CN101733110A - Three-dimensional ordered macroporous oxide catalyst for diesel soot purification and preparation method thereof - Google Patents

Abstract

The invention relates to a macroporous composite metal oxide catalyst for purifying diesel soot and a preparation method thereof. The present invention firstly provides an oxidation catalyst for the combustion of soot particles emitted by diesel vehicles, which is composed of more than one element among rare earth metals, transition metals and basic metals as active components and has a three-dimensional ordered macroporous structure Simple metal oxides or composite metal oxides, wherein the average pore diameter of the catalyst is 50nm-1μm. The use of the above-mentioned catalyst with a three-dimensional ordered macropore structure is beneficial to the diffusion of soot particles in the pores, improves the utilization rate of the active surface area of the catalyst, and greatly reduces the combustion temperature of the soot particles. The present invention also provides the preparation method of the above-mentioned catalyst, which is obtained by impregnating the colloidal crystal template with the organic complexing agent solution containing the salt of the active component, and then calcining the above-mentioned catalyst.

Description

Three-dimensional ordered macroporous oxide catalyst for diesel soot purification and preparation method thereof

technical field

The invention relates to a technology for purifying soot particles emitted by diesel vehicles, in particular to a three-dimensional ordered macroporous oxide catalyst for purifying diesel soot and a preparation method thereof, belonging to the technical field of environmental protection.

Background technique

Improving the activity of the catalyst for purifying soot particulate matter (PM) from diesel vehicle exhaust, reducing the combustion temperature of soot particulate matter, so that the soot particulate matter trap can work continuously for a long time is the most direct way to reduce the soot particulate matter emitted by diesel engines method. Since the elimination reaction of soot is a gas-solid (soot)-solid (catalyst) three-phase complex deep oxidation reaction process, the improvement of catalyst activity is not only closely related to the redox performance of the oxide catalyst itself, but also to the solid The contact degree of catalyst and PM is closely related. For catalysts with the same active component, the higher the contact ability with soot, the better the activity. However, due to the large particle size of the soot particles (the diameter of a single soot particle is greater than 25nm), it is difficult to enter the micropores of the catalyst or carrier for reaction. Diffusion also has a certain resistance, and the soot particles can only contact the outer surface of the catalyst, so that the utilization rate of the active surface area is greatly reduced.

Composite metal oxides with fixed structures such as perovskite, perovskite-like, spinel, scheelite or Ce-based solid solution have flexible design features and unique physical properties that can be "chemically tailored" (such as ferromagnetism, ferroelectricity, superconductivity, thermal conductivity, adsorption, etc.), this type of catalyst also has high catalytic activity for the combustion of soot. Chinese patent CN1743067A discloses several perovskite and perovskite-like series nano-ultrafine particle catalysts that can be used to catalyze the combustion of carbon particles in diesel engine exhaust. The use of such catalysts can significantly reduce the combustion temperature of carbon particles, making them Reach the temperature range required for diesel vehicle exhaust purification. Although this type of catalyst is nano-ultrafine particles, which can improve the contact performance between the catalyst and carbon particles, the pore size of the catalyst is less than 10nm, and it is difficult for soot particles to enter the catalyst pores for reaction, and can only contact the outer surface of the catalyst. The active specific surface area utilization rate is low. Therefore, the preparation of macroporous catalysts is of great significance for diesel soot combustion.

According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), macroporous materials refer to porous materials with a pore diameter greater than 50 nm, and can be divided into ordered macroporous materials and disordered macroporous materials according to the order and disorder of their channels. hole material. Three-dimensionally ordered macroporous materials (3DOM materials, Three-dimensionally Ordered Macroporous Materials) have two characteristics of specific composition and periodic ordered macropores, with large pore size, uniform pore distribution, and orderly arrangement of channels. Compared with other porous materials, Its unique pore structure is conducive to the entry of substances into the pores from all directions, reduces the diffusion resistance of substances, provides the best flow rate and higher efficiency for the diffusion of substances, and has broad application prospects in many fields such as catalysts and carrier materials.

At present, the method for preparing three-dimensional ordered macroporous materials is mainly the colloidal crystal template method, which generally includes the following steps: First, artificially stack monodisperse microspheres into a three-dimensional ordered structure similar to opal in nature. Substances, so-called colloidal crystals (or synthetic opal), are face-centered cubic (fcc) structures, in which colloidal particles account for 74% (volume ratio), and air accounts for 26% (volume ratio); secondly, the liquid precursor The gaps between the colloidal crystals are filled with solids and converted into solid skeletons in situ; finally, the microspheres are removed to obtain a solid skeleton in the gaps between the original microspheres, and the positions occupied by the original microspheres become interconnected holes. The resulting three-dimensional ordered structure is the inverse structure of opal, known as inverse opal.

Chinese patent publication CN101199929A discloses a macroporous Pt/ _CeO2 catalyst for water gas shift reaction and its preparation method. The catalyst uses three-dimensional ordered macroporous _CeO2 prepared from polystyrene colloidal crystals as a template as a carrier. The noble metal Pt is loaded as the active component. The three-dimensional ordered macroporous carrier-supported catalyst has the characteristics of high activity, good selectivity and good stability when used in water gas shift reaction.

Most of the technical solutions disclosed in existing reports on macroporous metal oxides use organic salts such as metal alkoxides, oxalates, and acetates as sources of active components. However, the alkoxide precursors of transition metals and lanthanide metals are difficult to prepare, and the cost is high, which is not suitable for the preparation of 3DOM composite metal oxides; although the oxalates and acetates of common metals do not have such problems, each The reactivity of the metals with acids and bases is different, and the solubility of the generated oxalate and acetate in the reaction medium is different, which will lead to the stoichiometric ratio of the metal oxide obtained after roasting and the original stoichiometric ratio. Inconsistent, it is difficult to obtain the required chemical composition of composite metal oxides; currently, metal organic salts are only used to prepare simple metal oxides.

In view of the above-mentioned problems of metal organic salts, some current researches have begun to focus on the use of inorganic salts of active components to prepare metal oxides. Nitrate is a common common salt. If nitrate can be used as a raw material, the cost will be greatly reduced. . However, the melting point of nitrate is very low. When the colloidal crystal template method is used to prepare metal oxides, the nitrate has already decomposed before the colloidal crystal template is removed, and it is difficult to obtain the 3DOM structure. The nitrate can be converted into a metal precursor with a higher melting point through complexation, which can penetrate into the colloidal crystal template and convert into the corresponding metal oxide without melting, thereby obtaining a three-dimensional ordered macroporous structure. Wu Quanzhou and others reported in "Research on Preparation of Three-Dimensional Ordered Macroporous Metal Oxide Materials from Nitrate" (Acta Chemica Sinica, Volume 63, No. 10, 2005, 891-896): Citric acid can be used to complex the nitrate Metal ions, which are converted into complexes with higher melting points, and further calcined to obtain three-dimensional ordered macroporous metal oxide materials: Al ₂ O ₃ , CeO ₂ , Cr ₂ O ₃ , NiO, MgO, In ₂ O ₃ , CeO ₂ /Al ₂ O ₃ , Cr ₂ O ₃ /Al ₂ O ₃ and NiO/Al ₂ O ₃ . The process method disclosed in this document is a technical solution for preparing simple metal oxides with three-dimensional ordered macroporous structure. Since citric acid is prone to self-combustion at relatively low temperatures (about 100-300 ° C), the reaction conditions are not properly controlled. , it may lead to failure to obtain the 3DOM structure. In addition, citric acid itself is a solid, and as a complexing agent, it is not as convenient as a liquid complexing agent in operation. For example, the aqueous solution of citric acid needs to be refluxed for a long time to obtain a colloid-like solution before it can be used as a complexing agent. Moreover, due to the different coordination abilities of citric acid to different metal ions, citric acid is used as a complexing agent to prepare perovskite-type, perovskite-like, spinel-type, scheelite-type, and Ce-based solid solution When three-dimensionally ordered macroporous composite metal oxides are used, the composition of the obtained composite metal oxides is difficult to keep consistent with the metal molar ratio in the precursor solution, and it is difficult to obtain composite metal oxides that meet the requirements of the stoichiometric ratio.

In view of the above-mentioned characteristics of the three-dimensional ordered macroporous structure, the preparation and development of metal oxides with a three-dimensional ordered macroporous structure, such as simple metal oxides and perovskite type, perovskite-like type, spinel type, scheelite Mineral type, Ce-based solid solution type composite metal oxide, which is used as a catalyst for the combustion of soot particles emitted by diesel vehicles, can improve the utilization rate of the active surface of the catalyst, reduce the combustion temperature of soot particles, reduce the exhaust pollution of diesel vehicles, and protect Environment matters.

Contents of the invention

In order to solve the above technical problems, the object of the present invention is to provide a catalyst for the combustion of soot particles, which is a simple metal oxide or perovskite type, perovskite-like type, spinel type, scheelite type , Ce-based solid solution and other types of composite metal oxides, the contact area between the catalyst and the soot particles is large, and the utilization rate of the active surface area is also high.

The purpose of the present invention is also to provide a method for preparing the above-mentioned soot particle combustion catalyst, which uses a colloidal crystal template method to prepare simple metal oxides or composite metal oxides with high catalytic activity and three-dimensional ordered macroporous structure.

In order to achieve the above object, the present invention firstly provides an oxidation catalyst for the combustion of soot particles emitted from diesel vehicles, which is a three-dimensional ordered macroporous oxide catalyst for purifying diesel soot, which is composed of rare earth metals, transition metals and alkalis. Simple metal oxides or composite metal oxides that have more than one element in the active metal and have a three-dimensional ordered macroporous structure, wherein the composite metal oxide is perovskite type, perovskite-like type , spinel type, scheelite type or Ce-based solid solution type composite metal oxide.

The inventors of the present invention have found through research that when using a catalyst with larger pores to process soot particles from diesel vehicles, the soot particles can enter the interior of the catalyst and contact the active surface of the internal pores of the catalyst, and the combustion temperature is higher than that used at present Other purification catalysts are much lower. However, due to the large particle size of soot (the diameter of a single soot particle is greater than 25nm), in order for the soot particles to enter the internal pores of the catalyst smoothly, a certain pore size requirement must be met, that is, the catalyst is required to have a macroporous structure. According to the definition of IUPAC, pores with a pore diameter greater than 50 nm are called macropores, so the macroporous metal oxide catalyst for purifying diesel soot of the present invention has an average pore diameter of 50 nm-1 μm in the internal pores, which belongs to the macroporous metal oxide catalyst. .

The pore structure of the macroporous metal oxide catalyst provided by the invention has a large pore size, and the pore distribution is uniform, and the pores are arranged in an orderly manner, belonging to a three-dimensional ordered macropore structure. The oxidation catalyst is a three-dimensional ordered macroporous metal oxide catalyst. The unique pore structure facilitates the entry of substances into the pores from all directions, reduces the diffusion resistance of soot particles, and provides the best flow rate and higher efficiency.

The oxidation catalyst for the combustion of diesel vehicle exhaust soot particles can be a simple metal oxide, perovskite type, perovskite-like type, spinel type, scheelite type or Ce-based solid solution type composite metal oxide . The chemical composition of simple metal oxides can be expressed as M _a O _b , where M is any one of the metal elements, such as: Li, Na, K, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Pb, Ce, Pr, Nd, Sm, Eu, etc.; the chemical composition of composite metal oxides can be expressed as Ln _1-x A _x M _{1-y By} O _3. Ln _2-z A _z M _{1-y By O 4} , Ln _1-x A _x M _2-w B _w O ₄ , Ln _1-x A _x M _{1-y By} O ₄ , Ce _{1- m} Zr _m O ₂ or Ce _1-mn Zr _m Pr _n O ₂ , where Ln is a rare earth metal, A is an alkali metal, including alkali metal or alkaline earth metal, M is a transition metal, and B is a transition metal different from M metal, and x=0-0.95, y=0-0.95, z=0-1.95, w=0-1.95, m=0-0.99, n=0-0.99; wherein, rare earth metals include La, Ce, Pr, One or more of Nd and Sm, etc.; transition metals include one or more of Fe, Co, Mn, Ni, Cu and Cr, etc.; alkaline metals include alkali metals and/or alkaline earth metals, including Li, One or more of Na, K, Rb, Cs, Mg, Ca, Sr and Ba, etc.

According to the specific technical solution of the present invention, the above oxidation catalyst provided by the present invention can be obtained by impregnating the colloidal crystal template with the organic complexing agent solution containing the salt of its active component as the impregnating liquid, and then roasting.

The present invention also provides the preparation method of above-mentioned oxidation catalyst, it comprises the following steps:

Mix and dissolve the salt containing the active component in the organic complexing agent according to a predetermined stoichiometric ratio, and add a co-solvent to obtain a catalyst precursor solution;

Using the obtained catalyst precursor solution as an impregnating liquid, add a colloidal crystal template to impregnate and dry repeatedly, then raise the temperature to a target temperature of 450°C-1000°C in an air atmosphere, and keep it warm for 4-10h.

According to the specific technical solution of the present invention, in the catalyst precursor solution containing the salt of the active component, the organic complexing agent and the co-solvent, the total concentration of metal ions can be controlled to be 0.05-3mol/L.

According to the specific technical solution of the present invention, the air flow rate in the air atmosphere can be controlled to 30-300mL/min, and the temperature increase can be programmed to a target temperature of 450°C-1000°C at a rate below 2°C/min.

In order to ensure the performance of the obtained metal oxide catalyst, the salt of the active component used in the preparation method provided by the present invention may be an inorganic salt capable of providing the active component, preferably a nitrate. The present invention uses an organic complexing agent to convert nitrate into a metal precursor with a higher melting point through a complexing method, and the precursor can penetrate into a colloidal crystal template and convert into a corresponding metal oxide without melting, thereby obtaining a three-dimensional organic ordered macroporous structure. Adopting the technical solution provided by the invention can avoid the problem that the nitrate containing the active component decomposes when the colloidal crystal template is not removed due to the low melting point of the nitrate, and the problem that the metal oxide with a 3DOM structure cannot be obtained.

Organic complexing agents suitable for use in the present invention are liquid dihydric alcohols or polyhydric alcohols, such as ethylene glycol, glycerol, and the like. When ethylene glycol is used as the organic complexing agent, the ethylene glycol solution of the metal nitrate can oxidize the nitrate in situ at a lower temperature before the template is burned to generate the corresponding metal glyoxylate, The glyoxylate can be converted to the corresponding metal oxide by further calcination, and the polymer template can be removed to obtain the 3DOM metal oxide material.

In order to dilute the mixed solution containing the salt of the active component and the organic complexing agent and reduce its viscosity, a certain amount of co-solvent can be added to the mixed solution, which is conducive to the penetration of the precursor solution into the template under the action of capillary force, and further transformation is a solid skeleton. The co-solvents suitable for the present invention can be commonly used co-solvents in this field, such as methanol, ethanol and the like.

The colloidal crystal template that the present invention adopts can be polymethyl methacrylate (PMMA) template, polystyrene (PS) template, the copolymer template (P(S-MMA)) of styrene and methyl methacrylate) or PS and PMMA templates with carboxyl functional groups on the surface can be either commercially purchased or self-prepared. Wherein, the preparation of polymethyl methacrylate template or polystyrene template etc. can adopt the method that comprises the following steps to carry out:

1. Preparation of monodisperse polymer microspheres by soap-free emulsion polymerization

Under nitrogen protection, mix acetone and double-distilled water, and preheat to 60-90°C with a water bath, add monomer methyl methacrylate or styrene, and continue heating to 60-90°C with a water bath;

Under the protection of nitrogen, add an aqueous initiator solution at 60-90°C, wherein the initiator can include potassium persulfate and azobisisobutyronitrile and other commonly used initiators in the preparation of colloidal crystal templates, and continue stirring for 2-30h, Obtain monodisperse polymethyl methacrylate or polystyrene microsphere emulsion; Preferably, the surface of the obtained microsphere should be relatively smooth, and the particle size is relatively uniform. Adopting this microsphere can make the metal oxide finally obtained have better shape and structure;

2. Preparation of colloidal crystal templates by centrifugal deposition method or evaporation deposition method

The microsphere emulsion is placed in a centrifuge tube, and centrifuged at a speed of 1000-10000rpm, preferably 1000-5000rpm, for 1-30h, and the preferred processing time is 10-20h to obtain a tightly packed colloidal crystal template, or the microsphere emulsion Place in a flat-bottomed container, slowly evaporate in a drying oven at a temperature of 40-80°C, and deposit microspheres to obtain a colloidal crystal template.

According to a specific embodiment of the present invention, a polymethyl methacrylate template or a polystyrene template can be prepared using a preparation method including the following specific parameters and specific steps:

Mix 30-100ml of acetone and 50-300ml of twice distilled water to obtain a mixed solution, heat in a water bath to 60-90°C, then add 30-120ml of monomeric methyl methacrylate or styrene, and heat in a water bath to 60-90°C;

Add initiator potassium persulfate 0.001g-0.500g and azobisisobutyronitrile 0.001g-0.500g 60-90°C aqueous solution, and keep stirring for 2-30h to obtain monodisperse polymethyl methacrylate or polystyrene micro For spherical emulsion, the whole reaction process is carried out under the protection of nitrogen. The particle size of the obtained monodisperse microspheres can be adjusted by controlling the amount of the monomer, the amount of the initiator, the stirring speed, the reaction temperature and the reaction time. The particle size of the obtained microspheres Between 100nm-1μm;

Place the microsphere emulsion in a centrifuge tube and centrifuge at a speed of 1000rpm-5000rpm for 10-20h to obtain a tightly packed colloidal crystal template, or place the microsphere emulsion in a flat-bottomed container and dry it at a temperature of 40-80°C Slowly evaporated in the box, the microspheres were deposited to obtain a colloidal crystal template.

The present invention also provides a method for purifying soot particles emitted by diesel vehicles, which includes the process of using the above-mentioned oxidation catalyst to catalyze the combustion of soot particles emitted by diesel vehicles for purification.

The oxidation catalyst for the combustion of diesel vehicle exhaust soot particles is a simple metal oxide, perovskite type, perovskite-like type, spinel type, scheelite type or Ce with a three-dimensional ordered macroporous structure. Based solid solution type composite metal oxide, its internal regular and orderly pores and large pore size are enough to make the soot particles diffuse smoothly in the pores, so that the soot particles can not only contact the active outer surface of the catalyst, but also make the The soot particles diffuse into the pores from all directions, and fully contact with the active inner surface of the catalyst, especially the active center, so that the utilization rate of the active surface of the soot particle catalyst is greatly improved, and the combustion temperature of the soot particles is greatly reduced. Within the temperature range of vehicle exhaust emissions, carbon particles can basically be completely burned.

Simple oxides and composite metal oxides (perovskite type, perovskite-like type, spinel type, scheelite type or Ce-based solid solution) prepared by colloidal crystal template method with three-dimensional ordered macroporous structure type, etc.), its preparation process is simple and easy, and the reaction process is easy to control.

Three-dimensional ordered macroporous oxide catalyst, its average pore size is between 50nm-1μm, the pores are arranged in an orderly manner, soot particles can diffuse into the pores from all directions, and fully contact with the active center of the catalyst, so the active surface area of the catalyst is utilized The efficiency is greatly improved, so that the combustion temperature of soot particles can be greatly reduced, and the temperature at which soot particles are burned into CO ₂ can be reduced to within the exhaust temperature range of diesel vehicle exhaust. By comparing the activities of the catalysts, it can be known that the three-dimensional ordered macroporous oxide catalyst prepared by the present invention has better catalytic activity than corresponding conventional catalysts, nano particle catalysts and disordered macroporous catalysts.

Description of drawings

Fig. 1a and Fig. 1b are the 3DOM CeO that embodiment 1 prepares _2Scanning electron micrographs;

Fig. 1c is the scanning electron micrograph of the 3DOM LaFeO that embodiment ₂ prepares;

Figure 1d is a scanning electron micrograph of 3DOM La _0.9 K _0.1 FeO prepared in Example ₃ ;

Figure 1e _is a scanning electron micrograph of 3DOM LaFe _0.7 Co _0.3 O prepared in Example 4;

Fig. 1 f is the 3DOM _ZrO that embodiment 5 prepares Scanning electron micrograph;

Fig. 1g is the scanning electron micrograph of _{the 3DOMAl2O3} that embodiment 6 prepares;

Fig. 2a is the disordered macroporous CeO that comparative example ₁ prepares Scanning electron micrograph;

Figure 2b is a scanning electron micrograph of the disordered macroporous LaFeO prepared in Comparative Example ₂ ;

Figure 2c is a scanning electron micrograph of the disordered macroporous La _0.9 K _{0.1 FeO} prepared in Comparative Example 3;

Fig. 3 is the X-ray diffraction pattern of 3DOM CeO ₂ , 3DOM LaFeO ₃ , 3DOMLa _0.9 K _0.1 FeO ₃ and Ce _0.75 Zr _0.25 O ₂ prepared in Examples 1-3, 7;

Fig. 4 is a graph showing the relationship between the concentration and temperature of CO ₂ generated from 3DOM CeO ₂ , 3DOM LaFeO ₃ and 3DOMLa _0.9 K _0.1 FeO ₃ catalyzed oxidation of soot particles prepared in Examples 1-3.

Detailed ways

The implementation and beneficial effects of the present invention are described below through specific examples, but the implementation scope of the present invention should not be construed in any way.

Catalyst activity evaluation method:

Use fixed bed microreactor-gas chromatography detection system;

Specific parameters: catalyst sample 100mg, the mass ratio of catalyst to soot particles is 10:1;

Specific steps: use the ultrasound-assisted method, that is, place the weighed catalyst and soot particles in a small beaker, stir evenly with a medicine spoon, then add 3ml of ethanol to it, and ultrasonically 3-10min to make the soot particles enter the pores of the catalyst sample In the channel, wherein the control gas flow rate is 50ml/min, the volume content of NO in the gas is 2000ppm, the volume content of _O2 is 5%, and the balance is He;

After the soot particles enter the pores of the catalyst sample, they are heated, wherein the heating rate is controlled to be about 2° C./min.

Evaluation method: The oxidation ability of the catalyst is expressed by the combustion temperature of soot particles, among which, the ignition temperature (T ₁₀ ), the temperature corresponding to the maximum combustion rate (T ₅₀ ) and the burnout temperature (T ₉₀ ), which represent the corresponding temperature points when 10%, 50% and 90% of soot combustion is completed, and the calculation method is to integrate the curve of CO ₂ and CO produced by carbon black combustion in the temperature-programmed oxidation reaction, CO ₂ The temperature points corresponding to the values of 10%, 50%, and 90% of the sum of CO integral areas are T ₁₀ , T ₅₀ , and T ₉₀ .

The pore size of the catalyst was determined from SEM photographs.

Colloidal crystal template preparation method:

1) Preparation of monodisperse polymer microspheres by soap-free emulsion polymerization

Add 50ml of acetone and 150ml of double-distilled water into a 1000ml four-necked flask, preheat it to 70°C in a 70°C water bath, and add 70ml of monomeric methyl methacrylate (or styrene) into the preheated four-necked flask medium; while preheating the reactants, weigh 0.090g of initiator potassium persulfate K ₂ S ₂ O ₈ and 0.1538g of azobisisobutyronitrile (AIBN), dissolve them in 150ml of water, and heat them in a water bath to 70°C; When the reaction monomer is preheated to 70°C, add an aqueous initiator solution at 70°C, and continue stirring for 2-10 hours to obtain a monodisperse polymethyl methacrylate (or polystyrene) with a solid content of 5-10%. ball emulsion;

2) Preparation of colloidal crystal templates by centrifugal deposition or evaporation deposition

Place an appropriate amount of microsphere emulsion in a centrifuge tube and centrifuge at a speed of 1000-5000rpm for 10-20h to obtain a tightly packed colloidal crystal template;

Alternatively, put an appropriate amount of microsphere emulsion in a flat-bottomed container (such as a beaker), slowly evaporate in a drying oven at a temperature of 40-80° C., and deposit the microspheres to obtain a colloidal crystal template.

Embodiment 13DOM CeO ₂ simple metal oxides

Take a small amount of polymethyl methacrylate microsphere emulsion with a particle size of 446nm, centrifuge at a speed of 3000rpm for 10h to obtain a PMMA colloidal crystal template, and dry naturally;

Weigh a certain amount of cerium nitrate, dissolve it in ethylene glycol, transfer the resulting solution to a volumetric flask, and constant volume with methanol (methanol volume fraction is 5-50%), the concentration of metal ions in the prepared solution is 2.0mol/ L, to obtain the precursor solution of 3DOM _CeO2 ;

Add the precursor solution of 3DOM _CeO2 dropwise to the dried PMMA colloidal crystal template until the solution is immersed in the PMMA template. Raise the temperature to 500° C. at a heating rate of ≤2° C./min in a tube furnace, and roast (keep heat) for 5 hours to obtain 3DOM CeO ₂ .

Figure 1a and Figure 1b are scanning electron microscope (SEM) photos of different magnifications of 3DOM CeO ₂ prepared in this example. It can be seen from the overall morphology of 3DOM CeO ₂ in the figure that 3DOM CeO ₂ has a three-dimensional ordered macroporous structure with an average pore diameter of about 248nm; the X-ray diffraction pattern of 3DOM CeO ₂ prepared in this example is shown in Figure 3, The diffraction peaks are all characteristic diffraction peaks of the fluorite cubic structure of pure CeO ₂ , which indicates that the composition of the catalyst prepared in this example is CeO ₂ .

Comparative Example 1 Disordered macroporous CeO ₂

Take a small amount of the 3DOM _CeO2 precursor solution obtained in Example 1, put it in a muffle furnace, raise the temperature to 500°C at a heating rate of ≤2°C/min, and bake it for 5h to obtain a disordered honeycomb macropore Structured CeO ₂ , that is, disordered macroporous CeO ₂ , its surface morphology is shown in Figure 2a.

Activity Evaluation 1

The 3DOM CeO2 prepared in Example 1 _, the disordered macroporous CeO2 prepared in Comparative Example ₁ and the non-macroporous _CeO2 were evaluated according to the above-mentioned catalyst activity evaluation method, and the activity evaluation results of 3DOM _CeO2 are shown in Figure 4 (Wherein, the ordinate is CO _{concentration} , and the ordinate is temperature), and the activity evaluation data of the above three catalysts are shown in Table 1.

Ultrasound assists soot particles to enter the pores of 3DOM CeO ₂ and disordered macroporous CeO ₂ . Under these conditions, 3DOM CeO ₂ makes the ignition temperature of soot particles lower than 294°C, and the peak temperature (T ₅₀ ) is 386 ℃, and the burnout temperature is lower than 412°C. Compared with disordered macroporous CeO ₂ , its light-off temperature (T ₁₀ ), temperature corresponding to the maximum burning rate (T ₅₀ ) and burnout temperature (T ₉₀ ) are all lower. Low, where T ₁₀ is 70°C lower and T ₅₀ is 67°C lower.

Comparing the catalytic activity of non-macroporous CeO ₂ , disordered macroporous CeO ₂ and 3DOM CeO ₂ for the combustion of soot, the order of catalytic activity is: 3DOM CeO ₂ >disordered macroporous CeO ₂ >non-macroporous CeO ₂ .

Table 1:

Catalyst T ₁₀ /℃ T ₅₀ /℃ T ₉₀ /℃ 3DOM CeO ₂ 294 386 412 Disordered macroporous CeO ₂ 338 405 436 Non-macroporous CeO ₂ 368 436 509

Embodiment 23DOM LaFeO ₃ composite metal oxides

Take a small amount of polystyrene microsphere emulsion with a particle size of 367nm, centrifuge at a speed of 3000rpm for 20h to obtain a PS colloidal crystal template, and dry naturally;

Weigh lanthanum nitrate and ferric nitrate according to the stoichiometric ratio (molar ratio 1:1), add ethylene glycol therein, magnetically stir for 2 h, transfer the resulting solution to a volumetric flask, and dilute to volume with methanol (the volume fraction of methanol is 30%), the concentration of metal ions in the solution is 1.5mol/L, to obtain the precursor solution of 3DOM _LaFeO3 , this solution is the precursor solution of 3DOM _LaFeO3 composite metal oxide catalyst;

Add the precursor solution of 3DOM LaFeO ₃ dropwise to the dry PS colloidal crystal template until the solution is immersed in the PS template. In a tube furnace, the temperature was raised to 600°C at a heating rate of <2°C/min, and calcined for 5 hours to obtain 3DOM LaFeO ₃ .

Figure 1c is a scanning electron micrograph of 3DOM LaFeO ₃ prepared in this example. It can be seen from the figure that the 3DOM LaFeO ₃ prepared using PS colloidal crystals as a template in this example has a regular three-dimensional ordered macroporous structure with an average pore diameter of about 320 nm; the X-ray diffraction of the 3DOM LaFeO ₃ prepared in this example The spectrum is shown in Figure 3, and the results show that the 3DOM LaFeO ₃ prepared in this example has a perovskite structure.

Comparative Example 2 Disordered macroporous LaFeO ₃

Take a small amount of 3DOM LaFeO ₃ precursor solution and place it in a crucible, raise the temperature to 600°C in a muffle furnace at a heating rate of ≤2°C/min, and bake it for 5 hours to obtain LaFeO with a disordered honeycomb macroporous structure ₃ , that is, disordered macroporous LaFeO ₃ ;

Figure 2b is a scanning electron micrograph of the disordered macroporous _LaFeO3 prepared in this comparative example. It can be seen from the figure that the _LaFeO3 obtained by directly roasting the precursor solution in a muffle furnace in this comparative example has a honeycomb macroporous structure , the average pore size is greater than 50nm.

Activity Evaluation 2

According to the evaluation method of above-mentioned catalyst activity, the 3DOM _LaFeO3 prepared by Example 2, the disordered macroporous LaFeO3 prepared by Comparative Example ₂ and the non-macroporous _LaFeO3 are evaluated, and the activity evaluation results of _3DOMLaFeO3 are as shown in Figure 4 ( Abscissa is temperature, and ordinate is _CO Concentration), the activity evaluation data of above-mentioned three kinds of catalysts are shown in Table 2;

With the assistance of ultrasound, soot particles enter the pores of 3DOM LaFeO ₃ and disordered macropore LaFeO ₃ , and the combustion temperature of soot particles decreases.

Comparing the catalytic activity data of 3DOM LaFeO ₃ , disordered macroporous LaFeO ₃ and non-macroporous LaFeO ₃ catalysts with three different morphologies, it can be known that the combustion temperature of soot particles corresponding to 3DOM LaFeO ₃ is the lowest, and the effect on the combustion of soot is the lowest. Highest catalytic activity.

Table 2:

Catalyst T ₁₀ /℃ T ₅₀ /℃ T ₉₀ /℃ 3DOM LaFeO ₃ 348 416 444 Disordered macroporous LaFeO ₃ 368 444 455 Non-macroporous LaFeO ₃ 386 488 530

Embodiment 33DOMLa _0.9 K _0.1 FeO ₃ composite metal oxides

Take a small amount of polymethyl methacrylate microsphere emulsion with a particle size of 487nm, centrifuge at a speed of 2000rpm for 15h, discard the supernatant to obtain a PMMA colloidal crystal template, and dry naturally;

Weigh lanthanum nitrate, potassium nitrate and ferric nitrate according to the stoichiometric ratio (9:1:10 in molar ratio), add ethylene glycol therein, stir magnetically for 2 hours, transfer the resulting solution to a volumetric flask, and dilute to volume with methanol (methanol volume fraction is 40%), the metal ion concentration in _the prepared solution is 2.0mol/L, and the precursor solution of 3DOMLa _0.9 K _0.1 FeO is obtained, and this solution is the precursor of 3DOM La _0.9 K _{0.1 FeO} composite metal oxide catalyst body solution;

In the dried PS colloidal crystal mold, add dropwise the precursor solution of 3DOM La _0.9 K _{0.1 FeO} until the solution is immersed in the PMMA template. After the impregnation is complete, remove the excess solution by suction filtration to obtain a precursor/PMMA composite. Naturally dry, then place in a tube furnace to raise the temperature to 650°C at a rate of ≤2°C/min, and bake for 5 hours to obtain 3DOM La _0.9 K _0.1 FeO ₃ .

Figure 1d is a scanning electron micrograph of 3DOM La _0.9 K _0.1 FeO ₃ prepared in this example. As can be seen from the figure, the La _0.9 K _0.1 FeO ₃ prepared using PMMA colloidal crystals as a template has a three-dimensional ordered macroporous structure, which belongs to a three-dimensional ordered macroporous catalyst, with an average pore diameter of about 400 nm; the 3DOM La prepared in this example The X-ray diffraction pattern of _0.9 K _0.1 FeO ₃ is shown in Figure 3, and the results show that the 3DOM La _0.9 K _0.1 FeO ₃ prepared in this example is a perovskite oxide.

Comparative example 3 Disordered macroporous La _0.9 K _0.1 FeO ₃

Take a small amount of 3DOM La _0.9 K _0.1 FeO ₃ precursor solution and place it in a crucible, raise the temperature to 650°C in a muffle furnace at a heating rate of ≤2°C/min, and bake it for 5 hours to obtain a disordered honeycomb macropore Structure of La _0.9 K _0.1 FeO ₃ , that is, disordered macroporous La _0.9 K _0.1 FeO ₃ .

Figure 2c is the scanning electron microscope photo of the disordered macroporous La _0.9 K _0.1 FeO ₃ prepared in this comparative example. It can be seen from the figure that the La _0.9 K _0.1 FeO ₃ obtained by directly roasting the precursor solution in a muffle furnace is Honeycomb disordered macroporous catalyst, the average pore diameter is greater than 50nm.

Activity Evaluation 3

3DOMLa _0.9 K _0.1 FeO 3 prepared _in Example 3, the disordered macroporous La _0.9 K _0.1 FeO ₃ prepared in Comparative Example 3 and the non-macroporous La _0.9 K _0.1 FeO ₃ were evaluated according to the above-mentioned catalyst activity evaluation method, 3DOM The activity evaluation results of La _0.9 K _0.1 FeO ₃ are shown in Figure 4; the activity evaluation data of the above three catalysts are shown in Table 3.

With the assistance of ultrasound, soot particles enter the channels of 3DOM La _0.9 K _0.1 FeO ₃ and disordered macropores La _0.9 K _0.1 FeO ₃ , and the combustion temperature of soot particles decreases, which is different from that of non-macropores La _0.9 K _0.1 FeO ₃ , Compared with the disordered macroporous La _0.9 K _0.1 FeO ₃ , the combustion temperature of soot particles corresponding to 3DOM La _0.9 K _0.1 FeO ₃ is the lowest, and the catalytic activity for the combustion of soot is the highest.

table 3:

Catalyst T ₁₀ /℃ T ₅₀ /℃ T ₉₀ /℃ 3DOM La _0.9 K _0.1 FeO ₃ 305 366 379 Disordered macroporous La _0.9 K _0.1 FeO ₃ 325 370 390 Non-macroporous La _0.9 K _0.1 FeO ₃ 334 445 503

Embodiment 43DOM LaFe _0.7 Co _0.3 O ₃ composite metal oxide

Take a small amount of polymethyl methacrylate microsphere emulsion with a particle size of 362nm, centrifuge at a speed of 7200rpm for 1h, discard the supernatant to obtain a PMMA colloidal crystal template, and dry naturally;

Weigh lanthanum nitrate, iron nitrate and cobalt nitrate according to the stoichiometric ratio (molar ratio 10:7:3), add ethylene glycol therein, stir magnetically for 2 hours, transfer the resulting solution to a volumetric flask, and dilute to volume with methanol (methanol volume fraction is 35%), metal ion concentration is 2.0mol/L in the prepared solution, obtains _the precursor solution _{of 3DOMLaFe0.7Co0.3O3} , and _{this solution is the precursor of 3DOMLaFe0.7Co0.3O3 composite metal} oxide catalyst body solution; add it dropwise to the dry PMMA template until the solution is immersed in the PMMA template. After the impregnation is complete, remove the excess solution by suction filtration to obtain a precursor/PMMA composite, dry it naturally, and then place it in a tube furnace 3DOM LaFe _0.7 Co _0.3 O ₃ was obtained by raising the temperature to 650° C. at a heating rate of ≤2° C./min and roasting for 5 hours.

Figure 1e is a scanning electron micrograph of the 3DOM LaFe _0.7 Co _0.3 O ₃ prepared in this example. It can be seen from the figure that the LaFe _0.7 Co _0.3 O ₃ prepared using PMMA colloidal crystals as a template has a three-dimensional ordered macroporous structure, which belongs to a three-dimensional ordered macroporous catalyst, with an average pore diameter of about 268 nm.

Embodiment 53DOM ZrO ₂ simple metal oxides

Take a small amount of polymethyl methacrylate microsphere emulsion with a particle size of 446nm, centrifuge at a speed of 3000rpm for 10h, discard the supernatant to obtain a PMMA colloidal crystal template, and dry naturally;

Weigh zirconium nitrate, dissolve it in a mixture of ethylene glycol and ethanol (50%), transfer the resulting solution to a volumetric flask, and obtain a precursor solution of 3DOM _ZrO , which is used to impregnate the dried PMMA template, to be impregnated After completion, the excess solution was removed by suction filtration to obtain the precursor/PMMA composite, which was dried naturally, then placed in a tube furnace to raise the temperature to 500°C at a heating rate of ≤2°C/min, and roasted for 5h to obtain 3DOM ZrO ₂ .

Figure 1f is a scanning electron micrograph of 3DOM ZrO ₂ prepared in this example. It can be seen from the figure that the ZrO ₂ prepared using PMMA colloidal crystals as a template has a three-dimensional ordered macroporous structure, which belongs to a three-dimensional ordered macroporous catalyst, with an average pore diameter of about 378nm.

Embodiment 63 DOM Al ₂ O ₃ simple metal oxides

Take a small amount of polystyrene microsphere emulsion with a particle size of 144nm, and centrifuge it at a speed of 5500rpm for 20h to obtain a PS colloidal crystal template, and dry it naturally;

Weigh aluminum nitrate, add ethylene glycol therein, magnetically stir for 2h, transfer the solution obtained in the volumetric flask, constant volume with methanol (the volume fraction of methanol is 30%), the metal ion concentration in the prepared solution is 1.5mol /L, this solution is the precursor solution of 3DOM Al ₂ O ₃ ;

The dried PS colloidal crystal template was impregnated with the precursor solution of 3DOM Al ₂ O ₃ , and after the impregnation was complete, the excess solution was removed by suction filtration to obtain the precursor/PS composite, which was dried naturally, and then placed in a tube furnace to Raise the temperature to 700°C at a heating rate of <2°C/min, and calcine for 5 hours to obtain 3DOMAl ₂ O ₃ .

Fig. 1g is a scanning electron micrograph of 3DOM Al ₂ O ₃ prepared in this example. It can be seen from the figure that the 3DOM Al ₂ O ₃ prepared using PS colloidal crystals as a template in this example has a regular three-dimensional ordered macroporous structure with an average pore diameter of about 100 nm.

Embodiment 73DOM Ce _0.75 Zr _0.25 O ₂ composite metal oxides

Take a small amount of polymethyl methacrylate microsphere emulsion with a particle size of 454nm, centrifuge at a speed of 3000rpm for 10h to obtain a PMMA colloidal crystal template, and dry naturally;

Weigh cerium nitrate and zirconium nitrate according to the stoichiometric ratio (molar ratio 3:1), add a mixture of ethylene glycol and ethanol (the volume fraction of ethanol is 50%), magnetically stir for 2 hours, and transfer the resulting solution to a volumetric flask , use ethanol to make up the volume, and the metal ion concentration in the prepared solution is 2.0mol/L to obtain the precursor solution of 3DOM Ce _0.75 Zr _0.25 O ₂ ; impregnate the dried PMMA template into the precursor of 3DOMCe _0.75 Zr _0.25 O ₂ In the solution, after the impregnation is complete, the excess solution is removed by suction filtration, and the precursor/PMMA composite is obtained, dried naturally, and then placed in a tube furnace to raise the temperature to 650°C at a heating rate of ≤2°C/min, and roasted 5h, 3DOM Ce _0.75 Zr _0.25 O ₂ was obtained.

The X-ray diffraction pattern of 3DOM Ce _0.75 Zr _{0.25 O} prepared in this embodiment is shown in Figure 3, in the spectrogram of the catalyst sample prepared in this embodiment and pure CeO _The fluorite-type cubic structure does not appear _ZrO The characteristic peaks indicate that 3DOM Ce _0.75 Zr _0.25 O ₂ exists in one crystal phase without phase separation.

Claims (10)

1. an emission of diesel engine soot particulate burns and uses oxidation catalyst, it is as active component and simple metal oxide or composite metal oxide with three-dimensional ordered macroporous structure by more than one the element in rare earth metal, transition metal and the alkalinous metal, wherein, described composite metal oxide is Ca-Ti ore type, perovskite-like type, spinel-type, scheelite type or Ce based solid solution type composite metal oxide, wherein, the average pore size of this catalyst is 50nm-1 μ m.

2. oxidation catalyst as claimed in claim 1, wherein, the chemical composition of described simple metal oxide is M _aO _b, in the formula, M is any one in the metallic element.

3. oxidation catalyst as claimed in claim 1, wherein, the chemical composition of described composite metal oxide is Ln _1-xA _xM _1-yB _yO ₃, Ln _2-zA _zM _1-yB _yO ₄, Ln _1-xA _xM _2-wB _wO ₄, Ln _1-xA _xM _1-yB _yO ₄, Ce _1-mZr _mO ₂Or Ce _1-m-nZr _mPr _nO ₂, in the formula, Ln is a rare earth metal, and A is an alkalinous metal, comprises alkali metal or alkaline-earth metal, and M is a transition metal, and B is the transition metal that is different from M, and x=0-0.95, y=0-0.95, z=0-1.95, w=0-1.95, m=0-0.99, n=0-0.99;

Described rare earth metal comprises one or more among La, Ce, Pr, Nd and the Sm;

Described transition metal comprises one or more among Fe, Co, Mn, Ni, Cu and the Cr;

Described alkalinous metal comprises alkali metal and/or alkaline-earth metal, comprises among Li, Na, K, Rb, Cs, Mg, Ca, Sr and the Ba one or more.

4. as each described oxidation catalyst of claim 1-3, wherein, this oxidation catalyst is that the organic complex agent solution that will contain the salt of its active component floods colloidal crystal template as maceration extract, the process roasting obtains then, and described organic complexing agent is liquid dihydroxylic alcohols or polyalcohol.

5. the preparation method of each described oxidation catalyst of claim 1-4, it may further comprise the steps:

The nitrate that will contain active component is dissolved in the organic complexing agent according to predetermined stoichiometric proportion mixing, and adds cosolvent, obtains the complex catalyst precursor liquid solution, and wherein, described organic complexing agent is ethylene glycol or glycerine, and described cosolvent is methyl alcohol or ethanol;

Utilize resulting complex catalyst precursor liquid solution as maceration extract, the adding colloidal crystal template floods repeatedly, drying, is warming up to 450 ℃-1000 ℃ then in air atmosphere, insulation 4-10h.

6. preparation method as claimed in claim 5, wherein, in the complex catalyst precursor liquid solution of described nitrate, organic complexing agent and the cosolvent that contains active component, the total concentration of metal ion is 0.05-3mol/L.

7. preparation method as claimed in claim 5, wherein, the air velocity in the described air atmosphere is 30-300mL/min.

8. preparation method as claimed in claim 5, wherein, with the following heating rate temperature programming to 450 of 2 ℃/min ℃-1000 ℃.

9. preparation method as claimed in claim 5, wherein, the preparation method of described colloidal crystal template may further comprise the steps:

Under nitrogen protection, acetone and redistilled water are mixed, and be preheated to 60-90 ℃ with water-bath, add monomers methyl methacrylate or styrene, continue to be heated to 60-90 ℃ with water-bath;

Under nitrogen protection, add 60-90 ℃ initiator solution, continue to stir 2-10h, obtain single polymethyl methacrylate or polystyrene microsphere emulsion of disperseing;

The microballoon emulsion is placed centrifuge tube, rotating speed centrifugal treating 1-30h with 1000-10000rpm obtains closelypacked colloidal crystal template, perhaps the microballoon emulsion is placed in the Flat bottom container, with the slowly evaporation in drying box of 40-80 ℃ temperature, the microballoon deposition obtains colloidal crystal template.

10. the method for purification of diesel car discharging soot particulate, it comprises the process that the burning of the soot particulate that adopts each described oxidation catalyst catalytic diesel oil car discharging of claim 1-4 purifies.

Images