Preparation method and application of wide-temperature-range Mn-based NH3-SCR denitration catalyst

Abstract

The invention discloses a preparation method and application of a wide-temperature-range Mn-based NH3-SCR denitration catalyst, particularly relates to a catalyst for effectively degrading an atmospheric pollutant NO, and belongs to the field of atmospheric pollution treatment and environment-friendly catalytic environment. According to the catalyst, firstly, a coprecipitation method is adopted, non-toxic Mn with good low-temperature activity and low cost is selected as a metal active component, Ti (SO4) 2 is selected as a carrier precursor, Ce and Nb are selected as auxiliaries, the proportion of all the components is optimized, and the Mn0. 1Ce0. 1Nb0. 03TiOx-CP catalyst with better activity is prepared. However, the low-temperature activity of the catalyst still needs to be improved, so that the Mn0. 1Ce0. 1Nb0. 03TiOx-CP catalyst is subjected to enhanced modification treatment by adopting different preparation methods, the influence of different precipitators, different pH values and different aging time on the activity of the catalyst is discussed, and a series of catalysts are prepared. According to the present invention, the Mn0. 1Ce0. 1Nb0. 03TiOx-CP catalyst with the optimal low temperature activity and the widest operation temperature window is synthesized, the highest NO conversion rate at 250 DEG C can achieve 98.5%, and the T80 temperature interval is 166-443 DEG C. Compared with the Mn0. 1Ce0. 1Nb0. 03TiOx-CP catalyst prepared by using the conventional co-precipitation method, the low temperature activity is further reduced, and the T80 operation temperature interval is further broadened. In addition, the preparation method is simple in process and suitable for industrial production, and preparation conditions are easy to control. Meanwhile, a characterization result shows that the catalyst prepared by adopting a reverse coprecipitation method mainly presents an amorphous structure, so that the oxidation-reduction performance of the catalyst and the interaction force among the components are enhanced, and the denitration activity of the catalyst is favorably improved.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a wide temperature range Mn-based NH3-SCR denitration catalyst, specifically a catalyst for effectively degrading the air pollutant NO, belonging to the field of air pollution control and environmental catalysis. Background Art

[0002] Nitrogen oxides (NO x ) is one of the main pollutants in the atmosphere, mainly coming from waste gas emissions from fixed and mobile pollution sources. x It not only harms human health, but also produces photochemical smog, acid rain, greenhouse effect, and leads to environmental pollution such as ozone depletion. x The emission of pollutants is one of the important contents of current air pollution control.

[0003] NH3 selective catalytic reduction (NH3-SCR) technology has become an effective method for removing NO from flue gas from stationary and mobile sources. x NH3-SCR technology uses liquid ammonia or urea as the ammonia source, and selectively reacts with NO under the action of a catalyst. x The process of generating non-toxic and harmless N2 and H2O. The catalyst is the core of NH3-SCR technology, and the performance of the catalyst will directly affect the denitrification effect of the entire NH3-SCR system. x The development of catalysts is imperative.

[0004] Traditional commercial V2O5-WO3(MoO3) / TiO2 denitrification catalysts at home and abroad have poor low-temperature activity (<300℃), narrow operating temperature window (300-400℃), and vanadium species have defects such as biological toxicity and poor anti-toxicity, which limit their scope of use. Mn-based catalysts have excellent low-temperature SCR activity due to their variable valence states and excellent redox ability. They are non-toxic and low-priced, and are environmentally friendly SCR catalysts that can replace V-based catalysts. They have attracted widespread attention. However, single Mn-based catalysts still have disadvantages such as narrow operating temperature window and low activity at high temperature, which limits their practical application. Therefore, it is urgent to modify Mn-based catalysts and develop an environmentally friendly NH3-SCR denitrification catalyst with low cost, high efficiency, excellent activity and wide operating temperature window to meet the increasingly stringent NO x Emission standards.

[0005] The design idea of ​​this patent is to first screen out non-toxic Mn with good low-temperature activity and low cost as the metal active component. First, the content of the active component Mn was optimized, and the molar ratio of the carrier to the active component was n(Ti(SO4)2):n(Mn(NO3)2·4H2O)=1:0.1, which has better low-temperature activity, but the operating temperature window is narrow. According to literature reports, the introduction of additives Ce and Nb will improve the low-temperature activity of the catalyst and broaden the operating temperature window, but the low-temperature denitrification activity after the introduction of additives Ce and Nb is still unsatisfactory. It was thought that the special physical and chemical properties of the additives Ce and Nb should have higher low-temperature activity, but they failed to show it. Because the preparation method of the catalyst will affect the morphology, structure, specific surface area of ​​the catalyst, the dispersibility of each component and its interaction force, etc., thereby affecting its reaction performance. According to literature reports, the tandem coprecipitation method and the parallel coprecipitation method can improve the low-temperature activity of the catalyst, but the low-temperature denitrification activity of the prepared catalyst is still unsatisfactory. It was thought that the catalysts prepared by the sequential addition co-precipitation method and the parallel addition co-precipitation method should have higher low-temperature activity, but this was not the case. Summary of the invention

[0006] The purpose of the present invention is to prepare a method and application of a wide temperature range Mn-based NH3-SCR denitrification catalyst using a reverse coprecipitation method. The reverse coprecipitation method refers to the process of dripping a solution into a precipitant and gradually precipitating, which can precipitate the desired substance more efficiently. The first problem solved by the present invention is to develop a highly active, cheap and non-toxic Mn-based metal oxide catalyst with independent intellectual property rights; the second problem solved by the present invention is to broaden the operating temperature window of the catalyst, especially its low-temperature activity, to achieve a NO conversion rate of more than 80% at 166-443°C. The third problem solved by the present invention is to prepare Mn by a reverse coprecipitation method. 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst, the preparation method has simple process, low cost, high efficiency, easy control and is suitable for industrial production.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A preparation method and application of a wide temperature range Mn-based NH3-SCR denitration catalyst, comprising the following steps:

[0009] (a) Weigh the active component Mn(NO3)2·4H2O, the additive Ce(NO3)4·6H2O, and the additive C in the stoichiometric ratio. 10 H5B 20 Dissolve in deionized water and stir until completely dissolved to obtain a clear solution;

[0010] (b) adding a measured amount of Ti(SO4)2 carrier to the transparent solution obtained in step (a);

[0011] (c) adding the solution of step (b) dropwise into excess ammonia water under stirring, and adjusting the pH value to 9.5 with hydrochloric acid;

[0012] (d) stirring the solution obtained in step (c) for 1 h and then aging for 1 h;

[0013] (e) transferring the solution obtained in step (d) into a centrifuge tube and centrifuging to wash until neutral;

[0014] (f) placing the sample catalyst obtained in step (e) in an oven at 110° C. and drying overnight;

[0015] (g) Grind the sample obtained in step (f) into fine powder, place it in a muffle furnace, and roast it for 5 hours to obtain Mn 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst.

[0016] According to the above scheme, the molar ratio of the carrier to the active component is n(Ti(SO4)2):n(Mn(NO3)2·4H2O)=1:0.1;

[0017] According to the above scheme, the molar ratio of the carrier to the auxiliary agent Ce is n(Ti(SO4)2):n(Ce(NO3)4·6H2O)=1:0.1;

[0018] According to the above scheme, the molar ratio of the carrier to the additive Nb is n(Ti(SO4)2):n(C 10 H5B 20 )=1:0.03;

[0019] According to the above scheme, the mass of Ti(SO4)2 is 3g;

[0020] According to the above scheme, the reverse coprecipitation method preparation conditions include precipitant, pH value and aging time;

[0021] According to the above scheme, the precipitant includes NH3·H2O, Na2CO3 and NaOH;

[0022] According to the above scheme, the pH values ​​are 9, 9.5, 10 and 10.5;

[0023] According to the above scheme, the aging time is 0.5h, 1h, 3h and 5h;

[0024] The present invention also provides the use of the NH3-SCR NO degradation catalyst prepared by the preparation method described in any one of the above technical solutions in tail gas denitrification.

[0025] The present invention has the following advantages:

[0026] 1. Mn prepared by reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -RCP metal oxide catalyst has excellent low-temperature catalytic activity and a wide temperature operating window. The highest NO conversion rate can reach 98.5% at 250℃. 80 The temperature range is 166~443℃.

[0027] 2. The catalyst is prepared by reverse co-precipitation method, which has simple process, low cost, high efficiency, easy control and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The catalytic activity test diagram of the catalysts prepared in Examples 1, 2 and 3.

[0029] Figure 2 The catalytic activity test diagram of the catalysts prepared in Examples 4, 5 and 6.

[0030] Figure 3 These are the catalytic activity test graphs of the catalysts prepared in Examples 1, 7, 8, 9 and 10.

[0031] Figure 4 These are the catalytic activity test graphs of the catalysts prepared in Examples 1, 11, 12, 13 and 14.

[0032] Figure 5 The catalytic activity test diagram of the catalysts prepared in Example 1 and Example 12.

[0033] Figure 6 The XRD spectra of the catalysts prepared in Example 1 and Example 12 are shown.

[0034] Figure 7 H2-TPR spectra of the catalysts prepared in Example 1 and Example 12.

[0035] Figure 8 The XPS spectra of the catalysts prepared in Example 1 and Example 12 are shown. DETAILED DESCRIPTION

[0036] The present invention will be further described below through some implementation examples, but the present invention is not limited thereto.

[0037] Example 1 Synthesis of Mn by coprecipitation 0.1 Ce 0.1 Nb 0.03 TiO x -CP Catalyst

[0038] Weigh 0.31375g of Mn(NO3)2·4H2O, 0.5428g of Ce(NO3)2·6H2O, and 0.2018g of C 10 H5B 20 , 30ml deionized water, stir until dissolved, add 3g Ti(SO4)2, add ammonia water dropwise to adjust pH≈10 while stirring after complete dissolution, stir for 1h, age for 1h, then transfer to a centrifuge tube for centrifugation, centrifuge and wash until neutral, dry the obtained precipitate in an oven at 110℃ for 12h, and finally calcine at 500℃ in a muffle furnace under air atmosphere for 5h. The calcined powder is pressed into tablets at a pressure of 20Mpa by a tablet press and crushed to 20-40 mesh, thus obtaining Mn 0.1 Ce 0.1 Nb 0.03 TiO x catalyst.

[0039] Catalyst Evaluation

[0040] The activity evaluation of the catalyst was carried out in a homemade continuous flow fixed bed reactor. The reaction tube is a quartz tube with an inner diameter of 6mm and a length of 33cm. The reaction temperature is measured by a thermocouple placed in the middle of the reaction tube, and the reaction temperature is controlled by a program temperature controller. The gas flow is controlled by a mass flow meter. The reaction raw gas: 400ppmNH3, 400ppmNO, 3%O2 and balance gas Ar. In the experiment, the catalyst dosage is 0.2g, the reaction temperature is 100℃~450℃, and sampling is performed every 50℃. The detection is carried out with a flue gas analyzer (GERMANY, MRU, VARIO PLUS) to calculate the conversion rate of NO. The NO conversion curve of the catalyst at different temperature points is shown in the figure below. Figure 1 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0041] Example 2 Synthesis of Mn by reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -RCP Catalyst

[0042] Weigh 0.31375g of Mn(NO3)2·4H2O, 0.5428g of Ce(NO3)2·6H2O, and 0.2018g of C 10 H5B 20, 30ml deionized water, stir and mix until dissolved, add 3g Ti(SO4)2, then add the completely dissolved mixed solution dropwise into excess ammonia water, adjust pH≈10 with hydrochloric acid, stir for 1h, age for 1h, then transfer to a centrifuge tube for centrifugation, centrifuge and wash until neutral, dry the obtained precipitate in an oven at 110℃ for 12h, and finally calcine at 500℃ in a muffle furnace in an air atmosphere for 5h. The calcined powder is pressed into a tablet press at a pressure of 20Mpa and crushed to 20-40 mesh, thus obtaining Mn 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst.

[0043] Catalyst Evaluation

[0044] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 1 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0045] Example 3: Synthesis of Mn by coprecipitation 0.1 Ce 0.1 Nb 0.03 TiO x -HCP Catalyst

[0046] Weigh 0.31375g of Mn(NO3)2·4H2O, 0.5428g of Ce(NO3)2·6H2O, and 0.2018g of C 10 H5B 20 , 30ml deionized water, stir and mix until dissolved, add 3g Ti(SO4)2, add excess urea while stirring after complete dissolution, then put the solution into a magnetic stirring water bath and stir continuously at 90℃ for 12h, then transfer it into a centrifuge tube for centrifugation, centrifuge and wash until neutral, dry the obtained precipitate in an oven at 110℃ for 12h, and finally calcine at 500℃ in a muffle furnace in an air atmosphere for 5h. The calcined powder is pressed into tablets at a pressure of 20Mpa by a tablet press and crushed into 20-40 mesh, thus obtaining Mn 0.1 Ce 0.1 Nb 0.03 TiO x -HCP catalyst.

[0047] Catalyst Evaluation

[0048] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 1 The 100℃, 150℃, maximum NO conversion rate and T 80The operating window temperature is shown in Table 2.

[0049] Embodiments 4 to 6

[0050] Compared with Example 3, only the precipitant is different. Example 4 uses NH3·H2O as the precipitant, Example 5 uses Na2CO3 as the precipitant, and Example 6 uses NaOH as the precipitant. The other processes are the same as Example 3 to obtain various finished catalysts.

[0051] Catalyst Evaluation

[0052] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 2 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0053] Embodiments 7 to 10

[0054] Compared with Example 3, only the pH value is different. The pH value of Example 7 is about 9, the pH value of Example 8 is about 9.5, the pH value of Example 9 is about 10, and the pH value of Example 10 is about 10.5. The other processes are the same as in Example 3 to obtain various finished catalysts.

[0055] Catalyst Evaluation

[0056] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 3 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0057] Examples 11 to 14

[0058] Compared with Example 3, only the aging time is different. The aging time of Example 11 is 0.5 h, the aging time of Example 12 is 1 h, the aging time of Example 13 is 3 h, and the aging time of Example 14 is 5 h. The other processes are the same as in Example 3 to obtain various finished catalysts.

[0059] Catalyst Evaluation

[0060] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 4 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0061] Composition table of metal oxide catalysts of Examples 1 to 14:

[0062] The composition of the metal oxide catalyst in the specific embodiment is shown in Table 1:

[0063] Activity evaluation results:

[0064] The specific activity evaluation results are shown in Table 2:

[0065] The Mn screened out by reverse coprecipitation 0.1 Ce 0.1 Nb 0.03 TiO x -RCP (t = 1h) was characterized and analyzed to study its structure-activity relationship, and its catalyst was abbreviated as Mn 0.1 Ce 0.1 Nb 0.03 TiO x -RCP.

[0066] XRD characterization

[0067] exist Figure 6 In the analysis of the basic Mn 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst and Mn prepared by reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst sample XRD spectrum. It can be seen from the figure that the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst, still no obvious phase X-ray diffraction peak was observed, which means that there is no relatively complete crystal form in the catalyst, and the internal structure of the catalyst is amorphous. At this time, the interaction between Mn, Ce, Nb, and Ti elements inhibits the formation of crystals, thereby promoting the improvement of the catalytic activity of the catalyst. Therefore, the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst shows better low temperature activity and wider operating temperature window.

[0068] TPR characterization

[0069] The reducible species in the catalyst are crucial for the completion of the redox cycle in the NH3-SCR reaction. Figure 7H2-TPR results for two different catalysts are shown. In the temperature range of 100-800 °C, Mn 0.1 Ce 0.1 Nb 0.03 TiO x and Mn 0.1 Ce 0.1 Nb 0.03 TiO x Four peaks were fitted in the H2-TPR diagram of the -RCP catalyst. The low-temperature reduction peaks at 365°C and 430°C were attributed to the reduction of MnO2→Mn2O3, the reduction peaks at 441°C and 505°C were attributed to the reduction of Mn2O3→Mn3O4, the reduction peaks at 520°C and 538°C were attributed to the reduction of Mn3O4→MnO, and the reduction peaks at 583°C and 585°C were attributed to Ce. 4+ →Ce 3+ Since the reduction temperature of Nb oxide is above 800℃, no Nb oxide reduction peak is observed in the TPR test results of the two catalyst samples. By comparison, it can be found that compared with the basic Mn 0.1 Ce 0.1 Nb 0.03 TiO x Compared with the catalyst, the Mn 0.1 Ce 0.1 Nb 0.03 TiO x The reduction peak of the -RCP catalyst gradually moves toward the low temperature direction, indicating that the catalyst prepared by the reverse coprecipitation method enhances the synergistic effect between the components, reduces the reduction temperature, improves the reducibility of the catalyst, and thus promotes the improvement of the catalytic activity of the catalyst. 0.1 Ce 0.1 Nb 0.03 TiO x -One of the reasons why RCP catalysts exhibit excellent denitrification activity.

[0070] XPS characterization

[0071] The Mn 0.1 Ce 0.1 Nb 0.03 TiO x and Mn 0.1 Ce 0.1 Nb 0.03 TiO x -Chemical states of surface species of RCP catalysts. Figure 8 The characteristic peaks of Mn 2p, Ce 3d, Ti 2p, O 1s and Nb 3d in the two catalysts are shown. Figure 8(a) shows the Mn 2p spectrum of the catalyst. It can be seen from the figure that the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -Mn of RCP catalyst 2+ and Mn 4+ The shift to lower binding energy indicates that the chemical state of the active component Mn in the catalyst after plasma modification has changed, the electron cloud density of the Mn species in the catalyst has increased, the chemical environment around the Mn species in the catalyst has changed, and the interaction force between the components has been enhanced. Figure 8 (b) shows the Ce3d spectrum of the catalyst. It can be seen from the figure that the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x -Ce of RCP catalyst 3+ and Ce 4+ The shift to low binding energy indicates that the chemical state of Ce in the catalyst prepared by the reverse coprecipitation method has changed, the electron cloud density of Ce species in the catalyst has increased, the chemical environment around Ce species in the catalyst has changed, and the interaction force between the components has been enhanced. Figure 8 (c) shows the Ti 2p spectrum of the catalyst. 0.1 Ce 0.1 Nb 0.03 TiO x The peak of the -RCP catalyst shifts toward low binding energy, indicating that the chemical state of Ti in the catalyst prepared by the reverse coprecipitation method has changed, the electron cloud density of the Ti species in the catalyst has increased, the chemical environment around the Ti species in the catalyst has changed, and the interaction force between the components has been enhanced. Figure 8 (d) shows the O1s spectrum of the catalyst. It can be observed from the figure that the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO x The peak of the -RCP catalyst shifts to a lower binding energy, indicating that the catalyst prepared by the reverse coprecipitation method increases the O β and O α The electron cloud density changes the chemical environment around the O species in the catalyst. Figure 8 (e) shows the Nb 3d spectrum of the catalyst. It can be observed from the figure that the Mn prepared by the reverse coprecipitation method 0.1 Ce 0.1 Nb 0.03 TiO xThe peak of the -RCP catalyst shifts toward low binding energy, indicating that the chemical state of Nb in the catalyst prepared by the reverse coprecipitation method has changed, the electron cloud density of the Nb species in the catalyst has increased, the chemical environment around the Nb species in the catalyst has changed, and the interaction force between the components has been enhanced.

Claims

1. A preparation method and application of a wide temperature range Mn-based NH3-SCR denitration catalyst, the preparation method comprising the following steps: (a) Weigh the active component Mn(NO3)2·4H2O, the additive Ce(NO3)4·6H2O, and the additive C in the stoichiometric ratio. 10 H5B 20 Dissolve in deionized water and stir until completely dissolved to obtain a clear solution; (b) adding a measured amount of Ti(SO4)2 carrier to the transparent solution obtained in step (a); (c) adding the solution of step (b) dropwise into excess ammonia water under stirring, and adjusting the pH value to 9.5 with hydrochloric acid; (d) stirring the solution obtained in step (c) for 1 h and then aging for 1 h; (e) transferring the solution obtained in step (d) into a centrifuge tube and centrifuging to wash until neutral; (f) placing the sample catalyst obtained in step (e) in an oven at 110° C. and drying overnight; (g) Grind the sample obtained in step (f) into fine powder, place it in a muffle furnace, and roast it for 5 hours to obtain Mn 0.1 Ce 0.1 Nb 0.03 TiO x -RCP catalyst.

2. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to claim 1, characterized in that: The molar ratio of the carrier to the active component is n(Ti(SO4)2):n(Mn(NO3)2·4H2O)=1:0.

1.

3. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1-2, characterized in that: The molar ratio of the carrier to the auxiliary agent Ce is n(Ti(SO4)2):n(Ce(NO3)4·6H2O)=1:0.

1.

4. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1 to 3, characterized in that: The molar ratio of the carrier to the additive Nb is n(Ti(SO4)2):n(C 10 H5B 20 )=1:0.

03.

5. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1 to 4, characterized in that: The carrier is a precursor Ti(SO4)2.

6. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1 to 5, characterized in that: NH3·H2O was used as the precipitant.

7. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1 to 6, characterized in that: A pH of about 9.5 was used.

8. The preparation method and application of the wide temperature range Mn-based NH3-SCR denitration catalyst according to any one of claims 1 to 7, characterized in that: The aging time used was 1 h.

9. Use of any one of the catalysts for NH3-SCR degradation of NO according to any one of claims 1 to 8 in exhaust gas denitration.

Images