CN116550379A

CN116550379A - Exhaust gas treatment catalyst and preparation method and application thereof

Info

Publication number: CN116550379A
Application number: CN202310833718.8A
Authority: CN
Inventors: 李振国; 李凯祥; 吴志新; 任晓宁; 杨正军; 颜燕; 邵元凯; 吴撼明; 闫峰; 王懋譞; 周冰洁; 刘亚涛
Original assignee: China Automotive Technology and Research Center Co Ltd; CATARC Automotive Test Center Tianjin Co Ltd
Current assignee: China Automotive Technology and Research Center Co Ltd; CATARC Automotive Test Center Tianjin Co Ltd
Priority date: 2023-07-10
Filing date: 2023-07-10
Publication date: 2023-08-08
Anticipated expiration: 2043-07-10
Also published as: CN116550379B

Abstract

The invention relates to the technical field of catalysts, and in particular provides an exhaust gas treatment catalyst, a preparation method and application thereof, wherein the preparation method comprises the following steps: adding a silicon source into the aqueous solution of the structure directing agent to form a mixture, and stirring until the silicon source is completely hydrolyzed and the mixture becomes transparent to obtain molecular sieve matrix liquid; dissolving soluble active metal salt in a complexing agent solution to obtain a metal complex solution; dropwise adding the metal complex solution into the molecular sieve base body fluid, stirring until no precipitate exists visually, continuously adding the hydrophobic compound, and stirring to obtain a precursor solution; crystallizing and centrifuging the precursor solution, and drying and roasting the solid obtained after centrifugation to obtain a tail gas treatment catalyst; the tail gas treatment catalyst comprises a hydrophobic molecular sieve and a metal complex embedded in the hydrophobic molecular sieve. The prepared catalyst has high-temperature activity and high-temperature hydrothermal stability, is very suitable for purifying tail gas with high temperature and high steam content, and has good catalytic performance.

Description

Exhaust gas treatment catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of catalysts, in particular to a tail gas treatment catalyst and a preparation method and application thereof.

Background

Tail for ammonia-hydrogen dual-fuel engineIn terms of gas emissions, the technology of selective catalytic reduction SCR (Selective Catalyst Reduction) acts as internationally recognized NO _x Processing techniques have been widely used in a number of countries. Catalysts are the core and key of SCR technology. Vanadium-based catalyst (V) using titanium tungsten powder as carrier ₂ O ₅ -WO ₃ /TiO ₂ ) The catalyst has wide application in China, but has the problems of high toxicity, low-temperature conversion rate, poor high-temperature selectivity and the like. With the advent of molecular sieve catalysts, copper-based and iron-based molecular sieve catalysts were successively investigated for the removal of NO by SCR technology _x The molecular sieve catalyst has higher activity.

However, for the new hydrogen-ammonia dual-fuel engine, because the exhaust conditions are greatly different from those of the traditional diesel vehicle, the molecular sieve catalyst is easy to deactivate when purifying the tail gas of the hydrogen-ammonia dual-fuel engine, and the catalytic performance is poor, so that a catalyst suitable for treating the tail gas of the hydrogen-ammonia dual-fuel engine is needed.

Disclosure of Invention

In view of the above, the present invention aims to provide an exhaust gas treatment catalyst, and a preparation method and application thereof.

Based on the above object, a first aspect of the present invention provides a method for preparing an exhaust gas treatment catalyst, comprising:

adding a silicon source into the aqueous solution of the structure directing agent to form a mixture, and stirring until the mixture becomes transparent to obtain molecular sieve matrix liquid;

dissolving soluble active metal salt in a complexing agent solution to obtain a metal complex solution;

dropwise adding the metal complex solution into the molecular sieve base fluid, stirring until no precipitate exists visually, continuously adding a hydrophobic compound, and stirring to obtain a precursor solution;

crystallizing and centrifuging the precursor solution, and drying and roasting the solid obtained after centrifuging to obtain a tail gas treatment catalyst;

the tail gas treatment catalyst comprises a hydrophobic molecular sieve and a metal complex embedded in the hydrophobic molecular sieve.

Optionally, the metal complex solution is added dropwise to the molecular sieve base body fluid, stirred until no precipitation is observed visually, and the hydrophobic compound is continuously added, and stirred to obtain a precursor solution, wherein the method comprises the following steps:

and (3) dropwise adding the metal complex solution into the molecular sieve base fluid, stirring until no precipitate exists visually, adding methanol and/or ethanol, stirring, continuously adding a hydrophobic compound, and stirring to obtain a precursor solution.

Optionally, the molar ratio of the silicon source, the structure guiding agent and the water is 0.5-1.25: 0.2 to 1.0: 10-100, wherein the mole ratio of the soluble active metal salt to the complexing agent to the hydrophobic compound is 0.001-0.1: 0.05-0.5: 0.01-0.1.

Optionally, the hydrophobic compound comprises a hydrophobic group, wherein the hydrophobic group is a hydrocarbon group containing silicon and having a carbon chain length of 10-20 carbon atoms.

Optionally, the complexing agent is a catalyst containing-NH ₂ And the relative molecular mass is not more than 10000.

Optionally, the complexing agent is at least one of ethylenediamine, tetraethylenepentamine, pentaethylenehexamine and triethanolamine.

Optionally, the structure directing agent is at least one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, N-trimethyl-1-adamantylammonium hydroxide, polyvinylpyrrolidone; and/or the hydrophobic molecular sieve has at least one of a framework structure type of BEA, CHA, MFI, AFX, FAU, LTA, OFF.

Optionally, the silicon source is at least one of silicon dioxide, ethyl orthosilicate, silica sol and pure silicon molecular sieve.

The second aspect of the invention provides an exhaust gas treatment catalyst prepared by the preparation method according to any one of the first aspect.

A third aspect of the present invention provides the use of the exhaust gas treatment catalyst of the second aspect described above in the purification of motor vehicle exhaust gases.

According to the tail gas treatment catalyst, the preparation method and the application thereof provided by the invention, the soluble active metal salt is dissolved in the complexing agent to prepare the metal complex solution, so that the stability of the soluble active metal is improved, the metal complex solution is added into the molecular sieve base fluid, so that the metal complex can be embedded into the molecular sieve, the high-temperature stability and the high-temperature activity of the catalyst are further improved, then the hydrophobic compound is added, the hydrophobic compound is loaded on the surface of the molecular sieve, the hydrophobic performance of the molecular sieve can be obviously improved, meanwhile, the embedding of the metal complex is not influenced, the prepared catalyst has high-temperature activity and high-temperature thermal stability, and is very suitable for purifying tail gas with high temperature and high water vapor content, and the catalytic performance is good.

Drawings

In order to more clearly illustrate the technical solutions of the present invention or related art, the drawings that are required to be used in the description of the embodiments or related art will be briefly described below, and it is apparent that the drawings in the following description are only embodiments of the present invention, and other drawings may be obtained according to the drawings without inventive effort to those of ordinary skill in the art.

FIG. 1 is a scanning image of a transmission electron microscope on a 200nm scale of an exhaust gas treatment catalyst prepared in example 1 of the present invention;

FIG. 2 is a scanning image of a transmission electron microscope on the scale of 50nm of the exhaust gas treatment catalyst prepared in example 1 of the present invention;

FIG. 3 is a scanning electron microscope-20 nm-scale of the catalyst for treating exhaust gas prepared in example 1 of the present invention.

Detailed Description

The present invention will be further described in detail with reference to specific embodiments in order to make the objects, technical solutions and advantages of the present invention more apparent.

It should be noted that unless otherwise defined, technical terms used in the following examples have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.

For the novel hydrogen-ammonia dual-fuel engine, the exhaust condition is greatly different from that of the traditional diesel vehicle, firstly, the temperature range of the tail gas of the traditional diesel vehicle is wider (200-500 ℃) under the normal working condition, and the temperature is generally lower than 200 ℃ during cold start, so that the low-temperature activity requirement on the tail gas catalyst of the traditional diesel vehicle is higher, and the high-temperature activity requirement on the tail gas catalyst of the traditional diesel vehicle is not higher. However, for the novel hydrogen-ammonia dual-fuel engine, the exhaust temperature is generally 400-500 ℃, which puts higher demands on the high-temperature activity of the catalyst. Secondly, the traditional diesel vehicle exhaust gas contains about 10% of water vapor, so that the hydrothermal stability requirement on the traditional diesel vehicle exhaust gas catalyst is not high. However, for the novel hydrogen-ammonia dual-fuel engine, the tail gas contains 30-40% of water vapor, so that more severe requirements are put forward on the hydrothermal stability of the catalyst.

Therefore, the novel hydrogen-ammonia dual-fuel engine tail gas requires that the catalyst have good high-temperature activity and high-temperature hydrothermal stability. However, some of the currently used SCR catalysts and molecular sieve catalysts can cause irreversible deactivation due to high temperature and the existence of only 10% of water vapor, while 30-40% of water vapor in the tail gas of the hydrogen-ammonia dual-fuel engine can cause more serious irreversible degradation of the catalysts.

Based on the above, the invention provides an exhaust gas treatment catalyst suitable for a hydrogen-ammonia dual-fuel engine, which can solve the problem that NO is in the exhaust gas of the hydrogen-ammonia dual-fuel engine _x The difficult problem of high-temperature hydrothermal deactivation of the catalyst in the process is eliminated.

The first aspect of the present invention provides a method for preparing an exhaust gas treatment catalyst, comprising:

s1, adding a silicon source into an aqueous solution of a structure directing agent to form a mixture, and stirring until the mixture becomes transparent to obtain a molecular sieve matrix solution;

s2, dissolving soluble active metal salt in a complexing agent solution to obtain a metal complex solution;

step S3, dropwise adding the metal complex solution into the molecular sieve matrix liquid, stirring until no precipitate exists visually, continuously adding a hydrophobic compound, and stirring to obtain a precursor solution;

step S4, crystallizing and centrifuging the precursor solution, and drying and roasting the solid obtained after centrifugation to obtain a tail gas treatment catalyst;

Specifically, in step S1, the mixture is stirred until the mixture becomes transparent, indicating that the silicon source has been completely hydrolyzed in the aqueous solution of the structure directing agent at this time, to obtain a molecular sieve-based fluid. And adding a silicon source into the structure guiding agent aqueous solution, fully stirring and hydrolyzing to obtain molecular sieve matrix liquid, wherein the structure guiding agent is used for guiding the silicon source to form a silicon molecular sieve with a specific structure on the basis of the structure guiding agent.

According to the invention, the silicon molecular sieve with a specific structure formed on the basis of the structure guiding agent can improve the high-temperature stability of the whole molecular sieve structure so as to improve the high-temperature stability of the finally obtained tail gas treatment catalyst. Meanwhile, the molecular sieve structure has special structures such as pores, gaps or channels, so that the subsequent metal complex can be embedded into the molecular sieve structure, and the stability and activity of the whole catalyst are improved.

In step S2, the soluble active metal salt is dissolved in the complexing agent to prepare a metal complex solution, and the active metal exists in the form of a metal complex, so that the form of the metal complex is more stable compared with the free metal ion or metal oxide and other forms, and the high-temperature stability and high-temperature activity of the prepared exhaust gas treatment catalyst can be further improved.

In the step S3, the metal complex solution is added into the molecular sieve base fluid and stirred until no precipitate exists visually, so that the metal complex can be embedded into the molecular sieve, and the high-temperature stability and high-temperature activity of the catalyst are improved. After the metal complex is embedded into the molecular sieve, the hydrophobic compound is added, and the hydrophobic compound is loaded on the surface of the molecular sieve, so that the hydrophobic property of the molecular sieve can be obviously improved, and meanwhile, the embedding of the metal complex is not influenced, so that the prepared catalyst has high-temperature activity and high-temperature hydrothermal stability, is very suitable for purifying tail gas with high temperature and high water vapor content, and has good catalytic performance.

In step S4, the drying may be vacuum drying, air drying, sun drying, or the like.

In this embodiment, the drying is performed for 10-12 hours at 50-200 ℃ under vacuum, preferably for 10.5-11.5 hours at 80-180 ℃ under vacuum, and more preferably for 11 hours at 100-150 ℃. The vacuum drying is the drying under the negative pressure state, the required drying temperature is lower, and the phenomenon that the metal complex is migrated to the surface of the molecular sieve matrix due to the volatilization of the solvent during the drying can be avoided, so that the high-temperature stability of the catalyst is influenced. If directly dried in air, the drying temperature required is high, resulting in the metal complex being easily migrated to the surface of the molecular sieve matrix when the solvent is volatilized, so that the high temperature stability of the catalyst is affected.

The roasting is performed for 2-8 hours in the air at 200-800 ℃, preferably for 3-6 hours in the air at 400-700 ℃, and more preferably for 4-5 hours in the air at 500-600 ℃. When preliminary drying is carried out, most of the solvent is volatilized, and when high-temperature roasting is carried out continuously, metal complex is hardly migrated to the surface of the molecular sieve matrix, so that the high-temperature stability of the catalyst is not affected.

The tail gas treatment catalyst prepared by the invention comprises a hydrophobic molecular sieve and a metal complex embedded in the hydrophobic molecular sieve, the hydrophobic molecular sieve improves the hydrophobic property of the tail gas treatment catalyst, and the high or low water vapor content does not cause great influence on the hydrophobic molecular sieve, so that the problems of deactivation and the like in the tail gas with higher water vapor content are avoided, and the hydrothermal stability of the tail gas is improved; meanwhile, the metal complex is embedded into the hydrophobic molecular sieve, so that the high-temperature stability and the catalytic activity of the whole tail gas treatment catalyst are improved.

In some embodiments, the step S3 of adding the metal complex solution dropwise to the molecular sieve base solution, stirring until no precipitate is visible, continuing to add the hydrophobic compound, and stirring to obtain a precursor solution, including:

and (3) dropwise adding the metal complex into the molecular sieve base fluid, stirring until no precipitate exists visually, adding methanol and/or ethanol, stirring, continuously adding a hydrophobic compound, and stirring to obtain a precursor solution.

Specifically, in step S3, methanol and/or ethanol is added before the hydrophobic compound is added. Methanol and ethanol are organic matters, but the mutual solubility effect of the methanol and the ethanol and water is good, so that the addition of the methanol and/or the ethanol can promote the mutual solubility of a hydrophobic compound added subsequently and a molecular sieve matrix liquid, and can promote the growth of a molecular sieve so that the grain growth of the molecular sieve is larger, and the metal complex is easier to embed into the molecular sieve, so that the tail gas treatment catalyst with stable structure is formed. Meanwhile, the molecular chains of methanol and ethanol are shorter, the relative molecular mass is smaller, and the metal complex is not hindered from being embedded into the molecular sieve.

Methanol and/or ethanol may be added, and it means that only methanol, only ethanol, or a mixture of methanol and ethanol may be added.

In some embodiments, the molar ratio of the silicon source, the structure directing agent, and the water is 0.5 to 1.25:0.2 to 1.0: 10-100, preferably, the molar ratio of the silicon source, the structure directing agent and the water is 0.9-1.1: 0.3 to 0.8: 30-50, more preferably, the molar ratio of the silicon source, the structure directing agent and the water is 1.0:0.4:35. the water is solvent water in the aqueous solution of the structure directing agent.

Specifically, when the molar ratio of the silicon source, the structure directing agent and the water is 0.5-1.25: 0.2 to 1.0: when the content of the silicon source, the structure guiding agent and the water is in the range of 10-100, the content of the molecular sieve matrix in the finally obtained molecular sieve matrix liquid and the proportion of the silicon source and the structure guiding agent in the molecular sieve matrix are both moderate, and the molecular sieve matrix has better structural stability. Preferably, when the molar ratio of the silicon source, the structure directing agent and the water is 0.9-1.1: 0.3 to 0.8: and when the molecular sieve is within the range of 30-50, the content of the molecular sieve matrix in the finally obtained molecular sieve matrix liquid and the proportion of the silicon source and the structure guiding agent in the molecular sieve matrix are both better, and the molecular sieve matrix has better structural stability. More preferably, when the molar ratio of the silicon source, structure directing agent, and water is 1.0:0.4:35, the content of the molecular sieve matrix in the finally obtained molecular sieve matrix liquid and the proportion of the silicon source and the structure guiding agent in the molecular sieve matrix are optimal, and the molecular sieve matrix has excellent structural stability.

When the silicon source content is too small, the hydrophobic property of the exhaust gas treatment catalyst is lowered; when the silicon source content is too high, it is disadvantageous to form a structurally stable molecular sieve matrix.

When the content of the structure directing agent is too low, the content of the molecular sieve matrix in the obtained molecular sieve matrix liquid is too low, so that the molecular sieve matrix does not contain enough subsequent metal complex intercalation, so that part of metal complex is loaded on the surface of the molecular sieve matrix, on one hand, the high-temperature stability of the whole catalyst is reduced, on the other hand, the loading of subsequent hydrophobic compounds is influenced, the hydrophobic performance of the whole catalyst is influenced, and the high-temperature hydrothermal stability of the catalyst is reduced.

When the content of the structure directing agent is too much but the content of the solvent water is small, the molecular sieve matrix content in the obtained molecular sieve matrix liquid is too much, so that the metal complex and the hydrophobic compound added later cannot react with the molecular sieve matrix more sufficiently, resulting in poor performance of the obtained catalyst.

Illustratively, the molar ratio of the silicon source, the structure directing agent, and the water may be 0.5:0.2: 100. 0.5:1.0: 10. 1.25:0.2: 100. 1.25:1.0: 10. 0.7:0.9: 40. 0.9:0.3: 30. 1.1:0.3: 50. 1.1:0.5: 40. 0.9:0.7: 45. 1.0:0.4:35, etc.

In some embodiments, the molar ratio of the soluble active metal salt, the complexing agent, and the hydrophobic compound is 0.001 to 0.1: 0.05-0.5: 0.01-0.1, preferably, the mole ratio of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.003-0.01: 0.1 to 0.2:0.03 to 0.07, more preferably, the molar ratio of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.006:0.15:0.05.

specifically, when the mole ratio of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.001-0.1: 0.05-0.5: when the content of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.01-0.1, the obtained tail gas treatment catalyst has good catalytic activity and hydrothermal stability; preferably, when the mole ratio of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.003-0.01: 0.1 to 0.2: when the content of the soluble active metal salt, the complexing agent and the hydrophobic compound is 0.03-0.07, the catalytic activity and the hydrothermal stability of the obtained tail gas treatment catalyst are good; more preferably, when the molar ratio of the soluble active metal salt, complexing agent and hydrophobic compound is 0.006:0.15: at 0.05, the content of the soluble active metal salt, the complexing agent and the hydrophobic compound is optimal, and the obtained tail gas treatment catalyst has good catalytic activity and hydrothermal stability.

When the content of the soluble active metal salt is too low, the catalytic activity of the obtained tail gas treatment catalyst is poor; when the content of the soluble active metal salt is too high, the soluble active metal salt is too much to be fully combined with the complexing agent to form a stable metal complex, so that part of soluble active metal ions are free, and waste is caused.

When the content of the complexing agent is too low, the complexing agent is too little to completely complex the active metal ions, so that part of metal ions cannot form a stable metal complex, and the high-temperature stability of the catalyst is reduced; when the complexing agent content is too high, too much complexing agent does not complex with enough metal ions, and waste of the complexing agent is caused.

When the content of the hydrophobic compound is too low, the hydrophobic compound is too small to entirely cover the surface of the molecular sieve matrix, so that the hydrophobic property of the catalyst is lowered; when the content of the hydrophobic compound is too high, the hydrophobic compound is too much, and after the hydrophobic compound completely covers the surface of the molecular sieve matrix, part of the hydrophobic compound is still left, so that waste is caused.

Illustratively, the mole ratio of the soluble active metal salt, complexing agent, and hydrophobic compound may be 0.001:0.05:0.01, 0.001:0.5:0.1, 0.002:0.09:0.08, 0.1:0.5:0.1, 0.003:0.1:0.03, 0.01:0.2:0.07, 0.006:0.15:0.05, etc.

The active metal can be at least one of Cu, fe, V, W, mn, ce, sm, pt, pd, rh, co, and the metals are metals with very high catalytic activity, and can be used as active components of the exhaust gas treatment catalyst to improve the catalytic activity of the exhaust gas treatment catalyst.

The soluble active metal salt may be chlorate, nitrate, etc. Illustratively, the soluble active metal salt may be copper nitrate, ferric chloride, vanadium chloride, platinum nitrate, palladium chloride, rhodium chloride, or the like, or may be a mixture of copper nitrate and platinum nitrate, or a mixture of vanadium chloride and palladium chloride, or the like.

In some embodiments, the hydrophobic compound comprises a hydrophobic group that is a hydrocarbon group containing silicon and having a carbon chain length of 10 to 20 carbon atoms.

Specifically, the hydrophobicity of the hydrocarbon group containing silicon is higher, so that the hydrophobicity of the prepared tail gas treatment catalyst can be further improved.

The chain length of hydrocarbon molecules with the carbon chain length of 10-20 carbon atoms is moderate, so that the hydrophobic compound can be loaded on the surface of a molecular sieve matrix, and the outer surface of the hydrophobic compound is modified, so that the hydrophobic property and the hydrothermal stability of the prepared catalyst are improved, and meanwhile, the hydrophobic compound cannot enter the molecular sieve and cannot influence the stability and the reactivity of the metal complex in the molecular sieve.

When the carbon chain length is less than 10 carbon atoms, the molecular chain of the hydrophobic compound is too short, so that the hydrophobic compound can be embedded into the molecular sieve matrix, and the hydrophobic compound embedded into the molecular sieve matrix can influence the stability and the reaction activity of the metal complex embedded into the molecular sieve matrix, so that the prepared catalyst has poor high-temperature stability and high-temperature activity. When the carbon chain length is longer than 20 carbon atoms, the molecular chain of the hydrophobic compound is too long, so that the too long carbon chain can cause easy occurrence of clusters when the hydrophobic compound is baked in the step S4, so that the hydrophobic property thereof is affected, and at the same time, the too long carbon chain can cause too poor solubility of the hydrophobic compound, so that the hydrophobic compound is not easily dissolved in the molecular sieve base liquid, so that the reaction effect is affected.

The hydrocarbon group may be at least one of a hydrocarbon group containing an aryl group, an ester, an ether, an amine, an amide and the like, a hydrocarbon group containing a double bond, a polyoxypropylene group, a long-chain perfluoroalkyl group, a polysiloxane group, and preferably a polysiloxane.

In some embodiments, the complexing agent is a solution comprising-NH ₂ And the relative molecular mass is not more than 10000. Preferably, the relative molecular mass is no more than 5000, more preferably no more than 2000.

Specifically, the complexing agent contains-NH ₂ Is an organic compound containing-NH ₂ The organic matter is organic alkali, the reaction solution is alkaline due to the addition of the complexing agent, the alkaline environment is favorable for the synthesis of the molecular sieve, the complexing reaction efficiency of the metal and the complexing agent is higher in the alkaline environment, and the obtained metal complex is more stable.

The relative molecular mass is not more than 10000, so that the formed metal complex is not too large, and can smoothly enter the inside of the molecular sieve matrix to form a stable embedded structure. When the relative molecular mass exceeds 10000, the formed metal complex is too long to enter the inside of the molecular sieve matrix, and the high-temperature stability of the catalyst is affected.

Illustratively, the complexing agent may be at least one of ethylenediamine, tetraethylenepentamine, pentaethylenehexamine, triethanolamine. Specifically, the complexing agent may be only ethylenediamine, tetraethylenepentamine, pentaethylenehexamine or triethanolamine, or may be a mixture of ethylenediamine and tetraethylenepentamine, or a mixture of pentaethylenehexamine and triethanolamine.

In some embodiments, the structure directing agent is at least one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, N-trimethyl-1-adamantylammonium hydroxide, polyvinylpyrrolidone.

In particular, the structure directing agent provides a specific molecular sieve framework structure for directing a silicon source to form a silicon molecular sieve of a specific structure based on the structure directing agent. Illustratively, the structure directing agent may be triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, N-trimethyl-1-adamantylammonium hydroxide, polyvinylpyrrolidone, and may also be triethylamine and tetraethylammonium hydroxide.

In some embodiments, the hydrophobic molecular sieve has at least one of the framework structure types BEA, CHA, MF, AFX, FAU, LTA, OFF.

Specifically, both BEA, CHA, MFI, AFX, FAU, LTA and OFF are codes for framework types defined by the structure committee of the international zeolite association, representing specific framework structures.

The molecular sieve with the framework structure has a regular and symmetrical structure, and compared with an irregular structure, the regular and symmetrical structure type has good topological structure stability, so that the structural stability of the whole hydrophobic molecular sieve is improved, and the high-temperature stability of the whole tail gas treatment catalyst is further improved. Preferably, the framework structure type of the hydrophobic molecular sieve is MFI, and the stability of the MFI framework structure is very good, so that the prepared exhaust gas treatment catalyst has excellent high-temperature stability.

In some embodiments, the silicon source is at least one of silica, ethyl orthosilicate, silica sol, and pure silicon molecular sieve.

Specifically, the silicon source can be silicon dioxide, ethyl orthosilicate, silica sol or pure silicon molecular sieve, or can be a mixture of silicon dioxide and ethyl orthosilicate, or a mixture of silica sol and pure silicon molecular sieve. And the silicon source is added in the S1, so that the hydrophobicity of the formed silicon molecular sieve matrix is better due to the good hydrophobicity of the silicon source.

The pure silicon molecular sieve is a molecular sieve containing only two elements of silicon and oxygen, the framework type of the pure silicon molecular sieve can be at least one of MFI, BEA, CHA, and the MFI, the BEA and the CHA are all codes of the framework type defined by the International Zeolite Association structure Commission.

The tail gas treatment catalyst prepared by the invention comprises a hydrophobic molecular sieve and a metal complex embedded in the hydrophobic molecular sieve, wherein the hydrophobic molecular sieve is used as a carrier to inhibit the competitive adsorption effect of water vapor in the tail gas in the catalytic reaction process, so that the catalytic purification effect of active components is ensured, and the catalyst is suitable for the high-water-content tail gas atmosphere of a hydrogen-ammonia dual-fuel engine. The metal complex is embedded into the hydrophobic molecular sieve, so that the catalyst active metal exerts more obvious nano-size effect.

The tail gas treatment catalyst has high-temperature activity and high-temperature hydrothermal stability, is very suitable for purifying tail gas with high temperature and high steam content, and has good catalytic performance.

A third aspect of the present invention provides the use of the exhaust gas catalyst of the second aspect described above in the purification of motor vehicle exhaust gases.

Specifically, the exhaust catalyst disclosed by the invention can be used for purifying the exhaust of a hydrogen-ammonia dual-fuel engine. The tail gas treatment catalyst prepared by the invention has high temperature stability and high temperature activity, is suitable for high temperature tail gas of a hydrogen-ammonia dual-fuel engine, has good hydrophobic property and excellent high temperature hydrothermal stability, is suitable for tail gas with higher water vapor content of the hydrogen-ammonia dual-fuel engine, and can solve the problem of NO in the tail gas of the hydrogen-ammonia dual-fuel engine _x The difficult problem of high-temperature hydrothermal deactivation of the catalyst in the process is eliminated.

The present invention will be described in further detail with reference to the following examples.

Example 1

A method for preparing an exhaust gas treatment catalyst, comprising the steps of:

(1) Mixing deionized water and tetrapropylammonium hydroxide, continuously stirring for 10 minutes, continuously adding ethyl orthosilicate into the mixture, continuously stirring for 6 hours, completely hydrolyzing the ethyl orthosilicate, and obtaining a molecular sieve matrix liquid after the mixture becomes transparent; wherein, the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 1.0:0.4:35;

(2) CuCl is added ₂ Dissolving in ethylene glycolPreparing a Cu-EDA metal complex solution in a mixed solution of amine and water, wherein the CuCl ₂ The molar ratio of ethylenediamine is 0.006:0.15;

(3) Dropwise adding the Cu-EDA metal complex solution into the molecular sieve base fluid, stirring for 30min, continuously adding polysiloxane, and maintaining the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.006:0.15:0.05, vigorously stirring for 2 hours to obtain a precursor solution;

(4) Transferring the precursor solution into a 500 ml reaction kettle, crystallizing at 170 ℃ for 4 days, taking out the reaction kettle, repeatedly centrifuging and flushing the mixture for 3 times at 1000-10000rpm by using a mixed solution of water and ethanol with the volume ratio of 1:1, pouring out the solid after the supernatant is clear and not turbid, drying at 80 ℃ under vacuum for overnight, roasting in air at 550 ℃ for 8 hours, taking out the sample, and continuing to stir in H ₂ And (3) maintaining the temperature of 200 ℃ in the airflow and reducing for 2 hours to obtain the tail gas treatment catalyst.

Fig. 1-3 are TEM scanning diagrams of the catalyst, the dimensions are 200nm, 50nm and 20nm respectively, the figures show the sample morphology under different sizes, and the figures can clearly see that the active species metal complex (white small particles) is uniformly distributed in the hydrophobic molecular sieve, so that the metal complex is uniformly distributed in the molecular sieve, and the size is uniform.

Example 2

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the ethyl orthosilicate is replaced by a pure silicon molecular sieve.

Example 3

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the ethyl orthosilicate was replaced with silica.

Example 4

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that:

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 0.5:0.2:10.

example 5

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 1.25:1.0:100.

example 6

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 2.0:0.4:35.

example 7

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 0.3:0.4:35.

example 8

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 1.0:1.5:35.

example 9

the mol ratio of the tetraethoxysilane to the tetrapropylammonium hydroxide to the water is 1.0:0.1:35.

example 10

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.001:0.05:0.01.

example 11

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.1:0.5:0.1.

example 12

Preparation method of exhaust gas treatment catalyst and preparation of example 1The steps are the same, the difference is that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.0009:0.15:0.05.

example 13

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 1.2:0.15:0.05.

example 14

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 1.2:0.03:0.05.

example 15

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 1.2:0.6:0.05.

example 16

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 1.2:0.6:0.008.

example 17

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 1.2:0.6:0.12.

example 18

(3) Dropwise adding the Cu-EDA metal complex solution into the molecular sieve base fluid, stirring for 30min, adding 0.015mol of methanol, stirring, continuously adding polysiloxane, and maintaining the CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.006:0.15: and (3) stirring vigorously for 2h to obtain a precursor solution.

Example 19

Preparation method of exhaust gas treatment catalyst and preparation step of example 1The steps are the same, and the difference is that: cuCl is added ₂ And is replaced by cobalt nitrate.

Example 20

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: cuCl is added ₂ And is replaced by ferric nitrate.

Example 21

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the ethylene diamine is replaced by tetraethylene pentamine.

Example 22

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: the ethylene diamine was replaced with triethanolamine.

Example 23

A method for preparing an exhaust gas treatment catalyst, which is the same as the preparation procedure of example 1, except that: tetrapropylammonium hydroxide was replaced with N, N-trimethyl-1-adamantylammonium hydroxide.

Comparative example 1

(2) Adding polysiloxane into molecular sieve matrix liquid to obtain solution B, transferring the solution B into a 500 ml reaction kettle, crystallizing at 170 ℃ for 4 days, taking out the reaction kettle, repeatedly centrifuging and flushing the mixture for 3 times at 1000-10000rpm with a mixed solution of water and ethanol in a volume ratio of 1:1, pouring out the solid after the supernatant is clear and free from turbidity, drying at 80 ℃ under vacuum for overnight, roasting in air at 550 ℃ for 8 hours, taking out the sample, and continuing to stir in H ₂ Reducing for 2 hours at 200 ℃ in the airflow to obtain a sample 1;

(3) CuCl is added ₂ Dissolving in a mixed solution of ethylenediamine and waterPreparing Cu-EDA metal complex solution, wherein CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.006:0.15: and 0.05, adding the sample 1 into the solution, uniformly stirring to form paste, drying at 110 ℃ for 8 hours, and continuously roasting in air at 550 ℃ for 3 hours to obtain the tail gas treatment catalyst.

Comparative example 2

A method for preparing an exhaust gas treatment catalyst, which is the same as comparative example 1, is different in that:

(4) CuCl is added ₂ Dissolving in a mixed solution of ethylenediamine and water to obtain Cu-EDA metal complex solution, wherein CuCl ₂ The molar ratio of ethylenediamine to polysiloxane was 0.006:0.15: and 0.05, adding the sample 1 into the solution, heating to 80 ℃ for ion exchange reaction for 6 hours, performing high-speed centrifugation to realize solid-liquid separation, repeatedly washing the solid with 50 ml deionized water for 3 times until the filtrate is colorless, uniformly stirring, keeping 110 ℃ for drying for 8 hours, and continuously roasting in air at 550 ℃ for 3 hours to obtain the tail gas treatment catalyst.

Comparative example 3

A method for preparing an exhaust gas treatment catalyst, which is the same as in example 1, is different in that: no hydrophobic compound was added.

Comparative example 4

A method for preparing an exhaust gas treatment catalyst, which is the same as in example 1, is different in that: the complexing agent ethylenediamine is not used, and CuCl is directly added ₂ Added to the molecular sieve base fluid.

Comparative example 5

A method for preparing an exhaust gas treatment catalyst, which is the same as in example 18, except that: the methanol is replaced by isopropanol.

Comparative example 6

A method for preparing an exhaust gas treatment catalyst, which is the same as in example 18, except that: the methanol is replaced by glycerol.

The exhaust gas catalysts prepared in each example and comparative example were subjected to performance test as follows.

1. Fresh sample Performance verification experiment

The catalysts prepared in the above examples and comparative examples were prepared into 40-60 mesh powder samples in the following conditionsNH on micro fixed bed reactor ₃ -SCR catalytic performance evaluation. The test heating rate was evaluated at 5℃per minute. Simulated atmosphere composition: 500ppm NO,500ppm NH ₃ ，5% O ₂ ，N ₂ To balance the gas, the total flow rate was 1000mL/min, the reaction space velocity was 30000 h ^-1 。

The test results are shown in Table 1 below, in which the low temperature performance index T ₅₀ Represented when NO _x The conversion reaches the lowest temperature corresponding to 50%; high temperature performance index T ₅₀ Represented when NO _x The highest temperature corresponding to 50% conversion rate; temperature window index T ₉₀ Represented when NO _x The corresponding temperature range when the conversion exceeds 90%, N ₂ Selectivity refers to the arithmetic mean of the nitrogen selectivity data for each test temperature point in the range of 175-600 ℃.

TABLE 1 fresh sample Performance test results

2. High-temperature hydrothermal aging performance verification test

The catalyst prepared in each example and comparative example is prepared into 40-60 mesh powder sample, and the powder sample is prepared into a high-temperature hydrothermal aging sample in a tubular furnace through high-temperature hydrothermal treatment so as to simulate the environment of the catalyst in a long term in the actual running process of an engine, thereby knowing the high-temperature hydrothermal stability of the catalyst in the actual application process.

The treatment conditions of the hydrothermal aging are as follows: 40vol.% of water vapor, air as balance gas, and aging at 750 ℃ for 24 hours at constant temperature, wherein the total flow is 1500 ml/min, and the airspeed is 30000 h ^-1 (notably, the amount of water vapor in the conventional hydrothermal aging treatment conditions was 10vol.%, and in this test, the water vapor content was increased to 40vol.% in order to more accurately simulate the hydrogen-ammonia dual fuel engine exhaust environment).

Respectively performing NH on the hydrothermal aging samples on a micro fixed bed reactor ₃ -SCR catalytic performance evaluation. The evaluation test conditions were the same as those of the fresh samples, and the test results are shown in Table 2 below.

TABLE 2 Performance test results list of hydrothermal aging samples

As can be seen from tables 1 and 2, the catalyst for treating exhaust gas prepared in each example has slightly different catalytic performance and high-temperature thermal performance due to different contents of each component, but the catalyst for treating exhaust gas prepared in each example has excellent catalytic performance, good low-temperature performance and high-temperature performance, wide temperature window and N ₂ The catalyst has high selectivity, and the hydrothermal aging sample in the embodiment has good low-temperature performance and high-temperature performance, so that the catalyst is not deactivated in a high-temperature hydrothermal environment, and the catalyst has good catalytic performance, and the catalyst for treating the tail gas prepared by the method has good hydrothermal stability and good catalytic performance in a high-temperature and high-humidity environment.

In comparative example 1, in the preparation process, a hydrophobic compound is added into a molecular sieve base fluid, a sample 1 is obtained after drying and roasting, and then the sample 1 is directly added into a Cu-EDA metal complex solution, and finally the tail gas treatment catalyst is prepared. In the method, the hydrophobic compound is added into the molecular sieve base fluid so that the hydrophobic compound is loaded on the surface of the molecular sieve, the subsequent embedding of the Cu-EDA metal complex into the molecular sieve is influenced, and the high-temperature stability of the catalyst is further reduced, so that the prepared tail gas treatment catalyst has poor performance.

In comparative example 2, the whole preparation method is the same as that of comparative example 1, except that sample 1 is directly added into the Cu-EDA metal complex solution, and then the post-treatment is performed after the temperature is raised to 80 ℃ for 6 hours of ion exchange reaction, and compared with comparative example 1, although the ion exchange reaction performed for a period of time can help the Cu-EDA metal complex to be embedded into the molecular sieve, the subsequent embedding of the Cu-EDA metal complex into the molecular sieve is still affected due to the hydrophobic compound carried on the surface of the molecular sieve, so that the performance of the prepared catalyst for treating tail gas is still poor.

In comparative example 3, since the hydrophobic compound was not added, the prepared exhaust gas treatment catalyst had poor hydrophobic property, and the catalyst had poor performance after hydrothermal treatment, and both high temperature performance and low temperature performance were poor.

In comparative example 4, since ethylenediamine, a complexing agent, was not used, cuCl was directly reacted ₂ The catalyst is added into molecular sieve base fluid, so that active metal ions are dissociated in the molecular sieve or on the surface of the molecular sieve, and the high-temperature stability of the catalyst is seriously reduced, so that the prepared tail gas treatment catalyst has poor catalyst performance after high-temperature hydrothermal treatment, and the high-temperature performance and the low-temperature performance are poor.

In comparative examples 5 and 6, since methanol is replaced with isopropanol or glycerol, the metal complex is blocked from being embedded into the molecular sieve due to the longer molecular chains and larger relative molecular mass of isopropanol and glycerol compared with methanol, so that the hydrothermal stability of the catalyst is affected, and the finally prepared catalyst for treating tail gas has poor performance.

In summary, the catalyst for treating tail gas and the preparation method and application thereof provided by the invention have the advantages that the soluble active metal salt is dissolved in the complexing agent to prepare the metal complex solution, so that the stability of the soluble active metal is improved, the metal complex solution is added into the molecular sieve base fluid, so that the metal complex can be embedded into the molecular sieve, the high-temperature stability and the high-temperature activity of the catalyst are further improved, then the hydrophobic compound is added, the hydrophobic compound is loaded on the surface of the molecular sieve, the hydrophobic performance of the molecular sieve can be obviously improved, meanwhile, the embedding of the metal complex is not influenced, the prepared catalyst has both the high-temperature activity and the high-temperature hydrothermal stability, is very suitable for purifying tail gas with high temperature and high water vapor content, and has good catalytic performance.

Those of ordinary skill in the art will appreciate that: the discussion of any of the embodiments above is merely exemplary and is not intended to suggest that the scope of the invention (including the claims) is limited to these examples; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the invention, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the invention as described above, which are not provided in detail for the sake of brevity.

The present embodiments are intended to embrace all such alternatives, modifications and variances which fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, and the like, which are within the spirit and principles of the embodiments of the invention, are intended to be included within the scope of the invention.

Claims

1. A method for preparing an exhaust gas treatment catalyst, comprising:

2. The method of claim 1, wherein the step of adding the metal complex solution dropwise to the molecular sieve base fluid, stirring until no precipitation occurs visually, continuing to add the hydrophobic compound, and stirring to obtain a precursor solution, comprises:

3. The preparation method according to claim 2, wherein the molar ratio of the silicon source, the structure directing agent and the water is 0.5 to 1.25:0.2 to 1.0: 10-100, wherein the mole ratio of the soluble active metal salt to the complexing agent to the hydrophobic compound is 0.001-0.1: 0.05-0.5: 0.01 to 0.1.

4. The method according to claim 2, wherein the hydrophobic compound contains a hydrophobic group which is a hydrocarbon group containing silicon and having a carbon chain length of 10 to 20 carbon atoms.

5. The method according to claim 1, wherein the complexing agent is-NH-containing ₂ And the relative molecular mass is not more than 10000.

6. The method according to claim 5, wherein the complexing agent is at least one of ethylenediamine, tetraethylenepentamine, pentaethylenehexamine, and triethanolamine.

7. The method according to claim 1, wherein the structure directing agent is at least one of triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, N-trimethyl-1-adamantylammonium hydroxide, polyvinylpyrrolidone; and/or the hydrophobic molecular sieve has at least one of a framework structure type of BEA, CHA, MFI, AFX, FAU, LTA, OFF.

8. The method of claim 1, wherein the silicon source is at least one of silica, ethyl orthosilicate, silica sol, and pure silicon molecular sieve.

9. An exhaust gas treatment catalyst characterized by being prepared by the preparation method of any one of claims 1-8.

10. Use of the exhaust gas treatment catalyst according to claim 9 for the purification of motor vehicle exhaust gases.