Pd / Mn3O4-MnO catalyst and its preparation method and application in catalytic oxidation of formaldehyde

Abstract

The present invention relates to the field of pollution control and technology, and in particular to Pd / Mn 3 O 4 -MnO catalyst and its preparation method and application in catalytic oxidation of formaldehyde, Pd is uniformly loaded on MnO by liquid phase reduction method 2 The Pd-loaded Mn 3 O 4 In the process of formaldehyde catalytic oxidation, formaldehyde first reacts with Pd / Mn 3 O 4 The intermediate HCOOH is oxidized to form HCOOH, which is further oxidized to form CO on Pd / MnO. 2 and H 2 O, the step-by-step catalytic oxidation makes the prepared Pd-loaded two-component oxide catalyst have higher catalytic performance and better stability under different relative humidity. The present invention provides a catalyst for catalytic oxidation of formaldehyde at room temperature, which has the characteristics of low Pd loading, simple preparation materials, high room temperature reaction activity, good stability and good water resistance.

Description

Technical Field

[0001] The invention relates to the field of pollution control and technology, and in particular to a Pd / Mn3O4-MnO catalyst and a preparation method thereof, and application thereof in catalytic oxidation of formaldehyde. Background Art

[0002] The rapid development of my country's economy and society has greatly improved people's material living standards, but the resulting environmental problems, especially indoor air pollution, continue to endanger people's health. Formaldehyde (HCHO) is a ubiquitous carcinogenic indoor air pollutant. Long-term exposure can lead to a variety of diseases, such as skin allergies, asthma, acute poisoning, neurasthenia and even multiple cancers. Exploring effective methods to eliminate formaldehyde is crucial to improving the economy and safety of air quality. Among the many methods for removing formaldehyde, catalytic oxidation technology can convert formaldehyde into harmless carbon dioxide and water at a lower temperature. However, considering the requirements of its application environment, catalytic oxidation also has some technical difficulties, such as the high loading rate of precious metals, which will limit its commercial application due to its high cost; the accumulation of waste on the catalyst surface, the interaction between the catalyst and the dissociation reactants, and the inhibition of the redox ability of the catalyst poisoning. All these phenomena usually lead to severe deactivation of the catalyst after long-term operation, thereby inhibiting the treatment efficiency of catalytic oxidation.

[0003] At present, the catalysts used to remove indoor formaldehyde pollution mainly include transition metal oxide catalysts and precious metal-loaded catalysts. The effect of transition metal oxides in catalyzing the oxidation of formaldehyde is general and often requires higher reaction temperatures. Precious metal-loaded catalysts are better in catalyzing the oxidation of formaldehyde, but if the loading rate is too high, commercial applications will be limited by their high costs. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a Pd / Mn3O4-MnO catalyst and its application in catalytic oxidation of formaldehyde, to provide an efficient and inexpensive catalyst for catalytic oxidation of formaldehyde at room temperature, and to construct a two-component metal oxide-loaded Pd catalyst with the characteristics of low loading rate, simple preparation materials, high reaction activity at room temperature, good stability and good water resistance.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The first object of the present invention is to provide a method for preparing a Pd / Mn3O4-MnO catalyst, comprising the following steps:

[0007] (1) Preparation of δ-MnO2;

[0008] (2) Preparation of Pd / MnO2:

[0009] S21, placing sodium citrate, polyvinyl pyrrolidone and Na2PdCl4 in water and mixing them evenly to obtain a palladium-containing solution;

[0010] S22, sequentially adding an aqueous solution of ascorbic acid and a dispersion of the δ-MnO2 powder obtained in step (1) to the palladium-containing solution obtained in S21, stirring at 80° C., centrifuging, rinsing, drying, crushing and sieving to obtain Pd / MnO2;

[0011] (3) Preparation of Pd / Mn3O4-MnO catalyst:

[0012] The Pd / MnO2 prepared in step S22 is subjected to a reduction reaction in a H2 / Ar atmosphere at 200-350°C to obtain a Pd / Mn3O4-MnO catalyst.

[0013] Preferably, in S21, the molar ratio of sodium citrate to Na2PdCl4 is 20:1, and the molar ratio of polyvinyl pyrrolidone to Na2PdCl4 is 20:1.

[0014] Preferably, in S22, the mass fraction of ascorbic acid in the ascorbic acid aqueous solution is 1.07%, the molar ratio of ascorbic acid to Na2PdCl4 is 20:1, and the mass ratio of Pd element to δ-MnO2 in Na2PdCl4 is 0.2:100.

[0015] Preferably, in S22, the stirring time is 4 hours.

[0016] Preferably, the volume ratio of H2 / Ar in step (3) is 5-20%.

[0017] Preferably, the reduction time in H2 / Ar atmosphere is 0.5-2h.

[0018] The second object of the present invention is to provide a Pd / Mn3O4-MnO catalyst prepared by the above preparation method.

[0019] The third object of the present invention is to protect the application of the above Pd / Mn3O4-MnO catalyst in catalytic oxidation of formaldehyde at room temperature.

[0020] Preferably, for static formaldehyde removal scenarios, the application method is: placing the catalyst in a box or room containing formaldehyde gas, catalytically oxidizing formaldehyde at room temperature, the catalytic time is 30-120 minutes, and the formaldehyde gas concentration range is 0-500ppm.

[0021] Preferably, for the dynamic formaldehyde removal scenario, the application method is: place the catalyst that has been crushed and sieved to 40-60 mesh in the middle of the fixed bed reactor, and introduce a mixed gas of formaldehyde / oxygen / water vapor into it at 30,000-60,000 hours. -1Under the condition of space velocity, Pd / Mn3O4-MnO is used as catalyst to catalyze the oxidation of formaldehyde, the catalytic reaction temperature is 18-80℃, and the formaldehyde concentration is 0-100ppm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The method of catalytic oxidation of formaldehyde at room temperature of the present invention is: -1 Under the condition of an air velocity of 1.5°C, high-purity air and 100 ppm of formaldehyde blown off by nitrogen are introduced, and when the reaction temperature is only 18°C, the Pd / Mn3O4-MnO(1h) sample of Example 1 can completely oxidize formaldehyde, and the degradation rate of formaldehyde reaches 100%. Its performance is better than other types of manganese oxide catalysts reported so far. The raw materials of the catalyst of the present invention are easy to obtain and the preparation is simple.

[0024] 2. The present invention uniformly loads Pd on MnO2 by a liquid phase reduction method to achieve a low loading rate of the precious metal Pd of 0.17%. A Pd-loaded Mn3O4-MnO two-component metal oxide catalyst is in situ constructed by a hydrogen reduction method, so that formaldehyde is oxidized to an intermediate HCOOH on Pd / Mn3O4, and the intermediate is further oxidized and decomposed into CO2 and H2O on Pd / MnO. The step-by-step catalytic oxidation makes the prepared Pd-loaded two-component oxide catalyst show higher catalytic performance and better stability under different relative humidities.

[0025] 3. In the present invention, metal Pd is loaded on δ-MnO2 by a liquid phase reduction method. In a H2 / Ar atmosphere, metal Pd and carrier δ-MnO2 are co-reduced to obtain a Pd-loaded Mn3O4-MnO two-component metal oxide catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Field emission scanning electron microscope images of the Pd / MnO2 catalyst of Comparative Example 1 of the present invention, the Pd / Mn3O4 catalyst of Comparative Example 2, the Pd / Mn3O4-MnO(0.5h) catalyst of Example 2, the Pd / Mn3O4-MnO(1h) catalyst of Example 1, and the Pd / Mn3O4-MnO(2h) catalyst of Example 3;

[0027] Figure 2 Field emission transmission electron microscopy images of the Pd / MnO2 catalyst of Comparative Example 1 and the Pd / Mn3O4-MnO(1h) catalyst of Example 1;

[0028] Figure 3 The catalysts of Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were heated to 100 ppm HCHO concentration and 60000 h / min space velocity. -1Performance curve of formaldehyde catalytic oxidation under test conditions;

[0029] Figure 4 This is a stability test chart of the Pd / Mn3O4-MnO(1h) catalyst of Example 1 under different relative humidities. DETAILED DESCRIPTION

[0030] The following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

[0031] Example 1

[0032] The preparation method of δ-MnO2 in the present invention can be prepared by conventional technical means. In this embodiment, δ-MnO2 is prepared by the method in the following steps (1).

[0033] The preparation method of Pd / Mn3O4-MnO catalyst comprises the following steps:

[0034] (1) Preparation of δ-MnO2:

[0035] S11, vigorously stir and mix 50 mL of 0.126 M KMnO4 and 80 mL of 0.04 M (NH4)2C2O4·H2O aqueous solution in a 60°C water bath for 60 minutes to obtain a mixed solution;

[0036] S12, the mixed solution in step S11 was transferred to a 200 mL autoclave and kept at 110° C. for 24 hours, the final precipitate was centrifuged and washed several times, and dried at 80° C. overnight, and the product was named δ-MnO2;

[0037] (2) Preparation of Pd / MnO2:

[0038] S21, dissolving sodium citrate and PVP in deionized water, adding a Na2PdCl4 solution with a mass concentration of 2 g / L dropwise into the mixed solution, wherein the molar ratio of sodium citrate to Na2PdCl4 is 20:1, and the molar ratio of PVP to Na2PdCl4 is 20:1, and vigorously stirring in a water bath at 80°C for 5 minutes to obtain a palladium-containing solution;

[0039] S22, then the aqueous solution of ascorbic acid is added dropwise to the above solution, after 1 hour, the prepared δ-MnO2 powder (dispersed in 50 ml of deionized water, ultrasonically pretreated) is added to the palladium-containing solution, and stirred in a water bath at 80°C for another 4 hours, the precipitate is centrifuged, rinsed with distilled water several times, rinsed with ethanol once, and finally the product is dried in an oven at 80°C, crushed through a 40-mesh sieve by tabletting, and Pd / MnO2 catalyst is obtained;

[0040] (3) Preparation of Pd / Mn3O4-MnO catalyst:

[0041] The Pd / MnO2 catalyst prepared in step S22 was reduced in a 10 vol.% H2 / Ar atmosphere at 200°C for 1 h, and crushed by tabletting and passing through a 40-mesh sieve to obtain a Pd / Mn3O4-MnO (1h) catalyst.

[0042] Example 2

[0043] The preparation steps are the same as those in Example 1, except that the reduction for 1 h in step (3) of Example 1 is replaced by reduction for 30 min, and the preparation is named Pd / Mn3O4-MnO (0.5 h).

[0044] Example 3

[0045] The preparation steps are the same as those in Example 1, except that the reduction for 1 h in step (3) of Example 1 is replaced by reduction for 2 h, and the reaction is named Pd / Mn3O4-MnO (2 h).

[0046] Example 4

[0047] (1) Preparation of δ-MnO2:

[0048] S11, vigorously stir and mix 50 mL of 0.126 M KMnO4 and 80 mL of 0.04 M (NH4)2C2O4·H2O aqueous solution in a 70°C water bath for 50 minutes to obtain a mixed solution;

[0049] S12, the mixed solution in step S11 was transferred to a 200 mL autoclave and kept at 105° C. for 25 hours, the final precipitate was centrifuged and washed several times, and dried at 80° C. overnight, and the product was named δ-MnO2;

[0050] (2) Preparation of Pd / MnO2:

[0051] S21, dissolving sodium citrate and PVP in deionized water, adding a Na2PdCl4 solution with a mass concentration of 2 g / L dropwise into the mixed solution, wherein the molar ratio of sodium citrate to Na2PdCl4 is 20:1, and the molar ratio of PVP to Na2PdCl4 is 20:1, and vigorously stirring in a water bath at 80°C for 5 minutes to obtain a palladium-containing solution;

[0052] S22, then the aqueous solution of ascorbic acid was added dropwise to the above solution, after 1 hour, the prepared δ-MnO2 powder (dispersed in 50 ml of deionized water, ultrasonically pretreated) was added to the palladium-containing solution, and stirred in a water bath at 80°C for another 4 hours, the precipitate was centrifuged, rinsed with distilled water several times, rinsed with ethanol once, and finally the product was dried in an oven at 80°C, crushed through a 50-mesh sieve by tabletting, and Pd / MnO2 catalyst was obtained;

[0053] (3) Preparation of Pd / Mn3O4-MnO catalyst:

[0054] The Pd / MnO2 catalyst prepared in step S22 was reduced in a 5 vol.% H2 / Ar atmosphere at 300°C for 1 h, and crushed by tabletting and passing through a 50-mesh sieve to obtain a Pd / Mn3O4-MnO (1h) catalyst.

[0055] Example 5

[0056] (1) Preparation of δ-MnO2:

[0057] S11, 50 mL of 0.126 M KMnO4 and 80 mL of 0.04 M (NH4)2C2O4·H2O aqueous solution were vigorously stirred and mixed in a water bath at 80°C for 30 minutes to obtain a mixed solution;

[0058] S12, the mixed solution in step S11 was transferred to a 200 mL autoclave and kept at 100° C. for 26 hours, the final precipitate was centrifuged and washed several times, and dried at 80° C. overnight, and the product was named δ-MnO2;

[0059] (2) Preparation of Pd / MnO2:

[0060] S21, dissolving sodium citrate and PVP in deionized water, adding a Na2PdCl4 solution with a mass concentration of 2 g / L dropwise into the mixed solution, wherein the molar ratio of sodium citrate to Na2PdCl4 is 20:1, and the molar ratio of PVP to Na2PdCl4 is 20:1, and vigorously stirring in a water bath at 80°C for 5 minutes to obtain a palladium-containing solution;

[0061] S22, then the aqueous solution of ascorbic acid was added dropwise to the above solution, after 1 hour, the prepared δ-MnO2 powder (dispersed in 50 ml of deionized water, ultrasonically pretreated) was added to the palladium-containing solution, and stirred in a water bath at 80°C for another 4 hours, the precipitate was centrifuged, rinsed with distilled water several times, rinsed with ethanol once, and finally the product was dried in an oven at 80°C, crushed through a 60-mesh sieve by tabletting, and Pd / MnO2 catalyst was obtained;

[0062] (3) Preparation of Pd / Mn3O4-MnO catalyst:

[0063] The Pd / MnO2 catalyst prepared in step S22 was reduced in a 20 vol.% H2 / Ar atmosphere at 350°C for 1 h, and crushed by tabletting and passing through a 60-mesh sieve to obtain a Pd / Mn3O4-MnO (1h) catalyst.

[0064] Comparative Example 1

[0065] The Pd / MnO2 catalyst prepared in step (2) of Example 1 was used.

[0066] Comparative Example 2

[0067] Pd / MnO2 was prepared by the same method as step (1) to step (2) of Example 1. Pd / MnO2 was reduced in 10% by volume H2 / Ar at 150°C for 30 min, with a gas flow rate of 100 mL / min and a heating rate of 5°C / min. The obtained product was named Pd / Mn3O4 catalyst.

[0068] Examples 1-3 of the present invention all prepared Pd / Mn3O4-MnO catalysts with excellent catalytic performance and high Pd loading rate. The following uses the Pd / Mn3O4-MnO(1h), Pd / Mn3O4-MnO(0.5h), and Pd / Mn3O4-MnO(2h) catalysts of Examples 1-3 as examples to compare and study the Pd / MnO2 catalyst of Comparative Example 1 and the Pd / Mn3O4 catalyst of Comparative Example 2. The specific research methods and results are as follows:

[0069] Performance Characterization

[0070] 1. Catalyst activity test

[0071] 0.1 g of Pd / MnO2, Pd / Mn3O4, Pd / Mn3O4-MnO(1h), Pd / Mn3O4-MnO(0.5h), Pd / Mn3O4-MnO(2h) catalysts were placed in a fixed bed reactor for catalytic activity evaluation. The experimental conditions were: 100 ppm HCHO, 54.5% high purity air, 40% water vapor, 5.5% HCHO stripped with N2, and the air velocity was 60000 h -1 , the carbon dioxide concentration was detected by gas chromatography.

[0072] 2. Catalyst stability and water resistance test

[0073] Stability and water resistance tests were conducted on Pd / Mn3O4-MnO(1h): 0.1 g of the catalyst was placed in a fixed bed reactor for catalytic stability and water resistance evaluation. The experimental conditions were: 100 ppm HCHO, and the water-gas ratios were 0, 20%, 0, 40%, 0, 60%, 0, 80%, 0, 40%, respectively. The test was conducted for 2 hours under each condition.

[0074] Results and Discussion

[0075] from Figure 1 A picture and Figure 2 As can be seen from Figure A, the catalyst prepared in Comparative Example 1 is nanoflower-like Pd / MnO2.

[0076] from Figure 1 As can be seen from Figure B, the catalyst prepared in Comparative Example 2 is nanoflower-like Pd / Mn3O4.

[0077] from Figure 1 It can be seen from Figure C that the catalyst prepared in Example 2 is nanoflower-shaped Pd / Mn3O4-MnO (0.5h).

[0078] from Figure 1 D Figure and Figure 2 As can be seen from Figure B, the catalyst prepared in Example 1 is nanoflower-shaped Pd / Mn3O4-MnO(1h).

[0079] from Figure 1 It can be seen from E that the catalyst prepared in Example 3 is nanoflower-like Pd / Mn3O4-MnO (2h);

[0080] The catalytic performance results of different catalysts are as follows Figure 3 The results show that the formaldehyde conversion rate of Pd / MnO2 is less than 40% within 80°C, the formaldehyde conversion rate of Pd / Mn3O4 is 90% at 80°C, the formaldehyde conversion rate of Pd / Mn3O4-MnO (0.5h) and Pd / Mn3O4-MnO (2h) at 20°C reaches more than 90%, and Pd / Mn3O4-MnO (1h) has the best performance in catalytic decomposition of formaldehyde, with a formaldehyde conversion rate of 100% at 20°C.

[0081] Figure 4 This is a stability test chart of the Pd / Mn3O4-MnO(1h) catalyst of Example 1 under different relative humidity. The results show that the formaldehyde conversion rate of Pd / Mn3O4-MnO(1h) is the highest when the relative humidity is 40%, and after 18 hours, the formaldehyde conversion rate of the catalyst can still reach more than 90%, indicating that Pd / Mn3O4-MnO(1h) has high stability.

[0082] In summary, the Pd-loaded two-component oxide Pd / Mn3O4-MnO catalyst prepared by the method of the present invention has higher catalytic performance and better stability under different relative humidity.

[0083] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a Pd / Mn3O4-MnO catalyst, characterized in that: The steps include: (1) Preparation of δ-MnO2; (2) Preparation of Pd / MnO2: S21, placing sodium citrate, polyvinyl pyrrolidone and Na2PdCl4 in water and mixing them evenly to obtain a palladium-containing solution; S22, sequentially adding the ascorbic acid aqueous solution and the dispersion of δ-MnO2 powder to the palladium-containing solution obtained in S21, stirring at 80° C., centrifuging, rinsing, drying, crushing and sieving to obtain Pd / MnO2; (3) Preparation of Pd / Mn3O4-MnO catalyst: The Pd / MnO2 prepared in step S22 is subjected to a reduction reaction in a H2 / Ar atmosphere at 200-350°C to obtain a Pd / Mn3O4-MnO catalyst; Among them, in S21, the molar ratio of sodium citrate to Na2PdCl4 is 20:1, and the molar ratio of polyvinyl pyrrolidone to Na2PdCl4 is 20:1; In S22, the mass fraction of ascorbic acid in the ascorbic acid aqueous solution is 1.07%, the molar ratio of ascorbic acid to Na2PdCl4 is 20:1, and the mass ratio of Pd element to δ-MnO2 in Na2PdCl4 is 0.2:

100.

2. The method for preparing the Pd / Mn3O4-MnO catalyst according to claim 1, characterized in that: In S22, the stirring time is 4 hours.

3. The method for preparing the Pd / Mn3O4-MnO catalyst according to claim 1, characterized in that: In step (3), the volume ratio of H2 / Ar is 5-20%.

4. The method for preparing the Pd / Mn3O4-MnO catalyst according to claim 1, characterized in that: The reduction time in H2 / Ar atmosphere is 0.5-2h.

5. A Pd / Mn3O4-MnO catalyst prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the Pd / Mn3O4-MnO catalyst according to claim 5 for catalytic oxidation of formaldehyde at room temperature.

7. Use of the Pd / Mn3O4-MnO catalyst according to claim 6 for catalytic oxidation of formaldehyde at room temperature, characterized in that: For static formaldehyde removal scenarios, the application method is: place the catalyst in a box or room containing formaldehyde gas, catalytically oxidize formaldehyde at room temperature, the catalytic time is 30-120 minutes, and the formaldehyde gas concentration range is 0-500ppm.

8. Use of the Pd / Mn3O4-MnO catalyst for catalytic oxidation of formaldehyde at room temperature according to claim 6, characterized in that: For the dynamic formaldehyde removal scenario, the application method is: place the pressed, crushed and sieved catalyst of 40-60 mesh in the middle of the fixed bed reactor, and introduce a mixed gas of formaldehyde / oxygen / water vapor into it at 30,000-60,000 hours. -1 Under the condition of space velocity, Pd / Mn3O4-MnO is used as catalyst to catalyze the oxidation of formaldehyde, the catalytic reaction temperature is 18-80℃, and the formaldehyde concentration is 0-100ppm.

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