CN104549221A - Preparation method of low-temperature SCR catalyst with wide service temperature - Google Patents

Abstract

The invention discloses a preparation method of a low-temperature SCR catalyst with a wide service temperature, which belongs to the technical field of material preparation and waste gas treatment. The method is implemented by dipping soluble chromium salts, soluble zirconium salts and soluble cerium salts in a porous carrier, and firing the obtained product, so that the low-temperature SCR catalyst is obtained, wherein the percentage content of a Cr element is 50-75%, the molar ratio of Ce and Zr elements is (4:1)-(1:1), the obtained low-temperature SCR catalyst can play a role in a temperature range of 120-300 DEG C and has certain sulfur resistance, and the catalyst is relatively applicable to the denitration treatment of low-temperature NOx-containing exhaust gas.

Description

A preparation method of low-temperature SCR catalyst with wide service temperature

technical field

The invention relates to a method for preparing a low-temperature SCR catalyst with a wide service temperature, and belongs to the technical field of material preparation and waste gas treatment.

Background technique

Coal-fired power plant boilers, cement industrial kilns and glass and ceramic industrial kilns are one of the main stationary sources of atmospheric NOx pollution in my country. At present, the Yangtze River Delta, Pearl River Delta and Beijing-Tianjin-Hebei have formed large-scale NOx pollution areas in my country, which pose a major threat to the sustainable development of economy and society. NH ₃ Selective Catalytic Reduction (NH ₃ -SCR) technology is the most important technical solution for the removal of NOx from industrial waste gas. This solution uses NH ₃ to reduce NOx with the assistance of catalysts to generate harmless nitrogen. The core of this technology is the SCR catalyst. At present, the catalyst commonly used in industry is V ₂ O ₅ -WO ₃ -TiO ₂ catalyst, but its activation temperature is higher than 300°C, and the catalytic effect is not good at low temperature.

In the process of coal-fired boiler exhaust gas treatment, if the SCR catalytic module is placed before the desulfurization device, the SCR catalyst must withstand the harsh working conditions of high sulfur, high dust, high corrosion and strong erosion, and the service life of the catalyst is threatened , so the denitration operation is often arranged behind the desulfurization device, which can prevent the SO ₂ in the exhaust gas from poisoning the denitrification catalyst. At present, the technical capacity of wet desulfurization and semi-dry desulfurization in China is very large, and the subsequent flue gas temperature is very high. Low and high water content, it is difficult to use the common V ₂ O ₅ -WO ₃ -TiO ₂ catalyst directly, and the exhaust gas must be reheated to above 320°C, which consumes a lot of energy. In addition, due to the complexity of coal types in China and the high dust content in the exhaust gas, the denitrification device has to be placed after the dust removal device. Due to the limitation of the dust removal device, the temperature of the flue gas must be lowered to below 300°C before dust removal can be performed. Difficulties using common _V2O5 - _{WO3 - TiO2} catalysts. At the same time, glass kilns and cement kilns often produce NOx-containing exhaust gas with a temperature below 250 °C. These practical situations urgently require the development of new low-temperature SCR catalysts that can catalyze the reduction of NOx to nitrogen by _NH3 at low temperatures.

At present, the common low-temperature SCR mainly includes noble metal catalysts, high vanadium catalysts, manganese oxide catalysts, molecular sieve catalysts and rare earth catalysts. Among them, precious metal catalysts are difficult to be applied on a large scale because of their high price. Although high-vanadium catalysts can solve the problem of low-temperature activity, they will oxidize SO ₂ commonly found in exhaust gas to SO ₃ , resulting in catalyst failure; manganese oxide catalysts have excellent low-temperature activity. , but its catalytic performance is unstable, and its performance will be deteriorated due to the transformation of manganese oxide crystal form. In addition, the catalytic effect of manganese-based SCR catalysts is significantly reduced at higher temperatures (such as above 250 ° C); molecular sieve catalysts are often exchanged by metal ions To prepare, its active temperature is still not low enough. The rare earth element Ce has been found to have a good prospect for SCR catalysis. Cr/Ce binary oxides (200910080836.6) and Cr/V/Ce ternary oxides as low-temperature SCR catalysts have been disclosed (201110452611.6), but Cr The applicable temperature of the /Ce binary oxide catalyst is not high when the mole percentage of Ce element is high, and its catalytic effect decreases obviously when the reaction temperature is raised above 250 °C. The addition of V element is very beneficial to the improvement of the sulfur resistance of the catalyst, but this is at the expense of the SCR catalytic effect at low temperature, because the V oxide has poor performance in catalytic SCR reaction at low temperature.

To sum up, the preparation of an SCR catalyst with good catalytic effect at 120°C to 300°C is the difficulty and focus of the current development of low-temperature SCR catalytic materials.

Contents of the invention

The purpose of the present invention is to obtain a ternary oxide catalyst with better low-temperature SCR performance by introducing ZrO ₂ and adjusting the mole percentage of Cr element.

The object of the present invention is achieved through the following technical scheme: soluble cerium salt, soluble zirconium salt and soluble chromium salt are dissolved in water, and the molar percentage of chromium element in chromium, zirconium, cerium three kinds of metal elements is 75%～50% %, the molar ratio of zirconium and cerium is 1:1~1:4, put the porous carrier into the solution, the amount of porous carrier is 0.005~0.1mol metal element/10g porous carrier, heat under stirring, and make the solvent volatilize gradually To dryness, it is calcined at 400-600°C for 3-5 hours under air atmosphere to obtain a chromium/zirconium/cerium ternary oxide catalyst.

The technical feature of the present invention is also that: the cerium salt in the method is selected from cerium nitrate, cerium chloride and cerium acetate, or any mixture of two in any ratio; the chromium salt in the described method is selected from chromium nitrate (III), chromium (III) acetate, chromous oxalate (II) and chromium (III) tartrate any one or the mixture of any several in any ratio; The zirconium salt in the described method is selected from zirconium nitrate, Any one of zirconium oxynitrate, zirconium acetate and zirconium oxychloride or a mixture of any several in any proportion; the porous carrier in the method is porous alumina, porous silica, porous SiC ceramics, porous cordierite ceramics And any one of the porous mullite ceramics.

The catalyst has a good SCR catalytic effect at 120-300°C, and is very suitable for the SCR treatment of NOx-containing waste gas from special industrial furnaces such as metallurgy, cement, and glass.

Detailed ways

The invention provides a method for preparing a catalyst for selective catalytic reduction of nitrogen oxides at low temperature. The specific process is as follows: dissolve soluble cerium salts, soluble zirconium salts and soluble chromium salts in water, and dissolve them in three kinds of chromium, zirconium and cerium The molar percentage of chromium in the metal element is 75%~50%, the molar ratio of zirconium and cerium is 1:1~1:4, the porous carrier is put into the solution, and the amount of porous carrier is 0.005~0.1mol metal element/ 10g of the porous carrier is heated under stirring to gradually evaporate the solvent to dryness, and calcined at 400-600° C. for 3-5 hours in an air atmosphere to obtain a chromium/zirconium/cerium ternary oxide catalyst.

The technical feature of the present invention is also that: the cerium salt in the method is selected from cerium nitrate, cerium chloride and cerium acetate, or any mixture of two in any ratio; the chromium salt in the described method is selected from chromium nitrate (III), chromium (III) acetate, chromous oxalate (II) and chromium (III) tartrate any one or the mixture of any several in any ratio; The zirconium salt in the described method is selected from zirconium nitrate, Any one of zirconium oxynitrate, zirconium acetate and zirconium oxychloride or a mixture of any several in any proportion; the porous carrier in the method is porous alumina, porous silica, porous SiC ceramics, porous cordierite ceramics And any one of the porous mullite ceramics.

Several specific examples are enumerated below to further understand the present invention.

Example 1:

Dissolve 0.6 mol of chromium nitrate, 0.3 mol of cerium nitrate and 0.1 mol of zirconium nitrate in 400 mL of water, add 100 g of porous silica pellet carrier with a specific surface area of 400 m ² /g, and heat and stir the system at 90°C Evaporate to dryness and ignite in a nitrogen atmosphere at 400°C for 3 hours to obtain a catalyst capable of simultaneous desulfurization and denitrification at low temperature, which can remove NOx in a gas stream containing 500ppmNOx and 500ppmNH at ₂₀₀ °C at a space velocity of 5000/h 95% (the oxygen concentration in the gas stream is greater than 10%).

Example 2:

Dissolve 0.075 mol of chromium nitrate, 0.0125 mol of cerium nitrate and 0.0125 mol of zirconium nitrate in 200 mL of water, add 100 g of porous active γ-alumina carrier with a specific surface area of 280 m ² /g, and heat and stir the system at 90 ° C to evaporate Dry, burn in a nitrogen atmosphere at 600°C for 5 hours to obtain a catalyst capable of simultaneous desulfurization and denitrification at a low temperature. This catalyst can remove 90% of NOx in a gas stream containing 500ppmNOx and 500ppmNH ₃ at a space velocity of 4000/h and 150°C % (the oxygen concentration in the gas stream is greater than 10%).

Example 3:

Dissolve 0.5 mol of chromium nitrate, 0.4 mol of cerium nitrate and 0.1 mol of zirconium nitrate in 1000mL of water, and load the solution on ^2000g of porous cordierite carrier added to it after several times of impregnation and burning. It is a square hole of 2mm×2mm, and the loaded porous cordierite ceramics is burned in a nitrogen atmosphere at 450°C for 5 hours to obtain a catalyst capable of simultaneous desulfurization and denitrification at a low temperature. It can remove 90% of NOx in the gas stream containing 500ppmNOx and 500ppmNH ₃ (the oxygen concentration in the gas stream is greater than 10%).

Example 4:

Dissolve 0.6 mol of chromium nitrate, 0.3 mol of cerium nitrate and 0.1 mol of zirconium nitrate in 1000 mL of water, and load the solution on the carrier by adding 2000 g of porous SiC ceramic tubes to it through multiple immersion and burning. The pressure drop is 3000Pa at 1m/min, and the loaded porous cordierite ceramics are burned in a nitrogen atmosphere at 500°C for 4 hours to obtain a catalyst capable of simultaneous desulfurization and denitrification at low temperature. At 200°C, 93% of NOx in the gas stream containing 800ppmNOx and 800ppmNH ₃ can be removed (the oxygen concentration in the gas stream is greater than 10%).

Example 5:

Dissolve 0.6 mol of chromium nitrate, 0.2 mol of cerium nitrate and 0.2 mol of zirconium nitrate in 1000 mL of water, and load the solution on 2000 g of porous mullite carrier, which has a cross-sectional area of 0.0225 m ² , after multiple immersion and burning. The channel is a square hole of 2 mm × 2 mm, and the loaded porous cordierite ceramics is burned in a nitrogen atmosphere at 450 ° C for 5 hours to obtain a catalyst capable of simultaneous desulfurization and denitrification at a low temperature. ℃ can remove 80% of NOx in the gas stream containing 500ppmNOx and 500ppmNH ₃ (the oxygen concentration in the gas stream is greater than 10%).

Claims (5)

1. the preparation method of the low-temperature SCR catalyst of a wider serviceability temperature, it is characterized in that solubility cerium salt, solubility zirconates and solubility chromic salts soluble in water, at chromium, zirconium, in cerium three kinds of metallic elements, the molar percentage of chromium element is 75% ~ 50%, the molar ratio of zirconium and cerium is 1:1 ~ 1:4, porous carrier is dropped in this solution, the consumption of porous carrier is 0.005 ~ 0.1mol metallic element/10g porous carrier, under agitation heat, solvent is evaporated into gradually dry, in air atmosphere, calcine 3 ~ 5 hours at 400 ~ 600 DEG C, obtain chromium/zirconium/cerium ternary oxide catalyst.

2. the preparation method of a kind of low-temperature SCR catalyst of wider serviceability temperature as claimed in claim 1, is characterized in that: the cerium salt in described method is selected from the arbitrary proportion mixture of any one or two kinds in the middle of cerous nitrate, cerium chloride and cerous acetate.

3. the preparation method of a kind of low-temperature SCR catalyst of wider serviceability temperature as claimed in claim 1, is characterized in that: the chromic salts in described method is selected from any one or arbitrary proportion mixtures several arbitrarily in the middle of chromic nitrate (III), chromium acetate (III), the sub-chromium (II) of ethanedioic acid and chromic tartrate (III).

4. the preparation method of a kind of low-temperature SCR catalyst of wider serviceability temperature as claimed in claim 1, is characterized in that: the zirconates in described method is selected from any one or arbitrary proportion mixtures several arbitrarily in the middle of zirconium nitrate, zirconyl nitrate, acetic acid zirconium and zirconyl chloride.

5. the preparation method of a kind of low-temperature SCR catalyst of wider serviceability temperature as claimed in claim 1, is characterized in that: the porous carrier in described method is any one in the middle of Woelm Alumina, porous silica, porous SiC ceramics, porous cordierite ceramic and porous mullite pottery.