CN115845911A - Mn-based low-temperature C 3 H 6 Preparation method and application of SCR catalyst - Google Patents
Mn-based low-temperature C 3 H 6 Preparation method and application of SCR catalyst Download PDFInfo
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Abstract
The invention relates to a preparation method of a Mn/ZSM-5 catalyst prepared by adopting a dielectric barrier discharge plasma synergistic coprecipitation method and application of the Mn/ZSM-5 catalyst in denitration of nitrogen oxides. The catalyst is prepared by taking ZSM-5 as a carrier and transition metal Mn as an active component by adopting a coprecipitation method. Firstly, weighing Mn (NO) in a metering ratio 3 ) 2 ·4H 2 Adding a proper amount of deionized water to dissolve the O, adding a metered ZSM-5 molecular sieve, adding an alkaline precipitator to adjust the pH value to 9-11, stirring for 2-4 h, aging for 1-3 h, filtering and washing the obtained solution until the pH value is unchanged, drying for 12h in a drying oven at 110 ℃, then carrying out DBD plasma treatment, tabletting, and grinding into a 20-40-mesh catalyst, namely the Mn/ZSM-5 catalyst. The Mn/ZSM-5 molecular sieve catalyst has high denitration capability under the low-temperature condition, and can effectively remove NO and hydrocarbons. In addition, compared with the traditional roasting activation, the DBD plasma activation can generate higher active manganese species dispersity, larger pore diameter and richer oxygen vacancies, so that the catalyst has higher catalytic activity at low temperature.
Description
Technical Field
The invention relates to a preparation method of a Mn/ZSM-5 catalyst prepared by adopting a dielectric barrier discharge plasma synergistic coprecipitation method and application of the Mn/ZSM-5 catalyst in denitration of nitrogen oxides.
Background
Nitrogen oxides are the main air pollutants emitted by fuel combustion and stationary and mobile sources. Traditional SCR is an efficient fixed source nitrogen oxide removal method due to its high efficiency in the 300-500 deg.c range (>90%) and high stability to be widely used. However, catalyst toxicity (active component vanadium species) is a difficulty of the subject. In addition, a non-vanadium based catalyst for selective catalytic reduction of nitrogen oxides by hydrocarbons will become a promising denitration technology. The additional advantages of using vehicle fuel directly without additional space to store reductant and simultaneously achieving the elimination of hydrocarbons and nitric oxide from pollution sources with non-vanadium based catalysts make this technology even more attractive. And NH 3 HC-SCR systems do not require additional reductant compared to SCR, and can directly utilize hydrocarbons in diesel exhaust. Thus, the entire aftertreatment system can be more compact and significant fuel losses can be avoided in its practical application.
The SCR technology requires a relatively high reaction temperature (above 300 ℃), but it can be combined with NH if SCR of HC on low-concentration nitrogen oxides occurs on a catalyst with high denitration activity at low temperatures 3 SCR competes and is more practical for removing nitrogen oxides from mobile sources. Among the numerous hydrocarbon reducing agents, propylene (C) 3 H 6 ) Due to its relatively strong reactivity and comprehensive considerations, it has been extensively studied in the selective catalytic reduction of hydrocarbons. However, for non-noble metals C 3 H 6 SCR catalysts, most of the reports still focusing on high temperature activity, with respect to low temperature C 3 H 6 -SCR non-noble goldThe reports of the generic catalyst are very limited.
The design idea of this patent is at first to select the metal active ingredient that possesses good nitrogen oxide desorption effect, green and low cost under the low temperature condition, and the different preparation methods of catalyst can promote the highly dispersed of active ingredient and can strengthen the interact of active ingredient between the carrier again, improve the low temperature denitration activity of catalyst. Therefore, a great deal of exploration work is carried out, and preparation methods such as an impregnation method, a coprecipitation method and the like are explored, so that the effects are not ideal. The low-temperature activity of the catalyst can be obviously enhanced by the plasma technology reported in the literature, and the plasma enhancement is compared with the plasma enhancement of 'dipping + conventional roasting' and 'dipping + Dielectric Barrier Discharge (DBD)', but the plasma enhancement effect is not ideal; therefore, specific parameters (time, power and the like) of the DBD plasma activation are further refined and explored, so that the low-temperature activity of the catalyst can be remarkably improved, but the low-temperature activity is not remarkably improved.
Disclosure of Invention
Aiming at the defects in the technology, the invention aims to provide the preparation method of the Mn-based catalyst for low-temperature denitration, and the prepared catalyst has the advantages of environmental protection and higher catalytic activity at low temperature.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
mn-based low-temperature C 3 H 6 -a process for the preparation of an SCR catalyst, comprising the steps of:
(1) Stirring and dissolving the active component in deionized water to obtain a precursor solution;
(2) Immersing a ZSM-5 molecular sieve carrier into a precursor solution, adding an alkaline precipitator, adjusting the pH value, stirring, filtering, drying, treating by Dielectric Barrier Discharge (DBD) plasma, tabletting, and grinding to obtain the Mn-based catalyst.
The active components selected in the step (1) are selected from manganese nitrate, manganese carbonate and manganese sulfate, and the loading amount of the active components on the carrier is 3-15% (based on the mass of the carrier as 100%).
In the step (2), the precipitant is sodium hydroxide, ammonia water or ammonium carbonate.
The Mn-based low temperature C 3 H 6 -a process for the preparation of an SCR catalyst, comprising the steps of:
(1) Dissolving the active component in deionized water, and stirring to obtain a precursor solution;
(2) Immersing a ZSM-5 molecular sieve carrier into the precursor solution, adding an alkaline precipitator, adjusting the pH to 9-11, stirring for 2-4 h, aging for 1-3 h, filtering and washing the obtained solution until the pH is unchanged, drying for 12h in a drying oven at 110 ℃, then carrying out DBD plasma treatment, tabletting, grinding into a catalyst with 20-40 meshes, namely the Mn-based low-temperature C catalyst 3 H 6 -an SCR catalyst.
The Mn-based catalyst is applied to low-temperature denitration.
In the invention, the active component is manganese salt which is at least one of manganese nitrate, manganese carbonate and manganese sulfate, the mass of the carrier is 100%, the mass percentage content of Mn in the active component is 3-15%, and the manganese salt is preferably manganese nitrate.
In the present invention, the alkaline precipitant is at least one of sodium hydroxide, ammonia water and ammonium carbonate, and the precipitant is preferably ammonia water.
The method takes a ZSM-5 molecular sieve with higher specific surface area as a carrier, loads an active component manganese oxide, fully stirs, filters, dries, and carries out DBD plasma treatment. The catalyst obtained by the invention has the advantages of environmental protection, no toxicity and the like, and has higher denitration efficiency under the low-temperature condition.
Compared with the prior art, the technical scheme provided by the invention has the beneficial technical effects that:
1. using C produced by internal combustion engines 3 H 6 As a reducing agent to replace conventional NH 3 As reducing agent, with simultaneous removal of NO produced by the internal combustion engine x And C 3 H 6 Two major pollutants;
2. DBD plasma is adopted to replace the traditional roasting, so that the Mn-based catalyst is activated in a green and efficient manner;
3. mn-based catalyst prepared by DBD plasma synergistic coprecipitation method at C 3 H 6 The SCR domain exhibits low temperature activity, itNO at 120-270 DEG C x The conversion rate is over 96 percent.
4. The preparation method has simple process, low cost and high catalytic activity for SCR reaction, and can be used for preparing C in motor vehicle exhaust 3 H 6 Realizes purification, has simple preparation conditions, is easy to control and is suitable for industrial production.
FIG. 1 is a graph showing the results of measuring the catalytic activity of catalysts prepared in examples 1 and 2.
FIG. 2 is a graph showing the results of measuring the catalytic activity of the catalysts prepared in examples 1 and 3.
FIG. 3 is a graph showing the results of measuring the catalytic activity of catalysts prepared in examples 3, 4, 5 and 6.
FIG. 4 is a graph showing the results of measuring the catalytic activity of the catalysts prepared in examples 3, 7, 8 and 9.
FIG. 5 is a graph showing the results of measuring the catalytic activity of the catalysts prepared in examples 3, 10, 11 and 12.
FIG. 6 is a graph showing the results of measuring the catalytic activity of catalysts prepared in examples 3 and 13.
FIG. 7 is an XPS map of catalysts prepared in examples 1, 2, 3 and 13.
FIG. 8 is a py-FTIR plot of the catalysts prepared in examples 1, 2, 3 and 13.
Detailed Description
The present invention will be further described with reference to the following specific examples.
Example 1
The preparation method of the Mn catalyst for low-temperature denitration comprises the following steps:
(1) Measuring 0.355mL of manganese nitrate, and dissolving in 30mL of deionized water to obtain a precursor solution;
(2) Adding 2g of carrier to dissolve in the precursor solution, standing for 40min, putting into a water bath kettle with constant temperature of 80 ℃ for water bath and drying, then drying in an oven with temperature of 110 ℃ for 12h, roasting in a muffle furnace at 550 ℃ for 3h, tabletting, and grinding into catalyst particles with the size of 20-40 meshes to obtain Mn-based low-temperature C 3 H 6 SCR catalyst, named Mn 7 /ZSM-5-IM-C(550℃，3h)。
Example 2
Compared to example 1, only the preparation method of the catalyst is different, and a coprecipitation method is used: adding 2g of carrier to dissolve in a precursor solution, adding a proper amount of ammonia water, controlling the pH =10, stirring for 2h, aging for 1h, filtering and washing until the pH is unchanged, drying the precipitate at 110 ℃ for 12h, then roasting, tabletting, grinding into catalyst particles of 20-40 meshes, and obtaining the Mn-based low-temperature C 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-CPM-C(550℃，3h)
Example 3
Compared with the example 1, the Mn-based low-temperature C prepared by adopting the same process as the example 1 and adopting the Dielectric Barrier Discharge (DBD) plasma treatment for 10min (100W) with only different catalyst activation 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(100W，10min)。
Example 4
According to the evaluation method of embodiment 3, except that the content of manganese nitrate was reduced to 3%, the Mn-based low-temperature C was obtained 3 H 6 -SCR catalyst named Mn 3 /ZSM-5-IM-DBD(100W，10min)。
Example 5
According to the evaluation method of embodiment 3, except that the content of manganese nitrate was increased to 10%, the Mn-based low temperature C was obtained 3 H 6 -SCR catalyst named Mn 10 /ZSM-5-IM-DBD(100W，10min)。
Example 6
According to the evaluation method of embodiment 3, except that the content of manganese nitrate was increased to 15%, the Mn-based low temperature C was obtained 3 H 6 -SCR catalyst named Mn 15 /ZSM-5-IM-DBD(100W，10min)。
Example 7
According to the evaluation method of embodiment 3, the difference is that the time of Dielectric Barrier Discharge (DBD) plasma treatment is reduced to 5min, and the prepared Mn-based low-temperature C 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(100W，5min)。
Example 8
Evaluation according to embodiment 3A valence method, which is different in that the time of Dielectric Barrier Discharge (DBD) plasma treatment is increased to 20min, and the prepared Mn-based low-temperature C 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(100W，20min)。
Example 9
According to the evaluation method of embodiment 3, except that the time of Dielectric Barrier Discharge (DBD) plasma treatment was increased to 30min, the Mn-based low temperature C was obtained 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(100W，30min)。
Example 10
According to the evaluation method of embodiment 3, except that the power of Dielectric Barrier Discharge (DBD) plasma treatment was reduced to 50W, the obtained Mn-based low temperature C was 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(50W，10min)。
Example 11
According to the evaluation method of embodiment 3, except that the power of Dielectric Barrier Discharge (DBD) plasma treatment was reduced to 80W, the Mn-based low temperature C was obtained 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(80W，10min)。
Example 12
According to the evaluation method of embodiment 3, except that the power of Dielectric Barrier Discharge (DBD) plasma treatment was increased to 130W, the resulting Mn-based low temperature C was obtained 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-IM-DBD(130W，10min)。
Example 13
According to the evaluation method of embodiment 2, only the activation of the catalyst is different, the Mn-based low temperature C is prepared by treating the catalyst with Dielectric Barrier Discharge (DBD) plasma for 10min (100W), and the other processes are the same as those of embodiment 2 3 H 6 -SCR catalyst named Mn 7 /ZSM-5-CPM-DBD(100W，10min)。
Example 14
The catalysts prepared in examples 1 to 13 were evaluated under the following conditions: 400ppmNO,400ppmc3H6,6% 2 And the rest of Ar, the space velocity is 30000h -1 . The NO conversion at different temperatures is shown in the table1。
TABLE 1 NO conversion at different temperatures
The data in table 1 illustrate that the denitration efficiency of the catalyst prepared by different activation methods, different contents of active components, different time and different power of Dielectric Barrier Discharge (DBD) plasma treatment and different preparation methods of the catalyst are different, wherein the co-precipitation method is adopted to prepare Mn under the conditions that the DBD plasma treatment is 10min (100W) and the content of the active component, namely manganese nitrate, is 7% 7 The low-temperature denitration efficiency of the/ZSM-5-CPM-DBD (100W, 10min) is the highest.
XPS characterization
Further analysis by XPS, DBD plasma and calcination activation were used to identify the valence and chemical properties of the component elements in the catalyst. The valence states of the Mn and O elements were examined by high resolution XPS spectroscopy of Mn2p and O1s orbitals, as shown in fig. 7. No significant jittery satellite peaks were observed in the Mn2p spectra for all samples (Mn) 2+ ) (FIG. 7 a), whereas a broad range of peaks appear at 645.4 + -3 eV in the Mn2p3/2 spectrum, indicating that Mn exists in the "+4" and "+3" oxidation states. As shown in FIG. 7a, with Mn 7 ZSM-5-IM-C (550 ℃,3 h) comparison, mn 7 Higher surface Mn species concentrations were present for the/ZSM-5-IM-DBD (10min, 100W) catalyst, indicating that more Mn species favors C 3 H 6 -low temperature activity of SCR. However, mn 7 the/ZSM-5-IM-DBD (10min, 100W) catalyst also has a high concentration of Mn species, but its activity is still poor. Activation of Mn-based catalysts by DBD results in higher concentrations of Mn than calcination 4+ And more balanced Mn 4+ With Mn 3+ Ratio of (d) (fig. 7). Therefore, it can be inferred from the XPS results that the excellent low temperature activity of Mn-based catalysts is not dependent solely on the Mn content (Mn) 4+ Or Mn 3+ ) And is Mn 4+ And Mn 3+ The synergistic effect of (A). In addition, mn can be observed after DBD plasma treatment 4+ Move to lower binding energy, reflectThe DBD bombardment can promote electrons from the catalyst Mn 3+ To Mn 4+ And further generating crystal lattice oxygen vacancies.
py-FTIR characterization
In order to study the acidity of the surface of the manganese catalyst on low temperature C 3 H 6 -influence of SCR, detection of acid sites on the catalyst surface by fourier transform infrared spectroscopy with adsorbed pyridine. The results of the infrared spectroscopy are shown in FIG. 8. The adsorption temperature was 40 ℃ and the desorption temperatures were 150 ℃ and 300 ℃.1545cm- 1 、1612cm -1 And 1446cm -1 The strips of (A) correspond to
And Lewis acid sites. Furthermore, the band at 1492cm1 is due to the Lewis acid complex. It is widely reported that more Bronsted and Lewis acid sites contribute to high temperature C 3 H 6 -SCR. However, it can be observed that the conventional calcination-activated manganese catalysts exhibit a significantly higher ≥ er>
And Lewis acid site density, but poor low temperature activity (FIG. 8), indicating that
And Lewis acid is not low temperature C 3 H 6 Unique and absolute factors of the SCR. Studies show that Mn 3+ And Mn 4+ The Lewis acidity formed may be NH 3 -active sites of adsorption of NO by a manganese based catalyst in SCR; however, at low temperatures C 3 H 6 In SCR, few activation sites for C3H6 are reported. Notably, the 7Mn/ZSM-5-IM-DBD catalyst showed lower Broensted acid sites (consistent with XPS) and higher oxygen vacancies (XPS results) at 40 deg.C, 150 deg.C and 300 deg.C compared to 7 Mn/ZSM-5-IM-C. Meanwhile, the 7Mn/ZSM-5-CPM-DBD catalyst shows a remarkable abundance of Bronsted acid sites (consistent with XPS)And oxygen vacancies (XPS results). Previous studies have demonstrated that oxygen vacancies favor the transfer between chemisorbed oxygen and lattice oxygen, thereby promoting redox efficiency. In addition, formed by hydroxyl groups>
The acidity may be C 3 H 6 Active sites of adsorption and activation. Thus, the Fourier transform infrared spectrum of the absorbing pyridine and C are combined 3 H 6 SCR activity results can be inferred->
Or Lewis acids other than low temperature C 3 H 6 -the only factor of the SCR. />
Acidity at low temperature C 3 H 6 -SCR plays an important role. Py-FTIR combined with XPS results indicated low temperature C 3 H 6 SCR is hydroxy (-OR `)>
acidity) with the oxygen vacancies at the surface of the catalyst, rather than a single effect. />
Claims (10)
1. A preparation method of a Mn-based catalyst for low-temperature denitration is characterized by comprising the following steps:
(1) Stirring and dissolving the active component in deionized water to obtain a precursor solution;
(2) Dissolving a metered carrier into the precursor solution obtained in the step (1), adding an alkaline precipitator, adjusting the pH value, stirring, filtering, drying, performing Dielectric Barrier Discharge (DBD) plasma treatment, tabletting, and grinding to obtain the Mn-based catalyst.
2. The method of preparing a Mn-based catalyst for low-temperature denitration according to claim 1, wherein the activation method is a Dielectric Barrier Discharge (DBD) plasma.
3. The method of preparing a Mn-based catalyst for low-temperature denitration according to claim 1, wherein the DBD plasma is treated for 5 to 30min at a power of 50 to 130W.
4. The method of claim 1, wherein the support is a ZSM-5 molecular sieve.
5. The method of preparing an Mn-based catalyst for low-temperature denitration according to claim 1, wherein the active component in step (1) is at least one selected from the group consisting of manganese nitrate, manganese carbonate and manganese sulfate, and the loading amount of the active component on the carrier is 3% to 15%.
6. The method of claim 1, wherein the precipitant in step (2) is selected from the group consisting of sodium hydroxide, ammonia, and ammonium carbonate.
7. The method for preparing a Mn-based catalyst for low-temperature denitration according to claim 1, wherein the mass percentage of Mn as an active component is 3% to 15% based on 100% of the mass of the carrier.
8. The method of claim 1, wherein the method comprises the steps of:
(1) Dissolving an active component in deionized water to prepare a precursor solution;
(2) Putting a carrier into a precursor solution, adding an alkaline precipitator, adjusting the pH value to 9-11, stirring for 2-4 h, aging for 1-3 h, filtering and washing the obtained solution until the pH value is unchanged, drying for 12h in a drying oven at 110 ℃, then carrying out DBD plasma treatment, tabletting, and grinding to 20 ℃ C40 mesh catalyst, namely Mn-based low-temperature C 3 H 6 -an SCR catalyst.
9. A Mn-based catalyst obtained by the method for producing a Mn-based catalyst for low-temperature denitration according to any one of claims 1 to 8.
10. Use of a Mn-based catalyst according to any one of claims 1 to 9 for low temperature denitration in denitration of exhaust gas.
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| CN108435238A (en) * | 2018-04-20 | 2018-08-24 | 重庆理工大学 | A kind of Mn-La-Ce catalyst of Selective Catalytic Reduction of NO and its application |
| CN113398941A (en) * | 2021-05-31 | 2021-09-17 | 杭州电子科技大学 | Preparation process of high-efficiency carbon smoke removal catalyst and product thereof |
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| CN108435238A (en) * | 2018-04-20 | 2018-08-24 | 重庆理工大学 | A kind of Mn-La-Ce catalyst of Selective Catalytic Reduction of NO and its application |
| CN113398941A (en) * | 2021-05-31 | 2021-09-17 | 杭州电子科技大学 | Preparation process of high-efficiency carbon smoke removal catalyst and product thereof |
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