Preparation method and application of radio frequency discharge plasma enhanced modified Mn-based denitration catalyst

Abstract

The invention discloses a preparation method and application of a radio frequency discharge plasma enhanced modified Mn-based 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 catalyst with better activity is prepared. However, the low-temperature activity of the catalyst still needs to be improved, and the preparation process is time-consuming, so that the Mn0. 1Ce0. 1Nb0. 03TiOx catalyst is subjected to enhanced modification treatment by adopting radio frequency plasma, different plasma discharge atmospheres, discharge power and discharge time are discussed, and a series of catalysts are prepared. According to the present invention, the low-temperature activity of the Mn0. 1Ce0. 1Nb0. 03TiOx-AP 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%, and the T80 temperature range is 148-428 DEG C. Compared with the basic Mn0. 1Ce0. 1Nb0. 03TiOx catalyst, the low-temperature activity is further reduced, and the T80 temperature range is further widened. In addition, the modification method is simple in process, low in cost, short in time, easy to control and suitable for industrial production. Meanwhile, characterization results show that after plasma modification, the catalyst mainly presents an amorphous structure, the oxidation-reduction performance of the catalyst and the interaction force among the components are enhanced, and improvement of the denitration activity of the catalyst and widening of an operation temperature window are facilitated.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a radio frequency discharge plasma enhanced modified Mn-based 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, low activity at high temperature, and long traditional calcination time, which limit their practical application. Therefore, it is urgent to study the modification of Mn-based catalysts and develop an environmentally friendly NH3-SCR denitrification catalyst with low cost, short activation time, better activity and wider operating temperature window to meet the increasingly stringent NO x Emission standards.

[0005] The design idea of ​​this patent is to enhance the modified Mn-based denitrification catalyst by using radio frequency discharge plasma coupled co-precipitation method. 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. According to literature reports, the co-precipitation method can also improve the low-temperature activity of the catalyst and broaden the operating temperature window, but the low-temperature denitrification activity of the catalyst prepared by the co-precipitation method is still unsatisfactory. It was thought that the catalyst prepared by the co-precipitation method should have higher low-temperature activity, but it also failed to show it. So we analyzed: the low-temperature activity of the catalyst mainly lies in the interaction between the components in the catalyst. According to literature reports, the use of radio frequency discharge plasma can enhance the interaction of the catalyst. Therefore, we use radio frequency discharge plasma coupled co-precipitation method to enhance the modified Mn-based denitrification catalyst, which is rarely reported. Summary of the invention

[0006] The purpose of the present invention is to provide a preparation method and application of a radio frequency discharge plasma enhanced modified Mn-based denitrification catalyst. The preparation method has simple process, low cost, short time, easy control, and is suitable for industrial production. 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 148-428°C. The third problem solved by the present invention is to use plasma enhanced modification to treat Mn 0.1 Ce 0.1 Nb 0.03 TiO x Catalyst, saving a lot of catalyst activation time.

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

[0008] A preparation method and application of a radio frequency discharge plasma enhanced modified Mn-based 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 aqueous ammonia dropwise to the solution of step (b) while stirring to adjust the pH value to 10;

[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) Grinding the sample obtained in step (f) into fine powder, treating it with plasma and adjusting the appropriate plasma parameters to obtain Mn 0.1 Ce 0.1 Nb 0.03 TiO x -AP 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 plasma parameters include discharge atmosphere, discharge power and discharge time;

[0021] According to the above scheme, the discharge atmosphere includes N2, H2 and Air;

[0022] According to the above scheme, the discharge powers are 100W, 150W, 200W and 250W;

[0023] According to the above scheme, the discharge time is 5min, 10min, 15min and 20min;

[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 0.1 Ce 0.1 Nb 0.03 TiO x -AP metal oxide catalyst has excellent low-temperature catalytic activity and a wide temperature operating window. The highest NO conversion rate can reach 98% at 250℃. 80 The temperature range is 148-428℃.

[0027] 2. Plasma-enhanced modification of catalysts can replace traditional calcination. This preparation method has simple process, short time, low cost, 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, 3 and 4.

[0029] Figure 2 These are the catalytic activity test graphs of the catalysts prepared in Examples 1, 5, 6, 7 and 8.

[0030] Figure 3 These are the catalytic activity test graphs of the catalysts prepared in Examples 1, 9, 10, 11 and 12.

[0031] Figure 4 The catalytic activity test diagram of the catalysts prepared in Example 1 and Example 10.

[0032] Figure 5 The XRD spectra of the catalysts prepared in Example 1 and Example 10 are shown.

[0033] Figure 6 H2-TPR spectra of the catalysts prepared in Example 1 and Example 10.

[0034] Figure 7 The XPS spectra of the catalysts prepared in Example 1 and Example 10 are shown. DETAILED DESCRIPTION

[0035] The present invention will be further described below through some implementation examples, but the present invention is not limited thereto.

[0036] Example 1Mn 0.1 Ce 0.1 Nb 0.03 TiO x Catalyst synthesis

[0037] Weigh 0.31375g of Mn(NO3)2·4H2O, 0.5428g of Ce(NO3)2·6H2O, and 0.2018g of C 10 H5B20 , 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.

[0038] Catalyst Evaluation

[0039] 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.

[0040] Example 2Mn 0.1 Ce 0.1 Nb 0.03 TiO x -Synthesis of RF-Air Catalyst

[0041] 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 while stirring after complete dissolution to adjust pH≈10, stir for 1h, age for 1h, then transfer to a centrifuge tube for centrifugation, centrifuge and wash until neutral, dry the precipitate in an oven at 110℃ for 12h, grind the catalyst into powder, and then use plasma in Air atmosphere, 200W power, discharge for 10min to treat the catalyst. The treated powder is pressed into tablets with 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 -RF-Air catalyst.

[0042] Catalyst Evaluation

[0043] 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.

[0044] Embodiments 3 to 12

[0045] Compared with Example 2, only the plasma discharge atmosphere, discharge power and discharge time are different. Examples 3 to 4 have different discharge atmospheres, Examples 5 to 8 have different discharge powers, and Examples 9 to 12 have different discharge times. The other processes are the same as Example 2 to obtain various finished catalysts.

[0046] Catalyst Evaluation

[0047] According to the evaluation method of Example 1, the conversion curves of the catalyst for NO at different temperature points are shown in Examples 3 to 4. Figure 1 As shown, Examples 5 to 8 are as Figure 2 As shown in Examples 9 to 12 Figure 3 The 100℃, 150℃, maximum NO conversion rate and T 80 The operating window temperature is shown in Table 2.

[0048] Composition table of metal oxide catalysts of Examples 1 to 12:

[0049] The composition of the metal oxide catalyst in the specific embodiment is shown in Table 1:

[0050] Activity evaluation results:

[0051] The specific activity evaluation results are shown in Table 2:

[0052] The Mn selected under different plasma conditions 0.1 Ce 0.1 Nb 0.03 TiO x -RF-Air-200W-10min The optimal catalyst 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 -AP.

[0053] XRD characterization

[0054] exist Figure 5 In the analysis of the basic Mn 0.1 Ce 0.1 Nb 0.03 TiO x Catalyst and Mn treated with optimal plasma conditions 0.1 Ce 0.1 Nb 0.03 TiO x -AP catalyst sample XRD spectrum. It can be seen from the figure that after plasma treatment, Mn 0.1 Ce 0.1 Nb 0.03 TiO x -AP 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 crystallization, thereby promoting the improvement of the catalytic activity of the catalyst. Therefore, after plasma treatment, Mn 0.1 Ce 0.1 Nb 0.03 TiO x -AP catalyst shows better low temperature activity and wider operating temperature window.

[0055] TPR characterization

[0056] The reducible species in the catalyst are crucial for the completion of the redox cycle in the NH3-SCR reaction. Figure 6 H2-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 0.03TiO x Four peaks were fitted in the H2-TPR diagram of the -AP catalyst. The low-temperature reduction peaks at 361°C and 430°C were attributed to the reduction of MnO2→Mn2O3, the reduction peaks at 460°C and 505°C were attributed to the reduction of Mn2O3→Mn3O4, the reduction peaks at 524°C and 538°C were attributed to the reduction of Mn3O4→MnO, and the reduction peaks at 582°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 -AP catalyst reduction peak gradually moved toward low temperature, indicating that plasma treatment enhanced the synergistic effect between the components, lowered the reduction temperature, improved the reducibility of the catalyst, and thus promoted the improvement of the catalytic activity of the catalyst. 0.1 Ce 0.1 Nb 0.03 TiO x -AP catalyst exhibits excellent denitrification activity.

[0057] XPS characterization

[0058] 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 AP catalysts. Figure 7 The characteristic peaks of Mn 2p, Ce 3d, Ti 2p, O 1s and Nb 3d in the two catalysts are shown. Figure 7 (a) shows the Mn 2p spectrum of the catalyst. It can be seen from the figure that after plasma treatment, the Mn 0.1 Ce 0.1 Nb 0.03 TiO x -Mn of AP 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 7 (b) shows the Ce3d spectrum of the catalyst. It can be seen from the figure that after plasma treatment, the Mn 0.1 Ce 0.1 Nb 0.03 TiO x -Ce of AP catalyst 3+ and Ce 4+ The shift to lower binding energy indicates that the chemical state of Ce in the catalyst has changed after plasma treatment, which has increased the electron cloud density of Ce species in the catalyst, changed the chemical environment around Ce species in the catalyst, and enhanced the interaction between the components. Figure 7 (c) shows the Ti 2p spectrum of the catalyst. 0.1 Ce 0.1 Nb 0.03 TiO x The peak of the -AP catalyst shifts toward low binding energy, indicating that the chemical state of Ti in the catalyst after plasma modification 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 7 (d) shows the O1s spectrum of the catalyst. It can be observed from the figure that after plasma treatment, the Mn 0.1 Ce 0.1 Nb 0.03 TiO x The peak of -AP catalyst shifts to lower binding energy, indicating that the plasma-modified catalyst increases the O β and O α The electron cloud density changes the chemical environment around the O species in the catalyst. Figure 7 (e) shows the Nb 3d spectrum of the catalyst. It can be observed from the figure that the Mn 0.1 Ce 0.1 Nb 0.03 TiO x The peak of the -AP catalyst shifts toward low binding energy, indicating that the chemical state of Nb in the catalyst has changed after plasma treatment, which increases the electron cloud density of the Nb species in the catalyst, changes the chemical environment around the Nb species in the catalyst, and enhances the interaction between the components.

Claims

1. A preparation method and application of a radio frequency discharge plasma enhanced modified Mn-based 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 aqueous ammonia dropwise to the solution of step (b) while stirring to adjust the pH value to 10; (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) Grinding the sample obtained in step (f) into fine powder, treating it with plasma and adjusting the appropriate plasma parameters to obtain Mn 0.1 Ce 0.1 Nb 0.03 TiO x -AP catalyst.

2. The method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement 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 method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement according to any one of claims 1 to 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 method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement 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 method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement according to any one of claims 1 to 4, characterized in that: The carrier is a precursor Ti(SO4)2.

6. The method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement according to any one of claims 1 to 5, characterized in that: The plasma discharge atmosphere is Air.

7. The method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement according to any one of claims 1 to 6, characterized in that: The plasma discharge power is 200W.

8. The method for preparing a Mn-based denitration catalyst by radio frequency discharge plasma enhancement according to any one of claims 1 to 7, characterized in that: The plasma discharge time is 10 min.

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

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