CN111905709A

CN111905709A - Mesoporous cerium-titanium-based low-temperature denitration catalyst and preparation method thereof

Info

Publication number: CN111905709A
Application number: CN202010756177.XA
Authority: CN
Inventors: 刘小浩; 刘冰; 刘洁; 姜枫; 胥月兵
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2020-11-10

Abstract

The invention discloses a mesoporous cerium titanium-based low-temperature denitration catalyst and a preparation method thereof, and belongs to the technical field of environmental chemical industry. The invention adopts a hydrothermal synthesis method to prepare the rare earth cerium titanium catalyst, and adopts a template agent F127 to adjust the molar ratio of cerium to titanium and adjust the conditions of hydrothermal reaction to form a structure with mesoporous channels, thereby adjusting the specific surface area of the catalyst, and the specific surface area of the prepared catalyst is up to 160m²In g, in the presence of nitrogen oxidesThe low-temperature activity is good in the selective catalytic reduction reaction. According to the method, in the process of mixing a cerium source and a titanium source compound, the solution is controlled to be acidic by dropwise adding nitric acid, the reaction is carried out by a two-step hydrothermal method, and then a sample is prepared by vacuum filtration and roasted to obtain the catalyst. In addition, the rare earth cerium-titanium-based low-temperature denitration catalyst prepared by the method does not contain toxic vanadium, and is green and environment-friendly.

Description

Mesoporous cerium-titanium-based low-temperature denitration catalyst and preparation method thereof

Technical Field

The invention relates to a mesoporous cerium-titanium-based low-temperature denitration catalyst and a preparation method thereof, belonging to the technical field of environmental chemical industry.

Background

Nitrogen Oxides (NO) emitted from industrial waste gas and motor vehicle exhaust_x) Is one of the main precursors of fine particulate matters (PM2.5) in the atmosphere, and can also generate photochemical smog and nitric acid type acid rain, thereby seriously harming human health and destroying the ecological environment. Ammonia selective catalytic reduction (NH)₃SCR) technology is currently the most widely used technology for nitrogen oxide abatement (denitration). However, conventional vanadium-based NH₃SCR denitration catalysts suffer from the following disadvantages: 1. main active component V in catalyst₂O₅The catalyst is a highly toxic substance, and a large amount of highly toxic waste catalysts are generated while the emission reduction of nitrogen oxides is promoted, so that the environment and the human health are seriously harmed, secondary pollution is generated, and the waste SCR flue gas denitration catalyst (vanadium base) is brought into dangerous waste for management in 2014 in China so as to prevent the serious pollution to the environment; 2. the active temperature window is narrow, needs to be controlled within the range of 300-400 ℃, and cannot meet the requirement of low temperature<200 ℃) of SCR denitration technology. Therefore, the environment-friendly high-efficiency non-vanadium-based low-temperature NH is researched and developed₃SCR catalysts are an ongoing task in the current field of denitration.

Rare earth cerium oxide (CeO)₂) The rare earth metal oxide/rare earth composite material has the advantages of excellent redox performance, easily-regulated structure, no toxicity and the like, and is also a rare earth resource great country and has abundant rare earth resource reserves. Therefore, the high-efficiency rare earth cerium titanium based low-temperature NH is designed₃SCR catalyst, replacing traditional toxic vanadium-based catalyst, not only contributing to the efficient utilization of rare earth resources in our country, but also preventing and treating NO_xPollution and secondary pollution of the waste vanadium-based catalyst, and has wide application prospect and environmental benefit. So far, conventional leachingNH (NH) at low temperature due to small specific surface area of cerium-titanium-based catalyst prepared by impregnation method and precipitation method₃The low activity in the SCR denitration reaction seriously hinders the development and application of the high-efficiency cerium titanium-based denitration catalyst. Thus the current cerium titanium based low temperature NH₃The challenge and problem faced in the research of SCR denitration catalysts is how to improve the low-temperature activity of the catalyst. The key to the problem of improving the low-temperature activity of the catalyst is to optimize the structure of an active site by regulating and controlling the structure or the composition of the cerium-titanium-based catalyst, increase the specific surface area of the catalyst to expose more active sites, and enhance the acidity of the catalyst to increase the catalytic activity of the catalyst.

Disclosure of Invention

[ problem ] to

Conventional vanadium based NH₃SCR denitration catalyst with main active component V₂O₅Is a highly toxic substance, and has a narrow active temperature window and cannot meet the requirement of low temperature<200 deg.C) SCR denitration technology. Rare earth cerium titanium base NH₃SCR catalysts are able to solve the traditional vanadium-based NH₃The problem that SCR denitration catalyst is poisonous, but the traditional cerium-titanium-based catalyst prepared by the impregnation method and the precipitation method has small specific surface area and NH is generated at low temperature₃The low activity in the SCR denitration reaction seriously hinders the development and application of the high-efficiency cerium-titanium-based denitration catalyst.

[ solution ]

In order to solve the problems, the invention provides a mesoporous cerium-titanium-based low-temperature denitration catalyst prepared by a hydrothermal synthesis method, and the method can regulate and control the specific surface area of the catalyst by adopting a specific template agent, regulating the content of cerium and titanium and adjusting the conditions of hydrothermal reaction, and can prepare the catalyst with the specific surface area as high as 160m²A catalyst per gram; the catalyst prepared by the method has good low-temperature nitrogen oxide denitration catalytic activity.

The invention provides a preparation method of a mesoporous cerium titanium-based low-temperature denitration catalyst, which comprises the following steps:

(1) placing the titanium-containing compound in water to form a solution or suspension, stirringDropwise adding HNO in the state₃Adding a cerium-containing compound to the solution until the solution is acidic, and uniformly mixing the solution and the solution to obtain a solution A;

(2) adding template F127 into ethanol under stirring to form a solution or suspension, and adding HNO under stirring₃Making the solution acidic, then adding urea, and stirring uniformly, wherein the solution is marked as solution B;

(3) transferring the solution A and the solution B obtained in the step (1) and the step (2) to a container for hydrothermal reaction, and carrying out hydrothermal reaction for 1-72h at 80-100 ℃; then raising the temperature to 120-140 ℃ for hydrothermal reaction for 5-10 h;

(4) after the hydrothermal reaction is finished, carrying out solid-liquid separation, washing and drying the obtained solid, and then roasting at the temperature of 300-500 ℃ for 4-12h to obtain the cerium titanium-based low-temperature denitration catalyst.

In an embodiment of the present invention, the cerium-containing compound in step (1) is any one or more of cerium nitrate, cerium chloride, and cerium phosphate.

In one embodiment of the present invention, the titanium-containing compound in step (1) is any one or more of titanium sulfate, titanium chloride, tetrabutyl titanate, and ammonium titanyl oxalate.

In one embodiment of the invention, the ratio of the amount of cerium to titanium in the cerium-containing compound and the titanium-containing compound in step (1) is 1 (2-10).

In one embodiment of the present invention, the amount ratio of the cerium and titanium substances in the cerium-containing compound and the titanium-containing compound in step (1) is 1: 5.

In one embodiment of the invention, the stirring in the step (1) is magnetic stirring, and the stirring time is 0.5-2 hours.

In one embodiment of the present invention, the HNO in step (1) and step (2)₃The concentration of the solution is 4-10mol/L, HNO is dripped₃Until the pH of the solution is 2-6.

In one embodiment of the present invention, in the solution A in the step (1), the concentration of the cerium-containing compound is 0.05 to 0.35mol/L, and the concentration of the titanium-containing compound is 0.70 to 0.10 mol.

In one embodiment of the invention, the concentration of the template F127 in the solution B in the step (2) is 0.005-0.015 mol/L.

In one embodiment of the present invention, the ratio of the amount of the template F127 to the sum of the cerium-containing compound and the titanium-containing compound in step (2) is 1 (200 to 400).

In one embodiment of the present invention, the ratio of the amount of the template F127 to the optimum amount of the sum of the cerium-containing compound and the titanium-containing compound in step (2) is 1: 200.

In one embodiment of the present invention, the amount ratio of the template F127 to urea in step (2) is 1: 200-400.

In one embodiment of the present invention, the solid-liquid separation in step (4) is suction filtration separation.

In one embodiment of the present invention, the washing in step (4) is performed with water and absolute ethanol respectively until the pH value of the washing solution is 7-9.

In one embodiment of the present invention, the drying in step (4) is drying at 80-120 ℃ for 4-24h under normal pressure.

In an embodiment of the invention, the method in the step (4) further comprises tabletting, crushing and sieving the prepared rare earth cerium titanium based low-temperature denitration catalyst by a 40-60-mesh sieve.

The invention provides a rare earth cerium titanium-based low-temperature denitration catalyst prepared by the method.

In one embodiment of the invention, the rare earth cerium-based low-temperature denitration catalyst contains 10-50% of cerium and 50-90% of titanium by mass, and the atomic ratio of cerium to titanium is 1 (2-10).

The invention provides an application of the catalyst in a nitrogen oxide denitration reaction.

In one embodiment of the invention, in the denitration reaction, the reaction temperature is 150-.

[ advantageous effects ]:

(1) compared with the traditional vanadium-based denitration catalyst, the rare earth cerium-titanium-based low-temperature denitration catalyst prepared by the method does not contain toxic and harmful components to the environment and human bodies, and is more environment-friendly.

(2) The method can realize the accurate regulation and control of the specific surface area of the cerium-titanium-based low-temperature denitration catalyst by adopting the template agent F127, regulating and controlling the molar ratio of cerium to titanium and regulating the hydrothermal reaction condition, and can prepare the cerium-titanium-based low-temperature denitration catalyst with the specific surface area as high as 160m²The catalyst has a uniform pore channel.

(3) The rare earth cerium-titanium-based low-temperature denitration catalyst prepared by the invention is applied to selective catalytic reduction denitration of nitrogen oxides, has high catalytic reaction activity, still has high catalytic activity at a low temperature range (200-220 ℃), and has the conversion rate of the nitrogen oxides of more than 90%.

Drawings

FIG. 1 is a high power transmission electron micrograph of catalyst A prepared in example 1.

FIG. 2 is N of catalyst A prepared in example 1₂Adsorption and desorption curve chart.

FIG. 3 is N of catalyst B prepared in example 2₂Adsorption and desorption curve chart.

FIG. 4 is N of catalyst H prepared in comparative example 1₂Adsorption and desorption curve chart.

Fig. 5 shows the results of the nox denitration evaluation of the catalyst a and the catalyst H, I, J, K in the comparative example.

Detailed Description

[ example 1 ] preparation of catalyst A

(1) 11.25g of tetrabutyl titanate is weighed out and dissolved in 40mL of absolute ethanol under stirring, and 0.4mL of HNO with 66 percent (analytically pure) mass fraction is added dropwise under stirring at room temperature₃The solution is made to be acidic, 3.012g of cerous nitrate hexahydrate is weighed and dissolved in the solution after the solution is stirred for 1 hour, the solution is marked as A solution, namely the quantity ratio of cerium and titanium in the A solution is 1: 5;

(2) weighing 2.6g of template F127 and dissolving in 40ml of absolute ethyl alcohol, wherein the ratio of the addition amount of the template F127 to the amount of the substances of the tetrabutyl titanate and the cerous nitrate hexahydrate is 1:200, the solution is heated to 40 ℃ and stirred for one hour, after which 0.4ml of 66% (analytically pure) HNO are added with stirring₃And (3) adding 4.8g of urea into the solution after the solution is acidic, and stirring for 10min, wherein the ratio of the amount of the template agent F127 to the amount of the urea substance is 1:400, marking the obtained solution as a solution B;

(3) adding the solution A and the solution B into a 250ml hydrothermal reaction kettle, mixing, carrying out hydrothermal reaction for 48 hours at 80 ℃, then heating to 120 ℃, and carrying out hydrothermal reaction for 5 hours at 120 ℃;

(4) and after the hydrothermal reaction is finished, carrying out vacuum filtration and separation on the formed solid, washing the obtained solid with deionized water and ethanol until the pH value of the washing liquid is neutral, completely washing the added template agent, then drying the template agent for 12h at the normal pressure of 100 ℃, and then roasting the template agent for 4h at the temperature of 400 ℃ in the air to obtain a sample, thus obtaining the rare-earth cerium-titanium-based catalyst which takes tetrabutyl titanate as a titanium source and takes F127 as the template agent.

Finally, tabletting, crushing and screening 40-60 mesh particles for activity evaluation, wherein the prepared catalyst is marked as catalyst A. The morphology is shown in figure 1, and as can be seen from figure 1, the small-particle CeTi catalyst with the particle size of about 5nm and uniform distribution is prepared. Catalyst A was subjected to N₂Adsorption and desorption test of N₂As shown in the attached figure 2, the adsorption and desorption curves show that the synthesized cerium-titanium catalyst shows a typical IV-type isotherm, and can be judged as a mesoporous material, namely N₂The adsorption and desorption curves are shown in the table 1, and the related data such as the specific surface area pore volume and the like of the catalyst A are obtained.

[ example 2 ] preparation of catalyst B

(1) Weighing 12.37g of tetrabutyl titanate, dissolving in 40mL of absolute ethanol under stirring, and dropwise adding 0.4mL of HNO with the mass fraction of 66% (analytically pure) under stirring at room temperature₃And (3) dissolving the solution in acid, stirring for 1h, and then weighing 1.588g of cerous nitrate hexahydrate to be dissolved in the solution, wherein the solution is marked as A solution, namely the amount ratio of cerium and titanium in the A solution is 1: 10;

(2) weighing 2.6g of template agent F127, dissolving in 40ml of absolute ethyl alcohol, heating the solution to 40 ℃, stirring for one hour,subsequently, 0.4ml of 66% (analytically pure) HNO was added with stirring₃Adding 4.8g of urea into the solution after the solution is acidic, stirring for 10min, and marking the obtained solution as a solution B;

steps (3) to (4) were the same as in example 1.

Finally, tabletting, crushing and screening 40-60 mesh particles for activity evaluation, wherein the prepared catalyst is marked as catalyst B.

N on catalyst B₂Adsorption and desorption test of N₂The adsorption and desorption curves are shown in figure 2 and are represented by N₂The adsorption and desorption curves are shown in the table 1, and the related data such as the specific surface area pore volume and the like of the catalyst are obtained.

[ example 3 ] preparation of catalyst C

(1) 9.73g of tetrabutyl titanate are weighed out and dissolved in 40mL of absolute ethanol under stirring, and 0.4mL of HNO with 66 percent (analytically pure) mass fraction is added dropwise under stirring at room temperature₃And (3) making the solution acidic, stirring for 1h, and then weighing 4.98g of cerous nitrate hexahydrate to be dissolved in the solution, wherein the solution is marked as A solution, namely the amount ratio of cerium and titanium in the A solution is 1: 2.5;

(2) weighing 2.6g of template F127 and dissolving in 40ml of absolute ethanol, heating the solution to 40 ℃, stirring for a while, and then adding 0.4ml of HNO with 66 percent (analytically pure) of mass fraction while stirring₃Adding 4.8g of urea into the solution after the solution is acidic, stirring for 10min, and marking the obtained solution as a solution B;

steps (3) to (4) were the same as in example 1.

Finally, the catalyst is pressed into tablets, crushed and screened to obtain particles of 40-60 meshes for activity evaluation, and the prepared catalyst is marked as catalyst C.

EXAMPLE 4 preparation of catalyst D, E

Step (1) is the same as step (1) in example 1.

(2) 1.3g and 1.7g of template agent F127 are respectively weighed and dissolved in 40ml of absolute ethyl alcohol, namely the ratio of the addition amount of the template agent F127 to the amount of the substances of the sum of tetrabutyl titanate and cerous nitrate hexahydrate is as follows: 1:400, 1:300, heating the solution to 40 DEG CStirring for one hour, then adding 0.4ml of 66% (analytically pure) HNO while stirring₃After the solution is acidic, 2.4g (corresponding to 1.3g of F127) of urea and 3.1g (corresponding to 1.7g of F127) of urea are respectively added into the solution and stirred for 10min, namely, the ratio of the amount of the template agent F127 to the amount of the urea substance is kept as follows: 1:400, marking the obtained solution as a solution B;

steps (3) to (4) were the same as in example 1.

Finally, the pellets of 40-60 mesh were pressed, crushed and screened for activity evaluation, and the prepared catalysts were labeled as catalysts D (corresponding to 1.3gF127) and E (corresponding to 1.7gF 127).

[ example 5 ] preparation of catalyst F, G

Steps (1) to (2) are the same as in example 1;

(3) preparing two parts of the same solution A and solution B, adding the solution A and the solution B into a 250ml hydrothermal reaction kettle, mixing, carrying out hydrothermal reaction on one part of mixed solution at 90 ℃ for 48 hours, then heating to 130 ℃, and carrying out hydrothermal reaction at 130 ℃ for 5 hours; the other part was reacted hydrothermally at 70 ℃ for 48h, then warmed to 100 ℃ and hydrothermally at 100 ℃ for 5 h.

Step (4) was the same as in example 1.

Finally, after tabletting, crushing and screening 40-60 mesh particles for activity evaluation, the prepared catalyst is marked as catalyst F (corresponding to hydrothermal reaction at 90 ℃ for 48h, then heating to 130 ℃ and hydrothermal reaction at 130 ℃ for 5h), (corresponding to hydrothermal reaction at 70 ℃ for 48h, then heating to 100 ℃ and hydrothermal reaction at 100 ℃ for 5 h).

Comparative example 1 changing the kind of the template agent

The template F127 in example 1 was replaced with 2.32g of template P123, and the rest of the procedure was the same as in example 1, to obtain a cerium-titanium catalyst using P123 as the template (the molar ratio of cerium to titanium was the same as in example 1), and finally, the catalyst was tableted, crushed and screened to 40-60 mesh for activity evaluation, and the catalyst thus obtained was designated as catalyst H.

N on catalyst H₂Adsorption and desorption test of N₂The adsorption and desorption curves are shown in figure 4 and are represented by N₂Catalyst obtained from adsorption and desorption curvesThe specific surface area and pore volume of catalyst H prepared with the P123 template are shown in Table 1, which is a significant reduction in the specific surface area and pore volume of catalyst H compared to catalysts A and B.

TABLE 1 specific surface area and pore volume of catalyst A, B, H

Comparative example 2 No template agent was added

Weighing 4.175g of titanium sulfate to be dissolved in deionized water, stirring under magnetic force until the titanium sulfate is completely dissolved, then adding 1.439g of cerous nitrate hexahydrate compound into the titanium sulfate solution under stirring, after the cerous nitrate hexahydrate is completely dissolved, slowly dropwise adding an ammonia water solution under stirring, testing the pH value of the solution, and stopping adding the ammonia water after the pH value of the solution is 10. And (3) continuously performing magnetic stirring at normal temperature for 3 hours to obtain a light yellow suspension, aging in air for two days, performing vacuum filtration, and washing impurities on the surface of the sample by using deionized water until the surface of the catalyst is neutral. The obtained sample was dried at 100 ℃ under normal pressure for 12 hours and calcined at 400 ℃ for 5 hours. Finally, tabletting, crushing and screening 40-60 mesh particles for activity evaluation, wherein the prepared catalyst is marked as a catalyst I.

Comparative example 3 changing the calcination temperature of the catalyst

Catalyst J was prepared by modifying the calcination temperature of the catalyst in step (4) of example 1 to 500 c and the remaining steps under the same conditions as in example 1.

Comparative example 4

The hydrothermal reaction conditions of the catalyst were changed, the hydrothermal reaction was carried out for 48 hours at 120 ℃ in step (3) by a one-step hydrothermal method, and the catalyst K was prepared by the same procedures as in example 1.

Example 6 application of the prepared catalyst in denitration of nitrogen oxide

NH₃The SCR activity test is carried out on an atmospheric miniature fixed bed reaction device, a reaction system is formed by a heating furnace and a reactor, and a quartz tube is used as the reactor.

The test method comprises the following steps: 0.2g of the prepared catalyst was weighed into a reactor, the total flow of feed gas was 100mL/min (standard condition), and the gas composition was: 1000ppm NO by volume; 1000ppm NH₃；3％O₂；200ppm SO₂； N₂Is the balance gas. Introducing reaction synthesis gas at normal temperature for 30min, purging air in a reaction tube, heating to 150 ℃ at a heating rate of 10 ℃ per minute, stabilizing for 2 min, heating to 550 ℃ at a heating rate of 2 ℃ per minute, and recording NH at different reaction temperatures₃、NO、N₂The amount of O. In the experimental process, the heating mode adopts temperature programming, and the temperature of the heating furnace is controlled by a temperature controller. And when the data reaches the data acquisition point, staying for a period of time, and recording the data after the data is stable.

NO and NO in reaction off-gas₂The British SIGNAL group Model 4000VM NO was used_xChemical luminescence analyzer for on-line qualitative and quantitative analysis of NH₃And N₂O was subjected to on-line qualitative and quantitative analysis using Nicolet IS50 analyzer, Thermo Fisher, USA.

NO_xCalculation method of conversion:

and (3) testing the denitration of nitrogen oxide:

0.2g of each of the catalysts A to K was placed in a fixed bed reactor and passed through N at 200 ℃₂After being cooled to room temperature for 1h by gas purging, the reaction is carried out. Evaluation conditions were as follows: the reaction space velocity is 30000mL/g/h, the reaction temperature is 150-: 1000ppm NO by volume; 1000ppm NH₃；3％O₂. The evaluation results are shown in Table 2.

As can be seen from the evaluation data of catalyst activity in Table 1, the prepared catalysts A-F can obtain very high conversion rate in the low temperature range (200 ℃ C. and 220 ℃ C.) when being used in the denitration reaction of nitrogen oxides, and the catalysts A and C can obtain NO at 220 ℃ C_xThe conversion rate can reach 100%, and the activity of the catalyst G is poor, which indicates that the control of the hydrothermal reaction condition is crucial.

TABLE 2 results of catalytic activity of catalysts A-G at 200 and 220 deg.C

Catalyst and process for preparing same	Conversion of nitrogen oxides at 200 ℃	Conversion of nitrogen oxides at 220 ℃
			A	92％	100％
B	75％	93％
			C	92％	100％
D	87％	97％
			E	88％	98％
F
		90％	98％
G				65％	86％

The catalytic performance of H-K is shown in figure 4, and the conversion rate of the catalyst H in the 200-220 ℃ interval is 86-97 percent; the conversion rate of the catalyst I in the temperature range of 200-220 ℃ is 65-88%, and compared with the catalyst A, the activity of the catalyst is obviously reduced. The conversion rate of the catalyst J in the 200-220 ℃ interval is 66-85%, and compared with the catalyst A in the figure 4, the activity is obviously reduced. The conversion rate of the catalyst K in the 200-220 ℃ interval is 26-36%, compared with the catalyst A in FIG. 4, the activity is obviously reduced and is worse than that of the catalyst H, I, J.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing a mesoporous cerium-titanium-based low-temperature denitration catalyst is characterized by comprising the following steps of:

(1) putting titanium-containing compound into water to form solution or suspension, and dropwise adding HNO under stirring₃Adding a cerium-containing compound to the solution until the solution is acidic, and uniformly mixing the solution and the solution to obtain a solution A;

2. The method according to claim 1, wherein the cerium-containing compound in step (1) is any one or more of cerium nitrate, cerium chloride and cerium phosphate; the titanium-containing compound in the step (1) is any one or more of titanium sulfate, titanium chloride, tetrabutyl titanate and ammonium titanyl oxalate.

3. The method according to claim 1, wherein the amount ratio of the cerium to titanium in the cerium-containing compound and the titanium-containing compound in step (1) is 1:2 to 1: 10.

4. The method according to claim 1, wherein the concentration of the cerium-containing compound in the solution A in step (1) is 0.05 to 0.35mol/L, and the concentration of the titanium-containing compound is 0.70 to 0.10 mol.

5. The method as claimed in claim 1, wherein the ratio of the amount of the template F127 in step (2) to the amount of the substance of the sum of the cerium-containing compound and the titanium-containing compound in step (1) is 1 (200- & 400).

6. The method as claimed in claim 1, wherein the mass ratio of the template F127 to the urea in step (2) is 1 (200-400).

7. The cerium-titanium-based low-temperature denitration catalyst prepared by the method of any one of claims 1 to 6.

8. The cerium-titanium-based low-temperature denitration catalyst according to claim 7, wherein the rare earth cerium-based low-temperature denitration catalyst contains 10% to 50% of cerium and 50% to 90% of titanium by mass, and the atomic ratio of cerium to titanium is 1 (2-10).

9. The use of the cerium-titanium-based low-temperature denitration catalyst as set forth in claim 7 in a denitration reaction of nitrogen oxides.

10. The use as claimed in claim 9, wherein the denitration reaction is carried out at a reaction temperature of 150-.