CN113713851B - Preparation method of In/H-beta catalyst for improving sulfur resistance and water resistance - Google Patents

Abstract

The invention discloses a preparation method of an In-H/beta catalyst for improving sulfur resistance and water resistance. The preparation method comprises the following steps: mixing raw materials comprising amino acid, a silicon source, an aluminum source, an M source, an organic amine template agent and water for reaction to obtain reaction gel; crystallizing the reaction gel to obtain an M-beta molecular sieve; mixing with ammonium salt solution, and ion exchanging to obtain H-beta molecular sieve; step 4: mixing the H-beta molecular sieve with indium salt solution, and obtaining the In/H-beta molecular sieve after ion exchange. The amino acid can promote crystallization In the preparation process as a guiding agent, and can lead the finally prepared In/H-beta catalyst to obtain strongerAcid active center, thus can be in SO ₂ And H ₂ Under O interference, the best CH is shown ₄ SCR catalytic activity and cycle performance.

Description

A preparation method for In/H-β catalyst that improves sulfur and water resistance

Technical field

The present application relates to the technical field of selective catalytic reduction denitration, and in particular to a preparation method of In-H/β catalyst that improves sulfur and water resistance.

Background technique

Nitrogen oxides ( _NOx ) emitted by the combustion of fossil fuels not only cause damage to the human respiratory system, but also cause photochemical smog, acid rain and other serious environmental problems. In this regard, researchers have proposed a series of solutions, and selective catalytic reduction (SCR) denitrification is currently considered the best way to convert NO _x into N ₂ to solve NO _x emissions, of which CH ₄ is the main component of natural gas. Composition, abundant reserves, complete civilian use and low price, it is the most promising technology among NO _x removal technologies.

The development of efficient catalysts is of great significance for the commercialization of CH ₄ -SCR technology. Zeolite-based catalysts have attracted increasing attention due to their high internal surface area, uniform micropore system, considerable ion exchange capacity, and high thermal stability. Beta molecular sieve has three-dimensional 12-membered ring channels with pore sizes of 0.55×0.55nm and 0.76×0.64nm. It is one of the most important zeolite frameworks in SCR applications and can be used as an effective catalyst carrier. Metals or metal oxides are often incorporated into the zeolite framework to further enhance its catalytic performance. Pan et al. found that the In/H-β catalyst prepared by the indium salt impregnation method has higher catalytic performance in the CH ₄ -SCR system. By further optimizing the preparation conditions, our research group can also prepare a more active In/H-β catalyst.

However, in industrial applications, in addition to considering the catalytic performance of the catalyst itself, factors such as SO ₂ and high concentrations of water vapor that interfere with the SCR process also need to be considered. During the experiment, it was found that the current In/H-β catalyst’s tolerance to sulfur dioxide and water vapor still needs to be improved. In the absence of SO ₂ and H ₂ O, the NO _x removal efficiency can reach more than 90%, but after adding 100 ppm SO ₂ and 5vol.% H ₂ O to the raw steam, the NO _x removal efficiency drops sharply (only about 10 %). Therefore, it is necessary to improve the catalytic performance of In/H-β catalyst in the presence of SO ₂ and H ₂ O by improving the preparation method.

Contents of the invention

This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a preparation method for an In/H-β catalyst that still has good CH ₄ -SCR catalytic performance in the presence of SO ₂ and H ₂ O.

The first aspect of this application provides a preparation method of In/H-β catalyst, which preparation method includes the following steps:

Step 1: Mix and react raw materials including amino acids, silicon sources, aluminum sources, M sources, organic amine templates, and water to obtain a reaction gel;

Step 2: Crystallize the reaction gel, cool, wash, dry and roast to obtain M-β molecular sieve;

Step 3: Mix and react M-β molecular sieve with ammonium salt solution, complete ion exchange, wash, dry and roast to obtain H-β molecular sieve;

Step 4: Mix and react H-β molecular sieve with indium salt solution, complete ion exchange, wash, dry and roast to obtain In/H-β molecular sieve;

Wherein, M is at least one of an alkali metal and an alkaline earth metal.

The preparation method according to the embodiment of the present application has at least the following beneficial effects:

As a guiding agent, amino acids will promote crystallization during the preparation process and enable the final In/H-β catalyst to obtain stronger Acid active center, thus able to show the best _CH4 -SCR catalytic activity and cycle performance under the interference of _SO2 and _H2O .

In some embodiments of the present application, the silicon source is calculated as silica, and the molar ratio of amino acid/silica is 0.1 to 0.5. Furthermore, the molar ratio of proline/silica is preferably 0.15 to 0.45, more preferably 0.2 to 0.4, and even more preferably 0.3.

In some embodiments of the present application, the aluminum source and M source are calculated as oxides, the organic amine template is calculated as quaternary ammonium ions, the molar ratio of silicon dioxide/alumina is 5 to 200, and the molar ratio of M oxide/silica is The molar ratio is 0.01 to 0.4, and the molar ratio of quaternary ammonium ions/silica is 0.1 to 0.8.

In some embodiments of the present application, the molar ratio of water/silica is 5-50.

In some embodiments of the present application, the amino acid is selected from at least one of proline, alanine, glutamic acid, histidine, serine, and arginine.

In some embodiments of the present application, the amino acid is proline.

As a guide agent, amino acids will promote crystallization during the preparation process and generate a certain number of mesopores in the β molecular sieve. The existence of these mesopores will promote the diffusion of reactants and products and thereby improve the catalytic performance. However, during further experiments, the inventor found that the tolerance of the In/H-β catalyst to sulfur dioxide and water vapor is not only limited by the factor of mesopores, but is also related to other physical and chemical properties. Compared with other amino acids, the unique cyclic side chain of proline enables the final prepared In/H-β catalyst to obtain stronger Acid active center, thus able to show the best _CH4 -SCR catalytic activity and cycle performance under the interference of _SO2 and _H2O .

In some embodiments of the present application, the silicon source is selected from at least one of white carbon black, water glass, ethyl orthosilicate, silica sol, silica gel and solid silica gel.

In some embodiments of the present application, the aluminum source is selected from at least one of aluminum salts, aluminates, metaaluminates, aluminum hydroxide, pseudoboehmite, aluminum sec-butoxide, and aluminum isopropoxide.

In some embodiments of the present application, M is selected from at least one of lithium, sodium, potassium, cesium, strontium, calcium, and barium.

In some embodiments of the present application, the source of M is selected from at least one of bases and salts of M, including but not limited to sodium hydroxide, potassium hydroxide, sodium chloride, potassium chloride, etc.

In some embodiments of the present application, the organic amine template is selected from diethylamine, triethylamine, morpholine, tetraethylammonium hydroxide, tetraethylammonium chloride, tetraethylammonium bromide, tetraethylammonium At least one of ammonium iodide and the like.

In some embodiments of the present application, the concentration of indium ions in the indium salt solution is 0.01 to 0.1 mol/L.

In some embodiments of the present application, the crystallization temperature of the reaction gel in step 2 is 100-220°C, and the crystallization time is 5-200 hours.

In some embodiments of the present application, the reaction temperature of the ion exchange reaction in steps 3 to 4 is 70 to 100°C, and the reaction time is 20 min to 12 hours.

In some embodiments of the present application, in step 3, the ion exchange reaction, washing, and drying are repeated 1 to 3 times and then roasted.

In some embodiments of the present application, the calcining temperature in steps 2 to 4 is 400 to 600°C, and the calcining time is 1 to 6 hours.

In some embodiments of the present application, the drying temperature in steps 2 to 4 is 60 to 150°C, and the drying time is 1 to 24 hours.

The second aspect of this application provides an In/H-β catalyst, which is prepared by the aforementioned preparation method.

The third aspect of the present application provides an In/H-β catalyst. The In/H-β catalyst The concentration of acid sites is 50 μmol/g or more. Preferred,/> The concentration of the acid site is 60 μmol/g or more, 70 μmol/g or more, 80 μmol/g or more, 90 μmol/g or more, 100 μmol/g or more, 110 μmol/g or more, or 120 μmol/g or more. /> The concentration of acid sites was calculated from the integrated molar extinction coefficient (IMEC).

In some embodiments of the present application, The concentration ratio of acid sites/Lewis acid sites is above 0.55. Preferred,/> The ratio of acid/Lewis acid is 0.6 or more, 0.65 or more, 0.7 or more, or 0.72 or more. The concentration of Lewis acid sites is also calculated from the integrated molar extinction coefficient (IMEC).

In some embodiments of the present application, the concentration of Lewis acid sites is above 140 μmol/g. Preferably, the concentration of Lewis acid sites is 145 μmol/g or more, 150 μmol/g or more, 155 μmol/g or more, 160 μmol/g or more, or 165 μmol/g or more.

In some embodiments of the application, the In/H-β catalyst has a methane selectivity of more than 80% (detection conditions: the feed gas contains 400ppm NO, 400ppm CH ₄ , 10vol.% O ₂ , 100ppm SO ₂ , 5vol. %H ₂ O, the rest is Ar as the balance gas, the flow rate is 100mL/min, the space velocity is 23600h ^-1 , the programmed temperature rise rate is 4℃/min (100-650℃), the catalyst dosage is 100mg). Furthermore, the methane selectivity is above 85%, above 90%, above 95%, above 98%, above 99%.

In some embodiments of the application, the In/H-β catalyst contains 400ppm NO, 400ppmCH ₄ , 10vol.% O ₂ , 100ppm SO ₂ , 5vol.% H ₂ O in the feed gas, and the rest is Ar as a balance gas, Under the testing conditions of flow rate 100mL/min, space velocity 23600h ^-1 , programmed heating rate 4℃/min (100-650℃), and catalyst dosage 100mg, the performance is more than 30%, more than 35%, more than 38%, more than 40%. nitrogen oxide removal rate. And after three cycles, there are still nitrogen oxide removal rates of more than 30%, more than 35%, more than 36%, and more than 37% at 650°C.

In some embodiments of the present application, the In/H-β catalyst includes an H-β molecular sieve carrier and indium supported on the H-β molecular sieve carrier. More specifically, indium is evenly distributed on the surface and inside of the H-β molecular sieve carrier.

In some embodiments of the present application, the content of indium in the In/H-β catalyst is 2 to 8 wt% of the total mass of the In/H-β catalyst. Preferably, the indium content is above 3wt%, above 3.5wt%, above 4wt%, above 4.5wt%, or above 5wt%. Preferably, the indium content is below 7.5 wt%, below 7.4 wt%, below 7.3 wt%, below 7.2 wt%, or below 7.1 wt%.

In some embodiments of the present application, the Si/Al molar ratio in the In/H-β catalyst is above 25.

In some embodiments of the present application, the In/Al molar ratio in the In/H-β catalyst is above 0.7. Preferably it is 0.71 or more, 0.72 or more, 0.73 or more, 0.74 or more, 0.75 or more, 0.76 or more, 0.77 or more, 0.78 or more, 0.79 or more, and 0.8 or more.

The fourth aspect of this application provides a denitrification method that uses selective catalytic reduction to treat exhaust gas, using CH ₄ as the reducing agent, and the aforementioned In/H-β catalyst as the catalyst.

A fifth aspect of the present application provides a purification treatment device. The purification treatment device includes an SCR reactor, and the SCR reactor is equipped with the aforementioned In/H-β catalyst.

Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application.

Description of the drawings

Figure 1 is the result of the denitrification activity comparative test of the present application. Among them, (a) is the change of nitrogen oxide removal rate with temperature of molecular sieve catalysts prepared by different amino acids, (b) is the change of methane conversion rate with temperature of molecular sieve catalysts prepared by different amino acids, (c) is the change of methane selectivity with temperature of molecular sieve catalysts prepared by different amino acids, (d) is the change of nitrogen oxide removal rate of In/H-β-P molecular sieve catalyst in multiple TPSR cycles. .

Figure 2 is the X-ray of the In/H-β-P, In/H-β-H, In/H-β-R, In/H-β-S and In/H-β-B molecular sieve catalysts of the present application. Diffraction (XRD) pattern results.

Figure 3 is an electron paramagnetic resonance (EPR) spectrum of the In/H-β-P and In/H-β-B molecular sieve catalysts of the present application.

Figure 4 is an electron microscope and imaging result combined with energy dispersive X-ray (EDX) spectrum analysis of the In/H-β-P sample of the present application. Among them, a is the result of scanning electron microscopy, and the scale bar in the figure is 1 μm; b~f is the result of electron microscopy combined with EDX spectrum analysis, the scale bar in the figure is 100 nm, and c~f reflect the element distribution of Al, Si, O, and In respectively.

Figure 5 is the imaging results of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of the In/H-β-P sample of the present application. Among them, the scale in a is 100nm, the scale in b is 50nm, and the lower left corner of b is the lattice stripe with a scale of 10nm.

Figure 6 is the magic angle rotation solid-state nuclear magnetic (MAS NMR) detection results of the In/H-β-P sample of the present application. Among them, a is the result of ²⁹ Si, and b is the result of ²⁷ Al.

Figure 7 is the XPS measurement spectrum of the In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S molecular sieve catalysts of the present application. Among them, a is the In 3d _5/2 spectrum result, and b is the O1s spectrum result.

Figure 8 shows the hydrogen temperature programmed reduction (H ₂ -TPR) of the In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S molecular sieve catalysts of the present application. Below are the reducibility results of In.

Figure 9 is the NH ₃ -TPD curve of the In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S molecular sieve catalysts of the present application.

Figure 10 is the infrared spectrum (Py-IR) of the adsorbed pyridine of the In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S molecular sieve catalysts of the present application. ).

Detailed ways

The concept of the present application and the technical effects produced will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without exerting creative efforts are all The scope of protection of this application.

The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application and cannot be understood as limiting the present application.

In the description of this application, several means one or more, plural means two or more, greater than, less than, exceeding, etc. are understood to exclude the original number, and above, below, within, etc. are understood to include the original number. If there is a description of first and second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the order of indicated technical features. relation.

In the description of this application, reference to the description of the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" is intended to be in conjunction with the description of the embodiment. or examples describe specific features, structures, materials, or characteristics that are included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Example 1

This embodiment provides an In/H-β catalyst, and its preparation method is as follows:

Step 1: Dissolve 0.16g NaAlO ₂ and 0.05g NaOH in 12.5g tetraethylammonium hydroxide (TEAOH, 25%) and 2.6mL deionized water, then add proline (P) under ultrasonic conditions to stir evenly, A mixture is obtained. Then dissolve 2g of fumed silica in the mixture and shake well to obtain a reaction gel. Subsequently, the obtained reaction gel was aged for 4 h at room temperature in a magnetic stirrer, so that the composition in the reaction gel was 0.3 proline: 1.0 SiO ₂ : 0.023 Al ₂ O ₃ : 0.048 Na ₂ O: 0.636 TEAOH in terms of molar ratio. :20H ₂ O.

Step 2: The aged reaction gel is rotated and crystallized in a homogeneous reactor at a temperature of 140°C at a constant speed of 10 rpm for 48 hours. After cooling to room temperature, the dispersion was filtered, rinsed with deionized water to pH=7, and then dried at 80°C for 12 hours. Finally, the powder is calcined in an air atmosphere at 500°C for 3 hours to remove the template agent and obtain Na-β molecular sieve.

Step 3: Perform ion exchange between Na-β molecular sieve and 1M (NH ₄ ) ₂ SO ₄ solution at a solid-liquid mass ratio of 1:20 at 85°C for 4 hours, then filter to separate the solid, wash with distilled water, and incubate at 110 Dry at ℃. This ion exchange procedure was repeated twice to ensure complete cation exchange. Subsequently, it was calcined in an air atmosphere at 500°C for 3 hours to obtain H-β molecular sieve.

Step 4: Dissolve 3g H-β molecular sieve in 100ml 0.033M indium nitrate solution, and perform ion exchange at 85°C for 8h, then filter to separate the solid, wash with distilled water until pH=7, and incubate at 80°C Dry for 12 hours. Subsequently, it was calcined in an air atmosphere at 500°C for 3 hours to obtain In/H-β molecular sieve.

Comparative Examples 1 to 7 provide an In/H-β molecular sieve. The difference between its preparation method and Example 1 is that different amino acids are used, specifically alanine (A), glutamic acid (E), Acid (H), serine (S), threonine (T), arginine (R) and aspartic acid (D). In order to distinguish Example 1 from Comparative Examples 1 to 7, the finally obtained molecular sieve product is followed by the corresponding amino acid abbreviation -P, the products of Comparative Examples 1 to 7 are respectively recorded as In/H-β-A, In/H-β-E, In/H-β-H, In/H-β-S, In/H-β -T, In/H-β-R and In/H-β-D.

Comparative Example 8 provides an In/H-β molecular sieve. The difference between its preparation method and Example 1 is that no amino acid is added in step 1. In addition, due to the absence of the influence of amino acids, the crystallization time in step 2 is extended to 6 days. This molecular sieve is designated as In/H-β-B.

CH ₄ -SCR performance comparison test

The In/H-β-X catalyst was evaluated for selective catalytic reduction of _NOx using a continuous flow fixed-bed reactor. The specific process is as follows:

(1) Make the molecular sieve catalysts prepared in Example 1 and Comparative Examples 1 to 8 into particles at 20 MPa, then grind them, and screen out samples with a particle size of 40-60 mesh (0.250 to 0.425 mm) for the next reaction.

(2) Weigh 100 mg of catalyst sample and put it into the center of the fixed-bed continuous flow reactor. The raw material gas contains 400 ppm NO, 400 ppm CH ₄ , 10 vol.% O ₂ , 100 ppm SO ₂ , 5 vol. % H ₂ O, and the rest is Ar as a balance gas. The raw gas flow rate is 100mL/min, and the space velocity (GHSV) is 23600h ^-1 . The reactor temperature was increased with a temperature gradient of 4°C/min between 100°C and 650°C.

Catalyst activity was monitored using temperature programmed surface reaction (TPSR) technology. NO concentration was measured continuously by a nitrogen oxide analyzer (ThermoScientific, 42i). CH _{concentration} was measured using an online gas chromatograph (GC-2014C, Shimadzu, Japan) equipped with a Porapak-Q column and a flame ionization detector (FID). The N ₂ O content formed during the SCR reaction was analyzed using an Agilent 7890B GC equipped with 5A molecular sieves.

In the CH ₄ -SCR reaction process, the ideal reaction formula is: CH ₄ +2NO+O ₂ =CO ₂ +N ₂ +2H ₂ O. In the presence of oxygen, CH ₄ reduces NO _x to generate nitrogen, water and carbon dioxide. Four indicators are used to evaluate the denitrification activity of the catalyst: nitrogen oxide removal rate (η), methane conversion rate (γ), methane selectivity (α), and nitrogen selectivity (S _N2 ).

In the formula, c(NO _x ) _in is the initial concentration of NO _x before reaction (ppm);

c(NO _x ) _out is the concentration of NO _x after the reaction (ppm);

c(CH ₄ ) _in is the initial concentration of CH ₄ before reaction (ppm);

c(CH ₄ ) _out is the concentration of CH ₄ after the reaction (ppm);

c(N ₂ O) is the concentration of N ₂ O formed (ppm).

The detection results of the denitration activity of Example 1 and Comparative Examples 1 to 8 are shown in Figure 1, where a represents the nitrogen oxide removal rate result. It can be seen from a that the nitrogen oxide removal rates of In/H-β molecular sieves made of different amino acids are also significantly different. When using proline-mediated In/H-β-P, Under the interference of SO ₂ and H ₂ O, the nitrogen oxide removal rate is the highest, which can reach 40%, while the detection results of Comparative Examples 1 to 7 are all less than 30%. Comparative Example 8 did not use amino acids to participate in the reaction, and its nitrogen oxide removal rate was only 10% at the highest under the same conditions. In addition, it can be seen that the nitrogen oxide removal rate of In/H-β-D and In/H-β-T is almost 0 below 600°C. Even at 650°C, the nitrogen oxide removal rate is still only 3%. Less than. Although the nitrogen oxide removal rate of In/H-β-B prepared without adding amino acids is similar to the former two below 600°C, the nitrogen oxide removal rate at 650°C is significantly higher than the first two.

Molecular sieves with a nitrogen oxide removal rate of more than 20% are sorted from high to low according to the nitrogen oxide removal rate as In/H-β-P (40%)>In/H-β-A (29%)>In/ H-β-H (28.7%)>In/H-β-R (25.9%)>In/H-β-S (24.3%)>In/H-β-E (20.4%). Among them, due to the low nitrogen oxide removal rate of In/H-β-A under low temperature conditions, it will not be further characterized, but only In/H-β-P, In/H-β-H, In /H-β-R, In/H-β-S for further study.

As can be seen from Figure 1, b, as the temperature increases, all four molecular sieves show higher _CH4 conversion rates, with no obvious difference between the four catalysts, indicating that methane is the key reducing agent, and in all CH ₄ -The consumption in the SCR reaction is approximately the same. It can be seen from c in Figure 1 that the CH ₄ selectivity of the four molecular sieves first increases and then decreases, with the best methane selectivity around 500°C. Methane selectivity is positively related to catalytic performance, especially in the low temperature region. The methane selectivity of In/H-β-P is the highest at 500°C, reaching 100%. Therefore, at the optimal reaction temperature, In/H-β-P can achieve the ideal stoichiometric reaction of _CH4 and _NOx in _CH4 -SCR. When the temperature continues to increase, the _CH selectivity decreases due to competition from methane side reactions.

In addition, the In/H-β-P catalyst still showed excellent durability in repeated tests under the interference conditions of SO ₂ and H ₂ O. The results are shown in d of Figure 1, from top to bottom, respectively. The results of the nitrogen oxide removal rate during the first cycle (1st), the second cycle (2nd), and the third cycle (3rd). It can be seen from the figure that even under the interference of SO ₂ and H ₂ O, after experiencing three temperature cycles up to 650°C, the nitrogen oxide removal rate remains almost the same, especially in the high temperature area, after three cycles , there is still a nitrogen oxide removal rate of up to 37.9% at 650°C.

Composition and structural characterization

ICP method to measure the indium content and Si/Al ratio of In/H-β-P, In/H-β-H, In/H-β-R, In/H-β-S and In/H-β-B , the results are shown in Table 1.

Table 1. Comparison of element content in molecular sieves

As can be seen from the table, the Si/Al ratio of the catalyst is roughly around 25, which is also close to the ratio of the initial reaction gel. Previous research results have shown that the In/H-β molecular sieve with an indium content of approximately 7wt%, prepared by ion exchange with a 0.033M indium solution, has the best NO removal efficiency. The indium content in the molecular sieve prepared by the above method is in the range of 5.7-7.1wt%, and the indium content from the lowest to the highest is In/H-β-S<In/H-β-P<In/H-β- H<In/H-β-R<In/H-β-B. This trend is inconsistent with the order of catalytic activity of NO in _CH4 -SCR, indicating that the indium loading may not be the key factor leading to high denitrification efficiency. On the other hand, the best denitration catalyst of In/H-β-P has the highest In/Al ratio of 0.8, indicating that it has the highest degree of ion exchange.

Figure 2 shows the X-ray diffraction of In/H-β-P, In/H-β-H, In/H-β-R, In/H-β-S and In/H-β-B molecular sieve catalysts ( XRD) pattern. In In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S, 7.8°, 13.5°, and 21.5 corresponding to H-β molecular sieves can be observed. °, 22.5°, 25.2°, 27.1°, 29.7°, 33.4° and 43.7° characteristic reflections. Therefore, under the action of amino acids, the pure crystalline β phase without impurities can be completely crystallized within 2 days. At the same time, no peak of In ₂ O ₃ was detected, which indicates that indium has been successfully exchanged in the form of extra-framework cations and is in a highly dispersed state, and the amount of indium oxide detected by X-ray diffraction is negligible. The In/H-β-B sample only shows a broad peak at about 32°, indicating that even if the crystallization time is extended by 3 times to 6 days, the amorphous phase still exists in it.

Based on the above results, it is speculated that the addition of amino acids promotes the crystallization of β molecular sieves. Further verification tests are as follows: 5,5-dimethylpyrroline-N-oxide (DMPO) is added to the initially synthesized reaction gel. Comparing the in-situ EPR spectra of Na-β-P gel synthesized with proline and Na-β-B gel synthesized without amino acids, the results are shown in Figure 3. It can be seen from the figure that there are obvious differences between the two. Due to the resonance transition of DMPO-·OH, Na-β-P presents a quadruple mode in the ratio of 1:2:2:1, splitting into 1.5mT, while Na-β-B does not have this characteristic of Na-β-P at all. a pattern. Therefore, the pro-crystallization effect of amino acids may be caused by the induction of free radicals.

The structural properties of molecular sieves were analyzed, and the results are shown in Table 2. Among them, S _BET is the BET surface area, measured by the nitrogen adsorption method when the relative pressure range is 0.05 to 0.3; V _total is the total pore volume, calculated from the amount of nitrogen adsorbed when P/P ₀ = 0.98; V _meso is the medium The pore volume is calculated by the t-plot method; d _meso is the mesopore diameter, which is calculated by the BJH method.

Table 2. Molecular sieve structure analysis results

As can be seen from the table, In/H-β-P shows the highest mesopore volume of 0.27cm ³ /g and the highest total pore volume of 0.42cm ³ /g; followed by In/H-β-S and In/H -β-R. The possible reasons why In/H-β-P has the highest mesopore volume and total pore volume are its better compatibility with molecular sieve synthesis and the special stability of the unique cyclic side chain of the proline molecule. However, it can be seen that the mesopore size of molecular sieves is not completely consistent with its nitrogen oxide removal rate and methane selectivity.

Scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) spectrum was used to analyze the nanoscale morphology and composition of the In/H-β-P sample. The results are shown in Figure 4, where a is the result of the scanning electron microscope, and b~ f is the quantitative analysis result of the EDX spectrum. It can be clearly observed from the figure that uniform nanoparticles with an average grain size of ~150nm are observed. Al, Si and O elements are evenly distributed in the molecular sieve, while In is also relatively uniform throughout the molecular sieve. Geographically distributed, but slightly aggregated on the surface. According to the EDX analysis results, the weight concentration of indium is approximately 6%, which is consistent with the ICP analysis results, confirming that indium is evenly distributed on the surface and interior of the crystal.

Transmission electron microscopy (TEM) imaging was performed on the In/H-β-P sample. The results are shown in Figure 5a, indicating the mosaic structure of the In/H-β-P molecular sieve, in which there are a large number of microstructures with a size of 10-20 nm. The crystals co-generate medium crystals, forming obvious nanometer mesopores with clear edges. Further inspection was carried out by high-resolution TEM (HRTEM), and the results, shown in Figure 5, b, indicate that the particles are fully crystalline, as evidenced by the large number of lattice fringes spread across the specimen (b, lower left inset). The presence of these mesopores allows easy transportation of reactants and products while preventing side reactions. Therefore, the modulation of proline resulted in In/H-β-P showing more exposed active catalytic sites. These active catalytic sites can enhance hydrothermal stability and resistance to toxicity.

Magic angle rotation solid-state nuclear magnetic resonance (MAS NMR) was used to detect the coordination structure of the In/H-β-P sample. The results are shown in Figure 6, where a is the result of ²⁹ Si and b is the result of ²⁷ Al. As can be seen from a, ²⁹ Si MAS NMR shows a main peak at -110.8ppm and a shoulder peak at -102.6ppm. The former is a characteristic of the unique silicon tetrahedral structure in the H-β lattice, and the latter is due to Hydrolysis of the Si-O-Al(Si) bond, corresponding to Si-OH-Al(Si). The peak width around -110.8 ppm may be due to different Si sites in the β framework. Si-OH-Al(Si) is usually considered to be the source of acid sites on In/H-β catalysts. As can be seen from b, ²⁷ Al MAS NMR shows two main peaks at 54.8 and 57.6 ppm, corresponding to the tetrahedral coordination in β zeolite at T1-T2 and T3-T9 framework aluminum positions, respectively. These tetrahedrally coordinated Al sites, with a charge of 3+, produce a negatively charged skeleton that is compensated by exchangeable cations such as In-containing cations. The weak peak close to 0 ppm indicates that the octahedral aluminum content in In/H-β-P is negligible.

Chemical states and redox experiments

Photoelectron spectroscopy (XPS) results of In/H-β-P, In/H-β-H, In/H-β-R, In/H-β-S and In/H-β-B are shown in Figure 7 is shown, where a is the measurement result of the In 3d _5/2 spectrum, from which it can be seen that the three chemical states of indium correspond to In ₂ O ₃ at about 445eV, InO ⁺ at about 446eV, and In(OH at about 447eV). ) _3-z ^z+ . Table 3 compares the curve-fit contents of these indium states, showing that the proportions of the three indium species in the four catalysts are nearly identical. The exchanged InO ⁺ and In(OH) _3-z ^z+ are the main types of indium, and the exchanged InO ⁺ species are the active sites of the CH4 _- SCR reaction. On the other hand, the binding energy (BE) values of In/H-β-X catalysts vary among different catalysts. For In/H-β-P, the BE values of the three types of indium are the highest, indicating that indium has a stronger interaction with the proline-modulated beta zeolite framework.

b is the measurement result of O1s spectrum. It can be seen from the figure that it is deconvoluted into two main peaks at 532.7eV and 533.6eV, corresponding to different forms of oxygen on the surface: surface oxygen of _Oβ and hydroxyl group of _Oγ of oxygen. Due to its high mobility, _Oβ can participate in the oxidation process, which plays a key role in the SCR of NO. Through deconvolution and curve fitting, the O _β /(O _β + O _γ ) ratio in the sample was obtained. The results are referred to Table 3. There is no significant difference in the narrow range between 0.57-0.59. Therefore, different amino acid mediations will not change the chemical valence state of oxygen elements on the catalyst surface.

Table 3. Chemical state of surface elements of molecular sieve catalysts

Hydrogen temperature programmed reduction (H ₂ -TPR) was used to study the reducing properties of In in different molecular sieve samples. The results are shown in Figure 8. As can be seen from the figure, all samples exhibit a broad reduction signal between 200°C and 500°C, with peaks concentrated at 300-400°C. This result indicates that there is no bulk In ₂ O ₃ that requires a higher reduction temperature. , indicating from the side that the incorporated In ³⁺ is in a highly dispersed state. The reduction peak of In/H-β-P appears at the highest temperature centered at ~365°C, indicating that its reduction temperature requirement is higher. This may indicate that the electronic interaction between indium and the zeolite framework is stronger, thereby delaying the reduction of indium oxide. .

Surface acidity experiment

Previous results have shown that adjusting the Si/Al ratio in H-β molecular sieve catalysts changes the number of acid sites in the composite in metal oxide/β catalysts. However, in this scheme, the Si/Al ratio remains around ∼25 in all H-β-X samples. XPS spectra and H ₂ -TPR results also prove that their surface indium and oxygen species are similar. The stronger interaction of the indium species with the In/H-β-P framework revealed by the high binding energy suggests that proline may improve the zeolite properties. Therefore, its surface acidity was further investigated.

The NH ₃ -TPD curves of In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S catalysts are shown in Figure 9. These NH ₃ -TPD curves can be decomposed into peak I located below 200°C, corresponding to weak acid sites; peak II located between 200-350°C, corresponding to medium acid sites; peak III located between 350-650°C, Corresponds to strong acid sites. Table 4 shows the fitting results of the NH ₃ -TPD curve. It can be seen that In/H-β-P has the highest number of acid sites, especially strong acid sites. The order of acid number is In/H-β-P, In/H-β-H, In/H-β-R and In/H-β-S, which is closely related to the CH ₄ -SCR performance reflected in Figure 1 Related, confirming the important role of acid sites in denitration catalysis.

Table 4. Number and distribution of acid sites on the surface of molecular sieve catalysts

a: Peak corresponding temperature (°C).

b: Peak area (a.u.).

c: Calculation method: Integrated molar extinction coefficient (IMEC).

Pyridine (Py) has higher selectivity and stability than _NH3 and can be easily distinguished by FTIR spectroscopy sted and Lewis acidic sites. The infrared spectra (Py-IR) of adsorbed pyridine on the four catalysts are shown in Figure 10. The bands around 1540cm ^-1 and 1450cm ^-1 respectively correspond to the adsorption of pyridine on/> The pyridinium ion (PyH+) formed at the acid site and the pyridine interacting with the Lewis acid site. The band at 1490cm ^-1 is formed by the interaction of PyH+ and pyridine coordinated with Lewis acid. Estimated based on the spectral bands at 1540cm ^-1 and 1450cm ^-1 /> The amount of acid, Lewis acid and B/L, the results are shown in Table 4. Consistent with the NH ₃ -TPD results,/> The order of acid amount and B/L ratio is In/H-β-P>In/H-β-H>In/H-β-R>In/H-β-S, which is positively correlated with catalytic activity. Therefore, in CH ₄ -SCR using In/H-β catalyst, the number of strong acid sites and/> The density of the acid centers plays a crucial role. In addition, combined with the data in Table 2, it can be seen that the mediated effect of amino acids adjusts the catalytic activity of the molecular sieve without affecting the silicon-aluminum ratio of the framework.

Combining the NH ₃ -TPD and Py-IR results, the reason why the In/H-β-P catalyst shows the best CH ₄ -SCR activity is that it has stronger The acid active center thus facilitates stronger interactions with indium oxide and indium hydroxy species. In addition, the FT-IR spectra of In/H-β-P and proline were compared. The characteristic FT-IR peak of proline was not found in In/H-β-P. Therefore, proline is only synthesized in In/H-β-P. stage interacts with the beta molecular sieve framework, which has been completely removed by subsequent washing and roasting steps. That is, the addition of proline only adjusts the acidity of the generated catalyst, but will not be added to the final catalyst.

Example 2

This embodiment provides a method for preparing an In/H-β catalyst. The difference from Example 1 is that the crystallization temperature is 220°C and the crystallization time is 48 hours. The In/H-β catalyst prepared by this method was found to maintain a high nitrogen oxide removal rate and methane selectivity under the interference of SO ₂ and H ₂ O using the same detection conditions mentioned above.

Examples 3 to 6

Examples 3 to 6 respectively provide a method for preparing an In/H-β catalyst. The difference from Example 1 is that the amount of proline is adjusted so that the molar ratio of proline to silica in the reaction gel after aging is are 0.1, 0.2, 0.4, 0.5. Referring to the above method for testing, it was found that under the interference of SO ₂ and H ₂ O, compared with the preparation method using other amino acids or not using amino acids under the same conditions, the molecular sieve catalysts prepared in Examples 3 to 6 also maintained a higher nitrogen oxide removal rate and methane selectivity.

Examples 7 to 9

Examples 7 to 9 respectively provide a method for preparing an In/H-β catalyst. The difference from Example 1 is that the concentrations of the indium nitrate solution are adjusted to 0.01M, 0.06M and 0.1M respectively. The In/H-β catalyst prepared by these methods was found to maintain a high nitrogen oxide removal rate and methane selectivity under the interference of SO ₂ and H ₂ O using the same detection conditions mentioned above.

Example 10

This embodiment provides an exhaust gas treatment device. The exhaust gas treatment device includes at least one SCR reactor. One end of the SCR reactor is connected to an input flow system. The input flow system includes a plurality of inlets, respectively for supplying water into the SCR reactor. Introduce methane and waste gas. The In/H-β catalyst prepared by any one of the methods in Examples 1 to 9 is also pre-installed in the SCR reactor.

The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above-mentioned embodiments. Various changes can be made within the knowledge scope of those of ordinary skill in the art without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments may be combined with each other without conflict.

Claims (9)

1. The preparation method of In/H-β catalyst is characterized by comprising the following steps: Step 1: Mix and react raw materials including amino acids, silicon sources, aluminum sources, M sources, organic amine templates, and water to obtain a reaction gel; Step 2: Crystallize the reaction gel, cool, wash, dry and roast to obtain M-β molecular sieve; Step 3: Mix and react M-β molecular sieve with ammonium salt solution, complete ion exchange, wash, dry and roast to obtain H-β molecular sieve; Step 4: Mix and react H-β molecular sieve with indium salt solution, complete ion exchange, wash, dry and roast to obtain In/H-β molecular sieve; Wherein, M is at least one of an alkali metal and an alkaline earth metal, and the amino acid is proline. 2. The preparation method according to claim 1, characterized in that, in the reaction gel, the silicon source has a molar ratio of amino acid/silica calculated as silica from 0.1 to 0.5. 3. The preparation method according to claim 2, characterized in that the aluminum source and the M source are calculated as oxides, the organic amine template agent is calculated as quaternary ammonium ions, and the mole of silicon dioxide/alumina The ratio is 5~200, the molar ratio of M oxide/silica is 0.01~0.4, and the molar ratio of quaternary ammonium ions/silica is 0.1~0.8. 4. The preparation method according to any one of claims 1 to 3, characterized in that in steps 2 to 4, the roasting temperature is 400-600°C, and the roasting time is 1-6 hours. 5. In/H-β catalyst prepared by the preparation method according to any one of claims 1 to 4. 6. The In/H-β catalyst according to claim 5, characterized in that the concentration of Brønsted acid sites is above 50 μmol/g. 7. The In/H-β catalyst according to claim 6, characterized in that the concentration ratio of Brønsted acid sites/Lewis acid sites is above 0.55. 8. Denitrification method, characterized in that the exhaust gas is treated by selective catalytic reduction, CH4 is used as the reducing agent, and the In/H-β catalyst according to any one of claims 5 to 7 is selected as the catalyst. 9. Purification treatment device, characterized in that it includes an SCR reactor, and the SCR reactor is equipped with the In/H-β catalyst according to any one of claims 5 to 7.