CN113083324A

CN113083324A - Formaldehyde oxidation catalyst used at room temperature and preparation method thereof

Info

Publication number: CN113083324A
Application number: CN202110408717.XA
Authority: CN
Inventors: 郭耘; 赵海林; 顾涵; 王丽; 詹望成; 郭杨龙; 王筠松
Original assignee: East China University of Science and Technology
Current assignee: East China University of Science and Technology
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2021-07-09
Anticipated expiration: 2041-04-16
Also published as: CN113083324B

Abstract

The invention provides Pt/NiO @ NiMnO for formaldehyde oxidation at room temperature_x(2.5<x<3) A catalyst and a preparation method thereof. The catalyst has a core-shell structure as a carrier, NiO nanoparticles as a core and NiMnO as a shell layer_xAmorphous complex oxide of which 2.5<x<3; the active component is Pt, and the Pt loading amount is 0.1-1.0 wt.%. The preparation method comprises the steps of preparation of a carrier with a core-shell structure, loading of an active component, reduction activation of a catalyst and the like. The catalyst of the invention has high formaldehyde oxidation activity and good stability, and can completely convert 300ppm of formaldehyde into CO at room temperature₂And H₂O, and the conversion rate remained stable for 60 hours continuously. The catalyst has the advantages of low Pt loading capacity, low price, simple preparation and good formaldehyde purification effect, and is suitable for industrial production and application.

Description

Formaldehyde oxidation catalyst used at room temperature and preparation method thereof

Technical Field

The invention relates to the field of environmental catalysis and the field of indoor air purification, and the formaldehyde in air is catalytically oxidized under room temperature. The catalyst can be used for catalytically oxidizing 300ppm of formaldehyde gas into carbon dioxide and water at room temperature, the conversion rate of formaldehyde can reach 100%, and the conversion rate is kept stable after continuous reaction for 60 hours.

Background

Formaldehyde is an important chemical raw material and widely exists in building materials, decoration materials and textiles. The formaldehyde in these materials is slowly released and ubiquitous in the indoor environment, becoming a major indoor air pollutant. The long-term exposure in even a low-concentration formaldehyde environment can cause great harm to human bodies, and respiratory diseases and even carcinogenesis can be caused. The condition that the indoor formaldehyde exceeds the standard in China is still very serious, so that the method for effectively eliminating the formaldehyde in the indoor air has great application value.

The currently widely applied indoor formaldehyde purification technology is physical or chemical adsorption and photocatalysis. Adsorption technology has limited energy absorption capacity, so the adsorption material needs to be replaced regularly, the application cost is high, and secondary pollution can be generated. The light source required by the photocatalytic technology is generally high-energy ultraviolet light, the energy consumption is high, byproducts are easily generated to cause secondary pollution, and in addition, the photocatalyst is also easily inactivated. The room temperature formaldehyde oxidation catalysis technology is an ideal indoor formaldehyde purification method due to the advantages of high purification efficiency, no secondary pollution, no need of additional energy input and the like, and the key point is the formaldehyde oxidation catalyst with high activity and high stability.

The catalyst for formaldehyde oxidation at room temperature is generally a catalyst taking noble metal as an active component, for example, patent CN 106040230a supports Pt on boehmite and is applied to formaldehyde catalytic oxidation reaction, and the catalyst is found to have good adsorption performance on formaldehyde, and can oxidize part of formaldehyde at room temperature. When the Pt content is 2-2.5 wt.%, the conversion rate of formaldehyde at normal temperature is 72%, and 60%^oC can be completely converted. In patent CN 106492792A, a supported formaldehyde oxidation catalyst is prepared by taking an acid-treated titanium dioxide nanobelt as a carrier and Pt as an active component. Wherein the loading amount of Pt is 0.5 wt.%, the particle size is 2-4 nm, and Pt in a metal state and an ionic state coexists. The catalyst has the full conversion temperature of formaldehyde of 41.9% under the environment with room temperature and relative humidity RH = 0-80%, the Pt loading capacity is improved to 1.5 wt%, and the formaldehyde is at room temperatureThe conversion rate reaches 100 percent. The type and nature of the support also has a significant effect on the catalyst activity. Such as Colussi et al (Catalysis Today 253 (2015)) 163-₂，TiO₂，Al₂O₃And ZrO₂Equal load of 1wt.% Pt for formaldehyde oxidation reaction, Pt/Al₂O₃Highest activity, 25^oThe formaldehyde conversion at C was 62%. Patent CN 106964348A compares P25, Al₂O₃And the effect of AlOOH as a support on the activity of Pt-based catalysts, 1wt.% Pt/AlOOH formaldehyde activity was higher than Pt/P25 and Pt/Al under the same conditions₂O₃。

The Pt-based catalyst has good catalytic performance for formaldehyde oxidation reaction, but the research on the stability of the catalyst is less. In addition, most catalysts have high Pt content, and the application of Pt-based catalysts in indoor formaldehyde purification is limited due to high price and small storage amount. Therefore, the development of a Pt-based catalyst with low load, high activity and stability has great practical significance by selecting a proper carrier.

Disclosure of Invention

Aiming at the defects of high Pt loading, high price and limited application of the prior Pt-based catalyst for realizing the full conversion of formaldehyde, the invention aims to develop a catalyst which can completely convert indoor harmful gas formaldehyde into CO at room temperature₂And H₂O, or a salt thereof. The catalyst has the characteristics of low platinum loading capacity, high formaldehyde oxidation activity, high stability, relatively low price and the like. The formaldehyde eliminating agent is suitable for effectively eliminating formaldehyde in closed spaces or semi-closed spaces such as production workshops, building material and decoration material markets, home environments and the like.

The purpose of the invention can be realized by the following technical scheme: a formaldehyde oxidation catalyst used at room temperature comprises a carrier and an active component.

The carrier is of a core-shell structure, NiO nano particles are used as a core, and amorphous composite oxide NiMnO is used_xIs a shell, wherein 2.5<x<3。

The active component is Pt, and the loading amount of the Pt is 0.1-1 wt.%.

In the carrier, the particle size of the NiO nano-particles is 2-20 nm.

In the carrier, the molar ratio of Ni/(Ni + Mn) is 0.1-0.5.

The carrier is obtained by the following method: the precipitation sequence is controlled by controlling the addition sequence of manganese and nickel precursors, after a precipitator is added, a coprecipitate with a nickel salt precipitate at the center and a manganese-nickel composite precipitate as a shell layer is formed, and then the coprecipitate is washed, dried and roasted to obtain NiO @ NiMnO with a core-shell structure_x（2.5<x<3) Carrier

The Mn precursor comprises manganese nitrate, manganese sulfate, manganous chloride and manganese acetate.

The Ni precursor comprises nickel nitrate, nickel sulfate, nickel chloride and nickel acetate.

The precipitator is one or more of sodium carbonate, sodium hydroxide, ammonia water or oxalic acid, and the addition molar amount of the precipitator is 2 times or more of the total molar amount of the metal ions.

The roasting temperature of the carrier is 350-450 ℃.

A method for preparing a formaldehyde oxidation catalyst, the method comprising the steps of:

soaking the carrier in a Pt precursor aqueous solution, and finally drying, roasting and reducing by hydrogen to obtain Pt/NiO @ NiMnO_x（2.5<x<3) A catalyst.

The precursor of Pt is selected from H₂PtCl₆、Pt(NO₃)₂、PtCl₄、Pt(NH₃)₄Cl₂And Pt (NH)₃)₄(NO₃)₂One kind of (1).

H₂The reduction temperature is between 200 ℃ and 300 ℃, and the reduction time is 0.5-2 hours. Compared with the prior art, the invention has the following advantages.

1. In the preparation process of the catalyst carrier, the selection of the type of the precipitator, the roasting temperature and the auxiliary agent can greatly influence the crystal phase of manganese species and the structure of the carrier. Different crystalline phases, e.g. amorphous manganese oxide, Mn₂O₃、Mn₃O₄Etc. to nailThe aldehyde oxidation activity has a significant effect. Through a large number of experiments, the invention preferably selects amorphous NiMnO_x（2.5<x<3) The crystal phase with optimal activity is adopted; the NiO nano-particles are preferably selected as the core, so that on one hand, the redox performance of the manganese oxide and the adsorption performance of formaldehyde can be enhanced, on the other hand, the interaction between the carrier and the active component Pt can be promoted, the chemical state of Pt can be adjusted, and further, the formaldehyde oxidation performance of the catalyst can be improved.

2. The carrier is prepared by a distributed precipitation method, and the precipitator is one or more of sodium carbonate, sodium hydroxide, ammonia water or oxalic acid. Firstly adding a nickel precursor and a precipitator into deionized water to form a nickel salt precipitate, and then simultaneously adding the nickel precursor, the manganese precursor and the precipitator to form a manganese-nickel composite precipitate at the periphery of the nickel salt precipitate. Washing, drying and roasting the obtained precipitate to obtain NiO @ NiMnO_x（2.5<x<3) A carrier with a core-shell structure. The Pt is loaded on the carrier by an impregnation method, for example, the carrier is impregnated in a Pt precursor water solution, and finally Pt/NiO @ NiMnO is obtained by drying, roasting and hydrogen reduction activation_x（2.5<x<3) A catalyst.

Drawings

FIG. 1 shows the stability of the catalyst obtained in examples 13 to 15 at 25 ℃ in the formaldehyde oxidation reaction.

Detailed Description

The formaldehyde oxidation catalyst and the preparation method thereof according to the present invention are further illustrated by the following specific examples, and it should be noted that the following examples are only for describing the contents of the present invention, and the scope of the present invention is not limited to these examples. It is within the scope of the present invention to make simple modifications or substitutions to the methods, procedures or conditions for preparing the catalyst of the present invention without departing from the spirit or essential attributes thereof; the basic operations used in the examples are conventional and well known to those skilled in the art, unless otherwise specified. The evaluation of the formaldehyde oxidation activity of the catalyst is carried out in a fixed bed reactor, the formaldehyde concentration is 300ppm, the balance is air, and the mass space velocity is 40000 mL/g.h.

Example 1

Adding 0.016 mol of Mn (NO)₃)₂Dissolving the manganese oxalate into 200 mL of deionized water, and adding 0.032 mol of oxalic acid as a precipitator to obtain manganese oxalate precipitate. Filtering, washing, drying and roasting the precipitate at 350 ℃ for 2 hours to obtain amorphous MnO_x（1.5<x<2) A catalyst.

Example 2

Adding 0.016 mol of Mn (NO)₃)₂Dissolving the manganese oxalate into 200 mL of deionized water, and adding 0.032 mol of oxalic acid as a precipitator to obtain manganese oxalate precipitate. Filtering, washing and drying the precipitate, and roasting at 400 ℃ for 2 hours to obtain MnO₂A catalyst.

Example 3

Adding 0.016 mol of Mn (NO)₃)₂Dissolving the manganese oxalate into 200 mL of deionized water, and adding 0.032 mol of oxalic acid as a precipitator to obtain manganese oxalate precipitate. Filtering, washing and drying the precipitate, and roasting at 450 ℃ for 2 hours to obtain Mn₂O₃A catalyst.

Example 4

0.016 mol of Ni (NO)₃)₂Dissolving the nickel oxalate into 200 mL of deionized water, and adding 0.032 mol of oxalic acid as a precipitator to obtain nickel oxalate precipitate. And filtering, washing and drying the precipitate, and roasting at 400 ℃ for 2 hours to obtain the NiO catalyst.

Example 5

Preparation of MnO in example 1_x（1.5<x<2) Oxide, then 0.004 mol Ni (NO) by the isovolumetric impregnation method₃)₂Drying and roasting at 400 ℃ for 2 hours to obtain 0.2NiO/MnO_x（1.5<x<2) Catalyst, wherein the molar ratio Ni/(Ni + Mn) is 0.2.

Example 6

NiO oxide was prepared as in example 2, and then 0.004 mol Mn (NO) was impregnated by an equal volume impregnation method₃)₂Drying and roasting at 400 ℃ for 2 hours to obtain 0.2MnO_x/NiO（1.5<x<2) Catalyst, wherein the Mn/(Ni + Mn) molar ratio is 0.2.

Example 7

0.001 mol of Ni (NO)₃)₂Dissolving the nickel oxalate into 200 mL of deionized water, and adding 0.002 mol of oxalic acid as a precipitator to obtain nickel oxalate precipitate. Then 0.018 mol of Mn (NO)₃)₂And 0.001 mol of Ni (NO)₃)₂Dissolving the solution in the above liquid, adding 0.038 mol oxalic acid as precipitant to form composite precipitate of manganese oxalate and nickel oxalate around the nickel oxalate precipitate. Filtering, washing and drying the obtained precipitate, and roasting at 400 ℃ for 2 hours to obtain 0.1NiO @ NiMnO of a core-shell structure_x（2.5<x<3) A catalyst.

Example 8

0.002 mol of Ni (NO)₃)₂Dissolving the nickel oxalate into 200 mL of deionized water, and adding 0.004 mol of oxalic acid as a precipitator to obtain nickel oxalate precipitate. Then 0.016 mol of Mn (NO)₃)₂And 0.002 mol of Ni (NO)₃)₂Dissolving the solution in the above liquid, adding 0.036 mol oxalic acid as precipitant to form composite precipitate of manganese oxalate and nickel oxalate around the nickel oxalate precipitate. Filtering, washing and drying the obtained precipitate, and roasting at 400 ℃ for 2 hours to obtain 0.2NiO @ NiMnO of a core-shell structure_x（2.5<x<3) A catalyst.

Example 9

The catalysts obtained in examples 1 to 8 were subjected to a formaldehyde oxidation activity test. Evaluation of catalytic Formaldehyde oxidation activity of each catalyst was carried out in a fixed bed reactor (quartz tube, inner diameter 6 mm) under normal pressure. The mass of the catalyst is 0.30 g, the concentration of formaldehyde is 300ppm, and N₂The bubbling flow rate and the air flow rate are respectively 30 and 170 mL/min, and the mass space velocity is WHSV = 40000 mL g^-1·h^-1. The temperature of the catalyst bed layer is increased from 25 ℃ to 200 ℃, and the temperature rising rate is 2 ℃/min. And (3) detecting the concentration of the formaldehyde in the inlet and the outlet on line by using a GC2060 gas chromatograph (Porapak-Q chromatographic column). The conversion of formaldehyde was calculated using the following formula: conversion = (C)_in-C_out）/C_inX 100%. Wherein C is_inAnd C_outConcentration (ppm) of formaldehyde at the inlet and outlet, respectively. The formaldehyde oxidation activity of the catalyst obtained in each of the examples is shown in Table 1. As can be seen from Table 1, pure manganese oxide activityIn poor, different crystalline forms of manganese oxide, amorphous MnO_x（1.5<x<2) The total conversion temperature is the lowest and is 138 ℃. The activity of the pure nickel oxide catalyst is worse, and the full conversion temperature of 300ppm formaldehyde reaches 188 ℃. NiO is simply supported in MnO_x（1.5<x<2) The formaldehyde oxidation activity of the catalyst is not improved. The existence of the core-shell structure greatly improves the activity of the nickel-manganese composite catalyst, wherein 0.2NiO @ NiMnO_x（2.5<x<3) The activity is highest, and the full conversion temperature of 300ppm formaldehyde is 97 ℃. Generally speaking, for catalysts containing no noble metal, the conversion rate of formaldehyde at room temperature is very low, and the elimination of formaldehyde at room temperature in daily life is difficult to meet. In order to further improve the formaldehyde purification efficiency at room temperature, the subsequent examples were carried out with Pt loading, and the formaldehyde purification effect was tested.

TABLE 1 catalysts obtained in examples 1 to 8 have catalytic Formaldehyde oxidation activity

Example 10

MnO preparation by the method of example 1_x（1.5<x<2) A carrier;

2g of MnO was taken_x（1.5<x<2) The carrier was immersed in 2 mL of a solution having a concentration of 0.001g_PtH/mL₂PtCl₆Drying the mixture in an aqueous solution, roasting the dried mixture for 2 hours at 400 ℃ in an air atmosphere, and finally reducing the dried mixture for 1 hour in hydrogen at 300 ℃ to obtain Pt/MnO_x（1.5<x<2) Catalyst wherein Pt loading was 0.1 wt.%.

Example 11

Prepared by the method of example 7 to give 0.1NiO @ NiMnO_x（2.5<x<3) A carrier;

2g of 0.1NiO @ NiMnO was taken_x（2.5<x<3) The carrier was immersed in 2 mL of a solution having a concentration of 0.001g_PtH/mL₂PtCl₆Drying in an aqueous solution, roasting for 2 hours at 400 ℃, and finally reducing for 1 hour in hydrogen at 300 ℃ to obtain Pt/0.1NiO @ NiMnO_x（2.5<x<3) Catalyst and process for preparing sameWherein the Pt loading is 0.1 wt.%.

Example 12

Prepared by the method of example 8 to obtain 0.2NiO @ NiMnO_x（2.5<x<3) A carrier;

2g of 0.2NiO @ NiMnO was taken_x（2.5<x<3) The carrier was immersed in 2 mL of a solution having a concentration of 0.001g_PtH/mL₂PtCl₆Drying in an aqueous solution, roasting for 2 hours at 400 ℃, and finally reducing for 1 hour in hydrogen at 300 ℃ to obtain Pt/0.2NiO @ NiMnO_x（2.5<x<3) Catalyst wherein Pt loading was 0.1 wt.%.

Example 13

The catalyst was prepared analogously to example 12, with the difference that H was used₂PtCl₆The concentration of the aqueous solution was 0.002g_Ptand/mL. The prepared Pt/0.2NiO @ NiMnO_x（2.5<x<3) Catalyst Pt loading was 0.2 wt.%.

Example 14

The catalyst was prepared in a similar manner to example 13, except that sodium carbonate was used as the precipitant in the preparation of the carrier, and the amount of sodium carbonate added was 0.040 mol. The prepared Pt/0.2NiO @ NiMnO_x（2.5<x<3) Catalyst Pt loading was 0.2 wt.%.

Example 15

The catalyst was prepared in a similar manner to example 13, except that the precursor of Pt was Pt (NO)₃)₂Pt (NO) used₃)₂The concentration of the aqueous solution was 0.002g_Ptand/mL. The prepared Pt/0.2NiO @ NiMnO_x（2.5<x<3) Catalyst Pt loading was 0.2 wt.%.

Example 16

The preparation method of the catalyst is similar to that of example 14, except that the calcination temperature of the carrier is 450 ℃ and the calcination time is 2 hours. The prepared Pt/0.2NiO @ NiMnO_x（2.5<x<3) Catalyst Pt loading was 0.2 wt.%.

Example 17

The formaldehyde oxidation activity of the catalysts obtained in examples 10 to 16 was measured by the method of example 9, and the formaldehyde oxidation activity of each of the catalysts obtained is shown in table 2. The stability test was performed on catalysts (examples 13 to 15) having a formaldehyde conversion of 100% at room temperature. The test conditions were similar to the activity test except that the catalyst bed temperature was always controlled at 25 ℃ and the conversion of formaldehyde was measured every 1 hour. The formaldehyde oxidation stability of the catalysts obtained in examples 13 to 15 is shown in FIG. 1.

As can be seen from table 2, the room temperature formaldehyde oxidation activity of the catalysts obtained in the examples was greatly improved after Pt loading. The introduction of NiO is also beneficial to the oxidation of formaldehyde, and particularly, Pt is loaded at NiO @ NiMnO_x（2.5<x<3) The structure of the carrier shows the best formaldehyde catalytic activity, and when the Pt loading is 0.2 wt.%, Pt/0.2NiO @ NiMnO_x（2.5<x<3) The catalyst can completely oxidize 300ppm formaldehyde at room temperature. The catalyst with the same components and structure prepared by the type of the precipitator and the type of the Pt precursor in the preparation process of the replaced carrier has similar formaldehyde oxidation activity, and is beneficial to industrial production and application of the catalyst. As can be seen from the stability test results of FIG. 1, the Pt loading was 0.2 wt.% Pt/0.2NiO @ NiMnO_x（2.5<x<3) The catalyst continuously reacts for 60 hours, the conversion rate of formaldehyde at room temperature is maintained at 100%, and the catalyst has stable formaldehyde oxidation performance and practical application value.

TABLE 2 catalysts obtained in examples 10 to 16 have formaldehyde catalytic oxidation activity

Claims

1. A formaldehyde oxidation catalyst used at room temperature, which comprises a carrier and an active component, and is characterized in that: the carrier is of a core-shell structure, NiO nano particles are used as cores, and amorphous composite oxide NiMnO is used_xIs a shell, wherein 2.5<x<3; the active component is Pt, and the loading amount of the Pt is 0.1-1 wt.%.

2. The formaldehyde oxidation catalyst according to claim 1, wherein the NiO nanoparticles in the support have a particle size of 2 to 20 nm.

3. The formaldehyde oxidation catalyst according to claim 1, wherein the molar ratio of Ni/(Ni + Mn) in the carrier is 0.1 to 0.5.

4. The formaldehyde oxidation catalyst according to claim 1, wherein the carrier is obtained by the following method: the precipitation sequence is controlled by controlling the addition sequence of manganese and nickel precursors, after a precipitator is added, a coprecipitate with a nickel salt precipitate at the center and a manganese-nickel composite precipitate as a shell layer is formed, and then the coprecipitate is washed, dried and roasted to obtain NiO @ NiMnO with a core-shell structure_x（2.5<x<3) And (3) a carrier.

5. The formaldehyde oxidation catalyst as set forth in claim 4 wherein the Mn precursor includes manganese nitrate, manganese sulfate, manganous chloride and manganese acetate.

6. The formaldehyde oxidation catalyst according to claim 4, wherein the Ni precursor comprises nickel nitrate, nickel sulfate, nickel chloride and nickel acetate.

7. The formaldehyde oxidation catalyst according to claim 4, wherein the precipitant is one or more selected from the group consisting of sodium carbonate, sodium hydroxide, ammonia water and oxalic acid, and the precipitant is added in a molar amount of 2 times or more of the total molar amount of the metal ions.

8. The formaldehyde oxidation catalyst according to claim 4, wherein the calcination temperature of the carrier is 350-450 ℃.

9. A method for preparing the formaldehyde oxidation catalyst as set forth in any one of claims 1 to 8, characterized in that the method comprises the steps of: soaking the carrier in Pt precursor water solution, and finally drying and roastingAnd reducing the mixture by hydrogen to obtain Pt/NiO @ NiMnO_x（2.5<x<3) A catalyst.

10. The method of claim 9, wherein the precursor of Pt is selected from H₂PtCl₆、Pt(NO₃)₂、PtCl₄、Pt(NH₃)₄Cl₂And Pt (NH)₃)₄(NO₃)₂One kind of (1).