CN105056940B - The method that plasmaassisted sol-gal process prepares efficient oxidation catalyst - Google Patents

Abstract

The present invention relates to a kind of method that plasmaassisted sol-gal process prepares efficient oxidation catalyst, decompose the organic matter and nitrate in gel at normal temperatures using the active particle in plasma, prepare the oxidative catalyst that active component is MnOx or MnCeOx.The present invention has the advantage that effect is：（1）There is higher activity and selectivity to nitrogen oxides catalysis oxidation；（2）With wider Acclimation temperature window；（3）Preparation technology is simple, cost is relatively low, can be widely applied to the denitrating catalyst preparation process of flue gas selective catalytic oxidation.

Description

A Method for Preparing Efficient Oxidative Catalysts by Plasma-Assisted Sol-Gel Method

technical field

The invention belongs to the field of pollutant control, and relates to a catalyst and a preparation method, in particular to a method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method.

Background technique

With the rapid economic growth and industrial development, the pollution problem caused by the burning of industrial dyes has become increasingly serious, which has caused great harm to the human body and brought a crisis that cannot be ignored to the environment. Especially the emission of nitrogen oxides, sulfur oxides and nitrogenous substances, acid rain, ozone depletion, photochemical smog, and global warming are not unrelated. The pollution of nitrogen oxides and sulfur oxides in the industrial production process has become a hot spot of global concern. Its treatment is also the focus of scientific research.

Domestic industrial waste gas is still in its infancy, and the treatment is mainly to remove it separately. Using WFGD to treat SO ₂ , and using SCR and SNCR technology to treat nitrogen oxides jointly, this step-by-step treatment method has complex equipment, large floor space, high operating costs, and secondary pollution. It not only wastes resources, but also brings a great burden to the factory, and the actual benefit is not high. How to design a reasonable treatment process and find a suitable catalyst to deal with these pollutants at one time, so as to maximize benefits and minimize pollution is the focus of this patent research.

Among the nitrogen oxides emitted from coal-burning flue gas, 90% to 95% exist in the form of NO. NO is difficult to dissolve in water, and it is difficult to remove it by WFGD. After analysis, after NO is oxidized into soluble NO2, the integration of desulfurization and denitrification can be realized by _WFGD . The key of this technology is to realize the efficient oxidation of NO, so that the flue gas contains a certain proportion of NO ₂ (about 50%). A large number of studies have shown that catalytic oxidation is an effective means of oxidizing NO, especially the catalyst with MnO _x -CeO ₂ as the active component, not only has a good price, but also has good catalytic oxidation performance of NO. The catalyst activity of MnO _x -CeO ₂ composite oxide prepared by sol-gel method is higher than that of other traditional preparation methods, because the MnCeO _x solid solution structure is formed in it, and more surface active oxygen is formed, which is more conducive to catalytic oxidation reaction.

Contents of the invention

The invention provides a method for preparing a high-efficiency catalytic oxidation catalyst by using a plasma-assisted sol-gel method. The active particles in the plasma are used to decompose organic matter and nitrate in the gel at room temperature, and the catalytic performance is better than that prepared by the sol-gel method. better.

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, using active particles in the plasma to decompose organic matter and nitrate in the gel at room temperature, and preparing an oxidizing catalyst whose active component is MnOx or MnCeOx .

Preferably, in MnCeOx, the molar ratio of Mn and Ce is 0.3˜3:1.

As preferably, the method for preparing an efficient oxidizing catalyst by the plasma-assisted sol-gel method comprises the following steps:

(1) Calculate and weigh the amount of cerium nitrate and manganese nitrate according to the molar ratio of Mn and Ce, dissolve it with deionized water to obtain a mixed solution, weigh the complexing agent and polyethylene glycol, and pour the previous mixed solution, Stir to obtain a mixed solution;

(2) Heat the mixed solution and stir until the solution becomes a colloid;

(3) Put the dried colloid in a mortar, fully grind it into particles below 40 mesh, and set aside;

(4) The sample is subjected to plasma treatment to prepare the catalyst.

Preferably, in step (1), the molar ratio of the complexing agent to the metal ion is 1.1-1.5:1, and the weight of polyethylene glycol is 5-15% of the weight of the complexing agent.

Preferably, the complexing agent is citric acid monohydrate.

Preferably, in step (2), the heating temperature is 70-90°C.

As a preference, in step (4), the plasma treatment includes the following steps:

(a) The sample is filled between the rod-shaped electrode and the wall of the quartz tube in the discharge quartz tube, and the processing gas is introduced to expose it to the corresponding atmosphere; the outside of the quartz tube is wrapped with a copper sheet as a power supply electrode, and the rod-shaped electrode is grounded;

(b) Turn on the AC power supply so that the effective voltage is between 8 and 12kV, and the discharge frequency reaches 7 to 10MHz, and it is treated by dielectric barrier discharge for 10 to 180 minutes.

Preferably, the processing gas is one of oxygen, a mixed gas of oxygen and nitrogen, or a mixed gas of oxygen and argon.

As preferably, the method for preparing an efficient oxidizing catalyst by the plasma-assisted sol-gel method comprises the following steps:

(1) Put 35.8g of 50% manganese nitrate solution into a beaker, dissolve it with deionized water, and stir at room temperature to obtain a homogeneous solution; pour 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol into the previous mixture , stirring at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the mixed solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the dried colloid in a mortar, fully grind it into particles below 40 mesh, and set aside;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, pass through the simulated air containing 21% oxygen, and wrap the copper sheet outside the quartz tube as the power supply electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply so that the effective voltage is 9kV, and the discharge frequency reaches 8.5MHz, and it is treated by dielectric barrier discharge for 90 minutes.

As preferably, the method for preparing an efficient oxidizing catalyst by the plasma-assisted sol-gel method comprises the following steps:

(1) Put 26.9g of 50% manganese nitrate solution and 10.9g of cerium nitrate hexahydrate into a beaker, dissolve them in deionized water, stir at room temperature to obtain a mixed solution, and mix 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol , pour the previous mixed solution, and stir at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the mixed solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the dried colloid in a mortar, fully grind it into particles below 40 mesh, and set aside;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, pass through the simulated air containing 21% oxygen, and wrap the copper sheet outside the quartz tube as the power supply electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5MHz, and use the method of dielectric barrier discharge for 90min.

The reaction process for the catalyst of the present invention to selectively catalyze and oxidize nitrogen oxides in flue gas is as follows: at a reaction temperature of 50-450°C, _O2 is used as an oxidant, and the catalyst of the present invention is used to catalytically oxidize NO into NO2. _The reaction formula as follows:

Compared with the traditional technology, the present invention has the advantages of:

(1) High activity and selectivity for catalytic oxidation of nitrogen oxides;

(2) It has a wide temperature adaptation window;

(3) The preparation process is simple and the cost is low, and it can be widely used in the preparation process of denitrification catalyst for selective catalytic oxidation of flue gas.

Description of drawings

Fig. 1 is the spectrogram that the present invention carries out X-ray photoelectron spectrum test to sample;

Fig. 2 is the spectrogram that the present invention carries out X-ray diffraction to the sample.

detailed description

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

Example 1

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, comprising the steps of:

(1) Put 35.8g of 50% manganese nitrate solution into a beaker, dissolve it with deionized water, and stir at room temperature to obtain a homogeneous solution; pour 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol into the previous mixture , stirring at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the colloid in a drying oven and dry it at 110°C for 12 hours, put the dried colloid sample in a mortar, grind it into particles below 40 mesh, and wait for plasma treatment;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, and pass through the simulated air containing 21% oxygen; the outside of the quartz tube is wrapped with copper sheet as the power electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5MHz, and use the method of dielectric barrier discharge for 90min.

The prepared catalyst is pulverized and sieved to obtain catalyst particles with a particle diameter between 80 mesh and 60 mesh. Take 0.2 mg of the catalyst particle and put it into a catalyst activity evaluation device, and the activity evaluation is carried out in a fixed-bed reactor with an internal diameter of 8 mm. . Set the composition of the simulated flue gas to 400ppmNO, 5%O ₂ , N ₂ as the balance gas, and the space velocity to 360000mL ^-1 g ^-1 h ^-1 ; use the testo flue gas analyzer to detect the downstream flue gas. The test results show that when the reaction temperature is 275°C and 325°C, the NO catalytic oxidation rates of the MnOx catalyst are 59.4% and 70.50%, respectively, compared with the catalytic efficiencies of 31.8% and 44.4% of the MnOx prepared by the calcination method under the same conditions , there is a significant improvement.

Example 2

A certain amount of catalyst powder sample of Example 1 was taken, and the energy spectrum of O 1s was analyzed by performing X-ray photoelectron spectroscopy on the sample, and its spectrum is shown in FIG. 1 . The test instrument is Thermo ESCALAB 250. It can be seen from the analysis spectrum 1 that peak 1 is lattice oxygen, peak 2 is surface unsaturated oxygen species, and peak 3 is adsorbed oxygen and adsorbed water species. The large areas of peaks 2 and 3 indicate that there are many active oxygen species on the surface of the catalyst, which is beneficial to the catalytic oxidation reaction.

Example 3

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, comprising the steps of:

(1) Put 26.9g of 50% manganese nitrate solution and 10.9g of cerium nitrate hexahydrate into a beaker, dissolve them in deionized water, and stir at room temperature to obtain a mixed solution; mix 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol , pour the previous mixed solution, and stir at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the colloid in a drying oven and dry it at 110°C for 12 hours, put the dried sample in a mortar, and grind it into particles below 40 mesh, and then treat it with plasma;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, and pass through the simulated air containing 21% oxygen; the outside of the quartz tube is wrapped with copper sheet, which is used as the power supply electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5MHz, and use the method of dielectric barrier discharge for 90min.

Utilizing the activity evaluation device and method in Example 1, the test results show that when the reaction temperature is 300°C, the NO catalytic oxidation rate of the MnCeOx catalyst is 81.2%, which is higher than that of the MnCeOx prepared by the calcination method under the same conditions. The efficiency is 59.4%, which is significantly improved.

Example 4

Put 0.07g of the catalyst powder sample of Example 3 into a physical/chemical adsorption apparatus for BET testing. The test was carried out by the AUTOSORB-1-C physical/chemical adsorption instrument produced by Quanta Corporation of the United States. BET results showed that the specific surface area of the catalyst was 101.5m ² /g, the total pore volume was 0.228cc/g, and the average pore diameter was 89.6Å. It is much better than the specific surface area of MnCeOx catalyst prepared by traditional calcination method, which is 68.9m ² /g.

Example 5

A certain amount of catalyst powder sample of Example 3 was taken, and the sample was subjected to X-ray diffraction to analyze its diffraction pattern to obtain the composition of the material, the structure and shape of the atomic molecules inside the material. The X-ray diffraction spectrum is shown in Figure 2, and the test instrument is X`Pert PRO from PANalytical Company. Analysis of the diffraction pattern Figure 2 shows that the diffraction peaks of cerium oxide and manganese oxide crystals in this catalyst are very weak, and the diffraction peak of cerium oxide at 28.5° moves to 29°, which proves that Mn ions enter the ceria crystal lattice and form a good solid solution structure.

Example 6

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, comprising the steps of:

(1) Put 17.9g of 50% manganese nitrate solution and 21.7g of cerium nitrate hexahydrate into a beaker, dissolve them in deionized water, and stir at room temperature to obtain a mixed solution; mix 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol , pour the previous mixed solution, and stir at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the colloid in a drying oven and dry it at 110°C for 12 hours, put the dried sample in a mortar, and grind it into particles below 40 mesh, and then treat it with plasma;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, and pass through the simulated air containing 21% oxygen; the outside of the quartz tube is wrapped with copper sheet as the power electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5 MHz, and use the method of dielectric barrier discharge for 90 minutes.

Using the activity evaluation device and method in Example 1, the test results show that when the reaction temperature is 300°C, the NO catalytic oxidation rate of the MnCeOx catalyst is 70.8%.

Example 7

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, comprising the steps of:

(1) Put 26.9g of 50% manganese nitrate solution and 10.9g of cerium nitrate hexahydrate into a beaker, dissolve them in deionized water, and stir at room temperature to obtain a mixed solution; mix 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol , pour the previous mixed solution, and stir at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the colloid in a drying oven and dry it at 110°C for 12 hours, put the dried sample in a mortar, and grind it into particles below 40 mesh, and then treat it with plasma;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, and pass in a mixed gas containing 10% oxygen and 90% nitrogen; the outside of the quartz tube is wrapped with a copper sheet as a power supply electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5MHz, and use the method of dielectric barrier discharge for 90min.

Using the activity evaluation device and method in Example 1, the test results show that when the reaction temperature is 275°C, the NO catalytic oxidation rate of the MnCeOx catalyst is 80.6%.

Example 8

A method for preparing an efficient oxidizing catalyst by a plasma-assisted sol-gel method, comprising the steps of:

(1) Put 26.9g of 50% manganese nitrate solution and 10.9g of cerium nitrate hexahydrate into a beaker, dissolve them in deionized water, and stir at room temperature to obtain a mixed solution; mix 27.3g of citric acid monohydrate and 2.73g of polyethylene glycol , pour the previous mixed solution, and stir at room temperature to obtain a mixed solution;

(2) Heat the beaker containing the solution in a water bath at 80°C, and stir continuously with an electromagnetic stirrer until the solution becomes a colloid;

(3) Put the colloid in a drying oven and dry it at 110°C for 12 hours, put the dried sample in a mortar, and grind it into particles below 40 mesh, and then treat it with plasma;

(4) Fill the sample between the rod-shaped electrode in the discharge quartz tube and the wall of the quartz tube, and pass in a mixed gas containing 10% oxygen and 90% argon; the outside of the quartz tube is wrapped with a copper sheet as a power supply electrode, and the rod-shaped electrode is grounded;

(5) Turn on the AC power supply, so that the effective voltage is at 9kV; make the discharge frequency reach 8.5MHz, and use the method of dielectric barrier discharge for 90min.

Using the activity evaluation device and method in Example 1, the test results show that when the reaction temperature is 325°C, the NO catalytic oxidation rate of the MnCeOx catalyst is 77.3%.

Claims (1)

1. a kind of method that plasmaassisted sol-gal process prepares efficient oxidation catalyst, it is characterised in that including following Step：

（1）26.9g 50% manganese nitrate solution and 10.9g six nitric hydrate ceriums are loaded into beaker, with deionized water dissolving, often Temperature stirring obtains mixed liquor, by 27.3g monohydrate potassiums and 2.73g polyethylene glycol, the mixed liquor before pouring into, stirring at normal temperature Obtain mixed solution；

（2）The beaker of mixed solution is will be equipped with, is placed in 80 DEG C of water-bath and heats, and is uninterruptedly stirred using magnetic stirrer, Until solution is changed into colloid；

（3）Dried colloid is put in mortar, the particle below 40 mesh is fully ground into, it is stand-by；

（4）Sample is filled in electric discharge quartz ampoule between stick electrode and quartzy tube wall, the simulation containing 21% oxygen is passed through empty Gas, quartz ampoule outer wrap copper sheet, as power supply pole is connect, stick electrode is grounded；

（5）AC power is opened, effective voltage is in 9kV；It is 8.5MHz to reach discharge frequency, utilizes dielectric barrier discharge Method processing, continues 90min.