Multi-grain-boundary cerium-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to a multi-grain-boundary cerium-based catalyst as well as a preparation method and application thereof. The multi-grain-boundary cerium-based catalyst comprises a multi-grain-boundary cerium dioxide carrier and an active component loaded on the carrier, the active component comprises any one or a combination of at least two of copper oxide, manganese oxide or cobalt oxide. According to the multi-grain-boundary cerium-based catalyst, multi-grain-boundary CeO2 is adopted as a carrier, and compared with a traditional single-crystal Ce-based catalyst, the multi-grain-boundary Ce-based catalyst has rich grain boundary defects, so that generation of an oxygen vacancy active structure is promoted, and higher photochemical reaction activity is achieved. The structural advantages are beneficial to adsorption and activation of reactants and generation of active oxygen species, so that the deep oxidation performance of the catalyst on VOCs is remarkably improved. Compared with the traditional thermocatalysis, the application of the photothermal catalysis technology reduces the energy consumption of external heating. The multi-grain-boundary cerium-based catalyst has excellent low-temperature degradation capability and reaction stability, so that the multi-grain-boundary cerium-based catalyst has a good application prospect in purification of VOCs (Volatile Organic Compounds) in industrial flue gas.

Description

Technical Field

[0001] This invention relates to the field of volatile organic compound oxidation and removal technology, and in particular to a polycrystalline cerium-based catalyst, its preparation method, and its uses. Background Technology

[0002] Volatile organic compounds (VOCs) have a significant negative impact on air pollution and public health due to their high chemical reactivity and teratogenic, carcinogenic, and mutagenic effects. Toluene, in particular, is a major precursor to urban photochemical smog and atmospheric compound pollution due to its photoreactivity, making it a key focus of atmospheric chemistry research and regional air quality control. Among numerous end-of-pipe treatment technologies, photothermal catalysis is highly favored in the field of pollutant degradation due to its mild reaction conditions, high energy efficiency, and wide applicability to various reaction systems.

[0003] In recent years, Ce-based catalysts have attracted much attention and have been widely used in the field of industrial exhaust gas purification, such as selective catalytic reduction of nitrogen oxides (NH3-SCR), catalytic oxidation of carbon monoxide and volatile organic compounds, and catalytic removal of soot particles in diesel vehicle exhaust. Numerous studies have shown that Ce-based catalysts exhibit good activity in the catalytic oxidation of VOCs.

[0004] However, Ce-based catalysts exhibit weak photoreactivity, preventing the complete degradation of VOCs in photothermal catalytic oxidation reactions with relatively low light intensity. Furthermore, studies have shown that single-crystal Ce-based catalysts exhibit weak long-term reaction stability and resistance to carbon deposition, failing to meet the reaction activity and stability requirements for practical industrial pollutant treatment.

[0005] Therefore, how to provide a Ce-based catalyst with high photoreactivity, good stability, and strong resistance to carbon deposition, and its preparation method, has become an urgent technical problem to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a polycrystalline cerium-based catalyst, its preparation method, and its applications. Compared to traditional single-crystal Ce-based catalysts, the polycrystalline cerium-based catalyst of the present invention exhibits superior low-temperature degradation capability and reaction stability in the photothermal catalytic oxidation reaction of toluene due to its enhanced ability to generate active oxygen species.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a polycrystalline cerium-based catalyst, the polycrystalline cerium-based catalyst comprising a polycrystalline cerium dioxide support and an active component supported on the support; the active component comprising any one or a combination of at least two of copper oxide, manganese oxide or cobalt oxide.

[0009] The polycrystalline cerium-based catalyst provided by this invention uses polycrystalline CeO2 as a support. Compared with traditional single-crystal Ce-based catalysts, the introduction of grain boundaries, a two-dimensional structural defect, often results in higher interfacial energy, making them preferential regions for oxygen vacancy generation and reactant activation. The locally electron-rich oxygen vacancies give the polycrystalline Ce-based catalyst a greater advantage in adsorbing toluene and oxygen molecules. Oxygen vacancies rapidly transfer electrons to the antibonding orbitals of oxygen molecules, promoting bond breaking and leading to the dissociation of oxygen molecules to generate reactive oxygen species. This stronger ability to generate reactive oxygen species can further participate in the deep oxidation of toluene. Therefore, the polycrystalline Ce-based catalyst exhibits excellent low-temperature degradation capability and reaction stability in the photothermal catalytic oxidation of toluene.

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0011] In some embodiments, the mass fraction of the active component in the polycrystalline cerium-based catalyst is 1 wt.%-10 wt.%, for example, it can be 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, 7.5 wt.%, 8 wt.%, 8.5 wt.%, 9 wt.%, 9.5 wt.%, or 10 wt.%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, with the balance being the support.

[0012] In some embodiments, the active component includes copper oxide.

[0013] In a second aspect, the present invention provides a method for preparing a polycrystalline cerium-based catalyst as described in the first aspect, the method comprising the following steps:

[0014] A mixture of cerium salt and alcohol solvent is stirred to obtain a mixture. The mixture undergoes a solvothermal reaction to obtain a precipitate. The precipitate is then calcined to obtain a polycrystalline cerium dioxide support.

[0015] A mixed active component salt solution and a polycrystalline cerium dioxide support are evaporated to obtain a product, which is then subjected to a second calcination to obtain the polycrystalline cerium-based catalyst.

[0016] The polygrain boundary cerium-based catalyst provided by this invention employs a solvothermal method and an impregnation method. Compared to the traditional hydrothermal method, the solvothermal method allows for better control of the crystal nucleus growth rate and promotes the formation of high-density grain boundaries. This invention utilizes alcohol solvents, which exhibit steric hindrance at high temperatures, effectively preventing the aggregation of nanocrystals during growth. Furthermore, the presence of hydroxyl groups in the alcohol solvents can form stable complexes with the cerium precursor salt, controlling the growth direction and size of the grains.

[0017] The preparation method provided by this invention is simple and has low manufacturing cost.

[0018] In some embodiments, the mass ratio of the cerium salt to the alcohol solvent is 1:(2-8), for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] In some embodiments, the cerium salt comprises any one or a combination of at least two of cerium nitrate, cerium sulfate, cerium chloride, or cerium acetate. Typical but non-limiting combinations include combinations of cerium nitrate and cerium sulfate, combinations of cerium sulfate and cerium chloride, combinations of cerium chloride and cerium acetate, combinations of cerium nitrate, cerium chloride, and cerium acetate, combinations of cerium nitrate, cerium sulfate, and cerium acetate, combinations of cerium sulfate, cerium chloride, and cerium acetate, or combinations of cerium nitrate and cerium acetate, preferably cerium nitrate.

[0020] In some embodiments, the alcohol solvent includes any one or a combination of at least two of ethylene glycol, glycerol, or diethylene glycol. Typical but non-limiting combinations include combinations of ethylene glycol and glycerol, combinations of ethylene glycol and diethylene glycol, combinations of glycerol and diethylene glycol, and preferably ethylene glycol.

[0021] In some embodiments, the active component salt solution includes any one or a combination of at least two of the active component's nitrate, active component's acetate, or active component's sulfate.

[0022] In some embodiments, the stirring time is 2h-4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In some embodiments, the temperature of the solvothermal reaction is 150°C-200°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In some embodiments, the solvothermal reaction time is 4h-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] In some embodiments, the temperature of the first calcination is 350°C-500°C, for example, it can be 350°C, 400°C, 450°C or 500°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In some embodiments, the first calcination time is 2h-5h, for example, it can be 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] In some embodiments, the calcination atmosphere for both the first and second calcinations is an oxygen-containing atmosphere.

[0028] In this invention, the second calcination is carried out in an oxygen-containing atmosphere. Calcination in an oxygen-containing atmosphere firstly removes residual organic matter from the catalyst precursor, preventing it from interfering with the CO2 yield performance evaluation index in the toluene catalytic degradation performance evaluation. Furthermore, since the toluene catalytic performance evaluation process is conducted in an oxygen-containing atmosphere, pre-calcining the catalyst in an oxygen-containing atmosphere allows for the acquisition of a more complete and stable crystal structure, ensuring long-term stability during subsequent performance evaluations.

[0029] In some embodiments, the evaporation method includes water bath heating.

[0030] In some embodiments, the water bath heating temperature is 70°C-90°C, for example, it can be 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In some embodiments, drying is further performed after evaporation and before the second calcination.

[0032] In some embodiments, the second calcination temperature is 300℃-500℃, for example, it can be 300℃, 350℃, 400℃, 450℃ or 500℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0033] In some embodiments, the second calcination time is 2h-5h, for example, it can be 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Thirdly, the present invention provides the use of a polycrystalline cerium-based catalyst as described in the first aspect, said polycrystalline cerium-based catalyst for catalytic degradation of volatile organic compounds.

[0035] The polycrystalline cerium-based catalyst provided by this invention has good application prospects in the catalytic degradation of volatile organic compounds (VOCs).

[0036] In some embodiments, the polycrystalline cerium-based catalyst is used for photothermal catalytic oxidative degradation of toluene.

[0037] The polycrystalline cerium-based catalyst provided by this invention exhibits excellent low-temperature degradation capability and reaction stability when degrading toluene in industrial waste gas due to its enhanced ability to generate active oxygen species.

[0038] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0039] (1) Cerium salt and alcohol solvent are mixed in a mass ratio of 1:(2-8). After stirring for 2-4 hours, a mixture is obtained. The mixture is subjected to a solvothermal reaction at 150℃-200℃ for 4-8 hours to obtain a precipitate. After washing and drying, the precipitate is calcined at 350℃-500℃ for 2-5 hours in an air atmosphere to obtain a polycrystalline cerium dioxide support.

[0040] (2) Mix the active component salt solution and the polycrystalline cerium dioxide support, and heat and evaporate the mixture in a water bath at 70℃-90℃ to obtain the product. After drying the product, calcine it at 300℃-500℃ for 2h-5h to obtain the polycrystalline cerium-based catalyst.

[0041] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0042] Compared with the prior art, the present invention has at least the following beneficial effects:

[0043] (1) The polycrystalline cerium-based catalyst provided by the present invention uses polycrystalline CeO2 as a support. Compared with the traditional single-crystal Ce-based catalyst, the polycrystalline Ce-based catalyst has the ability to generate active oxygen species and the photochemical reaction activity enhanced due to the formation of abundant oxygen vacancies induced by grain boundary defects. This is beneficial to the deep degradation of toluene and has excellent low-temperature degradation ability and reaction stability in the photothermal catalytic oxidation reaction of toluene.

[0044] (2) The preparation method of the polycrystalline cerium-based catalyst provided by the present invention is prepared by solvothermal method and impregnation method, which can better control the growth rate and growth direction of crystal nuclei, and is conducive to the formation of high-density grain boundaries; the preparation method provided by the present invention is simple and has low manufacturing cost.

[0045] (3) The polycrystalline cerium-based catalyst provided by the present invention has enhanced oxygen activation performance and toluene deep degradation ability induced by traditional photochemical processes in photothermal catalytic reactions compared with traditional thermocatalytic reactions. At the same time, the catalyst’s own light absorption and heat conversion ability under light irradiation can greatly reduce the energy demand for external heating in traditional thermocatalysis.

[0046] (4) The polycrystalline cerium-based catalyst provided by the present invention has good application prospects in the catalytic degradation of volatile organic compounds (VOCs). Attached Figure Description

[0047] Figure 1 These are the XRD patterns of the cerium-based catalysts prepared in Example 1 and Comparative Examples 1-3 of this invention;

[0048] Figure 2 This is a TEM image of the single-crystal cerium dioxide catalyst prepared in Comparative Example 2 of this invention;

[0049] Figure 3 This is an HR-TEM image of the single-crystal cerium dioxide catalyst prepared in Comparative Example 2 of this invention;

[0050] Figure 4 This is a TEM image of the polycrystalline cerium dioxide catalyst prepared in Comparative Example 3 of this invention;

[0051] Figure 5 This is an HR-TEM image of the polycrystalline cerium dioxide catalyst prepared in Comparative Example 3 of this invention;

[0052] Figure 6 These are TEM images and elemental distribution diagrams of the single-crystal cerium-based catalyst prepared in Comparative Example 1 of this invention;

[0053] Figure 7 This is an HR-TEM image of the single-crystal cerium-based catalyst prepared in Comparative Example 1 of this invention;

[0054] Figure 8 These are TEM images and elemental distribution diagrams of the polycrystalline cerium-based catalyst prepared in Example 1 of this invention;

[0055] Figure 9 This is an HR-TEM image of the polycrystalline cerium-based catalyst prepared in Example 1 of this invention;

[0056] Figure 10These are the reaction temperatures of the cerium-based catalysts prepared in Examples 1 and Comparative Examples 1-3 of the present invention under various light intensities;

[0057] Figure 11 The cerium-based catalysts prepared in Example 1 and Comparative Examples 1-3 of this invention are used under light intensity of 635 mW / cm². 2 The following is a graph showing the toluene degradation conversion rate;

[0058] Figure 12 The cerium-based catalysts prepared in Example 2 and Comparative Example 4 of this invention are used under light intensity of 635 mW / cm². 2 The following is a graph showing the toluene degradation conversion rate;

[0059] Figure 13 The cerium-based catalysts prepared in Example 3 and Comparative Example 5 of this invention are used under light intensity of 635 mW / cm². 2 The following is a graph showing the toluene degradation conversion rate;

[0060] Figure 14 The cerium-based catalyst prepared in Comparative Example 6 of this invention is used under a light intensity of 635 mW / cm². 2 The following is a graph showing the toluene degradation conversion rate;

[0061] Figure 15 These are graphs showing the toluene degradation conversion rates of the cerium-based catalysts prepared in Example 1 and Comparative Examples 1-3 of this invention under thermal catalysis and photothermal catalysis, respectively.

[0062] Figure 16 These are CO2 yield graphs of the cerium-based catalysts prepared in Example 1 and Comparative Examples 1-3 of this invention under thermal catalysis and photothermal catalysis, respectively.

[0063] Figure 17 The EPR of the cerium-based catalysts prepared in Example 1 and Comparative Example 1 of this invention is compared with that of O. v Test spectrum;

[0064] Figure 18 These are the PL test spectra of the cerium-based catalysts prepared in Example 1 and Comparative Example 1 of this invention;

[0065] Figure 19 This is a long-term stability diagram of the polycrystalline cerium-based catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0066] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0067] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0068] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0069] Example 1

[0070] This embodiment provides a polycrystalline cerium-based catalyst, which includes a polycrystalline cerium dioxide support and an active component Cu with a mass fraction of 5 wt.% supported on the support;

[0071] The preparation method of the polycrystalline cerium-based catalyst provided in this embodiment includes the following steps:

[0072] (1) Ce(NO3)3·6H2O and ethylene glycol were mixed in a mass ratio of 1:3 and stirred for 3 hours to obtain a mixture. The mixture was subjected to a solvothermal reaction at 180°C for 6 hours to obtain a precipitate. The precipitate was washed with deionized water and ethanol alternately, dried under vacuum at 60°C overnight, and the precipitate was calcined at 400°C for 3 hours in air to obtain a polycrystalline cerium dioxide support.

[0073] (2) Mix Cu(CH3COO)2 solution and polycrystalline cerium dioxide support, stir vigorously to mix evenly, heat and evaporate in a water bath at 85°C to obtain the product, dry at 100°C overnight, and calcine the product at 400°C for a second time for 3 hours to obtain the polycrystalline cerium-based catalyst.

[0074] Example 2

[0075] This embodiment provides a polycrystalline cerium-based catalyst, which includes a polycrystalline cerium dioxide support and an active component Mn with a mass fraction of 2 wt.% supported on the support;

[0076] The preparation method of the polycrystalline cerium-based catalyst provided in this embodiment includes the following steps:

[0077] (1) Ce(NO3)3·6H2O and ethylene glycol were mixed in a mass ratio of 1:5 and stirred for 2 hours to obtain a mixture. The mixture was subjected to a solvothermal reaction at 150°C for 8 hours to obtain a precipitate. The precipitate was washed with deionized water and ethanol alternately, dried under vacuum at 60°C overnight, and the precipitate was calcined at 350°C for 5 hours in an air atmosphere to obtain a polycrystalline cerium dioxide support.

[0078] (2) Mix Mn(CH3COO)2 solution and polycrystalline cerium dioxide support, stir vigorously to mix evenly, heat and evaporate in a water bath at 70°C to obtain the product, dry at 100°C overnight, and calcine the product at 300°C for a second time for 5 hours to obtain the polycrystalline cerium-based catalyst.

[0079] Example 3

[0080] This embodiment provides a polycrystalline cerium-based catalyst, which includes a polycrystalline cerium dioxide support and an active component Co with a mass fraction of 8 wt.% supported on the support;

[0081] The preparation method of the polycrystalline cerium-based catalyst provided in this embodiment includes the following steps:

[0082] (1) Ce(NO3)3·6H2O and ethylene glycol were mixed in a mass ratio of 1:7 and stirred for 4 hours to obtain a mixture. The mixture was subjected to a solvothermal reaction at 200°C for 4 hours to obtain a precipitate. The precipitate was washed alternately with deionized water and ethanol, dried under vacuum at 60°C overnight, and the precipitate was calcined at 450°C for 2 hours in an air atmosphere to obtain a polycrystalline cerium dioxide support.

[0083] (2) Mix Co(NO3)3·6H2O solution and polycrystalline cerium dioxide support, stir vigorously to mix evenly, heat and evaporate in a water bath at 90°C to obtain the product, dry at 100°C overnight, and calcine the product at 500°C for 2 hours to obtain the polycrystalline cerium-based catalyst.

[0084] Comparative Example 1

[0085] This comparative example provides a single-crystal cerium-based catalyst, which differs from Example 1 only in that, in the preparation of this single-crystal cerium-based catalyst, ethylene glycol is replaced with sodium hydroxide solution (concentration of 6 mol / L) in step (1). In the mixed solution, Ce 3+ The concentration is 0.05 mol / L. The solvothermal reaction is replaced by a hydrothermal reaction. The hydrothermal reaction temperature is 100℃, and the single crystal cerium dioxide support is prepared by hydrothermal treatment for 24 hours. The single crystal cerium dioxide support is used for impregnation reaction in step (2).

[0086] Comparative Example 2

[0087] This comparative example provides a single-crystal cerium-based catalyst. The only difference from Comparative Example 1 is that Cu(CH3COO)2 was not added in step (2) when preparing the single-crystal cerium-based catalyst.

[0088] Comparative Example 3

[0089] This comparative example provides a polycrystalline cerium-based catalyst, which differs from Example 1 only in that Cu(CH3COO)2 was not added in step (2) when preparing the polycrystalline cerium-based catalyst.

[0090] Comparative Example 4

[0091] This comparative example provides a single-crystal cerium-based catalyst, which differs from Example 2 only in that, in the preparation of this single-crystal cerium-based catalyst, a single-crystal cerium dioxide support is used for impregnation reaction in step (2).

[0092] Comparative Example 5

[0093] This comparative example provides a single-crystal cerium-based catalyst, which differs from Example 3 only in that, in the preparation of this single-crystal cerium-based catalyst, a single-crystal cerium dioxide support is used for impregnation reaction in step (2).

[0094] Comparative Example 6

[0095] This comparative example provides a polycrystalline cerium-based catalyst, which differs from Example 1 only in that, in the preparation of this polycrystalline cerium-based catalyst, Cu(CH3COO)2 is replaced with an equal amount of Fe(NO3)3 in step (2).

[0096] test:

[0097] The XRD patterns of the cerium-based catalysts prepared in Example 1 and Comparative Examples 1-3 are shown below. Figure 1 As shown, from Figure 1 As can be seen, all samples exhibited the same diffraction peaks as pure CeO2 (PDF#00-034-0394); and no obvious Cu phase characteristic peaks were detected in Example 1. This indicates that Cu species are highly dispersed as fine species on the CeO2 surface.

[0098] Figures 2-5 The images show TEM and HR-TEM images of the single-crystal cerium dioxide support and the polycrystalline cerium dioxide support prepared by Comparative Examples 2 and 3 of this invention, respectively. As can be seen from the images, the catalyst of Comparative Example 2 has a single-crystal structure, while the catalyst of Comparative Example 3 has a polycrystalline structure, and the presence of abundant nanocrystalline boundaries can be observed.

[0099] Figures 6-9The figures show TEM images, elemental distribution maps, and HR-TEM images of the single-crystal cerium-based catalyst and the polycrystalline cerium-based catalyst prepared in Comparative Example 1 and Example 1, respectively. As can be seen from the figures, the loading of Cu did not change the morphology and grain boundary characteristics of the catalysts; the catalyst in Example 1 still exhibited a polycrystalline structure, and the catalyst in Comparative Example 1 still exhibited a single-crystal structure. Figure 7 and Figure 9 No Cu particles were observed in the HR-TEM images, while EDS results showed that Cu species were successfully loaded and highly dispersed.

[0100] Figure 10 The figures show the reaction temperatures of the cerium-based catalysts prepared in Examples 1 and Comparative Examples 1-3 of this invention under various light intensities. As can be seen from the figures, under the same light intensities, Examples 1 and Comparative Examples 1 have similar photothermal conversion capabilities, which is reflected in similar reaction temperatures.

[0101] Figure 11 The results show that Comparative Example 3 of the present invention has a significant advantage over Comparative Example 2 in the degradation of toluene, but both exhibit a decrease in reactivity with increasing reaction time. (The text also mentions CuO, but this seems unrelated to the preceding sentence and likely refers to a different topic.) x The reactivity of the active components in Example 1 and Comparative Example 1 was significantly improved compared to Comparative Example 3 and Comparative Example 2; among them, Example 1 exhibited the best photothermal catalytic performance.

[0102] Figure 12 and Figure 13 The display shows that the active ingredient was replaced with MnO. x and CoO x Examples 2-3 also exhibited the same activity advantage compared to Comparative Examples 4-5. Their activity advantage compared to CuO... x The smaller activity advantage between active component catalysts can be attributed to the fact that the multiple valence states and strong oxidation capabilities of Mn and Co themselves make them less dependent on the defect configuration of the support, thereby reducing the activity difference between polycrystalline cerium-based catalysts and single-crystal cerium-based catalysts.

[0103] Figure 14 The display shows that replacing the active component with FeO x Comparative Example 6 showed poorer toluene degradation activity and catalytic stability compared to Example 1, indicating that the loading of Fe reduced the reactive sites of polycrystalline cerium dioxide, which is not conducive to the deep oxidation of toluene.

[0104] Figure 15 and Figure 16The figures show the toluene degradation conversion rate and CO2 yield of the cerium-based catalysts prepared in Example 1 and Comparative Example 1, respectively. As can be seen from the figures, the polycrystalline cerium-based catalyst of Example 1 has better toluene conversion and mineralization capabilities than the single-crystal cerium-based catalyst of Comparative Example 1 under the same reaction conditions.

[0105] Figure 17 The figures show the EPR spectra of the cerium-based catalysts prepared in Example 1 and Comparative Example 1 of this invention. In the figures, g=2.003 corresponds to the oxygen vacancy signal under dark vacuum conditions. As shown in the figure, Example 1 has a higher oxygen vacancy concentration than Comparative Example 1, which is conducive to the adsorption of reactants.

[0106] Figure 18 The results show that Example 1 exhibits a higher luminescence intensity compared to Comparative Example 1, indicating that Example 1 has a lower photogenerated carrier separation capability. This means that the high concentration of oxygen vacancies in Example 1 are recombination sites for photogenerated electrons and holes, which is detrimental to the participation of photogenerated electrons in O2 activation. However, Example 1 demonstrates a superior reactive oxygen species generation capability, indicating that its active sites have higher photochemical reactivity than Comparative Example 1, resulting in superior toluene deep oxidation capability. Figure 7 and Figure 8 Higher toluene conversion rate and CO2 mineralization rate.

[0107] Figure 19 This is a long-term stability diagram of the polycrystalline cerium-based catalyst prepared in Example 1 of this invention. As can be seen from the diagram, the polycrystalline cerium-based catalyst has excellent resistance to carbon deposition and water vapor stability. Under low light intensity and water vapor conditions, the catalytic activity decreases because some active sites are occupied by intermediate products or water vapor molecules. However, after the catalytic conditions are restored to the initial state, the catalytic activity also recovers to the original level. This shows that the presence of carbon deposits and water molecules does not cause irreversible damage to the catalyst's own structure. The polycrystalline cerium-based catalyst has good long-term stability.

[0108] The polycrystalline cerium-based catalysts prepared in the examples and comparative examples were tested. 20 mg of catalyst was coated onto a 25 mm diameter glass fiber membrane using a vacuum filtration method to form an extremely thin catalyst bed. The glass fiber membrane was then placed in a self-made reactor, and a reaction gas flow was introduced to test the catalyst's degradation effect on toluene gas under different xenon lamp irradiation intensities. Before introducing the reaction gas flow, the catalyst was pretreated under xenon lamp irradiation for 10 min to achieve a stable reaction temperature. The reaction was maintained for 120 min, and the concentrations of toluene and CO2 before and after the reaction were detected using a gas chromatograph equipped with a flame ionization detector (FID).

[0109] The test conditions were: reaction space velocity of 20,000–40,000 mL / g·h, with toluene concentration of 100–300 ppm. The xenon lamp irradiation intensity was 635 mW / cm². 2 The results of the activity test under the conditions are shown in Table 1 below.

[0110] Table 1

[0111]

[0112] The test results show that:

[0113] (1) As can be seen from Examples 1-3, the present invention uses polycrystalline CeO2 as a support. Compared with the traditional single-crystal Ce-based catalyst, the polycrystalline Ce-based catalyst has abundant nanocrystalline defects, which leads to an increase in oxygen vacancies and further enhances the ability to generate active oxygen species. It has excellent low-temperature degradation ability and reaction stability when degrading toluene in industrial waste gas.

[0114] (2) As can be seen from Example 1 and Comparative Example 1, by using polycrystalline CeO2 as a support, the active oxygen species generation capacity of the polycrystalline Ce-based catalyst is enhanced, and it has excellent low-temperature degradation capacity and reaction stability when degrading toluene in industrial waste gas. However, if single-crystal CeO2 is used as a support, its catalytic activity and stability will be significantly reduced. In addition, the active sites of polycrystalline CeO2 have higher photochemical reaction activity than those of single-crystal CeO2, which is the fundamental reason why the polycrystalline cerium-based catalyst has a stronger active oxygen species generation capacity and higher photothermal catalytic toluene oxidation performance.

[0115] (3) As can be seen from Example 1 and Comparative Examples 2-4, the present invention can achieve the technical effect of increasing oxygen vacancy defects by loading a specific metal oxide as an active component on the surface of a polycrystalline CeO2 support, while retaining the intrinsic difference in activity caused by the difference in the support. However, when no active component is loaded or other metals are loaded, it cannot improve the activity and stability of the catalyst for catalytic degradation of VOCs under mild reaction conditions.

[0116] (4) As can be seen from Example 1 and Comparative Example 6, when other active components are loaded, the technical effect of efficient degradation of toluene cannot be achieved, indicating that the reasonable selection of active components is particularly important for the degradation of toluene.

[0117] In summary, this invention utilizes polycrystalline CeO2 as a support. Compared to traditional single-crystal Ce-based catalysts, polycrystalline Ce-based catalysts possess more abundant grain boundary defects, promoting the formation of reactive structures with oxygen vacancies and thus enhancing the generation capacity of reactive oxygen species. Simultaneously, the loading of various types of active metals improves the light absorption and heat transfer performance of the cerium dioxide support, enhancing its reaction performance under mild conditions while retaining the differences in support defect configuration. Among these factors, the advantages of reactive oxygen species generation, the advantages of reactant adsorption and activation due to support defect configuration, and the enhanced photochemical reactivity of the polycrystalline cerium-based catalyst result in excellent low-temperature degradation capability and reaction stability in the photothermal catalytic degradation of toluene in industrial waste gas.

[0118] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polycrystalline cerium-based catalyst, characterized in that, The polycrystalline cerium-based catalyst comprises a polycrystalline cerium dioxide support and an active component supported on the support; The active component includes any one or a combination of at least two of copper oxide, manganese oxide, or cobalt oxide.

2. The polycrystalline cerium-based catalyst according to claim 1, characterized in that, The mass fraction of the active component in the polycrystalline cerium-based catalyst is 1 wt.%-10 wt.%, with the remainder being a support; And / or, the active component includes copper oxide.

3. A method for preparing a polycrystalline cerium-based catalyst as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: A mixture of cerium salt and alcohol solvent is stirred to obtain a mixture. The mixture undergoes a solvothermal reaction to obtain a precipitate. The precipitate is then calcined to obtain a polycrystalline cerium dioxide support. A mixed active component salt solution and a polycrystalline cerium dioxide support are evaporated to obtain a product, which is then subjected to a second calcination to obtain the polycrystalline cerium-based catalyst.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the cerium salt to the alcohol solvent is 1:(2-8); And / or, the alcohol solvent includes any one or a combination of at least two of ethylene glycol, glycerol, or diethylene glycol.

5. The preparation method according to claim 3 or 4, characterized in that, The stirring time is 2-4 hours; And / or, the temperature of the solvothermal reaction is 150℃-200℃; And / or, the solvothermal reaction time is 4h-8h.

6. The preparation method according to any one of claims 3-5, characterized in that, The first calcination temperature is 350℃-500℃; And / or, the first calcination time is 2h-5h; And / or, the calcination atmosphere for both the first and second calcinations is an oxygen-containing atmosphere.

7. The preparation method according to any one of claims 3-6, characterized in that, The evaporation method includes water bath heating; And / or, the water bath heating temperature is 70℃-90℃; And / or, the second calcination temperature is 300℃-500℃; And / or, the second calcination time is 2h-5h.

8. The preparation method according to any one of claims 3-7, characterized in that, The preparation method includes the following steps: (1) Cerium salt and alcohol solvent are mixed in a mass ratio of 1:(2-8). After stirring for 2-4 hours, a mixture is obtained. The mixture is subjected to a solvothermal reaction at 150℃-200℃ for 4-8 hours to obtain a precipitate. After washing and drying, the precipitate is calcined at 350℃-500℃ for 2-5 hours in an air atmosphere to obtain a polycrystalline cerium dioxide support. (2) Mix the active component salt solution and the polycrystalline cerium dioxide support, and heat and evaporate the mixture in a water bath at 70℃-90℃ to obtain the product. After drying the product, calcine it at 300℃-500℃ for 2h-5h to obtain the polycrystalline cerium-based catalyst.

9. Use of a polycrystalline cerium-based catalyst as described in claim 1 or 2, characterized in that, The polycrystalline cerium-based catalyst is used for the catalytic degradation of volatile organic compounds.

10. The use of the polycrystalline cerium-based catalyst according to claim 9, characterized in that, The polycrystalline cerium-based catalyst is used for photothermal catalytic oxidation and degradation of toluene.

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