A manganese-based rare earth metal catalyst, a preparation method and application thereof

Abstract

The present application relates to the technical field of VOCs treatment, and provides a manganese-based rare earth metal catalyst, a preparation method and application thereof, the manganese-based rare earth metal catalyst comprises a metal oxide, the molecular formula of the metal oxide is RMn2O5, wherein R is a rare earth metal element; and the preparation method comprises the following steps: (1) mixing a rare earth metal salt, a manganese salt and an oxidizing agent, performing a first stirring oxidation reaction to obtain a first system; (2) mixing an alkaline substance and the first system, and sequentially performing a second stirring reaction and a hydrothermal reaction to obtain a post-reaction material containing the manganese-based rare earth metal catalyst. In the present application, the RMn2O5 catalyst improves the stability of the catalyst and has high catalytic activity, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of VOCs treatment technology, and in particular to a manganese-based rare earth metal catalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are air pollutants with boiling points between 50 and 260°C at room temperature and normal pressure. They mainly include alkanes, aromatic hydrocarbons, alkenes, halogenated hydrocarbons, esters, aldehydes, ketones, and other compounds. VOC emissions come from a variety of sources, including outdoor sources (industrial processes and transportation) and indoor sources (household products such as building materials, consumer goods, furniture, combustion byproducts, and cooking). Chemical industrial processes, especially petroleum industrial processes, account for a significant proportion of VOC emissions. Due to their characteristics of easy diffusion, toxicity, carcinogenicity, and volatility, most VOCs not only damage the ozone layer but, more seriously, can interact with other air pollutants (such as NOx). x and SO x The reaction forms photochemical smog, and long-term exposure can threaten human health and cause irreversible damage. Furthermore, under the influence of certain climate activities, localized air pollution can easily evolve into large-scale regional pollution, which is even more difficult to manage. Therefore, the best way to control volatile organic compounds is to eliminate them before they are emitted.

[0003] Propane is a saturated hydrocarbon among VOCs and is relatively stable within the VOCs spectrum. Recently, with the increased use of liquefied petroleum gas (LPG), propane emissions have been rising. To address the propane emission problem, an efficient and safe method for processing propane is needed.

[0004] Existing methods for treating propane in VOCs mainly fall into two categories: destruction and recovery. Recovery methods primarily include adsorption, absorption, membrane separation, and condensation. Adsorption, absorption, and membrane separation are commonly used in industry. Destruction methods mainly include catalytic oxidation, thermal incineration, biodegradation, photocatalytic decomposition, and non-thermal plasma oxidation. Thermal incineration and catalytic oxidation are commonly used in industry. The difficulties in recovery technologies include: expensive recovery materials, large material consumption, high material loss, and low recovery efficiency. Challenges in destruction technologies include: low catalytic efficiency, high energy consumption, and a decrease in material efficiency as the treatment process progresses. The advantages and disadvantages of commonly used VOCs treatment methods are summarized in Table 1.

[0005] Table 1

[0006]

[0007]

[0008] This demonstrates that catalytic oxidation, compared to other methods, boasts advantages such as low energy consumption and high efficiency. Therefore, it is widely used in industry to treat large quantities of VOCs waste gas. The core of catalytic oxidation lies in the catalyst, but most catalysts for VOCs treatment can be categorized into precious metal catalysts and non-precious metal catalysts. While precious metal catalysts exhibit good catalytic performance, they suffer from poor durability, susceptibility to poisoning, and high cost. Non-precious metal catalysts, although cheaper than precious metal catalysts, generally have relatively poorer catalytic performance.

[0009] Therefore, the treatment of propane waste gas using catalytic oxidation requires the development of a catalyst that is inexpensive, highly efficient, and highly stable. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a manganese-based rare earth metal catalyst, its preparation method, and its application, solving the problem of simultaneously achieving high treatment efficiency and stability in existing VOCs catalysts.

[0011] To achieve this objective, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a manganese-based rare earth metal catalyst, wherein the manganese-based rare earth metal catalyst comprises a metal oxide, wherein the molecular formula of the metal oxide is RMn2O5, and R is a rare earth metal element.

[0013] This invention first utilizes a non-precious metal oxide catalyst to replace a precious metal catalyst, and selects Mn-based oxide as the catalyst among non-precious metals. However, the crystal form of Mn-based oxides is prone to transformation at different temperatures, which leads to a decrease in catalytic activity during the catalytic process. Therefore, to solve the problem of crystal form transformation of Mn-based oxides at different temperatures, rare earth metal elements are added to Mn-based oxides to form a new RMn2O5 catalyst, thereby improving the stability of the catalyst.

[0014] Taking YMn2O5 as an example, its generating formula is:

[0015] 5Y 3+ +7Mn 2+ +3MnO4 - +26OH - →5YMn2O5+13H2O

[0016] Preferably, R is any one or a combination of at least two of Y, Sm, Gd or Pr, with Y being the most preferred.

[0017] The present invention further prefers the rare earth metal element R to be Y, because compared with other rare earth metal elements, Y can better balance the stability and activity of the catalyst. For example, although the manganese-based metal oxide prepared by the rare earth metal element Pr has high catalytic activity, the catalyst has low stability; although the manganese-based metal oxide prepared by the rare earth metal element Gd has high stability, the catalyst has low catalytic activity.

[0018] And / or, the manganese-based rare earth metal catalyst has a mullite orthorhombic structure.

[0019] The manganese-based rare earth metal catalyst in this invention possesses a mullite orthorhombic structure. The improved stability of mullite compared to other binary Mn oxides is mainly attributed to its unique structure. Mn and O ions constitute the basic ligand units (i.e., octahedrons and pyramids). Relatively inexpensive Y... 3+ Ions are filled into the space surrounding the Mn ligand units. Mullite compounds have empty channels in their lattice, and together with their unique ligand field, the formation energy of their structure is reduced, thereby improving the thermal stability of mullite oxide and making its structure more stable than binary oxides such as α-MnO2.

[0020] And / or, the manganese-based rare earth metal catalyst is doped with nitrogen element, the content of which is 0.01 to 0.5 wt%, for example, it can be 0.01 wt%, 0.07 wt%, 0.12 wt%, 0.18 wt%, 0.23 wt%, 0.29 wt%, 0.34 wt%, 0.4 wt%, 0.45 wt%, or 0.5 wt%.

[0021] The present invention further preferably incorporates nitrogen (N) doping into the manganese-based rare earth metal catalyst. Nitrogen doping has the advantage of increasing the specific surface area of ​​the catalyst and improving its activity.

[0022] The nitrogen element is doped on the surface of the metal oxide.

[0023] Preferably, the manganese-based rare earth metal catalyst satisfies at least one of the following conditions:

[0024] A. The pore size range of the manganese-based rare earth metal catalyst is 0.01 to 160 nm, for example, it can be 0.01 nm, 17.79 nm, 35.57 nm, 53.34 nm, 71.12 nm, 88.9 nm, 106.67 nm, 124.45 nm, 142.23 nm or 160 nm, etc.;

[0025] B. The specific surface area of ​​the manganese-based rare earth metal catalyst is 80–250 m². 2 / g, for example, could be 80m 2 / g、99m 2 / g、118m 2 / g、137m 2 / g、156m 2 / g、175m 2 / g、194m 2 / g、213m 2 / g、232m 2 / g or 250m 2 / g etc.;

[0026] C. The particle size range of the manganese-based rare earth metal catalyst is 6.3nm to 14.8nm, for example, it can be 6.3nm, 6.5nm, 7nm, 7.6nm, 8nm, 8.5nm, 8.9nm, 9nm, 10nm, 11nm, 12nm or 12.5nm, 13nm, 14nm, 14.8nm, etc.

[0027] In a second aspect, the present invention provides a method for preparing the manganese-based rare earth metal catalyst described in the first aspect, the method comprising the following steps:

[0028] (1) Mix rare earth metal salts, manganese salts and oxidants, and carry out the first stirring oxidation reaction to obtain the first system;

[0029] (2) Mix the alkaline substance and the first system, and carry out the second stirring reaction and hydrothermal reaction in sequence to obtain the reaction material containing manganese-based rare earth metal catalyst.

[0030] The preparation method described in the second aspect of the present invention preferably first performs a first stirring oxidation reaction to make the reactants uniformly stirred, and then mixes alkaline substances to perform a second stirring reaction and a hydrothermal reaction, which can realize the preparation of manganese-based rare earth metal catalysts; while if all rare earth metal salts, manganese salts, oxidants and alkaline substances are mixed and reacted in one step, there is a defect that the catalyst particles are not uniformly stirred, which ultimately leads to the catalyst particles becoming coarse.

[0031] Moreover, in step (2), the second stirring reaction is carried out first, followed by the hydrothermal reaction. Compared with the direct hydrothermal reaction, the direct hydrothermal reaction has the disadvantages of uneven and insufficient reaction between the reactants and the alkali, and the local excessive alkali precipitation is too fast, which increases the size of the precipitate particles.

[0032] Preferably, the anion of the rare earth metal salt in step (1) includes acetate and / or nitrate, and / or the cation of the rare earth metal salt includes Y. 3+ 、Sm 3+ Gd 3+ or Pr 3+ Any one or at least two of them.

[0033] Furthermore, the rare earth metal salt includes any one or a combination of at least two of yttrium nitrate hexahydrate, samarium nitrate hexahydrate, gadolinium nitrate hexahydrate, or praseodymium nitrate hexahydrate.

[0034] And / or, the anion of the manganese salt includes any one or a combination of at least two of acetate, nitrate, or chloride ions; and / or, the cation of the manganese salt is a divalent manganese ion.

[0035] Furthermore, the manganese salt includes hydrated manganese acetate, manganese chloride, and / or manganese nitrate.

[0036] And / or, the oxidant is KMnO4.

[0037] Preferably, the molar ratio of Mn in the oxidant to Mn in the manganese salt is (0.4-0.5):1, for example, it can be 0.4:1, 0.42:1, 0.43:1, 0.44:1, 0.45:1, 0.46:1, 0.47:1, 0.48:1, 0.49:1 or 0.5:1, etc.

[0038] Preferably, the alkaline substance in step (2) includes sodium hydroxide and / or urea, with urea being the preferred choice.

[0039] This invention further prefers urea as the alkaline substance. Compared to using substances such as sodium hydroxide or ammonia, urea has two advantages. First, unlike the strong alkali NaOH, urea does not directly release OH- ions but reacts slowly with water during the reaction process to release OH- ions, causing the reactants to precipitate slowly, thereby reducing particle growth and particle size. At the same temperature and reaction time, in the preparation of 1.0N-YMn2O5, the time for urea to react completely is reduced, thus increasing the time for particle growth. This results in a larger particle size compared to 1.25N-YMn2O5. However, in the preparation of 1.5N-YMn2O5, the amount of OH- ions released by urea per unit time increases, accelerating the precipitation of reactants and thus increasing particle size. Second, urea can act as a nitrogen dopant, incorporating nitrogen into the final catalyst. Nitrogen doping increases the specific surface area of ​​the catalyst and improves its activity, further enhancing the overall performance of the catalyst.

[0040] Preferably, the molar ratio of the alkaline substance to the manganese salt in step (2) is (7-12):1, for example, it can be 7:1, 7.4:1, 7.8:1, 8.2:1, 8.6:1, 9:1, 9.4:1, 9.8:1, 10.2:1, 10.5:1, 11:1, 11.5:1 or 12:1, etc., preferably (7-10.5):1, and / or, the pH range after mixing the alkaline substance and the first system is 9-12, for example, it can be 9, 9.4, 9.7, 10, 10.4, 10.7, 11, 11.4, 11.7 or 12, etc.

[0041] The present invention further preferably controls the amount of alkaline substance added within the above range or controls the pH of the system within the above range after its addition, so as to obtain catalyst powder with smaller particle size and higher catalytic activity.

[0042] Preferably, the second stirring reaction satisfies the following: the time of the second stirring reaction is 0.5 to 1 hour, for example, it can be 0.5 hours, 0.56 hours, 0.62 hours, 0.67 hours, 0.73 hours, 0.78 hours, 0.84 hours, 0.89 hours, 0.95 hours, or 1 hour, etc., and / or the rotation speed of the second stirring reaction is 1000 to 1100 r / min, for example, it can be 1000 r / min, 1010 r / min, 1020 r / min, 1030 r / min, 1045 r / min, 1050 r / min, 1060 r / min, 1070 r / min, 1080 r / min, or 1100 r / min, etc.

[0043] Preferably, the hydrothermal reaction satisfies the following conditions: the hydrothermal reaction temperature is 200-220℃, for example, it can be 200℃, 203℃, 205℃, 207℃, 209℃, 212℃, 214℃, 216℃, 218℃ or 220℃, etc., but is not limited to the listed values, other unlisted values ​​within this range are also applicable, and / or, the hydrothermal reaction time is 20-50 min, for example, it can be 20 min, 24 min, 27 min, 30 min, 34 min, 37 min, 40 min, 44 min, 47 min or 50 min, etc.

[0044] Preferably, the first stirring oxidation reaction satisfies the following: the time of the first stirring oxidation reaction is 0.5 to 1 hour, for example, it can be 0.5 hours, 0.56 hours, 0.62 hours, 0.67 hours, 0.73 hours, 0.78 hours, 0.84 hours, 0.89 hours, 0.95 hours, or 1 hour, etc., and / or, the rotation speed of the first stirring oxidation reaction is 1000 to 1100 r / min, for example, it can be 1000 r / min, 1010 r / min, 1020 r / min, 1030 r / min, 1045 r / min, 1050 r / min, 1060 r / min, 1070 r / min, 1080 r / min, or 1100 r / min, etc.

[0045] Preferably, the preparation method further includes: (3) sequentially performing solid-liquid separation, washing and drying on the reacted material to obtain the manganese-based rare earth metal catalyst.

[0046] Preferably, the solid-liquid separation includes centrifugal separation.

[0047] Preferably, the washing process includes washing with alcohol at least once, followed by washing with acid at least once.

[0048] The present invention does not impose any special restrictions on the solid-liquid separation in the above process. Any device and method known to those skilled in the art for solid-liquid separation can be used. It can also be adjusted according to the actual process. For example, it can be filtration, centrifugation or sedimentation separation, or a combination of different methods.

[0049] The present invention does not impose any special restrictions on the drying process described above. Any device and method known to those skilled in the art for drying can be used. Adjustments can also be made according to the actual process. For example, it can be air drying, vacuum drying, oven drying, or freeze drying, or a combination of different methods.

[0050] Preferably, the drying includes vacuum drying.

[0051] Preferably, the vacuum degree of the vacuum drying is 60℃~80℃, for example, it can be 60℃, 63℃, 65℃, 67℃, 69℃, 72℃, 74℃, 76℃, 78℃ or 80℃, etc.

[0052] Preferably, the vacuum drying temperature is 80-100℃, for example, it can be 80℃, 83℃, 85℃, 87℃, 89℃, 92℃, 94℃, 96℃, 98℃ or 100℃.

[0053] Preferably, the vacuum drying time is 12 to 20 hours, for example, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours or 20 hours.

[0054] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0055] (1) Mix rare earth metal salt, manganese salt and oxidant KMnO4 according to the molecular formula, wherein the molar ratio of Mn in the oxidant to Mn in the manganese salt is (0.4~0.5):1, and carry out the first stirring oxidation reaction at 1000~1100r / min for 0.5~1h to obtain the first system;

[0056] (2) Mix urea and the first system, and sequentially carry out a second stirring reaction at 1000-1100 r / min for 0.5-1 h and a hydrothermal reaction at 200-220℃ for 20-50 min to obtain the reaction material containing manganese-based rare earth metal catalyst; wherein, the molar ratio of urea to manganese salt is (7-12):1, and / or, the pH range after mixing urea and the first system is 9-12;

[0057] (3) The reaction material is subjected to solid-liquid separation, washing and drying in sequence to obtain the manganese-based rare earth metal catalyst.

[0058] Thirdly, the present invention provides the application of the manganese-based rare earth metal catalyst described in the first aspect and / or the manganese-based rare earth metal catalyst prepared by the preparation method of the manganese-based rare earth metal catalyst described in the second aspect in the treatment of VOCs, preferably in the treatment of hydrocarbon-containing VOCs.

[0059] Preferably, when the catalyst is used in VOCs treatment, the temperature of VOCs treatment is 150-250°C, for example, it can be 150°C, 162°C, 173°C, 184°C, 195°C, 206°C, 217°C, 228°C, 239°C or 250°C.

[0060] Preferably, when the catalyst is used in VOCs treatment, the gas space velocity is 30,000 to 33,000 mL·h. -1 For example, it could be 30000 mL·h -1 30334 mL·h -1 30667mL·h -1 31000mL·h -1 31334 mL·h -1 31667 mL·h -1 32000mL·h -1 32334 mL·h -1 32667mL·h -1 Or 33000 mL·h -1 wait.

[0061] Compared with the prior art, the present invention has at least the following beneficial effects:

[0062] (1) The manganese-based rare earth metal catalyst provided by the present invention contains a metal oxide with the molecular formula RMn2O5. The catalyst has high stability and high catalytic activity, and has broad application prospects.

[0063] (2) The manganese-based rare earth metal catalyst provided by this invention is doped with nitrogen, which has the advantage of increasing the specific surface area of ​​the catalyst and improving its catalytic activity. Under preferred conditions, it has the advantage of increasing the specific surface area of ​​the catalyst and improving its catalytic activity for propane. 90 Below 240℃, T 50 At temperatures below 223℃, the conversion rate reaches 100% of the initial conversion rate after 100 hours of catalytic reaction, with almost no decrease in catalytic activity; moreover, under optimal conditions, the stability decreases by less than 3% after adding 5% water, demonstrating excellent resistance to water aging.

[0064] (3) The preparation method of manganese-based rare earth metal catalyst provided by the present invention can prepare catalyst containing RMn2O5 in a good way, and the preparation process is simple to operate, easy to scale up industrially, and has broad application prospects. Attached Figure Description

[0065] Figure 1 These are the XRD patterns of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of this invention, and the XRD pattern of the manganese-based rare earth metal catalyst after catalytic reaction in Example 6.

[0066] Figure 2 This is a SEM image of the manganese-based rare earth metal catalyst prepared in Example 1 of this invention.

[0067] Figure 3 This is an EDS scan image of the manganese-based rare earth metal catalyst prepared in Example 1 of the present invention (where the dots represent N elements).

[0068] Figure 4 This is a SEM image of the manganese-based rare earth metal catalyst prepared in Example 4 of this invention.

[0069] Figure 5 This is a SEM image of the manganese-based rare earth metal catalyst prepared in Example 6 of this invention.

[0070] Figure 6 This is an EDS scan image of the manganese-based rare earth metal catalyst prepared in Example 6 of the present invention (where the dots represent N elements).

[0071] Figure 7 This is a SEM image of the manganese-based rare earth metal catalyst prepared in Example 7 of this invention.

[0072] Figure 8 This is an EDS scan image of the manganese-based rare earth metal catalyst prepared in Example 7 of the present invention (where the dots represent N elements).

[0073] Figure 9 This is the isothermal adsorption-desorption curve of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of this invention.

[0074] Figure 10 This is a particle size distribution curve of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of this invention.

[0075] Figure 11 These are catalytic activity test curves of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of this invention.

[0076] Figure 12 These are durability test diagrams of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of this invention catalyzing propane at 275°C.

[0077] Figure 13 These are water aging resistance test diagrams of the manganese-based rare earth metal catalysts prepared in Examples 4 and 6 of this invention. Detailed Implementation

[0078] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0079] It should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0080] Unless otherwise specified, the reagents used in the following examples and comparative examples are of analytical grade AR.

[0081] Example 1

[0082] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst, the method comprising the following steps:

[0083] (1) A first stirring oxidation reaction was carried out at 1050 r / min for 0.8 h according to the molecular formula YMn2O5, which is a mixture of rare earth metal salt (Y(NO3)3·6H2O), manganese salt (Mn(CH3COO)2·4H2O) and oxidant KMnO4, with the molar ratio of Mn in the oxidant to Mn in the manganese salt being 0.43:1, to obtain the first system;

[0084] (2) Mix urea and the first system, and carry out a second stirring reaction at 1050 r / min for 0.8 h at pH 10. Then transfer it to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 206 °C for 30 min to obtain the reaction material containing manganese-based rare earth metal catalyst; wherein, the molar ratio of urea to manganese salt is 8:1.

[0085] (3) The reaction material was washed with water three times, ethanol three times, and 1% nitric acid once. After each washing, it was centrifuged and dried at 0 kPa and 75°C for 15 h to obtain the manganese-based rare earth metal catalyst.

[0086] Example 2

[0087] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst, the method comprising the following steps:

[0088] (1) A first system was obtained by mixing rare earth metal salt (Y(NO3)3·6H2O), manganese salt (MnCl2) and oxidant KMnO4 according to the molecular formula YMn2O5, wherein the molar ratio of Mn in the oxidant to Mn in the manganese salt was 0.4:1, and the first stirring oxidation reaction was carried out at 1100 r / min for 0.5 h.

[0089] (2) Mix urea and the first system, and carry out a second stirring reaction at 1000 r / min for 1 h at pH 12. Then transfer it to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 206°C for 20 min to obtain the reaction material containing manganese-based rare earth metal catalyst; wherein, the molar ratio of urea to manganese salt is 10.5:1.

[0090] (3) The reacted material was washed with water three times, ethanol twice, and 1.5% nitric acid once. After each washing, the material was centrifuged and dried at 0 kPa and 80°C for 20 h to obtain the manganese-based rare earth metal catalyst.

[0091] Example 3

[0092] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst, the method comprising the following steps:

[0093] (1) A first system was obtained by mixing rare earth metal salt (Y(CH3COO)2), manganese salt (Mn(CH3COO)2·4H2O) and oxidant KMnO4 according to the molecular formula YMn2O5, wherein the molar ratio of Mn in the oxidant to Mn in the manganese salt was 0.5:1, and the first stirring oxidation reaction was carried out at 1000r / min for 1h.

[0094] (2) Mix urea and the first system, and carry out a second stirring reaction at 1100 r / min for 0.5 h at pH 9. Then transfer it to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 206 °C for 50 min to obtain the reaction material containing manganese-based rare earth metal catalyst; wherein, the molar ratio of urea to manganese salt is 7:1.

[0095] (3) The reaction material was washed with water twice, ethanol three times, and nitric acid once. After each washing, it was centrifuged and dried at 0 kPa and 100°C for 12 h to obtain the manganese-based rare earth metal catalyst.

[0096] Example 4

[0097] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for step (2), in which urea is replaced with sodium hydroxide solution (concentration of 10wt%, and the number of moles of sodium hydroxide is the same as the number of moles of urea), the preparation method is the same as in Example 1, and will not be repeated here.

[0098] Example 5

[0099] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for step (2), in which urea is replaced with ammonia (concentration of 20wt%, and the number of moles of N is the same as the number of moles of N in urea), the preparation method is the same as in Example 1, and will not be repeated here.

[0100] Example 6

[0101] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for the amount of urea in step (2), which is 1.25 times that in Example 1, the preparation method is the same as in Example 1, and will not be repeated here.

[0102] Example 7

[0103] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for the amount of urea in step (2), which is 1.5 times that in Example 1, the preparation method is the same as in Example 1, and will not be repeated here.

[0104] Example 8

[0105] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for the molar ratio of urea to manganese salt in step (2) being 14:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0106] Example 9

[0107] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. Except for the molar ratio of urea to manganese salt in step (2) being 0.5:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0108] Example 10

[0109] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as in Example 1 except that Y(NO3)3·6H2O is replaced with Sm(NO3)3·6H2O, and will not be repeated here.

[0110] Example 11

[0111] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as in Example 1 except that Y(NO3)3·6H2O is replaced with Pr(NO3)3·6H2O, and will not be repeated here.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing a manganese-based metal catalyst. The preparation method is the same as that in Example 1 except that Y(NO3)3·6H2O is not added, and will not be repeated here.

[0114] Comparative Example 2

[0115] This comparative example provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as in Example 1 except that step (1) is not performed separately, and the rare earth metal salt, manganese salt and urea are directly mixed and then steps (2) and (3) are performed. Therefore, it will not be repeated here.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing a manganese-based rare earth metal catalyst. Except for step (2), in which a second stirring reaction is not performed and a hydrothermal reaction is carried out directly, the preparation method is the same as that in Example 1, and will not be repeated here.

[0118] Comparative Example 4

[0119] This comparative example provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as in Example 1, except that the molar ratio of Mn in the oxidant to Mn in the manganese salt is 2.5:1, and will not be repeated here.

[0120] Comparative Example 5

[0121] This comparative example provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as in Example 1, except that the molar ratio of Mn in the oxidant to Mn in the manganese salt is 0.3:1, and will not be repeated here.

[0122] Catalytic performance test:

[0123] A. Catalytic activity test: O2 = 10%, C3H8 = 0.1%, with the remainder N2 as the balance gas, and the gas hourly space velocity (GHSV) is 33000 mL / g. -1 ·h -1 The relationship between catalytic activity and reaction temperature was tested.

[0124] B. Stability test: O2 = 10%, C3H8 = 0.1%, with the remainder N2 as the balance gas; gas hourly space velocity (GHSV) is 33000 mL / g. -1 ·h -1 The durability of the catalyst for propane catalysis at 275℃ was tested. Furthermore, 5% H2O was added to the feed gas to measure the catalyst's water resistance. The 1.25N-YMn2O5 sample, which showed the best catalytic performance, was compared with the unmodified sample.

[0125] For example, XRD, TEM, isothermal adsorption-desorption curves and particle size distribution were performed on the catalysts in Example 1 (denoted as 1.0N-YMn2O5), Example 4 (denoted as NaOH-YMn2O5), and Examples 6-7 (denoted as 1.25N-YMn2O5 and 1.5N-YMn2O5, respectively). The catalyst in Example 6 after catalytic reaction was subjected to XRD detection to characterize whether the crystal form of the catalyst changed before and after catalysis.

[0126] The XRD diagram of the above embodiment is as follows: Figure 1 As shown, from Figure 1 It can be seen that the present invention can prepare YMn2O5 crystalline oxide, and the crystal form of the catalyst remains basically unchanged after the catalytic reaction.

[0127] The SEM and EDS scan images of the above embodiments are shown below. Figures 2-8 ,from Figures 2-8 It can be seen that using urea can dope N elements into YMn2O5 crystalline oxide, and the grains are finer.

[0128] Figure 9 These are the isothermal adsorption-desorption curves of the catalysts prepared in Examples 1, 4 and 6-7 of this invention. Figure 10These are the particle size distribution curves of the catalysts prepared in Examples 1, 4, and 6-7 of this invention. From... Figures 9-10 It can be seen that the specific surface area of ​​the catalyst sample using urea is significantly larger than that using sodium hydroxide, and the specific surface area of ​​the urea catalyst first increases and then decreases with increasing N content in the sample. Among them, NaOH-YMn2O5, S BET =86.5335m 2 / g, 1.0N-YMn2O5, S BET =140.9693m 2 / g, 1.25N-YMn2O5, S BET =223.3585m 2 / g, 1.5N-YMn2O5, S BET =131.5766m 2 / g. The 1.25N-YMn2O5 sample using urea had the largest specific surface area (S). BET =223.3585m 2 / g) is made using sodium hydroxide NaOH-YMn2O5(S BET =86.5335m 2 The surface area of ​​the 1.25N-YMn2O5 sample was 2.58 times that of the g sample, indicating that the 1.25N-YMn2O5 sample exposed more active sites.

[0129] Figure 11 These are the catalytic activity test curves of the catalysts prepared in Examples 1, 4 and 6-7 of this invention. Figure 12 This is a durability test of the catalysts prepared in Examples 1, 4, and 6-7 of this invention for catalyzing propane at 275°C. Figures 11-12 It can be seen that the urea catalyst oxidizes propane more readily than the sodium hydroxide catalyst, exhibiting higher catalytic activity. The order of catalytic activity of the samples for propane is: 1.25N-YMn2O5 > 1.0N-YMn2O5 > 1.5N-YMn2O5 > NaOH-YMn2O5. The 1.0N-YMn2O5, 1.25N-YMn2O5, 1.5N-YMn2O5, and NaOH-YMn2O5 samples were reacted under the conditions of 1000ppm propane feed gas, 10% O2, and N2 as residual gas, yielding T... 50 The temperatures at which 50% conversion is achieved are: 221℃, 216℃, 225℃, and 240℃. The cold start temperature (T) for 1.25N-YMn2O5 is also specified. 50The lowest values ​​indicate that the urea-based catalyst exhibits higher activity for the catalytic oxidation of propane at low temperatures compared to the sodium hydroxide-based catalyst. The catalytic oxidation temperatures To for propane using 1.5N-YMn2O5, 1.25N-YMn2O5, and 1.0N-YMn2O5 are... 90 The temperatures at which 90% conversion is achieved are all below 250℃, specifically: 243℃, 239℃, and 246℃. Meanwhile, the temperature at which NaOH-YMn2O5 achieves 90% conversion is below 250℃. 90 The temperature is 285℃. All catalysts using urea have a T... 90 and T 50 Both are lower than those using sodium hydroxide catalysts, indicating that the urea catalyst has higher activity for the catalytic oxidation of propane at low temperatures compared to the sodium hydroxide catalyst. The T5 of 1.25N-YMn2O5 90 and T 50 The lowest value indicates the highest catalytic oxidation activity. Figure 12 The results showed that at 275℃, the conversion rate of both urea and sodium hydroxide catalysts reached over 20%, and the catalytic conversion efficiency remained stable within 100 hours without change. Although the catalytic efficiency using urea was significantly higher than that using sodium hydroxide catalyst, the stability of the urea catalyst was not significantly different from that of the sodium hydroxide catalyst. This indicates that the urea catalyst not only improved the catalytic performance of the YMn2O5 catalyst but also perfectly preserved the high stability characteristic of the mullite catalyst.

[0130] The composition and catalytic performance of the above-mentioned examples and comparative examples were tested, and the results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] The following points can be observed from Table 1:

[0135] (1) As can be seen from Examples 1-3, the preparation method of the manganese-based rare earth metal catalyst provided by the present invention is carried out according to the molecular formula YMn2O5 and nitrogen element is doped with urea. The catalyst has high stability and high catalytic activity. The catalyst can obtain a mullite structure with a pore size range of 6.3-15.2 nm and a specific surface area of ​​130-224 m². 2 Within the range of / g, the T90 for propane is below 240℃ and the T50 is below 223℃. After 100h of catalytic reaction, the conversion rate reaches 100% of the initial conversion rate, and the catalytic activity does not decrease, indicating broad application prospects.

[0136] (2) As can be seen from Example 4, compared with the use of urea in Example 1, under the condition of the same molar sodium hydroxide as precipitant, the catalyst particles precipitate faster, and after addition, it directly becomes strong alkaline compared with the weak acidity of the solution in Example 1, thereby making the catalyst particles larger. Moreover, the price of sodium hydroxide is higher than that of urea, and the cost is higher than that of Example 1.

[0137] As can be seen from Example 5, compared with the use of urea in Example 1, the use of ammonia water to directly provide the alkali source accelerates the precipitation rate of catalyst particles, thereby increasing the particle size of the catalyst, and the catalytic activity is lower than that of the Example.

[0138] This indicates that the present invention preferably uses urea to provide the N source, which has better catalytic activity.

[0139] (3) Comparing Examples 1 and 6-9, it can be seen that the amount of urea added has a significant impact on the specific surface area of ​​the catalyst, which ultimately affects the catalytic activity of the catalyst. In this invention, the amount of urea added is preferably controlled within a reasonable range, thereby reasonably controlling the N content in the catalyst and better ensuring the catalytic activity of the catalyst. In Example 8, the amount of urea added was too high, and the decomposition of urea during the synthesis process produced a large amount of ammonia, causing the system pressure to be too high and exceed the limit of the reactor. In Example 9, the amount of urea added was too low, and it was impossible to generate enough OH. - This ensures that an alkaline environment is met for catalyst formation.

[0140] (4) Comparing Examples 1 and 10-11, it can be seen that in Example 10, the catalyst with poor crystallinity after replacing Y(NO3)3·6H2O with Sm(NO3)3·6H2O had a lower catalytic effect than the catalyst synthesized using Y(NO3)3·6H2O. In Example 11, after replacing Y(NO3)3·6H2O with Pr(NO3)3·6H2O, a mullite-structured compound could not be synthesized within the same time frame, indicating that the metal catalyst cannot be synthesized in a short reaction time.

[0141] (5) In Comparative Example 1, without the addition of Y(NO3)3·6H2O, there was no source of rare earth metal ions, and the mullite catalyst was not synthesized. In Comparative Example 2, the reactants were not sufficiently stirred, resulting in uneven mixing and larger reactant particles. In Comparative Example 3, the alkali was not sufficiently stirred with the reactants, causing local over-alkaliness, which accelerated precipitation and led to coarser particle size. In Comparative Example 4, the high molar ratio of Mn in the oxidant to Mn in the manganese salt meant that some substances failed to participate in the reaction and existed as impurities, affecting the catalytic effect of the catalyst. In Comparative Example 5, when the molar ratio of Mn in the oxidant to Mn in the manganese salt became 0.3:1, a mullite catalyst could not be formed.

[0142] Comparative test of water aging resistance:

[0143] Using the catalysts in the examples as test samples, water aging resistance tests were conducted. Specifically, during the stability test, 5% H2O was added to the feed gas to measure the catalyst's water resistance. The conversion rate after catalytic performance stabilization was used as a benchmark for comparison. The comparative experimental diagrams for Examples 4 and 6 are shown below. Figure 13 As shown, from Figure 13 It can be seen that the 1.25N-YMn2O5 sample has significantly better water aging resistance compared with the unmodified sample. In Example 4, the stability of the sample without urea modification decreased by 6-9% after adding 5% water (i.e., the conversion rate decreased by 6-9% after stabilization), while the stability of the sample with 5% water in Example 6 decreased by only 2-3%. This shows that the present invention preferably uses urea modification to achieve better water aging resistance.

[0144] Comparing Examples 1 with Examples 9 and 11, it can also be seen that no mullite structure was formed in Examples 9 and 11, and their resistance to water aging was much lower than that of Example 1. This will not be elaborated further here.

[0145] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A manganese-based rare earth metal catalyst with excellent resistance to water aging, used in the treatment of hydrocarbon-containing VOCs, characterized in that, The manganese-based rare earth metal catalyst includes a metal oxide, the molecular formula of which is YMn2O5. The manganese-based rare earth metal catalyst has a mullite orthographic structure; The manganese-based rare earth metal catalyst is doped with nitrogen. The preparation method of the manganese-based rare earth metal catalyst includes the following steps: (1) A rare earth metal salt, a manganese salt, and an oxidant are mixed and subjected to a first stirring oxidation reaction to obtain a first system; the cation of the rare earth metal salt is Y. 3+ The anion of the manganese salt includes any one or a combination of at least two of acetate, nitrate, and chloride ions; the cation of the manganese salt is a divalent manganese ion; the oxidant is KMnO4. (2) Mix urea and the first system, and carry out the second stirring reaction and hydrothermal reaction in sequence to obtain the reaction material containing manganese-based rare earth metal catalyst; the hydrothermal reaction satisfies the following conditions: the temperature of the hydrothermal reaction is 200~220℃ and the time of the hydrothermal reaction is 20~50min; The molar ratio of urea to manganese salt is (7~10.5):1; The molar ratio of Mn in the oxidant to Mn in the manganese salt is (0.43~0.5):

1.

2. The manganese-based rare earth metal catalyst according to claim 1, characterized in that, The manganese-based rare earth metal catalyst satisfies at least one of the following conditions: A. The pore size range of the manganese-based rare earth metal catalyst is 7.4~15.2 nm; B. The specific surface area of ​​the manganese-based rare earth metal catalyst is 80~250m². 2 / g; C. The particle size range of the manganese-based rare earth metal catalyst is 6.3 nm to 14.8 nm.

3. A method for preparing a manganese-based rare earth metal catalyst according to claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) A rare earth metal salt, a manganese salt, and an oxidant are mixed and subjected to a first stirring oxidation reaction to obtain a first system; the cation of the rare earth metal salt is Y. 3+ ; (2) Mix urea and the first system, and carry out a second stirring reaction and a hydrothermal reaction in sequence to obtain the reaction material containing manganese-based rare earth metal catalyst; the molar ratio of urea to manganese salt is (7~10.5):1; The molar ratio of Mn in the oxidant to Mn in the manganese salt is (0.43~0.5):

1.

4. The preparation method according to claim 3, characterized in that, The anions of the rare earth metal salts mentioned in step (1) include acetate and / or nitrate.

5. The preparation method according to claim 3, characterized in that, In step (2), the pH range after mixing urea and the first system is 9-12.

6. The preparation method according to claim 3, characterized in that, The second stirring reaction satisfies the following conditions: the second stirring reaction time is 0.5~1h, and / or the second stirring reaction speed is 1000~1100r / min.

7. The application of a manganese-based rare earth metal catalyst according to claim 1 or 2, and / or a catalyst prepared by the method of preparing a manganese-based rare earth metal catalyst according to any one of claims 3 to 6, in the treatment of hydrocarbon-containing VOCs.

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