Cerium-based catalyst, preparation method thereof and application of cerium-based catalyst in catalytic oxidation of nitric oxide

Abstract

The invention relates to the technical field of denitration, and discloses a cerium-based catalyst, a preparation method thereof and application of the cerium-based catalyst in catalytic oxidation of nitric oxide. The cerium-based catalyst contains CeO2 and a transition metal oxide, and the transition metal oxide is selected from at least one of an oxide of Mn, an oxide of Co, an oxide of Ni and an oxide of Cu; on the basis of the total weight of the cerium-based catalyst, the mass content of the transition metal oxide is 0.5-20%. The cerium-based catalyst provided by the invention is prepared by taking rare earth oxide CeO2 as a unique or main catalyst carrier and adding a small amount of specific transition metal oxide. Compared with a traditional catalyst, the cerium-based catalyst has the advantages that the catalytic activity is obviously improved, and high-temperature pretreatment hardly affects the performance of the catalyst and even has a positive effect.

Description

Technical Field

[0001] The present invention relates to the technical field of denitration, and in particular to a cerium-based catalyst and a preparation method thereof, and application of the cerium-based catalyst in catalytic oxidation of nitrogen monoxide. Background Art

[0002] Nitrogen oxides (NOx) are one of the main atmospheric pollutants that form nitric acid rain and photochemical smog and damage the ozone layer. They are highly toxic and have an annual global emission of 35-58 million tons. Nitrogen oxides (NOx) exist in the form of various compounds, including NO, N2O, N2O3, NO2, N2O4, and N2O5. NO and NO2 are the most abundant nitrogen oxides in the atmosphere and cause the most serious air pollution. Among them, nitric oxide (NO) accounts for 90%-95% of the total NOx, causing serious harm to the natural environment and human production and life. Using catalytic oxidation to oxidize NO in flue gas to NO2 and then absorb it has become a hot spot in the research of denitrification technology at home and abroad. Among them, the catalytic oxidation of NO to NO2 is the key and difficulty. In the research of catalysts for this method, low-temperature activity, sulfur resistance, and water poisoning resistance are the three most critical elements in catalyst development. Under actual working conditions, the technical requirements can be met by partially oxidizing NO in the flue gas to NO2 with an oxidation degree of 50%-60%. Therefore, the development of stable oxidation catalysts with good medium and low temperature performance has important theoretical significance and application value.

[0003] Chinese patent application CN111167477A discloses a method for preparing a cobalt-modified NO catalytic oxidant, in which a viscous catalyst with Ru, Co, Ce and Zr as active components is prepared by coprecipitation. The catalyst has good catalytic oxidation activity and sulfur and water resistance. It can be used in the conditions of 700ppm NO, 5vol% O2, N2 carrier gas, temperature of 250℃ and space velocity of 30000h -1 Under the following conditions, the NO oxidation rate can reach 60%, at 200ppm SO2, 5vol% H2O, 700ppm NO, 5vol% O2, temperature of 250℃, and space velocity of 30000h -1 Under the same conditions, the oxidation activity was above 35% for 12 hours continuously.

[0004] Chinese patent application CN108421558A discloses a strip-shaped manganese-based catalyst for NO catalytic oxidation and a preparation method thereof. The catalyst is prepared by a wet impregnation method, with manganese oxide as a catalyst precursor and H-β molecular sieve or ZSM-5 molecular sieve as a catalyst carrier. The manganese-based catalyst is easy to knead and extrude during the molding operation, has good plasticity, is not easy to deform, and the prepared catalyst has high mechanical strength and good catalytic performance, which can well meet the requirements of industrial applications.

[0005] Chinese patent CN106513009B discloses a catalyst for NO catalytic oxidation and its preparation method, using vanadium-titanium iron concentrate as a carrier and manganese oxide as an active component, and adopts an impregnation method to prepare a composite catalyst for NO catalytic oxidation. The catalyst raw materials are cheap and easy to obtain, the preparation method is simple, the catalytic conversion temperature window is wide, and the maximum conversion rate of NO to NO2 can reach 81.7%, which can achieve the effect of synergistic purification of nitrogen oxides by wet desulfurization process, and has broad prospects for industrial application.

[0006] The catalysts with certain NO oxidation performance and their preparation methods disclosed in the prior art have relatively complex components, many factors affecting the performance of the catalysts during the preparation process, and relatively high preparation costs, making it difficult to industrialize production. In addition, the prior art rarely mentions the medium and low temperature performance of the catalysts, making it difficult to realize application under working conditions. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems that the components of the catalyst with NO oxidation performance in the prior art are relatively complex, there are many factors affecting the performance of the catalyst during the preparation process, the preparation cost is relatively high, and it is not easy to industrialize production. A cerium-based catalyst and a preparation method thereof and the use of the cerium-based catalyst in catalytic oxidation of nitrogen monoxide are provided. The cerium-based catalyst provided by the present invention has simple components, has the advantage of achieving NO oxidation under medium and low temperature conditions, and the preparation method is simple, easy to operate, and has strong promotion.

[0008] In order to achieve the above object, the first aspect of the present invention provides a cerium-based catalyst, the cerium-based catalyst contains CeO2 and a transition metal oxide, wherein the transition metal oxide is selected from at least one of an oxide of Mn, an oxide of Co, an oxide of Ni and an oxide of Cu;

[0009] Based on the total weight of the cerium-based catalyst, the mass content of the transition metal oxide is 0.5-20%.

[0010] Preferably, the specific surface area of ​​the cerium-based catalyst is ≤100m 2 / g, preferably 10-100m 2 / g.

[0011] Preferably, the particle size of the cerium-based catalyst is ≤300 nm.

[0012] The second aspect of the present invention provides a method for preparing the cerium-based catalyst as described above, the method comprising the following steps:

[0013] (1) preparing a precursor salt solution by mixing a cerium salt and a transition metal salt, wherein the transition metal in the transition metal salt is selected from at least one of Mn, Co, Ni and Cu;

[0014] (2) adding an acid to the precursor salt solution to form a mixed solution;

[0015] (3) Under stirring conditions, co-precipitating the alkali solution and the mixed solution, and controlling the pH value of the co-precipitation to be 8-11. After the co-precipitation is completed, stirring is continued, and then solid-liquid separation is performed, and the solid product is washed and dried to obtain a precursor;

[0016] (4) calcining the precursor.

[0017] Preferably, in step (1), the total metal ion concentration of cerium ions and transition metal ions in the precursor salt solution is 0.2 to 0.6 mol / L.

[0018] Preferably, in step (1), the cerium salt is cerous nitrate.

[0019] Preferably, in step (1), the transition metal salt is selected from at least one of nitrate, acetate, sulfate and hydrochloride.

[0020] Preferably, the transition metal salt is selected from at least one of manganese nitrate, manganese acetate, manganese sulfate, manganese chloride, cobalt nitrate, cobalt sulfate, cobalt chloride, nickel nitrate, nickel sulfate, nickel chloride, copper nitrate, copper sulfate and copper chloride.

[0021] Preferably, in step (2), the molar number of the acid is 0.5 to 6 times the total molar number of the cerium salt and the transition metal salt in the precursor salt solution.

[0022] Preferably, the acid is nitric acid and / or hydrochloric acid.

[0023] Preferably, in step (3), the concentration of metal cations in the alkali solution is 0.2 to 1.5 mol / L.

[0024] Preferably, the alkali in the alkali solution is selected from NaOH and / or Na2CO3.

[0025] Preferably, the volume ratio of the alkali solution to the mixed solution is 0.5-3:1.

[0026] Preferably, in step (3), the stirring is continued for 2 to 6 hours.

[0027] Preferably, in step (4), the calcination conditions include: a temperature of 400 to 800° C., a time of 4 to 6 hours, and an air atmosphere.

[0028] A third aspect of the present invention provides a use of the cerium-based catalyst described above in the catalytic oxidation of nitric oxide.

[0029] A fourth aspect of the present invention provides a method for catalytically oxidizing nitrogen monoxide, the method comprising: contacting the cerium-based catalyst described above with a reaction gas containing nitrogen monoxide, oxygen and an inert gas to react;

[0030] Wherein, the reaction temperature is 175-400°C, preferably 275-325°C.

[0031] Preferably, the total flow rate of the reaction gas is 0.8-1.2 L / min, and the air velocity is (4-6)×10 5 h -1 .

[0032] Preferably, the content of nitric oxide in the reaction gas is 250-350 ppm, and the volume content of oxygen is 4-6%.

[0033] Preferably, the loading amount of the cerium-based catalyst is 0.1 to 0.15 g.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] (1) The cerium-based catalyst provided by the present invention uses rare earth oxide CeO2 as the sole or main catalyst carrier, and a small amount of specific transition metal oxide is added. Compared with traditional catalysts, the cerium-based catalyst of the present invention not only has significantly improved catalytic activity, but also has almost no effect on catalyst performance after high-temperature pretreatment, and even has a positive effect.

[0036] (2) The cerium-based catalyst of the present invention is prepared by a coprecipitation method, with rare earth oxide CeO2 as the sole or main catalyst carrier and a small amount of transition metal oxide added. Therefore, the preparation method is simple and easy to operate, and the catalyst components are simple and low in cost. At the same time, compared with the catalyst obtained by the traditional preparation method, the cerium-based catalyst of the present invention not only has significantly improved catalytic activity, but also has almost no effect on the catalyst performance after high-temperature pretreatment, and even has a positive effect.

[0037] (3) The catalyst prepared by the method described in the present invention is used for NO catalytic oxidation and achieves partial oxidation of NO at about 250°C. Its performance basically meets the requirements of the selective catalytic oxidation absorption technology (SCO) for NO oxidation rate. Therefore, it is a NO catalytic oxidation catalyst with industrial application prospects.

[0038] (4) The present invention can prepare a cerium-based catalyst by mixing a metal salt solution and an acid solution, adjusting the pH with an alkali solution, and drying the resulting precipitate and then calcining it at a high temperature. Therefore, the preparation method (using a parallel flow co-precipitation method) and the synthesis process of the present invention are simple and easy to operate and control, low in cost, suitable for application and promotion, and meet the requirements of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 are SEM (transmission electron microscope) images of the catalysts prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2;

[0040] Figure 2 It is a catalytic activity diagram of the catalysts prepared in Example 1, Example 2, Example 3, and Comparative Example 1 under simulated flue gas conditions. DETAILED DESCRIPTION

[0041] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0042] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0043] The cerium-based catalyst provided by the present invention contains CeO2 and a transition metal oxide, wherein the transition metal oxide is selected from at least one of an oxide of Mn, an oxide of Co, an oxide of Ni and an oxide of Cu. In a preferred case, the transition metal oxide is selected from one of an oxide of Mn, an oxide of Co, an oxide of Ni and an oxide of Cu; in this embodiment, the cerium-based catalyst contains only a rare earth oxide CeO2 and a transition metal oxide, and still has good catalytic performance.

[0044] The cerium-based catalyst provided by the present invention has simple ingredients, contains rare earth oxide CeO2 as the only or main catalyst carrier, and also contains a small amount of transition metal oxide. In some embodiments, the mass content of the transition metal oxide can be 0.5-20% based on the total weight of the cerium-based catalyst.

[0045] In some embodiments, the BET specific surface area of ​​the cerium-based catalyst is ≤100 m 2 / g, preferably 10-100m 2 / g. In the present invention, the particle size distribution of the cerium-based catalyst is relatively wide. In some embodiments, the particle size of the cerium-based catalyst is ≤300nm.

[0046] The method for preparing a cerium-based catalyst provided by the present invention comprises the following steps:

[0047] (1) preparing a precursor salt solution by mixing a cerium salt and a transition metal salt, wherein the transition metal in the transition metal salt is selected from at least one of Mn, Co, Ni and Cu;

[0048] (2) adding an acid to the precursor salt solution to form a mixed solution;

[0049] (3) Under stirring conditions, co-precipitating the alkali solution and the mixed solution, and controlling the pH value of the co-precipitation to be 8-11. After the co-precipitation is completed, stirring is continued, and then solid-liquid separation is performed, and the solid product is washed and dried to obtain a precursor;

[0050] (4) calcining the precursor.

[0051] In the method described in the present invention, a precursor solution is first prepared, then an acid is added to the precursor solution, and then an alkali solution is added to control the pH value of the coprecipitation to 8-11, and finally the precursor obtained by coprecipitation is roasted to obtain the cerium-based catalyst of the present invention. The preparation method is simple and easy to operate, and the catalyst components are simple and low in cost. Compared with the catalyst obtained by the traditional preparation method, the cerium-based catalyst prepared by the method described in the present invention not only has significantly improved catalytic activity, but also has almost no effect on the catalyst performance due to high-temperature pretreatment, and even has a positive effect.

[0052] In the process of preparing the precursor salt solution in step (1), the dosage ratio of the cerium salt and the transition metal salt can be specifically determined according to the components of the catalyst finally obtained. In one embodiment, the total metal ion concentration of cerium ions and transition metal ions in the precursor salt solution in step (1) can be 0.2 to 0.6 mol / L, for example, 0.2 mol / L, 0.2.5 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L or 0.6 mol / L. In a more preferred embodiment, the preparation process of the precursor salt solution includes: weighing the cerium salt and the transition metal salt according to the catalyst components and dissolving them in deionized water.

[0053] Preferably, the transition metal in the transition metal salt is one of Mn, Co, Ni and Cu. The catalyst is prepared by using a transition metal salt and a cerium salt. The preparation method is simple, easy to operate, and low in cost. The obtained product has a simple composition, containing only rare earth oxide CeO2 and a transition metal oxide, but it still has good catalytic performance.

[0054] In the present invention, the cerium salt can be any salt of cerium with various metal elements known in the art. In a preferred embodiment, in step (1), the cerium salt is cerous nitrate, more preferably cerous nitrate hexahydrate (cerous nitrate hexahydrate).

[0055] In the present invention, the transition metal salt can be various salts commonly found in the art. In some embodiments, the transition metal salt in step (1) can be selected from at least one of nitrates, acetates, sulfates and hydrochlorides. In some more preferred embodiments, the transition metal salt can be selected from at least one of manganese nitrate, manganese acetate, manganese sulfate, manganese chloride, cobalt nitrate, cobalt sulfate, cobalt chloride, nickel nitrate, nickel sulfate, nickel chloride, copper nitrate, copper sulfate and copper chloride.

[0056] The inventors have found that in the method of the present invention, before adding alkali to the precursor salt solution for coprecipitation, adding acid to the precursor salt solution for treatment can improve the performance of the catalyst. In some embodiments, the acid is nitric acid and / or hydrochloric acid. In the present invention, the acid can be a concentrated acid. In a more specific embodiment, the concentration of the nitric acid can be 60-70% by mass; the concentration of the hydrochloric acid can be 35-40% by mass.

[0057] In some preferred embodiments, in step (2), the molar number of the acid is 0.5 to 6 times the total molar number of the cerium salt and the transition metal salt in the precursor salt solution.

[0058] In the present invention, the alkali solution added in step (3) has two functions, one of which is to act as a precipitant to co-precipitate the cerium salt and the transition metal salt in the precursor salt solution, and the other is to control the pH value of the co-precipitation to be 8 to 11. In the present invention, the process of the co-current co-precipitation includes: titrating the alkali solution and the mixed solution into the reaction device for co-precipitation. Since the acid is added to the mixed solution, it is acidic, and therefore, the alkali solution needs to be dripped into the reaction device quickly and in large quantities to ensure that the pH value of the co-precipitation reaches 8 to 11.

[0059] In the present invention, the alkali in the alkali solution is selected from NaOH and / or Na2CO3. In some embodiments, the concentration of metal cations in the alkali solution in step (3) can be 0.2 to 0.8 mol / L. In a preferred embodiment, the alkali in the alkali solution is NaOH and Na2CO3; and the molar concentration ratio of NaOH to Na2CO3 is 1:1.

[0060] In the method of the present invention, there is no particular limitation on the time of the co-precipitation, as long as the mixed solution is dripped completely. In some embodiments, the volume ratio of the alkali solution to the mixed solution can be 0.5 to 3:1.

[0061] In some preferred embodiments, in order to make the coprecipitation more complete, in step (3), the stirring time may be continued for 2 to 6 hours.

[0062] In step (3), the solid-liquid separation method can be a commonly used method in the art, such as filtration. In one embodiment, the washing process includes: washing the solid product with deionized water until the washing liquid is neutral. In a more preferred embodiment, the drying conditions in step (3) include: a temperature of 60 to 90° C. and a time of 12 to 24 hours.

[0063] In step (4) of the present invention, the calcination can be carried out in a muffle furnace. In some preferred embodiments, the calcination conditions include: a temperature of 400 to 800° C. and a time of 4 to 6 hours. In the present invention, the calcination can be carried out in an air atmosphere.

[0064] The present invention can prepare a cerium-based catalyst by mixing a metal salt solution and an acid solution, adjusting the pH with an alkali solution, and drying the obtained precipitate and then calcining it at a high temperature. Therefore, the preparation method (adopting a parallel flow co-precipitation method) and the synthesis process of the present invention are simple and easy to operate and control, with low cost, suitable for application and promotion, and meet the requirements of industrial production.

[0065] The present invention also provides a use of the cerium-based catalyst described above in catalytic oxidation of nitrogen monoxide. The cerium-based catalyst described in the present invention has simple components and has the advantage of achieving oxidation of NO under medium and low temperature conditions.

[0066] The present invention also provides a method for catalytically oxidizing nitrogen monoxide, which comprises: contacting the cerium-based catalyst mentioned above with a reaction gas containing nitrogen monoxide, oxygen and an inert gas to react.

[0067] In some embodiments, the reaction temperature is 175-400° C., preferably 275-325° C. When the reaction temperature is 275-325° C., the cerium-based catalyst can achieve a good catalytic oxidation rate of nitrogen monoxide.

[0068] In some embodiments, the content of nitric oxide in the reaction gas may be 250-350 ppm, and the volume content of oxygen may be 4-6%. In other embodiments, the total flow rate of the reaction gas is 0.8-1.2 L / min, and the space velocity is (4-6)×10 5 h -1 .

[0069] In the present invention, the method for catalytic oxidation of nitrogen monoxide can be implemented in a fixed bed quartz reactor. The loading amount of the cerium-based catalyst in the fixed bed quartz reactor can be determined according to the total flow rate of the reaction gas. In some embodiments, the loading amount of the cerium-based catalyst is 0.1 to 0.15 g.

[0070] The cerium-based catalyst prepared by the method described in the present invention is used for NO catalytic oxidation, and partial oxidation of NO is achieved at about 250° C. The performance basically meets the requirements of the selective catalytic oxidation absorption technology (SCO) for NO oxidation rate, and a good catalytic oxidation rate can be achieved between 275 and 325° C. Therefore, it is a NO catalytic oxidation catalyst with industrial application prospects.

[0071] The following examples further illustrate the cerium-based catalyst and its preparation method as well as the application of the cerium-based catalyst in catalytic oxidation of nitrogen monoxide. The examples are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0072] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0073] Example 1

[0074] (1) Weighing 8.6 g of cerous nitrate hexahydrate and 0.7 g of manganese nitrate, dissolving them in 50 mL of deionized water, and stirring them at room temperature for 0.5 h to obtain a precursor salt solution, wherein the concentration of cerium ions is 0.4 mol / L and the concentration of manganese ions is 0.078 mol / L;

[0075] (2) adding 4 mL of concentrated nitric acid solution to the precursor salt solution, stirring thoroughly for 1 h until the mixture is uniformly mixed to obtain a mixed solution, wherein the molar number of nitric acid is 0.5 times the total molar number of cerium salt and manganese salt in the precursor salt solution;

[0076] (3) Weigh 16 g of NaOH and 42.4 g of Na2CO3 and dissolve them in 1 L of deionized water to prepare a mixed alkali solution with a molar concentration of 0.4 mol / L NaOH and 0.4 mol / L Na2CO3;

[0077] (4) Under the condition of room temperature and magnetic stirring, the mixed solution and the mixed alkali solution are co-precipitated in parallel. During the titration process, the pH value of the precipitate is controlled to be about 11 until the mixed solution is titrated completely, wherein the volume ratio of the mixed alkali solution to the mixed solution is 0.5. After the titration, the mixture is stirred vigorously for 2 hours at room temperature, filtered, and the filter cake is washed with deionized water until the pH value of the filtrate is about 7. The filter cake is dried at 60°C for 12 hours, and placed in a muffle furnace, and calcined at 450°C in an air atmosphere for 6 hours to obtain catalyst A1.

[0078] According to ICP measurement, the mass content of manganese oxide (mixture of manganese oxides) in Catalyst A1 prepared in Example 1 was about 5%.

[0079] Example 2

[0080] (1) Weighing 8.6 g of cerous nitrate hexahydrate and 1.16 g of cobalt nitrate, dissolving them in 50 mL of deionized water, and stirring them at room temperature for 0.5 h to obtain a precursor salt solution, wherein the concentration of cerium ions is 0.4 mol / L and the concentration of cobalt ions is 0.127 mol / L;

[0081] (2) adding 4 mL of concentrated nitric acid solution to the precursor salt solution, stirring thoroughly for 1 h until the mixture is uniformly mixed, to obtain a mixed solution, wherein the molar number of nitric acid is 1 times the total molar number of cerium salt and cobalt salt in the precursor salt solution;

[0082] (3) Weigh 16 g of NaOH and 42.4 g of Na2CO3 and dissolve them in 1 L of deionized water to prepare a mixed alkali solution with a molar concentration of 0.4 mol / L NaOH and 0.4 mol / L Na2CO3;

[0083] (4) Under the condition of room temperature and magnetic stirring, the mixed solution and the mixed alkali solution are co-precipitated in parallel. During the titration process, the pH value of the precipitate is controlled to be about 10.5 until the mixed solution is titrated completely, wherein the volume ratio of the mixed alkali solution to the mixed solution is 1.2. After the titration, the mixture is stirred vigorously for 4 hours at room temperature, filtered and washed with deionized water until the pH value of the filtrate is about 7. The filter cake is dried at 90°C for 12 hours, and placed in a muffle furnace, and calcined at 750°C in an air atmosphere for 6 hours to obtain catalyst A2.

[0084] According to ICP measurement, the mass content of cobalt oxide (mixture of cobalt oxides) in the catalyst A2 prepared in this Example 2 was 10%.

[0085] Example 3

[0086] (1) Weighing 8.6 g of cerous nitrate hexahydrate and 1.16 g of cobalt nitrate, dissolving them in 50 mL of deionized water, and stirring at room temperature for 0.5 h to obtain a precursor salt solution, wherein the concentration of cerium ions is 0.4 mol / L and the concentration of manganese ions is 0.156 mol / L;

[0087] (2) adding 4 mL of concentrated nitric acid solution to the precursor salt solution, stirring thoroughly for 1 h until the mixture is uniformly mixed to obtain a mixed solution, wherein the molar number of nitric acid is 0.5 times the total molar number of cerium salt and cobalt salt in the precursor salt solution;

[0088] (3) Weigh 16 g of NaOH and 42.4 g of Na2CO3 and dissolve them in 1 L of deionized water to prepare a mixed alkali solution with a molar concentration of 0.4 mol / L NaOH and 0.4 mol / L Na2CO3;

[0089] (4) Under the condition of room temperature and magnetic stirring, the mixed solution and the mixed alkali solution are co-precipitated in parallel. During the titration process, the pH value of the precipitate is controlled to be about 10.5 until the mixed solution is titrated completely, wherein the volume ratio of the mixed alkali solution to the mixed solution is 0.5. After the titration, the mixture is stirred vigorously for 4 hours at room temperature, filtered and washed with deionized water until the pH value of the filtrate is about 7. The filter cake is dried at 90°C for 12 hours, and placed in a muffle furnace, and calcined at 450°C in an air atmosphere for 6 hours to obtain catalyst A2.

[0090] According to ICP measurement, the mass content of cobalt oxide (mixture of cobalt oxides) in the catalyst A3 prepared in this Example 3 was about 10%.

[0091] Comparative Example 1

[0092] The method of Example 1 is followed, except that manganese nitrate is not added in step (1) and step (2) is not performed.

[0093] Specific operations include:

[0094] Weigh 8.6 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), dissolve it in 50 mL of deionized water, and stir it at room temperature for 0.5 h to prepare a metal salt solution;

[0095] Weigh 16g of NaOH and 42.4g of Na2CO3 and dissolve them in 1L of deionized water to prepare a mixed alkali solution with a molar concentration of 0.4mol / L NaOH and 0.4mol / L Na2CO3;

[0096] Under the conditions of room temperature and magnetic stirring, the metal salt solution and the mixed alkali solution were co-precipitated in parallel. During the titration process, the pH value of the precipitate was controlled to be about 11 until the metal salt solution was titrated completely, wherein the volume ratio of the mixed alkali solution to the metal salt solution was 0.5. After the titration, the mixture was stirred vigorously for 2 hours at room temperature and washed with deionized water until the pH value of the filtrate was about 7. The filter cake was dried at 60°C for 12 hours, and placed in a muffle furnace, and calcined at 450°C in an air atmosphere for 6 hours to obtain the catalyst DA1.

[0097] Comparative Example 2

[0098] The method of Example 2 is followed, except that cobalt nitrate is not added in step (1) and step (2) is not performed.

[0099] Specific operations include:

[0100] Weigh 8.6 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), dissolve it in 50 mL of deionized water, and stir it at room temperature for 0.5 h to prepare a metal salt solution;

[0101] Weigh 16g of NaOH and 42.4g of Na2CO3 and dissolve them in 1L of deionized water to prepare a mixed alkali solution with a molar concentration of 0.4mol / L NaOH and 0.4mol / L Na2CO3;

[0102] Under the conditions of room temperature and magnetic stirring, the above metal salt solution and the mixed alkali solution were co-precipitated in parallel. During the titration process, the pH value of the precipitate was controlled to be about 10.5 until the mixed solution was titrated completely, wherein the volume ratio of the mixed alkali solution to the mixed solution was 1.2. After the titration, the mixture was stirred vigorously for 4 hours at room temperature, filtered and washed with deionized water until the pH value of the filtrate was about 7. The filter cake was dried at 90°C for 12 hours, and placed in a muffle furnace, and calcined at 750°C in an air atmosphere for 6 hours to obtain the catalyst DA2.

[0103] Test Example 1

[0104] The specific surface areas of the catalysts prepared in the examples and comparative examples were tested using BET. The results are shown in Table 1.

[0105] Table 1

[0106] serial number <![CDATA[Specific surface area (m 2 / g)]]> Example 1 80.81 Example 2 35.62 Example 3 72.68 Comparative Example 1 80.98 Comparative Example 2 38.79

[0107] Test Example 2

[0108] The catalysts prepared in the examples and comparative examples were characterized by transmission electron microscopy. The particle sizes of the catalysts are shown in Table 2.

[0109] from Figure 1It can be seen from the SEM electron microscope image that the sample in comparative example 1 presents a loose sheet structure, and the sample in comparative example 2 presents a thick block structure. The sample in example 1 presents a small nanoparticle structure, and the nanoparticles of the secondary microstructure are about 6nm; the sample in example 2 also presents a nanoparticle structure, and the particle size distribution is more than 50nm.

[0110] Table 2

[0111] serial number Particle size (nm) Example 1 6.2 Example 2 52.0 Example 3 8.9 Comparative Example 1 8.0 Comparative Example 2 35.6

[0112] Test Example 3 Evaluation of Catalyst Performance

[0113] A fixed bed quartz reactor was used to evaluate the catalyst activity. The catalyst bed temperature was controlled by a programmable temperature controller. The reaction gas was mixed online by three mass flow meters. The reaction gas was 300ppm NO, 5% O2, and Ar gas was used as the balance gas. The total reaction gas flow rate was controlled to 1L / min, and the space velocity was 5×105h -1 , the catalyst loading amount is 0.12g (20-40 mesh), the temperature range is 175-400℃, 25℃ is a heating point, the heating rate is 5℃ / min, heating and ventilation are carried out simultaneously, and data collection is carried out after the concentrations of NOx and NO2 at each temperature point remain stable. At the beginning of the evaluation, the initial temperature of 175℃ needs to be maintained for a long time, and the temperature evaluation will start after the NOx concentration reaches the set value. The nitrogen monoxide conversion rates of the catalysts prepared in the examples and comparative examples at different temperatures are shown in Table 3. The catalytic activity diagram of the catalysts prepared in Example 1, Example 2, Example 3, and Comparative Example 1 under simulated flue gas conditions is shown in Figure 3. Figure 2 As shown, the control group in the figure means no catalyst was added.

[0114] Table 3

[0115]

[0116] Figure 2 The catalytic oxidation conditions of the catalysts prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 under simulated flue gas exhaust are shown. From the results in the figure, it can be seen that the catalytic performance of the catalysts prepared in Example 1 and Example 2 under simulated flue gas exhaust can achieve a good catalytic oxidation rate between 275 and 325°C, which can basically meet the requirements under working conditions.

[0117] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A cerium-based catalyst, characterized in that The cerium-based catalyst contains CeO2 and a transition metal oxide, wherein the transition metal oxide is selected from at least one of an oxide of Mn, an oxide of Co, an oxide of Ni and an oxide of Cu; Based on the total weight of the cerium-based catalyst, the mass content of the transition metal oxide is 0.5-20%.

2. The cerium-based catalyst according to claim 1, characterized in that The specific surface area of ​​the cerium-based catalyst is ≤100m 2 / g, preferably 10-100m 2 / g; Preferably, the particle size of the cerium-based catalyst is ≤300 nm.

3. A method for preparing a cerium-based catalyst according to claim 1 or 2, characterized in that: The method comprises the following steps: (1) preparing a precursor salt solution by mixing a cerium salt and a transition metal salt, wherein the transition metal in the transition metal salt is selected from at least one of Mn, Co, Ni and Cu; (2) adding an acid to the precursor salt solution to form a mixed solution; (3) Under stirring conditions, co-precipitating the alkali solution and the mixed solution, and controlling the pH value of the co-precipitation to be 8-11. After the co-precipitation is completed, stirring is continued, and then solid-liquid separation is performed, and the solid product is washed and dried to obtain a precursor; (4) calcining the precursor.

4. The method according to claim 3, characterized in that In step (1), the total metal ion concentration of cerium ions and transition metal ions in the precursor salt solution is 0.2 to 0.6 mol / L.

5. The method according to claim 3 or 4, characterized in that: In step (1), the cerium salt is cerous nitrate.

6. The method according to any one of claims 3 to 5, characterized in that: In step (1), the transition metal salt is selected from at least one of nitrate, acetate, sulfate and hydrochloride; Preferably, the transition metal salt is selected from at least one of manganese nitrate, manganese acetate, manganese sulfate, manganese chloride, cobalt nitrate, cobalt sulfate, cobalt chloride, nickel nitrate, nickel sulfate, nickel chloride, copper nitrate, copper sulfate and copper chloride.

7. The method according to any one of claims 3 to 6, characterized in that: In step (2), the molar number of the acid is 0.5 to 6 times the total molar number of the cerium salt and the transition metal salt in the precursor salt solution; Preferably, the acid is nitric acid and / or hydrochloric acid.

8. The method according to any one of claims 3 to 7, characterized in that: In step (3), the concentration of metal cations in the alkali solution is 0.2 to 1.5 mol / L; Preferably, the alkali in the alkali solution is selected from NaOH and / or Na2CO3; Preferably, the volume ratio of the alkali solution to the mixed solution is 0.5-3:

1.

9. The method according to any one of claims 3 to 8, characterized in that: In step (3), the stirring is continued for 2 to 6 hours.

10. The method according to any one of claims 3 to 9, characterized in that: In step (4), the calcination conditions include: a temperature of 400 to 800° C., a time of 4 to 6 hours, and an air atmosphere.

11. Use of the cerium-based catalyst according to claim 1 or 2 in catalytic oxidation of nitrogen monoxide.

12. A method for catalytic oxidation of nitric oxide, characterized in that: The method comprises: contacting the cerium-based catalyst according to claim 1 or 2 with a reaction gas containing nitrogen monoxide, oxygen and an inert gas to react; Wherein, the reaction temperature is 175-400°C, preferably 275-325°C.

13. The method according to claim 12, characterized in that The total flow rate of the reaction gas is 0.8-1.2 L / min, and the space velocity is (4-6)×10 5 h -1 ; Preferably, the content of nitric oxide in the reaction gas is 250-350 ppm, and the volume content of oxygen is 4-6%; Preferably, the loading amount of the cerium-based catalyst is 0.1 to 0.15 g.

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