CN112973770A

CN112973770A - Nitrogen oxide methane selective catalytic reduction catalyst and application method thereof

Info

Publication number: CN112973770A
Application number: CN202110109963.5A
Authority: CN
Inventors: 武光军; 杨俊�; 常煜鹏; 戴卫理; 关乃佳; 李兰冬
Original assignee: Nankai Cangzhou Bohai New Area Green Chemical Research Co ltd
Current assignee: Nankai Cangzhou Bohai New Area Green Chemical Research Co ltd
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2021-06-18
Anticipated expiration: 2041-01-27
Also published as: CN112973770B

Abstract

The invention provides a nitrogen oxide methane selective catalytic reduction catalyst and an application method thereof. The catalyst is prepared by taking rare earth Ce and metal Ga as active components and taking molecular sieves (MFI, CHA and BEA) as carriers through an organic acid-assisted impregnation method. The catalyst can be used for converting nitrogen oxides into harmless nitrogen under the condition of oxygen enrichment by using methane as a reducing agent. The reaction conditions are as follows: the reaction temperature is 350-^‑1. The prepared catalyst not only has good activity and hydrothermal stability, but also has the advantages of simple and easy operation of preparation process, long catalytic life and the like, and the influence of water vapor on the reaction activity of the catalyst is reversible, so that the catalyst is suitable for large-scale industrial application and popularization。

Description

Nitrogen oxide methane selective catalytic reduction catalyst and application method thereof

Technical Field

The invention belongs to the field of catalysts, and relates to a nitrogen oxide methane selective catalytic reduction catalyst and application thereof, in particular to preparation of a bimetallic molecular sieve catalyst and application thereof in selective catalytic reduction of nitrogen oxide methane.

Background

Nitrogen oxides (NOx) are one of the major atmospheric pollutants and have caused a number of environmental problems. Catalytic Reduction (SCR) is a method for reducing nitrogen oxides to harmless nitrogen under the action of a specific catalyst, is a main method for removing and purifying nitrogen oxides, and is widely used. The primary reductant for current catalytic reduction processes is ammonia (NH)₃) I.e. NH₃-SCR. However, ammonia has a certain toxicity and strong corrosivity, and has high storage and transportation costs. Natural gas as a clean fuel contains methane (CH) as the main component₄). In the context of the large scale advancement of coal-fired boilers "coal-to-gas", in recent years, CH has been used₄Selective catalytic reduction of nitrogen oxides (CH) for a reductant₄SCR) are receiving increasing attention. But due to CH₄High dissociation energy of valence bond, therefore, finding a compound capable of activating CH₄Catalyst of (2) is CH₄One difficulty in SCR research. In recent years, zeolite molecular sieve catalysts supported by Co, In and Pd metals have been used on CH₄Excellent denitration activity is shown in SCR reaction. The applicant discloses In an issued patent (patent number CN201711315106.0) a molecular sieve catalyst for methane selective catalytic reduction, the main active components of which are bimetal Cr-In and Ru-In, an H-SSZ-13 molecular sieve is taken as a carrier, and the catalyst is prepared by adding a catalyst carrier into a reactor, wherein the catalyst carrier is a catalyst carrier prepared by adding₄SCR shows better catalytic performance. However, considering that the metal Cr has certain biotoxicity and is not friendly to the environment, and the metal Ru is a noble metal and has higher price, therefore, the high-CH-content metal Ru has been developed₄The non-noble metal catalyst with SCR activity and without Cr has very important practical significance and application value.

Disclosure of Invention

The invention aims to provide an environment-friendly nitrogen oxideA selective catalytic reduction catalyst for methane and an application method thereof. The catalyst takes bimetal Ce-Ga as an active component, does not contain toxic metals such as Cr and the like and noble metals, takes a zeolite molecular sieve as a carrier, and is applied to CH for the first time₄-in an SCR reaction. Under the synergistic effect of Ce and Ga species, the Ce-Ga/molecular sieve catalyst is in CH₄SCR shows high activity and stability. The catalyst has simple preparation process, easy operation and long reaction life, and is suitable for large-scale application in industrial production.

The invention provides a selective catalytic reduction catalyst for nitrogen oxide methane. The catalyst is prepared by taking soluble gallium salt and soluble cerium salt as raw materials and taking a molecular sieve as a carrier through an organic acid-assisted impregnation method. The catalyst comprises the following components in percentage by mass:

2 to 5 percent of metal Ga

1 to 4 percent of metal Ce

91-97% of molecular sieve

Wherein, the molecular sieve is a silicon-aluminum molecular sieve and a silicon-phosphorus-aluminum molecular sieve with MFI, BEA and CHA structures.

Preferably, the molecular sieve is a ZSM-5 molecular sieve, and Si/Al is 25-35.

The organic acid is any one of citric acid, glutamic acid or salicylic acid, and the molar ratio is that the organic acid: (Ce + Ga) is 0 to 1.5.

Preferably, the organic acid is citric acid, and the molar ratio of the organic acid: (Ce + Ga) ═ 1.

Further preferably, H₂H-ZSM-5 (100 wt.%), Ce (0.02 wt.%), Ga (0.04 wt.%), and citric acid (Ga + Ce) (1 mol.%).

The soluble gallium salt is gallium nitrate and gallium chloride, and the soluble cerium salt is cerium nitrate, cerium chloride, cerium sulfate and cerium acetate.

The invention provides a nitrogen oxide methane selective catalytic reduction catalyst, and a preparation method thereof comprises the following steps:

(1) dissolving organic acid in measured water, adding measured soluble gallium salt and soluble cerium salt, violently stirring for 0.3-2 hours, adding measured molecular sieve carrier, and continuously stirring for 6-24 hours to obtain uniformly mixed slurry.

(2) Evaporating the mixed slurry to dryness at low temperature, and drying at 80-120 ℃ for 6-20 hours;

(3) the product obtained in the step (2) is mixed with 10% H₂Reducing in Ar at 300-800 deg.C for 0.5-2 hr, and then adding 10% O₂Oxidizing in Ar for 0.5-2 hours at 200-500 ℃;

(4) and (4) directly extruding and forming the product obtained in the step (3) to obtain a formed catalyst, or coating the formed catalyst on cordierite ceramic or metal corrugated plates with fixed shapes to obtain a monolithic catalyst.

The invention provides a nitrogen oxide methane selective catalytic reduction catalyst, and an application method thereof comprises the following steps:

(1) placing the shaped catalyst or monolithic catalyst in a fixed bed reactor at 10% O₂Pretreating for 1 hour at 300-400 ℃ in an Ar atmosphere;

(2) the temperature of the reactor is raised to 300-600 ℃ for CH₄SCR reaction, wherein the concentration of nitrogen oxide at the reaction inlet is 100-2000ppm, the molar ratio of methane to nitrogen oxide is 1-3, and the volume space velocity of the reaction is 1000-100000h^-1。

Preferably, the volume space velocity of the reaction is 40000-60000 h^-1. The methane/nitrogen oxide molar ratio was 1.45.

The catalyst for selective catalytic reduction of nitrogen oxides methane provided by the invention can be used for formula treatment of fixed source nitrogen oxides, such as flue gas denitration processes of boilers in thermal power plants, steel plants, cement plants and the like.

The invention provides a selective catalytic reduction catalyst for nitrogen oxide methane, which is prepared from CH₄High activity and stability in the SCR reaction. The catalyst has simple preparation process, easy operation and long reaction life.

Compared with the prior art, the invention also has the following advantages and effects:

(1) the catalyst shows excellent nitrogen oxide purification effect, and the nitrogen oxide purification efficiency can reach more than 95% at most;

(2) the catalyst component is environment-friendly and does not contain noble metal, and the preparation cost is low;

(3) the influence of the water vapor on the reaction activity of the catalyst is reversible, and the activity can be recovered after water removal.

Drawings

FIG. 1 is an XRD spectrum of a Ce-Ga/H-ZSM-5 catalyst prepared by a citric acid auxiliary impregnation method;

FIG. 2a is an SEM photograph of an H-ZSM-5 catalyst;

FIG. 2b is an SEM photograph of a Ce-Ga/H-ZSM-5 catalyst prepared by a citric acid assisted impregnation method;

FIG. 3 is CH of Ce-Ga/H-ZSM-5 catalyst prepared by citric acid auxiliary impregnation method₄-SCR reaction activity profile;

FIG. 4 is a Ce-Ga/H-ZSM-5 catalyst in CH₄-water vapor stability test patterns in SCR reactions;

FIG. 5a is CH for 3% single component Ga/H-ZSM-5 catalyst₄-SCR reaction activity profile;

FIG. 5b is CH for 4% single component Ga/H-ZSM-5 catalyst₄-SCR reaction activity profile;

FIG. 5c is CH for 5% single component Ga/H-ZSM-5 catalyst₄-SCR reaction activity profile.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

Technical terms in the present invention are defined in the following, and terms not defined are understood in the ordinary sense in the art.

Example 1:

(1) preparation of Ce-Ga/H-ZSM-5 catalyst

The raw materials are as follows: h₂O H-ZSM-5 (mass ratio) 100, Ce H-ZSM-5 (mass ratio) 0.02, Ga H-ZSM-5 (mass ratio) 0.04, citric acid (Ga + Ce) 1 (molar ratio)

Dissolving metered citric acid in water, adding metered gallium nitrate and cerium nitrate, violently stirring for 0.5 hour, adding H-ZSM-5(Si/Al is 28) powder, and continuously stirring for 24 hours to obtain uniformly mixed slurry; evaporating the mixed slurry to dryness at low temperature, and drying in an oven at 90 ℃ for 15 hours; the dried sample was at 10% H₂Reduction in Ar at 650 ℃ for 1 hour at 10% O₂Oxidizing in Ar at 350 ℃ for 1 hour, cooling to room temperature, and directly extruding and molding the sample.

(2) Catalyst Ce-Ga/H-ZSM-5 in CH₄Application to SCR reactions

0.12g of 20-40 mesh shaped catalyst is weighed and placed in a fixed bed reactor under 10% of O₂After pretreatment for 1 hour at 350 ℃ in the Ar atmosphere, the temperature of the reactor is adjusted to 300 ℃, and reaction mixed gas is introduced, wherein the space velocity of the reaction volume is 60000h^-1The balance gas comprises the following components in percentage by weight: NO-2750 ppm, CH₄4000ppm, i.e. a methane/nitrogen oxide molar ratio of about 1.45, O₂＝4％，H₂O is 6%, He is balance gas; detecting a data point in the reaction process every 50 ℃, recording the temperature range of 300-_XThe analyzer (Ecotech EC9841) and the gas chromatograph record the reaction data at different temperatures, and the results are shown in fig. 3.

The catalyst results show that the conversion rate of nitrogen oxides increases with the increase of the reaction temperature, when the reaction temperature exceeds 450 ℃, the conversion rate of nitrogen oxides into nitrogen is close to 90%, and when the reaction temperature exceeds 550 ℃, the conversion rate can reach more than 95%, as shown in table 1.

Example 2:

the procedure was followed as for the starting materials and procedures in example 1, except that citric acid was used in an amount of 0, i.e., no organic acid was added; the catalyst is as in example 1 in CH₄Application method of SCR reaction, the results show that nitrogen oxides generate nitrogen at 550 ℃The conversion was about 77%, as shown in table 1.

Example 3:

the procedure is as in example 1 except that the fixed Ga content is 4% and the modulated Ce metal loading is 1%, and the catalyst is in CH as in example 1₄The results of the application of the SCR reaction show a conversion of nitrogen oxides to nitrogen of 70% at 550 ℃.

Example 4:

the starting materials and procedures of example 1 were followed except that the co-impregnated organic acids were changed to glutamic acid and salicylic acid; the catalyst is as in example 1 in CH₄The results of the application of the SCR reaction are shown in Table 1. As can be seen from the table, the catalytic activity of the catalyst can be obviously improved by using the organic acid for auxiliary impregnation, wherein the citric acid has the best effect of improving the citric acid to about 95 percent at 550 ℃ from 77 percent when the organic acid is not added, and the glutamic acid has the effect of reaching 84 percent at most and the salicylic acid has the worst effect of improving the salicylic acid by about 2 percent.

Table 1: organic acid double-metal Ce-Ga/H-ZSM-5 catalyst NO_xEffect of conversion

Example 5:

the raw materials and procedure of example 1 were followed except that the citric acid/metal (Ga + Ce) molar ratio was adjusted to 0.5 and 1.5; the catalyst is as in example 1 in CH₄The results of the application of the SCR reaction are shown in Table 2. When the mole ratio of citric acid to metal (Ga + Ce) is 0.5, the conversion rate of nitrogen oxide to nitrogen at 550 ℃ can reach 83%; when the citric acid/metal (Ga + Ce) molar ratio is 1.5, the conversion rate of nitrogen oxide generating nitrogen at 550 ℃ can also reach 80%. But both less than the conversion of a citric acid/metal (Ga + Ce) molar ratio of 1And (4) rate.

Table 2: citric acid dosage to bimetallic Ce-Ga/H-ZSM-5 catalyst NO_xEffect of conversion

Example 6:

the procedure of example 1 was followed except that the molecular sieve support was changed to a CHA structure molecular sieve, i.e., an H-SSZ-13(Si/Al ═ 24) molecular sieve; the catalyst is as in example 1 in CH₄The results of the application method of the SCR reaction show that the conversion rate of nitrogen oxides into nitrogen at 550 ℃ is about 82 percent and is less than that of H-ZSM-5 molecular sieve.

Example 7:

the raw materials and steps in example 1 were followed to obtain 2% Ce-4% Ga/H-ZSM-5 catalyst; the catalyst is as in example 1 in CH₄Application method of SCR reaction, except that the space velocity of the reaction volume is respectively adjusted to 40000h^-1And 90000h^-1The results show that the conversion of nitrogen oxides to nitrogen at 550 ℃ is 90% and 72%, respectively.

Example 8:

the raw materials and steps in example 1 were followed to obtain 2% Ce-4% Ga/H-ZSM-5 catalyst; the catalyst is as in example 1 in CH₄Application method of SCR reaction, except that in the reaction mixture, CH₄The contents of the components were adjusted to 2750ppm and 5500ppm, i.e., the molar ratio of methane to nitrogen oxides was adjusted to 1 and 2, and the results showed that the conversion of nitrogen oxides to nitrogen at 550 ℃ was 85% and 81%, respectively.

Example 9: stability test of catalyst

The raw materials and steps in example 1 were followed to obtain 2% Ce-4% Ga/H-ZSM-5 catalyst; the catalyst is as in example 1 in CH₄The SCR reaction is carried out using H in the reaction mixture₂The content of the O component was adjusted to 0 or 6%, whereby the effect of water vapor on the catalyst performance was examined.

FIG. 4 is a Ce-Ga/H-ZSM-5 catalyst in CH₄Water vapor stability test in SCR reactions. As can be seen from the figure, when NO water vapor was present in the reaction system, NO was converted to N within the first 30 hours₂The conversion of (a) was maintained at about 92%; when 6% of water vapor is introduced into the reaction system, NO is converted into N₂The conversion rate of (A) is reduced to only about 89%, and can be maintained for 150 hours; when the water vapor in the mixed gas is removed again, NO is converted into N₂Can be substantially restored to the level of the anhydrous state. The results show that the influence of water vapor on the reaction activity of the catalyst is reversible, and the catalyst has excellent stability.

Comparative example 1: CH of single-component Ga/H-ZSM-5 catalyst₄-SCR activity

Single-component Ga/H-ZSM-5 catalysts having metal Ga loadings of 3%, 4% and 5% were prepared according to the raw materials and procedures of example 1, except that only metal Ga was added without adding metal Ce, and Ga: H-ZSM-5 was mixed at ratios (mass ratios) of 0.03, 0.04 and 0.05; the catalyst is as in example 1 in CH₄The results of the application of the SCR reaction are shown in FIG. 5, and it can be seen that NO is converted into N₂The highest conversions of 59%, 49% and 52%, respectively, are much lower than those of the bicomponent Ce-Ga/H-ZSM-5 catalyst.

Claims

1. A nitrogen oxide methane selective catalytic reduction catalyst is characterized in that: the catalyst is prepared by taking soluble gallium salt and soluble cerium salt as raw materials and a molecular sieve as a carrier through an organic acid assisted impregnation method, and comprises the following components in percentage by mass:

1 to 4 percent of metal Ce

2 to 5 percent of metal Ga

91-97% of molecular sieve

2. The catalyst of claim 1, wherein: the preparation method comprises the following steps:

(1) adding soluble gallium salt and soluble cerium salt into an organic acid aqueous solution according to the measurement, adding a molecular sieve carrier after violently stirring for 0.3-2 hours, and continuously stirring for 6-24 hours to obtain uniform mixed slurry;

3. The catalyst according to claim 1 or 2, characterized in that: the organic acid is any one of citric acid, glutamic acid or salicylic acid, and the molar ratio is that the organic acid: (Ce + Ga) is 0 to 1.5.

4. The catalyst of claim 3, wherein: the organic acid is citric acid, and the molar ratio is that the organic acid: (Ce + Ga) ═ 1.

5. The catalyst according to claim 1 or 2, characterized in that: the molecular sieve is a ZSM-5 molecular sieve, and Si/Al is 25-35.

6. The catalyst of claim 5, wherein: h₂H-ZSM-5 (100 wt.%), Ce (0.02 wt.%), Ga (0.04 wt.%), and citric acid (Ga + Ce) (1 mol.%).

7. The catalyst according to claim 1 or 2, characterized in that: the soluble gallium salt is one or a mixture of more than two of gallium nitrate and gallium chloride; the soluble cerium salt is one or a mixture of more than two of cerium nitrate, cerium chloride, cerium sulfate and cerium acetate.

8. The method for using the catalyst according to claim 1, wherein: the method comprises the following steps: placing the formed catalyst or monolithic catalyst into a fixed bed reactor, and adding 10% of O₂Pre-treating for 1 hour at 300-400 ℃ by/Ar, and then carrying out CH₄-an SCR reaction; the reaction temperature is 300-600 ℃, the concentration of nitrogen oxide at the reaction inlet is 100-2000ppm, the molar ratio of methane to nitrogen oxide is 1-3, and the volume space velocity of the reaction is 1000-100000h^-1。

9. The method for using the catalyst according to claim 8, wherein: the volume space velocity of the reaction is 40000-60000 h^-1。

10. The method for using the catalyst according to claim 8, wherein: the methane/nitrogen oxide molar ratio was 1.45.