A method for precisely improving the stability of noble metal-catalyzed CO oxidation and its preparation method

Abstract

A method for precisely improving the stability of noble metal-catalyzed CO oxidation and its preparation method, belonging to the field of catalysts. It adopts a combination of electrostatic adsorption-coprecipitation-impregnation methods. Phosphomolybdic acid is used to modify TiO2. The precursor solution of Pt is poured into a container containing the modified TiO2 support and stirred at 60°C - 80°C, and then dried; the dried catalyst is ground into powder and calcined in a muffle furnace at 400°C - 600°C. The resistance of the obtained catalyst to SO2 and H2O determines the stability of the catalyst.

Description

Technical Field

[0001] The present invention relates to a catalyst, specifically to precisely improve the stability of noble metal-catalyzed oxidation of CO, which can be used for CO in the tail gases of sintering, coking, boilers, etc., and belongs to the field of environmental engineering. Background Art

[0002] The waste gases discharged in industrial production such as iron and steel and coking plants contain a large amount of harmful gases such as CO and SO2. CO is one of the pollution control targets. It is a flammable and explosive gas pollutant. When the content of CO in the air reaches 1.2%, it will cause death to people within 1 - 3 minutes. Under general conditions, the removal of CO requires high temperature, high energy consumption, and there may also be explosion accidents. The CO discharged from sintering flue gas and the heating furnaces of rolling mills accounts for more than 80% of the CO discharged from iron and steel plants, belonging to the hardest-hit areas. In the process of sintering machines, when ore powder, flux, and bulk materials are mixed in a certain ratio and then mixed with water for sintering, iron-rich sinter ore is produced by combustion, and incomplete combustion leads to the generation of a large amount of CO gas.

[0003] The catalytic oxidation method has the characteristics of good stability, less secondary investment, and strong flue gas applicability. In the low-temperature catalytic oxidation of CO, noble metals are generally used as active molecules. Platinum group metals are one of the most widely used noble metals in current CO catalysts, and they have the advantages of high catalytic activity, good stability, and long service life. The catalytic activity of Pt for CO depends on the particle size of platinum, the charge transfer between platinum and the substrate, and the reducibility of the substrate. At the same time, compared with other noble metals, Pt can have better sulfur resistance in flue gases containing SO2 and H2O. Even so, SO2 and H2O will still have a certain impact on Pt-based noble metal catalysts.

[0004] Sintered ore contains S element, so sintering flue gas inevitably contains SO2 gas. The poisoning of the catalyst by SO2 can quickly deactivate the catalyst. At low temperatures, SO2 can occupy the active sites, resulting in the inability of reaction gases to be adsorbed. At high temperatures, it can be oxidized into sulfates with H2O at the active sites, causing the catalyst to be deactivated. Therefore, the resistance of the catalyst to SO2 and H2O determines the stability of the catalyst. Summary of the Invention

[0005] The present invention aims to develop a noble metal catalyst that can stably catalyze CO in flue gas in the presence of SO2 and H2O by means of simple catalyst preparation methods, without affecting the normal catalytic oxidation of CO by the catalyst. In the methods for improving the sulfur resistance of catalysts, the activity of CO is often sacrificed. This results in the inability to improve the CO oxidation ability and sulfur resistance simultaneously. The present invention designs a method to precisely deposit sulfur-resistant oxides near noble metals. While improving the sulfur resistance of the catalyst, the activity of CO does not decrease. The catalyst prepared by this method can stably exist under actual flue gas conditions and has prospects for industrial production.

[0006] A catalyst for removing CO according to the present invention is characterized in that a noble metal element Pt is loaded on an oxide support; the oxide support is selected from TiO2 modified TiO2. The preparation method of the catalyst comprises the following steps:

[0007] (1) Put the precursor solution of phosphomolybdic acid and the TiO2 support in a beaker and stir at room temperature. Adjust the pH value of the solution to 1 - 2 using an acidic substance; adjust the temperature to 60°C - 80°C and heat and stir. After 5 h, put it in an oven to dry; grind the dried material into powder and then calcine it in a muffle furnace at 300°C - 500°C for 2 h.

[0008] (2) Put the modified TiO2 support in a beaker and stir. Pour the precursor solution of Pt into the solution and stir at 60°C - 80°C. After 5 h, put it in an oven to dry; grind the dried catalyst into powder and then calcine it in a muffle furnace at 400°C - 600°C.

[0009] The precursor of phosphomolybdic acid in step (1) is an ammonium phosphate substance and a molybdate substance, such as NH4H2PO4 and K2MoO4. The dosage of the precursor of phosphomolybdic acid is such that the molar ratio of the generated phosphomolybdic acid to Pt added in step (2) is 1:10 to 1:1. The loading amount of the metal element Pt in the product, that is, the mass percentage content, is 0.08% - 1.1%.

[0010] The Pt precursor described in step (2) and step (3) is any one or several of chloroplatinic acid hexahydrate, platinum nitrate, and tetraammineplatinum chloride.

[0011] The preparation process of the present invention is simple, the preparation conditions are easy to control, and the experimental raw materials are harmless to the environment. It is an environmentally friendly CO catalytic catalyst. Utilizing the characteristics of the high-temperature decomposition of phosphomolybdic acid, Pt adsorbed on phosphomolybdic acid is redispersed by high temperature, and at the same time, the exposed MoO3 and Pt are jointly anchored on TiO2. Therefore, two synergistic sites of Pt - MoO3 and Pt - TiO2 are generated.

[0012] According to the noble metal Pt-based catalyst described in the above technical solution, under the CO catalytic oxidation test conditions: 0.8% CO, 16% O2, with N2 as the balance gas, 30000h -1 space velocity, within the temperature range of 110°C - 300°C, the CO conversion rate can be maintained above 90%.

[0013] According to the noble metal Pt catalyst described in the above technical solution, under the stability test conditions: 0.8% CO, 50 ppm SO2, 16% O2, 15% H2O, with N2 as the balance gas, 30000h -1 space velocity, within the temperature range of 100 - 300°C, the CO conversion rate can be maintained above 90%.

[0014] Under the conditions of containing CO, oxygen or air, SO2, and H2O, the CO removal rate is above 96% at 100°C - 300°C, especially at 110°C - 170°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the CO catalytic oxidation conversion rate diagram in Example 1;

[0016] Figure 2 is the schematic diagram of CO catalytic stability in Example 1;

[0017] Figure 3 is the CO catalytic oxidation conversion rate diagram in Example 2;

[0018] Figure 4 is the schematic diagram of CO catalytic stability in Example 2;

[0019] Figure 5 is the schematic diagram of in-situ CO catalyst stability in Example 2;

[0020] Figure 6 is the schematic diagram of the test site; DETAILED DESCRIPTION OF THE INVENTION

[0021] The following is further illustrated by specific embodiments, but the present invention is not limited to the following examples.

[0022] The purity of platinum nitrate mentioned in the present invention is 99.9%, the purity of titanium dioxide mentioned in the present invention is 99.99%, the content of carbon monoxide in the gas used in this experiment is 5%, the content of oxygen is 40%, the content of sulfur dioxide is 0.1%, and the gas mixture is all nitrogen. H2O is injected into the gas mixing tank through an injection pump, vaporized and then enters the catalytic device.

[0023] Example 1 (Comparative Example)

[0024] Measure 8.35 ml of 5 g / L platinum nitrate solution and put it into a beaker. Place the beaker on a magnetic stirrer and heat it with stirring in a water bath at 500 r / min and 80 °C. Then weigh 4.98 g of TiO₂ and slowly pour it into the beaker. Stir until the catalyst dries up and solidifies, and then put it into an oven at 100 °C for 6 h to dry. Then use a grinding rod to grind the catalyst into powder and put it into a muffle furnace, and heat it up to 500 °C at a rate of 5 °C / min for calcination for 2 h. After cooling, screen the catalyst with a sieve to 40 - 60 mesh.

[0025] Example 2

[0026] Put 4.98 g of TiO₂ into a beaker and stir magnetically at room temperature. Add 0.02 g of NH₄H₂PO₄ and 0.73 g of K₂MoO₄. Adjust the pH value to about 1 and stir in a water bath at 80 °C. Stir until the catalyst dries up and solidifies, and then put it into an oven at 100 °C for 6 h to dry. Then use a grinding rod to grind the catalyst into powder and put it into a muffle furnace, and heat it up to 300 °C at a rate of 5 °C / min for calcination for 2 h.

[0027] Measure 8.35 ml of 5 g / L platinum nitrate solution and put it into a beaker. Place the beaker on a magnetic stirrer and heat it with stirring in a water bath at 500 r / min and 80 °C. Slowly pour the modified TiO₂ support into the beaker, stir until the catalyst dries up and solidifies, and then put it into an oven at 100 °C for 6 h to dry. Then use a grinding rod to grind the catalyst into powder and put it into a muffle furnace, and heat it up to 500 °C at a rate of 5 °C / min for calcination for 2 h.

[0028] Test Example 1:

[0029] Take the 1# catalyst in Example 1 as an example to conduct a CO catalytic experiment to test its CO catalytic oxidation activity and sulfur and water resistance performance. Test conditions: CO with a content of 0.8%, O₂ with a content of 16%, N₂ as the balance gas, and the space velocity is 30000 h -1 . The curve of CO catalytic efficiency changing with temperature is as Figure 1 shown. When the temperature of the catalyst is 100 °C, the catalyst starts to activate. At 120 °C, the CO conversion efficiency reaches 100%. The experimental conditions for passing sulfur and water are: CO content is 0.8%, O₂ content is 16%, SO₂ content is 50 ppm, H₂O content is 15%, N₂ as the balance gas, and the space velocity is 30000 h -1 , and the curve of CO catalytic efficiency changing with time is as Figure 2 shown. The temperature during the whole test stage is maintained at 170 °C. After passing sulfur for 1 h, the CO activity of the catalyst decreases rapidly. After 20 h, the CO catalytic efficiency of the catalyst gradually tends to be stable, and the CO conversion rate is stable at about 8%. This catalyst has a certain sulfur and water resistance performance.

[0030] Test Example 2

[0031] Taking the 2# catalyst in Example 2 as an example, a CO catalytic experiment was carried out to test its CO catalytic oxidation activity and sulfur and water resistance performance. Test conditions: CO with a content of 0.8%, O2 with a content of 16%, N2 as the balance gas, and the space velocity was 30000h -1 . The curve of CO catalytic efficiency varying with temperature is as Figure 3 shown. When the temperature of the catalyst was 100 °C, the catalyst began to activate. At 120 °C, the CO conversion efficiency reached 100%. The experimental conditions for passing sulfur and water were: the CO content was 0.8%, the O2 content was 16%, the SO2 content was 50 ppm, the H2O content was 15%, N2 as the balance gas, and the space velocity was 30000h -1 , and the curve of CO catalytic efficiency varying with time is as Figure 4 shown. The temperature during the whole test stage was maintained at 170 °C. In the first 60 hours, the CO conversion rate of the catalyst did not decrease significantly under the condition of passing sulfur and water. After 65 hours, the CO conversion rate decreased slightly, and the overall conversion rate remained above 90% without obvious attenuation. This catalyst has good sulfur and water resistance performance.

[0032] Test Example 3

[0033] Taking Example 2

[0034] Taking the 2# catalyst in Example 2 as an example, a on-site CO catalytic experiment was carried out on the flue gas of the heating furnace to test its CO catalytic oxidation activity and sulfur and water resistance performance. Test conditions: the CO content fluctuated between 1.5% - 7%, the O2 content fluctuated between 2% - 8%, the SO2 fluctuated between 10 ppm - 40 ppm, the NO fluctuated between 100 ppm - 200 ppm, the H2O content fluctuated between 1% - 10%, and the space velocity was 20000h -1 , and the curve of CO catalytic efficiency varying with time is as Figure 5 shown. The temperature during the whole test stage was maintained at 280 °C. Due to the large variation in flue gas conditions, the CO conversion rate fluctuated between 90% - 100%.

[0035] In the present invention, the anchor points are anchored on the carrier, and the noble metal is precipitated on the anchor points by the electrostatic repulsion and attraction to form an interaction. The anchor points are obtained from two different precursors in a certain proportion. The proportion of the anchor points in the whole catalyst is 0.1% - 1%. The proportion of the noble metal in the whole catalyst is 0.08% - 1.1%. There is a certain proportional relationship between the content of the anchor points and the noble metal. Through the anchor points, the catalytic stability of the noble metal in the sulfur - and water - containing flue gas conditions can be accurately protected, and it will not affect the CO catalytic activity of the catalyst. The CO catalyst maintains good catalytic activity and stability under actual flue gas conditions and has the value for industrial application.

Claims

1. A preparation method of a catalyst for precisely improving the stability of noble metal-catalyzed CO oxidation, characterized in that, It includes the following steps: (1) Place the precursor solution of phosphomolybdic acid and the TiO2 support in a beaker and stir at room temperature. Adjust the pH value of the solution to 1 - 2 using an acidic substance; adjust the temperature to 60°C - 80°C and heat with stirring. After 5 h, put it in an oven to dry; grind the dried material into powder and then calcine it in a muffle furnace at 300°C for 2 h; (2) Place the modified TiO2 support in a beaker and stir. Pour the precursor solution of Pt into the container containing the modified TiO2 support and stir at 60°C - 80°C. After 5 h, put it in an oven to dry; grind the dried catalyst into powder and then calcine it in a muffle furnace at 500°C.

2. The method according to claim 1, wherein The precursor of phosphomolybdic acid in step (1) uses ammonium phosphate substances and molybdate substances, and the dosage of the precursor of phosphomolybdic acid is such that the molar ratio of the generated phosphomolybdic acid to Pt added in step (2) is 1:10 to 1:

1.

3. The method according to claim 1, characterized in that, The Pt precursor described in step (2) is any one or several of chloroplatinic acid hexahydrate, platinum nitrate, and tetraammineplatinum chloride.

4. The method according to claim 1, wherein The loading amount, i.e., the mass percentage content, of the metal element Pt in the product is 0.08% - 1.1%.

5. The catalyst prepared by the method according to any one of claims 1 - 4.

6. Use of the catalyst prepared by the method according to any one of claims 1-4, characterized in that, It is used for the catalytic oxidation of CO containing SO2 and H2O.

7. The application according to claim 6, characterized in that, 0.8% CO, 50 ppm SO2, 16% O2, 15% H2O, with N2 as the balance gas, at a space velocity of 30000 h -1 -1, in the temperature range of 100 - 300 °C, the CO conversion rate can be maintained above 90%.

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