CN104084213A - Preparation method of iron manganese titanium catalyst for denitrating fixed-source smoke at low temperature and catalyst prepared through preparation method - Google Patents

Abstract

With the assistance of CTAB, the FMT(S) composite oxide catalyst was prepared by co-precipitation method. When the space velocity was 30000mL·g ^–1 ·h ^–1 , the conversion rate of the obtained composite oxide catalyst reached 100 at 100-350℃ %, the selectivity at 75-200 ° C is over 80%, and it has good water resistance, and has certain application prospects in the field of low-temperature denitrification. The invention discloses its preparation method.

Description

Preparation method of iron-manganese-titanium catalyst for low-temperature denitrification of stationary source flue gas and catalyst prepared therefrom

technical field

The invention relates to a low-temperature denitrification iron-manganese-titanium catalyst, which is suitable for flue gas denitrification of stationary sources such as coal-fired power plants.

Background technique

Nitrogen oxides (NO _x ), mainly including NO and NO ₂ , are one of the main air pollutants. It is estimated that the world emits about 58 million tons of _NOx into the atmosphere every year. NO _x is not only the main cause of nitric acid rain, but also one of the main sources of ozone layer destruction and photochemical smog formation. It has strong toxicity and seriously threatens human health and ecological environment balance. Divided by source, nitrogen oxides include mobile sources and stationary sources. Mobile sources mainly refer to motor vehicle exhaust, while stationary sources are of various types, including coal-fired power plants, cement kilns, steel factories, and glass factories. In our country, with the acceleration of the industrialization process and the extensive use of coal resources, the _NOx emitted into the atmosphere is increasing year by year. Statistics show that stationary source flue gas emissions have become the primary source of nitrogen oxides in my country. Therefore, the purification of nitrogen oxides in stationary source flue gas is imminent and has become one of the hotspots of my country's current environmental protection work, which is of great significance to the control of smog and air pollution.

In the control of flue gas emissions from stationary sources, ammonia (urea) selective catalytic reduction technology, namely NH ₃ (Urea)-SCR, is commonly used in industry. The current commercialized NH ₃ -SCR catalyst is V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ , which is only suitable for medium temperature (350-400°C) denitrification due to its activation temperature. Also because of this, its denitration unit is set before dust removal and desulfurization. But V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ catalyst has the following problems in use:

1. In practical applications, the active temperature range of the catalyst is between 350-400°C, and the narrow range often cannot meet the requirements of large temperature changes under the use conditions.

2. In the high temperature range, this type of catalyst has poor nitrogen selectivity.

3. Vanadium pentoxide is highly toxic and easy to cause environmental pollution.

4. SO ₂ is converted into SO ₃ and then reacts with excess NH ₃ , which is prone to sulfur poisoning and deactivates the catalyst. This leads to increased economic costs and energy consumption.

5. There is a lot of smoke and dust in the tail gas emitted by stationary sources. The smoke and dust often contain alkali metal or alkaline earth metal compounds and other substances that are likely to cause catalyst poisoning to cover the surface of the catalyst, shortening the service life of the catalyst.

If a catalyst can be invented to reduce its active temperature range to a certain extent, its denitration device can be installed after the desulfurization and dust removal device, so as to reduce the pollution and poisoning of the catalyst by sulfur and fly ash. At present, the research _and development of selective catalytic reduction (NH ₃ -SCR) catalysts using NH ₃ as a reducing agent at low temperatures is a hotspot in the research of stationary source denitrification. When manganese species are used as active components, manganese oxide-based catalysts are It has attracted much attention due to its superior catalytic activity in the SCR reaction. Donovan et al. loaded V, Cr, Mn, Fe, Cu, Ni, and Co on anatase TiO ₂ respectively. The comparison shows that at a temperature of 120 °C, the activities of various supported metal oxides are: Mn>Cu>Cr>Co>Fe>V>Ni, and Mn/ _TiO2 has the highest activity, generating _N2 selectivity and NO conversion Rates are all 100%. Kang et al. used sodium carbonate as a precipitating agent to prepare MNOx catalysts by precipitation method at a calcination temperature of 260-350 °C. It was found through characterization that the catalyst has a larger specific surface area, higher Mn loading and surface oxygen loading, and high-valence Mn species (Mn ₂ O ₃ and Mn ₃ O ₄ ). The conversion rate is above 90%. The selectivity of _N2 reaches 100% around 90°C.

However, the current low-temperature NH ₃ -SCR catalysts have one or more deficiencies in the following aspects: First, the activation temperature is not low enough. In practical applications, the gas temperature of the stationary source flue gas after dust removal and desulfurization is usually below 150°C, sometimes even below 100°C, but most of the catalysts currently researched cannot meet such requirements; secondly, the selectivity of the catalyst is not enough Well, there are many catalysts that achieve good conversion, but their selectivity is not good; finally, the stability of the catalyst is not good enough, especially the water resistance at low temperature. At present, it is difficult to find a low-temperature denitration catalyst that can satisfy these three conditions at the same time.

Contents of the invention

The purpose of the present invention is to provide a catalyst that can be widely used in stationary sources, especially low-temperature denitrification of tail gas from coal-fired power plants.

The principle of the present invention is as follows: the main factors affecting the activity of NH ₃ -SCR are: the acid site and acid amount of the catalyst, the redox property of the catalyst, the specific surface area, the active intermediate species and the like. To prepare a low-temperature denitrification catalyst, we must start from the following aspects: 1. Increase the specific surface area and pore volume of the catalyst, which is conducive to increasing the active sites per unit area and improving the diffusion capacity of reactant molecules in the catalyst. Accelerate the reaction speed; 2, increase the amount of Lewis acid sites on the surface of the catalyst, according to existing literature, Lewis acid sites are conducive to low-temperature SCR reactions; 3, enhance the redox performance of the catalyst, especially the ability to oxidize NO to NO ₂ , so It is beneficial to form a fast NH ₃ -SCR reaction, thereby speeding up the reaction speed; 4. Starting from the intermediate species, according to the existing data, nitrite species are easy to decompose at low temperature, if the intermediate species of nitrite can be generated, it is beneficial to low-temperature NH ₃ - SCR response.

Technical scheme of the present invention is as follows:

An iron-manganese-titanium catalyst for low-temperature denitrification of flue gas from a stationary source, the typical preparation method of which is as follows:

Dissolve 0.0025～0.01mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0025～0.01mol Mn(Ac) ₂ ·4H ₂ O and 0.05mol Ti(SO ₄ ) ₂ in CTAB solution, wherein the molar ratio of Fe and Mn 1:4~4:1, the molar ratio of Fe, Mn and Ti is 1~4:10, dissolved and then stirred for 30 minutes, and then the mixed solution was dropped into 150ml of ammonia (25%) solution "drop by drop". Maintain PH>9. During the whole reaction process, the system was stirred at a speed of 300rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol, dried in air at 110°C for 12 hours, and then placed in a muffle furnace to Heat up at a heating rate of 2°C/min, roast at 500°C for 6 hours, and cool to room temperature. The final product is pressed into tablets and sieved with 40-60 mesh to prepare the ferromanganese-titanium catalyst FMT(S) for low-temperature denitrification of stationary source flue gas. .

An iron-manganese-titanium catalyst for low-temperature denitrification of fixed-source flue gas prepared by the above-mentioned method, in which the _TiO2 crystals in the catalyst are mainly anatase, containing a small amount of rutile phase crystals, and other oxide species in the form of Existing in a dispersed state, the specific surface area of the catalyst can be as high as 100m ² /g or more.

The cationic surfactant cetyltrimethylammonium bromide (CTAB) has the positive charge of hydrophilic N ⁺ and the alkyl functional group of lipophilicity. In the process of catalyst preparation, by adding CTAB cationic surfactant, The low-temperature activity of the catalyst can be improved from the following aspects. First, the isoelectric point of metal iron, manganese and titanium oxides is generally less than 8. When the pH of the solution is > 9, the surface of the oxides is negatively charged, and the cationic surfactant hexadecyltrimethylammonium bromide is added (CTAB), its cations are easily adsorbed on the surface of the particles, forming a protective layer, which hinders the further growth of the grains, and at the same time, small micelles are easily formed between the surfactants, which is conducive to the formation of the pore structure, thereby forming Relatively large specific surface area and pore volume. Second, the addition of CTAB is beneficial to prevent the induction effect of manganese on TiO ₂ , thereby forming more anatase TiO ₂ crystal forms and reducing the generation of rutile TiO ₂ crystal forms. Third, the addition of CTAB is conducive to the formation of more Lewis acid sites, which is beneficial to NH ₂ species and is more conducive to low-temperature decomposition. Fourth, the addition of CTAB is conducive to the formation of nitrite species that are easily decomposed at low temperature. Fifth, the addition of CTAB is beneficial to increase the amount of lattice oxygen and enhance the redox performance.

The present invention is characterized in that cationic surfactant CTAB is used in the catalyst preparation process, and the prepared catalyst with specific composition has better low-temperature activity and selectivity.

Description of drawings

Fig. 1 NO conversion rate of FMT and FMT(S) composite oxide catalysts in NH ₃ -SCR reaction. Reaction conditions: [NO]=[NH ₃ ]=500ppm, [O ₂ ]=5%, N ₂ balance, catalyst mass=200mg, total flow rate=100mL·min ^-1 , space velocity=30,000mL·g ^-1 • h ^–1 .

Fig. 2 N ₂ selectivity of FMT and FMT(S) composite oxide catalysts in NH ₃ -SCR reaction. Reaction conditions: [NO]=[NH ₃ ]=500ppm, [O ₂ ]=5%, N ₂ balance, catalyst mass=200mg, total flow rate=100mL·min ^-1 , space velocity=30,000mL·g ^-1 • h ^–1 .

Fig. 3 FMT (S) is the conversion rate of NO in the NH ₃ -SCR reaction of the catalyst under the condition of passing water. Reaction conditions: [NO]=[NH ₃ ]=500ppm, [O ₂ ]=5%, N ₂ balance, the mass of the catalyst is 200 mg, the total flow rate is 100ml min ^-1 , [H ₂ O]=3.5%, GHSV＝30,000h ^-1 , T＝150℃.

Fig. 4 The XRD characterization results of composite oxide catalyst FMT(S) and FMT under the condition of calcination at 500°C.

Fig. 5 Composite oxide catalyst FMT(S) and pore distribution results of FMT.

Fig. 6 Characterization results of composite oxide catalyst FMT(S) and FMT adsorption-desorption isotherm.

Fig. 7 In situ diffuse reflectance characterization results of catalyst FMT(S) ammonia adsorption.

Figure 8: At 125°C, the in-situ diffuse reflectance characterization results of the catalyst FMT(S) were saturated with ammonia after being fed with NO+O ₂ .

Figure 9: At 125°C, the in-situ diffuse reflectance characterization results of the catalyst FMT(S) NO adsorption saturated after passing through NH ₃ +O ₂ .

Figure 10 The results of temperature-programmed desorption of _H2 in catalyst FMT(S).

Detailed ways

Example 1:

Add 0.015molCTAB to 400mL distilled water to obtain CTAB solution. 0.005mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.005mol Mn(Ac) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ were dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dropped "drop by drop" into 150ml of ammonia solution with a concentration of 25% by mass to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is pressed into tablets and sieved with 40-60 meshes to prepare the iron-manganese-titanium catalyst FMT(S) for low-temperature denitrification of stationary source flue gas.

Example 2:

In order to compare the effect of preparing samples, the FMT catalyst was prepared by co-precipitation method as follows: Take 0.005mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.005mol Mn(AC) ₂ ·4H ₂ O, 0.05molTi(SO ₄ ) ₂ was dissolved in the aqueous solution followed by stirring for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is pressed into tablets and sieved with 40-60 mesh to obtain the low-temperature denitrification catalyst FMT.

The products of Example 1 and Example 2 were tested for denitrification activity and selectivity and water resistance, and the products were characterized by nitrogen adsorption and desorption, wide-angle XRD, TPR, and In situ DRIFTS. The results are shown in Figures 1-10 respectively. The results in Figures 1 and 2 show that the low-temperature catalytic activity of the catalyst FMT(S) is much better than that of the catalyst FMT. When the space velocity is 30000mL g ^–1 h ^–1 , the obtained FMT (S) composite oxide catalyst is The conversion rate reaches 100%, and the selectivity reaches more than 80% at 75-200°C. The results in Figure 3 show that the FMT(S) composite oxide catalyst has good water resistance. The XRD results in Figure 4 show that the addition of CTAB inhibits the formation of the rutile phase, iron species and composite oxides exist in an amorphous form and are well dispersed on the surface of the catalyst, and there are more active high-valent metal ions on the surface of the FMT(S) catalyst. Good activity. Figures 5 and 6 show that the specific surface area of the product of the present invention can be as high as 109m ² /g through the nitrogen adsorption and desorption test, while the specific surface area of the sample prepared by the ordinary method is only 15m ² /g. See pore distribution and pore volume from BJH test result, the pore diameter of the sample of the present invention is little, and pore volume is big, and the addition of CTAB has increased catalyst surface active site quantity, has improved the diffusion characteristic of reactant gas in catalyst, is conducive to Improvement of catalyst activity. Figure 7 shows that the ammonia adsorption experiment shows that the surface of the FMT(S) composite oxide catalyst is dominated by Lewis acid sites. Figures 8 and 9 illustrate that _NH2 and nitrite adsorbed by Lewis acid sites are active intermediate species of the reaction. Figure 10 illustrates that the FMT(S) composite oxide catalyst has better redox performance.

Embodiment 3:

Take 0.015mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.0025mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0025mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 4:

Take 0.003mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.005mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.005mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 5:

Take 0.075mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.0075mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0075mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 6:

Take 0.015mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.01mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.01mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 7:

Take 0.015mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.0025mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.01mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 8:

Take 0.015mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.01mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0025mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Embodiment 9:

Take 0.015mol CTAB to 400ml distilled water to obtain CTAB solution. An appropriate amount of 0.0075mol Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0025mol Mn(AC) ₂ ·4H ₂ O, 0.05mol Ti(SO ₄ ) ₂ was dissolved in the CTAB solution and stirred for 30 minutes. Then the mixed solution was dripped into 150 ml of ammonia (25%) solution "drop by drop" to maintain pH>9. During the whole reaction, the system was stirred at a speed of 300 rpm for 3 hours. The resulting mixture was filtered, washed with distilled water and absolute ethanol several times, dried in air at 110°C for 12 hours, then placed in a muffle furnace, heated at a heating rate of 2°C/min, calcined at 500°C for 6 hours, and cooled to room temperature . The final product is compressed into tablets and sieved with 40-60 meshes to obtain the low-temperature denitration catalyst FMT(S). Its test result is as embodiment 1.

Claims (2)

1. for a method for making for the ferrimanganic titanium catalyst of stationary source flue gas low-temperature denitration, it is characterized in that it comprises the steps:

Get 0.003～0.075mol CTAB and add in 400mL distilled water, obtain CTAB solution, get 0.0025～0.01molFe (NO ₃) ₃9H ₂o, 0.0025～0.01mol Mn (Ac) ₂4H ₂o and 0.05mol Ti (SO ₄) ₂be dissolved in CTAB solution, wherein the mol ratio of Fe and Mn is 1:4～4:1, the mol ratio of Fe and Mn and Ti is 1～4:10, dissolve follow-up stirring 30 minutes, then mixed liquor " dropwise " is splashed in ammonia (25%) solution 150ml, maintain PH>9, in whole course of reaction, system stirs 3 hours with the speed of 300rpm, gained mixture after filtration, after distilled water and absolute ethanol washing, 110 ℃ of air dryings 12 hours, be put in again in Muffle furnace, firing rate with 2 ℃/min heats up, 500 ℃ of roasting 6h, be cooled to normal temperature, final product is through compressing tablet, 40-60 order sieves, make the ferrimanganic titanium catalyst FMT (S) for the denitration of stationary source flue gas low-temperature.

2. the ferrimanganic titanium catalyst for the denitration of stationary source flue gas low-temperature of preparing with method for making described in claim 1, is characterized in that: TiO in described catalyst ₂crystal take anatase as main, the crystal that contains a small amount of Rutile Type, other oxide species exists with dispersed form, the specific area of described catalyst can be up to 100m ²more than/g.