A manganese oxide heterojunction catalyst, its preparation method and application

Abstract

The application discloses a manganese oxide heterojunction catalyst and a preparation method and application thereof, and belongs to the technical field of catalytic materials. The manganese oxide heterojunction catalyst is composed of two manganese oxide phases of alpha-MnO2 and Mn2O3. The manganese oxide heterojunction catalyst is prepared from potassium permanganate and ammonium oxalate as starting materials through a hydrothermal method, a two-phase composite manganese oxide precursor is first prepared, phase transition of the precursor is realized through mechanical ball milling, and then the manganese oxide heterojunction catalyst is obtained. The preparation method provided by the application has the advantages of easy availability of raw materials, simple operation, and convenience for mass production, and the prepared catalyst has high intrinsic performance and rich active sites, can realize complete catalytic degradation of formaldehyde at 80 DEG C with high efficiency and stability, and has better comprehensive catalytic performance than most reported non-noble metal catalysts.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a manganese oxide heterojunction catalyst, its preparation method, and its application. Background Technology

[0002] Formaldehyde (HCHO) is one of the most toxic indoor air pollutants and has been identified as a carcinogen by the World Health Organization. However, its widespread use in building materials and textiles makes it an unavoidable presence in daily life. Therefore, developing efficient and safe formaldehyde removal technologies is a crucial issue concerning human health and safety. Among the various existing formaldehyde removal technologies, catalytic oxidation is widely recognized as the most promising solution due to its high efficiency, long-lasting energy saving, and environmental friendliness. The core of catalytic oxidation formaldehyde removal technology lies in developing highly active, low-cost formaldehyde oxidation catalysts.

[0003] Currently, commonly used formaldehyde oxidation catalysts can be divided into two categories: non-precious metal catalysts (MnO2, CeO2, and Co3O4, etc.) and precious metal catalysts (Pt, Au, Pd, and Ag, etc.). Supported precious metal catalysts, represented by Pt, can completely oxidize formaldehyde to CO2 and H2O at room temperature, but their high material cost severely restricts their practical application. While non-precious metal catalysts require temperatures above 60℃ to achieve complete formaldehyde oxidation, their low price attracts continuous exploration. Considering the overall cost-effectiveness of catalysts, non-precious metal catalysts are a more promising class for formaldehyde oxidation. In recent years, scholars from various countries have conducted extensive research on non-precious metal formaldehyde oxidation catalysts, among which manganese oxides exhibit relatively excellent catalytic performance and are the most representative non-precious metal formaldehyde oxidation catalysts. Research has found that modification strategies such as defect engineering, heteroatom doping, and morphology control can effectively improve the formaldehyde oxidation catalytic performance of manganese oxides. However, in general, non-precious metal catalysts still suffer from problems such as low activity, poor long-term working stability, and poor moisture resistance. Therefore, developing advanced non-precious metal catalyst design concepts and controllable synthesis methods remains a key issue that needs to be addressed in promoting the practical application of formaldehyde catalytic oxidation technology. Summary of the Invention

[0004] To address the shortcomings and deficiencies of the existing technologies, the primary objective of this invention is to provide a highly efficient manganese oxide heterojunction catalyst for formaldehyde removal. The catalyst of this invention possesses a structure characterized by numerous heterojunction-formed phase interfaces and oxygen-rich vacancies, exhibiting both high intrinsic catalytic activity and abundant active sites.

[0005] Another objective of this invention is to provide a method for preparing the aforementioned manganese oxide heterojunction catalyst. This invention employs a hydrothermal method combined with mechanical ball milling to synthesize the heterojunction catalyst. First, using potassium permanganate and ammonium oxalate as starting materials, a manganese oxide heterojunction catalyst precursor is prepared via a hydrothermal method. Subsequently, taking advantage of the easy phase transition of MnOOH, its phase transition to Mn2O3 is achieved through mechanical ball milling, ultimately forming the manganese oxide heterojunction catalyst. This method utilizes readily available raw materials, is simple to operate, and is suitable for mass production.

[0006] Another objective of this invention is to provide a highly efficient and inexpensive manganese oxide heterojunction catalyst for the catalytic oxidation of formaldehyde, which can efficiently and stably catalyze the oxidative decomposition of formaldehyde at 80°C, and its overall catalytic performance is superior to most reported non-precious metal catalysts.

[0007] The objective of this invention is achieved through the following technical solutions.

[0008] A manganese oxide heterojunction catalyst, wherein the manganese oxide heterojunction catalyst is composed of two phases, α-MnO2 and Mn2O3. A heterojunction refers to the interface formed between the two aforementioned phases; the manganese oxide is composed of Mn... 2+ Mn 3+ Mn 4+ Manganese oxide is formed from one or more different oxidation states, such as manganese oxide.

[0009] Preferably, the heterojunction interface of the manganese oxide heterojunction catalyst contains oxygen vacancies.

[0010] The preparation method of the above-mentioned manganese oxide heterojunction catalyst includes the following steps:

[0011] (1) Preparation of manganese oxide heterojunction catalyst precursor: potassium permanganate and ammonium oxalate were prepared by hydrothermal reaction;

[0012] (2) Preparation of manganese oxide heterojunction catalyst: The manganese oxide heterojunction catalyst precursor obtained in step (1) is obtained by mechanical ball milling to obtain manganese oxide heterojunction catalyst; the ball-to-material ratio of the mechanical ball milling is 10:1 to 200:1; the mechanical ball milling time is 5 to 120 min.

[0013] Preferably, the preparation of the manganese oxide heterojunction catalyst precursor in step (1) is as follows: potassium permanganate and ammonium oxalate are added to water, stirred, and after hydrothermal reaction, cooled to room temperature. The precipitate is washed and dried to obtain the manganese oxide heterojunction catalyst precursor.

[0014] More preferably, the stirring time is 5 seconds to 1 hour.

[0015] More preferably, the stirring time is 20 minutes.

[0016] More preferably, the washing is centrifugal washing; the drying temperature is 60-100℃ and the time is 6-10h.

[0017] Preferably, the concentration of potassium permanganate in step (1) is 0.1M to 0.5M, and the concentration of ammonium oxalate is 0.1M to 0.5M;

[0018] More preferably, the concentration of potassium permanganate is 0.257M and the concentration of ammonium oxalate is 0.143M;

[0019] Preferably, the molar ratio of potassium permanganate and ammonium oxalate in step (1) is 1 to 2.5:1;

[0020] More preferably, the molar ratio of potassium permanganate and ammonium oxalate in step (1) is 1.8:1;

[0021] Preferably, the temperature of the hydrothermal reaction in step (1) is 100-180°C and the time is 12-48h.

[0022] More preferably, the hydrothermal reaction is carried out at a temperature of 180°C for 24 hours.

[0023] Preferably, the mechanical ball milling in step (2) is carried out in a planetary ball mill jar; the mechanical ball milling is performed in an air atmosphere.

[0024] Preferably, the ball-to-material ratio in step (2) is 100:1 to 200:1, the grinding ball size is 4 to 8 mm, the rotation speed is 200 to 500 r / min, and the ball milling time is 25 to 60 min.

[0025] More preferably, the ball-to-material ratio of the mechanical ball mill is 100:1, the rotation speed is 500 r / min, and the ball milling time is 25 min.

[0026] More preferably, the grinding beads have particle sizes of 4, 6 and 8 mm, with a mass ratio of 1:2:1.

[0027] The above-mentioned manganese oxide heterojunction catalyst is used in the catalytic oxidation of formaldehyde.

[0028] Preferably, during the catalytic oxidation of formaldehyde, the formaldehyde concentration is 0–500 ppm (excluding 0), and the gas hourly space velocity is 0–500 L / g. cat -1 h -1 The reaction temperature is 0–200℃ and the humidity is 0–80% relative humidity.

[0029] The principle of this invention is as follows: For formaldehyde oxidation catalysts, the catalyst's adsorption capacity for formaldehyde molecules and its ability to activate oxygen molecules to generate reactive oxygen species are key factors determining its catalytic performance. Current non-precious metal catalysts often struggle to catalyze formaldehyde oxidation at low temperatures due to weak formaldehyde adsorption capacity or poor ability to continuously generate reactive oxygen species. The catalyst provided by this invention optimizes both formaldehyde adsorption and oxygen activation simultaneously by utilizing the synergistic effect of two different phases in a heterojunction and the defect-rich structure within the heterojunction, and provides a simple and easy preparation method to achieve this. First, a manganese oxide heterojunction catalyst precursor is prepared using potassium permanganate and ammonium oxalate as starting materials via a hydrothermal method. Subsequently, taking advantage of the easy phase transition of MnOOH, it is transformed into Mn2O3 under mechanical ball milling, ultimately forming the manganese oxide heterojunction catalyst. During ball milling of the manganese oxide heterojunction catalyst precursor, the high-energy mechanical force causes the metastable MnOOH phase to transform into Mn2O3, while the existing α-MnO2 phase remains unchanged under the mechanical force. Ultimately, ball milling forms a heterojunction catalyst composed of two phases: α-MnO2 and Mn2O3. Mn2O3 provides adsorption sites for formaldehyde molecules, while α-MnO2 decomposes oxygen molecules to generate active oxygen species. The defective structures at the interface caused by lattice mismatch provide active sites for the adsorption and activity of reactants. In summary, the formaldehyde oxidation catalyst provided by this invention possesses both high intrinsic activity and abundant active sites.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) This invention provides a manganese oxide heterojunction catalyst and a novel method for its preparation. The catalyst is synthesized using a simple two-step process of hydrothermal treatment and ball milling. Ball milling facilitates the phase transformation of MnOOH into Mn2O3, which is superior to the method of preparing Mn2O3 by high-temperature (>500℃) calcination of MnOOH (J Mater Sci (2007) 42: 9978-9982). Simultaneously, ball milling creates more oxygen-deficient structures that are beneficial to the oxidation of formaldehyde. The difference between heterojunction catalysts and traditional catalysts lies in the fact that heterojunction catalysts consist of two or more phases, providing synergistic catalytic active sites in the formaldehyde oxidation reaction; at the same time, the heterojunction contains abundant defect structures, providing active sites for the adsorption and activation of reactants.

[0032] (2) The preparation method of the manganese oxide heterojunction catalyst provided by the present invention has readily available raw materials, simple process and is easy to mass produce.

[0033] (3) The manganese oxide heterojunction catalyst obtained in this invention can achieve complete oxidation of formaldehyde at 80℃ and has a high mass ratio reaction rate (8.92 μmol g). -1 min -1Furthermore, it exhibits excellent stability and its overall catalytic performance is superior to most reported non-precious metal catalysts. Attached Figure Description

[0034] Figure 1 The X-ray diffraction patterns are of the hydrothermal precursor (named α-MnO2 / MnOOH), the target manganese oxide heterojunction catalyst (named α-MnO2 / Mn2O3-25), and related reference samples in Example 1 of this invention.

[0035] Figure 2 The images show (a) a transmission electron microscope (TEM) image and (b) a high-resolution TEM image of the α-MnO2 / Mn2O3 catalyst in Example 1 of this invention, along with selected area electron diffraction (SEED) images of the corresponding regions.

[0036] Figure 3a The image shows the O1s X-ray photoelectron spectrum of the catalyst α-MnO2 / Mn2O3-25 sample obtained in Example 1 of this invention.

[0037] Figure 3b The image shows the Mn 2p X-ray photoelectron spectrum of the catalyst α-MnO2 / Mn2O3-25 sample obtained in Example 1 of this invention.

[0038] Figure 4 The graph shows the formaldehyde conversion rates of the α-MnO2 / Mn2O3-25 and the comparative catalyst obtained in Example 1 of this invention at different temperatures.

[0039] Figure 5 The graph shows the stability test results of α-MnO2 / Mn2O3-25 obtained in Example 1 of this invention.

[0040] Figure 6 The X-ray diffraction patterns are shown for the heterojunction catalysts α-MnO2 / Mn2O3-T obtained at different ball milling times in Example 2 of this invention; where T refers to the ball milling time.

[0041] Figure 7 This is a graph showing the conversion rate of formaldehyde oxidation catalyzed by the heterojunction catalyst (α-MnO2 / Mn2O3-T) obtained at different ball milling times in Example 2 of the present invention.

[0042] Figure 8 The images show X-ray diffraction patterns of a series of heterojunction catalysts with different ball-to-material ratios obtained in Example 3 of this invention.

[0043] Figure 9 This is a graph showing the conversion rate of formaldehyde oxidation for a series of heterojunction catalysts with different ball-to-material ratios obtained in Example 3 of the present invention.

[0044] Figure 10The X-ray diffraction pattern of the heterojunction catalyst and related catalysts obtained under high-temperature calcination in Comparative Example 1 of this invention is shown.

[0045] Figure 11 This is a graph showing the conversion rate of formaldehyde oxidation catalyzed by the heterojunction catalyst and related catalysts obtained under high-temperature calcination in Comparative Example 1 of this invention.

[0046] Figure 12 The X-ray diffraction patterns are shown for different precursors and the catalyst obtained after ball milling in Comparative Example 2 of this invention.

[0047] Figure 13 This is a graph showing the conversion rate of formaldehyde oxidation catalyzed by different precursors and the catalyst obtained after ball milling in Comparative Example 2 of the present invention. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation methods and protection scope of the present invention are not limited thereto.

[0049] The commercial Mn2O3 used in the examples was purchased from Shanghai Maclean Biotechnology Co., Ltd.

[0050] Example 1

[0051] (1) Catalyst preparation:

[0052] Synthesis of α-MnO2 / MnOOH precursor: 18 mmol of potassium permanganate (KMnO4) and 10 mmol of ammonium oxalate ((NH4)2C2O4) were weighed and dissolved thoroughly in 70 mL of deionized water, and stirred for 20 min. The solution was then transferred to a 100 mL polytetrafluoroethylene reactor and heated to 180 °C for 24 h. After the reactants cooled to room temperature, the products were thoroughly washed by centrifugation and then vacuum dried at 80 °C for 6 h.

[0053] Synthesis of α-MnO2 / Mn2O3-25 catalyst: 200 mg of α-MnO2 / MnOOH precursor sample was weighed and placed in a 50 mL planetary ball mill jar for ball milling in air atmosphere. The ball-to-material ratio was 100:1, the ball diameters were 4, 6 and 8 mm (weight ratio 1:2:1), the rotation speed was 500 r / min, and the ball milling time was 25 min to obtain the target catalyst.

[0054] Preparation of reference α-MnO2 catalyst: 15.0 mmol KMnO4 and 6 mmol MnSO4 were dissolved in 120 mL deionized water. After stirring for 1 hour, the solution was transferred to a 200 mL polytetrafluoroethylene reactor. After reacting at 160 °C for 12 hours, the solution was naturally cooled to room temperature. The resulting precipitate was thoroughly washed (with ultrapure water and anhydrous ethanol, respectively) and dried to obtain reference α-MnO2.

[0055] Preparation of reference α-MnO2-25 catalyst: The reference α-MnO2 catalyst was synthesized under the same ball milling conditions as α-MnO2 / Mn2O3-25 as described above.

[0056] Preparation of reference Mn2O3-25 catalyst: Commercial Mn2O3 was synthesized under the same ball milling conditions as described above.

[0057] (2) Phase / structure characterization of the catalyst:

[0058] X-ray diffraction of the target catalyst α-MnO2 / Mn2O3-25 and the precursor sample (α-MnO2 / MnOOH) in this embodiment. Figure 1 As shown. Combined with XRD, it is confirmed that the precursor α-MnO2 / MnOOH of the manganese oxide heterojunction catalyst has a phase structure of a two-phase composite of α-MnO2 and MnOOH; the phase of the manganese oxide heterojunction catalyst is a two-phase composite of α-MnO2 and Mn2O3. High-resolution transmission electron microscopy results ( Figure 2 b) further confirms the existence of the α-MnO2 / Mn2O3 heterostructure. This was demonstrated using low-magnification transmission electron microscopy (TEM). Figure 2 In a) the sample morphology can be observed to be irregular nanoparticles.

[0059] Based on the results of X-ray photoelectron spectroscopy analysis of O1s and Mn 2p, ( Figure 3a and Figure 3b After ball milling, a large number of oxygen vacancies exist on the surface of the α-MnO2 / Mn2O3-25 catalyst.

[0060] (3) Catalytic formaldehyde oxidation performance test in this embodiment:

[0061] Changes in catalytic activity of α-MnO2 / MnOOH, α-MnO2 / Mn2O3-25 and other comparative catalysts at different temperatures ( Figure 4 The results show that the α-MnO2 / Mn2O3-25 catalyst exhibits excellent catalytic activity, capable of completely oxidizing 100 ppm formaldehyde to CO2 and H2O at 80 °C, with activity significantly superior to the corresponding comparative samples. This indicates that the presence of heterojunctions in the target catalyst effectively improves its catalytic activity. Furthermore, the high reactivity of the target catalyst is also reflected in its specific reaction rate, reaching 8.92 μmol g at 80 °C. -1 min -1 The overall target catalyst exhibits excellent stability ( Figure 5 This indicates that the catalytic performance of this manganese oxide heterojunction catalyst is superior to most reported non-precious metal catalysts.

[0062] Activity test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, and the gas hourly space velocity was 120 L / g. cat -1 h -1 .

[0063] Stability test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, the temperature was 80℃, and the gas hourly space velocity was 160 L / g. cat -1 h -1 .

[0064] Example 2

[0065] (1) Catalyst preparation:

[0066] In this embodiment, the only difference between the ball milling time in Example 1 and the rest of the preparation conditions is that the ball milling time is adjusted to 0 min, 10 min, 25 min, and 60 min. The resulting catalyst is labeled as α-MnO2 / Mn2O3-T, where T represents a different ball milling time.

[0067] (2) Phase / structure characterization of the catalyst:

[0068] The X-ray diffraction of α-MnO2 / Mn2O3-T obtained in this embodiment is as follows: Figure 6 As shown in the figure, XRD analysis results confirm that the catalyst's phase structure after ball milling for 10 min is a two-phase complex of α-MnO2 and amorphous manganese oxide, indicating that ball milling promotes the transformation of the MnOOH phase into amorphous manganese oxide. With the extension of ball milling time, the amorphous phase gradually transforms into the Mn2O3 phase, and further extension of ball milling time does not cause a change in the catalyst's phase structure but only further increases its crystallinity.

[0069] (3) Test of the catalytic formaldehyde oxidation performance of α-MnO2 / Mn2O3-T obtained in this embodiment:

[0070] Changes in catalytic activity of α-MnO2 / Mn2O3-T at different temperatures ( Figure 7 The results showed that the catalytic activity of α-MnO2 / Mn2O3-T increased continuously with the extension of ball milling time; however, the catalytic activity of formaldehyde began to decrease after the ball milling time exceeded 25 min. Among them, α-MnO2 / Mn2O3-25 could completely oxidize 100 ppm of formaldehyde to CO2 and H2O at 80℃, and its catalytic performance was far superior to that of other corresponding samples.

[0071] Activity test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, and the gas hourly space velocity was 120 L / g. cat -1 h-1 .

[0072] Example 3

[0073] (1) Catalyst preparation:

[0074] In the synthesis method of this embodiment, only the ball-to-material ratio in Example 1 was adjusted to 200:1, 100:1, and 20:1, while all other preparation conditions remained the same. The obtained catalysts were labeled as α-MnO2 / Mn2O3-Q200, α-MnO2 / Mn2O3-Q100, and α-MnO2 / Mn2O3-Q20, respectively.

[0075] (2) Phase / structure characterization of the catalyst:

[0076] The X-ray diffraction patterns of the catalysts α-MnO2 / Mn2O3-Q200, α-MnO2 / Mn2O3-Q100, and α-MnO2 / Mn2O3-Q20 obtained in this embodiment are as follows: Figure 8 As shown in the figure, XRD analysis revealed that the hydrothermal samples underwent phase transitions at different ball-to-material ratios. The α-MnO2 / Mn2O3-20 catalyst phase mainly consisted of α-MnO2 and a smaller amount of MnOOH, while α-MnO2 / Mn2O3-Q200 and α-MnO2 / Mn2O3-Q100 were composed of both α-MnO2 and Mn2O3. With increasing ball-to-material ratio, the diffraction peaks belonging to α-MnO2 intensified, and the phase transition from MnOOH to Mn2O3 was only induced when the ball-to-material ratio reached 100:1 or higher.

[0077] (3) Test of the catalytic formaldehyde oxidation performance of α-MnO2 / Mn2O3-Q200, α-MnO2 / Mn2O3-Q100, and α-MnO2 / Mn2O3-Q20 obtained in this embodiment:

[0078] Changes in catalytic activity at different temperatures Figure 9 The results show that α-MnO2 / Mn2O3-Q100 has good catalytic activity, and can completely oxidize 100ppm formaldehyde to CO2 and H2O at 80℃. This catalytic activity is far superior to that of other corresponding samples.

[0079] Activity test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, and the gas hourly space velocity was 120 L / g. cat -1 h -1 .

[0080] Comparative Example 1

[0081] (1) Catalyst preparation:

[0082] The hydrothermal precursor (α-MnO2 / MnOOH) and the target catalyst (α-MnO2 / Mn2O3-25) were prepared according to the method described in Example 1. The control sample (α-MnO2 / MnOOH-T400) was obtained by calcining the hydrothermal precursor at 400°C under nitrogen for 4 hours.

[0083] (2) Phase / structure characterization of the catalyst:

[0084] The X-ray diffraction of the catalyst obtained in this example is as follows: Figure 10 As shown in the figure, XRD analysis revealed that after high-temperature calcination, the MnOOH phase of α-MnO2 / MnOOH transformed into Mn3O4, while the α-MnO2 phase showed no significant change. Further increasing the calcination temperature (e.g., to 600℃) could promote the further transformation of MnOOH into Mn2O3, but α-MnO2 also began to thermally decompose into β-MnO2.

[0085] (3) Test of the catalytic formaldehyde oxidation performance of the catalyst obtained in this embodiment:

[0086] Changes in catalytic activity at different temperatures Figure 11 The results show that the α-MnO2 / Mn2O3-25 catalyst has excellent catalytic activity, and can completely oxidize 100 ppm formaldehyde to CO2 and H2O at 80℃. Its activity is far superior to the corresponding comparative sample (α-MnO2 / MnOOH-T400). This indicates that the catalyst obtained by inducing the phase change of MnOOH through ball milling has better performance, and the method is simple and energy-efficient.

[0087] Activity test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, and the gas hourly space velocity was 120 L / g. cat -1 h -1 .

[0088] Comparative Example 2

[0089] (1) Catalyst preparation:

[0090] Preparation of reference sample MnOOH: 1.25 mL of ethanol was mixed with 48.75 mL of deionized water to obtain an ethanol-water solution. 3.5 mmol of KMnO4 was added to the above ethanol-water solution, and after complete dissolution, the mixture was transferred to a 100 mL Teflon autoclave and kept at 140 °C for 12 h. The resulting precipitate was centrifuged, washed with deionized water and ethanol, and dried at 70 °C for 4 h to obtain the reference sample MnOOH.

[0091] Preparation of reference sample MnOOH-25: The reference sample MnOOH was obtained by ball milling under the same conditions as in Example 1.

[0092] (2) Phase / structure characterization of the catalyst:

[0093] Combined with XRD diffraction pattern ( Figure 12 As set out, the reference sample MnOOH is a pure phase with good crystallinity, and the ball-milled MnOOH-25 sample has two phases, MnOOH and Mn2O3.

[0094] (3) Test of the catalytic formaldehyde oxidation performance of the catalyst obtained in this embodiment:

[0095] Changes in catalytic activity at different temperatures Figure 13 The results show that the α-MnO2 / Mn2O3-25 catalyst has excellent catalytic activity, and can completely oxidize 100 ppm formaldehyde to CO2 and H2O at 80℃. Moreover, its activity is far superior to the corresponding comparative samples MnOOH and MnOOH-25. This indicates that the high activity of the α-MnO2 / Mn2O3-25 catalyst requires a precursor with a specific composite structure formed by α-MnO2 and MnOOH.

[0096] Activity test conditions: The reaction gas was a mixture of high-purity air containing 100 ppm formaldehyde, the relative humidity was 50%, and the gas hourly space velocity was 120 L / g. cat -1 h -1 .

[0097] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A manganese oxide heterojunction catalyst characterized by, The manganese oxide heterojunction catalyst is composed of two phases of alpha-MnO2 and Mn2O3; the preparation method comprises the following steps: (1) Preparation of manganese oxide heterojunction catalyst precursor: potassium permanganate and ammonium oxalate are prepared by hydrothermal reaction; the concentration of the potassium permanganate is 0.1 M-0.5 M, and the concentration of the ammonium oxalate is 0.1 M-0.5 M; the temperature of the hydrothermal reaction is 100-180 ℃, and the time is 12 h-48 h; (2) Preparation of manganese oxide heterojunction catalyst: the manganese oxide heterojunction catalyst precursor obtained in step (1) is obtained by mechanical ball milling to obtain the manganese oxide heterojunction catalyst; the ball-to-material ratio of the mechanical ball milling is 10:1-200:1; and the time of the mechanical ball milling is 5-120 min.

2. The manganite heterojunction catalyst of claim 1, wherein, The heterojunction interface of the manganese oxide heterojunction catalyst contains oxygen vacancies.

3. The method of producing a manganese oxide heterojunction catalyst according to any one of claims 1 to 2, characterized by, Comprise the following steps: (1) Preparation of manganese oxide heterojunction catalyst precursor: potassium permanganate and ammonium oxalate are prepared by hydrothermal reaction; the concentration of the potassium permanganate is 0.1 M-0.5 M, and the concentration of the ammonium oxalate is 0.1 M-0.5 M; the temperature of the hydrothermal reaction is 100-180 ℃, and the time is 12 h-48 h; (2) Preparation of manganese oxide heterojunction catalyst: the manganese oxide heterojunction catalyst precursor obtained in step (1) is obtained by mechanical ball milling to obtain the manganese oxide heterojunction catalyst; the ball-to-material ratio of the mechanical ball milling is 10:1-200:1; and the time of the mechanical ball milling is 5-120 min.

4. The production method according to claim 3, characterized by, Step (1) The preparation of the manganese oxide heterojunction catalyst precursor is specifically as follows: potassium permanganate and ammonium oxalate are added to water, stirred, cooled to room temperature after hydrothermal reaction, and the precipitate is washed and dried to obtain the manganese oxide heterojunction catalyst precursor.

5. The preparation method according to claim 4, characterized in that, The stirring time is 5 s-1 h; the drying temperature is 60-100 ℃, and the time is 6-10 h.

6. The preparation method according to claim 3, characterized in that, Step (2) The mechanical ball milling is carried out in a planetary ball mill jar; and the mechanical ball milling is in an air atmosphere.

7. The preparation method according to claim 3, characterized in that, Step (2) The ball-to-material ratio of the mechanical ball milling is 100:1-200:1; the rotating speed of the mechanical ball milling is 200-500 r / min; and the time of the mechanical ball milling is 25-60 min.

8. Application of the manganese oxide heterojunction catalyst according to any one of claims 1-2 in catalytic oxidation of formaldehyde.

9. Use according to claim 8, characterized in that, In the process of catalytic oxidation of formaldehyde, the concentration of formaldehyde is 0-500 ppm excluding 0, the gas space velocity is 120-500 L g cat -1 h -1 , the reaction temperature is 80-200 ℃, and the humidity is 0-80% relative humidity.

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