A silver-based catalyst, its preparation method and use in catalysing the oxidation of co

Abstract

The application provides a silver-based catalyst and a preparation method and application thereof in catalyzing CO oxidation, and belongs to the technical field of catalysts. In the application, an active metal component and an alkali metal are loaded on alumina, the addition of the alkali metal makes monatomic silver agglomerate, the oxidation performance of the catalyst is improved, the addition of the alkali metal effectively promotes the effect of the active metal in keeping sustained agglomeration, and the stability of the catalyst is greatly improved. The addition of the alkali metal additive ensures that silver is in a sustained agglomerated state, the active sites are increased, and the activity of the catalyst is improved. The silver-based catalyst provided by the application is suitable for catalyzing oxidation of low-concentration CO, and has good catalytic activity and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a silver-based catalyst, a preparation method thereof and application thereof in catalyzing CO oxidation. BACKGROUND

[0002] Industrial flue gas is an important source of CO emission, and the emission amount of sintering flue gas in the steel industry is large (flue gas flow 50-200 million Nm 3 / h), and the CO content is high (5000-10000 ppm). According to the annual production of 1.33 billion tons of sintered ore in China, 4000 m 3 of flue gas is emitted per ton of sintered ore, and the flue gas CO concentration is 6000 ppm. The annual emission amount of CO in sintering flue gas can reach 0.26 million tons. The large emission of CO in sintering flue gas seriously affects the air quality of each region. In recent years, the steel and coking industries have developed rapidly, and a large amount of sintering flue gas is emitted, which contains a certain amount of CO gas, and there is still no effective treatment method at the present stage. At the same time, when the CO concentration in the air reaches a certain amount, it can quickly combine with the hemoglobin of the human body to form carboxyhemoglobin, reduce the oxygen-carrying capacity of the blood, cause physiological and pathological changes, and even death. At the present stage, there is still a lack of research on low-concentration CO catalytic oxidation in China, and it is urgent to develop a high-efficiency and stable catalyst.

[0003] At present, the catalysts used in the catalytic oxidation method for controlling CO emission mainly include non-noble metal catalysts and noble metal catalysts. The activity of non-noble metal is greatly different from that of noble metal; the production cost of noble metal is high; and the silver-based catalyst has both the activity of noble metal and relatively low price, and has good oxygen adsorption capacity. However, the catalytic activity of the single-component silver-based catalyst for catalyzing CO oxidation is not high, and it is necessary to further improve the catalytic activity. The traditional methods for improving the activity of the catalyst include reducing atmosphere treatment and construction of carriers with different morphologies. The catalyst prepared by the above method has poor stability and cannot meet the requirement of long service life in industrial application. SUMMARY

[0004] Therefore, the present application aims to provide a silver-based catalyst, a preparation method thereof and application thereof in catalyzing CO oxidation. The silver-based catalyst provided by the present application has good catalytic CO oxidation activity and stability.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a silver-based catalyst, comprising the following steps:

[0007] Alumina, a soluble silver source solution, and a soluble alkali metal source solution are mixed and impregnated, and the impregnated solid-liquid mixture is dried to obtain a catalyst precursor loaded with the silver source and the alkali metal source;

[0008] The catalyst precursor loaded with the silver source and the alkali metal source is calcined to obtain a silver-based catalyst.

[0009] Preferably, the soluble alkali metal source is potassium nitrate and / or potassium acetate.

[0010] Preferably, the mass ratio of the aluminum oxide to the silver element in the soluble silver source is 1:0.01-0.02;

[0011] The mass ratio of the aluminum oxide to the alkali metal element in the soluble alkali metal source is 1:0.01-0.02.

[0012] Preferably, the immersion time is 2 to 3 hours.

[0013] Preferably, in the catalyst precursor loaded with a silver source and an alkali metal source, the loading amount of the silver source is 1 to 2 wt %, and the loading amount of the alkali metal source is 1 to 3 wt %.

[0014] Preferably, the calcination temperature is 500° C. and the calcination time is 3 h; the calcination is carried out in an air atmosphere.

[0015] The present invention provides a silver-based catalyst prepared by the above preparation method, comprising aluminum oxide and silver clusters supported on the surface of the aluminum oxide, wherein the silver clusters are doped with alkali metals.

[0016] The present invention provides use of the silver-based catalyst in catalyzing CO oxidation.

[0017] Preferably, the application method comprises the following steps:

[0018] A mixed atmosphere containing CO and oxygen is introduced into a container containing the silver-based catalyst according to claim 7 to carry out a catalytic CO oxidation reaction.

[0019] Preferably, the volume content of CO in the mixed atmosphere is 5000 to 10000 ppm;

[0020] The temperature of the catalytic CO oxidation reaction is 100-500° C., and the time is 20-30 minutes.

[0021] The present invention provides a method for preparing a silver-based catalyst, comprising the following steps: mixing alumina, a soluble silver source solution, and a soluble alkali metal source solution, impregnating the mixture, drying the impregnated solid-liquid mixture to obtain a catalyst precursor loaded with the silver source and alkali metal source; and calcining the catalyst precursor loaded with the silver source and alkali metal source to obtain a silver-based catalyst. The present invention loads active metal components and alkali metals onto alumina. The addition of alkali metals causes single-atom silver atoms to agglomerate, improving the oxidation performance of the catalyst. Simultaneously, the addition of alkali metals effectively promotes the continued agglomeration of the active metals, significantly improving the stability of the catalyst. The addition of alkali metal additives ensures that the silver remains in a continuously agglomerated state, increasing active sites and enhancing the activity of the catalyst. The silver-based catalyst provided by the present invention is suitable for the catalytic oxidation of low-concentration CO. The results of the examples show that the silver-based catalyst of the present invention can effectively promote silver agglomeration and CO oxidation reaction when used for the catalytic oxidation of low-concentration CO. The CO removal rate can reach 100% in a relatively low-temperature window, and the conversion rate can be maintained at 100% for 50 hours at 200°C. It has the advantages of good conversion rate and high stability, and is of great significance for achieving domestic low-concentration CO emission standards and reducing CO investment and operating costs.

[0022] The present invention uses silver as an active component. Compared with other precious metals, silver is cheap and easy to obtain. After adding an auxiliary alkali metal, a low loading amount of silver can still achieve a high conversion rate under certain conditions, and the stability of the catalyst is also improved with the addition of the alkali metal. At the same time, as the silver loading amount is reduced, the amount of precious metal used is greatly reduced, which can greatly reduce production costs. This is both economical and environmentally friendly, and the high cost caused by precious metals is suppressed to a certain extent from the source.

[0023] The silver-based catalyst provided by the present invention has high material stability and can maintain a 100% conversion rate at a certain temperature for a long time, thus solving the problem of poor catalyst stability.

[0024] The present invention provides a method for preparing the silver-based catalyst, which utilizes an impregnation method. This method is simple to operate, forms a stable silver cluster structure, and saves preparation time. The addition of an alkali metal causes the active metal components to continuously aggregate on the support, resulting in a stable structure, which is beneficial for improving the catalytic performance of the catalyst.

[0025] Furthermore, the preparation method of the present invention is simple to operate, has fewer steps, and is easy to control. The preparation time of the catalyst is relatively short and the output is relatively high. The raw materials and metal salts are cheap and easy to obtain. The raw materials are not restricted by time and region. The obtained catalyst has high catalytic activity, regular morphology, good controllability, and is easy to realize industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The microstructure diagram of the silver-based catalyst solid obtained in Examples 1-2 and Comparative Example 1;

[0027] Figure 2 The CO oxidation activity results of silver-based catalysts loaded with different amounts of alkali metals in Examples 1 and 2 are shown;

[0028] Figure 3 The CO oxidation activity results of silver-based catalysts loaded with different amounts of alkali metals in Examples 3 and 4 are shown;

[0029] Figure 4 Graph showing the CO temperature-increasing oxidation activity cycle results of the silver-based catalysts obtained in Comparative Example 1 and Example 2;

[0030] Figure 5 This is a graph showing the CO temperature-increasing oxidation activity cycle results of the silver-based catalysts obtained in Comparative Example 2 and Example 3. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a silver-based catalyst, comprising the following steps:

[0032] Alumina, a soluble silver source solution, and a soluble alkali metal source solution are mixed and impregnated, and the impregnated solid-liquid mixture is dried to obtain a catalyst precursor loaded with the silver source and the alkali metal source;

[0033] The catalyst precursor loaded with the silver source and the alkali metal source is calcined to obtain a silver-based catalyst.

[0034] The present invention involves mixing alumina, a soluble silver source solution, and a soluble alkali metal source solution, performing impregnation, and drying the impregnated solid-liquid mixture to obtain a catalyst precursor loaded with the silver source and the alkali metal source. In the present invention, the soluble alkali metal source is potassium nitrate, and the concentration of the soluble alkali metal source solution is preferably 10 to 20 wt%, more preferably 10 to 15 wt%.

[0035] In the present invention, the soluble silver source is preferably silver nitrate, and the concentration of the soluble silver source solution is 10-20 wt%, more preferably 10-15 wt%.

[0036] In the present invention, the specific surface area of ​​the alumina is preferably 120 to 130 m 2 / g. In the present invention, the mass ratio of the alumina to the silver element in the soluble silver source is preferably 1:0.01-0.02, more preferably 1:0.015; the mass ratio of the alumina to the alkali metal element in the soluble alkali metal source is preferably 1:0.01-0.02, more preferably 1:0.015. In the present invention, the mass ratio of the soluble silver source to the soluble alkali metal source is preferably 1-2:1-2, specifically preferably 1:1, 1:2, 2:1, or 2:2.

[0037] In the present invention, the mixing method is preferably: adding a soluble silver source solution and a soluble alkali metal source solution into a container containing aluminum oxide.

[0038] In the present invention, the impregnation is preferably performed at room temperature; the impregnation time is preferably 2 to 3 hours.

[0039] In the present invention, in the catalyst precursor loaded with a silver source and an alkali metal source, the loading amount of the silver source is preferably 1 to 2 wt%, more preferably 1.2 to 1.8 wt%, and further preferably 1.5 wt%; the loading amount of the alkali metal source is preferably 1 to 3 wt%, more preferably 1 to 2 wt%, and further preferably 1.5 wt%.

[0040] After the impregnation, the present invention dries the impregnated solid-liquid mixture. In the present invention, the drying temperature is preferably 80-100° C., and the drying time is preferably 10-12 hours.

[0041] After obtaining the catalyst precursor loaded with a silver source and an alkali metal source, the present invention calcines the catalyst precursor loaded with a silver source and an alkali metal source to obtain a silver-based catalyst. In the present invention, the calcination temperature is preferably 500°C, and the time is preferably 3 hours; the calcination is preferably carried out in an air atmosphere. In the present invention, the heating rate to the calcination temperature is preferably 5°C / min. In the present invention, during the calcination process, the silver source in the catalyst precursor decomposes to form silver element clusters, and the alkali metal elements in the alkali metal source are doped into the silver element clusters, promoting the agglomeration of the silver element.

[0042] After the calcination, the calcined product is preferably tableted, ground and sieved to obtain silver-based catalyst particles. In the present invention, the particle size of the silver-based catalyst particles is preferably 40 to 60 mesh.

[0043] The present invention provides a silver-based catalyst prepared by the above preparation method, comprising aluminum oxide and silver clusters supported on the surface of the aluminum oxide, wherein the silver clusters are doped with alkali metal elements.

[0044] The present invention provides the use of the silver-based catalyst in catalytic CO oxidation. In the present invention, the catalytic CO oxidation is preferably catalytic CO oxidation at low concentrations, and the CO concentration is preferably 5000 to 10000 ppm.

[0045] In the present invention, the source of CO in the catalytic CO oxidation is preferably industrial flue gas, specifically sintering flue gas from the steel industry. In the present invention, the CO content in the industrial flue gas is preferably 5000 to 10000 ppm.

[0046] In the present invention, the application method preferably includes the following steps:

[0047] A mixed atmosphere containing CO and oxygen is introduced into a container of a silver-based catalyst to carry out a catalytic CO oxidation reaction.

[0048] In the present invention, the catalytic CO oxidation reaction is preferably carried out in a gas-solid catalytic reactor. In the mixed atmosphere, the CO content is preferably 5,000 to 10,000 ppm; the volume ratio of CO to oxygen is preferably 1:10, with the balance being N2. In a specific embodiment of the present invention, the mixed gas comprises 1% CO + 10% O2 + the balance being N2.

[0049] In the present invention, the introduction rate of the mixed atmosphere is preferably 100 to 500 mL / min, more preferably 200 to 400 mL / min.

[0050] In the present invention, the temperature of the catalytic CO oxidation reaction is preferably 100-500° C., more preferably 200-400° C., and the time is 0.5 h.

[0051] The silver-based catalyst provided by the present invention, its preparation method, and its application in catalytic CO oxidation are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] 1) Place 1g of alumina in a beaker, add 0.1mL of AgNO3 solution (Ag concentration is 10wt%) and 0.1mL of KNO3 solution (K concentration is 10wt%), respectively, and load by immersion method for 2h;

[0054] 2) drying the loaded solid-liquid mixture at 100° C. for 12 hours, and then calcining at 500° C. for 3 hours to obtain a silver-based catalyst solid having a silver loading of 1 wt% and an alkali metal loading of 1 wt%, denoted as 1Ag-1K;

[0055] 3) The obtained silver-based catalyst solid is tableted, ground and sieved in sequence, and the obtained product particles are loaded into a fixed-bed quartz tube reactor for reaction.

[0056] Example 2

[0057] The difference from Example 1 is that 0.2 mL of KNO3 solution (K concentration is 10 wt%) is added, and the other operations are the same to obtain a silver-based catalyst solid with a silver loading of 1 wt% and an alkali metal loading of 2 wt%, which is recorded as 1Ag-2K.

[0058] Example 3

[0059] 1) Place 1g of alumina in a beaker, add 0.2mL of AgNO3 solution (Ag concentration is 10wt%) and 0.1mL of KNO3 solution (K concentration is 10wt%), respectively, and load by immersion method for 2h;

[0060] 2) drying the loaded solid-liquid mixture at 100° C. for 12 hours, and then calcining at 500° C. for 3 hours to obtain a silver-based catalyst solid having a silver loading of 2 wt% and an alkali metal loading of 1 wt%, which is designated as 2Ag-1K;

[0061] 3) The obtained silver-based catalyst solid is tableted, ground and sieved in sequence, and the obtained product particles are loaded into a fixed-bed quartz tube reactor for reaction.

[0062] Example 4

[0063] The difference from Example 1 is that 0.2 mL of KNO 3 solution (K concentration is 10 wt %) is added, and the other operations are the same to obtain a silver-based catalyst solid with a silver loading of 2 wt % and an alkali metal loading of 2 wt %, which is recorded as 2Ag-2K.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that no KNO3 solution was added, and the obtained silver-based catalyst solid was recorded as 1Ag.

[0066] Comparative Example 2

[0067] The difference from Example 3 is that no KNO3 solution was added, and the obtained silver-based catalyst solid was recorded as 2Ag.

[0068] Structural characterization and performance testing

[0069] The microstructure of the silver-based catalyst solid obtained in Examples 1-2 and Comparative Example 1 is shown in FIG. Figure 1 As shown in Figure 2, it can be seen that the silver particle size increases with the increase of K loading.

[0070] The CO oxidation activity results of silver-based catalysts loaded with different amounts of alkali metals in Examples 1 and 2 are as follows: Figure 2 During the activity test, 50 mg of sample was placed in a fixed bed and heated for 120,000 h in an atmosphere of 1% CO + 10% O2 + 89% N2. -1 Activity tests were conducted at a gas hourly space velocity of 1.5 Å. It was found that the catalytic activity of the silver-based catalyst was significantly improved after alkali metal doping, and the order of catalyst activity improvement was 2% alkali metal loading > 1% alkali metal loading > no alkali metal added.

[0071] The results of CO oxidation activity of silver-based catalysts with different amounts of alkali metal loading in Examples 3-4 are shown in Table 1. Figure 3 During the activity test, 50 mg of the sample was placed in a fixed bed and tested for activity under a 1% CO + 10% O2+ 89% N2 atmosphere at a gas hourly space velocity of 120000 h-1. -1 It can be found that the catalytic activity of the silver-based catalyst is significantly improved after doping with alkali metal, and the order of improvement of the catalyst activity is alkali metal loading 1% > alkali metal loading 2% > no alkali metal added.

[0072] Figure 4 The results of CO temperature programmed oxidation activity cycle of the silver-based catalysts obtained in Comparative Example 1 and Example 2 are shown in Figure 1. The activity cycle test was performed as follows: under a 1% CO + 10% O2+ 89% N2 reaction atmosphere, from 100 to 500°C, with a gradient of 50°C each time, and each gradient was maintained for 30 min for a complete activity evaluation. Then, from 100 to 500°C, with a gradient of 50°C each time, and each gradient was maintained for 30 min for a second cycle test. The catalysts added with alkali metal showed stable and excellent catalytic activity in the activity cycle test after the reaction, while the catalysts without alkali metal showed a significant decrease in activity after one cycle. This indicates that the method of adding alkali metal not only improves the reaction activity of the catalyst, but also has good reaction stability.

[0073] Figure 5 The results of CO temperature programmed oxidation activity cycle of the silver-based catalysts obtained in Comparative Example 2 and Example 3 are shown in Figure 2. The catalysts added with alkali metal showed stable and excellent catalytic activity in the activity cycle test after the reaction, while the catalysts without alkali metal showed a significant decrease in activity after one cycle. This indicates that the method of adding alkali metal not only improves the reaction activity of the catalyst, but also has good reaction stability.

[0074] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. Application of silver-based catalysts in catalytic CO oxidation; The preparation method of the silver-based catalyst comprises the following steps: Alumina, a soluble silver source solution, and a soluble alkali metal source solution are mixed and impregnated, and the impregnated solid-liquid mixture is dried to obtain a catalyst precursor loaded with a silver source and an alkali metal source; the soluble alkali metal source is potassium nitrate and / or potassium acetate; the catalyst precursor loaded with a silver source and an alkali metal source has a loading amount of 2 wt% of the silver source and a loading amount of the alkali metal source of 1 wt%; calcining the catalyst precursor loaded with the silver source and the alkali metal source to obtain a silver-based catalyst; The calcination temperature is 500°C and the time is 3 hours; the calcination is carried out in an air atmosphere; The silver-based catalyst comprises aluminum oxide and silver clusters supported on the surface of the aluminum oxide, wherein the silver clusters are doped with alkali metals; The application method comprises the following steps: A mixed atmosphere containing CO and oxygen is introduced into a container containing the silver-based catalyst to carry out a catalytic CO oxidation reaction; the temperature of the catalytic CO oxidation reaction is 200°C.

2. The use according to claim 1, characterized in that In the mixed atmosphere, the volume content of CO is 5000 to 10000 ppm; The time of the catalytic CO oxidation reaction is 20 to 30 minutes.

3. The use according to claim 1, characterized in that The mass ratio of the aluminum oxide to the silver element in the soluble silver source is 1:0.01-0.02; The mass ratio of the aluminum oxide to the alkali metal element in the soluble alkali metal source is 1:0.01-0.

02.

4. The use according to claim 1, characterized in that The immersion time is 2 to 3 hours.

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