CN103769239B - Honeycomb type denitrating catalyst with hierarchical porous structure and preparation method thereof - Google Patents

Abstract

The invention discloses a honeycomb-type denitration catalyst with a multi-level pore structure and a preparation method thereof. The catalyst has a honeycomb structure, and has micron-scale and nano-scale blind holes on the wall surface of the catalyst. The diameter is 0.1-1 micron, and the diameter of the nanoscale blind hole is 10-100nm. The process of the invention is simple, and a high-porosity honeycomb denitrification catalyst with a multi-level pore structure is obtained by adding PMMA (PS) microspheres and polyethylene oxide, as well as other additives and adjusting process conditions. The catalyst can produce more active centers, strong adsorption and mass transfer capabilities, and has the advantages of less catalyst consumption per unit volume, which not only ensures the catalytic performance of the catalyst but also reduces the usage of catalyst raw materials and finished products. weight per unit volume.

Description

Honeycomb type denitration catalyst with hierarchical pore structure and preparation method thereof

technical field

The invention relates to an ammonia (NH ₃ ) selective catalytic reduction (SCR) denitrification catalyst and a preparation method thereof, in particular to a high-porosity honeycomb denitrification catalyst with a micron-nanometer hierarchical pore structure and a preparation method thereof.

Background technique

Nitrogen oxides (NO _x ) are the main pollutants that cause acid rain and photochemical smog, and their emissions mainly come from stationary sources such as coal-fired boilers, industrial furnaces and mobile sources such as vehicle exhaust. After the phased results of SO ₂ control in China, China put forward the requirement to control the total _NOx emissions during the "Twelfth Five-Year Plan" period, that is, the total _NOx emissions in 2015 will be reduced by 10% compared with 2010. In addition, the "Emission Standard of Air Pollutants for Thermal Power Plants" was implemented in 2012, which requires NO _x (calculated as NO ₂ ) emissions to be 100 mg/m ³ . At present, in-furnace denitrification technology has been unable to meet the above _NOx emission requirements.

When in-furnace denitrification technologies such as low _NOx combustion can no longer meet the increasingly stringent emission regulations, flue gas denitrification is required to further reduce _NOx emissions. Wet flue gas denitrification has the disadvantages of low NO _x purification efficiency, large equipment capacity, difficult construction, high operating cost, and easy to cause secondary pollution. Dry denitrification technology can effectively solve the above problems. Among them, ammonia (NH ₃ ) selective catalytic reduction (Selective catalytic reduction, SCR) is currently the most widely recognized commercial method in the world. Due to the high content of nitrogen oxides, high concentration of smoke and complex components in the flue gas of coal-fired boilers, among various monolithic catalysts, honeycomb denitrification catalysts are favored, accounting for 80% of the share.

At present, the preparation process of honeycomb denitrification catalyst usually includes the following procedures: mixing catalyst materials with various additives to obtain sludge; extruding the sludge through a vacuum extruder; drying and roasting the extruded product; roasting the product Finished to size. The most critical process is the mixing of catalyst materials and various additives, in which the composition and amount of additives have a crucial impact on the performance of honeycomb catalysts. Additives mainly include tougheners, lubricants, binders and pore-forming agents. In the literature, the toughening agent is usually made of glass fiber (patent 201210491331.0, patent 201210051993.6, patent 200910030398.2, patent 200810212081.6), and the lubricant is usually one or more of glycerin, stearic acid, silicate and phosphate ester. Most of the agents are (carboxy)methyl cellulose, polyvinyl alcohol, water glass, safflower powder and epoxy resin (patent 201210250771.7), and the pore-forming agents are mostly pulp cotton, polyethylene oxide, and wood pulp. The purpose of these patents is mostly to investigate the compressive strength and wear strength of the catalyst (patent 201310193408.0, patent 201110005264.2), only the patent (201010154270.X) mentions adding pulp cotton as a pore-forming agent to increase porosity and reduce catalyst dosage, but Pulp has the problem of incomplete combustion and leaves ash, and the porosity of the resulting product is not high, only 35%. There is a mutual restriction between porosity and mechanical strength. When the porosity is high, the mechanical strength will decrease, but when the mechanical strength is high, the porosity cannot reach a high level. The catalytic effect of the catalyst has a great relationship with the porosity. If this problem can be solved and a catalyst with good mechanical strength and porosity can be obtained, then the amount of the catalyst will be reduced on the basis of maintaining a high activity, and then cut costs. However, there is no technology to overcome this problem yet.

Contents of the invention

The object of the present invention is to provide a honeycomb denitration catalyst with a micro-nano hierarchical pore structure. Good performance. In addition, because there are a large number of nanoscale and micronscale pores on the catalyst wall, the content of the catalyst per unit volume is reduced, and the usage amount becomes smaller.

In the catalytic reaction, the hierarchical pore structure can not only generate more active centers, but also has strong adsorption and mass transfer capabilities, which reduces the amount of catalyst per unit volume, thereby ensuring the catalytic performance of the catalyst and reducing the amount of catalyst. The amount of raw materials used and the weight per unit volume of the finished product. At present, there is no report on the application of the hierarchical porous structure to the honeycomb denitration catalyst.

The inventor found during research that although compressive strength and porosity are mutually restricted, by adjusting the composition and dosage of additives (especially by changing the composition and dosage of pore-forming agents), and further adjusting the process steps and conditions, A honeycomb type denitration catalyst with both of them at an optimal level can be obtained.

The present invention uses PMMA (polymethyl methacrylate) microspheres or PS (polystyrene) microspheres and polyethylene oxide as a composite pore-forming agent, and with the cooperation of other additives and technological methods, obtains micro-nano hierarchical pores structure, which makes the catalyst have higher porosity on the basis of higher mechanical strength.

Concrete technical scheme of the present invention is as follows:

A honeycomb type denitration catalyst with a multi-level porous structure is characterized in that: the catalyst has a honeycomb structure, and has micron-scale and nano-scale blind holes on the wall surface of the catalyst, and the diameter of the micron-scale blind holes is 0.1- 1 micron, the diameter of the nanoscale blind hole is 10-100nm.

In the catalyst of the present invention, there are obvious nanoscale and micronscale pores on the catalyst wall, so that under the same volume, the catalyst of the present invention has less active ingredient content, light weight and less consumption.

The porosity of the honeycomb type denitration catalyst of the present invention is 70-90%, and the pore volume is 0.5-0.9 cm ³ /g.

The honeycomb type denitration catalyst of the present invention is a composite oxide catalyst supported by titanium dioxide, including but not limited to V ₂ O ₅ -WO ₃ /TiO ₂ catalyst or V ₂ O ₅ -MoO ₃ /TiO ₂ catalyst.

The preparation method of the honeycomb type denitration catalyst with multi-level porous structure of the present invention is characterized in that, comprises the following steps:

(1) Mix the catalyst carrier and solid additive to obtain a uniform solid material;

(2) Add liquid additives and vanadium precursor solution to the uniformly mixed solid material, mix again, and stale after mixing;

(3) Mixing the stale material for the third time to obtain mud;

(4) Extrude the mud into shape, cut it to the required size and then age it;

(5) Apply resin coating on the surface of the aged product, and carry out end surface hardening treatment;

(6) The hardened product is subjected to secondary drying and roasting to obtain a catalyst.

In the above preparation method, when the catalyst is V ₂ O ₅ -WO ₃ /TiO ₂ , the catalyst carrier is WO ₃ /TiO ₂ and/or WO ₃ /TiO ₂ -SiO ₂ ; the catalyst is V ₂ O ₅ -MoO ₃ /TiO ₂ , the catalyst carrier is MoO ₃ /TiO ₂ . The catalyst carrier of the present invention can be purchased directly in the market, or can be prepared by itself using existing methods.

In the above preparation method, the solid additive includes glass fiber, methylcellulose and a composite pore-forming agent, and the composite pore-forming agent is polyethylene oxide and PMMA microspheres, or polyethylene oxide and PS microspheres;

In the above-mentioned preparation method, glass fiber consumption is 3-10 wt % of catalyst support, preferred 7 wt %; Methylcellulose consumption is 2-4 wt % of catalyst support, preferred 3 wt %; PMMA microsphere or PS microsphere The dosage is 2-15wt% of the catalyst carrier, preferably 5wt%; the dosage of polyethylene oxide is 3-7wt% of the catalyst carrier, preferably 5wt%.

In the above preparation method, the liquid additive includes stearic acid, lactic acid and water; the vanadium precursor solution is NH ₄ VO ₃ solution, wherein ethanolamine or oxalic acid is added to aid in dissolution.

In the above preparation method, the stearic acid consumption is 3-7 wt% of the catalyst carrier, preferably 5 wt%; the lactic acid consumption is 2-5 wt% of the catalyst carrier, preferably 5 wt%; the water consumption is 25 wt% of the catalyst carrier. -40 wt%, preferably 30 wt%.

In the above preparation method, stearic acid is dissolved in hot absolute ethanol and added.

In the above preparation method, PMMA microspheres or PS microspheres are purchased directly from the market, and the diameter of the spheres is in the range of 30-200 mm. Polyethylene oxide is also directly purchased from the market, and its molecular weight is 1×10 ⁵ -1×10 ⁶ .

In the above preparation method, the amount of NH ₄ VO ₃ is added according to the loading amount of V ₂ O ₅ .

In the above-mentioned preparation method, the solid additives are added in the order of glass fiber, polyoxyethylene, PMMA microspheres or PS microspheres, and methyl cellulose, because the glass fiber itself is relatively easy to agglomerate, and organic additives such as methyl cellulose have If a certain viscosity is added at the same time, the glass fibers will be seriously agglomerated and not well dispersed in the material, which will affect the uniformity of the sludge and further affect the mechanical strength of the catalyst after molding.

In the above preparation method, the purpose of multiple times of mixing is to mix all the materials evenly and have better plasticity to facilitate subsequent extrusion molding. The purpose of the first mixing is to roughly mix solid materials such as WO ₃ /TiO ₂ and WO ₃ /TiO ₂ -SiO ₂ , and then add solid additives in a certain order for blending. The purpose of the second mixing is to obtain mud with a moisture content of 25-40 wt.% and good plasticity. The purpose of the third mixing is to make the stale material more uniform and easy to extrude. After these three times of mixing, the moisture content of the sludge reaches 25-40 wt.%.

In the above preparation method, the mixing time in step (1) is 2-3 h. The mixing time in step (2) is 3-5 hours, and the aging is carried out at room temperature and in a sealed state for 24 hours. The mixing time in step (3) is 2-3 h.

In the above preparation method, in step (4), the extrusion pressure is 5-10 MPa, preferably 5 MPa;

In the above-mentioned preparation method, the purpose of aging is to obtain stable mud with better plasticity. The aging temperature was room temperature and the aging time was 24 h.

In the above preparation method, the purpose of end surface hardening is to prevent the cracking of the product during the subsequent drying and roasting process. The resin coating used for end face hardening is a mixture of vinyl chloride-vinyl acetate copolymer and ethyl acetate at a volume ratio of 1:1. The ratio of vinyl chloride to vinyl acetate in vinyl chloride-vinyl acetate copolymer is 86%: 14%.

In the above preparation method, the aging honeycomb catalyst is dried in the primary drying room to achieve uniform, slow and gradual drying to prevent cracking; the purpose of the secondary drying is to completely dry the honeycomb catalyst. The first drying temperature is 70 °C, and the drying time is 12-24 h, preferably 12 h; the second drying temperature is 100 °C, and the drying time is 24-48 h, preferably 48 h.

In the above preparation method, calcination can form a multi-level porous structure on the catalyst wall. During calcination, the heating rate is raised to 450-600 ℃ at a rate of 1 ℃/min, and the temperature is kept at 3-5 h. Preferably, it is raised to 500 ℃ and kept at 5 h.

In the present invention, PMMA or PS microspheres and polyethylene oxide are used as composite pore-forming agents, methyl cellulose is used as binder to improve plasticity, glass fiber is used as toughening agent to improve compressive strength, stearic acid is used as lubricant and The release agent is easy to extrude, lactic acid is used to strengthen the aging of the mud, and monoethanolamine or oxalic acid is used to promote the dissolution of ammonium metavanadate. Through the reasonable combination of various components, the obvious micron-sized blind holes on the catalyst wall are finally obtained. A honeycomb denitration catalyst with a hierarchical porous structure with obvious nano-scale blind holes.

The invention provides a molding process suitable for honeycomb composite oxide denitration catalyst, by adding polymethyl methacrylate (PMMA) or polystyrene (PS) microspheres and polyethylene oxide composite pore-forming agent, and other With the action of additives, a high-porosity honeycomb denitration catalyst with a hierarchical pore structure is obtained. The addition of additives will form micron-scale and nano-scale blind pores on the wall of the catalyst during the calcination process. The formation of these pores increases the porosity and pore volume of the catalyst, so that the catalyst can produce more active centers and stronger Adsorption and mass transfer capabilities, while the mechanical strength of the catalyst will not be greatly affected. The catalyst of the present invention is a medium-high temperature denitration catalyst, which has good N2 selectivity and catalytic denitration rate above 250°C. Because of the existence of pores on the catalyst wall, the catalyst content per unit volume is small, and the catalyst can be used to treat the same unit volume of flue gas. The amount used is small, thereby not only ensuring the catalytic performance of the catalyst but also reducing the amount of catalyst raw materials used and the weight per unit volume of the finished product. In addition, the nitrogen selectivity of the catalyst of the present invention is also very high at low temperature. Low selectivity of nitrogen will cause _N2O gas to be generated in the catalytic process, resulting in secondary pollution. The low temperature and high selectivity of _N2 of the catalyst of the present invention can avoid NO The generation of toxic nitrous oxide _by -products in the catalytic process gives the catalyst a better advantage in catalyzing flue gas with a certain temperature range.

The process of the invention is simple, and the catalyst is easy to form, hard to crack, high in success rate, high in mechanical strength and high in porosity through the control of additives and various process steps. The invention can be applied to the preparation and industrialized production of the honeycomb denitrification catalyst in thermal power plants, industrial boilers and industrial kilns.

Description of drawings

Fig. 1 is the pore size distribution figure of embodiment 1,2,3,4 obtained product.

Fig. 2 is the pore size distribution diagram of the product obtained in Examples 4 and 5.

Fig. 3 is the pore size distribution diagram of the product obtained in Examples 5 and 6.

Figure 4 is a pore size distribution diagram of the products obtained in Examples 6 and 7.

Fig. 5 is the SEM photo of the product obtained in Example 2.

Fig. 6 is the SEM photo of the product obtained in Example 3.

Fig. 7 is the SEM photo of the product obtained in Example 4.

Fig. 8 is the SEM photo of the product obtained in Example 8.

Fig. 9 is the denitration efficiency diagram of the products obtained in Examples 2, 3 and 4.

Fig. ₁₀ is the N selectivity figure of embodiment 2,3,4 obtained product.

detailed description

The advantages of the present invention are further described below through specific examples, and the following descriptions do not limit the present invention.

The preparation of the catalyst carrier is not the innovation point of the present invention. Those skilled in the art can purchase the required carrier in the market. The present invention mainly takes the V ₂ O ₅ -WO ₃ /TiO ₂ catalyst as an example to illustrate the preparation process of the present invention.

In the following examples, the used PMMA microspheres, PS microspheres and polyethylene oxide are commercially available products, the ball diameters of PMMA microspheres and PS microspheres are in the range of 30-200 mm, and the molecular weight of polyethylene oxide is between 1 × 10 ⁵ - 1×10 ⁶ range.

The catalysts obtained in the examples were subjected to mechanical strength tests, porosity, pore size distribution and pore volume tests, and SEM characterization and denitrification experiments were performed on the catalysts.

The mechanical strength test was carried out on an Instron-5569 electronic universal testing machine with a test speed of 5mm/min.

The porosity, pore size distribution and pore volume tests were carried out on a PoreMaster GT-60 mercury porosimeter, where the porosity refers to the ratio of the volume of the nano-scale and micro-scale blind pores on the catalyst wall to the macroscopic overall volume of the honeycomb catalyst .

The experimental method of catalyst denitrification is as follows:

The simulated flue gas was used to test the denitrification of the catalyst. The simulated flue gas composition was: 500 ppm NO, 500 ppm NH ₃ , 5.3 vol.% O ₂ , and He was the balance gas. Take 0.72ml catalyst sample, put it into the fixed bed reactor, enter according to the flue gas flow rate of 300 mL/min, control the reaction space velocity to 25000 h ^-1 , and control the reaction temperature from 150 ℃ to 450 ℃. The concentration of NOx at the outlet of the reactor was detected by a nitrogen oxide analyzer (Model-42i-HI, Thermo Electric Company, USA).

Calculation of removal efficiency or NOx conversion rate:

_N2 selectivity calculation:

Example 1

One mixing: add 16.67 g titanium tungsten powder, 3.33 g titanium tungsten silicon powder, 1.4 g (according to 7 wt.% of the total amount of titanium tungsten powder and titanium tungsten silicon powder, that is catalyst carrier WO ₃ /TiO ₂ -SiO 7 wt% of the mass of ₂ added, the same below) chopped glass fiber, 0.6 g (according to 3 wt.% of the total amount of titanium tungsten powder and titanium tungsten silicon powder added, that is, the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ Add 3wt% of the mass, the same below) methyl cellulose is added into the mixer, the mixing time is 2-3 h, and the mixing is completed.

Secondary mixing: take out the material mixed in the first time, add 1.0 g lactic acid (according to 5 wt.% of the total amount of titanium tungsten powder and titanium tungsten silicon powder, that is, the mass of the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ 5wt% added, the same below), 1.0 g (added according to 5 wt.% of the total amount of titanium tungsten powder and titanium tungsten silicon powder, that is, 5wt% of the mass of the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ , the same below ) stearic acid (dissolved in 5 ml of hot absolute ethanol), 0.2573 g of NH ₄ VO ₃ solution (based on the V ₂ O ₅ accounting for 1 wt.% of the catalyst carrier, dissolved with ethanolamine), and finally add an appropriate amount of deionized Water, so that the amount of water accounted for 30% of the mass of the catalyst carrier, to obtain a finer sludge with better plasticity. Add it to the mixing machine and knead for 3-5 hours. After the kneading is completed, it is completely sealed and aged for 24 hours.

Three times of mixing: Take out the stale materials and mix again, the mixing time is 2-3 hours.

After the mixing is completed, the material is injected into a vacuum extruder at 5 MPa for extrusion, and aged for 24 h after extrusion.

After aging, the surface of the product is coated with a layer of coating solution for end face hardening treatment. The coating solution is mixed with a resin and a solvent at a volume ratio of 1:1. The resin is vinyl chloride-vinyl acetate copolymer (chlorine The ratio of vinyl chloride to vinyl acetate in ethylene-vinyl acetate copolymer is 86%:14%, the same below), and the solvent is ethyl acetate.

The honeycomb catalyst after end surface hardening treatment was placed in a drying room at a temperature of 70 °C and a drying time of 12 h. Take it out, put the thoroughly dried catalyst into a muffle furnace for calcination, and the calcination conditions are as follows: the heating rate is 1 ℃/min to 500 ℃, and the temperature is kept for 5 h.

The calcined honeycomb catalyst is refined to the specified size. The obtained catalyst is 1wt.%V ₂ O ₅ -5 wt.%WO ₃ /TiO _{2 ,} with a smooth surface and no cracking phenomenon.

Example 2

The catalyst was prepared by the same method as in Example 1, except that the following method was used for one mixing: 16.67 g titanium tungsten powder, 3.33 g titanium tungsten silicon powder, 1.4 g (7 wt.%) chopped glass fiber, 0.6 g (3 wt.%) methyl cellulose, 1.0 g (according to 5 wt.% of the total amount of titanium tungsten powder and titanium tungsten silicon powder, 5 wt% of the mass of the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ Add, the same below) Polyethylene oxide is added into the mixer, the mixing time is 2-3 h, and the mixing is completed.

The resulting product has moderate viscosity, is easy to extrude, and has a smooth surface without cracking.

Example 3

One mixing: 16.67 g titanium tungsten powder, 3.33 g titanium tungsten silicon powder, 1.4 g (7 wt.%) chopped glass fiber, 0.6 g (3 wt.%) methyl cellulose, 1.0 g (according to titanium tungsten 5 wt.% of the total amount of powder and titanium tungsten silicon powder is added, that is, 5 wt% of the mass of the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ is added, the same below) polyethylene oxide, 1.0 g (according to titanium tungsten powder and titanium Add 5 wt.% of the total amount of tungsten silicon powder, that is, add 5 wt% of the mass of the catalyst carrier WO ₃ /TiO ₂ -SiO ₂ , the same below) PMMA microspheres are added to the mixer, and the mixing time is 2-3 h, the mixing is completed.

Secondary kneading: take out the first kneading material, add 1.0 g (5 wt.%) lactic acid, 1.0 g (5 wt.%) stearic acid (dissolved in 5 ml hot absolute ethanol), 0.2573 g NH ₄ VO ₃ solution (based on V ₂ O ₅ accounted for 1 wt.% of the catalyst carrier, dissolved with ethanolamine), and finally add an appropriate amount of deionized water, so that the amount of water accounts for 40% of the mass of the catalyst carrier to obtain a finely plasticized sludge. Add it to the mixing machine and knead for 3-5 hours. After the kneading is completed, it is completely sealed and aged for 24 hours.

Three times of mixing: Take out the stale materials and mix again, the mixing time is 2-3 hours.

After the mixing is completed, the material is injected into a vacuum extruder at 5 MPa for extrusion, and aged for 24 h after extrusion.

The surface of the aged product is coated with a layer of coating solution for end face hardening treatment. The coating solution is mixed with a resin and a solvent in a volume ratio of 1:1. The resin is vinyl chloride-vinyl acetate copolymer, and the solvent is to ethyl acetate.

The honeycomb catalyst after end face hardening was placed in a drying room at a temperature of 70 °C and a drying time of 12 h. Take it out and put it into the secondary drying room at 100 °C for 48 h.

The thoroughly dried catalyst was put into a muffle furnace for calcination. The calcination conditions were as follows: the heating rate was 1 ℃/min to 500 ℃, and the temperature was kept for 5 h.

The calcined honeycomb catalyst is refined to the specified size.

During the catalyst preparation process, the viscosity is moderate, it is easy to extrude, the surface is smooth, there is no cracking phenomenon, and the finished product rate is 100%.

Example 4

Preparation method is identical with embodiment 3, and difference is: add 2.0 gPMMA (10 wt.%). The obtained catalyst has a smooth surface without cracks.

Example 5

The preparation method was the same as in Example 4, except that the extrusion pressure of the vacuum extruder was 8 MPa. The obtained catalyst has a smooth surface without cracks.

Example 6

The preparation method was the same as in Example 3, except that the amount of PMMA added was 3.0 g (15 wt.%). The obtained catalyst has a smooth surface without cracks.

Example 7

The preparation method is the same as Example 4, except that the extrusion pressure of the vacuum extruder is 10 MPa. The obtained catalyst has a smooth surface without cracks.

Example 8

The preparation method is the same as in Example 3, except that the added microspheres are 1.0 g (5 wt.%) PS microspheres. The SEM photo of the obtained product is shown in Figure 8. It can be seen from the figure that after adding PS microspheres, many micron-sized blind holes appeared on the catalyst wall. The obtained catalyst has a smooth surface and no cracks.

Example 9

Preparation method is identical with embodiment 3, and difference is: add 0.4 gPMMA (2 wt.%). The obtained catalyst has a smooth surface without cracks.

Example 10

The preparation method is the same as that of Example 4, except that the extrusion pressure of the vacuum extruder is 2 MPa. The obtained catalyst has a smooth surface without cracks.

Example 11

The catalyst was prepared in the same manner as in Example 3, except that the amount of methyl cellulose was 0.4 g during the first mixing, accounting for 2 wt.% of the catalyst carrier. The obtained product is easy to extrude and has a smooth surface, but because the amount of methyl cellulose added is small, cracking occurs in the prepared catalyst, and the yield of products with a smooth surface and no cracking is 90.2%.

Example 12

The catalyst was prepared by the same method as in Example 3, except that the amount of methyl cellulose was 0.8 g during the first mixing, accounting for 4 wt.% of the catalyst carrier titanium dioxide.

The resulting product has a relatively high viscosity and sticks to the wall of the extruder and is difficult to extrude. Most of the catalyst surface after extrusion is rough and uneven, and the yield of the product with a smooth surface and no cracks is 20.9%.

Example 13

The preparation method is the same as in Example 3, except that the consumption of solid additives and liquid additives is different during the first mixing and second mixing, specifically:

One mixing: 16.67 g titanium tungsten powder, 3.33 g titanium tungsten silicon powder, 0.6g (3 wt.%) chopped glass fiber, 0.8 g (4wt.%) methylcellulose, 1.4 g (7wt.%) polyethylene oxide, 0.6 Add g (3wt.%) PMMA microspheres into the mixer, and the mixing time is 2-3 h, and the mixing is completed.

Secondary kneading: take out the first kneading material, add 0.4 g (2wt.%) lactic acid, 1.4 g (7wt.%) stearic acid (dissolved in 5 ml hot absolute ethanol), 0.2573 g NH ₄ VO ₃ solution (Based on V ₂ O ₅ accounting for 1 wt.% of the catalyst carrier, ethanolamine is used to aid in dissolution). Finally, an appropriate amount of deionized water is added so that the amount of water accounts for 25% of the mass of the catalyst carrier to obtain a sludge with better plasticity. Add it to the mixing machine and knead for 3-5 hours. After the kneading is completed, it is completely sealed and aged for 24 hours.

Example 14

Weigh 0.8936g of oxalic acid and 1.227g of ammonium molybdate (accounting for 5% of the total catalyst content based on MoO ₃ ) and dissolve them in 150 ml of deionized water, stir well to obtain a salt solution. Add 20 g of anatase titanium dioxide to the salt solution, and evaporate to dryness in an oil bath at 75 °C. Dry overnight at 100 ℃ and calcined at 500 ℃ for 2 h to obtain 5% MoO ₃ /TiO ₂ powder catalyst.

Primary mixing: the above MoO ₃ /TiO ₂ powder catalyst, 1.4 g (7 wt.%) chopped glass fiber, 0.6 g (3 wt.%) methylcellulose, 1.0 g (5 wt.%) poly Ethylene oxide and 1.0 g (5 wt.%) PMMA microspheres were added into the mixer, and the mixing time was 2-3 h, and the mixing was completed.

Secondary kneading: take out the first kneading material, add 1.0 g (5 wt.%) lactic acid, 1.0 g (5 wt.%) stearic acid (dissolved in 5 ml hot absolute ethanol), 0.2573 g NH ₄ VO ₃ solution (based on V ₂ O ₅ accounted for 1 wt.% of the catalyst carrier, dissolved with ethanolamine), and finally add an appropriate amount of deionized water, so that the amount of water accounts for 30% of the mass of the catalyst carrier to obtain a finely plasticized sludge. Add it to the mixing machine and knead for 3-5 hours. After the kneading is completed, it is completely sealed and aged for 24 hours.

Three times of mixing: Take out the stale materials and mix again, the mixing time is 2-3 hours.

After the mixing is completed, the material is injected into a vacuum extruder at 5 MPa for extrusion, and aged for 24 h after extrusion.

The surface of the aged product is coated with a layer of coating solution for end face hardening treatment. The coating solution is mixed with a resin and a solvent in a volume ratio of 1:1. The resin is vinyl chloride-vinyl acetate copolymer, and the solvent is to ethyl acetate.

The honeycomb catalyst after end face hardening was placed in a drying room at a temperature of 70 °C and a drying time of 12 h. Take it out and put it into the secondary drying room at 100 °C for 48 h.

The thoroughly dried catalyst was put into a muffle furnace for calcination. The calcination conditions were as follows: the heating rate was 1 ℃/min to 500 ℃, and the temperature was kept for 5 h.

The calcined honeycomb catalyst is refined to the specified size. The obtained catalyst has a smooth surface and no cracks.

comparative example

The catalyst was prepared according to the method of Example 2 in Patent 201110005264.2, and the performance parameters of the obtained catalyst are shown in Table 1 below.

Catalyst structure and performance characteristics of the present invention are as follows:

The results of mechanical strength, porosity, pore volume and specific surface area of the products obtained in the above-mentioned examples are shown in Table 1.

As can be seen from the above table, the product of the present invention also has higher porosity on the basis of higher mechanical strength. When no polyethylene oxide and PMMA microspheres were added, the porosity and pore volume of the resulting product were all low (Example 1). When PMMA microspheres were added, the porosity and pore volume changed with the amount of PMMA microspheres added. As can be seen from the comparison of Examples 3, 4, 6, and 9, the performance is very good when the PMMA dosage is 5% and 10%. Under the same addition amount of PMMA microspheres, as the extrusion pressure changes, the porosity and pore volume change. Through the comparison of Examples 4, 5, 7, and 10, it can be seen that the performance is the best when the extrusion pressure is 5MPa, and the extrusion pressure is 5MPa. When the outlet pressure is too high, some pores may be collapsed, reducing porosity and pore volume. Considering comprehensive factors such as cost, the preferred pressure is 5 MPa, and the preferred addition amount of PMMA microspheres is 5 wt.%. From the comparison of Examples 3 and 13, it can be seen that the combination of the amount of solid additives and liquid additives has a significant impact on the mechanical strength and porosity of the catalyst.

It can be seen from the comparison of the embodiment and the comparative example that the process of the present invention is simple and easy to implement, while the process of the comparative example is cumbersome and takes a long time. The catalyst obtained by the invention has high porosity, which reduces the weight of the catalyst per unit volume and the consumption of the catalyst, greatly saves raw materials and time, and reduces costs. Although the mechanical strength of the catalyst of the comparative example is higher than that of the present invention, the porosity is low and the catalyst consumption is large.

Catalyst structure and performance characteristics of the present invention are as follows:

Figure 1-Figure 4 is the pore size distribution diagram of the product. Example 1 does not add a pore-forming agent, and Example 2 only adds a pore-forming agent. As can be seen from Figure 1, when Examples 1 and 2 do not add a pore-forming agent or add a pore-forming agent alone, the multi-stage The pore structure is not obvious. Two kinds of pore-forming agents are added in Example 3-7 to create pores simultaneously. As can be seen from Figures 1-4, Example 3-6 has an obvious micro-nano pore structure, and the nano- and micro-pore diameters Centralized distribution. However, the multi-stage pore structure in Example 7 is not obvious, which may be caused by the collapse of the pores because the extrusion pressure is too large. In addition, the change of the pore volume shown on the graph has the same trend as that in Table 1.

5-7 are SEM images of Examples 2, 3, and 4. It can be seen from Figure 5 that the catalyst wall is relatively flat and there are no large blind holes. Fig. 6 is the SEM image of Example 3, because the composite pore-forming agent is used, larger and smaller blind holes appear on the catalyst wall at the same time, but the amount of blind holes is not much. FIG. 7 is a SEM image of Example 4, from which it can be seen that the number of blind holes has increased significantly. It can be seen from Figures 5 to 7 that the product obtained after adding PMMA microspheres and polyethylene oxide has obvious micropores, and with the increase of PMMA microspheres, the number of micrometer pores gradually increases. Figure 8 is the SEM of the product obtained by adding polyethylene oxide and PS microspheres, and blind holes can also be seen.

Figures 9 and 10 are the denitrification efficiency and _N2 selectivity diagrams of the products obtained in Examples 2, 3 and 4. It can be seen from the figure that the denitrification efficiencies of the catalysts obtained in Examples 2, 3, and 4 are all very good at 300-450°C, all close to 100%, and the _N2 selectivity in the entire temperature range is also very good, and adding After adding pore-forming agent, the low-temperature _N2 selectivity is greatly improved.

Claims (10)

1. A preparation method of a honeycomb denitration catalyst with a multi-level pore structure, characterized in that: the catalyst has a honeycomb structure, and has micron-scale and nano-scale blind holes on the wall surface of the catalyst, and the micron-scale blind holes The diameter of the nano-scale blind hole is 0.1-1 micron, and the diameter of the nano-scale blind hole is 10-100nm, including the following steps: (1) Mix the catalyst carrier and solid additive to obtain a uniform solid material; (2) Add liquid additives and vanadium precursor solution to the uniformly mixed solid material, mix again, and stale after mixing; (3) Mixing the stale material for the third time to obtain mud; (4) Extrude the mud into shape, cut it to the required size and then age it; (5) Apply resin coating on the surface of the aged product, and carry out end surface hardening treatment; (6) The hardened product is dried and roasted twice to obtain the catalyst; The catalyst carrier is one or more of WO ₃ /TiO ₂ , WO ₃ /TiO ₂ -SiO ₂ and MoO ₃ /TiO ₂ ; Described solid additive comprises glass fiber, methylcellulose and composite pore-forming agent, and described composite pore-forming agent is polyethylene oxide and PMMA microsphere, perhaps is polyethylene oxide and PS microsphere; Described liquid additive comprises stearin Acid, lactic acid and water; The resin coating is a mixture of vinyl chloride-vinyl acetate copolymer and ethyl acetate at a volume ratio of 1:1; The solid additives are added in the order of glass fiber, polyethylene oxide, PMMA microspheres or PS microspheres, and methyl cellulose; The amount of glass fiber is 3-10 wt% of the catalyst carrier; the amount of methylcellulose is 2-4 wt% of the catalyst carrier; the amount of PMMA microspheres or PS microspheres is 2-15 wt% of the catalyst carrier; the amount of polyethylene oxide The amount of stearic acid is 3-7 wt% of the catalyst carrier; the amount of lactic acid is 2-5 wt% of the catalyst carrier; the amount of water is 25-40 wt% of the catalyst carrier. 2. The preparation method according to claim 1, characterized in that: the vanadium precursor solution is NH ₄ VO ₃ solution, wherein ethanolamine or oxalic acid is added to aid in dissolution. 3. preparation method according to claim 1 is characterized in that: glass fiber consumption is 7 wt% of catalyst carrier; Methyl cellulose consumption is 3 wt% of catalyst carrier; PMMA microsphere or PS microsphere consumption is catalyst 5 wt% of the carrier; the amount of polyethylene oxide is 5 wt% of the catalyst carrier; the amount of stearic acid is 5 wt% of the catalyst carrier; the amount of lactic acid is 5 wt% of the catalyst carrier; the amount of water is 30 wt% of the catalyst carrier. 4. The preparation method according to claim 1, characterized in that: the mixing time in step (1) is 2-3 h; the mixing time in step (2) is 3-5 h; stale at room temperature, sealed state The mixing time in step (3) is 2-3 h; in step (4), the extrusion pressure is 5-10 MPa; the aging temperature is room temperature, and the aging time is 24 h. 5. The preparation method according to claim 4, characterized in that: in step (4), the extrusion pressure is 5 MPa. 6. The preparation method according to claim 1, characterized in that: in step (6), the first drying temperature is 70°C, and the drying time is 12-24 h; the second drying temperature is 100°C, and the drying time is 24-48 h; when roasting, increase the temperature to 450-600 °C at a rate of 1 °C/min, and keep it for 3-5 h. 7. The preparation method according to claim 6, characterized in that: in step (6), the first drying time is 12 h, and the second drying time is 48 h; in step (6), when roasting , at a rate of 1 °C/min to 500 °C, and held for 5 h. 8. The preparation method according to any one of claims 1-7, characterized in that: the molecular weight of polyethylene oxide is 1×10 ⁵ -1×10 ⁶ ; stearic acid is dissolved in hot absolute ethanol and added. 9. The honeycomb denitration catalyst with a hierarchical pore structure prepared according to the preparation method of the honeycomb denitration catalyst with a hierarchical pore structure according to claim 1. 10. The honeycomb type denitration catalyst according to claim 9, characterized in that: the porosity of the catalyst is 70-90%, and the pore volume is 0.5-0.9 cm ³ /g.