CN113996305A

CN113996305A - Medium-low temperature catalytic decomposition of N2O composite oxide catalyst and preparation method and application thereof

Info

Publication number: CN113996305A
Application number: CN202111390562.8A
Authority: CN
Inventors: 熊英; 赵玉梅; 于海彪; 王月娇; 崔俊硕; 高婧; 冯晓庚; 娄振宁; 单炜军
Original assignee: Liaoning University
Current assignee: Liaoning University
Priority date: 2021-11-23
Filing date: 2021-11-23
Publication date: 2022-02-01

Abstract

The invention relates to the technical field of catalytic materials and atmospheric pollution control. In particular relates to a medium-low temperature catalytic decomposition method for N₂O composite oxide catalyst, and a preparation method and application thereof. The catalyst is K_yGd_xM comprises an active component and an auxiliary agent, wherein the active component is a transition metal oxide Co₃O₄NiO and CuO, the auxiliary agent is one of rare earth metal Gd or alkali metal K, wherein y refers to the molar ratio of the added alkali metal K to the transition metal M, and 0<y is less than or equal to 0.03, x is the molar ratio of the added rare earth metal Gd to the transition metal M, 0<x is less than or equal to 0.1. The catalyst prepared by the invention not only has excellent catalytic N₂O decomposition activity and in actual N₂For NO in O waste gas treatment process_x、O₂、H₂O shows stronger resistance and is suitable for application in actual industrial production.

Description

Medium-low temperature catalytic decomposition of N2O composite oxide catalyst and preparation method and application thereof

Technical Field

The invention relates to a medium-low temperature catalytic decomposition method for N₂A composite oxide catalyst of O and a preparation method and application thereof belong to the technical field of catalytic materials and atmospheric pollution control.

Background

As a greenhouse gas, N₂O has a specific CO₂，CH₄Stronger potential value of greenhouse effect. In addition, it is stable in the troposphere and, once delivered to the stratosphere, is highly damaging to the ozone layer. Apart from nature, N₂The source of O is mainly human industrial production, including nitric acid and adipic acid production, tail gas discharged by fuel combustion and the like. Thus, N discharged from industrial production is eliminated₂O is one of the problems to be solved in the current environmental field. For decades, direct catalysis of N₂Decomposition of O to N₂And O₂Has been recognized as eliminating N₂O the most promising solution. To date, related researchers have developed a number of different types of catalysts for the direct catalytic decomposition of N₂O, such as a supported noble metal catalyst, a molecular sieve based catalyst, a metal oxide catalyst. Among them, the metal oxide catalyst is of interest to researchers because of its simple preparation method, environmental friendliness, low cost of raw materials, easy modulation of composition, and generally exhibiting superior medium and low temperature catalytic activity.

The main factors influencing the performance of the metal oxide catalyst comprise the preparation method, the calcination temperature, the doping of the auxiliary agent, the specific surface area and the crystalParticle size and presence of impurity gases, etc. Researchers have found that the introduction of another metal or metals as a promoter to a transition metal oxide helps to increase its catalytic activity. The catalytic journal (Catalysis Letters,118(2007):64-68) reports the addition of alkali metal Cs to NiO catalytic N₂The influence of O decomposition performance, and the experimental result shows that N is₂The temperature of O catalytic decomposition is reduced from 350 ℃ to 250 ℃, and T₅₀About 200 deg.c. Although the addition of the alkali metal additive has a remarkable effect of improving the catalytic performance of the transition metal oxide, the alkali metal additive has NO effect on actual tail gas of nitric acid plants, adipic acid plants and the like_x、H₂O、O₂、CO₂The poor gas resistance limits the practical N₂And (4) application in O treatment.

Then, researchers have developed researches on various types of auxiliaries, which mainly include: alkaline earth metals (Ca, Sr, Ba), transition metals (Cu, Zn, Ni, Fe, Mn), rare earth metals (La, Ce, Y, Pr, Sm, Tb) or other large radius metals (Pb, Ag, Bi). These metals not only increase the number of active sites of the transition metal oxide but also weaken the M — O (M ═ Co, Ni, Cu) bond to some extent as an aid. Although the weakening effect of the corresponding auxiliary agents on M-O bonds in the catalyst is far less than that of alkali metals, the introduction of the auxiliary agents greatly increases the number of active sites of metal oxides and the tolerance degree of the catalyst on impurity gases, and solves the problem that the performance of the alkali metal doped composite oxide catalyst is poor in impurity gas resistance. The patent CN102513117A research discloses a composite oxide composed of copper oxide and cerium oxide, which utilizes the synergistic effect of cerium atoms entering copper oxide crystal lattices to greatly improve the N ratio of the catalyst₂The activity and stability of O catalytic decomposition are realized, and N is realized at 400 DEG C₂Complete decomposition of O. The patent CN104624203A adopts a simple coprecipitation method to research and disclose a PbO and Co oxide matrix composite catalyst, which still maintains higher catalytic activity at low temperature (300 ℃) and has CO resistance₂、SO₂And the like, have excellent resistance.

Recently, the Zhao team (cat. commun.,2020,137,105948) has exchanged alkali goldThe metal K and the rare earth metal Y are jointly used as an auxiliary agent to modify Co₃O₄Prepared K/Y₂O₃-Co₃O₄The catalyst has good low-temperature N₂Catalytic activity for O decomposition (N at 400 ℃ C.)₂The conversion of O is stabilized at 100%) and a small amount of O is present in the reaction atmosphere₂And H₂And the better catalytic performance and physical properties can be kept when the catalyst is O. Therefore, the combination of the alkali metal and other metals with strong tolerance to impurity gases can further improve the catalytic activity and the tolerance to impurity gases of the metal oxide catalyst.

A series of rare earth metals Pr, Sm and Tb modified Co were synthesized by Abu-Zied group (J.Nanomater.,2015,580582; Catal.,2016,6, 70; appl.Surf.Sci.,2017,419,399-₃O₄And Gd, La, Sm, Nd, Pr, Tb and Y modified NiO catalyst for catalyzing and decomposing N₂O, they found that rare earth metals are prevalent with Co₃O₄NiO catalytic decomposition of N₂The activity of O reaction has certain promotion effect, wherein Gd and Y have the best effect as auxiliary agents. However, the preparation of these catalysts has been complicated, the promotion of each rare earth metal has not been extremely achieved by this preparation method, and these reports have not been made on the O resistance of each catalyst₂、NO_x、H₂And (4) researching the performance of impurity gases such as O and the like.

It is known that, so far, the direct catalytic decomposition of N by modifying transition metal oxide with alkali metal K and rare earth metal Gd as auxiliary agents₂The related report of O and even less about the O of the catalyst₂、NO_x、H₂And (3) studying the resistance of impurity gases such as O.

Disclosure of Invention

To solve the existing N₂The O decomposition catalyst has the defects of high catalytic activity and strong NO resistance_x、O₂、H₂The invention provides a preparation method which is simple, has good low-temperature catalytic activity and is used for solving the problem of impurity gases such as O and the like₂Of value in the elimination of O for the direct catalytic decomposition of N₂O is O₂And N₂The formula composition of the composite oxide catalyst and a general manufacturing method.

In order to achieve the purpose, the technical scheme of the invention is as follows: medium-low temperature catalytic decomposition of N₂A composite oxide catalyst of O, said catalyst being K₂O,Gd₂O₃And Co₃O₄Or NiO, CuO composite oxide, K for short_yGd_xM consists of an active component and an auxiliary agent, wherein the active component is a transition metal oxide Co₃O₄NiO and CuO, the auxiliary agent is one of rare earth metal Gd or alkali metal K, wherein y refers to the molar ratio of the added alkali metal K to the transition metal M, and 0<y is less than or equal to 0.03, x is the molar ratio of the added rare earth metal Gd to the transition metal M, 0<x is less than or equal to 0.1. Gd in the obtained catalyst₂O₃The mass percentage of the alkali metal K is 0 wt% to 18.42 wt%, and the mass percentage of the alkali metal K (calculated by oxide) is 0 wt% to 1.53 wt%.

The medium-low temperature catalytic decomposition of N₂A preparation method of the O composite oxide catalyst comprises the following steps:

1) dissolving soluble salt of transition metal M and soluble salt of Gd in deionized water to obtain precursor solution, continuously stirring at a specified temperature, dropwise adding precipitant solution into the precursor solution until the pH value of the solution reaches 9-10, continuously aging for 2-4, filtering and washing the obtained precipitate, drying at the temperature of 100 ℃ and 120 ℃, and calcining to obtain Gd_xM catalyst; the soluble salt of the transition metal M is one or more of nitrate, chloride, sulfate, carbonate, oxide, hydroxide or oxalate of Co, Ni and Cu; the soluble salt of Gd is one or more of nitrate, sulfate or chloride corresponding to Gd, and corresponding carbonate, oxide, oxalate or hydroxide can be used as an auxiliary agent precursor.

2) Reacting Gd obtained in step 1) at room temperature_xSoaking M catalyst in soluble salt of alkali metal K in the same volume for 12-24 hr, heating the obtained mixture in an electric heating jacket until the water is evaporated, drying at 100-120 deg.C, and calciningTo obtain K_yGd_xM catalyst.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 1) of specifying the temperature to be-3-90 ℃.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 1), wherein the precipitator is one or more of sodium carbonate, sodium hydroxide, potassium carbonate or ammonia water.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 1), wherein the molar concentration ratio of the mixed salt solution of the transition metal and Gd to the added precipitant is 1: 2-4.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 1), wherein the calcination is carried out for 3-5h at the temperature of 450-550 ℃ in the air atmosphere.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 2), wherein the soluble salt of the alkali metal K is one or more of nitrate and carbonate.

The medium-low temperature catalytic decomposition of N₂The preparation method of the O composite oxide catalyst comprises the step 2), wherein the calcination is carried out for 3-5h at the temperature of 450-550 ℃ in the air atmosphere.

The medium-low temperature catalytic decomposition of N₂The application of the composite oxide catalyst of O.

The application is characterized in that the method comprises the following steps: the catalyst is placed in a fixed bed quartz tube reactor under normal pressure to make the catalyst contain N₂The raw material gas of O passes through a fixed bed reactor, the balance gas is argon or helium, the gas volume space velocity is 10000-^-1The operation temperature is 200-600 ℃.

The invention has the beneficial effects that:

1) the catalyst prepared by the invention not only has excellent catalytic N₂O decomposition activity and in actual N₂For NO in O waste gas treatment process_x、O₂、H₂O shows stronger resistance and is suitable for application in actual industrial production.

2) The catalyst obtained by the invention has extremely small grain size and larger specific surface area, Gd₂O₃The high oxygen mobility and the oxygen storage capacity enhance the interaction between the catalyst and transition metal, so that the obtained catalyst has better structural stability. In addition, the alkali metal additive K can greatly enhance the electron-donating capability of the transition metal oxide, and K and Gd jointly serve as additives to modify the transition metal oxide, so that the synergistic effect of the K and Gd achieves the advantages of rich active sites, excellent catalytic activity and strong tolerance to impurity gases of the obtained catalyst.

Drawings

FIG. 1 shows that the catalysts obtained in examples 1 to 6 and comparative example 1 catalyze N₂Activity diagram of O decomposition.

FIG. 2 shows the impurity gas O in the catalyst obtained in example 1₂、NO、H₂Activity profile in the presence of O.

FIG. 3 shows the reactivity of the catalysts obtained in examples 7 to 9 and comparative examples 2 to 3 and the impurity gas O₂、NO、H₂Graph of reactivity in the presence of O.

FIG. 4 is a graph of the stability against impurity gases of the catalyst obtained in example 7.

Fig. 5 is an XRD analysis pattern of the catalysts obtained in examples 1, 2, 6,7 and comparative example 1.

Detailed Description

In order that those skilled in the art may more fully understand the present invention, the same is more particularly described in the following non-limiting examples or comparative examples, which are not intended to limit the invention in any way.

Example 1 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (1) -Gd_0.06Co

5.8206g of Co (NO)₃)₂·6H₂O and 0.5416g Gd (NO)₃)₃·6H₂O is mixed and dissolved in 100mL deionized water to obtain a precursor solution, and the precursor solution is added into the mixed solution drop by drop under the condition of continuous stirring at 40 DEG CEqual volume of 0.5 mol. L^-1Na of (2)₂CO₃And (3) continuously aging the solution until the pH value of the solution reaches 9.3, filtering and washing the obtained precipitate, drying at 110 ℃, and then calcining at 500 ℃ for 3 hours in an air atmosphere to obtain the S (1) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 11.93 wt.%.

Example 2 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (2) -Gd_0.01Co

Prepared as described in example 1, except that 0.0903g Gd (NO) was used₃)₃·6H₂O instead of 0.5416g Gd (NO) in example 1₃)₃·6H₂O to obtain the S (2) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 2.21 wt.%.

Example 3 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (3) -Gd_0.02Co

Prepared as described in example 1, except that 0.1806g Gd (NO) was used₃)₃·6H₂O instead of 0.5416g Gd (NO) in example 1₃)₃·6H₂O to obtain the S (3) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 4.32 wt.%.

Example 4 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (4) -Gd_0.04Co

Prepared as described in example 1, except that 0.3612g Gd (NO) was used₃)₃·6H₂O instead of 0.5416g Gd (NO) in example 1₃)₃·6H₂O to obtain the S (4) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 8.28 wt.%.

Example 5 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (5) -Gd_0.08Co

Prepared as described in example 1, except that 0.7224g Gd (NO) was used₃)₃·6H₂O alternative implementation0.5416g Gd (NO) in example 1₃)₃·6H₂O to obtain the S (5) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 15.30 wt.%.

Example 6 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (6) -Gd_0.1Co

Prepared as described in example 1, except that 0.9027g Gd (NO) was used₃)₃·6H₂O instead of 0.5416g Gd (NO) in example 1₃)₃·6H₂O to obtain the S (6) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage was 18.42 wt.%.

Comparative example 1A Medium-Low temperature catalytic decomposition of N₂Composite oxide catalyst B (1) -Co of O₃O₄

Prepared as described in example 1, but with a single 5.8206g Co (NO)₃)₂·6H₂O solution instead of 5.8206g Co (NO) in example 1₃)₂·6H₂O and 0.5416g Gd (NO)₃)₃·6H₂And mixing the solution of O to obtain the catalyst B (1).

Example 7 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (7) -K_0.02Gd_0.06Co

At room temperature, 0.0235g KNO₃Dissolved in 0.8mL of deionized water, 1.0000g of the complex oxide catalyst Gd obtained in example 1 was taken_0.06Co is impregnated in the KNO₃Soaking in the solution for 12h, placing the obtained mixture in an electric heating jacket, heating until the water content is evaporated to dryness, drying at 110 ℃ for 3h, and finally calcining at 500 ℃ in an air atmosphere for 3h to obtain the S (7) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage is 11.81 wt.%, and the K content is expressed as K₂The mass percentage in terms of O was 1.02 wt.%.

Example 8 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (8) -K_0.01Gd_0.06Co

Prepared as described in example 7, but with 0.0118g KNO₃Instead of 0.0235g KNO in example 7₃To obtain the S (8) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage is 11.81 wt.%, and the K content is expressed as K₂The mass percentage in terms of O was 0.51 wt.%.

Example 9 Medium-Low temperature catalytic decomposition of N₂O complex oxide catalyst S (9) -K_0.03Gd_0.06Co

Prepared as described in example 7, but with 0.0353g KNO₃Instead of 0.0235g KNO in example 7₃To obtain the S (9) catalyst. The Gd content in the obtained catalyst is Gd₂O₃The mass percentage is 11.81 wt.%, and the K content is expressed as K₂The mass percentage in terms of O was 1.53 wt.%.

Comparative example 2 Medium-Low temperature catalytic decomposition of N₂O composite oxide catalyst B (2) -K_0.01Co

Prepared as described in comparative example 1, but using 0.0126g of KNO as solid obtained in comparative example 1₃Soaking the aqueous solution in the same volume for 24 hours, placing the obtained mixture in an electric heating jacket, heating until the water content is evaporated to dryness, drying at 110 ℃, and calcining in the air for 3 hours at 500 ℃ to obtain the catalyst B (2).

Comparative example 3 Medium-Low temperature catalytic decomposition of N₂O composite oxide catalyst B (3) -K_0.02Co

Prepared as described in comparative example 2, but with 0.0252g KNO₃Instead of 0.0126g of KNO in comparative example 2₃To obtain the catalyst B (3).

Example 10 various medium-low temperature catalytic decomposition of N obtained in examples 1 to 6 and comparative example 1 at different temperatures₂Measurement of reactivity of O Complex oxide catalyst

The solid powders of the catalysts S (1) -S (6) and B (1) obtained in examples 1-6 and comparative example 1 were pressed into tablets and sieved to 40-60 mesh, 0.2g of the sieved catalyst was weighed and placed in a quartz fixed bed reactor, and pure Ar was introduced at 500 ℃ for pretreatment for 30min to remove water in the catalyst by purging. Subsequently, the bed temperature was reduced to different reaction temperatures and 2000ppmv of N was passed through the catalyst bed₂O/Ar, direct catalysis of N₂Decomposition of O to N₂And O₂The total flow rate of gas is 50 mL/min^-1，W/F＝0.24g·s^-1·mL^-1(W is the amount of catalyst used (g) and F is the flow rate of reaction gas (mL. multidot.s)^-1) Therefore the space velocity of the gas is 20000h^-1. The catalytic decomposition of N by the catalysts S (1) -S (6) and B (1) at the respective reaction temperatures was measured₂The results of the conversion of O are shown in FIG. 1. As is clear from FIG. 1, Co is caused to react with Gd as an auxiliary₃O₄Has been significantly improved, and as the molar ratio of Gd/Co is increased from 0.01 to 0.1, N₂The O conversion rate shows a tendency of increasing first and then decreasing, wherein the optimum proportion of the catalyst Gd_0.06Co can realize N at lower temperature (350 ℃), namely₂Complete conversion of O, T₉₀As low as 326 deg.c.

Example 11 tolerance test for the best active catalyst (catalyst obtained in example 1) to impurity gases

To determine O₂、NO_x、H₂Effect of O impurity gas on catalyst Activity the same procedure as in example 10 was followed except that the amount of N was 2000ppmv₂Respectively introducing 5 vol% of O into O/Ar reaction gas₂，100ppmv NO，2vol％H₂O or their mixture gas, likewise 20000h^-1Introducing the total space velocity into a catalyst bed layer, and measuring the catalytic decomposition N of the S (1) catalyst in the presence of impurity gas at each reaction temperature₂And (4) O conversion rate. The correlation results are shown in FIG. 2. In FIG. 2, (a) to (f) represent feed gases of 2000ppmv N, respectively₂O/Ar and 2000ppmv N₂O/Ar and impurity gas 5 vol% O₂，2vol％H₂O，100ppmv NO，5vol％O₂+100ppmv NO，5vol％O₂+100ppmv NO+2vol％H₂N calculated by S (1) catalytic reaction in the presence of O₂And (4) O conversion rate. The results show that when O is introduced₂、NO、H₂After O, catalyst S (1) catalyzes N₂T of O decomposition reaction₉₀(N₂The temperature at which the O conversion is 90%) increases from initially 331 ℃ to 410, 387 and 437 ℃ respectively, and when a mixture of these three gases is passed, T is₉₀Rising to 472 ℃.

Example 12 examples 7-9 and comparative examples 2-3Obtained medium-low temperature catalytic decomposition of N₂Measurement of reactivity of O Complex oxide catalyst and tolerance to impurity gas

The test method is the same as that of example 10, solid powder tablets of the catalysts S (7) -S (9) and B (2) -B (3) obtained in examples 7-9 and comparative examples 2-3 are respectively sieved to 40-60 meshes, 0.2g of the sieved catalyst is weighed and placed in a quartz fixed bed reactor, and pure Ar is introduced for pretreatment for 30min at 500 ℃ so as to remove moisture in the catalyst by purging. Subsequently, the bed temperature was reduced to different reaction temperatures and 2000ppmv of N was passed through the catalyst bed₂O/Ar, direct catalysis of N₂Decomposition of O to N₂And O₂The catalytic decomposition of N by the catalysts S (7) -S (9) and B (2) -B (3) at the respective reaction temperatures was measured₂The results of the conversion of O are shown in FIG. 3 (A). As is clear from FIG. 3A, compared with the catalyst S (1) using Gd alone, the catalytic activities of B (2) and B (3) using K alone as the auxiliary agent and S (7) -S (9) using K and Gd together as the auxiliary agent were all improved, and their catalytic performances were far superior to those of pure Co₃O₄(B(1))。

N to 2000ppmv₂Introducing 5 vol% of O into O/Ar reaction gas₂、100ppmv NO、2vol％H₂Mixed gas of O, B (2) and S (7) are measured at O at each reaction temperature₂、NO、H₂Catalytic decomposition of N in the presence of O₂The results of O conversion are shown in FIG. 3 (B). At this time, it can be found that, although the activities of the catalysts S (7) -S (9) in fig. 3(a) are not much different from those of B (2) and B (3), wherein S (7) is higher in catalytic activity than S (8) and S (9) and B (2) is higher in catalytic activity than B (3), the tolerance to impurity gases is better than those of B (2) and B (3).

Combining FIGS. 3(A) and 3(B), under ideal conditions (no impurity gas), catalysts S (7) and B (2) catalytically decompose N₂T of O reaction₉₀At 274 ℃ and 286 ℃; introducing O into the reaction system₂、NO、H₂After the mixture of O, S (7) and B (2) catalytically decompose N₂O reaction of corresponding T₉₀Elevated to 350 ℃ and 369 ℃ respectively, although O₂NO and H₂Introduction of O catalytic N to K, Gd-modified oxide S (7)₂The O decomposition reaction has a certain influence, howeverUnder such severe conditions, T₉₀Still as low as 350 c.

Example 13 Medium Low temperature catalytic decomposition of N obtained in example 7₂Impurity gas stability test of composite oxide catalyst of O

The test procedure was as in example 10, but with an N conversion of 2000ppmv₂Introducing 5 vol% of O into O/Ar reaction gas₂，100ppmv NO，2vol％H₂Mixed gas of O for 20000h^-1Introducing the total space velocity into a catalyst bed layer, injecting the sample once every half hour, and measuring the catalytic decomposition N of the S (7) catalyst under the coexistence condition of various impurity gases at the temperature of 350 DEG C₂And (4) O conversion rate. The test results are shown in FIG. 4. It was found that at 350 ℃ initially the catalyst S (7) catalytically decomposed N₂N obtained by reaction of O₂The conversion rate of O is higher, is more than 80% in 5h and then is reduced, but after the O is activated, the catalytic activity is recovered and can be maintained for the same time. In each cycle, S (7) may be N₂The O conversion rate is kept above 40% in the test time of 10.5h, which indicates that the catalyst S (7) modified by the transition metal oxide by taking K and Gd as the auxiliary agents has excellent impurity gas tolerance.

Example 14 XRD analysis of the catalysts obtained in examples 1, 2, 6,7 and comparative example 1

The catalysts S (1), S (2), S (6), S (7) and B (1) obtained in examples 1, 2, 6,7 and comparative example 1 were selected for XRD measurement as shown in FIG. 5. As can be seen from FIG. 5, the XRD diffraction peaks of catalysts S (1), S (2), S (6) and S (7) are all the same as that of pure Co₃O₄The standard diffraction peaks of (B (1)) are consistent, and compared with B (1), the diffraction peaks of other catalysts are not obviously shifted, which shows that the auxiliary agents Gd and K do not enter Co in the preparation process of the catalyst₃O₄Form a solid solution with the crystal lattice. In addition, the broader diffraction peaks of S (1), S (2) and S (6) compared with the catalyst B (1) prove that the average grain size of the metal oxide is greatly reduced by the introduction of Gd, and the average grain sizes of the catalysts B (1), S (1), S (2) and S (6) are respectively reduced from 29nm to 12nm, 5nm and 5nm by calculation of the Sherler equation. And for catalyst S (7) further doped with K, the average crystal grain size (5.2nm) was also almost noneAnd (6) changing. These results all show that Gd has a strong structure modification effect on the metal oxide catalyst as an auxiliary agent, so that more active sites are exposed on the catalyst, and the catalytic N of the Gd is further improved₂O decomposition activity.

Claims

1. Medium-low temperature catalytic decomposition of N₂O, wherein the catalyst is K_yGd_xM consists of an active component and an auxiliary agent, wherein the active component is a transition metal oxide Co₃O₄NiO and CuO, the auxiliary agent is one of rare earth metal Gd or alkali metal K, wherein y refers to the molar ratio of the added alkali metal K to the transition metal M, and 0<y is less than or equal to 0.03, x is the molar ratio of the added rare earth metal Gd to the transition metal M, 0<x≤0.1。

2. Medium and low temperature catalytic decomposition of N as claimed in claim 1₂A method for producing an O composite oxide catalyst, characterized by comprising the steps of:

1) dissolving soluble salt of transition metal M and soluble salt of Gd in deionized water to obtain precursor solution, continuously stirring at a specified temperature, dropwise adding precipitant solution into the precursor solution until the pH value of the solution reaches 9-10, continuously aging for 2-4, filtering and washing the obtained precipitate, drying at the temperature of 100 ℃ and 120 ℃, and calcining to obtain Gd_xM catalyst; the soluble salt of the transition metal M is one or more of nitrate, chloride, sulfate, carbonate, oxide, hydroxide or oxalate of Co, Ni and Cu;

2) reacting Gd obtained in step 1) at room temperature_xSoaking M catalyst in soluble salt of alkali metal K for 12-24 hr, heating the mixture in electric heating jacket until water is evaporated, stoving at 100-120 deg.c and calcining to obtain K_yGd_xM catalyst.

3. The medium-low temperature catalytic decomposition of N according to claim 2₂Of complex oxide catalysts of OThe preparation method is characterized in that in the step 1), the designated temperature is-3-90 ℃.

4. The medium-low temperature catalytic decomposition of N according to claim 2₂The preparation method of the O composite oxide catalyst is characterized in that in the step 1), the precipitator is one or more of sodium carbonate, sodium hydroxide, potassium carbonate or ammonia water.

5. The medium-low temperature catalytic decomposition of N according to claim 2₂The preparation method of the O composite oxide catalyst is characterized in that in the step 1), the molar concentration ratio of the mixed salt solution of the transition metal and Gd to the added precipitant is 1: 2-4.

6. The medium-low temperature catalytic decomposition of N according to claim 2₂The preparation method of the O composite oxide catalyst is characterized in that in the step 1), the calcination is carried out for 3-5h at the temperature of 450-550 ℃ in the air atmosphere.

7. Medium and low temperature catalytic decomposition of N according to claim 3₂The preparation method of the O composite oxide catalyst is characterized in that in the step 2), the soluble salt of the alkali metal K is one or more of nitrate and carbonate.

8. Medium and low temperature catalytic decomposition of N according to claim 3₂The preparation method of the O composite oxide catalyst is characterized in that in the step 2), the calcination is carried out for 3-5h at the temperature of 450-550 ℃ in the air atmosphere.

9. Medium and low temperature catalytic decomposition of N as claimed in claim 1₂The application of the composite oxide catalyst of O.

10. Use according to claim 9, characterized in that the method is as follows: placing the catalyst of claim 1 in a fixed bed quartz tube reactor at atmospheric pressure to containN₂The raw material gas of O passes through a fixed bed reactor, the balance gas is argon or helium, the gas volume space velocity is 10000-^-1The operation temperature is 200-600 ℃.