Manganese-based rare earth metal catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of VOCs treatment, and provides a manganese-based rare earth metal catalyst and 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, and R is a rare earth metal element; the preparation method comprises the following steps: (1) mixing a rare earth metal salt, a manganese salt and an oxidant, and carrying out a first stirring oxidation reaction to obtain a first system; and (2) mixing an alkaline substance and the first system, and sequentially carrying out a second stirring reaction and a hydrothermal reaction to obtain a post-reaction material containing the manganese-based rare earth metal catalyst. According to the RMn2O5 catalyst, the stability of the catalyst is improved, the catalytic activity is high, and the application prospect is wide.

Description

Technical Field

[0001] The present invention relates to the technical field of VOCs treatment, and in particular to a manganese-based rare earth metal catalyst and a preparation method and application thereof. Background Art

[0002] Volatile organic compounds (VOCs) are a type of air pollutant with a boiling point between 50 and 260°C at room temperature and pressure. They mainly include alkanes, aromatic hydrocarbons, olefins, halogenated hydrocarbons, esters, aldehydes, ketones and other compounds. The emission sources of volatile organic compounds are diverse, including outdoor sources (industrial processes and transportation) and indoor sources (household products such as building materials, consumer goods, furniture, combustion by-products and cooking). Among them, the largest source of VOCs is the chemical industry process, especially the petroleum industry process. Since volatile organic compounds are released into the environment, they are easy to diffuse, toxic, carcinogenic and volatile. Most volatile organic compounds will not only cause ozone layer damage to the environment, but more seriously, they will react with other air pollutants (such as NO x and SO x ) react to form photochemical smog, and long-term exposure will threaten human health and cause irreversible damage. In addition, under the influence of certain climate activities, local-scale air pollution is likely to evolve into larger-scale regional pollution, which is more difficult to deal with. Therefore, the best way to control volatile organic compounds is to eliminate them before they are emitted.

[0003] Propane is a saturated hydrocarbon in VOCs, and it is relatively stable in VOCs. Recently, with the increase in the use of liquefied petroleum gas, the emission of propane has increased. In order to solve the problem of propane emissions, it is necessary to find an efficient and safe way to deal with propane.

[0004] The existing methods for treating propane in VOCs mainly include two categories: destruction method and recovery method. Among them, the recovery method mainly includes: adsorption, absorption, membrane separation and condensation. Among them, the commonly used treatment methods in industry are adsorption, absorption and membrane separation methods. The destruction methods mainly include: catalytic oxidation, thermal incineration, biodegradation, photocatalytic decomposition and non-thermal plasma oxidation. Among them, the destruction technologies commonly used in industry are: thermal incineration and catalytic oxidation. For recovery technology, the difficulties it has are: expensive recycling materials, large amount of recycled materials, large loss of recycled materials, low recovery efficiency, etc. The difficulties in destruction technology include: low catalytic efficiency, high energy consumption, and the efficiency of processing materials will decrease 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] It can be seen from this that the catalytic oxidation method has the characteristics of low energy consumption and high efficiency compared to other methods. Therefore, the catalytic oxidation method can be used in industry to treat a large amount of VOCs waste gas. The core of the catalytic oxidation method lies in the catalyst, but most catalysts for treating VOCs can be divided into precious metal catalysts and non-precious metal catalysts. Although precious metal catalysts have good catalytic effects, they have the characteristics of poor durability, easy poisoning, and high prices. Although the price of non-precious metal catalysts is lower than that of precious metal catalysts, their catalytic effects are relatively poor.

[0009] Therefore, the use of catalytic oxidation to treat propane waste gas requires the development of a catalyst with low price, high treatment efficiency and high stability. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a manganese-based rare earth metal catalyst and a preparation method and application thereof, which solves the problem that it is difficult to achieve both treatment efficiency and stability in existing VOCs catalysts.

[0011] To achieve this object, the present invention adopts the following technical solutions:

[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, wherein R is a rare earth metal element.

[0013] The present invention firstly uses non-precious metal oxide catalysts to replace precious metal catalysts, and selects Mn-based oxides as catalysts among non-precious metals. However, the crystal form of Mn-based oxides is easy to change at different temperatures, and this change will lead to a decrease in catalytic activity during the catalytic process. Therefore, in order to solve the problem of crystal form change of Mn-based oxides at different temperatures, rare earth metal elements are added to Mn-based oxides to form new RMn2O5 catalysts, thereby improving the stability of the catalyst.

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

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

[0016] Preferably, R is any one of Y, Sm, Gd or Pr or a combination of at least two thereof, preferably Y.

[0017] The present invention further prefers that the rare earth metal element R is Y. This is 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 Pr rare earth metal element has high catalytic activity, the stability of the catalyst is low; although the manganese-based metal oxide prepared by the Gd rare earth metal element has high stability, the catalytic activity of the catalyst is low.

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

[0019] The manganese-based rare earth metal catalyst in the present invention has a mullite orthorhombic structure. The improvement of the stability of mullite relative to other binary Mn oxides is mainly due to the unique structure of mullite. Mn and O ions constitute the basic ligand unit (i.e., octahedron and pyramid). 3+ The ions are filled into the space around the Mn ligand unit. Mullite compounds have empty channels in their lattices, and together with their unique ligand field, they reduce the formation energy of their structure, thereby increasing the thermal stability of oxidized mullite 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 N element, and the content of N element is 0.01-0.5wt%, for example, it can be 0.01wt%, 0.07wt%, 0.12wt%, 0.18wt%, 0.23wt%, 0.29wt%, 0.34wt%, 0.4wt%, 0.45wt% or 0.5wt%, etc.

[0021] The present invention further preferably dopes N element into the manganese-based rare earth metal catalyst. Doping with N element has the advantages of increasing the specific surface area of ​​the catalyst and improving the activity of the catalyst.

[0022] The N 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 of the manganese-based rare earth metal catalyst is in the range of 0.01 to 160 nm, for example, 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;

[0025] B. The specific surface area of ​​the manganese-based rare earth metal catalyst is 80 to 250 m 2 / g, for example, it can 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 according to the first aspect, the preparation method comprising the following steps:

[0028] (1) mixing a rare earth metal salt, a manganese salt and an oxidant to perform a first stirring oxidation reaction to obtain a first system;

[0029] (2) mixing an alkaline substance and the first system, and sequentially performing a second stirring reaction and a hydrothermal reaction to obtain a reacted material containing a 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 stir evenly, and then mixes the alkaline substance to perform a second stirring reaction and a hydrothermal reaction, thereby realizing the preparation of a manganese-based rare earth metal catalyst; 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 stirred evenly, which eventually causes the catalyst particles to become coarse.

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

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

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

[0034] And / or, the anion of the manganese salt includes any one of acetate, nitrate or chloride ion or a combination of at least two thereof; 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) comprises sodium hydroxide and / or urea, preferably urea.

[0039] The present invention further prefers that the alkaline substance is urea. Compared with the use of sodium hydroxide or ammonia water and other substances, urea has two effects. First, compared with the strong base NaOH, urea does not directly release OH- but slowly reacts with water during the reaction to release OH- so that the reactants slowly precipitate, thereby reducing particle growth and reducing particle size. At the same temperature and reaction time, in the process of preparing 1.0N-YMn2O5, the time for urea to completely react is reduced, so the time for particle growth is increased, which leads to an increase in particle size compared with 1.25N-YMn2O5, but in the process of preparing 1.5N-YMn2O5, the amount of OH- released by urea per unit time increases, so that the reactants are accelerated to precipitate, thereby increasing the particle size; secondly, urea can play the role of N doping, so that the final catalyst is doped with N elements. The doping of N elements has the effect of increasing the specific surface area of ​​the catalyst and improving the activity of the catalyst, which can further improve the comprehensive 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 the alkaline substance added to be within the above range or controls the pH of the system after the addition to be within the above range, so as to obtain a catalyst powder with a smaller particle size and a higher catalytic activity of the catalyst.

[0042] Preferably, the second stirring reaction satisfies: the time of the second stirring reaction is 0.5 to 1 h, for example, it can be 0.5 h, 0.56 h, 0.62 h, 0.67 h, 0.73 h, 0.78 h, 0.84 h, 0.89 h, 0.95 h or 1 h, 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 temperature of the hydrothermal reaction is 200-220°C, for example, it can be 200°C, 203°C, 205°C, 207°C, 209°C, 212°C, 214°C, 216°C, 218°C or 220°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable, and / or, the time of the hydrothermal reaction is 20-50min, for example, it can be 20min, 24min, 27min, 30min, 34min, 37min, 40min, 44min, 47min or 50min, etc.

[0044] Preferably, the first stirring oxidation reaction satisfies: the time of the first stirring oxidation reaction is 0.5 to 1 h, for example, it can be 0.5 h, 0.56 h, 0.62 h, 0.67 h, 0.73 h, 0.78 h, 0.84 h, 0.89 h, 0.95 h or 1 h, 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 comprises: (3) sequentially performing solid-liquid separation, washing and drying on the reaction material to obtain the manganese-based rare earth metal catalyst.

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

[0047] Preferably, the washing comprises washing with alcohol at least once and then washing with acid at least once.

[0048] The present invention has no special limitation on the solid-liquid separation in the above process, and any device and method for solid-liquid separation known to those skilled in the art may be used, and may also be adjusted according to the actual process, such as filtration, centrifugation or sedimentation separation, or a combination of different methods.

[0049] The present invention has no particular limitation on the drying in the above process. Any drying device and method known to those skilled in the art can be used, and can also be adjusted 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 comprises vacuum drying.

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

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

[0053] Preferably, the vacuum drying time is 12 to 20 hours, for example, it can be 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 comprises the following steps:

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

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

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

[0058] In a third aspect, the present invention provides an 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 VOCs treatment, preferably in the treatment of VOCs containing hydrocarbons.

[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 30000-33000 mL·h -1 , for example, it can be 30000mL·h -1 、30334mL·h -1 、30667mL·h -1 、31000mL·h -1 、31334mL·h -1 、31667mL·h -1 、32000mL·h -1 、32334mL·h -1 、32667mL·h -1 or 33000mL·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 has a metal oxide with a molecular formula of RMn2O5, and 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 the present invention is doped with N element, which has the advantages of increasing the specific surface area of ​​the catalyst and improving the catalytic activity of the catalyst. Under preferred conditions, the T 90 Within 240℃, T 50 Within 223°C, the conversion rate after 100 hours of catalytic reaction is 100% of the initial conversion rate, and the catalytic activity hardly decreases; and under the optimal conditions, the stability decreases by less than 3% after adding 5% water, and the water aging resistance is excellent;

[0064] (3) The preparation method of the manganese-based rare earth metal catalyst provided by the present invention can well prepare a catalyst containing RMn2O5, and the preparation process is simple to operate, easy to scale up industrially, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is the XRD diagram of the manganese-based rare earth metal catalysts prepared in Examples 1, 4 and 6-7 of the present invention and the XRD diagram 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 the present invention.

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

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

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

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

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

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

[0073] Fig. 9 It is an isothermal adsorption-desorption curve diagram of the manganese-based rare earth metal catalyst prepared in Example 1, Example 4 and Examples 6 to 7 of the present invention.

[0074] Fig.10 It is a particle size distribution curve diagram of the manganese-based rare earth metal catalysts prepared in Example 1, Example 4 and Examples 6 to 7 of the present invention.

[0075] Fig.11 It is a catalytic activity test curve diagram of the manganese-based rare earth metal catalysts prepared in Example 1, Example 4 and Examples 6 to 7 of the present invention.

[0076] Fig.12 This is a durability test chart of the manganese-based rare earth metal catalysts prepared in Examples 1, 4, and 6-7 of the present invention catalyzing propane at 275°C.

[0077] Fig.13 This is a water aging resistance test chart of the manganese-based rare earth metal catalyst prepared in Example 4 and Example 6 of the present invention. DETAILED DESCRIPTION

[0078] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0079] It should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features indicated. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0080] Unless otherwise specified, the reagents used in the following examples and comparative examples are analytically pure AR;

[0081] Example 1

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

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

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

[0085] (3) The reaction material is sequentially washed with water three times, ethanol three times, and 1% nitric acid once, and after each washing, centrifugation is performed 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 preparation method comprising the following steps:

[0088] (1) mixing a rare earth metal salt (Y(NO3)3·6H2O), a manganese salt (MnCl2) and an oxidant KMnO4 according to the molecular formula YMn2O5, wherein the molar ratio of Mn in the oxidant to Mn in the manganese salt is 0.4:1, and performing a first stirring oxidation reaction at 1100 r / min for 0.5 h to obtain a first system;

[0089] (2) mixing urea and the first system, and performing a second stirring reaction at 1000 r / min for 1 hour at a pH of 12, and then transferring to a high-pressure reactor lined with polytetrafluoroethylene for a hydrothermal reaction at 206° C. for 20 minutes to obtain a reaction material containing a manganese-based rare earth metal catalyst; wherein the molar ratio of the urea to the manganese salt is 10.5:1;

[0090] (3) The reaction material is sequentially washed with water three times, ethanol twice, and 1.5% nitric acid once, and after each washing, centrifugation is performed 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 preparation method comprising the following steps:

[0093] (1) mixing a rare earth metal salt (Y(CH3COO)2), a manganese salt (Mn(CH3COO)2·4H2O) and an oxidant KMnO4 according to a molecular formula YMn2O5, wherein the molar ratio of Mn in the oxidant to Mn in the manganese salt is 0.5:1, and performing a first stirring oxidation reaction at 1000 r / min for 1 hour to obtain a first system;

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

[0095] (3) The reaction material is sequentially washed with water twice, ethanol three times, and 2.0% nitric acid once, and after each washing, centrifugal separation is performed and dried at 0 kPa and 100° C. for 12 h to obtain the manganese-based rare earth metal catalyst.

[0096] Example 4

[0097] The present embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as that of Example 1, except that urea in step (2) is replaced by a sodium hydroxide solution (the concentration is 10 wt %, and the molar number of sodium hydroxide is the same as the molar number of urea). Such preparation method will not be described in detail herein.

[0098] Example 5

[0099] The present embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as that of Example 1, except that urea in step (2) is replaced by aqueous ammonia (the concentration is 20wt%, and the molar number of N is the same as the molar number of N in urea), and will not be repeated here.

[0100] Example 6

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

[0102] Example 7

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

[0104] Example 8

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

[0106] Example 9

[0107] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as that of Embodiment 1 except that the molar ratio of urea to the manganese salt in step (2) is 0.5:1, and will not be described again.

[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 that of Example 1, except that Y(NO3)3·6H2O is replaced by Sm(NO3)3·6H2O, and will not be described again.

[0110] Embodiment 11

[0111] This embodiment provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as that of Example 1, except that Y(NO3)3·6H2O is replaced by Pr(NO3)3·6H2O, and will not be described in detail 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 Example 1 except that Y(NO3)3·6H2O is not added, and the details are not 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 Example 1 except that step (1) is not performed separately, and steps (2) and (3) are performed after the rare earth metal salt, manganese salt and urea are directly mixed. The details are not repeated here.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing a manganese-based rare earth metal catalyst. The preparation method is the same as Example 1 except that the second stirring reaction is not performed in step (2), and a hydrothermal reaction is performed directly. The details will not be described again.

[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 Example 1 except that the molar ratio of Mn in the oxidant to Mn in the manganese salt is 2.5:1, and the details are not 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 Example 1 except that the molar ratio of Mn in the oxidant to Mn in the manganese salt is 0.3:1, and the details are not repeated here.

[0122] Catalytic performance test:

[0123] A. Catalytic activity test: O2 = 10%, C3H8 = 0.1%, the remaining N2 is used as the balance gas, the gas hourly space velocity is 33000mL / g -1 ·h -1 , test the relationship between catalytic activity and reaction temperature;

[0124] B. Stability test: O2 = 10%, C3H8 = 0.1%, the remaining N2 is used as the balance gas, the gas hourly space velocity is 33000mL / g -1 ·h -1 , testing the durability of catalytic propane at 275°C. And adding 5% H2O to the raw gas to measure the water resistance of the catalyst, comparing the 1.25N-YMn2O5 sample with the best catalytic effect with the unmodified sample.

[0125] Exemplarily, XRD, TEM, isothermal adsorption-desorption curves and particle size distribution tests were performed on the catalysts in Example 1 (denoted as 1.0N-YMn2O5), Example 4 (denoted as NaOH-YMn2O5), and Examples 6 to 7 (denoted as 1.25N-YMn2O5 and 1.5N-YMn2O5, respectively), and XRD test was performed on the catalyst after catalytic reaction in Example 6 to characterize whether the crystal form of the catalyst changes 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 after the catalytic reaction, the crystal form of the catalyst does not change substantially.

[0127] The SEM and EDS scans of the above embodiments are shown in Figure 2 to Figure 8 ,from Figures 2 to 8 It can be seen that the use of urea can dope N element into YMn2O5 crystalline oxide, and the grains are finer.

[0128] Fig. 9 It is the isothermal adsorption-desorption curve of the catalyst prepared in Example 1, Example 4 and Examples 6-7 of the present invention. Fig.10is the particle size distribution curve of the catalysts prepared in Example 1, Example 4 and Examples 6 to 7 of the present invention. Figures 9-10 It can be seen that the specific surface area of ​​the catalyst sample using urea is much larger than that of the catalyst using sodium hydroxide, and the specific surface area of ​​the catalyst using urea shows a trend of first increasing and then decreasing with the increase of N content in the sample. 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 has the largest specific surface area (S BET =223.3585m 2 / g) is NaOH-YMn2O5 (S BET =86.5335m 2 / g) sample, which is 2.58 times the specific surface area of ​​the 1.25N-YMn2O5 sample, indicating that the 1.25N-YMn2O5 sample exposes more active sites.

[0129] Fig.11 It is the catalytic activity test curve of the catalysts prepared in Example 1, Example 4 and Examples 6-7 of the present invention. Fig.12 The durability test of the catalysts prepared in Examples 1, 4 and 6-7 of the present invention for catalyzing propane at 275°C. Figure 11-12 It can be seen that the catalyst using urea is easier to oxidize propane than the catalyst using sodium hydroxide, and shows higher catalytic activity. The catalytic activity of the samples for propane is in the following order: 1.25N-YMn2O5>1.0N-YMn2O5>1.5N-YMn2O5>NaOH-YMn2O5. The samples of 1.0N-YMn2O5, 1.25N-YMn2O5, 1.5N-YMn2O5, and NaOH-YMn2O5 were reacted under the conditions of 1000ppm propane as the raw gas, 10% O2, and N2 as the residual gas, and the obtained T 50 (temperature at which the conversion rate is 50%) are: 221°C, 216°C, 225°C, 240°C. The cold start temperature (T 50) is the lowest, indicating that the catalyst using urea is more active in catalytic oxidation of propane under low temperature conditions than the catalyst using sodium hydroxide. The catalytic oxidation temperature T of 1.5N-YMn2O5, 1.25N-YMn2O5, and 1.0N-YMn2O5 for propane 90 (the temperature at which the conversion rate is 90%) are all lower than 250°C, namely: 243°C, 239°C, 246°C. The T 90 is 285°C. The T 90 and T 50 The T values ​​of 1.25N-YMn2O5 are lower than those of the catalyst using sodium hydroxide, which indicates that the catalyst using urea has higher activity in catalytic oxidation of propane than the catalyst using sodium hydroxide under low temperature conditions. 90 and T 50 The lowest value indicates the highest catalytic oxidation activity. Fig.12 It shows that at 275°C, the conversion rate of the catalysts prepared by either urea or sodium hydroxide can reach more than 20%, and the catalytic conversion efficiency is stable within 100 hours without any change in catalytic efficiency. Although the catalytic efficiency of urea is significantly higher than that of the catalyst using sodium hydroxide, the stability of the catalyst using urea is not much different from that of the catalyst using sodium hydroxide, which shows that the catalyst using urea not only improves the catalytic performance of the YMn2O5 catalyst, but also perfectly retains the high stability of the mullite catalyst.

[0130] The compositions and catalytic performances of the above examples and comparative examples were tested, and the results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] From Table 1, we can see the following points:

[0135] (1) It can be seen from Examples 1 to 3 that the preparation method of the manganese-based rare earth metal catalyst provided by the present invention is prepared according to the molecular formula YMn2O5 and urea is used to dope nitrogen. The catalyst has high stability and high catalytic activity, wherein a mullite structure can be obtained in the catalyst, and the pore size range is within the range of 6.3 to 15.2 nm, and the specific surface area is within the range of 130 to 224 m 2 / g, T90 for propane is within 240℃, T50 is within 223℃, the conversion rate after 100h of catalytic reaction accounts for 100% of the initial conversion rate, the catalytic activity does not decrease, and the application prospects are broad.

[0136] (2) It can be seen from Example 4 that, compared with the use of urea in Example 1, under the condition of the same mole of sodium hydroxide as a precipitant, the precipitation speed of the catalyst particles is accelerated, and after the addition, the weak acidity of the solution in Example 1 is directly changed to a strong alkalinity, thereby increasing the size of the catalyst particles. In addition, the price of sodium hydroxide is higher than that of urea, and the cost is higher than that of Example 1.

[0137] It can be seen from Example 5 that 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 the catalyst particles, thereby increasing the particle size of the catalyst, and the catalytic activity is reduced compared with the example.

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

[0139] (3) By comparing Example 1 with Examples 6 to 9, it can be seen that the amount of urea added has a significant effect on the specific surface area of ​​the catalyst, which will ultimately affect the catalytic activity of the catalyst. The present invention preferably controls the amount of urea added within a reasonable range, thereby reasonably controlling the N content in the catalyst and better ensuring the catalytic activity of the catalyst; and the amount of urea added in Example 8 is too high, and the urea decomposition during the synthesis process produces a large amount of ammonia, which makes the system pressure too high and exceeds the limit of the reactor; the amount of urea added in Example 9 is too low, and it is impossible to generate enough OH - This creates an alkaline environment for the generation of catalysts.

[0140] (4) By comparing Example 1 and Examples 10 to 11, it can be seen that in Example 10, after Y(NO3)3·6H2O was replaced by Sm(NO3)3·6H2O, the crystallinity of the catalyst was poor, and the catalytic effect after evaluation was lower than that of the catalyst synthesized using Y(NO3)3·6H2O. In Example 11, after Y(NO3)3·6H2O was replaced by Pr(NO3)3·6H2O, no compound with a mullite structure could be synthesized within the same time, indicating that the metal catalyst could not be synthesized within a shorter reaction time.

[0141] (5) In Comparative Example 1, Y(NO3)3·6H2O was not added, and there was no source of rare earth metal ions, so the mullite structure catalyst could not be synthesized; in Comparative Example 2, the reactants were not sufficiently stirred, and the materials were not stirred evenly, resulting in large particles of the reactants. In Comparative Example 3, the alkali was not sufficiently stirred with the reactants, resulting in local over-alkalinity, which accelerated precipitation and caused the particles to become coarser. In Comparative Example 4, at a relatively high molar ratio of Mn in the oxidant to Mn in the manganese salt, some substances failed to participate in the reaction and thus existed as impurity phases, 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 was changed to 0.3:1, no mullite catalyst could be formed.

[0142] Comparative test of water aging resistance:

[0143] The catalyst in the example was used as a test sample to conduct a water aging resistance test, that is, 5% H2O was added to the raw gas during the stability test to measure the water resistance of the catalyst, and the conversion rate after the catalytic performance was stabilized was used as a benchmark for calculation and comparison. The comparative experimental diagram of Example 4 and Example 6 is shown in FIG. Fig.13 As shown, from Fig.13 It can be seen that the 1.25N-YMn2O5 sample has significantly better water aging resistance compared with the unmodified sample. The stability of Example 4, which is not modified by adding urea, decreases by 6-9% after adding 5% water (i.e., the conversion rate decreases by 6-9% after stabilization), while the stability of Example 6 decreases by only 2-3% after adding 5% water. This shows that the present invention preferably uses urea for modification and has better water aging resistance.

[0144] By comparing Example 1 with Example 9 and Example 11, it can also be seen that no mullite structure is formed in Example 9 and Example 11, and the water aging resistance is much lower than that of Example 1, which will not be described in detail here.

[0145] The present invention illustrates the detailed features of the present invention through the above embodiments, 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 improvement to the present invention, equivalent replacement of the technical features selected by the present invention, addition of auxiliary technical features, 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, characterized in that: The manganese-based rare earth metal catalyst comprises a metal oxide, and the molecular formula of the metal oxide is RMn2O5, wherein R is a rare earth metal element.

2. The manganese-based rare earth metal catalyst according to claim 1, characterized in that R is any one of Y, Sm, Gd or Pr or a combination of at least two; and / or, the manganese-based rare earth metal catalyst has a mullite orthorhombic structure; And / or, the manganese-based rare earth metal catalyst is doped with N element, and the content of N element is 0.01-0.8wt%.

3. The manganese-based rare earth metal catalyst according to claim 1 or 2, characterized in that: The manganese-based rare earth metal catalyst satisfies at least one of the following conditions: A. The pore size of the manganese-based rare earth metal catalyst is in the range of 0.01 to 160 nm; B. The specific surface area of ​​the manganese-based rare earth metal catalyst is 80 to 250 m 2 / g; C. The particle size of the manganese-based rare earth metal catalyst is in the range of 6.3 nm to 14.8 nm.

4. A method for preparing a manganese-based rare earth metal catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) mixing a rare earth metal salt, a manganese salt and an oxidant to perform 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 reacted material containing a manganese-based rare earth metal catalyst.

5. The preparation method according to claim 4, characterized in that: In step (1), the anion of the rare earth metal salt comprises acetate and / or nitrate; and / or the cation of the rare earth metal salt comprises Y 3+ 、Sm 3+ , Gd 3+ or Pr 3+ Any one or a combination of at least two of the following: And / or, the anion of the manganese salt includes any one of acetate, nitrate, and chloride ion or a combination of at least two thereof; and / or, the cation of the manganese salt is a divalent manganese ion; And / or, the oxidant is KMnO4.

6. The preparation method according to claim 4, characterized in that: The molar ratio of Mn in the oxidant to Mn in the manganese salt is (0.4-0.5):

1.

7. The preparation method according to claim 4, characterized in that: The alkaline substance in step (2) includes sodium hydroxide and / or urea, preferably urea.

8. The preparation method according to claim 4, characterized in that: The molar ratio of the alkaline substance to the manganese salt is (7-12):1, and / or the pH range after mixing the alkaline substance and the first system is 9-12.

9. The preparation method according to claim 4, characterized in that: The second stirring reaction satisfies: the time of the second stirring reaction is 0.5 to 1 h, and / or the speed of the second stirring reaction is 1000 to 1100 r / min; And / or, the hydrothermal reaction satisfies: the temperature of the hydrothermal reaction is 200-220° C., and / or, the time of the hydrothermal reaction is 20-50 min.

10. Use of a manganese-based rare earth metal catalyst as claimed in any one of claims 1 to 3, and / or a manganese-based rare earth metal catalyst prepared by the preparation method of a manganese-based rare earth metal catalyst as claimed in any one of claims 4 to 9 in VOCs treatment, preferably in the treatment of VOCs containing hydrocarbons.

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