Monolithic catalyst and preparation method and use thereof

Abstract

The present application discloses a monolithic catalyst with the function of selective adsorption-catalytic oxidation of organic waste gas and a preparation method and application thereof. The present application adopts a double coating design. A first coating is a molecular sieve primer coating. A second coating is an active component coating, which uses a neutral silica sol, so as to protect the activity and effectiveness of a noble metal and a catalytic promoter on the molecular sieve.

Claims

1. A preparation method of a monolithic catalyst, comprising steps of: (1) pretreating a cordierite carrier by immersing in tetraethyl ammonium hydroxide solution for 2-3 hours, taking out and drying; (2) mixing an alkaline silica sol with trimethoxysilane by a mass ratio of 2.5-10:1 to form a stable sol, adding an all-silicon Beta molecular sieve, and wet grinding to particle size of 500 nm or below on a ball mill to prepare a first coating slurry, wherein the mass ratio of the all-silicon Beta molecular sieve to the alkaline silica sol is 1:4-15; and immersing the cordierite carrier obtained after drying in step (1) in the first coating slurry, taking out, blowing to remove residual slurry in pores, drying, and calcining at 300-400° C. for 3-8 hours, so as to prepare a first coating catalyst; and (3) mixing a neutral silica sol with a dispersant by a mass ratio of 25-50:1, adding an all-silicon Beta molecular sieve noble metal catalyst comprising an all-silicon Beta molecular sieve carrier and noble metals and a catalytic promoter carried on the all-silicon Beta molecular sieve carrier, and wet grinding to particle size of 500 nm or below on the ball mill to prepare a second coating slurry, wherein a mass ratio of the all-silicon Beta molecular sieve carrier in the all-silicon Beta molecular sieve noble metal catalyst to the neutral silica sol is 1:3-10; and immersing the first coating catalyst obtained in step (2) in the second coating slurry, and taking out, blowing to remove residual slurry in pores, drying, and calcining at 300-400° C. for 3-8 hours to prepare the monolithic catalyst with the function of selective adsorption-catalytic oxidation of organic waste gas.

2. The preparation method according to claim 1, wherein, in step (1), a mass concentration of the tetraethyl ammonium hydroxide is 1%-5%.

3. The preparation method according to claim 1, wherein, in step (2), pH value of the alkaline silica sol is 9-10.

4. The preparation method according to claim 1, wherein, in step (2), the all-silicon Beta molecular sieve is a wet material synthesized by using organic template-free seed method comprising crystallizing for 12-24 hours and suction filtering.

5. The preparation method according to claim 1, wherein, in step (3), the dispersant is one or two selected from a group consisting of polyethylene glycol and polypropylene glycol; and the all-silicon Beta molecular sieve carrier is synthesized by using a seed method in the absence of an organic template comprising crystallizing for 12-24, washing with deionized water to neutral, suction filtering, and drying; the noble metals comprise noble metal I and noble metal II with a molar ratio of 1-5:1, the noble metal I is ruthenium, and the noble metal II is platinum and/or palladium; and the catalytic promoter is an oxide of an auxiliary elements, and the auxiliary element is at least one selected from a group consisting of the cerium, lanthanum, copper, and manganese.

6. The preparation method according to claim 5, wherein, based on a total mass of the all-silicon Beta molecular sieve noble metal catalyst as 100%, the total mass ratio of the noble metal is 0.01%˜0.5%, and the total mass ratio of the auxiliary elements is 0.1%˜5%.

7. The preparation method according to claim 1, wherein, a preparation method of the all-silicon Beta molecular sieve noble metal catalyst is an immersion method comprising immersing the all-silicon Beta molecular sieve in a solution containing a noble metal precursor and a catalytic promoter precursor for 1-2 hours, suction filtering, drying, and calcining at 300-500° C. for 2-4 hours.

8. The preparation method according to claim 7, wherein, the noble metal precursor is at least one selected from a group consisting of noble metal chloride and noble metal nitrate.

9. A monolithic catalyst prepared according to the preparation method of claim 1, comprising a cordierite carrier and a surface coating made from the first coating slurry and the second coating slurry, wherein, a ratio of a loading mass of the surface coating to the mass of the cordierite carrier is not less than 8%, and a falling off rate of the surface coating is not more than 1%.

10. Use of the monolithic catalyst according to claim 9 in catalytic oxidation treatment of organic waste gas.

Description

DETAILED DESCRIPTION

(1) The present application will be further described below in combination with examples. It should be understood that, these examples are only used to illustrate the present application, but not intended to limit the protection scope of the present application. The operation method without specific conditions illustrating in the following examples is usually performed under conventional conditions or a condition recommended by a manufacturer.

(2) For the monolithic catalysts in the following examples and comparative examples, a method for computing a loading rate is: the loading rate=a loading mass of a surface coating/mass of a cordierite carrier×100%. The method of computing a falling off rate is: the falling off rate=(the mass of the monolithic catalyst before a falling off test−the mass of the monolithic catalyst after a falling off test)/the loading mass of the surface coating×100%. The falling off test method is as follows. The coated catalyst is placed into an ultrasonic cleaner, so as to measure the falling off rate of the coating. A sample before and after ultrasound treatment are oven dried at 80° C. for 2 hours, and then calcined at 300° C. for 2 hours in a muffle furnace.

Example 1

(3) (1) All-silicon Beta molecular sieves were synthesized by an organic template-free seed method, in which crystallization time was 24 hours. Some of the products were washed to neutral with deionized water and then suction filtered and dried (dry material A), and some of the products were merely subjected to suction filtration, without being dried (wet material B).

(4) (2) The dry material A was immersed in a saline solution consisting of ruthenium (III) chloride, palladium nitrate dihydrate, platinum (II) nitrate and cerium (III) nitrate hexahydrate by an impregnation method for 1 hour, and then suction filtered and dried, and calcined at 300° C. for 4 hours to obtain a molecular sieve catalyst. The mass of Pu, Pd, Pt and Ce (calculated by elemental mass) was 0.4%, 0.05%, 0.05% and 0.1% of the mass of the molecular sieve catalyst respectively.

(5) (3) The cordierite carrier was pretreated by immersing in 2 wt % of tetraethyl ammonium hydroxide solution for 2 hours, taken out, and then dried.

(6) (4) A first coating was coated. An alkaline silica sol (pH=9˜10) and trimethoxysilane were mixed to form a stable sol, added with the wet material B, and wet ground on a ball mill to particle size of 500 nm or below to prepare a first coating slurry. The mass ratio of trimethoxysilane to the alkaline silica sol was 1:4, and the mass ratio of the wet material B (calculated by the mass of the all-silicon Beta molecular sieve) to the alkaline silica sol was 1:5. The pretreated cordierite carrier was immersed in the first coating slurry, taken out, blown by using stable airflow to remove the residual slurry in pores dried, and calcined at 400° C. for 4 hours to prepare a first coating catalyst.

(7) (5) A second coating was coated. An neutral silica sol and dispersant polyethylene glycol were mixed to form the sable sol, added with the prepared molecular sieve catalyst, and wet ground on the ball mill to particle size 500 nm or below to prepare a second coating slurry. The mass ratio of the dispersant to the neutral silica sol was 1:30, and the mass ratio of the molecular sieve catalyst (calculated by the mass of the dry material A) to the neutral silica sol was 1:4. The prepared first coating catalyst was immersed in the second coating slurry, taken out, blown by using the stable airflow to remove residual slurry in the pores, dried, calcined at 400° C. for 4 hours to prepare the monolithic catalyst with the function of selective adsorption-catalytic oxidation of organic waste gas.

(8) The prepared monolithic catalyst had a loading rate of 10.3 wt %, and a falling off rate of 0.17 wt %. Under a condition of airspeed 20,000 h.sup.−1, purification efficiencies of benzene, toluene, xylene and ethyl acetate are 99% or higher at 224° C., 196° C., 193° C. and 275° C. respectively.

Comparative Example 1

(9) The example differs from Example 1 only in that the first coating wet material B was coated by the coating method for the second coating, and the other conditions were the same as in Example 1. The loading rate of the prepared monolithic catalyst was <5 wt %, and the falling off rate was >5 wt %.

Comparative Example 2

(10) The example differs from the Example 1 only in that the second coating molecular sieve catalyst was coated by the coating method for the first coating, and the other conditions were the same as in Example 1. The prepared monolithic catalyst was tested for activity under the same conditions as those for the catalyst prepared in Example 1, and the purification efficiencies of benzene, toluene, xylene and ethyl acetate were <50% at 224° C., 196° C., 193° C. and 275° C. respectively.

Comparative Example 3

(11) The example differs from the example 1 only in that the step (3) was omitted or the pretreatment was carried out with same concentration of sulfuric acid, nitric acid or sodium hydroxide the etc, and the other conditions was the same as in Example 1. The loading rate of the prepared monolithic catalyst was <5 wt %, and the falling off rate was >2 wt %.

Example 2

(12) (1) All-silicon Beta molecular sieves were synthesized by the organic template-free seed method, in which crystallization time was 18 hours. Some of the products were washed to neutral with deionized water and then suction filtered and dried (dry material A), and some of the products were subjected to suction filtration, without being dried (wet material B).

(13) (2) The dry material A was immersed in a saline solution consisting of ruthenium (III) chloride, palladium nitrate dihydrate, lanthanum nitrate and manganous nitrate by the impregnation method for 2 hours, suction filtered, dried, and calcined at 300° C. for 3 hours to obtain the molecular sieve catalyst. The mass of Ru and Pd (calculated by elemental mass) was 0.15%, 0.10%, 0.5% and 0.5% of the mass of the molecular sieve catalyst respectively.

(14) (3) The cordierite carrier was pretreated by immersing in 3 wt % of tetraethyl ammonium hydroxide solution for 2 hours, taken out and then dried.

(15) (4) The alkaline silica sol (pH=9-10) and trimethoxysilane were mixed to form the stable sol, added with the wet material B, and wet ground on the ball mill to particle size of 500 nm or below to prepare the first coating slurry. The mass ratio of trimethoxysilane to the alkaline silica sol was 1:6, and the mass ratio of the wet material B (calculated by the mass of the all-silicon Beta molecular sieve) to the alkaline silica sol was 1:10. The pretreated cordierite carrier was immersed in the first coating slurry, blown by using the stable airflow to remove the residual slurry in the pores, dried, and calcined at 400° C. for 3 hours to prepare the first coating catalyst.

(16) (5) The neutral silica sol and dispersant polypropylene glycol were mixed to form the sable sol, added with the prepared molecular sieve catalyst, and wet ground on the ball mill to particle size of 500 nm or below to prepare the second coating slurry. The mass ratio of the dispersant to the neutral silica sol was 1:50, and the mass ratio of the molecular sieve catalyst (calculated by the mass of the dry material A) to the neutral silica sol was 1:4. The prepared first coating catalyst was immersed in the second coating slurry, taken out, blown by using the stable airflow to remove residual slurry in the pores, dried, and calcined at 400° C. for 3 hours.

(17) The prepared monolithic catalyst had a loading rate of 9.7 wt % and a falling off rate of 0.15 wt %. Under a condition of airspeed 20,000 h.sup.−1, the purification efficiencies of benzene, toluene, xylene and ethyl acetate were 99% or higher at 232° C., 209° C., 204° C. and 281° C. respectively.

Example 3

(18) (1) All-silicon Beta molecular sieves were synthesized by the organic template-free seed method, in which crystallization time was 12 hours. Some of the products were washed to neutral with deionized water, suction filtered and dried (dry material A), and some of the products were subjected to suction filtration, without being dried (wet material B).

(19) (2) The dry material A was immersed in a saline solution consisting of ruthenium (III) chloride, platinum (II) nitrate, cerium (III) nitrate hexahydrate and manganous nitrate by the impregnation method for 2 hours, suction filtered, dried, and calcined at 300° C. for 3 hours to obtain the molecular sieve catalyst. The mass of Ru, Pd and Pt (calculated by elemental mass) was 0.05%, 0.05%, 1.5% and 1.0% of the mass of the molecular sieve catalyst respectively.

(20) (3) The cordierite carrier was pretreated by immersing in 5 wt % of tetraethyl ammonium hydroxide solution for 3 hours, then taken out, and dried.

(21) (4) The alkaline silica sol (pH=9-10) and trimethoxysilane were mixed to form the stable sol, added with the wet material B, and wet ground on the ball mill to particle size of 500 nm or below to prepare the first coating slurry. The mass ratio of trimethoxysilane to the alkaline silica sol was 1:8, and the mass ratio of the wet material B to the alkaline silica sol was 1:4. The pretreated cordierite carrier was immersed in the first coating slurry, taken out, blown by using the stable airflow to remove the residual slurry in the pores, dried, and calcined at 300° C. for 4 hours to prepare the first coating catalyst.

(22) (5) The neutral silica sol and polypropylene glycol were mixed to form the sable sol, added with the prepared molecular sieve catalyst, and wet ground on the ball mill to particle size of 500 nm or below to prepare the second coating slurry. The mass ratio of the dispersant to the neutral silica sol was 1:30, and the mass ratio of the molecular sieve catalyst (calculated by the mass of the dry material A) to the neutral silica sol was 1:5. The prepared first coating catalyst was immersed in the second coating slurry, taken out, blown by using the stable airflow to remove the residual slurry in the pores, dried, and calcined at 300° C. for 4 hours.

(23) The prepared monolithic catalyst had a loading rate of 9.4 wt %, and a falling off rate of 0.11 wt %. Under a condition of airspeed 20,000 h.sup.−1, the purification efficiencies of benzene, toluene, xylene and ethyl acetate were more than 99% at 237° C., 213° C., 216° C. and 295° C. respectively.

(24) It should be understood that after reading the above description of the present application, those skilled in the art can make various changes and modifications to the present application, and these equivalent forms should be also considered as falling within the scope limited by the claims appended in the present application.