CN110327916B - High-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of diesel vehicle - Google Patents

High-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of diesel vehicle Download PDF

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Publication number
CN110327916B
CN110327916B CN201910613669.0A CN201910613669A CN110327916B CN 110327916 B CN110327916 B CN 110327916B CN 201910613669 A CN201910613669 A CN 201910613669A CN 110327916 B CN110327916 B CN 110327916B
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catalyst
manganese oxide
soot particles
diesel vehicle
oxide catalyst
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CN110327916A (en
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王仲鹏
高一博
刘文旭
刘伟
何芳
王秀菊
王立国
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University of Jinan
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University of Jinan
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D49/00Separating dispersed particles from gases, air or vapours by other methods
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86Catalytic processes
    • B01D53/8621Removing nitrogen compounds
    • B01D53/8625Nitrogen oxides
    • B01D53/8628Processes characterised by a specific catalyst
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/16Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/32Manganese, technetium or rhenium
    • B01J23/34Manganese

Abstract

The invention relates to a high-activity amorphous manganese oxide catalyst material for oxidizing soot particles and NO of a diesel vehicle, wherein the chemical structural formula of the catalyst is MnOx. The catalyst is prepared from manganese acetate, glycine, silicon dioxide and absolute ethyl alcohol. The method has the advantages of cheap and easily-obtained raw materials, mild conditions, simple preparation process and method, and has important scientific significance and good application prospect. The prepared amorphous manganese oxide catalyst has the characteristics of large specific surface area, small particle size and mesoporous structure. The catalyst can be used for catalyzing and oxidizing soot particles and NO of the diesel vehicle respectively.

Description

High-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of diesel vehicle
Technical Field
The invention relates to preparation of a high-activity amorphous manganese oxide catalyst for oxidizing diesel vehicle soot particles and NO, and application of the catalyst in catalytic oxidation for removing the diesel vehicle soot particles and catalytic oxidation of NO, belonging to the field of nano material preparation and catalytic application.
Background
The diesel engine is used as the indispensable main flow power of commercial vehicles and power locomotives, and has incomparable advantages from the aspects of power performance, economy, application universality, use convenience and the like. However, the pollutants emitted by diesel vehicles include particulate matter (PM, mainly soot), nitrogen oxides (NOx), andcarbon Oxides (CO) and unburned Hydrocarbons (HC) are seriously harming the natural environment and human health. Therefore, an efficient tail gas aftertreatment process is imperative. The particulate filter (DPF) is used to collect soot particles in the exhaust gas of a diesel vehicle, which can be at a higher temperature (>600 deg.C) is oxidized by oxygen. However, the exhaust temperature of diesel vehicles is generally lower than 400 ℃, it is difficult to sufficiently burn soot particles at a relatively low temperature, and the particulate filter is deactivated after long-term use. The nitrogen oxide discharged from the exhaust of the diesel engine is mainly NO, and the NO is quickly and efficiently oxidized into NO with stronger oxidizing capability in the catalytic aftertreatment of the tail gas 2 And facilitate the denitration of both catalytic oxidation of soot and subsequent Lean NOx Trap (LNT) and selective catalytic reduction NOx (scr) systems. Therefore, it is an urgent task to develop a highly active amorphous manganese oxide catalyst for oxidizing soot particles and NO of a diesel vehicle.
At present, the catalysts for catalytic purification of automobile exhaust used at home and abroad mainly comprise noble metal catalysts, eutectic point catalysts, multi-component composite oxide catalysts and the like. Wherein, the noble metal catalyst has good low-temperature activity, but is easy to be poisoned and deactivated by sulfur, and has poor high-temperature stability; and the noble metal is expensive, which restricts the practical application of the noble metal catalyst. The alkali metal salt catalyst with the eutectic point is melted at high temperature, so that the catalyst has fluidity, the contact state between the catalyst and soot particles is further improved, and the catalytic oxidation of the soot particles is promoted, but the defects of poor stability, corrosion to ceramic DPF and the like are also brought by the characteristics of low melting point and strong alkalinity of the alkali metal catalyst. The multi-component composite oxide catalyst is represented by perovskite or perovskite-like catalysts and spinel structure catalysts, and the oxides have the advantages of high mechanical strength, good thermal stability, low price, high catalytic activity and the like, but the multi-component composite oxide catalyst is used for soot particle combustion reaction and has single functionality.
As one of the largest families of transition metal oxides, MnOx is increasingly being concerned by its unique properties and potential applications in the fields of supercapacitors, magnetism, chemical sensing and catalysisAnd (6) note. These applications are based on the environmental friendliness, low toxicity, diversified morphological structure and low cost of MnOx. Given the nature of the multiple valence states in manganese, Mn forms several stable crystalline manganese oxides: MnO, MnO 2 、Mn 2 O 3 、Mn 3 O 4 And so on. As prospective candidates, some of the above manganese oxides have also been used as effective catalysts for removing Volatile Organic Compounds (VOCs) and diesel exhaust gas. Compared with the crystal manganese oxide, the amorphous manganese oxide has the characteristics of short-range order and long-range disorder, and metal ions in the short-range order structures can exert strong interaction at an atomic level, so that the catalyst shows extremely excellent catalytic performance; and Mn related to multi-valence manganese ions and with rich valence states of manganese elements 2+ /Mn 3+ Or Mn 3+ /Mn 4+ The redox cycle of (a) is more favorable for the enhancement of its redox performance.
For the above reasons, it is economically and practically important to research and develop a highly active amorphous manganese oxide catalyst for oxidizing soot particles and NO of diesel vehicles.
Disclosure of Invention
The invention aims to provide a high-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of a diesel vehicle.
The invention relates to a high-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of a diesel vehicle, which comprises the following preparation steps:
(1) weighing appropriate amount of manganese salt (MnC) in proportion 4 H 6 O 4 ·4H 2 O)、CH 2 NH 2 COOH、SiO 2 Dissolving in deionized water, and stirring to obtain mixed solution;
(2) heating in a water bath at 150 ℃ for 1 hour, dropwise adding NaOH serving as a precipitator into a beaker under continuous stirring, and controlling the pH of the solution to be approximately equal to 11;
(3) standing to room temperature, carrying out suction filtration on the precipitate mixture, and then washing, drying and calcining at high temperature; (4) and cooling to room temperature, and taking out to obtain the amorphous manganese oxide catalyst.
Compared with the prior art, the invention has the following obvious substantive characteristics.
1. The catalyst synthesized by the method is an amorphous manganese oxide catalyst.
2. The MnOx catalyst synthesized by the invention is prepared by reacting CH 2 NH 2 COOH as fuel, SiO 2 Used as a template and is also used in the preparation process of the catalyst.
3. The MnOx catalyst synthesized by the invention has the advantages of large specific surface area, small particle size and mesoporous structure.
4. The invention has the functions of removing soot particles of the diesel vehicle by catalytic oxidation, catalytically oxidizing NO and the like.
5. The method is simple and easy to implement, mild in preparation conditions, cheap and easily available in raw materials, and free of toxic reaction raw materials, so that the catalyst is an environment-friendly green synthetic catalyst.
Drawings
Fig. 1 is an XRD pattern of the MnOx catalyst prepared according to the present invention.
Fig. 2 is a graph of the pore size distribution curve of the MnOx catalyst prepared according to the present invention.
FIG. 3 shows the MnOx catalyst prepared by the present invention at O 2 Soot particle catalytic oxidation pattern under atmosphere.
FIG. 4 shows the presence of MnOx catalyst in NO + O prepared by the present invention 2 Soot particle catalytic oxidation pattern under atmosphere.
Fig. 5 is a NO oxidation pattern for a MnOx catalyst prepared according to the present invention.
The first embodiment is as follows:
(1) MnC is added into deionized water according to the mol ratio of (7: 1: 1) 4 H 6 O 4 ·4H 2 O、CH 2 NH 2 COOH、SiO 2 The mixed solution was stirred until completely dissolved.
(2) And (2) slowly adding a NaOH solution into the solution obtained in the step (1) under the condition of continuous stirring, and controlling the pH value of the solution to be approximately equal to 11.
(3) Standing to room temperature, carrying out suction filtration on the solution obtained in the step (2), then washing, drying, calcining, cooling to room temperature, taking out, and obtaining the sampleIs a high-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of diesel vehicles, and is abbreviated as MnOx-1. No obvious diffraction peak is found in the sample through XRD detection, and the amorphous property of the manganese oxide is shown. The specific surface area is 87.7m after being tested 2 (ii)/g; FIG. 2 is a plot of the pore size distribution of a sample, and it can be seen that this type of pore size distribution is of mesoporous material (pore size distribution between 2 and 50 nm), where the most probable diameter of MnOx-1 is 20 nm.
Example two:
(1) MnC was added in deionized water at a molar ratio (7: 1: 2) 4 H 6 O 4 ·4H 2 O、CH 2 NH 2 COOH、SiO 2 The resulting mixed solution was stirred until completely dissolved.
(2) And (2) slowly adding a NaOH solution into the solution obtained in the step (1) under the condition of continuous stirring, and controlling the pH value of the solution to be approximately equal to 11.
(3) And (3) standing to room temperature, carrying out suction filtration on the solution obtained in the step (2), washing, drying, calcining, cooling to room temperature, and taking out to obtain a sample, namely the high-activity amorphous manganese oxide catalyst for carbon smoke particles and NO of the diesel oxidation vehicle, which is abbreviated as MnOx-2. No obvious diffraction peak is found in the sample through XRD detection, and the amorphous property of the manganese oxide is shown. The specific surface area is tested to be 61.2 m 2 (iv) g; FIG. 2 is a plot of the pore size distribution of the sample, and it can be seen that this type of pore size distribution is of mesoporous materials (pore size distribution between 2 and 50 nm), where the most probable diameter of MnOx-2 is 22 nm.
Example three:
(1) MnC was added in deionized water at a molar ratio (7: 2: 1) 4 H 6 O 4 ·4H 2 O、CH 2 NH 2 COOH、SiO 2 The resulting mixed solution was stirred until completely dissolved.
(2) And (2) slowly adding a NaOH solution into the solution obtained in the step (1) under the condition of continuous stirring, and controlling the pH value of the solution to be approximately equal to 11.
(3) Standing to room temperature, carrying out suction filtration on the solution obtained in the step (2),and then washing, drying, calcining, cooling to room temperature, and taking out, wherein the obtained sample is the high-activity amorphous manganese oxide catalyst for oxidizing carbon smoke particles and NO of the diesel vehicle, and is abbreviated as MnOx-3. No obvious diffraction peak is found in the sample through XRD detection, and the amorphous property of the manganese oxide is shown. The specific surface area is tested to be 33.2 m 2 (ii)/g; FIG. 2 is a plot of the pore size distribution of the sample, and it can be seen that this type of pore size distribution is of mesoporous materials (pore size distribution between 2 and 50 nm), where the most probable diameter of MnOx-3 is 32 nm.
Example four
The amorphous manganese oxide catalysts prepared in the first, second and third examples are taken respectively, the exhaust atmosphere of a diesel engine is simulated, the Printex-U carbon black of Degussa company of Germany is used for replacing soot particles discharged by the diesel engine, and the soot catalytic combustion activity of the catalysts is evaluated by adopting a temperature programming oxidation technology. As shown in FIG. 3, at O 2 Under the atmosphere, the ignition temperature of soot combustion on the catalyst is generally 290-320 ℃ measured according to the soot combustion reaction conversion rate curve, and CO is generated 2 The selectivity of the catalyst reaches 100 percent, and no CO is generated to cause secondary pollution. As shown in FIG. 4, in NO + O 2 In the atmosphere, the ignition temperature for catalyzing soot combustion on the catalyst is reduced to 280-310 ℃, and CO is generated 2 The selectivity of the catalyst also reaches 100 percent, NO CO is generated, and the pollution gas NO can be eliminated. The catalyst prepared by the method has good catalytic activity and high selectivity, and is related to larger specific surface area and smaller particle size.
EXAMPLE five
The amorphous manganese oxide catalysts prepared in the first, second and third examples are used for NO oxidation reaction, the catalyst is pressed and ground, the catalyst with 40-80 meshes is screened out and filled into a reaction tube with the diameter of 6mm, and the experiment is carried out in a fixed bed reactor, wherein the reaction temperature is 100-600 ℃. As shown in FIG. 5, NO can be efficiently oxidized to NO when the amorphous manganese oxide catalyst is present 2 The NO conversion can exceed 10% even at low temperatures of 100 ℃. When the temperature exceeds 200 ℃, the amorphous manganese oxide catalyst accelerates the NO oxidation rate, NO 2 Reaching the maximum at 350-The large generation amount and the maximum NO conversion rate of three amorphous MnOx are about 55 percent, which shows that the synthesized amorphous manganese oxide catalyst has excellent NO oxidation capability.

Claims (5)

1. A preparation method of a high-activity amorphous manganese oxide catalyst for oxidizing soot particles and NO of a diesel vehicle is characterized by comprising the following steps:
(1) with CH 2 NH 2 COOH as fuel, SiO 2 MnC is added into deionized water according to a certain proportion as a template 4 H 6 O 4 ·4H 2 O、CH 2 NH 2 COOH、SiO 2 Stirring to form a mixed solution until the mixed solution is completely dissolved;
(2) heating in a water bath at 150 ℃ for 1 hour, continuously stirring, and dropwise adding a precipitator NaOH solution, wherein the pH value of the solution is controlled to be 9-11;
(3) and (3) standing to room temperature, filtering the precipitate mixed solution obtained in the step (2), washing with absolute ethyl alcohol and deionized water, drying, and calcining at high temperature to obtain the material, namely the high-activity amorphous manganese oxide catalyst with the mesoporous structure for oxidizing diesel vehicle carbon smoke particles and NO.
2. The preparation method of the high-activity amorphous manganese oxide catalyst for diesel vehicle soot particles and NO according to claim 1, is characterized in that the concentration of glycine is 1.0-1.5 mol/L.
3. The method for preparing the amorphous manganese oxide catalyst for highly active diesel vehicle soot particles and NO according to claim 1, wherein in the step (3), the precipitated product is washed with deionized water and ethanol in sequence to remove impurities; in drying the precipitated product, the washed precipitated product is dried at 140-180 ℃ for at least 4 h.
4. The method for preparing the amorphous manganese oxide catalyst for oxidizing the soot particles and NO of the diesel vehicle with high activity according to claim 1, is characterized in that: the molar ratio of the silicon dioxide to the glycine is 1-2.
5. The method of claim 1, wherein the catalyst is prepared from amorphous manganese oxide of highly active diesel soot particles and NO, and the catalyst is characterized in that: meanwhile, the catalyst has the function of catalyzing and oxidizing soot particles and NO of the diesel vehicle with high activity.
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