CN102350342B - Catalyst for selective catalytic reduction of NOx at low temperature with high activity and strong sulfur resistance - Google Patents

Abstract

The invention discloses a catalyst for selective catalytic reduction of _NOx with high activity and strong sulfur resistance, a preparation method and application. The catalyst is a supported catalyst with CrMn _1.5 O ₄ active crystal phase, and is composed of the following components by weight percentage: 10-30% of chromium manganese oxide and 70-90% of porous carrier. The preparation method comprises the following steps: dissolving chromium and manganese metal salts into citric acid solution; immersing the porous carrier in the mixed solution obtained above, raising the temperature and stirring until the water evaporates to obtain the mixture; drying the mixture at 100-150°C, Then calcined at 500-650° C. for 2-5 hours, ground and sieved to obtain the catalyst. The catalyst has good low-temperature activity, the space velocity is 30000h ^-1 , and NO _x can be removed efficiently at 180°C, and the removal rate is more than 90%. In the presence of high concentration of _SO2 , it has better sulfur resistance.

Description

Catalyst for selective catalytic reduction of NOx at low temperature with high activity and strong sulfur resistance

technical field

The invention belongs to the technical field of air purification, and in particular relates to a low-temperature removal of _NOx by ammonia selective catalytic reduction (NH ₃ -SCR) method in the field of environmental catalysis and a catalyst with high sulfur resistance and its preparation method and application.

Background technique

Ammonia selective catalytic reduction (NH ₃ -SCR) is the most effective and commercialized method for removing nitrogen oxides from stationary sources such as thermal power plants. In the traditional NH ₃ -SCR technology, according to the installation position of the SCR reactor relative to the electrostatic precipitator, the SCR technology can be divided into two methods: high dust content process and low dust content process. In the high dust content process, the SCR reactor is arranged between the boiler economizer and the air preheater. The advantage of this arrangement is that the flue gas temperature is high, which meets the requirements of the catalyst activity. The commercial catalyst V ₂ O ₅ - On WO ₃ /TiO ₂ , the conversion rate of NO reaches over 90% at 300°C. The disadvantage is that the high-dust flue gas contains a large amount of dust and _SO2 , which can easily lead to catalyst blockage and poisoning, and has high requirements on the anti-wear and anti-blocking performance of the catalyst. In the low dust content process, the SCR device is arranged after the dust removal system and before the desulfurization device. At this time, although the content of fly ash in the flue gas is greatly reduced, the influence of SO ₂ still exists, and the temperature of the exhaust gas also drops a lot. In order to meet the requirements of the catalytic reaction temperature, it is necessary to install steam heaters and flue gas heat exchangers, resulting in increased investment, and there are few industrial applications. The low-temperature NH ₃ -SCR technology is to place the SCR device after the dedusting and desulfurization system, which avoids the poisoning effect of fly ash and SO ₂ on the catalyst, and at the same time avoids the commercial V ₂ O ₅ -(WO ₃ )/TiO ₂ catalyst (>350°C), the energy consumption necessary for flue gas preheating has attracted the attention of many scholars in recent years. However, even after the flue gas passes through the electrostatic precipitator and desulfurization device, a small amount of SO ₂ remains, which leads to the deposition of sulfate on the surface of the catalyst and the poisoning of the active site, which reduces the activity of the catalyst.

Metal oxide catalysts have been commercialized at present, and are generally supported by TiO ₂ , SiO ₂ , Al ₂ O ₃ , etc. Among them, TiO ₂ has high resistance to SO ₂ toxicity and stability, and is the most commonly used support material. Active metal components include metal oxides such as V ₂ O ₅ , WO ₃ , Fe ₂ O ₃ , CuO, CrO _x , MnO _x , MoO ₃ , MgO, and NiO, or composite oxides formed by their interactions. Among commercial catalysts, V ₂ O ₅ is the most important main catalyst because it not only has high denitrification efficiency, but also can simultaneously promote the conversion of SO ₂ to SO ₃ in the flue gas, thereby achieving the purpose of simultaneous desulfurization and denitrification. There are many _studies on supported manganese-based catalysts. For example, the MnO _x /Al ₂ O ₃ catalyst _prepared by Kijlstra et al. (J.Catal., 1997, 171: 219-230) by impregnation method can The conversion rate of NO _x can reach 72% at 150℃, but its stability is not good. The conversion rate drops rapidly in the first 50 hours, and then gradually stabilizes at about 40%. MnO _x /TiO ₂ developed by Ettireddy et al. (Appl. Catal. B: Environ., 2007, 1-2: 123-134) has a high activity for ammonia selective catalytic reduction of NO in the presence of oxygen. At present, most commercial SCR catalysts use TiO ₂ as the carrier and V ₂ O ₅ , V ₂ O ₅ -MoO ₃ or V ₂ O ₅ -MoO ₃ -WO ₃ as the active component. Adding WO ₃ , MoO ₃ etc. as additives can effectively inhibit the reaction of V ₂ O ₅ and SO ₂ . However, the suitable activation temperatures of these catalysts are all medium and high temperatures, and basically have no applicable reactivity in the low temperature range. Therefore, the development of low-temperature SCR catalysts with high activity, high selectivity, and high sulfur tolerance is of great significance to its industrialization.

Contents of the invention

In order to solve the deficiencies in the above-mentioned prior art, the primary purpose of the present invention is to provide a catalyst for selective catalytic reduction of _NOx with high activity and strong sulfur resistance. The catalyst is a supported catalyst with CrMn _1.5 O ₄ active crystal phase synthesized in situ on an active carrier, which can efficiently remove nitrogen oxides and resist SO ₂ poisoning under low temperature conditions.

Another object of the present invention is to provide a method for preparing the above-mentioned catalyst.

Another object of the present invention is to provide the application of the above-mentioned catalyst.

The object of the present invention is achieved through the following technical solutions: a catalyst for selective catalytic reduction of _NO with high activity and strong sulfur resistance, the catalyst is a loaded catalyst with CrMn _1.5 O ₄ active crystal phase, by the following The component composition in terms of weight percent: 10-30% of chromium-manganese oxide and 70-90% of porous carrier; the chromium-manganese oxide is calculated by Cr ₂ O ₃ and MnO ₂ .

The catalyst in situ synthesizes an active crystal phase of CrMn _1.5 O ₄ on a porous support.

The molar ratio of the chromium element and the manganese element in the chromium manganese oxide is 1:1˜1:4.

The porous carrier is one of γ-Al ₂ O ₃ , active carbon, TiO ₂ and HZSM-5 molecular sieve with a silicon-aluminum ratio of 25.

The preparation method of the above-mentioned catalyst for selective catalytic reduction of _NOx with high activity and strong sulfur resistance comprises the following steps:

(1) The chromium metal salt and the manganese metal salt that the total molar amount is 0.1mol are dissolved in the citric acid solution that the concentration of 10～30mL is 1～4mol/L, stir, obtain mixed solution; The chromium metal salt and manganese metal The molar ratio of salt is 1:1～1:4;

(2) immersing the porous carrier in the mixed solution obtained in step (1), raising the temperature to 60-90° C., and stirring continuously until all the water evaporates to obtain the mixture;

(3) drying the mixture at 100-150° C. for 6-12 hours, then calcining at 500-650° C. for 2-5 hours, pressing into tablets, grinding and sieving to obtain the catalyst.

The stirring time in step (1) is 1 to 5 hours.

The tablet pressing in step (3) is performed under a pressure of 10kPa, and the particle fineness of the catalyst is 40-60 mesh.

The above-mentioned catalyst is used in the selective catalytic reduction of nitrogen oxides by ammonia in flue gas of medium and low temperature, and the medium and low temperature is 120-360°C.

The medium and low temperature flue gas contains high concentration SO ₂ . The concentration of the high-concentration _SO2 is 100-200ppm.

Compared with the prior art, the present invention has the following advantages and beneficial effects: the catalyst of the present invention has high activity and high selective catalytic reduction of nitrogen oxides under the conditions of medium and low temperature and high sulfur, and has strong resistance to sulfur poisoning Compared with commercial catalysts such as V ₂ O ₅ WO ₃ (MoO ₃ )/TiO ₂ , the cost is reduced by more than 30%; the catalyst has the characteristics of simple preparation, low cost, and high activity. The reducing agent NH ₃ can be derived from liquid ammonia or urea pyrolysis, and is easy to match with the existing flue equipment; it greatly reduces the poisoning and clogging of the SCR catalyst by SO ₂ and dust, and the poisoning effect of trace SO ₂ on the catalyst is weak, prolonging the service life of the catalyst; economical and efficient, Energy consumption is reduced.

Description of drawings

Figure 1 is the X-ray diffraction spectrum of the catalyst obtained in Example 1, where a is γ-Al ₂ O ₃ , and b is CrMnO _x /γ-Al ₂ O ₃ with CrMn _1.5 O ₄ phase.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

1. Preparation of catalyst

(1) Preparation of chromium-manganese impregnation solution:

Add 8.08g of chromium nitrate and 7.42g of manganese acetate into 25mL of citric acid solution with a concentration of 1mol/L, and stir at room temperature for 3 hours to obtain a mixed solution;

(2) Impregnation of the carrier:

Using the solution impregnation method, take 10g of γ-Al ₂ O ₃ carrier and immerse in the mixed solution obtained in step (1), raise the temperature to 60°C, and at the same time keep stirring until all the water evaporates to obtain the mixture;

(3) Activation of samples:

Dry the mixture obtained in step (2) at 100°C for 12 hours, and bake at 650°C for 5 hours;

(4) Forming of the catalyst:

The sample obtained in step (3) is pressed into tablets under a pressure of 10 kPa, and then ground and sieved to obtain 40-60 mesh particles to obtain the catalyst.

The X-ray diffraction of the obtained catalyst is shown in Figure 1, and a CrMn _1.5 O ₄ phase is formed on the surface of the catalyst.

2. Application of catalyst

N₂为平衡气。气体总流速860mL·min^-1，空速30000h^-1。2小时稳定后NO_x的转率为95.2％。加入100ppmSO₂检测NO_x的脱除效率，6小时后NO_x转化率稳定在90.4％。The catalysts loaded with chromium-manganese oxides of the present invention all have good low-temperature SCR activity. The catalyst prepared above was used for the _NOx removal reaction, the reaction temperature was controlled at 160°C, and the simulated flue gas was introduced: NO1000ppm, _NH3 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . After 2 hours of stabilization, the _NOx conversion rate was 95.2%. The removal efficiency of _NOx was detected by adding 100ppm _SO2 , and the _NOx conversion rate stabilized at 90.4% after 6 hours.

Example 2

N₂为平衡气。气体总流速860mL·min^-1，空速10000h^-1，稳定后NO_x的转率为87.8％。将反应温度升高至360℃，稳定后NO_x的转率为92.7％。The catalyst prepared in Example 1 was used for _NOx reaction, the reaction temperature was controlled at 120°C, and simulated flue gas was introduced: NO 1000ppm, NH ₃ 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , the space velocity is 10000h ^-1 , and the NO _x conversion rate is 87.8% after stabilization. The reaction temperature was increased to 360°C, and the conversion rate of NO _x was 92.7% after stabilization.

Example 3

N₂为平衡气。气体总流速860mL·min^-1，空速30000h^-1。SO₂浓度升高至200ppm检测NO_x的脱除效率，6小时后NO_x转化率为83.6％。The catalyst prepared in Example 1 was used for the _NOx removal reaction, the reaction temperature was controlled at 160°C, and simulated flue gas was introduced: NO 1000ppm, NH ₃ 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . The _NOx removal efficiency was detected when the _SO2 concentration was increased to 200ppm, and the _NOx conversion rate was 83.6% after 6 hours.

Example 4

Add 8.08g of chromium nitrate and 4.95g of manganese acetate to 25mL of citric acid solution with a concentration of 1mol/L, and stir at room temperature for 1 hour to obtain a mixed solution; use the solution impregnation method to take 10g of HZSM-5 (Si/Al=25) The molecular sieve carrier is immersed in the mixed solution obtained in step (1), and the temperature is raised to 70° C., while stirring continuously until the water is completely evaporated to obtain a mixture; the obtained mixture is dried at 150° C. for 6 hours, roasted at 500° C. for 5 hours, and then Tablet pressing under a pressure of 10kPa, grinding and sieving to obtain 40-60 mesh particles to obtain the catalyst. The X-ray diffraction pattern results of the obtained catalyst also showed that the CrMn _1.5 O ₄ phase was formed on the surface of the catalyst.

The obtained catalyst is directly loaded into a fixed-bed reactor, the reaction temperature is controlled at 180°C, and simulated flue gas is introduced: NO 1000ppm, NH ₃ 1000ppm, _N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . After 2 hours of stabilization, the _NOx conversion rate was 97.0%. After feeding 100ppm SO ₂ , the NO _x conversion rate stabilized at 91.5% after 6 hours.

Example 5

N₂为平衡气。气体总流速860mL·min^-1，空速30000h^-1。同时通入100ppm SO₂6小时后，改通入300ppm SO₂，6小时后NO_x的转化率仍有80.5％。The catalyst obtained in Example 4, which uses chromium manganese oxide as an active component and HZSM-5 (Si/Al=25) molecular sieve as a carrier, is passed into simulated flue gas: NO 1000ppm, NH ₃ 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . Simultaneously feed 100ppm SO ₂ for 6 hours, then change to 300ppm SO ₂ , the conversion rate of NO _x is still 80.5% after 6 hours.

Example 6

Add 4.04g of chromium nitrate and 9.90g of manganese acetate into 25mL of citric acid solution with a concentration of 1mol/L, stir at room temperature for 2 hours to obtain a mixed solution; adopt the solution impregnation method, take 10g of activated carbon carrier and immerse the mixture obtained in step (1). In the solution, raise the temperature to 80°C while stirring continuously until all the water evaporates to obtain a mixture; dry the obtained mixture at 120°C for 8 hours, and roast at 550°C for 3 hours, and the sample is pressed under a pressure of 10kPa and then ground and sieved Take 40-60 mesh particles to obtain the catalyst. The X-ray diffraction pattern results of the obtained catalyst also showed that the CrMn _1.5 O ₄ phase was formed on the surface of the catalyst.

N₂为平衡气。气体总流速860mL·min^-1，空速30000h^-1。稳定后NO_x的转率为95.5％。加入100ppm SO₂，6小时后NO_x转化率稳定在84.2％。The obtained catalyst is directly loaded into a fixed-bed reactor, the reaction temperature is controlled at 180°C, and simulated flue gas is introduced: NO 1000ppm, NH ₃ 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . The _NOx conversion rate after stabilization was 95.5%. With the addition of 100 ppm _SO2 , the _NOx conversion stabilized at 84.2% after 6 hours.

Example 7

Add 8.08g of chromium nitrate and 7.42g of manganese acetate into 25mL of citric acid solution with a concentration of 1mol/L, and stir at room temperature for 5 hours to obtain a mixed solution; adopt the solution impregnation method to get 10g of TiO _The carrier is immersed in the obtained solution of step (1). In the mixed solution, raise the temperature to 90°C while stirring continuously until the water is completely evaporated to obtain a mixture; dry the obtained mixture at 120°C for 6 hours, bake at 600°C for 4 hours, and then press it under a pressure of 10kPa and grind it. The 40-60 mesh particles are sieved to obtain the catalyst. The X-ray diffraction pattern results of the obtained catalyst also showed that the CrMn _1.5 O ₄ phase was formed on the surface of the catalyst.

N₂为平衡气。气体总流速860mL·min^-1，空速30000h^-1。稳定后NO_x的转率为92.5％。加入100ppm SO₂，6小时后NO_x转化率稳定在87.6％。The obtained catalyst is directly loaded into a fixed-bed reactor, the reaction temperature is controlled at 180°C, and simulated flue gas is introduced: NO 1000ppm, NH ₃ 1000ppm,

_N2 is the balance gas. The total gas flow rate is 860mL·min ^-1 , and the space velocity is 30000h ^-1 . The _NOx conversion rate after stabilization was 92.5%. With the addition of 100 ppm _SO2 , the _NOx conversion stabilized at 87.6% after 6 hours.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (2)

1. a kind of low-temperature selective catalytic reduction _NOx catalyst with high activity and strong sulfur resistance, it is characterized in that: this catalyst is to have CrMn _1.5 O _The supported catalyst of active crystal phase, by following weight percent Component composition: chromium manganese oxide 10-30% and porous carrier 70-90%; the chromium manganese oxide is calculated as Cr ₂ O ₃ and MnO ₂ ; the catalyst synthesizes CrMn _1.5 in situ on the porous carrier The active crystal phase of O ₄ ; the porous carrier is one of γ-Al ₂ O ₃ , activated carbon, TiO ₂ and HZSM-5 molecular sieve with a silicon-aluminum ratio of 25. 2. A kind of catalyst with high activity and strong sulfur resistance low-temperature selective catalytic reduction of NO _x according to claim 1, characterized in that: the molar ratio of chromium and manganese in the chromium manganese oxide 1:1～1:4. 3. A method for preparing a catalyst for selective catalytic reduction of _NOx at low temperature with high activity and strong sulfur resistance according to claim 1, characterized in that it comprises the following steps: (1) Dissolving 0.1 mol chromium metal salt and manganese metal salt in 10-30 mL of citric acid solution with a concentration of 1-4 mol/L and stirring to obtain a mixed solution; the chromium metal salt and manganese metal salt The molar ratio of manganese metal salt is 1:1～1:4; (2) Immerse the porous carrier in the mixed solution obtained in step (1), raise the temperature to 60-90°C, and stir continuously until all the water evaporates to obtain the mixture; (3) The mixture is dried at 100-150°C for 6-12 hours, then calcined at 500-650°C for 2-5 hours, pressed into tablets, ground and sieved to obtain the catalyst. 4. The preparation method according to claim 3, characterized in that the stirring time in step (1) is 1-5 hours. 5. The preparation method according to claim 3, characterized in that in step (3), the tableting is performed under a pressure of 10 kPa, and the particle size of the catalyst is 40-60 mesh. 6. The application of the catalyst according to claim 1 in the selective catalytic reduction of nitrogen oxides by ammonia in medium-low temperature flue gas, characterized in that: the medium-low temperature is 120-220°C. 7. The application according to claim 6, characterized in that: said medium and low temperature flue gas contains high concentration SO ₂ . 8. The application according to claim 7, characterized in that the concentration of the high-concentration SO ₂ is 100-200 ppm.

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