CN116020445A - La with cation defect x MnO 3±δ Catalyst, preparation method and application - Google Patents
La with cation defect x MnO 3±δ Catalyst, preparation method and application Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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Abstract
The invention provides La with cation defect x MnO 3±δ Catalyst, preparation method and application, the preparation method includes: weighing pretreated La 2 O 3 Dissolving the powder in deionized water, adding nitric acid to obtain a first mixed solution, adding Mn (CH) 3 COO) 2 ·4H 2 Mixing O and glycine to obtain a second mixed solution; placing the second mixed solution in a water bath kettle, heating at constant temperature, stirring until the solution is evaporated to gel state, and stopping heating; placing the gel samplePreliminary roasting is carried out in a muffle furnace; la obtained by preliminary phase formation 0.84 MnO 3‑δ Adding the catalyst into a mortar, fully grinding and transferring the mixture into a crucible, placing the crucible into a muffle furnace, and roasting at high temperature to obtain La 0.84 MnO 3‑δ The product is obtained. The invention has the advantages of cheap raw materials, simple operation in the preparation process, easy mass production and capability of preparing CO and C 3 H 8 Has good catalytic oxidation effect.
Description
Technical Field
The invention relates to the technical field of development and preparation of catalysts, in particular to La with cationic defect x MnO 3±δ Catalyst, preparation method and application.
Background
With the improvement of living standard, automobiles are indispensable in people's life. However, there are thousands of pollutants contained in automobile exhaust, and the main pollutants include: carbon oxides (CO, CO) 2 ) Hydrocarbon (CH) 4 、C 3 H 8 ) Oxynitride (NO, NO) 2 ) Sulfur oxides, and soot particles (lead compounds, heavy metal compounds, soot, etc.), sulfur oxides, and the like. The pollutants not only endanger the natural environment for human beings to live, but also have certain harm to the human body. Specifically, the carbon oxides refer to CO produced by insufficient combustion of fuel. And CO produced by insufficient combustion has a toxic effect on human tissue cells. Hydrocarbon refers to the unburned portion of the engine exhaust and also includes evaporation and dripping of oil from the oil supply system. Individual hydrocarbons only affect the body when present in high amounts, but are the main components responsible for photochemical pollution.
Researchers have investigated the reduction of CO and C in automobile exhaust by a variety of methods 3 H 8 Including adsorption, biodegradation, photocatalysis, thermal combustion, catalytic oxidation, and the like. For catalytic oxidation, metal catalysts for catalytic oxidation are currently classified into metal oxides, supported noble metal oxides (e.g., pt/Al 2 O 3 ) And metal composite oxide catalysts, etc. Perovskite oxide in the metal composite oxide is a "star" which has been studied in recent years, and the perovskite oxide is inexpensive in raw material, has and supports noble metal oxygenThe compounds have been widely focused on having catalytic activity comparable to that of the compounds and high thermal stability.
Perovskite oxides of the general formula ABO 3 Wherein the A-site ion is a metal ion with larger radius of alkaline earth or rare earth plasma, and the metal ion is coordinated with the nearest 12O to form the closest cubic packing, and acts as a framework of perovskite oxide to play a role of stabilization. The B-site ion is mostly a transition metal ion (such as Mn, co, ni, etc.) with smaller ionic radius, and coordinates with the nearest 6O, and is located in the octahedral center in cubic stacking, which generally affects the catalytic activity. Wherein, the perovskite oxide has an open structure, and the metal ions at the A/B position can be replaced by the metal ions with similar ion radius, thus creating diversity; and has the characteristics of higher oxidation-reduction performance, oxygen fluidity, ionic conductivity and the like. As a novel functional material, studies have been widely conducted in the fields of chemistry, materials, physics, and the like. The physical and chemical properties of perovskite metal oxides are intimately related to the metal ions in the a/B sites. For example, by Sr-doped LaSrCoO 3 Formation of La 0.8 Sr 0.2 CoO 3 Then, sr is removed by a wet etching method. Co in the B-position thereof according to conservation of charge 3+ Reduced valence state, co is produced 2+ . Thereby increasing the number of Lewis acid sites and promoting C 3 H 8 Is adsorbed and desorbed by (C), and Co 2+ The site also improves the reducibility of the catalyst and promotes the activation of active oxygen. The catalytic activity of propane is improved under the combined action of the two. Therefore, by rationally designing the metal ions at the a/B site of the perovskite metal oxide catalyst, the catalytic activity of the perovskite material can be improved.
Among the numerous perovskite metal oxides, laMnO 3 It is widely studied, generally used as an electrochemical sensor, as a material for coating a lithium-rich manganese-based positive electrode, and has the purpose of degrading RhB in water. LaMnO 3 The catalyst has a certain position in the catalytic field, not only can be efficiently out of stock, but also has the characteristic of pollution resistance compared with other catalysts in VOCs waste gas treatment. LaMnO, however 3 The crystalline phase structure of (C) is complete, so that the binding capacity of Mn-O bond is stronger, which is unfavorable for Mn-O bondFracture hinders fluidity of oxygen, and affects catalytic activity.
To further improve LaMnO 3 Often, the catalytic activity is increased by doping the metal ion (e.g., ni) at the B site, or doping the A site (e.g., sr) or etching with acid or alkali to increase the specific surface area, increase the surface active oxygen and increase the acid or alkali sites. However, currently for LaMnO 3 The loss of the a-site of (c) to form cation vacancies is less studied for catalytic activity.
Disclosure of Invention
Based on this, the object of the present invention is to provide a cation-deficient La x MnO 3±δ The catalyst, the preparation method and the application are used for solving the technical problems.
Specifically, the invention provides La with cation defect x MnO 3±δ Process for the preparation of a catalyst, wherein, when 0.8<x<1, corresponding La x MnO 3-δ The catalyst is A-site cation defective; when 1<x<1.2 corresponding La x MnO 3+δ The catalyst is B-site cation defective; when x=1, the corresponding LaMnO 3 The catalyst is an nondefective perovskite oxide;
when x=0.84, the corresponding La 0.84 MnO 3-δ The preparation method of the catalyst comprises the following steps:
step one: preparing a mixed solution
Weighing pretreated La with preset mass 2 O 3 Dissolving the powder in deionized water, adding nitric acid to dissolve completely to obtain a first mixed solution, and adding Mn (CH) with a preset material ratio into the first mixed solution when the first mixed solution is completely clear 3 COO) 2 ·4H 2 Mixing O and glycine to obtain a second mixed solution, wherein the first mixed solution is La (NO 3 ) 3 ；
Step two: precursor sample synthesis
Placing the second mixed solution in a water bath kettle, setting the temperature in the water bath kettle to be a first temperature, and heating and stirring at constant temperature until the solution is evaporated to gelStopping heating after shaping; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to be a second temperature, and performing preliminary roasting for realizing La 0.84 MnO 3-δ Primary phase formation of the catalyst;
step three: roasting to obtain the final product
La obtained by preliminary phase formation 0.84 MnO 3-δ Adding the catalyst into a mortar for full grinding, transferring the fully ground sample into a crucible, setting the temperature of a muffle furnace to be a third temperature, and placing the crucible into the muffle furnace for high-temperature roasting to obtain La with complete crystal phase structure 0.84 MnO 3-δ The final product.
La of said one cation deficiency x MnO 3±δ A method for preparing a catalyst, wherein in the first step, la is added 2 O 3 The method for preprocessing the powder comprises the following steps:
weighing La 2 O 3 Placing the raw materials into a crucible, transferring the crucible into a muffle furnace, heating to 1000 ℃ at a heating rate of 5 ℃/min for roasting for 2 hours to finally obtain pretreated La 2 O 3 And (3) powder.
La of said one cation deficiency x MnO 3±δ A method for preparing a catalyst, wherein in the first step, the ratio of the amount of glycine added to the total metal ion in the second mixed solution is as follows: n (glycine): n (total metal ions) =1.5:1.
La of said one cation deficiency x MnO 3±δ The preparation method of the catalyst comprises the following steps:
placing the second mixed solution in a water bath kettle, setting the temperature in the water bath kettle to 90 ℃, heating at constant temperature, stirring until the solution is evaporated to gel state, and stopping heating; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to 300 ℃, performing preliminary roasting, heating the gel sufficiently to spontaneous combustion to obtain a catalyst precursor, and further calcining the obtained catalyst precursor; wherein, in the calcination process, the temperature rising rate of 2 ℃/min is controlled, and the temperature is raised to 700 ℃ for calcination, and the duration of calcination is 6h.
La of said one cation deficiency x MnO 3±δ A method for preparing a catalyst, wherein La is prepared 0.84 MnO 3-δ Catalyst with corresponding specific surface area of 21.0m 2 /g。
La of said one cation deficiency x MnO 3±δ A method for preparing a catalyst, wherein La is prepared 0.84 MnO 3-δ The crystal phase structure of the catalyst is hexagonal.
The invention also provides La with cation defect x MnO 3±δ Catalyst, wherein La with cationic defect as described above is applied x MnO 3±δ The catalyst is prepared by a preparation method;
when 0.8<x<1, corresponding La x MnO 3-δ The catalyst is A-site cation defective; when 1<x<1.2 corresponding La x MnO 3+δ The catalyst is B-site cation defective; when x=1, the corresponding LaMnO 3 The catalyst is an nondefective perovskite oxide;
when x=0.84, la was prepared 0.84 MnO 3-δ The specific surface area of the catalyst is 21.0m 2 And/g, the crystal phase structure is hexagonal.
The invention also provides La with cation defect x MnO 3±δ Use of a catalyst, wherein the cation-deficient La x MnO 3±δ The catalyst uses La with cationic defects as described above x MnO 3±δ The catalyst is prepared by a preparation method of the cationic defect La x MnO 3±δ Catalyst for CO and C 3 H 8 Low temperature catalytic oxidation of (2).
La of said one cation deficiency x MnO 3±δ Use of a catalyst, wherein La is prepared when x=0.84 0.84 MnO 3-δ Catalyst, la was used 0.84 MnO 3-δ The method for carrying out catalytic oxidation on CO by the catalyst comprises the following steps:
50mg of La was purified using a gas chromatograph 0.84 MnO 3-δ The catalyst is mixed with 50mg quartz sand and then placed in a U-shaped quartz tube, a K-shaped thermocouple is placed at the top of a catalyst reaction fixed bed and contacts the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 1% CO,21% O 2 Balance gas N 2 ；
Regulating gas flow rate to 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 Finally, the reactants and products were analyzed on-line on a gas chromatograph.
La of said one cation deficiency x MnO 3±δ Use of a catalyst, wherein La is prepared when x=0.84 0.84 MnO 3-δ Catalyst, la was used 0.84 MnO 3-δ Catalyst pair C 3 H 8 The method for carrying out catalytic oxidation comprises the following steps:
50mgLa was purified by gas chromatography 0.84 MnO 3-δ The catalyst is mixed with 50mg of quartz sand and then placed in a quartz tube with the length of 30mm and the inner diameter of 10mm, a K-type thermocouple is placed at the top of a catalyst reaction fixed bed and contacted with the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 0.5% C 3 H 8 ，21％O 2 Balance gas N 2 ；
Regulating the total flow rate of the gas to be 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 The reactants and products were analyzed on-line on a gas chromatograph.
La prepared by the invention 0.84 MnO 3-δ The perovskite metal oxide catalyst is prepared by a glycine-nitrate combustion method, and compared with other preparation methods, the perovskite metal oxide catalyst has the advantages of low raw material cost, simple preparation process operation and easy mass production; in addition, la prepared by the invention 0.84 MnO 3-δ Perovskite metal oxide catalyst having catalytic activity superior to noble metal supported oxide and having catalytic activity on CO and C 3 H 8 Has good catalytic oxidation effect.
Additional features and advantages of the disclosure will be set forth in the description which follows, or in part will be obvious from the description, or may be learned by practice of the techniques of the disclosure.
In order to make the above objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
FIG. 1 is an XRD diffraction pattern of the products obtained in examples 1 to 5 of the present invention;
FIG. 2 is an FT-IR infrared spectrum of the products obtained in examples 1 to 5 of the invention;
FIG. 3 is a graph showing the performance of the catalytic CO oxidation reactions of the products obtained in examples 1 to 5 of the present invention;
FIG. 4 shows the product catalysis C obtained in examples 1 to 5 of the present invention 3 H 8 An oxidation reaction performance curve;
FIG. 5 is a graph showing the stability test of the catalytic CO oxidation reaction of the product obtained in example 2 of the present invention;
FIG. 6 shows the product catalysis C obtained in example 2 of the present invention 3 H 8 Oxidation stability test chart.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
The invention provides La with cation defect x MnO 3±δ Process for the preparation of a catalyst, wherein, when 0.8<x<1, corresponding La x MnO 3-δ The catalyst is A-site cation defective; when 1<x<1.2 corresponding La x MnO 3+δ The catalyst is B-site cation defective; when x=1, the corresponding LaMnO 3 The catalyst is an nondefective perovskite oxide;
when x=0.84, the corresponding La 0.84 MnO 3-δ The preparation method of the catalyst comprises the following steps:
step one: preparing a mixed solution
Weighing pretreated La with preset mass 2 O 3 Dissolving the powder in deionized water, adding nitric acid to dissolve completely to obtain a first mixed solution, and adding Mn (CH) with a preset material ratio into the first mixed solution when the first mixed solution is completely clear 3 COO) 2 ·4H 2 Mixing O and glycine to obtain a second mixed solution, wherein the first mixed solution is La (NO 3 ) 3 。
In step one, for La 2 O 3 The method for preprocessing the powder comprises the following steps:
weighing La 2 O 3 Placing the raw materials into a crucible, transferring the crucible into a muffle furnace, heating to 1000 ℃ at a heating rate of 5 ℃/min for roasting for 2 hours to finally obtain pretreated La 2 O 3 And (3) powder. In addition, the ratio of the amount of glycine added to the total metal ion species in the second mixed solution is: n (glycine): n (total metal ions) =1.5:1.
Step two: precursor sample synthesis
Placing the second mixed solution in a water bath kettle, and placing the water bath kettleAfter the temperature in the water heater is set to be the first temperature, heating and stirring at constant temperature until the solution is evaporated to gel state, and stopping heating; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to be a second temperature, and performing preliminary roasting for realizing La 0.84 MnO 3-δ The catalyst is initially phase-formed.
Specifically, the method comprises the following steps:
placing the second mixed solution in a water bath kettle, setting the temperature in the water bath kettle to 90 ℃, heating at constant temperature, stirring until the solution is evaporated to gel state, and stopping heating; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to 300 ℃, performing preliminary roasting, heating the gel sufficiently to spontaneous combustion to obtain a catalyst precursor, and further calcining the obtained catalyst precursor; wherein, in the calcination process, the temperature rising rate of 2 ℃/min is controlled, and the temperature is raised to 700 ℃ for calcination, and the duration of calcination is 6h.
Step three: roasting to obtain the final product
La obtained by preliminary phase formation 0.84 MnO 3-δ Adding the catalyst into a mortar for full grinding, transferring the fully ground sample into a crucible, setting the temperature of a muffle furnace to be a third temperature, and placing the crucible into the muffle furnace for high-temperature roasting to obtain La with complete crystal phase structure 0.84 MnO 3-δ The final product.
In this step, la was prepared 0.84 MnO 3-δ Catalyst with corresponding specific surface area of 21.0m 2 /g, la prepared 0.84 MnO 3-δ The crystal phase structure of the catalyst is hexagonal.
The technical scheme of the invention is described in more detail below in several examples.
Example 1: la (La) 0.8 MnO 3 Is synthesized by (a)
The oxide is selected to be dissolved into nitrate for synthesis:
1.3032g of pretreated La is weighed 2 O 3 Dissolving the powder in 5mL of deionized water, and slowly dripping HNO 3 Solution, waiting for La 2 O 3 The powder is completely dissolvedAfter dissolving to the transparent state, 2.4509g of Mn (CH) 3 COO) 2 ·4H 2 O is placed in a beaker, 2.0268g of glycine is added after dissolution, and deionized water is added;
placing the beaker into a water bath kettle, heating and stirring at constant temperature, wherein the temperature of the water bath kettle is set to 90 ℃, and stopping heating when the solution in the beaker is gradually steamed to be gel; placing the obtained gel sample in a muffle furnace for preliminary roasting, setting the temperature of the muffle furnace to 300 ℃, and transferring the obtained fluffy powder into a crucible after roasting;
finally, the obtained powder is roasted at the temperature rising rate of 2 ℃/min to 700 ℃ in the air atmosphere for 6 hours, and the prepared catalyst is La 0.8 MnO 3 A sample with a specific surface area of 23.12-1
m g。
Example 2: la (La) 0.84 MnO 3-δ Is synthesized by (a)
The oxide is selected to be dissolved into nitrate for synthesis:
1.3847g of pretreated La is weighed 2 O 3 Dissolving the powder in 5mL of deionized water, and slowly dripping HNO 3 Solution, waiting for La 2 O 3 After the powder was completely dissolved to a transparent state, 2.4509g of Mn (CH) 3 COO) 2 ·4H 2 O is placed in a beaker, 2.0831g of glycine is added after dissolution, and deionized water is added;
placing the beaker into a water bath kettle, heating and stirring at constant temperature, wherein the temperature of the water bath kettle is set to 90 ℃, and stopping heating when the solution in the beaker is gradually steamed to be gel; placing the obtained gel sample in a muffle furnace for preliminary roasting, setting the temperature of the muffle furnace to 300 ℃, and transferring the fluffy powder obtained by roasting into a crucible;
finally, the obtained powder is roasted in the air atmosphere at the rate of 2 ℃/min heating up to 700 ℃ for 6 hours to prepare La 0.84 MnO 3-δ A catalyst having a specific surface area of 21.0m 2 g -1 。
Example 3: la (La) 0.94 MnO 3-δ Is synthesized by (a)
The oxide is selected to be dissolved into nitrate for synthesis:
1.5476g of pretreated La is weighed 2 O 3 Dissolving the powder in 5mL of deionized water, and slowly dripping HNO 3 Solution, waiting for La 2 O 3 After the powder was completely dissolved to a transparent state, 2.4509g of Mn (CH) 3 COO) 2 ·4H 2 O is placed in a beaker, 2.1957g of glycine is added after dissolution, and deionized water is added;
placing the beaker into a water bath kettle, heating and stirring at constant temperature, wherein the temperature of the water bath kettle is set to 90 ℃, and stopping heating when the solution in the beaker is gradually steamed to be gel; placing the obtained gel sample in a muffle furnace for preliminary roasting, setting the temperature in the muffle furnace to 300 ℃, and transferring the fluffy powder obtained by roasting into a crucible;
finally, the obtained powder is roasted in the air atmosphere at the rate of 2 ℃/min heating up to 700 ℃ for 6 hours to prepare La 0.94 MnO 3-δ A catalyst having a specific surface area of 19.8m 2 g -1 。
Example 4: laMnO 3 Is synthesized by (a)
The oxide is selected to be dissolved into nitrate for synthesis:
1.6290g of pretreated La is weighed 2 O 3 Dissolving the powder in 5mL of deionized water, and slowly dripping HNO 3 Solution, waiting for La 2 O 3 After the powder was completely dissolved to a transparent state, 2.4509g of Mn (CH) 3 COO) 2 ·4H 2 O is placed in a beaker, 2.2520g of glycine is added after dissolution, and deionized water is added;
placing the beaker into a water bath kettle, heating and stirring at constant temperature, wherein the temperature of the water bath kettle is set to 90 ℃, and stopping heating when the solution in the beaker is gradually steamed to be gel; placing the obtained gel sample in a muffle furnace for preliminary roasting, setting the temperature in the muffle furnace to 300 ℃, and transferring the fluffy powder obtained by roasting into a crucible;
finally, the obtained powder is heated in air at a speed of 2 ℃/minRoasting at the temperature rate of 700 ℃ for 6 hours to obtain LaMnO 3 Catalyst having a specific surface area of 15.7m 2 g -1 。
Example 5: la (La) 1.15 MnO 3+δ Is synthesized by (a)
The oxide is selected to be dissolved into nitrate for synthesis:
1.8734g of pretreated La is weighed 2 O 3 Dissolving the powder in 5mL of deionized water, and slowly dripping HNO 3 Solution, waiting for La 2 O 3 After the powder was completely dissolved to a transparent state, 2.4509g of Mn (CH) 3 COO) 2 ·4H 2 O is placed in a beaker, 2.4209g of glycine is added after dissolution, and deionized water is added;
placing the beaker into a water bath kettle, heating and stirring at constant temperature, wherein the temperature of the water bath kettle is set to 90 ℃, and stopping heating when the solution in the beaker is gradually steamed to be gel; placing the obtained gel sample in a muffle furnace for preliminary roasting, setting the temperature in the muffle furnace to 300 ℃, and transferring the fluffy powder obtained by roasting into a crucible;
finally, the obtained powder is roasted in the air atmosphere at the rate of 2 ℃/min heating up to 700 ℃ for 6 hours to prepare La 1.15 MnO 3-δ Catalyst having a specific surface area of 12.7m 2 -1g。
In the present invention, la is used 0.84 MnO 3-δ The method for carrying out catalytic oxidation on CO by the catalyst comprises the following steps:
50mg of La was purified using a GC9310 gas chromatograph equipped with a TDX-01 column and a TCD detector 0.84 MnO 3-δ The catalyst is mixed with 50mg quartz sand and then placed in a U-shaped quartz tube, a K-shaped thermocouple is placed at the top of a catalyst reaction fixed bed and contacts the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 1% CO,21% O 2 Balance gas N 2 ；
Regulating gas flow rate to 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 Finally, the reactants and products were analyzed on-line on a gas chromatograph.
In the present invention, la is used 0.84 MnO 3-δ Catalyst pair C 3 H 8 The method for carrying out catalytic oxidation comprises the following steps:
50mgLa was detected by GC7900 gas chromatograph (equipped with TDX-01 column and TCD detector) 0.84 MnO 3-δ The catalyst is mixed with 50mg of quartz sand and then placed in a quartz tube with the length of 30mm and the inner diameter of 10mm, a K-type thermocouple is placed at the top of a catalyst reaction fixed bed and contacted with the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 0.5% C 3 H 8 ，21％O 2 Balance gas N 2 ；
Regulating the total flow rate of the gas to be 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 The reactants and products were analyzed on-line on a gas chromatograph.
The products prepared in examples 1 to 5 above were characterized. The specific characterization results are as follows:
referring to FIG. 1, a series of different defects of LaMnO can be obtained from the XRD diffraction pattern of FIG. 1 3-δ Is a crystal phase structure of (a). For accurate analysis, three strong diffraction peaks of 32.4 degrees, 46.5 degrees and 57.8 degrees can be seen by comparing standard PDF cards respectively, and the three strong diffraction peaks respectively correspond to hexagonal crystal phase LaMnO with complete crystal phase structure 3 (110), (202), (122) crystal planes (PDF#51-1515). The positions of the diffraction peaks for the five examples were approximately the same, indicating that the crystalline phases were similar. Further, in the enlarged view on the right side, it can be observed that: in examples 1 to 5, some cationic defects were present, and the diffraction peaks were shifted to a high angle, so that the crystal lattice was contracted. Wherein the main cause of lattice distortion is the formation of cationic defects at the A or B sites, which alters the Mn-O bond length and thus leads to octahedraMnO 6 To form different degrees of distortion of the crystalline phase.
Referring to FIG. 2, FIG. 2 shows FT-IR infrared spectra of products prepared in five examples. Wherein, according to literature report at 611cm -1 The telescopic vibration mode of Mn-O of example 4 was shown. The larger the wavenumber, the shorter the Mn-O bond, the stronger the bond and vice versa. Wherein, in examples 1 to 3, as the La defect at the A-site increases, the infrared wave numbers at the same Mn-O position shift toward lower wave numbers, indicating that the Mn-O bonds with the La defect at the A-site become weaker, facilitating the flow of surface oxygen. In example 5, however, the infrared wave number is shifted to a high wave number, indicating that an increase in La content in the catalyst would result in a strong Mn-O bond, unfavorably breaking, and thus in a decrease in oxygen fluidity.
Referring to fig. 3, fig. 3 is a graph showing the performance of the catalytic CO oxidation reaction of the products obtained in examples 1 to 5 according to the present invention, and it can be seen from fig. 3: complete conversion of CO to CO in example 2 2 The lowest temperature of (2) indicates the optimum activity. The corresponding reaction mechanism is Mars van-Krevelen mechanism: CO is adsorbed and activated on the surface of the catalyst, and the surface lattice oxygen is abstracted to generate first CO 2 And desorbing, and simultaneously breaking Mn-O bonds of the catalyst to form oxygen vacancies; o in air 2 Oxygen vacancies adsorbed on the surface of the catalyst and react with CO adsorbed on the surface of the catalyst to generate a second CO 2 And desorbing; through the two steps, the catalyst is recovered, and the catalytic reaction is circularly carried out.
Referring to FIG. 4, FIG. 4 shows the product catalyst C obtained in examples 1 to 5 of the present invention 3 H 8 The oxidation reaction curve can be seen from fig. 4: c in example 2 3 H 8 Complete conversion to CO 2 The lowest temperature of (2) indicates the optimum activity. The corresponding reaction mechanism is still Mars van-Krevelen mechanism: c (C) 3 H 8 Adsorbing and activating on the surface of the catalyst, capturing lattice oxygen on the surface to generate first CO 2 And desorbing, and simultaneously breaking Mn-O bonds of the catalyst to form oxygen vacancies; o in air 2 C adsorbed on the surface of the catalyst and adsorbed with the surface of the catalyst 3 H 8 The reaction is carried outGenerating a second CO 2 And desorbing; through the two steps, the catalyst is recovered, and the catalytic reaction is circularly carried out. In summary, example 2 is because it has the optimal oxygen transport capacity and it adsorbs CO and C 3 H 8 The strongest ability to cause it to have excellent CO and C 3 H 8 Low temperature catalytic oxidation properties of (2).
La prepared by the invention 0.84 MnO 3-δ Has catalytic activity superior to that of supported noble metal oxide, hereinafter La 0.84 MnO 3-δ Catalyst and existing catalysts CO and C 3 H 8 Comparison of catalytic oxidation performance:
table one, comparison of the activity of the different catalysts:
the comparison of the catalytic activities in Table I can be seen:
for CO catalytic oxidation activity, la 0.84 MnO 3-δ Temperature T at 50% CO conversion of the catalyst 50 The temperature was 120℃and the complete CO conversion temperature was 160 ℃. And for C 3 H 8 Catalytic oxidation, T 50 At 290 ℃, C 3 H 8 The complete conversion temperature was 340 ℃. La prepared by the invention 0.84 MnO 3-δ Catalyst with lower T 50 。La 0.84 MnO 3-δ Catalysts CO and C 3 H 8 The low-temperature catalytic oxidation performance is not quite different from that of noble metal supported oxide, but the synthesis method is simple and economical.
Experiments prove that: la when the A-site ion has a certain cation defect 0.84 MnO 3-δ Perovskite metal oxide catalyst has good low-temperature catalysis of CO and C 3 H 8 Activity of oxidation. In addition, la with cationic defect at A-position was prepared 0.84 MnO 3-δ Application to low-temperature catalytic oxidation of CO and C 3 H 8 Has good reaction stability in the catalytic reaction.
For the reaction stability test, please refer to fig. 5, in the process of testing the stability of the CO catalytic oxidation reaction for 50 hours, the CO conversion rate is reduced from 97% to 93% with the increase of the reaction time at 150 ℃, and the stability is maintained after 30 hours, which indicates that the catalyst has excellent reaction stability.
In addition, please refer to fig. 6, 50h C 3 H 8 In the process of testing the stability of the catalytic oxidation reaction, C is at 330 DEG C 3 H 8 The conversion rate is reduced from 96% to 93%, and the catalyst is stable after 30 hours, which shows that the catalyst has excellent reaction stability.
In conclusion, la with A-site cation defect prepared by the invention 0.84 MnO 3-δ Perovskite oxide catalyst with good low-temperature catalytic oxidation of CO and C 3 H 8 Is a reaction property of the polymer.
Finally, it should be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention, but it should be understood by those skilled in the art that the present invention is not limited thereto, and that the present invention is described in detail with reference to the foregoing examples: any person skilled in the art may modify or easily conceive of the technical solution described in the foregoing embodiments, or perform equivalent substitution of some of the technical features, while remaining within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. La with cation defect x MnO 3±δ A process for preparing the catalyst, characterized in that when 0.8<x<1, corresponding La x MnO 3-δ The catalyst is A-site cation defective; when 1<x<1.2 corresponding La x MnO 3+δ The catalyst is B-site cation defective; when x=1, the corresponding LaMnO 3 The catalyst is an nondefective perovskite oxide;
when x=0.84, the corresponding La 0.84 MnO 3-δ The preparation method of the catalyst comprises the following steps:
step one: preparing a mixed solution
Weighing pretreated La with preset mass 2 O 3 Dissolving the powder in deionized water, adding nitric acid to dissolve completely to obtain a first mixed solution, and adding Mn (CH) with a preset material ratio into the first mixed solution when the first mixed solution is completely clear 3 COO) 2 ·4H 2 Mixing O and glycine to obtain a second mixed solution, wherein the first mixed solution is La (NO 3 ) 3 ；
Step two: precursor sample synthesis
Placing the second mixed solution in a water bath kettle, setting the temperature in the water bath kettle to be a first temperature, heating at a constant temperature, stirring until the solution is evaporated to gel state, and stopping heating; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to be a second temperature, and performing preliminary roasting for realizing La 0.84 MnO 3-δ Primary phase formation of the catalyst;
step three: roasting to obtain the final product
La obtained by preliminary phase formation 0.84 MnO 3-δ Adding the catalyst into a mortar for full grinding, transferring the fully ground sample into a crucible, setting the temperature of a muffle furnace to be a third temperature, and placing the crucible into the muffle furnace for high-temperature roasting to obtain La with complete crystal phase structure 0.84 MnO 3-δ The final product.
2. A cation-deficient La according to claim 1 x MnO 3±δ A process for preparing a catalyst, characterized in that in the first step La is reacted with 2 O 3 The method for preprocessing the powder comprises the following steps:
weighing La 2 O 3 Placing the raw materials into a crucible, transferring the crucible into a muffle furnace, and adding at a heating rate of 5 ℃ per minuteRoasting at 1000 deg.c for 2 hr to obtain pretreated La 2 O 3 And (3) powder.
3. A cation-deficient La according to claim 2 x MnO 3±δ A method for preparing a catalyst, characterized in that in the first step, the ratio of the amount of glycine added to the total metal ion in the second mixed solution is: n (glycine): n (total metal ions) =1.5:1.
4. A cation-deficient La according to claim 3 x MnO 3±δ The preparation method of the catalyst is characterized by comprising the following steps:
placing the second mixed solution in a water bath kettle, setting the temperature in the water bath kettle to 90 ℃, heating at constant temperature, stirring until the solution is evaporated to gel state, and stopping heating; placing the obtained gel sample in a muffle furnace, setting the temperature of the muffle furnace to 300 ℃, performing preliminary roasting, heating the gel sufficiently to spontaneous combustion to obtain a catalyst precursor, and further calcining the obtained catalyst precursor; wherein, in the calcination process, the temperature rising rate of 2 ℃/min is controlled, and the temperature is raised to 700 ℃ for calcination, and the duration of calcination is 6h.
5. A cation-deficient La according to claim 4 x MnO 3±δ A method for preparing the catalyst is characterized in that La is prepared 0.84 MnO 3-δ Catalyst with corresponding specific surface area of 21.0m 2 /g。
6. A cation-deficient La according to claim 4 x MnO 3±δ A method for preparing the catalyst is characterized in that La is prepared 0.84 MnO 3-δ The crystal phase structure of the catalyst is hexagonal.
7. La with cation defect x MnO 3±δ Catalytic reactionAgent characterized in that La with cationic defect as described in any one of the preceding claims 1 to 6 is used x MnO 3±δ The catalyst is prepared by a preparation method;
when 0.8<x<1, corresponding La x MnO 3-δ The catalyst is A-site cation defective; when 1<x<1.2 corresponding La x MnO 3+δ The catalyst is B-site cation defective; when x=1, the corresponding LaMnO 3 The catalyst is an nondefective perovskite oxide;
when x=0.84, la was prepared 0.84 MnO 3-δ The specific surface area of the catalyst is 21.0m 2 And/g, the crystal phase structure is hexagonal.
8. La with cation defect x MnO 3±δ The use of a catalyst, characterized in that the cation-deficient La x MnO 3±δ Use of a catalyst as defined in any one of claims 1 to 6 for La with cationic defects x MnO 3-δ La with cation defect prepared by a preparation method of catalyst x MnO 3-δ Catalyst for CO and C 3 H 8 Low temperature catalytic oxidation of (2).
9. A cation-deficient La according to claim 8 x MnO 3±δ The use of a catalyst is characterized in that La is prepared when x=0.84 0.84 MnO 3-δ Catalyst, la was used 0.84 MnO 3-δ The method for carrying out catalytic oxidation on CO by the catalyst comprises the following steps:
50mg of La was purified using a gas chromatograph 0.84 MnO 3-δ The catalyst is mixed with 50mg quartz sand and then placed in a U-shaped quartz tube, a K-shaped thermocouple is placed at the top of a catalyst reaction fixed bed and contacts the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 1% CO,21% O 2 Balance gas N 2 ；
Regulating gas flow rate to 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 Finally, the reactants and products were analyzed on-line on a gas chromatograph.
10. A cation-deficient La according to claim 8 x MnO 3±δ The use of a catalyst is characterized in that La is prepared when x=0.84 0.84 MnO 3-δ Catalyst, la was used 0.84 MnO 3-δ Catalyst pair C 3 H 8 The method for carrying out catalytic oxidation comprises the following steps:
50mgLa was purified by gas chromatography 0.84 MnO 3-δ The catalyst is mixed with 50mg of quartz sand and then placed in a quartz tube with the length of 30mm and the inner diameter of 10mm, a K-type thermocouple is placed at the top of a catalyst reaction fixed bed and contacted with the reaction bed to control the reaction temperature;
controlling the flow rate of the reaction gas by a mass flowmeter, wherein the reaction gas comprises the following components: 0.5% C 3 H 8 ，21％O 2 Balance gas N 2 ；
Regulating the total flow rate of the gas to be 30mL min -1 Setting the airspeed of a chromatographic air outlet to be 36000mL h -1 g -1 The reactants and products were analyzed on-line on a gas chromatograph.
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