CN114797958A

CN114797958A - Long-term stable catalyst for eliminating ethylene at low temperature and preparation method thereof

Info

Publication number: CN114797958A
Application number: CN202210357560.7A
Authority: CN
Inventors: 孟祥举; 肖丰收; 赵胜泽
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2022-04-03
Filing date: 2022-04-03
Publication date: 2022-07-29
Anticipated expiration: 2042-04-03
Also published as: CN114797958B

Abstract

The invention relates to the field of environmental catalysis, and aims to provide a long-term stable catalyst for eliminating ethylene at low temperature and a preparation method thereof. The catalyst consists of a Beta molecular sieve and a noble metal active component loaded on the Beta molecular sieve, wherein the Beta molecular sieve is prepared by an organic template-free seed crystal method; the noble metal active component is any one or a mixture of at least two of noble metal elements of platinum, ruthenium, gold, silver or palladium. The catalyst can react with ethylene at the low temperature of-30 ℃ to 0 ℃ to play a role in purification. The catalyst has simple use condition and convenient operation, and can be effectively used for catalyzing and oxidizing the ethylene into carbon dioxide and water under the low-temperature condition; the catalytic product has no side products such as acetaldehyde, carbon monoxide, acetic acid and the like, and the conversion rate of ethylene can reach 100 percent. The catalyst has the advantages of low consumption, excellent high-speed resistance, no need of a specific light source, no consumption of electric power and heating power, and energy conservation; and the stability of the catalyst is excellent.

Description

Long-term stable catalyst for eliminating ethylene at low temperature and preparation method thereof

Technical Field

The invention relates to the field of environmental catalysis, in particular to a long-term stable catalyst for eliminating ethylene at low temperature and a preparation method thereof.

Background

Ethylene is a volatile organic pollutant with high photochemical activity and has serious harm to human health and ecological environment. The ethylene emission mainly comes from the hormone release of fruits, vegetables and flowers in local environments such as containers, warehouses and storerooms during the food transportation and preservation process due to the growth regulation of plants. The increase of the ethylene concentration in the local environment can accelerate the ripening, decay and rottenness of plants, and the long-term contact of human bodies can also cause dizziness, general discomfort, hypodynamia, unconsciousness and even consciousness loss. Therefore, the elimination of trace amounts of ethylene in local environments under low temperature conditions has become one of the hot research areas in recent years.

The existing ethylene elimination technology mainly comprises an adsorption technology, an ozone oxidation method and a catalytic oxidation method. The adsorption technology mainly adopts high specific surface materials such as active carbon, molecular sieve and the like to adsorb ethylene, but the adsorption material has limited adsorption capacity, needs to be regenerated or replaced regularly, and is easy to generate secondary pollution. The ozone oxidation method is an indirect method, and mainly comprises the steps of introducing an oxidant into a reaction system, carrying out ozone oxidation to eliminate ethylene, and further eliminating excessive ozone in the system. The method has the defects that the additional addition of oxidant ozone is needed to easily cause secondary pollution, the ozone elimination efficiency is low at low temperature, and other auxiliary means such as heating or catalytic ozone elimination are needed. The catalytic oxidation method utilizes oxygen in the air as an oxidant, does not need to add an additional oxidant, can completely catalyze and oxidize the ethylene at low temperature to generate a final product water and carbon dioxide, and is a direct and efficient trace ethylene elimination method.

The key point of the elimination of the ethylene by catalytic oxidation lies in the research and development of catalytic oxidation materials, and the current research reports that catalysts for the complete oxidation reaction of ethylene mainly comprise oxide catalysts, mesoporous silicon-based materials and the like. The document J.Am.chem.Soc.2010,132,2608-2613 adopts the mesoporous oxide catalyst with high exposed crystal face to load gold for the complete oxidation reaction of low-concentration ethylene, and can completely oxidize 76% of ethylene to generate carbon dioxide and water under the condition of 0 ℃, but the high-activity crystal face structure of the catalyst is difficult to keep stable in the reaction process, and the required reaction temperature of the oxide catalyst is high and the stability is poor. Angew. chem. int. Ed.2013,52, 6265-one 6268 adopts mesoporous silica-based material loaded platinum for the complete oxidation reaction of low-concentration ethylene, can completely catalyze and oxidize ethylene to generate carbon dioxide and water by 100% under the condition of 0 ℃, but has poor stability, is inactivated within 1-2 hours, and is difficult to be practically applied to ethylene elimination under the low-temperature condition.

The document ACS Catal.2012,8,1248-1258 reports that ZSM-5, Beta, Y and Mordenite four molecular sieves can completely oxidize ethylene into carbon dioxide and water at room temperature, but the stability does not exceed 20 hours. CN105344213A provides a catalyst for removing ethylene by low-temperature catalytic complete oxidation based on ZSM-5 molecular sieve, also can be a ZSM-5 microporous molecular sieve added with one or more auxiliary agents, has excellent activity, selectivity and catalyst life (durability) and long duration, and the conversion rate of ethylene is still more than 95% after the catalyst is used for 1000 hours with 500-fold reaction. But the catalyst is less active and less stable at low temperatures (<0 ℃).

The effect of eliminating ethylene under the condition of low temperature (<0 ℃) in the prior art is generally poor, and the temperature of fruits, vegetables and local environments such as containers, warehouses, storerooms and the like in the transportation and preservation processes is low, so that the prior art cannot meet the requirements.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of the existing catalytic oxidation method technology and provide a long-term stable catalyst for eliminating ethylene at low temperature and a preparation method thereof.

In order to achieve the above purpose, the solution of the invention is:

the catalyst for eliminating ethylene at low temperature is stable for a long time and consists of a Beta molecular sieve and a noble metal active component loaded on the Beta molecular sieve, wherein the Beta molecular sieve is prepared by an organic template-free seed crystal method; assuming that the weight of the catalyst is 100%, and the supported noble metal active component is calculated by the weight of the noble metal element, the weight percentage of the noble metal active component in the catalyst is 0.1-10%; the catalyst can react with ethylene at the low temperature of-30 ℃ to 0 ℃ to play a role in purification.

As a preferable mode of the present invention, the noble metal active component is any one or a mixture of at least two of noble metal elements of platinum, ruthenium, gold, silver or palladium; the noble metal active component is derived from any one or a mixture of at least two of a noble metal simple substance, a noble metal oxide or a noble metal inorganic salt.

In a preferred embodiment of the present invention, the noble metal oxide is platinum oxide, ruthenium oxide, gold oxide, palladium oxide, or silver oxide.

In a preferred embodiment of the present invention, the noble metal inorganic salt is potassium chloroplatinate, chloroplatinic acid, potassium hydrogen chloroplatinate, platinum chloride, palladium chloride, gold chloride or silver chloride.

As a preferred embodiment of the present invention, the mixture comprises: the noble metal oxide-based catalyst comprises a mixture of different noble metal simple substances, a mixture of different noble metal oxides, a mixture of different noble metal inorganic salts, a mixture of the noble metal simple substances and the noble metal oxides, a mixture of the noble metal simple substances and the noble metal inorganic salts, a mixture of the noble metal oxides and the noble metal inorganic salts, and a mixture of the noble metal simple substances, the noble metal inorganic salts and the noble metal oxides.

The invention further provides a preparation method of the catalyst, which comprises the following steps:

(1) synthesizing a Beta molecular sieve by an organic template-free seed crystal method;

(2) performing ion exchange on ammonium nitrate, potassium nitrate or sodium nitrate and a Beta molecular sieve, and then filtering, washing and drying; repeating the operation of the step for 2-3 times;

(3) roasting the Beta molecular sieve subjected to ion exchange at 400-600 ℃;

(4) dipping the roasted Beta molecular sieve into a soluble compound aqueous solution containing a noble metal active component, and carrying out ultrasonic treatment for 5-30 minutes; continuously stirring for 1-4 hours, and then aging overnight; stirring the mixed solution by using a glass rod at the temperature of 40-120 ℃, evaporating water in the mixed solution to dryness, uniformly loading the active components on a Beta molecular sieve, and continuously drying for 3-5 hours at the temperature of 100-150 ℃; and (3) moving the Beta molecular sieve containing the noble metal active component into a muffle furnace under the condition of air, nitrogen or oxygen, and roasting for 1-8 hours at 200-750 ℃ to obtain the catalyst.

The preferable scheme of the invention also comprises the heat treatment of the catalyst obtained in the step (4): and (3) placing the catalyst in a hydrogen atmosphere, and carrying out heat treatment at 200-400 ℃ for 1-4 hours to convert all or part of the noble metal active components in the catalyst into noble metal simple substances.

As a preferable aspect of the present invention, in the ion exchange operation in the step (2), the amount of ion exchange is controlled so that: after the Beta molecular sieve treated by ammonium nitrate is roasted, the mass content of sodium and potassium elements is infinitely close to 0 percent; or after roasting the Beta molecular sieve treated by potassium nitrate, the mass content of the contained sodium element is infinitely close to 0 wt%, and the mass content of the contained potassium element is 13 wt%; or after roasting the Beta molecular sieve treated by the sodium nitrate, the mass content of the potassium element is infinitely close to 0 wt%, and the mass content of the sodium element is 7 wt%.

The invention also provides a using method of the catalyst, which comprises the following steps:

(1) according to the requirements of practical application scenes, the catalyst is loaded on the wall surface of a honeycomb ceramic body, a metal screen structure or an open-cell foam body, or the catalyst is made into a spherical shape or a plate shape;

(2) the carrier loaded with the catalyst is placed in the gas containing ethylene, and the catalyst can react with the ethylene at the low temperature of-30-0 ℃ to play a role in purification.

The catalyst loaded by the template-free seed crystal method Beta molecular sieve carrier for low-temperature ethylene elimination is used for low-temperature ethylene elimination, can convert all ethylene into carbon dioxide and water, does not contain byproducts such as acetaldehyde, carbon monoxide and acetic acid, and has the ethylene conversion rate of up to 100 percent.

Compared with the prior art, the invention has the following beneficial effects:

1. the catalyst has simple use condition and convenient operation, and can be effectively used for catalyzing and oxidizing the ethylene into carbon dioxide and water under the low-temperature condition;

2. the catalytic product of the catalyst of the invention has no side products such as acetaldehyde, carbon monoxide, acetic acid and the like, and the conversion rate of ethylene can reach 100 percent.

3. The catalyst has the advantages of small dosage, excellent high-speed resistance, no need of a specific light source, no consumption of electric power and heat, and energy conservation.

4. Because the Beta molecular sieve synthesized by the organic template-free seed crystal method has excellent ethylene adsorption capacity and humidity resistance, and further combines the action of active components, the catalytic conversion rate of ethylene can keep 100 percent of conversion rate. For low-concentration ethylene (less than or equal to 10ppm), the ethylene can be completely catalytically oxidized into carbon dioxide and water only by using a very small amount of active components under the conditions of low temperature and normal humidity, the stability is very excellent, and the conversion rate of the ethylene is still kept at 100 percent within one month.

Detailed Description

To better illustrate the present invention and to facilitate the understanding of the technical solutions of the present invention, typical single non-limiting examples of the present invention are as follows:

example 1

Synthesizing a Beta molecular sieve by an organic template-free seed crystal method, carrying out ion exchange on the Beta molecular sieve by using ammonium nitrate, and then filtering, washing and drying; and repeating the ion exchange operation for 2-3 times, and roasting the obtained sample at 400 ℃. Soaking the roasted Beta molecular sieve in an aqueous solution containing chloroplatinic acid, performing ultrasonic treatment for 30 minutes, stirring for 4 hours, and aging overnight; stirring the mixed solution by a glass rod at 120 ℃, evaporating the water in the mixed solution to dryness to ensure that the active component is uniformly loaded on a Beta molecular sieve, and continuously drying for 5 hours at 150 ℃; then moving the catalyst to a muffle furnace under the air condition, and roasting the catalyst for 5 hours at the temperature of 400 ℃ to obtain a catalyst taking platinum as an active component; in the catalyst, the active component mass content is 0.1%.

Before use, the catalyst is firstly put into a hydrogen atmosphere, heat treated for 4 hours at 200 ℃ and then sieved into particles with the size of 40-60 meshes for later use.

Example 2

Synthesizing a Beta molecular sieve by an organic template-free seed crystal method, carrying out ion exchange on the Beta molecular sieve by using ammonium nitrate, and then filtering, washing and drying; the ion exchange operation was repeated 2 times, and the obtained sample was subjected to a calcination treatment at 600 ℃. Soaking the roasted Beta molecular sieve in an aqueous solution containing platinum oxide, performing ultrasonic treatment for 5 minutes, stirring for 4 hours, and aging overnight; stirring the mixed solution by a glass rod at 40 ℃, evaporating the water in the mixed solution to dryness to ensure that the active component is uniformly loaded on a Beta molecular sieve, and continuously drying for 4 hours at 150 ℃; then moving the catalyst to a muffle furnace under the oxygen condition, and roasting the catalyst for 1 hour at 750 ℃ to obtain a catalyst taking platinum as an active component; in the catalyst, the active component mass content is 0.2%.

Example 3

Synthesizing a Beta molecular sieve by an organic template-free seed crystal method, carrying out ion exchange on the Beta molecular sieve by using ammonium nitrate, and then filtering, washing and drying; the ion exchange operation was repeated 3 times, and the obtained sample was subjected to a calcination treatment at 500 ℃. Dipping the roasted Beta molecular sieve in an aqueous solution containing simple substance platinum, carrying out ultrasonic treatment for 15 minutes, stirring for 1 hour, and aging overnight; stirring the mixed solution by a glass rod at 100 ℃, evaporating the water in the mixed solution to dryness to ensure that the active component is uniformly loaded on a Beta molecular sieve, and continuously drying for 3 hours at 150 ℃; then moving the catalyst to a muffle furnace under the condition of nitrogen, and roasting the catalyst for 8 hours at 200 ℃ to obtain a catalyst taking platinum as an active component; in the catalyst, the active component mass content is 0.2%.

Example 4

The procedure was repeated as in example 1 except that the percentage of platinum was 5% and the heat treatment was controlled to 450 ℃ for 2 hours.

Example 5

The rest was the same as in example 1 except that a mixture of platinum oxide and elemental platinum (elemental platinum nanoparticles, the same applies hereinafter) was used in place of chloroplatinic acid, and the percentage of platinum was 10%.

Example 6

The rest was the same as in example 1 except that no hydrogen pretreatment was performed.

Example 7

The rest was the same as in example 2 except that no hydrogen pretreatment was performed.

Example 8

The rest was the same as in example 3 except that no hydrogen pretreatment was performed.

Example 9

The rest was the same as in example 4 except that no hydrogen pretreatment was performed.

Example 10

The rest was the same as in example 5 except that no hydrogen pretreatment was performed.

Example 11

The same procedure as in example 3 was repeated except that an aqueous solution containing platinum chloride was used for impregnation, to obtain a catalyst containing platinum as an active component.

Example 12

The same procedure as in example 3 was repeated except that an aqueous solution containing a mixture of platinum oxide and elemental platinum was used in the impregnation to obtain a catalyst containing platinum as an active component.

Example 13

The same procedure as in example 3 was repeated, except that an aqueous solution containing potassium chloroplatinate was used for the impregnation, to obtain a catalyst containing platinum as an active component.

Example 14

The procedure of example 3 was repeated except that a suspension aqueous solution containing elemental platinum was used for impregnation to obtain a catalyst containing platinum as an active component.

Example 15

The same procedure as in example 3 was repeated, except that an aqueous solution containing chloroauric acid was used for impregnation, to obtain a catalyst containing gold as an active component.

Example 16

The same procedure as in example 3 was repeated except that an aqueous solution containing palladium nitrate was used in the impregnation, to obtain a catalyst containing palladium as an active component.

Example 17

Otherwise the same procedure as in example 5 was repeated except that an aqueous solution containing silver nitrate was used in the impregnation, to obtain a catalyst containing silver as an active component.

Example 18

Otherwise, the same procedure as in example 3 was repeated except that an aqueous solution containing ruthenium chloride was used in the impregnation, to obtain a catalyst containing ruthenium as an active component.

Example 19

The procedure was as in example 3 except that ion exchange was conducted using sodium nitrate.

Example 20

The procedure was repeated in the same manner as in example 3 except that ion exchange was conducted using potassium nitrate.

Example 21

The rest is the same as the embodiment 3 except that the silver nitrate and palladium chloride containing aqueous solution is used in the impregnation, and the catalyst with silver and palladium as active components is obtained.

Example 22

The rest is the same as the embodiment 3 except that the water solution containing silver nitrate and chloroauric acid is used in the impregnation, and the catalyst with silver and gold as active components is obtained.

Example 23

The same procedure as in example 3 was repeated except that an aqueous solution containing ruthenium chloride and chloroplatinic acid was used in the impregnation to obtain a catalyst containing ruthenium and platinum as active components.

In each example, the amount of ion exchange was controlled when ion exchange was performed on the Beta molecular sieve such that: after the Beta molecular sieve treated by the ammonium nitrate is roasted, the mass content of the contained sodium and potassium elements is infinitely close to 0 wt%; after the Beta molecular sieve treated by potassium nitrate is roasted, the mass content of the contained sodium element is infinitely close to 0 wt%, and the mass content of the potassium element is 13 wt%; after the Beta molecular sieve treated by the sodium nitrate is roasted, the mass content of the contained potassium element is infinitely close to 0 wt%, and the mass content of the contained sodium element is 7 wt%.

Measurement of Performance

0.1g of the catalysts of examples 1 to 23 are respectively put in a tubular fixed bed reactor for experiment, and the experimental conditions are as follows: 21% of oxygen, 79% of nitrogen, the ethylene concentration was controlled to 100ppm, the reaction space velocity (GHSV) was 7500 mL/(g.h), the reaction temperature was-20 ℃ and the results of activity evaluation are shown in Table 1.

TABLE 1

0.1g of the catalysts of examples 1 to 5 are respectively put in a tubular fixed bed reactor for experiment, and the experimental conditions are as follows: 21 percent of oxygen and 79 percent of nitrogen, controlling the concentration of ethylene to be 100ppm, the reaction space velocity (GHSV) to be 7500 mL/(g.h), the reaction temperature to be-30-0 ℃, and the activity evaluation results to be shown in Table 2.

TABLE 2

Catalyst numbering	Reaction temperature/. degree.C	Ethylene conversion/%	Stability/hour
				Example 1	0	100	4
Example 2	-10	100	10
				Example 3	-10	100	150
Example 4	-30	100	400
				Example 5	0	100	1800

0.1g of the catalysts of examples 1 to 5 are respectively put in a tubular fixed bed reactor for experiment, and the experimental conditions are as follows: 21% of oxygen, 79% of nitrogen, the ethylene concentration was controlled to 2-100ppm, the reaction space velocity (GHSV) was 7500 mL/(g.h), the reaction temperature was-20 ℃, and the results of activity evaluation are shown in Table 2.

TABLE 3

Catalyst numbering	Ethylene concentration/ppm	Ethylene conversion/%	Stability/hour
				Example 1	2	100	200
Example 2	10	100	100
				Example 3	20	100	750
Example 4	50	100	800
				Example 5	100	100	1200

As can be seen from the performance test data of the above examples 1 to 23, the catalyst prepared by the Beta molecular sieve carrier prepared by the template-free seed crystal method has excellent low-temperature catalytic ethylene oxidation performance and stability. Because the stability of the catalyst is related to the content of the active components in the catalyst, and the proportion of the active components in each embodiment is greatly different, the stability of the corresponding catalyst is also different.

To complete the test in a reasonable time, the ethylene-containing mixed gas was fed at a certain space velocity during the performance test of examples 1 to 23. However, when the catalyst product of the present invention is applied to the actual cold insulation and corrosion prevention environment of fruits and vegetables, since the air inside the refrigerator has a certain fluidity due to refrigeration, the excellent low-temperature catalytic ethylene oxide function can be stably exerted for a long storage period of the fruits and vegetables by placing the catalyst in the refrigerator directly after being supported in a proper manner or being formed into a proper shape, and an additional gas circulation device is not required.

Comparative example 1:

the catalyst (Pt/MCM-41, Pt loading 1%) was prepared in the reference (Angew. chem. int. Ed.2013,52, 6265-.

Comparative example 2:

the catalyst (Ag/Beta, Ag loading 5%) was prepared in the reference (ACS Catal.2012,8, 1248-1258).

Comparative example 3:

the catalyst (Pt/ZSM-5, Pt loading 1%) was prepared according to the reference (CN 105344213A).

0.1g of the catalysts of comparative examples 1 to 3 are respectively put in a tubular fixed bed reactor for experiment, and the experimental conditions are as follows: 21% of oxygen, 79% of nitrogen, the ethylene concentration was controlled to 100ppm, the reaction space velocity (GHSV) was 7500 mL/(g.h), the reaction temperature was-10 to-30 ℃, and the results of activity evaluation are shown in Table 4.

TABLE 4

Catalyst numbering	Reaction temperature/. degree.C	Ethylene conversion/%	Stability/hour
				Comparative example 1	-10	70	0.5
Comparative example 2	-30	20	1
				Comparative example 3	-20	30	2

From the above results, it can be seen that the catalyst prepared by the Beta molecular sieve carrier prepared by the template-free seeding method of the present invention has the technical effects as claimed in the summary of the invention.

The applicant states that the present invention is illustrated by the above examples to show the detailed composition of the catalyst, but the present invention is not limited to the above detailed composition, i.e. it is not meant that the present invention must rely on the above detailed composition to be carried out. It should be understood by those skilled in the art that any modification of the present invention, equivalent replacement of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. The catalyst for eliminating ethylene at low temperature and with long-term stability is characterized by consisting of a Beta molecular sieve and a noble metal active component loaded on the Beta molecular sieve, wherein the Beta molecular sieve is prepared by an organic template-free seed crystal method; assuming that the weight of the catalyst is 100%, and the supported noble metal active component is calculated by the weight of the noble metal element, the weight percentage of the noble metal active component in the catalyst is 0.1-10%; the catalyst can react with ethylene at the low temperature of-30 ℃ to 0 ℃ to play a role in purification.

2. The catalyst according to claim 1, wherein the noble metal active component is any one or a mixture of at least two of the noble metal elements platinum, ruthenium, gold, silver or palladium; the noble metal active component is derived from any one or a mixture of at least two of a noble metal simple substance, a noble metal oxide or a noble metal inorganic salt.

3. The catalyst of claim 2 wherein the noble metal oxide is platinum oxide, ruthenium oxide, gold oxide, palladium oxide, or silver oxide.

4. The catalyst of claim 2, wherein the noble metal inorganic salt is potassium chloroplatinate, chloroplatinic acid, potassium hydrogen chloroplatinate, platinum chloride, palladium chloride, gold chloride, or silver chloride.

5. The catalyst of claim 2, wherein the mixture comprises: the noble metal oxide-based catalyst comprises a mixture of different noble metal simple substances, a mixture of different noble metal oxides, a mixture of different noble metal inorganic salts, a mixture of the noble metal simple substances and the noble metal oxides, a mixture of the noble metal simple substances and the noble metal inorganic salts, a mixture of the noble metal oxides and the noble metal inorganic salts, and a mixture of the noble metal simple substances, the noble metal inorganic salts and the noble metal oxides.

6. A method for preparing the catalyst of claim 1, comprising the steps of:

(3) roasting the Beta molecular sieve subjected to ion exchange at 400-600 ℃;

(4) dipping the roasted Beta molecular sieve into a soluble compound aqueous solution containing a noble metal active component, and carrying out ultrasonic treatment for 5-30 minutes; after continuously stirring for 1-4 hours, aging overnight; stirring the mixed solution by using a glass rod at the temperature of 40-120 ℃, evaporating water in the mixed solution to dryness, uniformly loading the active components on a Beta molecular sieve, and continuously drying for 3-5 hours at the temperature of 100-150 ℃; and (3) moving the Beta molecular sieve containing the noble metal active component into a muffle furnace under the condition of air, nitrogen or oxygen, and roasting for 1-8 hours at 200-750 ℃ to obtain the catalyst.

7. The method of claim 6, further comprising heat treating the catalyst obtained in step (4): and (3) placing the catalyst in a hydrogen atmosphere, and carrying out heat treatment at 200-400 ℃ for 1-4 hours to convert all or part of the noble metal active components in the catalyst into noble metal simple substances.

8. The method according to claim 6, wherein in the ion exchange operation of step (2), the amount of ion exchange is controlled so that: after the Beta molecular sieve treated by ammonium nitrate is roasted, the mass content of sodium and potassium elements is infinitely close to 0 percent; or after roasting the Beta molecular sieve treated by potassium nitrate, the mass content of the contained sodium element is infinitely close to 0 wt%, and the mass content of the contained potassium element is 13 wt%; or after roasting the Beta molecular sieve treated by the sodium nitrate, the mass content of the potassium element is infinitely close to 0 wt%, and the mass content of the sodium element is 7 wt%.

9. The method of using the catalyst of claim 1, comprising: