification catalyst with high performance in the low-temperature range.

[0005] To achieve the above objectives, the present invention provides a high-performance cerium-based denitration catalyst, which is obtained by gas-phase heating of cerium sulfate as raw material under low-flow-rate ammonia gas; the proportion of N element in the high-performance cerium-based denitration catalyst is 0.02% to 0.1%, and the proportion of S element is 1.325% to 16.473%.

[0006] This invention utilizes gas-phase heating to treat cerium sulfate, obtaining a nitrogen-doped cerium-based denitration catalyst. This catalyst exhibits a high cerium dioxide content and distinct crystal structure, along with significant changes in lattice fringes and even the appearance of fractured or missing interfaces, demonstrating successful grain boundary construction. Nitrogen doping and grain boundary construction effectively enhance the low-temperature denitration activity.

[0007] In some embodiments, preferably, the proportion of N element in the high-performance cerium-based denitrification catalyst of the present invention is 0.05%, and the proportion of S element is 8.9%.

[0008] This invention also provides a method for preparing the above-mentioned high-performance cerium-based denitration catalyst, comprising the following steps:

[0009] (1) Ce2(SO4)3·8H2O was compressed and sieved to obtain cerium sulfate precursor material;

[0010] (2) The cerium sulfate precursor is placed in a fixed-bed continuous flow quartz reactor, ammonia is introduced and the temperature is raised to 450℃~550℃, and the process is continued for 3h~10h to obtain the high-performance cerium-based denitrification catalyst.

[0011] This invention employs a gas-phase heating treatment method to prepare cerium-based catalysts. By controlling the treatment temperature and time, the acidity required for the low-temperature denitration catalyst is effectively ensured. Furthermore, the obtained catalyst simultaneously achieves N doping and grain boundary construction, thereby protecting the catalyst's reductive and oxidizing properties.

[0012] In some embodiments, as a preferred embodiment, ammonia gas is introduced in step (2) and the temperature is raised to 500°C to 550°C.

[0013] In some embodiments, as a preferred embodiment, in step (2), ammonia gas is introduced to raise the temperature to 450°C to 500°C and the process is continued for 5 to 10 hours.

[0014] In some embodiments, as a more preferred method, in step (2), ammonia gas is introduced to raise the temperature to 500°C and the process is carried out continuously for 5 hours.

[0015] In some embodiments, as a preferred method, the cerium sulfate precursor in step (1) is prepared by the following method: Ce2(SO4)3·8H2O is placed in a tablet press, the pressure is set to 10 kPa, and after holding for 1 minute, it is taken out and then sieved by stacking the upper and lower layers with 20 mesh and 40 mesh screens respectively. The sample on the 40 mesh screen is the cerium sulfate precursor.

[0016] In some embodiments, as a preferred embodiment, the heating rate in step (2) is 10°C / min, and a low-flow-rate ammonia temperature is used for warming treatment, with the flow rate controlled at 25 mL / min.

[0017] The present invention also provides the application of the above-mentioned high-performance cerium-based denitration catalyst in denitration catalysis at 150℃~250℃, preferably in denitration catalysis at 200℃~250℃.

[0018] The present invention has the following advantages over the prior art:

[0019] 1. This invention uses a gas-phase heating treatment method to prepare cerium-based catalysts. The preparation method is simple and easy to implement. The preparation process does not use solvents or require grinding, which can effectively avoid the loss of active species. The prepared catalyst has good thermal stability and excellent catalytic performance in the low-temperature region.

[0020] 2. Compared with conventional cerium-based catalysts prepared by gas-phase sulfidation, the cerium-based catalyst of this invention requires a much shorter time to reach approximately the same sulfur species ratio, achieving 8.9% in just 5 hours, while the latter requires 72 hours to reach 8.2%. Moreover, the cerium-based catalyst of this invention exhibits superior activity, mainly because the successful N doping and grain boundary construction protect its redox properties.

[0021] 3. Through the optimization and screening of raw materials and preparation conditions, this invention obtains a cerium-based catalyst suitable for low-temperature denitration, which has potential industrial application prospects;

[0022] 4. my country is rich in rare earth resources, making cerium-based materials readily available, while ammonia, as a common gas, is even cheaper and more readily available.

[0023] 5. Catalysts are prepared by heating ammonia gas at low flow rates, which results in low energy consumption, minimal pollution, and environmental friendliness. Attached Figure Description

[0024] Figure 1 The TG spectrum of the cerium sulfate precursor obtained in this invention is shown.

[0025] Figure 2 To screen different cerium-based catalysts SO4 obtained in Example 1 2- Comparison of NO conversion rates for / CeO2@NH3 (at different treatment temperatures);

[0026] Figure 3 To screen the different cerium-based catalysts SO4 obtained in Example 2 2- Comparison of NO conversion rates for / CeO2@NH3 (at different treatment times);

[0027] Figure 4 To screen the different cerium-based catalysts SO4 obtained in Example 3 2- Comparison of NO conversion rates for / CeO2@NH3;

[0028] Figure 5The cerium-based catalyst SO4 obtained in Example 4 2- XRD pattern of / CeO2@NH3;

[0029] Figure 6 The cerium-based catalyst SO4 obtained in Example 4 2- XPS graph of / CeO2@NH3;

[0030] Figure 7 The cerium-based catalyst SO4 obtained in Example 4 2- TEM image of / CeO2@NH3;

[0031] Figure 8 for Figure 7 The variation in lattice fringe spacing in the direction indicated by the middle arrow;

[0032] Figure 9 To compare the different cerium-based catalysts (SO4) obtained in Example 5 2- Comparison of NO conversion rates between / CeO2@NH3 and comparative catalysts;

[0033] Figure 10 For comparison, the cerium-based catalyst SO4 obtained in Example 5 2- TG comparison chart of / CeO2@NH3 and CeO2@SO2;

[0034] Figure 11 For performance comparison, different cerium-based catalysts (SO4) obtained in Example 6 2- Comparison of NO oxidation capacity between / CeO2@NH3 and some comparative catalysts;

[0035] Figure 12 For performance comparison, different cerium-based catalysts (SO4) obtained in Example 6 2- NO-TPD comparison chart of / CeO2@NH3 and some comparative catalysts. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0037] Example 1

[0038] The Ce2(SO4)3·8H2O used in the following embodiments was purchased from Shanghai Hushi Laboratory Equipment Co., Ltd.

[0039] The catalytic performance testing conditions for the obtained catalyst materials in the following embodiments are as follows: Catalytic reaction tests were conducted in a fixed-bed continuous flow quartz reactor. The catalyst particle size was 20–40 mesh, and the dosage was 100 mg. The reaction gas composition was: 500 ppm NO, 500 ppm NH3, 5% O2, with N2 as the equilibrium gas, and the gas hourly space velocity (GHSV) was 60,000 mL·mg / L. -1 ·h -1 Before the reaction, the catalyst needs to be purged with high-purity N2 at 150℃ for 0.5 h. The catalytic reaction is carried out at 150–250℃, and activity data are collected after the reaction reaches equilibrium. The NO conversion rate is calculated using the following formula:

[0040]

[0041] The cerium sulfate precursor was prepared using the following method:

[0042] 0.200 g of Ce₂(SO₄)₃·8H₂O was placed in a tablet press with a pressure of 10 kPa. After holding the pressure for 1 minute, the tablet was removed and sieved through 20-mesh and 40-mesh sieves. The sample collected from the 40-mesh sieve was taken as the desired cerium sulfate precursor. Its TG is shown in the appendix. Figure 1 As shown in the figure, the cerium sulfate precursor exhibits good thermal stability, requiring heating to above 600℃ in N2 to decompose, effectively ensuring the acidity required for the low-temperature denitrification catalyst. This indicates that the cerium sulfate precursor was successfully prepared.

[0043] Screening Example 1

[0044] Cerium-based catalysts for SO4 were prepared at different processing temperatures. 2- / CeO2@NH3

[0045] 0.2 g of cerium sulfate precursor was weighed and heated to 300 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 3 h, with a heating rate of 10 °C / min. This cerium-based catalyst is denoted as SO4. 2- / CeO2@NH3-300℃.

[0046] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 3 h, with a heating rate of 10 °C / min. This cerium-based catalyst is denoted as SO4. 2- / CeO2@NH3-500℃.

[0047] 0.2 g of cerium sulfate precursor was weighed and heated to 700 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 3 h, with a heating rate of 10 °C / min. This cerium-based catalyst is denoted as SO4.2- / CeO2@NH3-700℃.

[0048] The three cerium-based catalysts SO4 prepared above 2- The NH3-SCR activity results for / CeO2@NH3 are shown in [reference needed]. Figure 2 As can be seen from the figure, SO4 2- / CeO2@NH3 exhibits optimal catalytic performance at -500℃.

[0049] Screening Example 2

[0050] Cerium-based catalysts for SO4 were prepared with different treatment times. 2- / CeO2@NH3

[0051] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 1 h, with a heating rate of 10 °C / min. This cerium-based catalyst is denoted as SO4. 2- / CeO2@NH3-1h.

[0052] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 3 h, with a heating rate of 10 °C / min. This cerium-based catalyst is denoted as SO4. 2- / CeO2@NH3-3h.

[0053] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 5 h, with a heating rate of 10 °C / min. This cerium-based catalyst was denoted as SO4. 2- / CeO2@NH3-5h.

[0054] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor by ammonia gas and continuously treated for 10 h, with a heating rate of 10 °C / min. This cerium-based catalyst was denoted as SO4. 2- / CeO2@NH3-10h.

[0055] The four cerium-based catalysts SO4 prepared above 2- The NH3-SCR activity results for / CeO2@NH3 are shown in [reference needed]. Figure 3 As can be seen from the figure, SO4 2- / CeO2@NH3-5h exhibits the best catalytic performance.

[0056] Screening Example 3

[0057] Cerium-based catalysts for SO4 were prepared with different treatment times.2- / CeO2@NH3:

[0058] 0.2 g of cerium sulfate precursor was weighed and heated to 450 / 500 / 550 °C in a fixed-bed continuous flow quartz reactor under ammonia gas and continuously treated for 3, 5, and 10 h, with a heating rate of 10 °C / min. This cerium-based catalyst was denoted as SO4. 2- / CeO2@NH3-450 / 500 / 550℃-3 / 5 / 10h.

[0059] like Figure 4 As shown, the catalysts obtained when the treatment temperature is 450℃~550℃ and the time is 3~10h all exhibit excellent denitrification activity.

[0060] Elemental analysis was performed on the prepared samples. With increasing treatment temperature and time, the higher the degree of thermal decomposition of the precursor Ce₂(SO₄)₃·8H₂O, the greater the proportion of CeO₂ in the catalyst, and the smaller the proportions of N and S elements. Based on some test results in Table 1 below, the N element content of the catalyst can be roughly determined to be in the range of 0.02%–0.1%, and the S element content to be in the range of 1.325%–16.473%.

[0061] Table 1. Results of Organic Elemental Analyzer (CHNSO) Tests

[0062]

[0063]

[0064] Example 4

[0065] A cerium-based catalyst SO4 was prepared according to the above method, with a treatment temperature of 500℃ and a treatment time of 5h. 2- / CeO2@NH3:

[0066] 0.2 g of cerium sulfate precursor was weighed and heated to 500 °C in a fixed-bed continuous flow quartz reactor under ammonia gas and continuously treated for 5 h, with a heating rate of 10 °C / min. This cerium-based catalyst was relabeled as SO4. 2- / CeO2@NH3.

[0067] The prepared cerium-based catalyst SO4 2- / CeO2@NH3:

[0068] Its XRD pattern is shown below. Figure 5 The figure shows one strong diffraction peak and three weaker diffraction peaks, which is typical of the cubic fluorite structure of cerium dioxide. This indicates that the prepared SO4... 2-The / CeO2@NH3 sample contained a large amount of cerium dioxide and had a distinct crystal form;

[0069] Its XPS graph is shown below. Figure 6 As shown in the figure, a distinct peak exists in the N1s spectrum. This indicates that the prepared SO4... 2- Successful N doping in the / CeO2@NH3 sample;

[0070] Its TEM image is shown Figure 7 As can be seen from the figure, there are interfaces (i.e., grain boundaries) where the lattice fringes change significantly or even break and are missing. Figure 7 The variation of the lattice fringe spacing in the direction indicated by the middle arrow is as follows: Figure 8 As shown, measurements were taken from inside the crystal plane. The lattice fringe spacing is 0.313 nm, while near the grain boundaries, The lattice fringe spacing was significantly elongated (0.350 nm). This indicates that the prepared SO4... 2- Successful grain boundary construction in the / CeO2@NH3 sample.

[0071] The analysis results of organic elemental analysis showed that nitrogen accounted for 0.05% and sulfur accounted for 8.89%.

[0072] Comparative Example 5

[0073] Preparation of SO4 2- / CeO2@NH3 and comparative catalysts CeO2, W / CeO2, Ti / CeO2, CeO2@SO2

[0074] SO4 2- / CeO2@NH3 is the cerium-based catalyst prepared in Example 4, and the preparation process is described above.

[0075] Preparation of the comparative catalyst CeO2: Weigh 0.5g of cerium acetate into a crucible and place it in a muffle furnace. Heat the crucible to 500℃ at a rate of 3℃ / min and calcine for 5h. Then press and sieve the cerium-based catalyst (the process is the same as that for the pre-prepared cerium sulfate precursor). The cerium-based catalyst is named CeO2.

[0076] Preparation of the comparative catalyst W / CeO2: Weigh 0.02g of (NH4)6H2W 12 O 40xH2O and 0.30g CeO2 (powder) were placed in a beaker containing 30mL of distilled water and stirred at 35℃ for 2h in a magnetic stirrer. Then, the mixture was removed and allowed to stand at room temperature (around 25℃) for 4h. Next, it was placed in an oven and dried at 100℃ for 24h. After drying, argon gas was introduced into a fixed-bed continuous flow quartz reactor and heated to 500℃ for 3h. The mixture was then pressed into tablets and sieved (the process was the same as that for the pre-prepared cerium sulfate precursor). This cerium-based catalyst was designated W / CeO2.

[0077] Preparation of the comparative catalyst Ti / CeO2: Weigh 0.05g Ti(SO4)2 and 0.38g CeO2 (powder) into a beaker containing 30mL distilled water and stir in a magnetic stirrer at 35℃ for 2h. Then remove and let stand at room temperature (around 25℃) for 4h. Next, put it into an oven and dry at 100℃ for 24h. After drying, argon gas is introduced into a fixed-bed continuous flow quartz reactor and heated to 500℃ for 3h. Then it is pressed into tablets and sieved (the process is the same as the pre-prepared cerium sulfate precursor). This cerium-based catalyst is named Ti / CeO2.

[0078] Preparation of the comparative catalyst CeO2@SO2: 0.2g of CeO2 was weighed and introduced into a fixed-bed continuous flow quartz reactor with 1000ppm SO2 and 5% O2 (N2 was used as the balance gas). The reactor was heated to 150℃ and continuously treated for 72h, with the heating rate set to 10℃ / min. This cerium-based catalyst was denoted as CeO2@SO2.

[0079] The NH3-SCR activity results of the five cerium-based catalysts prepared above are shown in the figure. Figure 9 As can be seen from the figure, SO4 2- / CeO2@NH3-5h exhibits the best catalytic performance. Additionally, SO4 2- The TG comparison chart of / CeO2@NH3 and CeO2@SO2 is shown below. Figure 10 As can be seen from the figure, at 600–800℃, SO4 2- The weight loss percentage of / CeO2@NH3 was 8.89%, and that of CeO2@SO2 was 8.15%, with the S species mass percentages being almost identical in both cases. According to SO4... 2- The mass percentage of S species in / CeO2@NH3 can be estimated to be 1:16.4. Assuming that W and Ti elements maintain approximately the same proportion as Ce elements, the specific mass of each corresponding compound to be weighed during the preparation process can be determined.

[0080] Performance Comparison Example 6

[0081] SO4 2-Differences in redox performance between / CeO2@NH3 and comparative catalysts CeO2 and CeO2@SO2

[0082] According to Comparative Example 5, SO4 2- Both / CeO2@NH3 and CeO2@SO2 are loaded with approximately equal amounts of sulfur species. Since the presence of sulfur species weakens the catalyst's adsorption and activation capacity for NO, SO4... 2- A comparison of the NO oxidation capacity of / CeO2@NH3 with that of the comparative catalysts CeO2 and CeO2@SO2 is shown in the figure. Figure 11 See the NO-TPD comparison chart. Figure 12 As can be seen from the figure, compared to the significant reduction in CeO2@SO2, SO4... 2- / CeO2@NH3 exhibits significant "toughness," maintaining its ability to adsorb and activate NO while enhancing acidity, thus ensuring good redox performance. This may be related to N doping and grain boundary construction, which in turn improves the catalyst's catalytic performance.

Claims

1. A high-performance cerium-based denitration catalyst, characterized in that, The high-performance cerium-based denitration catalyst is obtained by gas-phase heating of cerium sulfate under low-flow-rate ammonia gas; the proportion of nitrogen in the high-performance cerium-based denitration catalyst is 0.02% to 0.1%, and the proportion of sulfur is 1.325% to 16.473%; The high-performance cerium-based decatalyst is prepared by the following method: (1) Ce2(SO4)3•8H2O was compressed into tablets and sieved to obtain cerium sulfate precursor material; (2) The cerium sulfate precursor is placed in a fixed-bed continuous flow quartz reactor, and ammonia gas is introduced to raise the temperature to 450℃~550℃ and continuously treated for 3h~10h to obtain the high-performance cerium-based denitration catalyst. When ammonia gas is introduced to raise the temperature to 500℃~550℃, the treatment time is 3h~10h. When ammonia gas is introduced to raise the temperature to 450℃~500℃, the treatment time is 5h~10h.

2. The high-performance cerium-based denitration catalyst according to claim 1, characterized in that, The high-performance cerium-based denitrification catalyst contains 0.05% nitrogen and 8.9% sulfur.

3. The method for preparing the high-performance cerium-based denitration catalyst according to claim 1, characterized in that, The preparation method includes the following steps: (1) Ce2(SO4)3•8H2O was compressed into tablets and sieved to obtain cerium sulfate precursor material; (2) The cerium sulfate precursor is placed in a fixed-bed continuous flow quartz reactor, and ammonia gas is introduced to raise the temperature to 450℃~550℃ and continuously treated for 3h~10h to obtain the high-performance cerium-based denitration catalyst. When ammonia gas is introduced to raise the temperature to 500℃~550℃, the treatment time is 3h~10h. When ammonia gas is introduced to raise the temperature to 450℃~500℃, the treatment time is 5h~10h.

4. The preparation method according to claim 3, characterized in that, In step (2), ammonia gas is introduced to raise the temperature to 500°C and the process is continued for 5 hours.

5. The preparation method according to claim 3, characterized in that, The cerium sulfate precursor in step (1) is prepared by the following method: Ce2(SO4)3•8H2O is placed in a tablet press, the pressure is set to 10 kPa, and after holding for 1 minute, it is taken out and then sieved by stacking the upper and lower layers with 20 mesh and 40 mesh screens respectively. The sample on the 40 mesh screen is the cerium sulfate precursor.

6. The preparation method according to claim 3, characterized in that, In step (2), the heating rate is 10℃ / min and the ammonia flow rate is 25mL / min.

7. The application of the high-performance cerium-based denitration catalyst according to claim 1 or 2 in denitration catalysis at 150℃~250℃.

8. The application of the high-performance cerium-based denitration catalyst according to claim 1 or 2 in denitration catalysis at 200℃~250℃.

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