CN111068710A

CN111068710A - Catalyst for burning carbon smoke and preparation method and application thereof

Info

Publication number: CN111068710A
Application number: CN201911283480.6A
Authority: CN
Inventors: 韦岳长; 梅雪垒; 张鹏; 俞旗; 赵震; 刘坚
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2020-04-28

Abstract

The invention provides a catalyst for burning soot, a preparation method and application thereof. The preparation method comprises the following steps: preparing a precursor solution containing metal ions and citric acid; dipping the colloidal crystal template into a precursor solution, aging for 38-48 h at 35-40 ℃ under vacuum, washing and drying to obtain a template with a precursor; heating the template with the precursor to 600-650 ℃ at the speed of 1-2 ℃/min under the aerobic condition, keeping for 4-6 h, and naturally cooling to obtain the catalyst for soot combustion. The catalyst prepared by the preparation method disclosed by the invention is perfect in microscopic appearance and ordered in macroporous arrangement, and can effectively improve the contact area of the catalyst and the soot and effectively catalyze the combustion of soot particles.

Description

Catalyst for burning carbon smoke and preparation method and application thereof

Technical Field

The invention relates to a catalyst, in particular to a catalyst for catalyzing combustion of soot particles, and belongs to the technical field of catalyst preparation.

Background

The diesel engine has high fuel efficiency and low CO₂The characteristics of emission and high durability, thereby having important effect on modern society and being widely applied to automobiles, ships and large-scale machinery. However, the main emissions of diesel engines are soot Particulates (PM) and NO_xThe pollution to the atmospheric environment is becoming more and more serious, and the ecological environment and the human health are seriously threatened. Pollutants emitted by motor vehicles are one of the main sources of PM2.5 in urban atmosphere, especially in large cities, particulate matters, VOC, polycyclic aromatic hydrocarbons and SO emitted by motor vehicles₂、NO_xAnd metal ions and the like are main components of PM 2.5. Therefore, the reduction of PM emission is an important task of diesel vehicle tail gas catalytic purification, and the development of research on the aspect has important environmental protection significance.

The catalytic deep oxidation combustion of the soot is the most effective means for eliminating the emission of soot particles, and various catalysts have been researched and proved to have good effects on the catalytic combustion of the soot, such as alkali metal oxides, transition metal oxides, perovskite type oxides, composite oxides carrying noble metals and cerium-based oxides. Noble metals have the best catalytic activity, but are expensive and limited in resources, as the search for alternative catalysts is urgent.

Disclosure of Invention

The invention aims to provide a catalyst for catalyzing combustion of soot particles.

The invention also aims to provide a preparation method of the carbon smoke particle combustion catalyst.

Still another object of the present invention is to provide a use of the above soot particulate combustion catalyst in catalytic combustion of soot particulates.

In order to achieve the above object, the present invention firstly provides a method for preparing a soot combustion catalyst, comprising the steps of:

preparing a precursor solution containing metal ions and citric acid;

dipping the colloidal crystal template into a precursor solution, aging for 38-48 h at 35-40 ℃ under vacuum, washing and drying to obtain a template with a precursor; dipping 3g-8g of colloidal crystal template in every 10mL of precursor solution;

heating the template with the precursor to 600-650 ℃ at the speed of 1-2 ℃/min under the aerobic condition, keeping for 4-6 h, and naturally cooling to obtain the catalyst for soot combustion.

The preparation method of the catalyst for burning the carbon smoke takes the centrifugally assembled polymethyl acrylate microspheres as a colloidal crystal template, takes the citric acid complex as a precursor solution, soaks the colloidal crystal template into the precursor solution, and obtains the catalyst for burning the carbon smoke through heat treatment_XAnd deep oxidation of CO.

The preparation method of the catalyst for burning the soot comprises the step of preparing a precursor solution containing metal ions and citric acid.

In one embodiment of the present invention, the precursor solution is prepared according to the following steps:

mixing (y-x) mol of lanthanum nitrate, xmol of potassium nitrate, 0.5ymol of nitric acid B and 0.5ymol of nitric acid B' to prepare an aqueous solution with the total metal ion concentration of 2ymol/L, adding citric acid (solid), and stirring for more than 2 hours in a water bath at 15-40 ℃ until the solution is clear to obtain a precursor solution, wherein x is 0.05-0.50 y, and y is 0.1-1.

Specifically, the nitric acid B is a nitrate of Mn or Ni, and the nitric acid B' is a nitrate of any one of Mn, Fe, Co, Ni and Cu.

Specifically, the molar ratio of citric acid to total metal ions is 0.5-1.5: 1.

the total metal ions refer to all metal ions in lanthanum nitrate, potassium nitrate, nitric acid B and nitric acid B'.

More specifically, the time for stirring in the water bath may be 3h to 7 h.

The preparation method of the catalyst for soot combustion comprises the step of preparing a Colloidal Crystal Template (CCT).

In one embodiment of the present invention, the colloidal crystal template can be prepared by the following steps:

stirring Methyl Methacrylate (MMA) monomer and water at 70-85 ℃ for more than 20min, and introducing Ar (as protective gas) into the reaction system to obtain emulsion A;

dissolving an initiator in water under the water bath condition of 70-85 ℃ to obtain a solution B;

mixing the solution B with the emulsion A, introducing Ar (as protective gas), and stirring and reacting for 1.5-2.5 h in a water bath at the temperature of 70-85 ℃ to obtain white suspension polymethyl methacrylate (PMMA);

and centrifuging the PMMA suspension at the rotating speed of 2000-4000 rpm for 8-14 h, removing supernatant liquid, and drying the solid at the temperature lower than 50 ℃ for more than 12h to obtain a Colloidal Crystal Template (CCT).

The prepared polymethyl methacrylate (PMMA) microspheres have the diameter of 150nm-600 nm.

Among them, MMA monomer is previously distilled under reduced pressure for purification. Specifically, the volume ratio of MMA monomer to water is (50-120): 310-240). For example, MMA monomer may be added in an amount of (50-120) mL, and water may be added in an amount of (310-240) mL.

Specifically, the initiator is recrystallized potassium persulfate (KPS), and KPS is dissolved in water in advance during the introduction process. The initiator used is a recrystallized aqueous solution of potassium persulfate, wherein the ratio of potassium persulfate to water is from 0.3g to 1.5 g: 40 mL.

The preparation method of the catalyst for burning the soot comprises the step of mixing the colloidal crystal template with the precursor solution.

Specifically, putting the CCT into a watch glass, slowly spraying the precursor solution into the watch glass, then putting the watch glass into a vacuum drying oven for full immersion, taking out a sample after aging, performing suction filtration to remove the redundant precursor solution, leaching the solid for three times by using a 95% ethanol solution, transferring the solid to a crucible, and drying in an oven at the temperature lower than 50 ℃ for more than 12 hours to obtain the soaked CCT.

And (3) soaking in a vacuum environment, and pumping out gas between the microspheres of the colloidal crystal template so that the precursor solution can enter gaps between the microspheres.

The invention also provides a catalyst for burning the soot, which is prepared by the preparation method of the catalyst for burning the soot. The catalyst is a three-dimensional ordered macroporous double perovskite type material-La_2-xK_xBB’O₆(x ═ 0.05 to 0.50, B ═ Mn, Ni, B ═ Mn, Fe, Co, Ni, and Cu), and the pore diameter is 100nm to 450 nm.

Because the catalytic combustion elimination reaction of the soot particles is a gas-solid (particulate matter) -solid (catalyst) three-phase complex deep oxidation reaction process, the improvement of the catalyst activity is closely related to the oxidation-reduction performance of the oxide catalyst and the contact degree of the solid catalyst and reactants. The higher the contact capacity of the catalyst with the particles, the better the activity. The catalyst is a three-dimensional ordered macroporous (3DOM) material, has the advantages of large specific surface area, high porosity, strong periodicity of pore structure arrangement, narrow pore size distribution and uniform and adjustable macroporous size, can effectively improve the contact area of the catalyst so as to improve the catalytic activity, and has larger specific surface area and better oxidation activity, so that the catalyst with the three-dimensional ordered macroporous structure has higher catalytic activity.

The catalyst for burning the soot can further load noble metal to obtain the noble metal-loaded catalyst.

The soot combustion catalyst of the present invention can be used to catalyze soot combustion, such as the purification of soot particulates emitted by an automotive vehicle.

The catalyst of the invention has better catalytic performance than a Pt-based catalyst under the condition of loose contact, can greatly reduce the use amount of noble metal and reduce the enterprise cost.

The catalyst for burning the soot can catalyze at the temperature of 150-400 ℃, and meets the use requirement of a motor vehicle during cold start.

When the catalyst is specifically used for catalyzing the combustion of the soot, the mass ratio of the soot to the catalyst for the combustion of the soot is 5-20: 1. The preparation method of the catalyst for burning the soot is simple and easy to implement, the preparation raw materials do not contain toxic and harmful substances, the reaction conditions are easy to obtain, and the preparation period is short. The pore diameter of the macropore is controllable within the range of 100-450nm, the obtained catalyst has large specific surface area and shows good carbon smoke catalytic activity and CO₂The selectivity and the catalytic activity of the catalyst are equivalent to those of the existing noble metal catalyst, and the catalyst has better catalytic performance than a Pt-based catalyst under the loose contact condition, and has higher application value in the field of catalytic purification of motor vehicle tail gas.

The catalyst for burning the carbon smoke has perfect microscopic appearance and ordered arrangement of macropores, and can effectively improve the contact area of the catalyst and the carbon smoke. The elements B and B 'are orderly and alternately arranged under the action of super exchange, and the unique arrangement structure is favorable for strong interaction of the elements B and B', so that active oxygen species are generated, the catalytic oxidation activity of particles discharged by a motor vehicle can be greatly improved, and particularly the low-temperature catalytic activity meets the requirement of cold start of the motor vehicle.

Drawings

FIG. 1a is a scanning electron micrograph of the colloidal crystal template (PMMA microspheres) prepared in example 1.

FIG. 1b is the 3DOM La prepared in example 2₂NiMnO₆Scanning electron micrograph (c).

FIG. 1c is the 3DOM La prepared in example 2₂NiFeO₆Scanning electron micrograph (c).

FIG. 1d is the 3DOM La prepared in example 2₂NiCoO₆Scanning electron micrograph (c).

FIG. 1e is the 3DOM La prepared in example 2₂NiCuO₆Scanning electron micrograph (c).

FIG. 1f is a 3DOM La prepared in example 3_1.95K_0.05NiCoO₆Scanning electron micrograph (c).

FIG. 1g is a 3DOM La prepared in example 3_1.80K_0.20NiCoO₆Scanning electron micrograph (c).

FIG. 2 shows catalyst 3DOM La prepared in example 2₂NiB’O₆X-ray diffraction pattern of (a).

FIG. 3 is catalyst 3DOM La prepared in example 2₂NiB’O₆The activity evaluation result of (4).

FIG. 4 shows catalyst 3DOM La prepared in example 3_2-xK_xNiCoO₆The activity evaluation result of (4).

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

Example 1

Single initiation preparation of Colloidal Crystal Template (CCT)

(1) Purification of initiator Potassium persulfate (KPS)

Approximately 10g of potassium persulfate (K) was weighed out by its solubility₂S₂O₈) Dissolving the white powder in about 100mL of water bath at 40 deg.C with a certain amount of water, rapidly filtering with a heated Buchner funnel, cooling with ice water to crystallize, filtering the crystals and washing with ice waterWashing until no SO is in the washing liquid₄ ^2-And (4) checking by using a barium chloride solution, finally, placing the white needle-shaped crystal in a vacuum drying oven (preventing KPS from decomposing) to dry for more than 12h at 50 ℃, and sealing and storing.

(2) Purification of monomeric Methyl Methacrylate (MMA)

Methyl methacrylate was distilled under reduced pressure at 40 ℃ to obtain purified methyl methacrylate.

(3) Synthesis of PMMA and assembly of Colloidal Crystal Template (CCT)

The four-necked bottle is placed into a water bath kettle, heating is started, the temperature is set to be 80 ℃, and 290mL of water is measured by a measuring cylinder and added into a reactor of the four-necked bottle. The middle opening of the four-opening bottle is communicated with a mechanical stirring paddle, and the other three openings are respectively communicated with Ar gas, a condensing tube and a rubber plug. After the instrument is fixed, the flow rate of Ar gas is introduced into the instrument at 30-40mL/min, and a stirring device is introduced to adjust the rotating speed to 350 rpm. After the water bath was heated to 80 ℃, 70mL MMA was added through the mouth of the rubber stopper with a glass funnel, and after stirring for 20min, 40mL of an aqueous solution containing 0.3g KPS (the aqueous solution of KPS was obtained by dissolving with 40mL water in a separate beaker at 80 ℃). The reaction was stopped after 2h at 80 ℃ and the resulting milky white reaction solution was filtered through a microporous membrane in a Buchner funnel for subsequent experiments. And putting the synthesized PMMA microspheres into a centrifuge tube, and centrifuging at the rotating speed of 3000rpm for 600min to obtain the CCT.

The scanning electron micrograph of the colloidal crystal template (PMMA microsphere) prepared in this example is shown in fig. 1 a.

Example 2

3DOM La₂NiB’O₆Preparation of double perovskite metal oxide catalyst

(1) Preparation of precursor solution

Weighing 4.33g of lanthanum nitrate, 1.45g of nickel nitrate and corresponding nitrate of 0.05mol B 'to dissolve in 10mL of distilled water, then adding 0.2mol of citric acid, and stirring for more than 2h under the condition of 35 ℃ water bath until the solution is clear to obtain a precursor solution, wherein the nitrate of B' is respectively Mn nitrate, Fe nitrate, Co nitrate and Cu nitrate.

(2) Impregnation and calcination of CCT

Weighing about 3g of CCT of example 1, pouring 10mL of the precursor solution obtained in the previous step on the CCT, putting the CCT into a vacuum drying oven for dipping for 48 hours at 40 ℃, taking out the CCT, then leaching the CCT with 95% ethanol solution for 3 times, using a Buchner funnel for pumping dry each time, and then transferring the solid above the Buchner funnel into an oven at 50 ℃ for drying for at least 12 hours. Transferring to a muffle furnace, heating to 650 deg.C at 1 deg.C/min under aerobic condition, and holding at the temperature for 4 hr to obtain solid 3DOM La₂NiB’O₆A double perovskite metal oxide catalyst.

In this example, the 3DOM La prepared in this example₂NiMnO₆FIG. 1b shows a scanning electron micrograph of (A). Preparation of the resulting 3DOM La₂NiFeO₆FIG. 1c shows a scanning electron micrograph of (A). Preparation of the resulting 3DOM La₂NiCoO₆FIG. 1d shows a scanning electron micrograph of (A). Preparation of the resulting 3DOM La₂NiCuO₆FIG. 1e shows a scanning electron micrograph of (A).

Catalyst 3DOM La prepared in this example₂NiB’O₆The X-ray diffraction pattern of (A) is shown in FIG. 2, and curve a in FIG. 2 is 3DOM La₂NiMnO₆Curve b is 3DOM La₂NiFeO₆Curve c is 3DOM La₂NiCoO₆Curve d is 3DOMLa₂NiCuO₆Curve e is 3DOM LaNiO₃. The 3DOM La prepared can be seen from FIG. 2₂NiB’O₆Are all mixed with LaNiO₃Diffraction peaks with similar positions, indicating that 3DOM La is prepared₂NiB’O₆The perovskite structure is still maintained.

Example 3

3DOM La_2-xK_xNiCoO₆(x-0.05-0.50) preparation of double perovskite Metal oxide catalyst

Preparation of precursor solution

Weighing (0.1-x) mol of lanthanum nitrate, xmol of potassium nitrate, 1.45g of nickel nitrate and 1.45g of cobalt nitrate, dissolving in 10mL of distilled water solution, adding 0.2mol of citric acid, and stirring for more than 2 hours under the condition of 35 ℃ water bath until the solution is clear to obtain a precursor solution. Specific value of x0.025, 0.050, 0.10, 0.15, 0.20 and 0.25 respectively, to obtain 3DOM La_1.95K_0.05NiCoO₆、3DOM La_1.90K_0.20NiCoO₆、3DOM La_1.80K_0.20NiCoO₆、3DOMLa_1.70K_0.30NiCoO₆、3DOM La_1.60K_0.40NiCoO₆And 3DOM La_1.50K_0.50NiCoO₆The precursor solution of (1).

Impregnation and calcination of CCT

Weighing about 3g of CCT of example 1, pouring 10mL of precursor solution obtained in the previous step on the CCT, putting the CCT into a vacuum drying oven at 40 ℃ for soaking for 48h, taking out the CCT, then leaching the CCT for 3 times by using 95% ethanol solution, drying the CCT by using a Buchner funnel each time, then transferring the solid above the Buchner funnel into a drying oven at 50 ℃ for drying for at least 12h, then transferring the solid to a muffle furnace, heating to 600 ℃ at the speed of 1 ℃/min, keeping the temperature at the temperature for 4h, and obtaining the solid with 3DOM La_2-xK_xNiCoO₆A double perovskite metal oxide catalyst.

3DOM La prepared in this example_1.95K_0.05NiCoO₆FIG. 1f shows a scanning electron micrograph of (A). Preparation of the resulting 3DOM La_1.80K_0.20NiCoO₆FIG. 1g shows a scanning electron micrograph of (A).

Example 4

The catalysts of example 2 and example 3 were characterized for activity.

The method of Temperature Programmed Oxidation (TPO) is utilized to simulate the catalytic combustion process of the soot under the real condition, the redox activity of the catalyst is evaluated by comparing the temperature required by burning the same quality of soot in an experiment, and the smaller the T50 value is, the better the catalytic activity is. Analyzing the reaction tail gas on a gas chromatograph to obtain CO₂And (4) selectivity. The reaction gas (simulated automobile exhaust) consists of: 0.2% NO, 10% O2, and 89.8% Ar (by volume), with a total gas flow of 50 mL/min.

100mg of the catalysts of examples 2 and 3 and 10mg of the simulated soot particles (the simulated diesel soot particles manufactured by Degussa company are selected for experiments, the particle size is controlled at 25nm), the two are uniformly mixed by a medicine spoon (loose contact) and then are filled into a quartz tube with the inner diameter of 6mm, the reaction gas is introduced, TOP is heated at the speed of 2 ℃/min, and the reaction tail gas is introduced into a gas chromatograph (SP-3420 type gas chromatograph manufactured by Beijing analytical instrument factory) for analyzing the product every 5 min. The results are shown in tables 1 and 2, and fig. 3 and 4.

TABLE 1

Catalyst and process for preparing same	T₁₀/℃	T₅₀/℃	T₉₀/℃	S_CO2 ^m(％)
					Soot particles emitted by motor vehicles	482	585	646	55.0
3DOM La₂NiMnO₆	296	384	418	98.4
					3DOM La₂NiFeO₆	273	369	412	96.9
3DOM La₂NiCoO₆	281	360	410	98.6
					3DOM La₂NiCuO₆	309	380	428	96.1

TABLE 2

Catalyst and process for preparing same	T₁₀/℃	T₅₀/℃	T₉₀/℃	S_CO2 ^m(％)
					3DOM La_1.95K_0.05NiCoO₆	272	357	402	98.9
3DOM La_1.90K_0.10NiCoO₆	284	346	391	99.1
					3DOM La_1.80K_0.20NiCoO₆	294	348	388	99.3
3DOM La_1.70K_0.30NiCoO₆	297	354	402	98.5
					3DOM La_1.60K_0.40NiCoO₆	293	361	395	99.4
3DOM La_1.50K_0.50NiCoO₆	284	349	395	98.6

As can be seen from fig. 1a, the Colloidal Crystal Template (CCT) prepared in example 1 has uniform particle size of PMMA microspheres, and the CCT stacking condition after centrifugal assembly is perfect.

As can be seen from FIGS. 1b to 1g, the prepared three-dimensionally ordered macroporous La_2-xK_xBB’O₆(x is 0.05-0.50) catalyst pore channels are communicated in a three-dimensional ordered manner, the pore diameter is uniform, the pore wall thickness is uniform, a clearly visible small pore window is displayed below each large pore, the pore diameter of each large pore is about 260nm, carbon smoke particles can enter the pore channels of the catalyst under the assistance of airflow, and the contact efficiency with the catalyst is improved.

As can be seen from Table 1 and FIG. 3, 3DOM La was prepared₂NiB’O₆The double perovskite metal oxide catalyst has good catalytic performance on soot, wherein 3DOM La₂NiCoO₆The best catalytic performance is shown among the four catalysts, T₅₀At 360 c, this is close to the catalytic activity of the noble metal Pt-based catalyst under loose contact.

As can be seen from Table 2 and FIG. 4, 3DOM La was prepared_2-xK_xNiCoO₆(x is 0.05-0.50) double perovskite metal oxide catalyst with excellent performance on carbon smoke catalysis, wherein 3DOM La_1.90K_0.10NiCoO₆The best catalytic performance is shown among the four catalysts, T₅₀At 346 c, which is superior to the catalytic activity of noble Pt-based catalysts under loose contact. Perovskite La with 3DOM structure and K-based non-noble metal substitution_2-xK_xNiCoO₆The (x is 0.05-0.50) double perovskite metal oxide catalyst has good practical application prospect in catalytic combustion of diesel soot particles, and can greatly reduce the use amount of noble metals and reduce the enterprise cost.

Claims

1. A preparation method of a catalyst for burning soot comprises the following steps:

preparing a precursor solution containing metal ions and citric acid;

2. The production method according to claim 1, wherein the precursor solution is produced by:

mixing (y-x) mol of lanthanum nitrate, xmol of potassium nitrate, 0.5ymol of nitric acid B and 0.5ymol of nitric acid B' to prepare an aqueous solution with the total metal ion concentration of 2ymol/L, adding citric acid, and stirring in a water bath at 15-40 ℃ for more than 2 hours until the solution is clear to obtain a precursor solution, wherein x is 0.05-0.50 y, and y is 0.1-1.

3. The method according to claim 2, wherein B is Mn or Ni, and B' is any one of Mn, Fe, Co, Ni, and Cu.

4. The preparation method according to claim 2, wherein the molar ratio of citric acid to total metal ions is 0.5-1.5: 1;

the water bath stirring time is preferably 2h-7 h.

5. The method of claim 1, wherein the colloidal crystal template is prepared by the steps of:

stirring methyl methacrylate monomer and water for more than 20min under the water bath condition of 70-85 ℃, and simultaneously introducing Ar into a reaction system to obtain an emulsion A;

mixing the solution B with the emulsion A, introducing Ar, and stirring and reacting for 1.5-2.5 h in a water bath at the temperature of 70-85 ℃ to obtain a white suspension polymethyl methacrylate;

centrifuging the polymethyl methacrylate suspension at the rotating speed of 2000rpm-4000rpm for 8h-14h, removing supernatant, and drying the solid at the temperature lower than 50 ℃ for more than 12h to obtain the colloidal crystal template.

6. The method as claimed in claim 5, wherein the volume ratio of the methyl methacrylate monomer to water is (50-120): (310-240);

preferably, the initiator is a recrystallized aqueous solution of potassium persulfate, wherein the ratio of potassium persulfate to water is from 0.3g to 1.5 g: 40 mL.

7. A soot combustion catalyst prepared by the method for preparing a soot combustion catalyst according to any one of claims 1 to 6.

8. The catalyst of claim 7, which is a three-dimensionally ordered macroporous material La_2-xK_xBB’O₆(x is 0.05-0.50) and the pore diameter is 100nm-450 nm.

9. Use of a soot-burning catalyst as claimed in claim 7 or 8 for catalyzing soot burning.

10. Use according to claim 9, wherein the mass ratio of the substance to be treated to the soot-burning catalyst is 5-20: 1.