阅读说明：本技术 钴或铜掺杂的水钠锰矿催化剂、制备方法及其应用 (Cobalt or copper doped birnessite catalyst, preparation method and application thereof ) 是由 何俊 阿布巴卡·约瑟夫 孙勇 任勇 连政 于 2020-09-10 设计创作，主要内容包括：一种钴或铜掺杂的水钠锰矿催化剂、制备方法及其应用,该催化剂由δ-MnO-2与Co或者Cu掺杂而构成,所述的Co或者Cu与Mn的摩尔比为0.01-0.25：1。方法包括将KMnO-4和草酸铵溶解在去离子水中,室温搅拌,然后移植到聚四氟乙烯容器中,将温度升至120-160℃下保持15-45分钟,然后冷却至室温,形成棕色沉淀物在真空下过滤,并用去离子水冲洗；然后将获得的沉淀物进行干燥,将硝酸钴和硝酸铜分别引入前驱体溶液中,将Co和Cu掺杂到δ-MnO-2中,微波条件下处理得到催化剂分别命名为xCo-δ-MnO-2和xCu-δ-MnO-2。具有能够扩展甲醛催化剂的种类,并能够有效的提升δ-MnO-2的催化活性的优点。(A birnessite catalyst doped with Co or Cu and its preparing process and application are disclosed, which is prepared from delta-MnO 2 And Co or Cu, wherein the molar ratio of Co or Cu to Mn is 0.01-0.25: 1. the method comprises mixing KMnO 4 Dissolving ammonium oxalate in deionized water, stirring at room temperature, transplanting into a polytetrafluoroethylene container, raising the temperature to 120-160 ℃, keeping for 15-45 minutes, cooling to room temperature, filtering under vacuum to form brown precipitate, and washing with deionized water; then drying the obtained precipitate, respectively introducing cobalt nitrate and copper nitrate into the precursor solution, and doping Co and Cu into delta-MnO 2 In the microwave treatment, the obtained catalyst is respectively named as xCo-delta-MnO 2 And xCu-delta-MnO 2 . With capability of expansionThe variety of the formaldehyde catalyst can be effectively improved, and the delta-MnO can be effectively improved 2 The catalytic activity of (3).)

1. A cobalt or copper doped birnessite catalyst is characterized in that: the catalyst consists of delta-MnO₂And Co or Cu, wherein the molar ratio of Co or Cu to Mn is 0.01-0.25: 1.

2. the cobalt or copper doped birnessite catalyst of claim 1, wherein: the molar ratio of Co or Cu to Mn is 0.05-0.2: 1.

3. the cobalt or copper doped birnessite catalyst of claim 3, wherein: the molar ratio of Co or Cu to Mn is 0.05: 1.

4. the cobalt or copper doped birnessite catalyst of claim 1, wherein: the catalyst consists of delta-MnO₂And Co doping.

5. The method of preparing a cobalt or copper doped birnessite catalyst of claim 1, wherein: the method comprises the following specific steps:

(1) mixing KMnO₄Dissolving ammonium oxalate in deionized water, stirring at room temperature, transplanting into a polytetrafluoroethylene container, raising the temperature to 120-160 ℃, keeping for 15-45 minutes, cooling to room temperature, filtering under vacuum to form brown precipitate, and washing with deionized water;

(2) then drying the obtained precipitate, respectively introducing cobalt nitrate and copper nitrate into the precursor solution, and doping Co and Cu into delta-MnO₂In the microwave treatment, the obtained catalyst is respectively named as xCo-delta-MnO₂And xCu-delta-MnO₂。

6. The method of preparing a cobalt or copper doped birnessite catalyst of claim 5, wherein: the KMnO₄The concentration of the ammonium oxalate is 10-30mg/ml, and the concentration of the ammonium oxalate is 5-10 mg/ml; both of which are concentrations in the final deionized water; the stirring time at room temperature is 15-40min, and the drying is drying in an oven at 90-110 ℃ for 10-15 hours.

7. The method of preparing a cobalt or copper doped birnessite catalyst of claim 5, wherein: the x is 0.01-0.2.

8. The method of preparing a cobalt or copper doped birnessite catalyst of claim 7, wherein: the x is 0.05-0.2.

9. The method of preparing a cobalt or copper doped birnessite catalyst of claim 7, wherein: the microwave conditions are as follows: the microwave treatment power is 500-700W, and the time is 20-40 min.

10. An application of a birnessite catalyst doped with cobalt or copper in catalytic oxidation of formaldehyde.

Technical Field

The application relates to the technical field of formaldehyde catalysts, in particular to a cobalt or copper doped birnessite catalyst, a preparation method and application thereof.

Background

Due to the carcinogenicity and other negative effects formaldehyde has on human health, researchers have recently focused on developing cost-effective transition metal-based catalysts for the oxidative degradation of formaldehyde (HCHO) in indoor environments. The catalytic oxidation method is a promising method for mineralizing formaldehyde into harmless CO₂And H₂And O. Researchers have devised various research strategies, such as defect engineering, etc., to improve the catalytic activity of catalysts in various applications, including oxidation reactions. The induction of structural defects (such as oxygen vacancies and structural lattice distortions) is currently a well-established technique for enhancing the catalytic activity of materials. These defect sites serve as active centers (or sites) for activating oxygen, water molecules to surface active oxygen species such as hydroxyl groups and the like, and it has been reported that they actively participate in most oxidation reactions, especially the oxidation of formaldehyde. Research can induce structural defects by varying synthesis conditions, material handling, ion exchange, and incorporation of metals or ions into the crystal lattice of the host material.

Polarz et al studied ZnO catalysts with varying degrees of oxygen deficiency, demonstrating that oxygen vacancies act directly to hydrogenate CO to CH₃Active center of OH. VO loaded with ceria for oxygen defects_xStudies of the effect of oxidative dehydrogenation of methanol on catalysts have shown that there is a direct correlation between oxygen defect density and catalytic activity for methanol oxidation, which acts to reduce the activation energy required for methoxy decomposition. The structural defects of multi-walled carbon nanotubes have been demonstrated to be active sites for benzene oxidation and promoters. Wang et al demonstrated chemical modification of the surface at delta-MnO₂Defects (pits) are formed on the surface, which results in the formation of unsaturated manganese and oxygen atoms, enhancing the activation of oxygen and the adsorption of formaldehyde.

Doping with metal cations is an important method to increase catalytic activity and induce defect formation. Genuino et al, studies have shown that, in MnO₂The substitution of Mn with Nb within the octahedral molecular sieve framework results in the creation of electrophilic sites for adsorption of CO and enhanced oxidation. Zhu et al, study showed that Ce was doped with delta-MnO₂Can generate oxygen vacancy, increase the oxygen species adsorbed on the surface and enhance the catalytic activity of formaldehyde oxidation. Also at delta-MnO₂The medium doped tungsten (W) promotes the formation of Mn vacancies and enhances the activity of surface adsorption of oxygen. Huang et al demonstrated the effect of Eu doping on ceria to generate surface oxygen defects, thereby enhancing its catalytic activity for thermal and photocatalytic oxidation of formaldehyde.

Among low-cost transition metal-based formaldehyde oxidation catalysts, manganese oxide catalysts are a promising low-temperature formaldehyde oxidation catalyst. Zhang et al, more recently demonstrated delta-MnO with layered structure₂Is MnO₂If the most active phase for formaldehyde oxidation can not only fully utilize delta-MnO₂The catalytic activity in formaldehyde oxidation and the improvement of the catalytic activity are very important for developing an effective catalyst for reducing formaldehyde in indoor environment.

Disclosure of Invention

The application aims at the defects in the prior art, and provides a catalyst which can expand the variety of formaldehyde catalysts and can effectively promote delta-MnO₂The catalytically active cobalt or copper doped birnessite catalyst of (a).

In order to solve the technical problem, the technical scheme adopted by the application is as follows: a birnessite catalyst doped with Co or Cu is prepared from delta-MnO₂And Co or Cu, wherein the molar ratio of Co or Cu to Mn is 0.01-0.25: 1.

preferably, the molar ratio of Co or Cu to Mn is 0.05-0.2: 1.

more preferably, the molar ratio of Co or Cu to Mn is 0.05: 1.

preferably, the catalyst consists of delta-MnO₂And Co doping. By doping cobalt, the catalytic oxidation of formaldehyde can be effectively reducedAnd (3) temperature.

Further, the application also provides a preparation method of the cobalt or copper doped birnessite catalyst, which comprises the following specific steps:

(1) mixing KMnO₄Dissolving ammonium oxalate in deionized water, stirring at room temperature, transplanting into a polytetrafluoroethylene container, raising the temperature to 120-160 ℃, keeping for 15-45 minutes, cooling to room temperature, filtering under vacuum to form brown precipitate, and washing with deionized water;

(2) then drying the obtained precipitate, respectively introducing cobalt nitrate and copper nitrate into the precursor solution, and doping Co and Cu into delta-MnO₂In the microwave treatment, the obtained catalyst is respectively named as xCo-delta-MnO₂And xCu-delta-MnO₂。

Preferably, the KMnO₄The concentration of the ammonium oxalate is 10-30mg/ml, and the concentration of the ammonium oxalate is 5-10 mg/ml; both at the final deionized water concentration.

Preferably, the stirring time at room temperature is 15-40 min.

Preferably, the drying is carried out in an oven at 90-110 ℃ for 10-15 hours.

Preferably, x is 0.01-0.2: 1.

Further preferably, x is 0.05 to 0.2.

Preferably, the microwave conditions are as follows: the microwave treatment power is 500-700W, and the time is 20-40 min.

The application also provides an application of the cobalt or copper doped birnessite catalyst in catalytic oxidation of formaldehyde. The application improves the treatment efficiency of formaldehyde and reduces the temperature for catalytic removal of formaldehyde, thereby reducing energy consumption. The application has the advantages and beneficial effects that:

1. the application researches the doping of birnessite delta-MnO₂The cobalt Co and the copper Cu in the catalyst have the influence on the low-temperature catalytic oxidation of the formaldehyde HCHO; mixing Co³⁺Incorporating delta-MnO₂Can strengthen Mn in the lattice structure⁴⁺And generation of oxygen vacancies and lattice defects, thereby promoting surface activityOxygen formation, thereby enhancing the catalytic activity of the low temperature oxidation of formaldehyde. However, the interaction of dopants and intermediates may also adversely affect the activity of the modified catalyst. On the other hand, although the surface oxygen vacancy and the surface active oxygen concentration are relatively increased, the concentration is delta-MnO as compared with the original one₂In contrast, copper doping suppresses the catalytic activity to a large extent. Specifically, in the presence of Cu, the catalytic activity is suppressed, and the suppression effect is enhanced as the doping ratio of Cu increases. Diffuse Reflection Infrared Fourier Transform (DRIFTS) analysis showed that in the presence of Cu carbonate intermediates accumulated on the catalyst surface, resulting in deactivation of the catalyst active sites. These findings will help one to better select catalysts containing metallic elements in terms of indoor environmental formaldehyde degradation.

2. The applicant has found through research that Mn is delta-MnO₂Partial substitution of elements within the lattice framework results in structural lattice distortion and the creation of oxygen vacancies, and promotes the activation and migration of oxygen; thus, based on the above studies, applicants have innovatively employed a Co and Cu pair as a dopant in the delta-MnO₂The role in the catalytic activity for formaldehyde oxidation is of great importance for the development of effective catalysts for the reduction of formaldehyde in indoor environments.

3. Delta-MnO as used in the present application₂Has a layered structure of MnO₂The most active phase for formaldehyde oxidation, delta-MnO₂Having catalytic activity in formaldehyde oxidation, wherein Mn is delta-MnO₂Partial substitution of elements within the lattice framework results in structural lattice distortion and the creation of oxygen vacancies and promotes oxygen activation and migration, while the delta-MnO is enhanced by the choice of dopants copper and cobalt₂The role in the catalytic activity for formaldehyde oxidation is of great importance for the development of effective catalysts for the reduction of formaldehyde in indoor environments. The application researches aiming at delta-MnO for the first time₂MnO of the specific crystal form₂The catalyst obtained by adopting the specific doping agent has the catalytic effect on formaldehyde, and a specific catalytic mechanism is researched and is a subsequent doping type delta-MnO₂The catalyst develops wider prospect and widens delta-MnO₂The metal with the specific crystal form capable of being dopedRange of species, delta-MnO for better subsequent development₂Formaldehyde catalysts offer more options.

Drawings

FIG. 1 (a) XRD pattern of starting material, 0.05Co delta-MnO₂and 0.05Cuδ-MnO₂

(b) Raman spectra of the starting Material, 0.05Co delta-MnO₂and 0.05Cuδ-MnO₂。

FIG. 2. delta. -MnO₂(a-c),0.05Coδ-MnO₂(d-f),0.05Cuδ-MnO₂FE-SEM, TEM, HRTEM image of (g-i).

FIG. 3 XPS spectra of Mn 2P (a) O1s (b) original delta MnO₂,0.05Coδ-MnO₂And 0.05Cu delta-MnO₂。

FIG. 4.Co 2p_3/2–2p_1/2Cleaved XPS.

FIG. 5 XPS of Cu 2 p.

FIG. 6 shows an infrared spectrum of the catalyst.

FIG. 7 study catalyst H₂-TPR。

FIG. 8 Formaldehyde in x Cu delta-MnO₂Catalytic conversion on catalyst study (x:0.05,0.1, 0.2), (170ppm, 45% RH,120,000 ml. g)^-1·h^-1)。

FIG. 9 catalytic conversion of Formaldehyde (170ppm,. about.45% RH,120,000 ml. g)^-1·h^-1)。

FIG. 10 GHSV to 0.05 Co-delta-MnO₂Effect of catalytic Activity (a), Co-delta-MnO₂10ppm,60 L·g^-1·h^-1Room temperature and catalytic stability test at 45% RH (b).

FIG. 11 DRIFTS results (a) delta-MnO₂(b)0.05Co-δ-MnO₂(c)0.05Cu-δ-MnO₂。

FIG. 12.0.2Cu delta-MnO₂The DRITFS results of (a) at RT (b) at high temperature (60-120 ℃) (c) absorption strength of formate and carbonate increasing with temperature.

Detailed Description

The present application is described in further detail below by way of specific examples, but the present application is not limited to only the following examples.

Examples

1. Synthesis of catalyst

Delta-MnO microwave assisted hydrothermal Synthesis Using microwave oven model MARS 5 (CEM Corp., USA)₂. A typical synthetic method is to mix 1g KMnO₄(national pharmaceutical group) and 0.4g of ammonium oxalate (alatin) were dissolved in 50ml of deionized water and stirred at room temperature for 30 minutes. The final solution was transferred to a 100ml teflon container held by an explosion-proof kevlar sleeve assembled in a support module. The synthesis temperature was controlled at 140 ℃ for 30 minutes and then cooled to room temperature, the brown precipitate formed was filtered under vacuum and rinsed with deionized water, the precipitate was dried in an oven at 105 ℃ for 12 hours, and the recovered catalyst was labeled delta-MnO₂. Then respectively preparing aqueous solutions of cobalt nitrate and copper nitrate to form precursor solutions, wherein the concentration of the aqueous solutions meets delta-MnO₂In a molar ratio of 0.05:1, followed by addition of delta-MnO₂Adding into the prepared precursor solution, processing under microwave condition to obtain catalyst, wherein the microwave processing power is 600W, the time is 30min, and the obtained catalyst is respectively named as 0.05 Co-delta-MnO₂And 0.05 Cu-delta-MnO₂。

2. Catalyst characteristics

The crystalline phase of the synthetic catalyst was identified using X-ray powder diffraction technique (XRD) performed on a D8Advanced (brueck, germany) instrument. Using a Renishaw inVia Raman microscope at 60-1800cm^-1At 532nm a raman spectrum is obtained. The morphological structure of the catalyst was observed on a Hitachi S-4800 Field Emission Scanning Electron Microscope (FESEM) equipped with EDS, and the sample was subjected to elemental analysis, where a sample was sputtered with Pt. TEM and HRTEM images were acquired with JEM-2100 (JOEL, Japan). The catalysts were analyzed for structural properties using a Micrometric 2020 analyzer. Before analysis, the samples were degassed at 200 ℃ for 3 hours to remove surface adsorbed moisture and gases. XPS analysis is carried out by a Kratos Axis Ultra DLS instrument to obtain the surface oxidation state and the chemical environment of the constituent elements of the catalyst. The elemental composition was determined by inductively coupled plasma mass spectrometry (PerkinElmer). Via H₂TPR in micrometer Autochem II (chemical adsorption analyzer)Information on the reducibility of the catalyst surface was obtained. About 50 mg of catalyst was loaded in a quartz tube at 150ml min^-1Degassing was carried out for 1 hour at the flow rate of Ar. At 30-500 deg.C for 5 min^-1The reduction curve was collected under temperature gradient. Information on surface reactions and intermediates was obtained using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) on Thermo Fisher, Nicolet 6700 equipped with Praying Mantis reaction cells at 30ml min^-1At a flow rate of N₂The equilibrium in 75ppm formaldehyde (21% oxygen) was obtained under the conditions.

3. Evaluation of catalytic Activity

Evaluating the catalytic activity of the catalyst on formaldehyde oxidation at the temperature of 30-120 ℃; in this test, 50 mg (40-60 mesh) of catalyst was weighed and loaded into a fixed bed reactor (6 mm caliber). 170ppm formaldehyde was produced by passing air through paraformaldehyde (97% AlfaAesar) in a water bath maintained at 30 ℃. The total feed flow on the catalyst bed was maintained at 100ml min^-1(120,000ml·g^-1·h^-1) The relative humidity was about 45%. CO produced in the exit stream can be monitored simultaneously on-line by Agilent 7890B GC equipped with FID and poly universal carbon detector/reactor (ARC)₂And unreacted formaldehyde concentration. CO 2₂Is the only reaction product detected. At 120,000 to 400,000ml g^-1·h^-1The effect of space velocity on catalytic activity was investigated in the GHSV range of (1). 60,000ml g at 25 DEG C^-1·h^-1In dynamic mode (2), the formaldehyde concentration was 10ppm (21% O/79% N)₂) The stability of formaldehyde and room temperature oxidation were studied for 72 hours. Because the reaction product is CO₂The conversion (%) of formaldehyde is calculated as follows:

wherein, CO_2outAnd HCHO_inRespectively represent the outlet CO₂(ppm) concentration and inlet formaldehyde (ppm) concentration.

4. Results and discussion

4.1 Structure, morphology and physicochemical Properties

Study of the synthesized MnO by XRD test₂Crystalline phase of catalyst (fig. 1 a). Layered birnessite MnO with poor crystallinity₂Diffraction peaks of (001), (002), (100) and (110) planes of (JCPDS No. 80-1098) are located at 2 θ 12.3 °, 24.5 °, 36.5 ° and 65.5 °, respectively. Two-dimensional layered birnessite MnO₂MnO shared primarily by edges₆Octahedra and different contents of Mn³⁺/Mn⁴⁺Composition, resulting in electrostatic charge imbalance and octahedral vacancies. Positively charged alkali metal cations such as K + or Na + and water molecules are located in the interlayer to provide charge balance, resulting in an interlayer spacing of 0.7 nm. The diffraction patterns of the three catalysts are similar, and no visible peak corresponding to Co and Cu exists, so that Co and Cu are shown in MnO₂Medium dispersion/binding was good. The weak nature of the peaks indicates that all catalysts are poorly crystalline. However, with the addition of the dopant, a reduction in peak intensity was found, indicating MnO₂Reduced crystallinity and structural disorder. In addition, raman spectra were collected to further understand the local structure of the catalyst and the effect of the dopant. The raman spectrum of the catalyst is shown in figure 1 b. All catalysts prepared were at 500 (v)₃)、570(ν₂) And 630cm^-1(ν₁) Three main absorption peaks are at the position, which is layered birnessite MnO₂The characteristic band of (1). 630cm^-1The Raman band of which is attributable to MnO₆V of the radical₁(Mn-O) symmetric stretching vibration, and 570cm^-1The spectral band of (A) is usually v in the fingerprint spectral band₂(Mn-O) in birnessite MnO₂MnO in the skeleton₆The base surface of the sheet vibrates telescopically. At 500cm^-1The peaks at the left and right are represented by MnO₆Bending vibrations of the group Mn-O-Mn. Even when 0.05Co and Cu were doped, the structure of birnessite did not collapse as shown in fig. 1b, indicating that the structure of birnessite was stable at low doping rates.

FIG. 2 is FE-SEM, TEM and HRTEM images of the original catalyst and the doped catalyst. Original delta-MnO₂From entanglements with an average size of 17.8nmNanochains are organized as nanospheres of about 110 nm. Even with Co and Cu doping, the nanosphere morphology remains. But with Co doping a large reduction in particle size was observed, forming smaller nanospheres of about 37.6nm, whereas with Cu doping large and dense agglomerated nanospheres were observed, assuming an irregular shape of about 147 nm. This is probably due to the incorporation of cobalt into the lattice structure of the birnessite, inhibiting the growth of manganese crystals, thereby reducing the particle size of the manganese crystals while significantly increasing the surface area, as shown in table S1 (176.3 m)²/g for 0.05Co δ-MnO₂；141.3m²/gδ-MnO₂). There have also been other reports that in the lattice structure of birnessite, Co ions substituted for Mn ions, resulting in lattice deformation, suppressing MnO₂Crystals grow to form smaller particle sizes. FE-SEM (FIG. 2g) and BET (Table S1) observed separately, Cu-. delta. -MnO₂Results in a significant reduction in surface area (61.8 m) due to larger particle size and particle agglomeration²In terms of/g). Similar observations were also found in other reports, indicating MnO₂The doping proportion of Cu in the alloy is low. In addition, delta-MnO to original₂In contrast, in Co-delta-MnO₂The smaller size nanospheres are visible in the TEM image of (FIG. 2e), while in the Cu-delta-MnO₂Larger nanospheres were observed in the TEM image of (fig. 2h), further confirming the FE-SEM results.

TABLE S1 surface area and chemical analysis

a.x represents Co and Cu dopants

HRTEM images further confirmed that the birnessite structure of the catalyst was consistent with XRD and Raman results. The 0.71nm lattice fringes that can be observed correspond to birnessite MnO₂(001) plane of (a). With the original delta-MnO₂In contrast, well-resolved lattice fringes were observed along the (001) plane of the nanochain (fig. 2c), and a decrease in lattice periodicity and long-range order was observed in the doped catalyst (fig. 2f and 2 i). This may be due to structural defects caused by lattice distortion,it is also possible to have a dopant incorporated into the delta-MnO₂Is caused in the lattice structure of (1). Compared with Cu-delta-MnO₂Co-delta-MnO can be observed₂With a higher degree of lattice distortion, consistent with XRD results.

The elemental composition of the catalyst is shown in table S1. Both the EDS and ICP-MS results show that the experimental amount of dopant present in the catalyst matrix is very close to the theoretical value. In the ICP-MS and EDS results, the K/Mn ratio of the doped catalyst remained nearly the same as the K/Mn of the original catalyst, indicating that the dopant did not substitute for K in the interlayer structure of birnessite⁺But dispersed or incorporated into MnO₂In the skeleton. This explains that the birnessite structure remains in the doped catalyst and further supports the adsorption of the dopant to the manganese ore bed. At the same time in other birnessite MnO₂Low doping rates of medium transition metals have also been reported similarly.

Table S2 summarizes the XPS results and is depicted in fig. 3. The peaks around 653.8-653.9eV and 641.9-643.5eV (FIG. 3a) are Mn 2p_1/2And Mn 2p_3/2And (4) splitting. Adding Mn 2p_3/2Further antichaking into two peaks with centers of 641.9-642.2eV and 643.3-643.45 respectively corresponding to Mn³⁺And Mn⁴⁺。Co 2p_1/2(795.12 eV) and Co 2p_3/2The cleavage value (FIG. 4) of (780.1eV) was 15.02eV, vs. Co³⁺The reported values are consistent. An oscillating peak around 943eV appears (FIG. 5), indicating Cu doping with Cu²⁺A state exists. Mn can be observed⁴⁺/Mn³⁺The ratio is reduced because the dopant replaces birnessite MnO₂Mn in the lattice⁴⁺Resulting in structural distortion and the generation of oxygen vacancies. When Mn is present⁴⁺Is removed or substituted, Mn is present³⁺In time of MnO₂Oxygen vacancies are present to maintain the electrostatic balance. The oxygen vacancies being formed by the crystal lattice O^2-Thereby creating an anion vacancy layer. Thus, catalyst Mn⁴⁺/Mn³⁺The lower the surface ratio of (a), the higher the oxygen vacancies are expected in the catalyst. Thus, based on 0.05Co delta-MnO₂Lowest Mn of⁴⁺/Mn³⁺Ratio, which we can expectHas higher oxygen vacancy density.

To further determine the effect of the dopant on the nature and surface composition of oxygen species on the catalyst, the O1s spectrum was deconvoluted into three peaks, corresponding to lattice oxygen (O), respectively_I) Surface active oxygen (O)_II) And surface adsorbed water molecules (O)_III). The peaks at 529.45-529.53 eV correspond to the structural lattice oxygen (Mn-O-Mn), and the peaks at 531.0-531.34 eV are associated with low coordination of surface oxygen, which favors terminal hydroxyl groups (OH)^-) And oxygen species (O) adsorbed on the surface of the defective oxide^-，O^2-) While the peaks at 533.1-533.4 eV are attributable to surface-adsorbed water molecules [5,29 ]]. As can be seen from FIG. 3b and Table S2, the delta MnO relative to the original delta MnO₂(0.31), the amount of adsorbed surface oxygen increased the amount of dopant added. With Mn 2p_3/2Consistent with HRTEM results, with 0.05Cu delta-MnO₂(0.36) in comparison, 0.05 Codelta-MnO₂The surface adsorbed oxygen content (0.44) was higher. It is well known that oxygen vacancies act as sites for the activation of molecular oxygen, water molecules, etc. into reactive or defective surface oxides, while also enhancing the mobility of oxygen [5,10,33]. This indicates that²⁺In comparison, more Co³⁺Incorporating delta-MnO₂May be due to the fact that the former has a coordination radius closer to Mn than the latter⁴⁺This results in more structural distortion and provides a site for the generation of reactive oxygen species. In addition, compared with the original MnO₂In contrast, a slight decrease in the binding energy of lattice oxygen and surface defect oxide was observed in the presence of the dopant, indicating that the interaction between Mn and O atoms is slightly weaker. This may be associated with structural defects that result in an increase in the electron density around the lattice oxygen, resulting in a reduction in the observed binding energy. When the transition metal is in MnO₂With upper occupation of Mn vacancies, octahedral MnO₆Structural deformation occurs to relieve induced stress caused by the transition metal.

In addition, the intensity ratio of the raman peak of the doped catalyst (v) was observed₁/ν₂) Generally increasing (fig. 1 b). This may indicate MnO₆The Mn-O bond of (B) is deformed and the dopant enters the crystal latticeInduced stress induced net delta-MnO₂Defects in the lattice framework form. 0.05Co delta-MnO₂Middle (v)₁/ν₂) Intensity ratio of peak higher than 0.05Cu delta-MnO₂V. of (A)₁/ν₂) The intensity ratio of the peaks, which indicates higher horizontal lattice distortion in the octahedral sheets in the presence of Co, further confirms the XPS, XRD and HRTEM results. Similar raman techniques are also used in other reports to determine the extent of structural defect formation. Furthermore, FTIR results (FIG. 6) were at 3440, 1050 and 1633cm^-1More intense peaks are shown nearby due to the binding of hydrates and OH in the birnessite interlayer structure, respectively^-Stretching vibration of, and structure H₂Flexural vibration of O-H bonds of O and OH groups [36]This further indicates that at 0.05Co delta-MnO₂There are more structural defects. The defect sites are reported to be sites that activate molecular oxygen to active surface oxygen or to defective oxides (e.g., superoxide).

To gain insight into the reduction behavior of the catalyst, we collected H₂The TPR profile is depicted in FIG. 7. Only one overlapping broad peak was observed, corresponding to a reduction in surface active oxygen and MnO₂Is continuously reduced. The broad peak can be further divided into four peaks: α, β, γ and δ, respectively representing adsorbed surface Oxygen (OH)^-，O^-，O^2-) Reduction of (2) and MnO₂Reduction to Mn₂O₃,Mn₂O₃Reduction to Mn₃O₄,Mn₃O₄Reduced to MnO.

Original delta-MnO₂The low onset temperature observed at 170 ℃ corresponds to a reduction in adsorbed surface oxygen. After adding Co and Cu, the initial reduction temperature is reduced to about 154 ℃ and 163 ℃ respectively. However, 0.05 Co. delta. -MnO₂The alpha peak of (A) has the highest peak intensity, thus indicating the incorporation of Co into delta-MnO₂Not only does the concentration of surface-active species increase in the layer, but it also increases their reactivity and enhances the mobility of lattice oxygen by the defects generated. The presence of oxygen vacancies increases the reactivity of the lattice oxygen, thereby promoting catalytic activity. Furthermore, in the presence of a dopant, M is addednO₂All temperatures for continuous reduction to MnO were reduced to lower temperatures (as shown in table S3). This indicates that the dopant improves the reducibility and lattice oxygen mobility of the catalyst surface as a whole. 0.05Co delta-MnO₂Can be attributed to its defective structure and excellent oxygen mobility in the surface and bulk phases.

TABLE S3 catalyst Activity (T)_50％and T_90％) And H₂Reduction temperature

4.2 catalytic conversion of Formaldehyde

Based on the original catalyst, under dynamic conditions (GHSV of 120L g)^-1·h^-1) The effect of the dopants (Co and Cu) on the catalytic activity of the synthesis catalyst was evaluated to achieve complete conversion of formaldehyde (-170 ppm). The effect of Relative Humidity (RH) on the catalytic oxidation effect of formaldehyde has been previously reported. Under moderate RH conditions, water molecules react with the defect sites to replenish the surface consumed OH^-The supply of (2). At higher relative humidity, water molecules and formaldehyde molecules can produce a competing effect, the former being adsorbed onto the surface and active sites of the catalyst, resulting in a reduction in the activity and in some cases deactivation of the catalyst. Thus, the relative humidity was maintained at a moderate level of 45% throughout the experiment.

As shown in fig. 5, the original delta-MnO₂Shows very high activity and can completely convert 170ppm of formaldehyde into CO at 90 DEG C₂. When delta-MnO is added₂Incorporation of Co (0.05 Co. delta. -MnO)₂) Thereafter, the complete conversion temperature was reduced from 90 ℃ to 80 ℃ to illustrate that Co is responsible for the delta-MnO in the formaldehyde catalyzed reaction₂The promotion of catalytic activity can effectively weaken the catalytic temperature condition. Unexpectedly, Cu modified delta-MnO₂The result is in contrast that the temperature at which formaldehyde is completely oxidized rises to 100 c, although the surface adsorbs slightly more oxygen species and vacancies than the original catalyst. As shown in the figure5, 0.05Co delta-MnO in the entire temperature range₂Relative to the original delta-MnO₂Exhibit improved activity. Copper doped delta-MnO, in contrast₂The activity decreases in almost all temperature ranges. In addition, although the reaction temperature was increased, the original delta-MnO₂And Cu doped delta-MnO₂The difference between the catalytic activities of (a) and (b) increases with the total cumulative reaction time (table S4). On this basis, the catalysis of the intermediate shows signs of deactivation or surface accumulation with increasing exposure to formaldehyde. An increase in the doped copper content (0.1 and 0.2) resulted in a further decrease in catalytic activity (FIG. 8), which further confirms the observed copper versus 0.05Cu delta-MnO₂Inhibition of catalytic activity. In contrast, with respect to the original delta-MnO₂All Co-doped catalysts (0.1 and 0.2) showed improved catalytic activity (fig. 8).

TABLE S4. delta. -MnO₂-Cu-MnO₂The difference in conversion between with the change in reaction temperature and time

For effective comparison, Table S3 gives 50% (T)_50％) And 90% (T)_90％) The temperature of the transition; Delta-MnO₂, 0.05Co-δ-MnO₂And 0.05 Cu-delta-MnO₂T of_50％74,63 and 85 ℃ respectively, and T_90％Respectively 87,77 and 97 deg.c. As is clear from the characterization results, 0.05 Co. delta. -MnO₂Due to surface defects, rich surface adsorption of Oxygen (OH)^-,O^-,O^2-) Easy reducibility and mobility of adsorbed oxygen and lattice oxygen. One reasonable explanation for the reduced catalytic activity of copper-doped catalysts is that the intermediates accumulate on the surface resulting in catalyst deactivation or the inability of contaminants to enter the active sites of the catalyst.

Furthermore, catalyst doping and surface modification have proven to be effective strategies for enhancing catalytic activity, primarily by creating defects and enriching the surface concentration of active oxygen. Structure of the productThe interaction of the defect with molecular oxygen can induce the activation of oxygen into active species such as hydroxyl, superoxide and superoxide. Eu-doped CeO with highest concentration of surface defect oxides₂The activity of (3) is improved because reduction of Ce results in generation of oxygen vacancies. The resulting vacancy points may serve as sites for oxygen activation into superoxides. The presence of surface defects increases the efficiency of the conversion of benzene to phenol by hydroxylation. It was similarly demonstrated that W adds MnO₂Resulting in the generation of oxygen vacancies and an increase in the concentration of surface active oxygen, thereby improving the catalytic oxidation efficiency of formaldehyde. Also, surface defects are critical to the dissociation of adsorbed water and molecular oxygen into reactive surface oxygen species, which thereby facilitates low temperature oxidation of formaldehyde.

Accordingly, the vacancies existing in the form of surface pores promote the formation of unsaturated oxygen and defective oxides, which significantly improves the activity of the formaldehyde oxidation catalyst. Also, a direct relationship between the oxygen vacancy density of the ceria-based catalyst and the CO oxidation reaction is established. As the reaction proceeds, the consumed surface adsorbed oxygen species are replenished by the reaction of water molecules, oxygen molecules, lattice oxygen, and defect sites. Thus, Co-doped delta-MnO₂It is not surprising that it exhibits excellent low temperature catalytic activity for formaldehyde due to its high oxygen vacancy and abundant active oxygen surface concentration.

To evaluate the activity of the catalyst at high throughput operation, at 120,240and 400 Lg^-1·h^-1At 170ppm formaldehyde and 45% RH, GHSV was studied for 0.05 Co-delta-MnO₂The effect of activity. As shown in FIG. 10a, the complete conversion temperature increased with increasing GHSV, 80 ℃ to 90 and 100 ℃ corresponding to 120,240and 400 Lg^-1·h^-1Even at high GHSV of 400 Lg^-1·h^-1In the case of (2), 0.05 Co-. delta. -MnO₂It is still very active and can completely convert formaldehyde even at temperatures of 100 ℃. This further demonstrates that the catalyst has good catalytic activity. Next, to evaluate the applicability of the catalyst in a typical indoor environment, it was 60L g at GHSV^-1·h^-1In the dynamic system of (2), the feed concentration of-10 ppm was investigatedRoom temperature catalytic efficiency and stability of the catalyst over 72 hours, as shown in figure 10 b. The results show that the average conversion is as high as 93.5% within 72 hours of operation. These results illustrate the stability of the catalyst, its high catalytic activity even at room temperature, and its potential for eliminating formaldehyde from a practical indoor environment.

4.3 reactions and mechanisms

To further understand the effect of surface reactions, formaldehyde oxidation mechanism and surface modification on catalyst reactivity, we performed in situ DRIFTS analysis with results shown in figure 11. In all spectra, at 1710cm^-1No peak was observed with respect to the C ═ O stretch band of the surface-adsorbed formaldehyde. At 3500 + 2900cm^-1The strong absorption bands in the zones indicate a large number of surface-adsorbed hydroxyl groups on the catalyst surface. Formate salts, methylenedioxy groups, carbonate salts and the like were observed on the catalyst. At 2830 and 2840 and 2865 and 2885cm^-1(v (CH) Telescopic), 1370-1373cm^-1(delta (CH) bend), 1567-1580cm^-1(ν_s(OCO)), and 1350-^-1(ν_as(OCO)) is characteristic of formate salts. The band split between the symmetric and asymmetric modes of C-O in formate indicates coordination of the formate pattern on the catalyst surface. For 0.05Co-, 0.05 Cu-and delta-MnO₂Split was 219, 225 and 227cm respectively^-1This indicates coordination of the bridge mode [43-45 ]]. At 2730 and 2732cm^-1(C-H expansion), 1440-1453cm^-1(δ(CH)), 1154-1161cm^-1 and 1015-1053cm^-1(v (CO) stretching) the observed band is characteristic of the Dialdehyde (DOM) [5,43,45 ]]. Carbonate bridges (1653, 1240 cm) were also observed^-1) And carbonate monodentate carbonate (1315-1331, 1470-1490cm^-1) Characteristic of [6,46 ]]While bands around 1620 are due to surface adsorbed water molecules.

On all catalysts, in addition to surface hydroxyl groups, three types of intermediates were found: DOM, formate and carbonate. In delta-MnO₂The crystal lattice structure of (A) is doped with Co, and a large amount of surface defect oxides and hydroxyl groups are generated due to surface defects, so that DOM substances are rapidly convertedAs an intermediate, this consisted of 1053 and 1154cm^-1The weak peak at (a) proves to be related to the stretching vibration of the dom (co). In addition, at 1498 and 1240cm^-1The nearby carbonates are characterized by only 0.05 Co-delta-MnO₂Appears as a shoulder and is at 1650cm, compared to other catalysts^-1The relative intensity of the nearby peaks is low. It is reported that oxides and hydroxyl groups with surface defects participate in the formation of formic acid intermediates, which further oxidize the surface carbonates to carbon dioxide. Thus, 0.05Co doped delta-MnO₂It is not surprising that the strongest formate peak and the relatively lower carbonate intensity peak are exhibited. This indicates that the rate of further oxidation of the carbonate followed by desorption from the catalyst surface is rapid, releasing the active sites to continue the reaction.

On the other hand, we observed that despite the original delta-MnO₂(Table S2) comparison, 0.05 Cu-delta-MnO₂The number of surface active oxides in (1) was slightly larger (Table S2), but the peak of carbonate at 0.05Cu (1653 cm)^-1) Doped MnO₂Almost becoming the dominant peak. Furthermore, 0.05 Cu-delta-MnO₂840cm^-1A new feature appears nearby, which is attributed to the carbonates. A reasonable explanation may be related to direct surface coordination between Cu ions and carbonates, resulting in surface accumulation and blocking of catalytically active sites.

In FIG. 12 delta-MnO doped for 0.2Cu is shown₂The DRIFTS scan of. A significant reduction in the intensity of all absorbance peaks was observed in the RT scan compared to the other catalysts (see inset absorbance scale of 0.05), indicating poor RT performance compared to the other catalysts and consistent with the activity test results (figure 8). Furthermore, over time, the peak of the carbonate species dominates the entire spectrum. It is noted, however, that the peak intensity of the catalyst is relatively high, compared with other catalysts (. delta. -MnO)₂,0.05Co-δ-MnO₂ and 0.05Cu-δ-MnO₂) In contrast, the main peak intensity of carbonate is weaker. However, the peak associated with formate is weak, especially the asymmetric COO stretching peak of formate (predominant in other catalysts, including 0.05 Cu. delta. -MnO)₂) At 1580cm only^-1Weak acromion of the bodyAs shown in fig. 12 a. E.g., delta-MnO previously doped at 0.05Cu₂Further confirming carbonate accumulation and accounting for Cu-doped δ -MnO₂And the inhibition increases with an increase in Cu. Accumulation of carbonate on the surface results in restricted access to the surface active sites and inhibits reoxidation of the reduced Mn active sites, thereby inhibiting further conversion of formaldehyde to its intermediates.

TABLE S2.Mn 2p_3/2And XPS analysis of O1s

To further understand the surface mechanism of Cu presence and carbonate accumulation, 0.2Cu doped delta-MnO was collected at elevated temperatures (60-120 deg.C)₂The DRIFTS scan of (a) was compared with the RT scan (fig. 12 b). As shown, carbonate peaks (1633 and 855 cm)^-1) The strength of (A) gradually decreases with increasing temperature, while the formate (COO 1583 cm)^-1Asymmetric stretching) strength gradually increases with increasing temperature and becomes a major feature at 120 ℃. The absorption intensity of formate and carbonate as a function of temperature is shown in FIG. 12 c. Interestingly, as the temperature increased, the carbonate oxidized to CO₂And formate formation are accompanied by the consumption of surface hydroxyl groups. This further confirms that surface hydroxyl species participate in the oxidation of formaldehyde to CO₂And H₂And (4) O. Studies have shown that the reaction of water molecules with defective oxides replenishes the surface hydroxyl groups consumed [6]. In addition, molecular oxygen can adsorb and activate on oxygen vacancies as surface and lattice oxygen is consumed. Final, Co-doped delta-MnO₂Can be attributed to its abundance of oxygen vacancies and its ability to replenish the consumed hydroxyl groups, which in turn maintains the catalytic reaction and increases catalytic activity.

Therefore, from the above observation results, it is known that: Delta-MnO₂The presence of Cu in the alloy leads to surface accumulation of carbonates and thus to partial surfaceInactivation and blocking of surface active sites. With the rising reaction temperature, the surface hydroxyl reacts with carbonate to generate CO₂The surface active sites are released to activate the formaldehyde and convert it to an intermediate. The peaks associated with the (CO) stretching vibrations of the DOM species were observed to decrease with increasing formate, indicating that as carbonate desorbs from the catalyst surface, the DOM species were converted to formate and further oxidized to carbonate. On the other hand, since in delta-MnO₂The lattice structure of (a) is doped with surface defects generated by Co to form a large amount of surface hydroxyl groups and defective oxides, and thus only weak characteristics associated with the DOM species are observed. Carbonates are easily oxidized and desorbed from the catalyst surface, and have high catalytic activity even under low temperature conditions.

Therefore, through the above examples and test results, the following conclusions can be drawn corresponding to the copper or cobalt doped catalyst obtained in the present application: successfully synthesizes delta-MnO doped with cobalt and copper by a microwave-assisted hydrothermal synthesis method₂The catalyst is proved to be delta-MnO through defect engineering dominated by a metal doping method₂An effective strategy for the formation of oxygen vacancies at the surface of the catalyst; at a low doping ratio of about 0.05 (atomic ratio), Co is shown to be more doped into delta-MnO₂Leading to the generation of surface defects; this is evidenced by the creation of lattice defects and oxygen vacancies, which enrich the surface concentration of active oxygen and enhance the mobility of oxygen. Experiments prove that compared with the original delta-MnO₂The catalyst, the generation of surface defects (oxygen vacancies and lattice distortion by Co incorporation) can successfully enhance the low temperature catalytic oxidation of formaldehyde. Under similar conditions, 170ppm formaldehyde, 120,000ml g was reached compared to the original catalyst to achieve complete oxidation at 90 ℃^-1·h^-1Complete oxidation was achieved at 80 ℃. In addition, Co-doped delta-MnO₂Under dynamic conditions (60,000 ml. g)^-1·h^-1) Shows activity on formaldehyde oxidation at room temperature (-10 ppm) with an average conversion of about 93.5% over 72 hours. All Co-doped catalysts are better than the original delta-MnO even at Co doping ratios as high as 0.2 molar ratio₂Has better activity.However, dopant-intermediate interactions may also adversely affect the activity of the modified catalyst. With the original delta-MnO₂In contrast, Cu doping results in a drastic suppression of catalytic activity despite the relatively increased concentration of surface oxygen vacancies and surface active oxygen. The copper inhibition increases with increasing doping ratio. Relative to the original delta-MnO₂In the presence of 0.05Cu delta-MnO₂In the case of (2), the temperature of complete conversion is raised to 100 ℃ in the presence of 0.2Cu delta-MnO₂In the case of (2), the temperature of complete conversion is raised to 120 ℃. DRIFTS results indicate that surface accumulation of carbonate in the presence of Cu probably accounts for Cu vs. delta-MnO₂Inhibition of catalytic activity. The amount of carbonate accumulated on the surface increases with the increase of Cu, indicating that surface coordination between Cu and the intermediate substance may occur, resulting in the blocking of the catalyst active sites.