Preparation Method and Application of Attapulgite Honeycomb Ceramic Supported Defect-Rich Oxide Monolithic Catalyst

Abstract

The present invention belongs to the field of environmental protection, and in particular to a preparation method and application of a defect-rich oxide monolithic catalyst loaded on concave soil honeycomb ceramics. A transition metal salt and agar powder are added to water, heated and stirred until transparent, and then naturally cooled to room temperature and immersed in the honeycomb ceramics, covered with plastic wrap and aged, and then purged, dried, and calcined in sequence to obtain a catalyst. The present invention utilizes transition metal ions to attach to the helical conformation of agar, resulting in crystallization deformation, while further hydrolysis reaction of the long chain of agar polysaccharide and the generation of detached small molecules, the polymer chain shortens, resulting in a large number of edge dislocation structures and defects. In addition, the concave soil honeycomb is a carrier, which has good adsorption properties for VOC gas molecules. At the same time, during preparation, Fe, Mg, Al ions can enter the crystal lattice of the active component to further promote the generation of defects, further enhance the catalytic oxidation activity of the catalyst, and the catalyst cost is low and easy to operate, and is expected to be promoted and applied.

Description

Technical field:

[0001] The invention belongs to the field of environmental protection, and in particular relates to a preparation method and application of an attapulgite honeycomb ceramic catalyst coated with a defect-rich oxide. Background technology:

[0002] Most volatile organic compounds (VOCs) can cause tropospheric ozone decomposition, photochemical smog, and various diseases, posing a threat to human life and health. Therefore, developing effective VOC removal technologies is of great significance and urgency. Over the years, various VOC recovery methods (i.e., adsorption, condensation, absorption, and membrane separation) and destruction technologies (i.e., incineration, catalytic oxidation, plasma catalysis, and biodegradation) have been developed for VOC emission reduction. Among them, catalytic oxidation is considered one of the most effective methods due to its high efficiency, low cost, and minimal secondary pollution, and has therefore attracted widespread attention.

[0003] Honeycomb monolithic catalysts are widely used in a variety of operating conditions due to their advantages, including a low thermal expansion coefficient, high mechanical strength, low bed pressure drop, excellent heat and mass transfer performance, and easy handling. Honeycomb monolithic catalysts typically consist of a carrier skeleton and a coating of active components. Because the active components are loaded onto the inner pore surfaces of the carrier, the diffusion distance of the reactant gas molecules is short, enabling rapid reactions and sufficient contact between the reactant gas molecules and the catalyst, thereby enhancing catalytic performance. The active components are typically coated onto the carrier using impregnation and sol-gel methods, providing support for the loading of the active components and a large specific surface area. Attapulgite is a natural, hydrous magnesium-rich silicate mineral with a layered chain transition structure. It exhibits excellent adsorption, catalytic properties, rheological properties, plasticity, and ion exchange capacity. It is also abundant, low-cost, and environmentally friendly. Attapulgite honeycombs, prepared using attapulgite as the primary raw material and supplemented with a binder, exhibit excellent adsorption properties. Active components are primarily categorized as precious metals and non-precious metals. Although noble metal catalysts have excellent catalytic activity, their high price and low toxicity resistance limit their potential applications. Therefore, the development of non-noble metal catalysts is particularly important.

[0004] Among non-precious metal catalysts, transition metal oxides have attracted widespread attention due to their environmental friendliness, low cost, abundant resources, and excellent catalytic performance in various redox reactions. However, their performance in the catalytic oxidation of VOCs is consistently inferior to that of precious metals. Currently, various methods have been developed to tailor catalytic performance, enabling transition metal oxide-based catalysts to possess the high activity and stability compared to precious metal-based catalysts. Defect engineering has attracted considerable attention due to its ability to promote oxygen activation and transfer and its ability to provide molecular chemical adsorption sites. Summary of the invention:

[0005] In view of the disadvantages of low activity and poor stability of transition metal oxides coated on ordinary honeycomb surfaces in degrading VOCs, the present invention provides a preparation method and application of a attapulgite honeycomb ceramic-loaded defect-rich oxide monolithic catalyst.

[0006] To achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a method for preparing a monolithic catalyst of attapulgite honeycomb ceramic supported defect-rich oxide, comprising the following steps:

[0007] (1) Weigh transition metal nitrate and agar powder and add them to deionized water, heat and stir until a transparent suspension is obtained.

[0008] Furthermore, the preparation method is to stir in a water bath at 60-90° C. until transparent, and then naturally cool to room temperature.

[0009] (2) Immersing the attapulgite honeycomb ceramic in the solution of step (1), covering it with plastic wrap and aging it for at least 72 hours, blowing and drying it after aging, and then calcining it in a muffle furnace at 300-500° C. for 2 hours to obtain the finished product.

[0010] In step (1), the transition metal nitrate can be any two of ferric nitrate, cobalt nitrate, manganese nitrate, nickel nitrate, and copper nitrate; and the mass ratio of agar powder to the transition metal nitrate is 1:1-1:4.

[0011] The attapulgite honeycomb ceramic in step (2) is a attapulgite honeycomb prepared with attapulgite as the main raw material. The diameter of the attapulgite honeycomb is about 3 cm, the number of holes is about 80, and the single hole diameter is about 0.3 cm. The immersion aging requires the entire honeycomb to be immersed in the suspension. During the purge, the air flow is uniform and slowly blows away the residual suspension in the pores.

[0012] Based on the honeycomb ceramic monolithic catalyst of the present invention, the present invention also provides an evaluation method for the catalytic oxidation of VOCs, comprising the following steps: placing the attapulgite honeycomb ceramic / defect-rich oxide monolithic catalyst into a reactor, bubbling xylene through N2, and simultaneously introducing air as a balance gas into the reaction device, then heating the reactor to perform catalytic oxidation degradation of xylene.

[0013] The present invention utilizes transition metal ions attached to the helical conformation of agar, causing crystallization deformation. Simultaneously, the further hydrolysis reaction of the long agar polysaccharide chains and the generation of detached small molecules shorten the polymer chains, resulting in a large number of defects and edge dislocation structures. This increases the specific surface area, produces a large number of metal valence ions, enriches the adsorbed oxygen species, and creates lattice defects, thereby enhancing the catalyst's low-temperature catalytic oxidation activity. Furthermore, during the calcination process, agar powder forms a second biocarbon film carrier layer on the honeycomb surface, which improves the catalyst's dispersibility and inhibits oxide grain growth and agglomeration. Furthermore, the honeycomb utilizes concave clay, which has a large specific surface area, a porous structure, and a surface rich in hydroxyl groups, providing specific adsorption for VOC gas molecules. Ions such as Fe, Mg, and Al in the concave clay can enter the oxide's lattice, synergistically promoting the removal of oxide defects.

[0014] Compared with the existing technology, the beneficial effects of the present invention are:

[0015] 1. The chain structure of agar is hydrolyzed to produce crystal deformation, which makes the transition metal oxide produce a large number of defects, and the active component - coating - honeycomb carrier catalyst is synthesized by high temperature carbonization to construct an adsorption-catalytic synergistic center, which is beneficial to activate the CH and CC bonds of VOCs gas molecules, open the benzene ring, and improve the deep oxidation ability of the catalyst.

[0016] 2. During the calcination process, agar powder forms a second bio-carbon film carrier layer on the honeycomb surface, which can improve the dispersion of the catalyst and inhibit the grain growth and agglomeration of oxides. The bio-carbon film's adsorption of VOCs and its synergistic catalytic effect with the active components improve the performance of the honeycomb catalyst in activating the CH and CC bonds in VOCs.

[0017] 3. The surface of the concave soil honeycomb is rough, which has better adhesion with the active components, large specific surface area, better dispersion, rich pore structure, and good adsorption of VOC gas molecules. At the same time, the Fe, Mg, Al ions of the concave soil honeycomb can enter the lattice of the active components to further promote the generation of defects and synergistically enhance the catalytic oxidation activity of the catalyst. Description of the drawings:

[0018] Figure 1 For Co x Mn y XRD pattern of O / attapulgite honeycomb ceramic monolithic catalyst;

[0019] Figure 2 , Figure 3 Co obtained in Example 1 x Mn y Scanning electron microscope image of the surface of O / attapulgite honeycomb ceramic monolithic catalyst with a scale of 1 μm;

[0020] Figure 4 For Co x Mn y O / attapulgite honeycomb ceramics and Co x Mn y EPR characterization of O / cordierite honeycomb ceramic catalyst;

[0021] Figure 5 This is a physical picture of concave clay honeycomb ceramics. Specific implementation method:

[0022] Example 1

[0023] 2.91g of cobalt nitrate and 2.50g of manganese nitrate were dissolved in 100mL of deionized water. 2g of agar powder was added, and the mixture was heated to 80°C with magnetic stirring until it became gel-like. The attapulgite honeycomb ceramic was then immersed in the solution, covered with plastic wrap, and aged for at least 72 hours. After purging and drying, the mixture was placed in a muffle furnace at 400°C for 2 hours to obtain the finished CoxMnyO / honeycomb ceramic monolithic catalyst.

[0024] Without affecting the overall structure of the attapulgite honeycomb ceramic, powder was scraped from the surface of the honeycomb ceramic, and an X-ray powder diffraction experiment was performed on the sample. At the same time, the morphology and structure of the coated honeycomb ceramic were observed under a scanning electron microscope. The Co x Mn y The XRD patterns of O / honeycomb ceramic monolithic catalysts are shown in Figure 2. Figure 1 As shown in the figure, by comparing the PDF card (PDF#42-1467), it can be seen that the diffraction peaks unique to Co3O4 appear at angles = 18.9°, 31.2°, 36.8°, 38.5°, 44.8°, 55.7°, 59.4°, and 65.3°. Considering that the ionic radius of Co and Mn is close, a solid solution phase may appear, and Mn is doped into the lattice of Co3O4, so the characteristic peaks of MnOx cannot be detected. At the same time, combined with scanning electron microscopy, Figure 2 , Figure 3 , which proves that the defect-rich cobalt-manganese mixed oxide is evenly dispersed on the honeycomb ceramic. In order to further verify whether the introduction of the attapulgite honeycomb further enhances the defects of the catalyst, we used EPR characterization to test the Co x Mn y O / attapulgite honeycomb ceramics and Co x Mn y O / cordierite honeycomb ceramic catalyst, characterization results show that Co x Mn y O / attapulgite honeycomb ceramics have a higher EPR peak, proving that the introduction of attapulgite honeycomb further enhances the defects of the catalyst.

[0025] The present invention also provides Co x Mn y The invention discloses an application method of an O / attapulgite honeycomb ceramic monolithic catalyst for thermal catalytic degradation of the VOC gas p-xylene.

[0026] The method is as follows: the Co obtained in Example 1 x Mn y The O / attapulgite honeycomb ceramic monolithic catalyst was placed in the quartz tube of the evaluation device. Paraxylene was bubbled with N2 and air was used as the balance gas. The initial concentration was tested. The temperature of the reactor was then raised and the real-time concentration was recorded every 10°C. The degradation rate of paraxylene was calculated. The temperature at which the degradation rate reached 90% was generally used as the evaluation temperature for the degradation of paraxylene, i.e., T 90 .

[0027] After the above method tested Co x Mn y T of O / honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 270℃.

[0028] Example 2

[0029] Dissolve 2.91g of cobalt nitrate and 2.41g of copper nitrate in 100mL of deionized water, add 3g of agar powder, heat the mixture to 80℃ and stir magnetically until the solution becomes gel-like, then immerse the kaolin honeycomb ceramic in it, cover it with plastic wrap and age it for at least 72 hours. After purging and drying, place it in a muffle furnace at 300℃ for 2h to obtain the finished product Co x Cu y O / attapulgite honeycomb ceramic monolithic catalyst.

[0030] Co was tested by the method of Example 1 x Cu y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 279℃.

[0031] Example 3

[0032] 2.91g of cobalt nitrate and 4.04g of ferric nitrate were dissolved in 100mL of deionized water, 6.95g of agar powder was added, the mixture was heated to 80℃ and magnetically stirred until the solution became gel-like, and then the attapulgite honeycomb ceramic was immersed in it, covered with plastic wrap and aged for at least 72 hours. After purging and drying, it was placed in a muffle furnace at 400℃ for 2h to obtain the finished product Co x Fe y O / attapulgite honeycomb ceramic monolithic catalyst.

[0033] Co was tested by the method of Example 1 x Fe y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 283℃.

[0034] Example 4

[0035] Dissolve 2.91g of cobalt nitrate and 2.41g of copper nitrate in 100mL of deionized water, add 1.33g of agar powder, heat the mixture to 80℃ and stir magnetically until the solution becomes gel-like, then immerse the kaolin honeycomb ceramic in it, cover it with plastic wrap and age it for at least 72 hours. After purging and drying, place it in a muffle furnace at 500℃ for 2h to obtain the finished product Co x Cu y O / attapulgite honeycomb ceramic monolithic catalyst.

[0036] Co was tested by the method of Example 1 x Cu y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 277℃.

[0037] Example 5

[0038] 2.50g manganese nitrate and 2.41g copper nitrate were dissolved in 100mL deionized water, 2g agar powder was added, the mixture was heated to 80℃ and magnetically stirred until the solution became gel-like, and then the attapulgite honeycomb ceramic was immersed in it, covered with plastic wrap and aged for at least 72 hours. After purging and drying, it was placed in a muffle furnace at 400℃ for 2h to obtain the finished product Mn x Cu y O / attapulgite honeycomb ceramic monolithic catalyst.

[0039] Mn was tested by the method of Example 1 x Cu y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 286℃.

[0040] Example 6

[0041] 2.50g manganese nitrate and 4.04g ferric nitrate were dissolved in 100mL deionized water, 3g agar powder was added, the mixture was heated to 80℃ and magnetically stirred until the solution became gel-like, and then the attapulgite honeycomb ceramic was immersed in it, covered with plastic wrap and aged for at least 72 hours. After purging and drying, it was placed in a muffle furnace at 400℃ for 2h to obtain the finished product Mn x Fe yO / attapulgite honeycomb ceramic monolithic catalyst.

[0042] Mn was tested by the method of Example 1 x Fe y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 288℃.

[0043] Comparative Example 1

[0044] 2.91g of cobalt nitrate was dissolved in 100mL of deionized water, 2g of agar powder was added, the mixture was heated to 80℃ and magnetically stirred until the solution became gel-like, and then the attapulgite honeycomb ceramic was immersed in it, covered with plastic wrap and aged for at least 72 hours. After purging and drying, it was placed in a muffle furnace at 400℃ for 2h to obtain the finished product Co x O / attapulgite honeycomb ceramic monolithic catalyst. Single oxides have fewer interface defects due to the formation of edge dislocations.

[0045] Co was tested by the method of Example 1 x T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 is 375℃.

[0046] Comparative Example 2

[0047] 2.91g of cobalt nitrate and 2.50g of manganese nitrate were dissolved in 100mL of deionized water. The mixture was heated to 80°C with magnetic stirring, and then a taupe honeycomb ceramic was placed in the mixture for impregnation. The mixture was covered with plastic wrap and aged for at least 72 hours. After purging and drying, the mixture was placed in a muffle furnace at 400°C for 2 hours to obtain the finished Co3O4-MnO / taupe honeycomb ceramic monolithic catalyst, with only the bimetallic oxide coating the honeycomb surface.

[0048] The T of Co3O4-MnO / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene was tested by the method of Example 1. 90 is 350℃.

[0049] Comparative Example 3

[0050] Dissolve 2.91g of cobalt nitrate and 2.50g of manganese nitrate in 100mL of deionized water, add 10g of agar powder, heat the mixture to 80℃ and stir magnetically until the solution becomes gel-like, then immerse the kaolin honeycomb ceramic in it, cover it with plastic wrap and age it for at least 72 hours. After purging and drying, place it in a muffle furnace at 400℃ for 2h to obtain the finished product Co x Mn yO / attapulgite honeycomb ceramic monolithic catalyst. Excessive agar reduces the exposure of active sites and inhibits the improvement of catalytic activity.

[0051] Co was tested by the method of Example 1 x Cu y T of O / attapulgite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 355℃.

[0052] Comparative Example 4

[0053] 2.91g of cobalt nitrate and 2.50g of manganese nitrate were dissolved in 100mL of deionized water, 2g of agar powder was added, and the mixture was heated to 80℃ and magnetically stirred until the solution became gel-like. Then, commercially available cordierite honeycomb ceramics were placed in it for immersion, covered with plastic wrap and aged for at least 72 hours. After purging and drying, it was placed in a muffle furnace at 400℃ for 2 hours to obtain the finished product Co x Cu y O / attapulgite honeycomb ceramic monolithic catalyst. The surface of cordierite honeycomb ceramic is smooth, and the adhesion to the catalyst is poor. At the same time, no metal ions enter the crystal of the active component, resulting in fewer defects. Figure 4 This feature was also confirmed by EPR characterization.

[0054] Co was tested by the method of Example 1 x Mn y T of O / cordierite honeycomb ceramic monolithic catalyst in the degradation of p-xylene 90 It is 364℃.

Claims

1. Application of an attapulgite honeycomb ceramic-supported defect-rich oxide monolithic catalyst in the catalytic oxidation degradation of VOCs, characterized by: The preparation steps are: (1) Weighing a transition metal salt and agar powder, adding them to deionized water, heating and stirring the solution until transparent, and obtaining a transparent solution; the transition metal salt is any two of ferric nitrate, cobalt nitrate, manganese nitrate, nickel nitrate, and copper nitrate; (2) The kaolin honeycomb ceramic is immersed in the transparent solution of step (1), sealed and aged, blown and dried, and then calcined in a muffle furnace to obtain a catalyst, wherein the agar powder forms a second carrier layer of biocarbon film on the honeycomb surface during the calcination process.

2. The use according to claim 1, characterized in that: The mass ratio of agar powder to transition metal salt is 1:1-1:

4.

3. The use according to claim 1, characterized in that: The heating and stirring temperature is 60-90°C.

4. The use according to claim 1, characterized in that The sealed aging time shall not be less than 72h.

5. The use according to claim 1, characterized in that The calcination conditions are 300-500°C for 2h.

Images