Formaldehyde catalyst as well as preparation method and application thereof

Abstract

The invention relates to a formaldehyde catalyst and a preparation method and application thereof, and the application comprises the following steps: connecting the formaldehyde catalyst with a power supply, introducing current, and carrying out an electrothermal formaldehyde oxidation reaction; the temperature of the electrothermal oxidation formaldehyde reaction is 50-110 DEG C. The oxygen for oxidizing HCHO under the electric heating condition mainly comes from active oxygen and lattice oxygen on the surface of the catalyst. In the electric heating mode, migration of lattice oxygen is enhanced through the electronic effect, and therefore HCHO oxidation is promoted. Local heating of a catalyst system is achieved by means of high energy efficiency of resistance Joule heat, meanwhile, current acts on a catalyst and reactants through the generated electron effect, activation of the reactants and generation of active oxygen are achieved, HCHO is completely removed near the normal temperature, a practical technology for indoor formaldehyde purification is achieved, the tail gas temperature is lower, and the service life is longer. And the method has practical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic oxidation of formaldehyde, and in particular to a formaldehyde catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Formaldehyde (HCHO) mainly comes from synthetic resin adhesives contained in household decoration materials, paints and varnishes. As early as 2004, it was classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Long-term continuous exposure to it will greatly increase the risks of nasopharyngeal carcinoma and leukemia. Therefore, people have been committed to developing efficient technologies and materials for removing HCHO.

[0003] Among the technologies for removing HCHO, catalytic oxidation is a technology for efficiently purifying formaldehyde. Currently, commonly used noble metal catalysts such as Pt, Au, and Pd have excellent room-temperature activity, but are costly; transition metal oxide catalysts have lower costs, but require higher temperatures to activate formaldehyde and active species. However, conventional heating methods such as electric furnaces and fuel heating have higher tail gas temperatures and are not suitable for indoor formaldehyde purification.

[0004] CN105013502A discloses a manganese-doped maghemite catalyst for thermal catalytic oxidation of formaldehyde and a preparation method thereof. Using iron salts and manganese salts as the main raw materials, a manganese-doped magnetite precursor is synthesized by the sodium hydroxide co-precipitation method, and then through washing, freeze-drying, screening, and roasting oxidation, a manganese-doped maghemite catalyst for thermal catalytic oxidation of formaldehyde is prepared. This type of catalyst is granular, has a spinel structure, and is weakly magnetic. It can effectively catalyze the oxidation of high-concentration formaldehyde and is used to remove high-concentration (>1000 mL / m 3 ) formaldehyde at 300 °C, and the formaldehyde removal rate reaches more than 90%; it has the advantages of high catalytic activity, low ignition temperature, good thermal stability, convenient separation and recovery, no secondary pollution, and low cost, and is suitable for the purification treatment of high-concentration formaldehyde in industrial waste gas. However, it requires a relatively high reaction temperature to achieve complete oxidation of formaldehyde and is not suitable for indoor formaldehyde purification.

[0005] In the prior art, there are defects such as low catalyst reaction activity, low formaldehyde conversion rate, and high required reaction temperature. Therefore, how to develop a formaldehyde catalytic oxidation reaction system and reaction method to further improve the formaldehyde oxidation efficiency and reduce the reaction temperature has become an urgent problem to be solved at present. Summary of the Invention

[0006] To solve the above technical problems, the object of the present invention is to provide a formaldehyde catalyst, a preparation method thereof and an application. The preparation method of the formaldehyde catalyst of the present invention adopts a simple impregnation method. Compared with methods such as electrodeposition, the impregnation method has a more controllable loading amount of the active component. The prepared formaldehyde catalyst further adopts an electrothermal catalysis application, using the high energy efficiency of resistive Joule heat to realize local heating of the catalyst system. At the same time, the electronic effect generated by the passing current acts on the catalyst and the reactants to realize the activation of the reactants and the generation of active oxygen, achieving almost room-temperature complete removal of HCHO and significantly improving the application efficiency of the formaldehyde catalyst.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a preparation method of a formaldehyde catalyst, and the preparation method includes the following steps:

[0009] Perform acid leaching treatment on the carrier, mix the active component and the solvent to obtain a suspension, and impregnate the suspension onto the carrier after acid leaching treatment to obtain a formaldehyde catalyst.

[0010] The carrier includes any one or a combination of at least two of nickel foam, iron foam or copper foam. Typical but non-limiting combinations include the combination of nickel foam and iron foam, the combination of iron foam and copper foam, the combination of nickel foam and copper foam, and the combination of nickel foam, iron foam and copper foam. Preferably, it is nickel foam.

[0011] The active component includes α-MnO 2 , β-MnO 2 , γ-MnO 2 or δ-MnO 2 or a combination of any one or at least two of them. Typical but non-limiting combinations include the combination of α-MnO 2 and β-MnO 2 , the combination of β-MnO 2 and γ-MnO 2 , the combination of γ-MnO 2 and δ-MnO 2 , the combination of α-MnO 2 and γ-MnO 2 , the combination of β-MnO 2 , γ-MnO 2 and δ-MnO 2 , the combination of α-MnO 2 , β-MnO 2 and δ-MnO 2 , or the combination of α-MnO 2 , β-MnO 2 , γ-MnO 2 and δ-MnO2 in combination, preferably δ-MnO 2 .

[0012] The present invention uses inexpensive manganese dioxide as the active component, which greatly reduces the manufacturing cost compared with traditional noble metal catalysts. And a formaldehyde catalyst is prepared by an impregnation method. The impregnation method has a large loading capacity and good repeatability, making the loading amount of the active component more controllable; at the same time, it is suitable for the loading of different crystal forms of MnO 2 , minimally affecting the properties of the MnO 2 catalyst; it can also achieve a better electrothermal heating effect, so as to exert the synergistic effect of the electrothermal effect and the electronic effect in the electrothermal mode, achieving a higher HCHO oxidation activity. Therefore, in this application, the MnO 2 catalyst is loaded on the carrier by an impregnation method to achieve excellent catalytic effects.

[0013] The different crystal forms of manganese dioxide used in the present invention can be prepared according to the preparation methods in the prior art. No additional specific limitations are imposed on its specific preparation methods and steps. Any method that can obtain the corresponding crystal form of manganese dioxide is acceptable. For example, it can be prepared by the following methods, but is not limited to the following methods:

[0014] For the preparation of α-MnO 2 : 0.525 g of MnSO 4 ·H 2 O and 1.25 g of KMnO 4 are first dissolved in 80 mL of deionized water and stirred for 30 min to form a homogeneous solution. Then, the solution is transferred to a 100 mL Teflon hydrothermal reaction kettle, placed in an oven at 160 °C and kept warm for 12 h. After the reaction is completed, the product is collected, washed, filtered, placed in an oven at 80 °C and dried overnight. Then, the dried sample is calcined at 300 °C for 3 h to obtain α-MnO 2 .

[0015] The process for preparing β-MnO 2 and γ-MnO 2 is similar to the above, except for the precursors, reaction temperature and reaction time. The specific differences are as follows:

[0016] For the preparation of β-MnO 2 : 1.69 g of MnSO 4 ·H 2 O and 2.28 g of (NH 4 ) 2 S 2 O 8 react at 140 °C for 12 h.

[0017] For the preparation of γ-MnO 2Preparation: 3.375 g of MnSO 4 ·H 2 O and 4.575 g of (NH 4 ) 2 S 2 O 8 React at 90 °C for 24 h.

[0018] For the preparation of δ-MnO 2 : Add 3.16 g of KMnO 4 and 1.24 g of (NH 4 ) 2 C 2 O 4 ·H 2 O to 70 mL of deionized water and stir for 30 min. Then transfer the homogeneous solution to a 100 mL Teflon-lined stainless steel autoclave and heat at 90 °C for 24 h. After cooling the autoclave to room temperature, collect the precipitate, wash it, centrifuge it 4 times at 8000 r / min with deionized water for 3 min each time, and then dry it at 105 °C.

[0019] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0020] Preferably, the diameter of the carrier is 10 mm - 30 mm, for example, it can be 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 24 mm, 26 mm, 28 mm or 30 mm, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the thickness of the carrier is 4 mm - 20 mm, for example, it can be 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm or 20 mm, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] The present invention further controls the diameter and thickness of the carrier to make the catalyst easier to match the reaction device during subsequent use.

[0023] Preferably, the pore size of the carrier is 40 ppi - 100 ppi, for example, it can be 40 ppi, 45 ppi, 50 ppi, 55 ppi, 60 ppi, 65 ppi, 70 ppi, 75 ppi, 80 ppi, 85 ppi, 90 ppi, 95 ppi or 100 ppi, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0024] The present invention further controls the pore size of the carrier to be 40 ppi - 100 ppi, providing sufficient space for the loading of the active component, while ensuring that the active component can adhere to the carrier without falling off. If the pores of the carrier are too large, on the one hand, the specific surface area decreases, which is not conducive to the loading of the powder MnO 2 of the active component, and on the other hand, it is not conducive to the reaction gas to contact with MnO 2 weakening the adsorption of HCHO by MnO 2 and resulting in a decrease in catalytic oxidation activity; if the pores of the carrier are too small, the relatively large specific surface area is not conducive to the dispersion degree of MnO 2 loading. The relative density of the metal of the carrier will also increase, making the conductivity increase, which is not conducive to the generation of resistive Joule heat; in addition, too small pores will also increase the gas resistance for the reaction gas to pass through, which will increase the pressure loss.

[0025] Preferably, the steps of the acid leaching treatment include: using an acid solution with a concentration of 0.1 mol / L - 1 mol / L to perform acid leaching treatment on the carrier. For example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0026] Preferably, the acid solution includes hydrochloric acid and / or sulfuric acid.

[0027] Preferably, after the acid leaching treatment, it further includes: washing with ethanol and / or deionized water 2 - 5 times. For example, it can be 2 times, 3 times, 4 times or 5 times, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. The purpose of the acid leaching treatment is to remove impurities.

[0028] Preferably, the solvent includes water.

[0029] Preferably, the solid content of the suspension is 20% - 50%. For example, it can be 20%, 25%, 30%, 35%, 40%, 45% or 50%, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0030] Preferably, after the impregnation treatment and before obtaining the formaldehyde catalyst, drying and calcination are included.

[0031] Preferably, the drying temperature is 70°C - 100°C. For example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the drying time is 12 h - 24 h. For example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0033] Preferably, the calcination temperature is 250°C - 350°C. For example, it can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0034] In the present invention, by further controlling the calcination temperature to be 250°C - 350°C, the best combination of the powder MnO 2 and the carrier is achieved within this temperature range; if the calcination temperature is too high, it will cause the crystal structure of the powder MnO 2 to change or the carrier structure to collapse, resulting in a decrease in catalytic performance; if the calcination temperature is too low, it is not conducive to the formation of highly active reaction sites of the powder MnO 2 , further reducing the reaction activity.

[0035] Preferably, the calcination time is 1 h - 5 h. For example, it can be 1 h, 2 h, 3 h, 4 h or 5 h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0036] As a preferred technical solution of the preparation method of the present invention, the preparation method includes the following steps:

[0037] The nickel foam is subjected to acid leaching treatment with 0.1 mol / L - 1 mol / L hydrochloric acid, and then the nickel foam is washed 2 - 5 times with ethanol and / or deionized water to obtain the acid-leached nickel foam; the active components are mixed with a solvent to obtain a suspension with a solid content of 20% - 50%; the suspension is impregnated onto the acid-leached nickel foam, dried at 70°C - 100°C for 12 h - 24 h, and then calcined at 250°C - 350°C for 1 h - 5 h to obtain the formaldehyde catalyst.

[0038] The nickel foam has a diameter of 10 mm - 30 mm, a thickness of 4 mm - 20 mm, and a pore size of 40 ppi - 100 ppi; the active components include any one or a combination of at least two of α-MnO 2 , β-MnO 2 , γ-MnO 2 or δ-MnO 2 .

[0039] Second aspect, the present invention provides a formaldehyde catalyst prepared by the preparation method described in the first aspect. The mass of the active component in the formaldehyde catalyst accounts for 40wt%-50wt% of the total mass of the formaldehyde catalyst. For example, it can be 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt% or 50wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0040] In the formaldehyde catalyst of the present invention, the mass of the active component accounts for 40wt%-50wt% of the total mass of the formaldehyde catalyst. The active component manganese dioxide is uniformly dispersed on the surface of the carrier. The formaldehyde catalyst surface has sufficient active oxygen and has significant catalytic oxidation activity for formaldehyde.

[0041] Third aspect, the present invention provides an application of the formaldehyde catalyst described in the second aspect. The application includes:

[0042] Connect the formaldehyde catalyst to a power source, pass an electric current, and carry out an electrothermal oxidation reaction of formaldehyde; the temperature of the electrothermal oxidation reaction of formaldehyde is 50°C - 110°C.

[0043] The present invention utilizes the high energy efficiency of resistive Joule heat to achieve local heating of the catalyst system. At the same time, the electronic effect generated by the passing of the current acts on the catalyst and the reactants to achieve the activation of the reactants and the generation of active oxygen, and is expected to achieve near-ambient temperature complete removal of HCHO, becoming a practical technology for indoor formaldehyde purification. Compared with the traditional thermal catalysis method, the electrothermal reaction system has high thermal efficiency and high reaction activity. For formaldehyde catalysts with different active components, the temperature at which formaldehyde is completely oxidized is lower than that of the conventional thermal catalysis mode, and the tail gas temperature is lower, which is more practical.

[0044] The temperature of the electrothermal oxidation reaction of formaldehyde is 50°C - 110°C. For example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0045] The temperature of the electrothermal oxidation reaction of formaldehyde in the present invention is 50°C - 110°C. The temperatures required for different crystal forms of manganese dioxide-loaded formaldehyde catalysts to achieve complete oxidation of formaldehyde are different. For example, δ-MnO 2 As a formaldehyde catalyst with an active component, the optimal temperature range for its electrothermal oxidation of formaldehyde is 50°C - 75°C, with α-MnO 2 As a formaldehyde catalyst with an active component, the optimal temperature range for its electrothermal oxidation of formaldehyde is 75°C - 90°C, with γ-MnO 2The optimal temperature range for the electrothermal oxidation of formaldehyde by the formaldehyde catalyst as the active component is 85°C - 95°C, with β-MnO 2 The optimal temperature range for the electrothermal oxidation of formaldehyde by the formaldehyde catalyst as the active component is 95°C - 110°C. If the temperature is too low, on the one hand, the activation of oxygen species on the catalyst cannot be stimulated, and on the other hand, it is not conducive to the desorption and regeneration of active sites. With the accumulation of reactants and intermediate products, the catalyst will be poisoned and deactivated; if the temperature is too high, it will cause an increase in energy consumption and cost.

[0046] Preferably, the magnitude of the current is 0.5A - 2A. For example, it can be 0.5A, 0.6A, 0.7A, 0.8A, 0.9A, 1.0A, 1.1A, 1.2A, 1.3A, 1.4A, 1.5A, 1.6A, 1.7A, 1.8A, 1.9A or 2A, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0047] In the present invention, by further controlling the magnitude of the current during the electrothermal catalytic reaction to be 0.5A - 2A, the temperature of the reaction is regulated. The greater the current, the higher the temperature of the electrothermal catalytic reaction system. However, when the current is too large, it will cause too high a reaction temperature and an increase in the line load, posing a safety hazard; if the current is too small, the electrothermal effect cannot be generated, resulting in the inability to reach the required reaction temperature and ultimately causing the deactivation of the catalyst.

[0048] Preferably, the voltage magnitude of the current is 0.9V - 1.5V. For example, it can be 0.9V, 0.95V, 1.0V, 1.1V, 1.15V, 1.2V, 1.25V, 1.3V, 1.35V, 1.4V, 1.45V or 1.5V, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0049] The numerical range described in the present invention not only includes the above-listed point values, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects:

[0051] (1) The present invention utilizes the high energy efficiency of resistive Joule heat to achieve local heating of the catalyst system. At the same time, the electronic effect generated by the passing current acts on the catalyst and reactants to achieve the activation of reactants and the generation of active oxygen, and is expected to achieve near-ambient temperature complete removal of HCHO, becoming a practical technology for indoor formaldehyde purification.

[0052] (2) Compared with the traditional thermal catalysis method, the electrothermal reaction system has high thermal efficiency and high reaction activity. For formaldehyde catalysts with different active components, the temperature at which formaldehyde reaches complete oxidation is lower than that of the conventional thermal catalysis mode, and the tail gas temperature is even lower, which is more practically significant. Description of the Drawings

[0053] Figure 1 It is a graph of formaldehyde conversion rate of the formaldehyde catalyst in Application Example 1 and Comparative Application Example 1 of the present invention at different reaction temperatures;

[0054] Figure 2 It is a graph of formaldehyde conversion rate of the formaldehyde catalysts in Application Examples 2 - 4 and Comparative Application Examples 2 - 4 of the present invention at different reaction temperatures;

[0055] Figure 3 It is a graph of the change of formaldehyde conversion rate with time in Application Example 10 and Comparative Application Example 7 of the present invention. Detailed Embodiments

[0056] The technical solutions of the present invention will be further described below with reference to the drawings and through specific embodiments. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] In the following examples and comparative examples, unless otherwise specified, all reagents and consumables are purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and technical means used are conventional methods and means in the art.

[0058] Example 1

[0059] This example provides a formaldehyde catalyst, and the preparation method of the formaldehyde catalyst includes the following steps:

[0060] (1) The nickel foam with a diameter of 19 mm, a thickness of 6 mm, and a pore size of 60 ppi is subjected to acid leaching treatment with 0.1 mol / L hydrochloric acid, and then the nickel foam is washed 3 times with ethanol and deionized water respectively to obtain the acid-leached nickel foam;

[0061] Mix δ-MnO 2 with water to obtain a δ-MnO 2 suspension with a solid content of 20%;

[0062] (2) The δ-MnO 2 suspension is impregnated onto the acid-leached nickel foam, dried at 80 °C for 12 h, and then calcined at 300 °C for 3 h to obtain a formaldehyde catalyst, denoted as δ-Mn / Ni.

[0063] Example 2

[0064] This embodiment provides a formaldehyde catalyst, and the preparation method of the formaldehyde catalyst includes the following steps:

[0065] (1) Acid-leach the nickel foam with a diameter of 19 mm, a thickness of 6 mm, and a pore size of 60 ppi using 0.1 mol / L hydrochloric acid, and then wash the nickel foam with ethanol and deionized water twice respectively to obtain the acid-leached nickel foam;

[0066] Mix γ-MnO 2 with water to obtain a γ-MnO 2 suspension with a solid content of 42%;

[0067] (2) Immerse the γ-MnO 2 suspension onto the acid-leached nickel foam, dry it at 80 °C for 12 h, and then calcine it at 300 °C for 3 h to obtain the formaldehyde catalyst, denoted as γ-Mn / Ni.

[0068] Example 3

[0069] This embodiment provides a formaldehyde catalyst, and the preparation method of the formaldehyde catalyst includes the following steps:

[0070] (1) Acid-leach the copper foam with a diameter of 25 mm, a thickness of 10 mm, and a pore size of 80 ppi using 0.5 mol / L hydrochloric acid, and then wash the copper foam with ethanol and deionized water five times respectively to obtain the acid-leached copper foam;

[0071] Mix β-MnO 2 with water to obtain a β-MnO 2 suspension with a solid content of 30%;

[0072] (2) Immerse the β-MnO 2 suspension onto the acid-leached copper foam, dry it at 90 °C for 12 h, and then calcine it at 320 °C for 2 h to obtain the formaldehyde catalyst, denoted as β-Mn / Ni.

[0073] Example 4

[0074] This embodiment provides a formaldehyde catalyst, and the preparation method of the formaldehyde catalyst includes the following steps:

[0075] (1) Acid-leach the copper foam with a diameter of 25 mm, a thickness of 10 mm, and a pore size of 80 ppi using 0.5 mol / L hydrochloric acid, and then wash the copper foam with ethanol and deionized water four times respectively to obtain the acid-leached copper foam;

[0076] Mix α-MnO 2 with water to obtain a α-MnO2 Suspension;

[0077] (2) Immerse the α-MnO 2 suspension into the acid-leached copper foam. After drying at 90 °C for 12 h, calcine it at 320 °C for 2 h to obtain a formaldehyde catalyst, denoted as α-Mn / Ni.

[0078] Example 5

[0079] This example provides a formaldehyde catalyst. The difference from Example 1 is only that when preparing this formaldehyde catalyst, the calcination temperature in step (2) is 400 °C.

[0080] Example 6

[0081] This example provides a formaldehyde catalyst. The difference from Example 1 is only that when preparing this formaldehyde catalyst, the calcination temperature in step (2) is 200 °C.

[0082] Comparative Example 1

[0083] This comparative example provides a formaldehyde catalyst. When preparing this formaldehyde catalyst, an electrodeposition method is used for preparation. The specific preparation method is as follows:

[0084] Weigh 100 ml of deionized water, weigh 0.02 mol / L manganese acetate, 0.01 mol / L ammonium acetate, and 10 ml of dimethyl sulfoxide (wt. 10%) and dissolve them in a beaker. Deposit at a current density of 2.0 mA / cm 2 , constant current of 0.0056 A, and at 70 °C for 60 min. Finally, wash it 3 times with deionized water and dry it in an oven at 80 °C for 12 h.

[0085] Application Example 1

[0086] This application example provides an application of a formaldehyde catalyst. The application includes:

[0087] Press the δ-Mn / Ni formaldehyde catalyst prepared in Example 1 tightly with two copper electrodes. Connect both ends to a DC power supply (DH1765-1) through a copper tube with one end open. Pass a current with a magnitude of 1.46 A and a voltage magnitude of 1.39 V. The temperature of the formaldehyde catalyst is 60 °C, and carry out an electrothermal oxidation formaldehyde reaction in the electrothermal (EH) mode. Denote this application example as δ-Mn / Ni-EH.

[0088] Application Example 2

[0089] This application example provides an application of a formaldehyde catalyst. The application includes:

[0090] The γ-Mn / Ni formaldehyde catalyst prepared in Example 1 was tightly pressed with two copper electrodes, and both ends were connected to a DC power supply (DH1765-1) through a copper tube with one end open. A current with a magnitude of 2.3 A and a voltage with a magnitude of 1.7 V was passed through. The temperature of the formaldehyde catalyst was 93 °C, and the electrothermal oxidation of formaldehyde reaction was carried out in the electrothermal (EH) mode. This application example was denoted as γ-Mn / Ni-EH.

[0091] Application Example 3

[0092] This application example provides an application of a formaldehyde catalyst, and the application includes:

[0093] The β-Mn / Ni formaldehyde catalyst prepared in Example 1 was tightly pressed with two copper electrodes, and both ends were connected to a DC power supply (DH1765-1) through a copper tube with one end open. A current with a magnitude of 2.5 A and a voltage with a magnitude of 1.8 V was passed through. The temperature of the formaldehyde catalyst was 100 °C, and the electrothermal oxidation of formaldehyde reaction was carried out in the electrothermal (EH) mode. This application example was denoted as β-Mn / Ni-EH.

[0094] Application Example 4

[0095] This application example provides an application of a formaldehyde catalyst, and the application includes:

[0096] The α-Mn / Ni formaldehyde catalyst prepared in Example 1 was tightly pressed with two copper electrodes, and both ends were connected to a DC power supply (DH1765-1) through a copper tube with one end open. A current with a magnitude of 2.2 A and a voltage with a magnitude of 1.6 V was passed through. The temperature of the formaldehyde catalyst was 90 °C, and the electrothermal oxidation of formaldehyde reaction was carried out in the electrothermal (EH) mode. This application example was denoted as α-Mn / Ni-EH.

[0097] Application Examples 5 - Application Example 6

[0098] Application Examples 5 and 6 respectively provide an application of a formaldehyde catalyst. The difference between this application and Application Example 1 is only that the formaldehyde catalysts prepared in Example 5 and Example 6 are respectively used, and the electrothermal oxidation of formaldehyde reaction is carried out in the electrothermal (EH) mode, and the electrothermal catalysis conditions remain unchanged.

[0099] Application Example 7

[0100] This application example provides an application of a formaldehyde catalyst. The difference from Application Example 1 is that a current with a magnitude of 1.7 A is passed through, and the electrothermal oxidation of formaldehyde reaction is carried out in the electrothermal (EH) mode.

[0101] Application Example 8

[0102] This application example provides an application of a formaldehyde catalyst. The difference from Application Example 1 is that the magnitude of the applied current is 1.6 A, and the electrothermal oxidation of formaldehyde reaction is carried out in the electrothermal (EH) mode.

[0103] Application Example 9

[0104] This application example provides an application of a formaldehyde catalyst. The difference from Application Example 1 is that the formaldehyde catalyst prepared in Comparative Example 1 is used for the electrothermal oxidation of formaldehyde reaction.

[0105] Application Example 10

[0106] This application example provides an application of a formaldehyde catalyst. Its application is exactly the same as that of Application Example 1, and its test conditions are: HCHO concentration of 100 ppm, no O 2 、total flow rate of 100 ml / min, N 2 balance.

[0107] The change of formaldehyde conversion rate with time under this condition is as Figure 3 shown.

[0108] Comparative Application Example 1 - Comparative Application Example 4

[0109] Comparative Application Example 1 - Comparative Application Example 4 respectively provide an application of a formaldehyde catalyst. In the preparation method, the catalysts prepared in Examples 1 - 4 are respectively used for the oxidation of formaldehyde reaction, and the reaction process is heated by an electric resistance furnace, that is, the oxidation of formaldehyde reaction is carried out in the conventional heating (CH) mode.

[0110] Comparative Application Example 5

[0111] This comparative application example provides an application of a formaldehyde catalyst. The difference from Application Example 1 is that the magnitude of the applied current is 3 A, the magnitude of the voltage is 2.1 V, the temperature of the formaldehyde catalyst δ-Mn / Ni is 150 °C, and the electrothermal oxidation of formaldehyde reaction is carried out in the electrothermal (EH) mode.

[0112] Comparative Application Example 6

[0113] This comparative application example provides an application of a formaldehyde catalyst. The difference from Application Example 1 is that the magnitude of the applied current is 0.2 A, the magnitude of the voltage is 0.45 V, the temperature of the formaldehyde catalyst δ-Mn / Ni is 25 °C, and the electrothermal oxidation of formaldehyde reaction is carried out in the electrothermal (EH) mode.

[0114] The test conditions for the above Application Example 1 - Application Example 8 and Comparative Application Example 1 - Comparative Application Example 6 are: testing in a quartz tube reactor (inner diameter 20 mm, length 100 mm), HCHO concentration of 100 ppm, 20% O 2 、total flow rate of 100 ml / min, N 2Balance. The test results are shown in Table 1 below.

[0115] Comparative Application Example 7

[0116] This comparative application example provides an application of a formaldehyde catalyst, which is exactly the same as that of Comparative Application Example 1. The test conditions are HCHO concentration of 100 ppm, no O 2 , total flow rate of 100 ml / min, N 2 Balance.

[0117] The change of formaldehyde conversion rate with time under this condition is as Figure 3 shown.

[0118] Table 1

[0119] Reaction temperature / °C Formaldehyde conversion rate / % Application Example 1 60 100％ Application Example 2 93 100％ Application Example 3 100 100％ Application Example 4 90 100％ Application Example 5 60 75％ Application Example 6 60 85％ Application Example 7 60 100％ Application Example 8 60 100％ Application Example 9 60 15％ Comparative Application Example 1 60 20％ Comparative Application Example 2 93 13％ Comparative Application Example 3 100 8％ Comparative Application Example 4 90 15％ Comparative Application Example 5 150 100％ Comparative Application Example 6 25 25％

[0120] It can be seen from the test results that:

[0121] (1) It can be seen from Application Examples 1 - 4 that the present invention realizes local heating of the catalyst system by utilizing the high energy efficiency of resistive Joule heat. At the same time, the electron effect generated by the passing current acts on the catalyst and the reactants, realizing the activation of the reactants and the generation of active oxygen, and is expected to achieve almost room-temperature complete removal of HCHO, becoming a practical technology for indoor formaldehyde purification.

[0122] (2) By comparing Application Example 1 with Application Examples 5 - 6, it can be seen that the present invention further controls the calcination temperature to be 250°C - 350°C, and the best performance of MnO 2 and the carrier is achieved within this temperature range; if the calcination temperature is too high, the crystal structure of MnO 2 will change, resulting in a decrease in catalytic activity; if the calcination temperature is too low, it is not conducive to the formation of active sites, and the formaldehyde oxidation activity is low.

[0123] (3) By comparing Application Example 1 with Application Examples 7 - 8, it can be seen that the present invention further controls the magnitude of the current during the electrothermal catalytic reaction to be 0.5 A - 2 A, thereby regulating the reaction temperature. The greater the current, the higher the temperature of the electrothermal catalytic reaction system. When the current changes within a suitable range, excellent catalytic effects can be achieved.

[0124] (4) It can be seen from Application Examples 1 - 4 and Comparative Application Examples 1 - 4 that the present invention uses a catalytic oxidation formaldehyde catalyst in the electrothermal mode. Compared with the traditional thermal catalytic method, the electrothermal reaction system has high thermal efficiency and high reaction activity. For formaldehyde catalysts with different active components, the temperature at which formaldehyde reaches complete oxidation is lower than that of the conventional thermal catalytic mode, and the tail gas temperature is lower, which is more practical.

[0125] (5) It can be seen from Application Example 1 and Comparative Application Examples 5 - 6 that by further controlling the temperature of the electrothermal reaction, the present invention has achieved complete conversion of formaldehyde at a relatively low temperature. An excessively high reaction temperature causes waste of resources, while a too low temperature is not conducive to improving the conversion rate of formaldehyde. If the temperature is too low, below 50 °C, on the one hand, it cannot activate the oxygen species of the catalyst, and on the other hand, it is not conducive to the desorption and regeneration of active sites. With the accumulation of reactants and intermediate products, the catalyst will be poisoned and deactivated.

[0126] (6) It can be seen from Application Example 1 and Application Example 9 that the formaldehyde catalyst prepared by the impregnation method in the present invention is more suitable for the electrothermal oxidation of formaldehyde reaction. However, the formaldehyde catalyst prepared by the electrodeposition method has a uniform and dense loading, resulting in the metal substrate surface being completely wrapped by weakly conductive MnO x , which causes the problem of excessive catalyst resistance and open - circuit non - conductivity, does not have the electrothermal heating effect, and its catalytic activity is worse.

[0127] (7) By Figure 3 It can be seen that the present invention has carried out electrothermal and thermal catalytic oxidation of HCHO tests in the absence of oxygen in the reaction atmosphere. Under this condition, the oxygen for oxidizing HCHO mainly comes from the active oxygen and lattice oxygen on the catalyst surface. At 60 °C, the HCHO conversion rate of Mn / Ni in the EH mode is higher than that in the CH mode, which indicates that the electronic effect enhances the migration of lattice oxygen, thereby promoting HCHO oxidation.

[0128] In summary, by utilizing the high energy efficiency of resistive Joule heat, the present invention realizes local heating of the catalyst system. At the same time, the electronic effect generated by the passing current acts on the catalyst and reactants to activate the reactants and generate active oxygen, and is expected to achieve near - room - temperature complete removal of HCHO, becoming a practical technology for indoor formaldehyde purification. Compared with the traditional thermal catalytic method, the electrothermal reaction system has high thermal efficiency and high reaction activity. For formaldehyde catalysts with different active components, the temperature at which formaldehyde reaches complete oxidation is lower than that of the conventional thermal catalytic mode, and the tail - gas temperature is lower, which is more practical.

[0129] The applicant declares that the above - mentioned is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and public scope of the present invention.

Claims

1. A method for preparing a formaldehyde catalyst, characterized in that: The preparation method comprises the following steps: The carrier is subjected to acid leaching treatment; the active component is mixed with a solvent to obtain a suspension, and the suspension is impregnated on the carrier subjected to the acid leaching treatment to obtain a formaldehyde catalyst; The carrier comprises any one of foamed nickel, foamed iron or foamed copper, or a combination of at least two thereof; The active component includes any one of α-MnO2, β-MnO2, γ-MnO2 or δ-MnO2 or a combination of at least two thereof.

2. The preparation method according to claim 1, characterized in that: The carrier has a diameter of 10 mm to 30 mm, a thickness of 4 mm to 20 mm, and a pore size of 40 ppi to 100 ppi.

3. The preparation method according to claim 1 or 2, characterized in that: The step of acid leaching treatment comprises: using an acid solution with a concentration of 0.1 mol / L-1 mol / L to perform acid leaching treatment on the carrier; Preferably, the acid solution comprises hydrochloric acid and / or sulfuric acid.

4. The preparation method according to any one of claims 1 to 3, characterized in that The solvent includes water.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The solid content of the suspension is 20%-50%.

6. The preparation method according to any one of claims 1 to 5, characterized in that: After the impregnation treatment, drying and calcination are performed before obtaining the formaldehyde catalyst; Preferably, the drying temperature is 70°C-100°C; Preferably, the drying time is 12h-24h.

7. The preparation method according to claim 6, characterized in that: The calcination temperature is 250°C-350°C; Preferably, the calcination time is 1 h-5 h.

8. A formaldehyde catalyst, characterized in that: The formaldehyde catalyst is prepared according to the preparation method according to any one of claims 1 to 7, and the mass of the active components in the formaldehyde catalyst accounts for 40wt%-50wt% of the total mass of the formaldehyde catalyst.

9. Use of the formaldehyde catalyst as claimed in claim 8, characterized in that: The applications include: The formaldehyde catalyst is connected to a power source, and current is passed through to carry out an electrothermal oxidation formaldehyde reaction; the temperature of the electrothermal oxidation formaldehyde reaction is 50°C-110°C.

10. The use according to claim 9, characterized in that: The magnitude of the current is 0.5A-2A; Preferably, the voltage of the current is 0.9V-1.5V.

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