Preparation method and application of Ce-based titanium nanotube medium-low temperature denitration catalyst

Abstract

The invention belongs to the technical field of powder catalysts, and discloses a preparation method and application of a Ce-based titanium nanotube medium-low temperature denitration catalyst. The catalyst is composed of a titanium nanotube carrier and loaded active components including rare earth metal cerium and transition metal niobium. The NOx conversion rate of the finally obtained catalyst in the wide temperature range of 183-350 DEG C reaches 80% or above, and the efficiency of 80% or above of poisoning catalysts with different contents of calcium and potassium in the temperature range of 227-350 DEG C is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder catalysts, and particularly relates to a preparation method and application of a Ce-based titanium nanotube medium and low temperature denitration catalyst. Background Art

[0002] In recent years, nitrogen oxides (NO x ) as one of the main pollutants in the atmosphere and an important precursor of PM2.5, NO existing in the atmospheric environment x is mainly NO. When NO in the atmosphere x exceeds a certain limit, it will cause a series of ecological and environmental problems (i.e., acid rain, photochemical smog, ozone layer depletion, etc.) and pose a serious threat to human health. Therefore, it is necessary to control the content of NO x emitted into the atmosphere by various industries. The sources of NO x are divided into mobile sources (motor vehicles, ships, etc.) and stationary sources. Stationary sources include the power industry (thermal power plants) and non-power industries (cement, steel, non-ferrous metals, chemical industries, etc.). In recent years, with the continuous reduction of NO x emissions in the thermal power industry, the proportion of NO x emissions from non-power industries such as steel, non-ferrous metals, chemical industries, and cement has been increasing year by year. And the steel industry is about to complete the ultra-low emission upgrade transformation, and the ultra-low emission transformation and upgrade of non-power industries such as cement for NO x is imminent.

[0003] According to the existing theoretical research and application practice, the ammonia selective catalytic reduction (NH3-SCR) technology has the advantages of a wide operating temperature range, high NO x conversion rate, and no secondary pollution, and has become one of the most effective and widely used technologies for removing NO x . And the catalyst is the key link of the SCR technology. At present, traditional V2O5 / TiO2, V2O5-WO3(MoO3) / TiO2 are the most widely used NH3-SCR denitration catalysts in commercial applications, and have excellent catalytic performance at medium and high temperatures (300-450 °C), and are widely used in the thermal power industry. In addition, these catalysts still have some other disadvantages, such as a narrow temperature window, sulfur poisoning inactivation, alkali (earth) metal poisoning inactivation, and the biological toxicity of vanadium species, which restrict the industrial application of complex flue gas in non-power industries. Therefore, studying a catalyst system with high activity, anti-poisoning, and environmental friendliness in the medium and low temperature range is an effective way to solve the above problems, thus promoting the innovation of catalyst technology.

[0004] The existing catalysts generally have the following disadvantages: poor denitrification activity at medium and low temperatures; the performance of the catalyst is easily affected by alkaline earth metals (CaO) and alkali metals (K2O) in the flue gas, resulting in poisoning and inactivation. Therefore, developing an NH3-SCR catalyst with high catalytic activity at medium and low temperatures and resistance to calcium and potassium poisoning is the key to controlling NO x ultra-low emissions in the cement industry. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a Ce-based titanium nanotube denitrification catalyst at medium and low temperatures. By studying and regulating the structure of the titanium dioxide support and loading the active component of metal oxide, the problems of poor activity at medium and low temperatures and poor resistance to poisoning by alkali / alkaline earth metals in the existing catalyst are solved.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a preparation method and application of a Ce-based titanium nanotube denitrification catalyst at medium and low temperatures, which are composed of the following components according to the molar ratio: 10 parts of support, and the support is titanium nanotube; the active components include 1 part of rare earth metal cerium and 0.75 part of transition metal niobium; the titanium nanotube is a hollow structure and is prepared from P25 as a precursor; the preparation method of the titanium nanotube support is as follows: 1) Mix P25 with 10 mol / L NaOH in the calculated proportion, stir at room temperature for 6 h until completely dispersed to obtain a mixed suspension; 2) Place the mixed suspension obtained in step 1) in an oven at 130 °C and keep it warm for 24 h to obtain a hydrothermal product; 3) Wash the hydrothermal product obtained in step 2) successively with 0.1 mol / L HCl solution and deionized water, soak and disperse it in excess absolute ethanol, and centrifuge to obtain a treated product; 4) Dry and grind the product in step 3) to obtain a titanium nanotube support.

[0007] In step 3), the HCl solution is washed until the pH = 1-2, the deionized water is washed until the pH = 7, and the soaking and dispersing time is 24 h; in step 4), the drying is carried out at 80 °C for more than 12 h.

[0008] The active components are rare earth metal cerium and transition metal niobium. Among them, the molar ratio of the active component to the support is cerium: niobium: titanium = 0.1: 0.075: 1. The technical solution adopted by the present invention is a preparation method and application of a Ce-based titanium nanotube denitrification catalyst at medium and low temperatures, which are specifically implemented according to the following steps: 1) Add the precursor of the active component cerium to deionized water according to the calculated molar ratio, stir at room temperature until completely dissolved, and then add the titanium nanotube support to obtain a mixed solution; 2) Place the mixed solution obtained in step 1) in an oil bath and heat it at 80 °C with stirring. Slowly evaporate the excess aqueous solution, and after drying, mixture A is obtained. 3) Add the precursor of the active component niobium in the calculated molar ratio to deionized water, stir at room temperature until completely dissolved, and then add mixture A obtained in step 2) to obtain a mixed solution. 4) Place the mixed solution obtained in step 3) in an oil bath and heat it at 80 °C with stirring. Slowly evaporate the excess aqueous solution, and after drying, mixture B is obtained. 5) Subject mixture B obtained in step 4) to calcination, grinding, and sieving to obtain the Ce-based titanium nanotube low-temperature denitration catalyst. 6) Add a certain amount of calcium nitrate tetrahydrate to deionized water. After stirring and dissolving, add the catalyst obtained in step 5) thereto, stir and disperse at room temperature, and after drying, calcination, grinding, and sieving, the calcium-poisoned catalyst corresponding to 5) is obtained. 7) Add a certain amount of potassium nitrate to deionized water. After stirring and dissolving, add the catalyst obtained in step 5) thereto, stir and disperse at room temperature, and after drying, calcination, grinding, and sieving, the potassium-poisoned catalyst corresponding to 5) is obtained.

[0009] In steps 2) and 4), the drying is carried out at 100 °C for more than 12 h; in steps 5), 6), and 7), the calcination is carried out at 500 °C for 5 h in an air atmosphere.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. Based on the active components Ce and Nb, a titanium nanotube support is added to this catalyst, increasing the acidic sites on the catalyst surface and the catalytic reduction performance of NO, and the NO conversion rate reaches over 80% in the wide temperature range of 183 - 350 °C; it has the advantages of high catalytic activity and wide temperature window. x Performance, and in the wide temperature range of 183 - 350 °C of NO x The conversion rate reaches over 80%; it has the advantages of high catalytic activity and wide temperature window.

[0012] 2. Based on the titanium nanotube support structure, this catalyst uses sodium hydroxide to form a hollow structure, effectively increasing the specific surface area and pore volume and pore diameter of the catalyst. The increase in specific surface area promotes the dispersion of active components, and the hollow structure effectively improves the anti-calcium and anti-potassium poisoning performance of the catalyst.

[0013] 3. The raw materials of the present invention are based on vanadium-free rare earth-based metal oxides, which are not only green and pollution-free, realizing the development and utilization of China's rare earth resources, and can be used for the purification treatment of NO in flue gas of non-electric industries such as cement, steel, non-ferrous metals, and chemical engineering. x Purification treatment. Description of the Drawings

[0014] Figure 1X-ray powder diffraction patterns of the fresh and poisoned catalysts with different calcium and potassium contents for Examples 1-6;

[0015] Figure 2 Scanning electron microscope images of the fresh and poisoned catalysts with different calcium and potassium contents for Examples 1, 2, 4, and 6;

[0016] Figure 3 Denitrification performance curves of the fresh and poisoned catalysts with different calcium contents for Examples 1-4;

[0017] Figure 4 Denitrification performance curves of the poisoned catalysts with different potassium contents for Examples 5 and 6; Detailed implementation manners

[0018] To make the content of the present invention more understandable, the technical solutions of the present invention will be further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0019] Example 1

[0020] Dissolve 3.2623 g of cerium nitrate hexahydrate in deionized water, stir and dissolve at room temperature, and add 6 g of TiO2. Subsequently, stir at room temperature for 2 h, heat and stir in an oil bath at 80 °C to remove moisture. The remaining solid is dried in an oven at 100 °C for more than 12 h to obtain powder A. Dissolve 3.0317 g of niobium oxalate hydrate in deionized water, add powder A after stirring and dissolving, stir at room temperature for 2 h, heat and stir in an oil bath at 80 °C to remove moisture, and the remaining solid is dried in an oven at 100 °C for more than 12 h to obtain powder B. Then, heat at a heating rate of 2 °C / min to 500 °C and calcine in an air atmosphere at 500 °C for 5 h. Grind and sieve the obtained solid, and the obtained sample is the NbCe / Ti catalyst, denoted as catalyst A;

[0021] Example 2

[0022] Dissolve 3.2623 g of cerium nitrate hexahydrate in deionized water, stir and dissolve at room temperature, and add 6 g of titanium nanotubes (TiNTs). Subsequently, stir at room temperature for 2 h, heat and stir in an oil bath at 80 °C to remove moisture. The remaining solid is dried in an oven at 100 °C for more than 12 h to obtain powder A. Dissolve 3.0317 g of niobium oxalate hydrate in deionized water, add powder A after stirring and dissolving, stir at room temperature for 2 h, heat and stir in an oil bath at 80 °C to remove moisture, and the remaining solid is dried in an oven at 100 °C for more than 12 h to obtain powder B. Then, heat to 500 °C at a heating rate of 2 °C / min and calcine in an air atmosphere at 500 °C for 5 h. Grind and sieve the obtained solid, and the obtained sample is the NbCe / TiNTs catalyst, denoted as catalyst B;

[0023] Example 3

[0024] Dissolve 0.1687 g and 0.4218 g of calcium nitrate tetrahydrate in deionized water respectively. After stirring and dissolving, add 2 g of catalyst A to each, and stir at room temperature for 5 h. Dry in an oven at 100 °C for more than 12 h, then raise the temperature to 500 °C at a heating rate of 2 °C / min, and calcine in an air atmosphere at 500 °C for 5 h. Grind the obtained solid and sieve it. The obtained samples are 2Ca-NbCe / Ti and 5Ca-NbCe / Ti catalysts, denoted as catalyst C and catalyst D;

[0025] Example 4

[0026] Dissolve 0.1687 g and 0.4218 g of calcium nitrate tetrahydrate in deionized water respectively. After stirring and dissolving, add 2 g of catalyst B to each, and stir at room temperature for 5 h. Dry in an oven at 100 °C for more than 12 h, then raise the temperature to 500 °C at a heating rate of 2 °C / min, and calcine in an air atmosphere at 500 °C for 5 h. Grind the obtained solid and sieve it. The obtained samples are 2Ca-NbCe / TiNTs and 5Ca-NbCe / TiNTs catalysts, denoted as catalyst E and catalyst F;

[0027] Example 5

[0028] Dissolve 0.0429 g and 0.1288 g of potassium nitrate in deionized water respectively. After stirring and dissolving, add 2 g of catalyst A to each, and stir at room temperature for 5 h. Dry in an oven at 100 °C for more than 12 h, then raise the temperature to 500 °C at a heating rate of 2 °C / min, and calcine in an air atmosphere at 500 °C for 5 h. Grind the obtained solid and sieve it. The obtained samples are 1K-NbCe / Ti and 3K-NbCe / Ti catalysts, denoted as catalyst G and catalyst H;

[0029] Example 6

[0030] Dissolve 0.0429 g and 0.1288 g of potassium nitrate in deionized water respectively. After stirring and dissolving, add 2 g of catalyst B to each, and stir at room temperature for 5 h. Dry in an oven at 100 °C for more than 12 h, then raise the temperature to 500 °C at a heating rate of 2 °C / min, and calcine in an air atmosphere at 500 °C for 5 h. Grind the obtained solid and sieve it. The obtained samples are 1K-NbCe / TiNTs and 3K-NbCe / TiNTs catalysts, denoted as catalyst I and catalyst J;

[0031] Figure 1 are the X-ray powder diffraction patterns of the catalysts in Examples 1-6. From Figure 1As can be seen from the left figure, diffraction peaks of TiO2 and CeO2 (28.6°, 56.3°) can be detected in the XRD patterns of all samples. As can be seen from the right figure, diffraction peaks of anatase TiO2 support (25.3°), CeO2 (28.6°, 33.1°, 47.5°, 56.3°, 59.0°), and H2Ti8O 17 (48.5°) can be detected in all samples. By comparing the XRD patterns on the left and right, it can be seen that the diffraction peak intensity of the catalyst decreases significantly after the addition of the TiNTs support on the right. The intensity of the diffraction peak reflects the crystallinity of the catalyst. After the addition of the TiNTs support, the crystallinity of the catalyst is relatively low, indicating that the addition of the TiNTs support is more conducive to the dispersion of the active components on the surface of the support.

[0032] Figure 2 SEM images of the catalysts of Examples 1-2, 4, and 6 are shown. It can be seen that the NbCe / Ti catalyst shows irregularly aggregated nanoparticles, and an amorphous tubular structure is observed for the NbCe / TiNTs catalyst. NbCe / TiNTs catalysts with different CaO and K2O contents all exhibit an amorphous tubular structure, indicating that the catalyst does not collapse due to K and Ca poisoning.

[0033] The denitrification performance of the catalysts of Examples 1-6 was tested. The activity of the catalyst is expressed by the NO x conversion rate, and the NO x concentration was detected using a Testo350 infrared flue gas analyzer. The specific test conditions are as follows: The NH3-SCR denitrification activity test was carried out in a fixed-bed quartz tube reactor. The catalyst loading was 0.2 g, the particle size was 40-60 mesh, the reaction temperature was 150-350 °C, the test temperature interval was 25 °C, and the concentration at each temperature was based on the final stable reading of the flue gas analyzer. The concentration of NO in the raw gas was 500 ppm, the concentration of the reducing gas NH3 was 500 ppm, the volume concentration of O2 was 5%, N2 was the balance gas, the total mixed flue gas volume was 200 mL / min, and the space velocity (GHSV) was 60000 h -1 ; A vertical tube furnace with a temperature control system provided the reaction temperature environment. The test results are shown in Figure 3 、 4 .

[0034] From Figure 3 、 4 it can be seen that for catalyst A in the test temperature range of 190-350 °C, the removal rate of NO x remains at about 80%, and in the temperature range of 225-350 °C, the removal rate of NO xThe removal rate is close to 100%. For catalyst B within the test temperature range of 183 - 350 °C, the catalyst's NO x removal rate remains at about 80%, and within the temperature range of 200 - 350 °C, the NO x removal rate is close to 100%. In addition, when TiO2 is the carrier, after being poisoned by 2 wt.% CaO, the NO x conversion rate reaches 80% in the range of 220 - 350 °C. After being poisoned by 5 wt.% CaO, the NO x maximum conversion rate of the catalyst is less than 60%; after being poisoned by 1 wt.% K2O, the NO x maximum conversion rate reaches 90% in the range of 150 - 350 °C. After being poisoned by 3 wt.% K2O, the catalyst has almost no activity. When TiNTs is the carrier, the poisoned catalysts of 2 wt.% CaO, 5 wt.% CaO, 1 wt.% K2O, and 3 wt.% K2O can achieve an NO x conversion rate of over 80% within the temperature ranges of 198 - 350 °C, 222 - 350 °C, 208 - 350 °C, and 227 - 350 °C respectively, showing a great improvement compared to before the modification of the carrier structure regulation.

[0035] The above are only the preferred embodiments of the present invention, and do not thereby limit the patent scope of the present invention. All equivalent transformations made according to the patent scope of the present invention should fall within the scope of the present invention.

Claims

1. A preparation method and application of a Ce-based titanium nanotube low-temperature denitration catalyst, characterized in that It consists of the following components according to the molar ratio: 10 parts of a carrier, which is titanium nanotubes; the active components include 1 part of rare earth metal cerium and 0.75 part of transition metal niobium; the titanium nanotubes are of a hollow structure and are prepared using P25 as a precursor; the preparation method of the titanium nanotube carrier is as follows: 1) Mix P25 and 10 mol / L NaOH in the calculated ratio and stir at room temperature for 6 h until completely dispersed, to obtain a mixed suspension; 2) Place the mixed suspension obtained in step 1) in an oven at 130 °C and keep it warm for 24 h to obtain a hydrothermal product; 3) Wash the hydrothermal product obtained in step 2) successively with 0.1 mol / L HCl solution and deionized water, soak and disperse it in excessive absolute ethanol, and centrifuge to obtain a treated product; 4) Dry and grind the product in step 3) to obtain the titanium nanotube carrier.

2. The preparation method and application of a Ce-based titanium nanotube medium and low temperature denitration catalyst according to claim 1, characterized in that, The active components are rare earth metal element cerium and transition metal element niobium. Among them, the molar ratio of the active components to the carrier is cerium:niobium:titanium = 0.1:0.075:

1.

3. The preparation method and application of a Ce-based titanium nanotube low-temperature denitration catalyst according to claim 1, characterized in that, It includes the following preparation steps: 1) Add the precursor of active component cerium in the calculated molar ratio to deionized water, stir at room temperature until completely dissolved, and then add the titanium nanotube carrier to obtain a mixed solution; 2) Place the mixed solution obtained in step 1) in an oil bath and heat and stir at 80 °C, slowly evaporate the excess aqueous solution, and obtain mixture A after drying; 3) Add the precursor of active component niobium in the calculated molar ratio to deionized water, stir at room temperature until completely dissolved, and then add mixture A obtained in step 2) to obtain a mixed solution; 4) Place the mixed solution obtained in step 3) in an oil bath and heat and stir at 80 °C, slowly evaporate the excess aqueous solution, and obtain mixture B after drying; 5) Calcinate, grind and sieve the mixture B obtained in step 4) to obtain the Ce-based titanium nanotube mid-low temperature denitration catalyst. 6) Add a certain amount of calcium nitrate tetrahydrate to deionized water, stir and dissolve it, then add the catalyst obtained in step 5) thereto, stir and disperse it at room temperature, and obtain the corresponding calcium-poisoned catalyst in 5) after drying, calcination, grinding and sieving; 7) Add a certain amount of potassium nitrate to deionized water, stir and dissolve it, then add the catalyst obtained in step 5) thereto, stir and disperse it at room temperature, and obtain the corresponding potassium-poisoned catalyst in 5) after drying, calcination, grinding and sieving.

4. The preparation method and application of a Ce-based titanium nanotube low-temperature denitration catalyst according to claim 3, characterized in that, The drying is carried out at 100 °C for more than 12 h; the calcination is carried out at 500 °C in an air atmosphere for 5 h.

5. The titanium nanotube support according to claim 1, characterized in that, In step 3), the HCl solution is washed until the pH = 1 - 2, the deionized water is washed until the pH = 7, and the soaking and dispersing time is 24 h.

6. The titanium nanotube support according to claim 1, wherein In step 4), the drying is carried out at 80 °C for more than 12 h.

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