CN112473688A

CN112473688A - Preparation method of rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst

Info

Publication number: CN112473688A
Application number: CN202011348975.5A
Authority: CN
Inventors: 王娜; 叶长飞; 葛成敏; 王磊; 杨厂; 谢会东; 陈诚
Original assignee: Shandong Dy New Material Technology Co ltd; Xian University of Science and Technology
Current assignee: Shandong Dy New Material Technology Co ltd; Xian University of Science and Technology
Priority date: 2020-11-26
Filing date: 2020-11-26
Publication date: 2021-03-12

Abstract

A process for preparing the denitration catalyst from rare-earth chelated vanadium at low cost and wide temp window from CeO₂‑WO₃‑TiO₂On the basis of the catalyst, vanadium oxide, La oxide and Cu oxide are introduced to modify the catalyst together, and the synergistic effect among the Ce oxide, the La oxide and the Cu oxide and the vanadium oxide is found, so that the problems of high cost and high toxicity caused by overhigh vanadium content in the low-temperature catalytic performance of the catalyst are solved, the performance of the denitration catalyst in a low-temperature section can be further improved, and the lower limit of the temperature of the activity window of the catalyst is widened.

Description

Preparation method of rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst

Technical Field

The invention relates to the technical field of environmental protection and catalysts, and particularly relates to a preparation method of a rare earth chelated vanadium denitration catalyst with low cost and a wide temperature window.

Background

Among the combustion products of fossil fuels, nitrogen oxides are one of the main pollutants, mainly including nitrogen monoxide, nitrogen dioxide, nitrous oxide, dinitrogen pentoxide, etc., wherein nitrogen monoxide and nitrogen dioxide are the main components, and the most harmful to the environment is caused. Atmospheric nitrogen oxides originate mainly from two sources: one from nature and the other from human production activities. Although the yield of nitrogen oxides generated in nature is huge, the nitrogen oxides are in an equilibrium state on the whole, and the influence on the environment is basically negligible; nitrogen oxides generated by human production activities mainly comprise that fossil fuels are mainly combusted into coal, such as thermal power plants, automobiles, airplanes and the like, and cause great harm to the living environment of human beings. At present, the mainstream commercial catalyst is still a vanadium-based catalyst, but the vanadium-based catalyst has the disadvantages of biotoxicity, labor waste and the like in recycling, particularly the low-temperature vanadium-based catalyst has high vanadium content and high biotoxicity, belongs to dangerous solid waste and is difficult to treat.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a preparation method of a rare earth chelated vanadium denitration catalyst with low cost and a wide temperature window, so that the problems of high cost and high toxicity caused by overhigh vanadium content in the catalytic performance of the catalyst at low temperature are solved, the performance of the denitration catalyst at a low temperature section can be further improved, and the lower limit of the temperature of the activity window of the catalyst is widened.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of a rare earth chelated vanadium denitration catalyst with low cost and a wide temperature window comprises the following steps;

step 1:

injecting 100 parts by mass of deionized water into a reaction kettle, starting stirring, controlling the temperature until the water temperature reaches 60-80 ℃, adding 0.01-0.5 part by mass of ammonia water, and uniformly stirring;

adding 10-20 parts by mass of silica sol into the reaction kettle under the condition of continuous stirring at the temperature, and uniformly stirring; sequentially adding 0.3-0.8 part by mass of ethanolamine, 0.2-0.6 part by mass of ammonium metavanadate, 0.1-4 parts by mass of ammonium metatungstate, 0.2-3 parts by mass of ammonium heptamolybdate, 8-10 parts by mass of cerium nitrate, 2-4 parts by mass of lanthanum nitrate and 0.1-0.5 part by mass of copper chloride, and uniformly stirring;

then adding 0.1-0.5 mass part of sodium dodecyl sulfate; adding 25-40 parts by mass of ammonia water to generate a precipitate;

then adding 50-70 parts by mass of titanium dioxide, and uniformly stirring; then adding 5-10 parts by mass of clay and stirring uniformly;

adding 20-50 parts by mass of titanium dioxide, and uniformly stirring to obtain uniformly stirred slurry;

step 2:

stopping stirring and heating the reaction kettle, and aging the slurry obtained in the step (1);

and step 3:

filtering the aged slurry obtained in the step 2 on a suction filter, washing with deionized water, and then evaporating water in an evaporation tank until the slurry is agglomerated and the surface is cracked to obtain dry agglomerated slurry;

and 4, step 4:

putting the caking slurry in the step (3) into a muffle furnace, and calcining by temperature programming; and then carrying out wet grinding on the calcined caking slurry to prepare powder, and finally drying and crushing to obtain the rare earth chelated vanadium denitration catalyst with low cost and wide temperature window.

The aging in the step 2 comprises the following specific steps: naturally aging in a reaction kettle for 0.5-5 hours.

The temperature programming conditions in the step 4 are as follows: heating to 100 ℃ and 120 ℃ at room temperature, and keeping the temperature for 0.5-5 h; then heating to 240 ℃ and 260 ℃, and preserving the heat for 1-6 h; then heating to the temperature of 360 ℃ and 380 ℃, and preserving the heat for 1-6 h; then heating to 450 ℃ and 500 ℃, and preserving the heat for 1-6 h; and finally, naturally cooling to room temperature.

The wet grinding method in the step 4 comprises the following grinding conditions: the time is 0.5-2h, so that the grain diameter of the obtained powder is D50 < 1.5 mu m, and D90 < 3 mu m.

The drying conditions in the step 4 are as follows: the temperature is 100 ℃ and 120 ℃, and the time is 12-24 hours until the moisture of the powder is less than 1%.

The crushing conditions in the step 4 are as follows: and grinding the dried and agglomerated powder into powder by a disc grinding mill.

The prepared rare earth chelated vanadium denitration catalyst is low in cost and wide in temperature window, and can be applied to denitration of fixed-source nitrogen oxides in any high-temperature environment.

The invention has the beneficial effects that:

the invention obtains good catalyst effect by researching the formula of the catalyst, and a certain content of CuO is added₂、La₂O₃And vanadium oxide to CeO₂-WO₃-TiO₂The basic catalyst is chelated and modified, and the cost is greatly saved compared with a low-temperature commercial vanadium-based catalyst on the basis of realizing the low-temperature denitration efficiency.

The invention further improves the catalyst effect by researching the preparation steps of the catalyst, and uses clay to replace part of TiO₂Further improves the mechanical property of the catalyst and prolongs the service life of the catalyst.

Detailed Description

The present invention will be described in further detail with reference to examples.

Example 1:

injecting 100 parts by mass of deionized water into a reaction kettle, starting stirring, controlling the temperature until the water temperature reaches 60 ℃, continuously stirring at the temperature, adding 10ml of silica sol, and uniformly stirring; then adding 0.3 mass part of ethanolamine and 0.4 mass part of ammonium metavanadate, sequentially adding 0.1g of ammonium metatungstate, 0.2g of ammonium heptamolybdate, 8g of cerium nitrate, 2g of lanthanum nitrate and 0.1g of copper chloride, uniformly stirring, and then adding 25 mass parts of ammonia water to form a precipitate; then 0.1g of sodium dodecyl sulfate and 50g of titanium dioxide are added and stirred uniformly; then 5g of clay is added and stirred evenly; adding 20g of titanium dioxide, uniformly stirring to obtain uniformly stirred slurry, and finally performing suction filtration on the slurry;

naturally aging in a reaction kettle for 0.5 hour;

continuously heating and stirring the aged slurry in an evaporation tank to evaporate the liquid until the slurry is agglomerated and the surface is cracked to obtain dry agglomerated slurry;

putting the caking slurry into a muffle furnace, heating to 100 ℃ at room temperature, and keeping the temperature for 0.5 h; then heating to 240 ℃, and preserving heat for 1 h; then heating to 380 ℃, and preserving the heat for 1 h; then heating to 500 ℃, and preserving heat for 1 h; then, naturally cooling to room temperature; and then carrying out wet grinding on the calcined agglomeration slurry to prepare powder, grinding for 0.5h to obtain powder with the particle size of D50 being less than 1.5 mu m and D90 being less than 3 mu m, finally drying for 18h at the temperature of 105 ℃ until the moisture of the powder is less than 1%, and grinding the dried agglomeration powder into powder by a disc grinder to obtain the rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst.

Example 2

Injecting 100 parts by mass of deionized water into a reaction kettle, starting stirring, controlling the temperature until the water temperature reaches 70 ℃, continuously stirring at the temperature, adding 15ml of silica sol, and uniformly stirring; then adding 0.6 mass part of ethanolamine and 0.5 mass part of ammonium metavanadate, sequentially adding 1g of ammonium metatungstate, 1g of ammonium heptamolybdate, 9g of cerium nitrate, 3g of lanthanum nitrate and 0.3g of copper chloride, uniformly stirring, and then adding 28 mass parts of ammonia water to form a precipitate; then 0.1g of sodium dodecyl sulfate and 60g of titanium dioxide are added and stirred uniformly; then 5g of clay is added and stirred evenly; adding 10g of titanium dioxide, uniformly stirring to obtain uniformly stirred slurry, and finally performing suction filtration on the slurry;

naturally aging in a reaction kettle for 3 hours;

putting the caking slurry into a muffle furnace, heating to 110 ℃ at room temperature, and keeping the temperature for 2 hours; then heating to 250 ℃, and preserving heat for 2 h; then heating to 370 ℃, and preserving heat for 2 h; then heating to 550 ℃, and preserving heat for 3 h; then, naturally cooling to room temperature; and then carrying out wet grinding on the calcined agglomeration slurry to prepare powder, grinding for 1.5h to obtain powder with the particle size of D50 being less than 1.5 mu m and D90 being less than 3 mu m, finally drying for 18h at the temperature of 105 ℃ until the moisture of the powder is less than 1%, and grinding the dried agglomeration powder into powder by a disc grinder to obtain the rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst.

Example 3

Injecting 100 parts by mass of deionized water into a reaction kettle, starting stirring, controlling the temperature until the water temperature reaches 80 ℃, continuously stirring at the temperature, adding 20ml of silica sol, and uniformly stirring; then adding 0.5 mass part of ethanolamine and 0.6 mass part of ammonium metavanadate, sequentially adding 2g of ammonium metatungstate, 3g of ammonium heptamolybdate, 10g of cerium nitrate, 4g of lanthanum nitrate and 0.5g of copper chloride, uniformly stirring, and then adding 33 mass parts of ammonia water to form a precipitate; then 0.2g of sodium dodecyl sulfate and 60g of titanium dioxide are added and stirred uniformly; then 8g of clay is added and stirred evenly; adding 20g of titanium dioxide, uniformly stirring to obtain uniformly stirred slurry, and finally performing suction filtration on the slurry;

naturally aging in a reaction kettle for 5 hours;

putting the caking slurry into a muffle furnace, heating to 120 ℃ at room temperature, and preserving heat for 6 hours; then heating to 260 ℃, and preserving heat for 6 hours; then heating to 380 ℃, and preserving the heat for 6 hours; then heating to 620 ℃, and preserving the heat for 6 hours; then, naturally cooling to room temperature; and then carrying out wet grinding on the calcined agglomeration slurry to prepare powder, grinding for 2h to obtain powder with the particle size of D50 being less than 1.5 mu m and D90 being less than 3 mu m, finally drying for 18h at the temperature of 105 ℃ until the moisture of the powder is less than 1%, and grinding the dried agglomeration powder into powder by a disc grinder to obtain the rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst.

Comparative example 1

The difference from example 1 is that cerium nitrate, lanthanum nitrate and copper chloride were not added, and the other conditions were the same.

Comparative example 2

The difference from example 1 is that lanthanum nitrate and copper chloride were not added, and the other conditions were the same.

Comparative example 3

The difference from example 1 was that cerium nitrate and copper chloride were not added, and the other conditions were the same.

Comparative example 4

The difference from example 1 is that cerium nitrate and lanthanum nitrate were not added, and the other conditions were the same.

Comparative example 5

The difference from example 1 is that cerium nitrate was not added, and the other conditions were the same.

Comparative example 6

The difference from example 1 is that lanthanum nitrate was not added, and the other conditions were the same.

Comparative example 7

Except for the difference from example 1, copper chloride was not added, and other conditions were the same.

Comparative example 8

Except that the clay was replaced with TiO2 in example 1, and the other conditions were the same.

The rare earth chelated vanadium denitration catalyst prepared by the method has low cost and a wide temperature window, can be applied to denitration of fixed source nitrogen oxides, and specifically comprises the following steps:

the catalysts prepared in the examples and the comparative examples are impregnated and coated on cordierite honeycomb carriers, the actual working conditions of the catalysts are simulated, 1g of the catalysts are weighed, a fixed bed continuous flow quartz tube reactor is adopted to carry out the activity test of the catalysts, and the SCR denitration activity test is respectively carried out at the temperatures of 200 ℃, 250 ℃, 350 ℃, 400 ℃, 420 ℃, 450 ℃ and 500 ℃. The method is a laboratory-level reaction, but can react the trend generated by modifying the basic catalyst, and provides a guide basis for further amplifying experiments.

The composition of the reaction mixture gas is (volume concentration): NO concentration 500ppm, NH₃In a concentration of 500ppm, SO₂In a concentration of 300ppm, O₂In a concentration of 5%, H₂The content of O is 5%, and the rest is N2. The test space velocity is 200000h^-1The above.

The catalyst has unpredictable fluctuations in catalytic effect before reaching stability, and after reaching stability, the catalytic effect is very stable for a considerable period of time until the catalytic performance is reduced due to the increased degree of deactivation. The invention will collect the NO conversion at 3h of reaction progress to ensure that the measured data is stable. The NO conversion rate can be obtained by measuring the NO at the outlet of the reactor through a monitoring instrument, and the NO conversion rate reflects the denitration activity of the catalyst.

In order to examine the catalyst activity window, the reaction temperature is increased at an interval of 5 ℃ after the catalyst is operated for 3 hours at 200 ℃ to be stable, the temperature at which the NO conversion rate firstly reaches or exceeds 95% is taken as the lower limit temperature of the catalyst activity window, and the temperature is continuously increased until the NO conversion rate firstly drops to or below 95% as the upper limit temperature of the catalyst activity window because the catalyst activity curve is in a parabola-like shape. This makes it possible to clearly reflect the activity window of the catalyst.

The catalytic results are detailed in Table 1

a, the reaction temperature is 200 ℃; b, the reaction temperature is 250 ℃; c, the reaction temperature is 300 ℃;

comparative example 1 is a catalyst studied earlier by the applicant: CeO (CeO)₂-WO₃-TiO₂Which serves as the base catalyst for this study. Generally, the denitration catalyst activity curve is in a shape similar to a parabola, the catalyst activity of the denitration catalyst increases rapidly before reaching the lower limit temperature of a reaction window until reaching the lower limit temperature of the window, once the reaction temperature enters the catalyst activity window, the catalyst activity slowly grows until being parallel, then slowly decreases, and when the reaction temperature exceeds the upper limit of the catalyst activity window, the catalyst activity significantly decreases. It is generally believed that NO and NH₃When reaction is carried out, SO₂SO may also be formed by oxidation₃But N isThe reaction progress of O reduction is more temperature sensitive, so increasing the temperature favors the progress of SCR denitration, but a continuous increase in temperature has an effect on the structure of the catalyst, so it is not more favorable for SCR denitration at higher temperatures, and therefore there is a reactive window for the catalyst.

Comparative examples 2 to 4 are modifications using cerium oxide, lanthanum oxide or Cu oxide alone based on comparative example 1, respectively. For the modification of cerium oxide in comparative example 2, the addition of cerium oxide can generally improve the catalyst activity, and as can be seen from the results of comparative example 2, the addition of cerium oxide allows the catalyst activity to be significantly improved, which may be associated with the improvement of catalyst dispersibility and the reduction of catalyst agglomeration, and the modification of cerium oxide can broaden the activity window of the catalyst. For the modification of La oxide in comparative example 3, in general, La oxide was used as a structure-maintaining aid in the catalyst, and the structure and valence of the active component of the catalyst could be maintained. It can be seen from the results of comparative example 3 that the activity of the catalyst was significantly reduced before 300 ℃ and slightly reduced in the 300 ℃ to 350 ℃ range after addition of the La oxide, which may be related to the catalyst showing that the oxide of the active component Ce was replaced by a portion of the La oxide, which widens the upper limit of the catalyst activity window, but also raises the lower limit of the catalyst activity window. For the modification of Cu oxide in comparative example 4, Cu oxide itself can be used as a catalyst to realize SCR reaction at medium temperature, but the activity is not significant at high temperature, and the introduction of Cu oxide also affects the valence state of Ce oxide. It can be seen from the results of comparative example 4 that the addition of Cu oxide significantly improves the denitration activity of the catalyst at 350 ℃ or lower. The Cu oxide widens the lower limit of the catalyst activity window, but also lowers the upper limit of the catalyst activity window.

According to the above experimental results, the applicant tried to introduce two elements of cerium oxide, La oxide or Cu oxide for catalyst performance examination. Comparative example 5 in which La oxide and Cu oxide were introduced for modification, the conversion rate of NO was higher between catalysts in which La oxide or Cu oxide was introduced alone than at 350 ℃ than in the case where La oxide and Cu oxide were not introducedThe conversion rate of NO of the basic catalyst of the compound is lower than that of the basic catalyst without introducing La oxide and Cu oxide when the temperature is more than 350 ℃, and the window temperature of the catalyst is widened at the upper limit and the lower limit relative to the basic catalyst, but the widening width is smaller than that of the catalyst with independently introducing La oxide or Cu oxide. It indicates that the interaction between the La oxide and Cu oxide modifiers is smaller and that the respective modifying effects are likely to be exerted more. Comparative example 6, in which cerium oxide and Cu oxide were introduced to modify the catalyst, the conversion rate of NO below 300 ℃ was higher than that of the catalyst in which cerium oxide and Cu oxide were introduced alone and that of the base catalyst in which cerium oxide and Cu oxide were not introduced, the conversion rate of NO at 350 ℃ was between the catalysts in which silica sol and Cu oxide were introduced alone, and higher than that of the base catalyst in which cerium oxide and Cu oxide were not introduced, and the conversion rate of NO at 350 ℃ was between the catalysts in which cerium oxide and Cu oxide were introduced alone, which was equal to that of the base catalyst in which cerium oxide and Cu oxide were not introduced, the lower limit temperature of the catalyst activity window was further widened. The cerium oxide and Cu oxide modifiers allow a further increase in the conversion of NO at temperatures below 300 ℃, which may result in further dispersion of the Ce oxide and Cu oxide on the catalyst surface and interaction due to the use of silica sol and introduction of Cu oxide. Comparative example 7 in which cerium oxide and La oxide were introduced for modification, the conversion rate of NO at 300 ℃ or lower was measured by introducing cerium oxide and La alone₂O₃The catalyst has a conversion rate of NO of 300 to 350 ℃ between catalysts in which ceria and La oxide are introduced alone, lower than that of a base catalyst in which ceria and La oxide are not introduced, and higher than that of a base catalyst in which ceria and La oxide are not introduced, and has a conversion rate of NO at high temperature higher than that of a catalyst in which ceria and La oxide are introduced alone and a base catalyst in which ceria and La oxide are not introduced, and a catalyst activity window temperature cannot be further widened. The cerium oxide and La oxide modifiers allow the conversion rate of NO to be further improved at low temperature of the catalyst, which may cause the oxide of Ce and La oxide on the surface of the catalyst to be further dispersed and to interact with each other due to the use of silica sol and the introduction of La oxide.

According to the analysis described above, the occurrence of events enabling further improvement in the catalyst performance is linked to the incorporation of cerium oxide, possibly due to the action of dispersion of the cerium oxide, the action of preventing agglomeration and the action of possible residual silicon. Thus, the cerium oxide, the La oxide and the Cu oxide are further introduced into the catalyst together for modification, and examples 1-3 show that when the cerium oxide, the La oxide and the Cu oxide are introduced together, unexpected synergistic effect may occur between the La oxide and the Ce oxide, the conversion rate of NO at the medium and low temperature sections is obviously further improved, and the upper limit of the activation window is obviously further expanded. On the basis of improving the dispersibility of La oxide, Cu oxide and Ce oxide on the surface of the catalyst, the La oxide, the Cu oxide and the Ce oxide are easy to interact, the Cu oxide can jointly affect the valence state of the Ce oxide, and the La oxide jointly affects the maintenance of the catalyst structure, so that the catalyst can better exert the synergistic effect of each component at the temperature of over 200 ℃, the catalyst performance is comprehensively improved, and the activity window of the catalyst is widened. The above three substances are modified together, which may promote the synergistic improvement of the beneficial factors and convert the adverse factors, so that the overall improvement of the catalyst performance occurs. The experimental research shows that the examples 1-3 can provide meaningful guidance for the rare earth chelated vanadium denitration catalyst with good catalytic effect, low cost and wide temperature window.

Claims

1. A preparation method of a rare earth chelated vanadium denitration catalyst with low cost and a wide temperature window comprises the following steps;

step 1:

then adding 50-70 parts by mass of titanium dioxide, and uniformly stirring;

then adding 5-10 parts by mass of clay and stirring uniformly;

step 2:

and step 3:

and 4, step 4:

2. The preparation method of the rare earth chelated vanadium low-cost and wide-temperature-window denitration catalyst according to claim 1, wherein the aging in the step 2 comprises the following specific steps: naturally aging in a reaction kettle for 0.5-5 hours.

3. The method for preparing the rare earth chelated vanadium low-cost and wide-temperature-window denitration catalyst according to claim 1, wherein the temperature programming conditions in the step 4 are as follows: heating to 100 ℃ and 120 ℃ at room temperature, and keeping the temperature for 0.5-5 h; then heating to 240 ℃ and 260 ℃, and preserving the heat for 1-6 h; then heating to the temperature of 360 ℃ and 380 ℃, and preserving the heat for 1-6 h; then heating to 500 ℃ and 620 ℃, and preserving the heat for 1-6 h; and finally, naturally cooling to room temperature.

4. The method for preparing a low-cost and wide-temperature-window denitration catalyst based on vanadium rare earth chelate according to claim 1, wherein the wet grinding conditions in the step 4 are as follows: the time is 0.5-2h, so that the grain diameter of the obtained powder is D50 < 1.5 mu m, and D90 < 3 mu m.

5. The method for preparing the rare earth chelated vanadium low-cost and wide-temperature-window denitration catalyst according to claim 1, wherein the drying conditions in the step 4 are as follows: the temperature is 100 ℃ and 120 ℃, and the time is 12-24 hours until the moisture of the powder is less than 1%.

6. The method for preparing a low-cost and wide-temperature-window denitration catalyst based on vanadium rare earth chelate according to claim 1, wherein the crushing conditions in the step 4 are as follows: and grinding the dried and agglomerated powder into powder by a disc grinding mill.

7. The rare earth chelated vanadium low-cost wide-temperature-window denitration catalyst prepared based on the method in claim 1 is characterized by being applicable to denitration of fixed-source nitrogen oxides in any low-temperature environment.