Vanadium phosphorus oxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to a vanadium phosphorus oxide catalyst and a preparation method and application thereof, the preparation method comprises the following steps: first roasting at least five metal salt-based eutectic solvents in an oxidizing gas atmosphere to obtain a high-entropy oxide; mechanically mixing the high-entropy oxide with a vanadium-phosphorus-oxide precursor, and then performing secondary roasting to obtain the vanadium-phosphorus-oxide catalyst, according to the preparation method, the high-entropy oxide and the vanadium-phosphorus-oxygen precursor are compounded to obtain the vanadium-phosphorus-oxygen catalyst with high catalytic activity, in the reaction of preparing maleic anhydride through catalytic oxidation of n-butane, high selectivity and yield of maleic anhydride are ensured while a high n-butane conversion rate is obtained, the n-butane conversion rate is preferably as high as 93.6% or above, and the yield of maleic anhydride is greatly improved. Meanwhile, the selectivity of the maleic anhydride is preferably as high as 62.6% or above, and the yield of the maleic anhydride is preferably as high as 61.0% or above; the preparation raw materials are wide in source, the preparation process is simple, cost is low, and industrial production is easy.

Description

Technical Field

[0001] This invention relates to the field of chemical catalysis technology, and in particular to a vanadium-phosphorus-oxygen catalyst, its preparation method, and its application. Background Technology

[0002] Maleic anhydride is one of the world's three major acid anhydrides (acetic anhydride, phthalic anhydride, and maleic anhydride), and also an important chemical product and intermediate. Currently, there are two main methods for the industrial production of maleic anhydride: benzene oxidation and n-butane oxidation. The reaction mechanism, equipment development, and catalyst design of the benzene oxidation method are relatively mature. However, with increasingly stringent environmental requirements, the benzene oxidation method has been gradually phased out due to drawbacks such as the toxicity of benzene, high raw material prices, low yield of the target product, and complex product separation processes. However, butane, as a cheap and environmentally friendly raw material for the preparation of maleic anhydride, has rapidly captured the market due to its wide availability and environmentally friendly production process. Therefore, the development of production technology for maleic anhydride via butane oxidation is particularly urgent and important.

[0003] However, the key to maleic anhydride production technology lies in improving catalyst performance and optimizing the process. Vanadium phosphorus oxygen catalyst (VPO catalyst), as the only industrially available catalyst for the oxidation of butane to maleic anhydride, suffers from poor selectivity for the target product and difficulty in simultaneously achieving high conversion and selectivity in the catalytic reaction. Currently, the catalytic performance of VPO catalysts is mainly improved by adding metal salts or metals as promoters. For example, CN104492468A discloses a method for preparing a catalyst for the oxidation of n-butane to maleic anhydride, which adds one or two of Ce, La, Fe, Nb, Zr, Bi, Ti, Co, Mo, Ni, and W as promoters to the vanadium phosphorus oxygen system. Although the catalytic performance is improved to some extent, the problems of low butane conversion and low maleic anhydride selectivity and yield still exist. Moreover, directly adding metals or metal salts can affect the structure of the VPO catalyst precursor and cause a large amount of metal to be lost during the preparation of the VPO catalyst precursor, resulting in pollution and waste. In addition, there are studies on VPO catalysts doped with hydrotalcite. For example, CN111701608A discloses a method for preparing vanadium-phosphorus-oxygen catalysts with hydrotalcite assistance. Although this method can solve problems such as VPO catalyst precursor structure changes and metal loss to some extent, hydrotalcite is an anionic layered compound, and its preparation limits the types of metals that can be used. The metal cation needs to have a suitable ionic radius (compared to Mg). 2+ Only when the ionic radius (0.072 nm) and charge number are similar can hydrotalcite-like intercalation materials be formed, and the improvement in conversion rate and selectivity of maleic anhydride preparation from n-butane is still limited.

[0004] Therefore, how to develop a vanadium-phosphorus-oxygen catalyst and its preparation method that can achieve both high n-butane conversion and high maleic anhydride selectivity to realize the efficient production of maleic anhydride has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention prepares a vanadium-phosphorus-oxygen catalyst with high lattice oxygen content and high specific surface area by combining high-entropy oxides and vanadium-phosphorus-oxygen precursors. This catalyst can efficiently catalyze the oxidation of n-butane to maleic anhydride, exhibiting high n-butane conversion and high maleic anhydride selectivity, while avoiding problems such as metal loss and secondary pollution caused by directly adding metals / metal salts.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0008] (1) At least five metal salt-based eutectic solvents are subjected to a first calcination in an oxidizing gas atmosphere to obtain high-entropy oxides;

[0009] (2) The high-entropy oxide described in step (1) is mechanically mixed with the vanadium phosphorus oxygen precursor, and then subjected to a second calcination to obtain the vanadium phosphorus oxygen catalyst.

[0010] This invention combines a high-entropy oxide with a vanadium phosphorus oxide precursor via mechanical mixing. The synergistic effect of these two components yields a vanadium phosphorus oxide catalyst with high lattice oxygen content and high specific surface area. The high-entropy oxide is a high-entropy material with multiple transition metal components. The synergistic effect of each metal component, combined with its structural stability and multi-orbital properties, promotes electron cloud flow while avoiding structural changes during the growth of the vanadium phosphorus oxide precursor and the formation of tetravalent vanadium during calcination activation, thus improving the catalytic activity and selectivity of the vanadium phosphorus oxide catalyst. Furthermore, the layered structure and disordered local structure of the high-entropy oxide after mechanical mixing increase the specific surface area of ​​the vanadium phosphorus oxide catalyst, further enhancing its catalytic activity. In the catalytic oxidation of n-butane to maleic anhydride, it exhibits high n-butane conversion, high maleic anhydride selectivity, and high maleic anhydride yield. Moreover, the raw materials are widely available, and the preparation process is simple, solving the current problems encountered in the n-butane oxidation method for maleic anhydride production.

[0011] It is worth noting that "at least five" in step (1) of the present invention refers to at least five metal salts.

[0012] Optionally, the ratio of the at least five metal salts is equimolar or nearly equimolar.

[0013] Preferably, the hydrogen bond donor in the metal salt-based eutectic solvent of step (1) includes lactic acid, ethylene glycol or uric acid, preferably lactic acid.

[0014] In a further preferred embodiment of the present invention, the hydrogen bond donor in the metal salt-based eutectic solvent of step (1) is lactic acid, which can form a rich hydrogen bond network, promote the formation of high-entropy oxides, and thus further improve the catalytic activity of the obtained vanadium-phosphorus-oxygen catalyst.

[0015] Preferably, the hydrogen bond acceptors in the metal salt-based eutectic solvent of step (1) include chloride salts of at least five soluble metals and / or acetate salts of soluble metals.

[0016] Preferably, the soluble metal includes Co, Ni, Fe, Mn, Cr, Zn, Bi, Cu, Li, Zr, U, Mg, Ce, Mo, In, Sb, Ti, La, Eu, Sm, Y, Yb or Gd, and more preferably Co, Ni, Fe, Mn, La, Cr, Zn, Bi, Cu, Zr, Mg, Ce or Eu.

[0017] The present invention further preferably includes the soluble metals Co, Ni, Fe, Mn, La, Cr, Zn, Bi, Cu, Zr, Mg, Ce or Eu, wherein at least five of them are combined to exert synergistic effects among the metal components, which is more conducive to improving the catalytic activity of the vanadium phosphorus oxygen catalyst.

[0018] Optionally, the metal salt-based eutectic solvent in step (1) is six or more metal salts, wherein the soluble metals in the six or more metal salts include a combination of metal A and metal B.

[0019] Preferably, the metal A includes any one or a combination of at least two of La, Ca, Sr, and Ba, wherein typical but non-limiting combinations include combinations of La and Ca, combinations of Ca and Sr, or combinations of Sr and Ba, etc.

[0020] Preferably, the metal B comprises any five or more combinations of Co, Ni, Fe, Mn, Cr, Zn, Bi, Cu, Li, Zr, U, Mg, Ce, Mo, In, Sb, Ti, Eu, Sm, Y, Yb, or Gd, wherein typical but non-limiting combinations include combinations of Co, Cr, Fe, Mn, and Ni, combinations of Co, Cr, Ce, Mn, and Ni, or combinations of Co, Cu, Ni, Mg, and Zn, etc.

[0021] Preferably, the metals in metal A and metal B are in equimolar or near-equimolar ratios.

[0022] Preferably, the ratio of the total number of moles of metal in metal A to the number of moles of any metal in metal B is the number of metal element types in metal B.

[0023] When this invention uses six or more metal salts, and the ratio of the total number of moles of metal A in the six metal salts to the number of moles of any metal in metal B is equal to the number of metal element types in metal B, the resulting high-entropy oxide is perovskite type, denoted as ABO. x , where 2≤x≤3, for example, it can be 2, 2.5 or 3, etc.

[0024] Optionally, the at least five metal salt-based eutectic solvents in step (1) of the present invention are prepared by the following method: the eutectic solvents are thoroughly mixed with at least five metal salts, and the mixture is continuously stirred for 50 to 80 minutes under sealed conditions at 60 to 80°C to obtain a homogeneous liquid, thereby obtaining at least five metal salt-based eutectic solvents.

[0025] Preferably, the molar ratio of hydrogen bond donor to hydrogen bond acceptor in the metal salt-based eutectic solvent in step (1) is (1-3):1, for example, it can be 1:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.7:1 or 3:1, etc., preferably (1.8-2.2):1.

[0026] Preferably, the oxidizing gas in the oxidizing gas atmosphere of step (1) includes O2 and / or air.

[0027] Preferably, the temperature of the first roasting in step (1) is 500 to 1000°C, for example, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, and preferably 600 to 1000°C.

[0028] The present invention further preferably uses a first calcination temperature of 600-1000°C, which is conducive to the formation of the high-entropy oxide, thereby improving the catalytic activity and selectivity of the vanadium-phosphorus-oxygen catalyst; if the first calcination temperature is too low, the high-entropy material cannot be formed; if the first calcination temperature is too high, the cost will increase.

[0029] Preferably, the heating rate of the first roasting in step (1) is 3 to 8 °C / min, for example, it can be 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min or 8 °C / min.

[0030] Preferably, the roasting time in step (1) is 1 to 4 hours, for example, 1 hour, 2 hours, 3 hours or 4 hours.

[0031] Preferably, the mass ratio of the high-entropy oxide to the vanadium phosphorus oxygen precursor in step (2) is (0.1-10):100, for example, it can be 0.1:100, 0.5:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100, etc., preferably (1-3):100.

[0032] In a further preferred embodiment of the present invention, the mass ratio of the high-entropy oxide to the vanadium-phosphorus oxygen precursor in step (2) is (1-3):100. Doping with a low amount of high-entropy oxide can significantly improve the catalytic activity of the obtained vanadium-phosphorus oxygen catalyst. When the amount of high-entropy oxide doping is small, the catalytic performance is not significantly improved. When the amount of high-entropy oxide doping is high, the catalytic performance is not further improved significantly, and the cost is slightly higher.

[0033] Preferably, the mechanical mixing method in step (2) includes ball milling.

[0034] Preferably, the ball milling includes vacuum ball milling.

[0035] Preferably, the ball-to-material ratio of the ball mill is (0.5 to 2):1, for example, it can be 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, etc.

[0036] Preferably, the rotational speed of the ball mill is 100 to 500 r / min, for example, it can be 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min.

[0037] Preferably, the ball milling time is 0.2 to 20 hours, for example, it can be 0.2 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 5 hours, 7 hours, 10 hours, 12 hours, 15 hours, 18 hours or 20 hours.

[0038] Preferably, the second roasting temperature in step (2) is 300-500℃, for example, it can be 300℃, 320℃, 350℃, 380℃, 400℃, 420℃, 450℃, 480℃ or 500℃, preferably 350-480℃.

[0039] Preferably, the second roasting time in step (2) is 6 to 24 hours, for example, 6 hours, 10 hours, 12 hours, 15 hours, 20 hours or 24 hours.

[0040] Preferably, in step (2), the atmosphere for the second roasting is a mixture of n-butane and air.

[0041] Preferably, the volume ratio of n-butane to air is (1-2):(98-99), for example, it can be 1:99, 1.2:98.8, 1.4:98.6, 1.6:98.4, 1.8:98.2 or 2:98, etc.

[0042] Preferably, after mechanical mixing in step (2), the mixed powder is first pressed into tablets and crushed, and then subjected to a second calcination.

[0043] Preferably, the preparation method of the vanadium-phosphorus-oxygen precursor includes: mixing a vanadium source, benzyl alcohol and a C3-C8 monohydric alcohol and sequentially subjecting them to a first heating and a first reflux to obtain a mixture; then mixing the mixture with a phosphorus source and sequentially subjecting them to a second heating and a second reflux to obtain a vanadium-phosphorus-oxygen precursor solution, and then obtaining the vanadium-phosphorus-oxygen precursor by solid-liquid separation and drying.

[0044] Preferably, the molar ratio of vanadium in the vanadium source to phosphorus in the phosphorus source is 1:(0.8 to 1.5), for example, it can be 1:0.8, 1:1.0, 1:1.2, 1:1.4 or 1:1.5, etc.

[0045] Preferably, the volume ratio of benzyl alcohol to C3-C8 monohydric alcohol is 1:(1-25), for example, it can be 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, 1:22 or 1:25, etc., preferably 1:(3-9).

[0046] Preferably, the C3-C8 monohydric alcohol includes any one or a combination of at least two of propanol, isobutanol, n-butanol, pentanol, hexanol, heptanol, or octanol, wherein typical but non-limiting combinations include combinations of propanol and isobutanol, combinations of isobutanol and n-butanol, or combinations of pentanol and hexanol, etc., with isobutanol being the preferred choice.

[0047] Preferably, the endpoint temperature of the first heating is 120-140°C, for example, it can be 120°C, 125°C, 130°C, 135°C or 140°C.

[0048] Preferably, the first reflux time is 3 to 10 hours, for example, it can be 3 hours, 5 hours, 8 hours or 10 hours.

[0049] Preferably, after the first reflux, the mixture is further cooled.

[0050] Preferably, the endpoint temperature of the second heating is 120-140°C, for example, it can be 120°C, 125°C, 130°C, 135°C or 140°C.

[0051] Preferably, the second reflux time is 6 to 18 hours, for example, it can be 6 hours, 8 hours, 10 hours, 12 hours, 15 hours or 18 hours.

[0052] Preferably, the drying temperature is 120-150°C, for example, it can be 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C.

[0053] Preferably, the drying time is 10 to 20 hours, for example, 10 hours, 12 hours, 15 hours, 18 hours, or 20 hours.

[0054] As a further preferred embodiment of the present invention, the preparation method of the vanadium-phosphorus-oxygen catalyst includes the following steps:

[0055] (1) At least five metal salt-based eutectic solvents are heated to 500-1000°C for 1-4 hours in O2 and / or air atmosphere at a heating rate of 3-8°C / min to obtain high-entropy oxides.

[0056] The hydrogen bond donors in the metal salt-based eutectic solvent include lactic acid, ethylene glycol, or uric acid, and the hydrogen bond acceptors include chloride salts and / or acetate salts of soluble metals; the soluble metals include at least five of the following: Co, Ni, Fe, Mn, Cr, Zn, Bi, Cu, Li, Zr, U, Mg, Ce, Mo, In, Sb, Ti, La, Eu, Sm, Y, Yb, or Gd; the molar ratio of hydrogen bond donors to hydrogen bond acceptors in the metal salt-based eutectic solvent is (1–3):1.

[0057] (2) The high-entropy oxide and vanadium-phosphorus-oxygen precursor described in step (1) are ball-milled at a mass ratio of (0.1-10):100 for 0.2-20 h at a ball-to-material ratio of (0.5-2):1 and a rotation speed of 100-500 r / min. The mixture is then calcined at 300-500 °C for 6-24 h to obtain the vanadium-phosphorus-oxygen catalyst.

[0058] The method for preparing the high-entropy oxide includes: mixing a vanadium source, benzyl alcohol, and a C3-C8 monohydric alcohol, heating the mixture to 120-140°C, and then refluxing it for 3-10 hours to obtain a mixture; mixing the mixture with a phosphorus source, heating the mixture to 120-140°C, and then refluxing it for 6-18 hours to obtain a vanadium-phosphorus-oxygen precursor solution; performing solid-liquid separation; and then drying the solution at 120-150°C for 10-20 hours to obtain the vanadium-phosphorus-oxygen precursor; the molar ratio of vanadium in the vanadium source to phosphorus in the phosphorus source is 1:(0.8-1.5); and the volume ratio of benzyl alcohol to the C3-C8 monohydric alcohol is 1:(1-25).

[0059] Optionally, the at least five metal salt-based eutectic solvents in step (1) of the present invention are prepared by the following method: the eutectic solvents are thoroughly mixed with at least five metal salts, and the mixture is continuously stirred for 50 to 80 minutes under sealed conditions at 60 to 80°C to obtain a homogeneous liquid, thereby obtaining at least five metal salt-based eutectic solvents.

[0060] In a second aspect, the present invention provides a vanadium-phosphorus-oxygen catalyst, which is prepared according to the preparation method of the vanadium-phosphorus-oxygen catalyst described in the first aspect.

[0061] The vanadium-phosphorus-oxygen catalyst obtained by the preparation method according to the first aspect of the present invention has a high specific surface area and high lattice oxygen content, excellent catalytic oxidation performance, and its raw materials are widely available, the preparation process is simple, the preparation cost is low, and it can be industrially produced.

[0062] Thirdly, the present invention provides an application of the vanadium-phosphorus-oxygen catalyst described in the second aspect, wherein the vanadium-phosphorus-oxygen catalyst is used for the selective catalytic oxidation of n-butane to maleic anhydride.

[0063] The vanadium phosphorus oxide catalyst prepared by the method described in this invention can be used for the catalytic oxidation of n-butane to maleic anhydride. It exhibits high catalytic activity and high selectivity under relatively mild conditions and is easy to apply industrially.

[0064] Compared with the prior art, the present invention has at least the following beneficial effects:

[0065] (1) The method for preparing the vanadium phosphorus oxygen catalyst provided by the present invention first prepares a high-entropy oxide with multiple orbitals, adjustable composition and stable structure by calcining it in an oxidizing gas atmosphere using a metal-based eutectic solvent. Then, the high-entropy oxide is mechanically mixed with the vanadium phosphorus oxygen precursor to obtain a vanadium phosphorus oxygen catalyst with high catalytic activity. After mechanical mixing, the high-entropy oxide has a layered structure and a disordered local structure under high entropy, which improves the specific surface area and intrinsic activity of the obtained vanadium phosphorus oxygen catalyst. It avoids the structural changes of the vanadium phosphorus oxygen precursor during growth and the generation of tetravalent vanadium during calcination and activation, thus having high maleic anhydride selectivity. The preparation method has a wide range of raw material sources and a simple preparation process. Compared with directly adding metals or metal salts, it also avoids the problems of metal loss and secondary pollution.

[0066] (2) The vanadium phosphorus oxygen catalyst provided by the present invention has a large specific surface area and a high lattice oxygen content. In the reaction of catalytic oxidation of n-butane to maleic anhydride, it exhibits a high n-butane conversion rate, preferably as high as 93.6% or more. At the same time, it ensures the selectivity and yield of maleic anhydride, with a selectivity preferably as high as 62.6% or more and a yield preferably as high as 61.0% or more.

[0067] (3) Application of the vanadium phosphorus oxygen catalyst provided by the present invention: The vanadium phosphorus oxygen catalyst is used to catalyze the oxidation of n-butane to maleic anhydride. It has high catalytic activity and high selectivity under relatively mild conditions, and the amount of vanadium phosphorus oxygen catalyst required is relatively small, which significantly reduces the cost of maleic anhydride production and makes it easy to industrialize. Attached Figure Description

[0068] Figure 1 The (CoCrFeMnNi)O prepared by the preparation method provided in Example 1 of this invention is... x SEM images of high-entropy oxides;

[0069] Figure 2 The La(CoCrFeMnNi)O prepared by the preparation method provided in Example 5 of this invention is... x SEM images of high-entropy oxides;

[0070] Figure 3 These are XRD patterns of the high-entropy oxides prepared by the preparation methods provided in Examples 1 and 6-7 of this invention. Detailed Implementation

[0071] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0072] I. Implementation Examples

[0073] Example 1

[0074] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0075] (1) Preparation of high-entropy oxides: Using lactic acid as a hydrogen bond donor, and CoCl2·6H2O, CrCl3·6H2O, FeCl3·6H2O, MnCl2·4H2O and NiCl2·6H2O as hydrogen bond acceptors in the same molar ratio, the hydrogen bond donors and acceptors were mixed at a molar ratio of 2:1 and continuously stirred for 60 min under sealed conditions at 70°C to form a homogeneous liquid, thus obtaining five metal-based eutectic solvents required for the preparation of high-entropy oxides; then, the five metal-based eutectic solvents were heated to 900°C at a heating rate of 5°C / min in an O2 atmosphere for a first calcination of 2 h to obtain (CoCrFeMnNi)O x High-entropy oxides;

[0076] (2) Preparation of vanadium phosphorus oxygen precursor: 20g V2O5, 40mL benzyl alcohol and 160mL isobutanol were mixed and stirred evenly, and then heated to 135℃ and refluxed for 3h. The mixture was cooled to 60℃, and then 15.5mL of 85% H3PO4 was slowly added dropwise. The mixture was then heated to 135℃ and refluxed for 12h to obtain a vanadium phosphorus oxygen precursor solution. After filtration, a blue precipitate was obtained. Finally, the precipitate was dried in air at 120℃ for 12h to obtain the vanadium phosphoric acid precursor.

[0077] (3) Preparation of vanadium phosphorus oxygen catalyst: The (CoCrFeMnNi)O catalyst prepared in step (1) is used as a catalyst. x The high-entropy oxide and the vanadium phosphoric acid precursor described in step (2) were ball-milled and mixed for 10 h at a mass ratio of 1:100, a material-to-ball ratio of 1.5:1 and a speed of 250 r / min. The mixture was then pressed into tablets, crushed and sieved to obtain a vanadium phosphoric oxygen catalyst precursor of 20-40 mesh. Subsequently, the precursor was calcined for 12 h at 430 °C in a mixed atmosphere of n-butane and air with a volume ratio of 1.4:98.6 to obtain the vanadium phosphoric oxygen catalyst.

[0078] In this embodiment, the vanadium-phosphorus oxide catalyst (CoCrFeMnNi)O prepared by the above method is used. x SEM images of high-entropy oxides are shown below. Figure 1 As shown, the nanoparticles are uniformly distributed; and the XPS results show that the ratio of lattice oxygen to surface oxygen is 3.80, thus confirming the successful preparation of the high-entropy oxide.

[0079] Example 2

[0080] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0081] (1) Preparation of high-entropy oxides: Using lactic acid as a hydrogen bond donor, and CoCl2·6H2O, CuCl2·2H2O, NiCl2·6H2O, MgCl2·6H2O and ZnCl2 as hydrogen bond acceptors in the same molar ratio, the hydrogen bond donors and acceptors were mixed at a molar ratio of 2.2:1 and continuously stirred for 80 min under sealed conditions at 60°C to form a homogeneous liquid, thus obtaining five metal-based eutectic solvents required for the preparation of high-entropy oxides; then, the five metal-based eutectic solvents were heated to 800°C in air at a heating rate of 8°C / min for a first calcination of 4 h to obtain (CoCuNiMgZn)O. x High-entropy oxides;

[0082] (2) Preparation of vanadium phosphorus oxygen precursor: 20g V2O5, 20mL benzyl alcohol and 180mL isobutanol were mixed and stirred evenly, and then heated to 120℃ and refluxed for 5h. The mixture was cooled to 60℃, and then 15.0mL of 80% H3PO4 was slowly added dropwise. The mixture was then heated to 120℃ and refluxed for 16h to obtain a vanadium phosphorus oxygen precursor solution. After filtration, a blue precipitate was obtained. Finally, the precipitate was dried in air at 135℃ for 10h to obtain the vanadium phosphoric acid precursor.

[0083] (3) Preparation of vanadium phosphorus oxygen catalyst: The (CoCuNiMgZn)O catalyst prepared in step (1) is used as a catalyst. x The high-entropy oxide and the vanadium phosphoric acid precursor described in step (2) were ball-milled and mixed for 5 hours at a mass ratio of 2:100, a material-to-ball ratio of 0.5:1 and a speed of 500 r / min. The mixture was then pressed into tablets, crushed and sieved to obtain a vanadium phosphoric oxygen catalyst precursor of 20-40 mesh. Subsequently, the precursor was calcined for 10 hours at 480°C in a mixed atmosphere of n-butane and air with a volume ratio of 1.8:98.2 to obtain the vanadium phosphoric oxygen catalyst.

[0084] Example 3

[0085] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0086] (1) Preparation of high-entropy oxides: Using lactic acid as a hydrogen bond donor, and CoCl2·6H2O, CrCl3·6H2O, CeCl3·6H2O, MnCl2·4H2O and NiCl2·6H2O in the same molar ratio as hydrogen bond acceptors, the hydrogen bond donors and acceptors were mixed in a molar ratio of 1.8:1 and continuously stirred for 60 min under sealed conditions at 80°C to form a homogeneous liquid, thus obtaining the five metal-based eutectic solvents required for the preparation of high-entropy oxides; then, the five metal-based eutectic solvents were heated to 1000°C in air at a heating rate of 3°C / min for a first calcination of 1 h to obtain (CoCrCeMnNi)O. x High-entropy oxides;

[0087] (2) Preparation of vanadium phosphorus oxygen precursor: 15g V2O5, 50mL benzyl alcohol and 150mL n-butanol were mixed and stirred evenly, and then heated to 140℃ and refluxed for 3h. The mixture was cooled to 60℃, and then 15.5mL of 88% H3PO4 was slowly added dropwise. The mixture was then heated to 140℃ and refluxed for 10h to obtain a vanadium phosphorus oxygen precursor solution. After filtration, a blue precipitate was obtained. Finally, the precipitate was dried in air at 120℃ for 14h to obtain the vanadium phosphoric acid precursor.

[0088] (3) Preparation of vanadium phosphorus oxygen catalyst: The (CoCrCeMnNi)O catalyst prepared in step (1) is used as a catalyst.x The high-entropy oxide and the vanadium phosphoric acid precursor described in step (2) were ball-milled for 12 hours at a mass ratio of 10:100, a material-to-ball ratio of 2:1 and a speed of 100 r / min. The mixture was then pressed into tablets, crushed and sieved to obtain a vanadium phosphoric oxygen catalyst precursor of 20-40 mesh. Subsequently, the precursor was calcined at 350°C for 15 hours in a mixed atmosphere of n-butane and air with a volume ratio of 1.6:98.4 to obtain the vanadium phosphoric oxygen catalyst.

[0089] Example 4

[0090] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0091] (1) Preparation of high-entropy oxides: Using lactic acid as a hydrogen bond donor, and LaCl3·6H2O, CoCl2·6H2O, CrCl3·6H2O, MnCl2·4H2O and MgCl2·6H2O in the same molar ratio as hydrogen bond acceptors, the hydrogen bond donors and acceptors were mixed in a molar ratio of 2:1 and continuously stirred for 70 min under sealed conditions at 70°C to form a homogeneous liquid, thus obtaining five metal-based eutectic solvents required for the preparation of high-entropy oxides; then, the five metal-based eutectic solvents were heated to 700°C in air at a heating rate of 6°C / min for a first calcination of 2 h to obtain (LaCoCrMnMg)O. x High-entropy oxides;

[0092] (2) Preparation of vanadium phosphorus oxygen precursor: 20g V2O5, 40mL benzyl alcohol and 160mL isobutanol were mixed and stirred evenly, and then heated to 130℃ and refluxed for 3.5h. The mixture was then cooled to 60℃, and 15.5mL of 85% H3PO4 was slowly added dropwise. The mixture was then heated to 130℃ and refluxed for 16h to obtain a vanadium phosphorus oxygen precursor solution. After filtration, a blue precipitate was obtained. Finally, the precipitate was dried in air at 120℃ for 14h to obtain the vanadium phosphoric acid precursor.

[0093] (3) Preparation of vanadium phosphorus oxygen catalyst: The (LaCoCrMnMg)O catalyst prepared in step (1) is used as a catalyst. x The high-entropy oxide and the vanadium phosphoric acid precursor described in step (2) were ball-milled and mixed for 9 hours at a mass ratio of 2:100, a material-to-ball ratio of 1.2:1 and a speed of 300 r / min. The mixture was then pressed into tablets, crushed and sieved to obtain a vanadium phosphoric oxygen catalyst precursor of 20-40 mesh. Subsequently, the precursor was calcined for 12 hours at 450°C in a mixed atmosphere of n-butane and air with a volume ratio of 1.4:98.6 to obtain the vanadium phosphoric oxygen catalyst.

[0094] Example 5

[0095] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0096] (1) Preparation of high-entropy oxides: Lactic acid was used as a hydrogen bond donor, and LaCl3·6H2O, CoCl2·6H2O, CrCl3·6H2O, FeCl3·6H2O, MnCl2·4H2O and NiCl2·6H2O were used as hydrogen bond acceptors in the same molar ratio, wherein the molar ratio of LaCl3·6H2O to any one of the other five metal salts was 5:1; the hydrogen bond donor and the hydrogen bond acceptor were mixed in a molar ratio of 2:1 and continuously stirred at 65°C for 65 min under sealed conditions to form a homogeneous liquid, thus obtaining the five metal-based eutectic solvents required for the preparation of high-entropy oxides; the five metal-based eutectic solvents were then heated to 600°C in air at a heating rate of 5°C / min for a first calcination of 2 h to obtain La(CoCrFeMnNi)O x High-entropy oxides;

[0097] (2) Preparation of vanadium phosphorus oxygen precursor: 20g V2O5, 40mL benzyl alcohol and 160mL isobutanol were mixed and stirred evenly, and then heated to 135℃ and refluxed for 3h. The mixture was cooled to 60℃, and then 15.5mL of 85% H3PO4 was slowly added dropwise. The mixture was then heated to 135℃ and refluxed for 16h to obtain a vanadium phosphorus oxygen precursor solution. After filtration, a blue precipitate was obtained. Finally, the precipitate was dried in air at 120℃ for 12h to obtain the vanadium phosphorus phosphate precursor.

[0098] (3) Preparation of vanadium phosphorus oxygen catalyst: The La(CoCrFeMnNi)O prepared in step (1) is used as a catalyst. x The high-entropy oxide and the vanadium phosphoric acid precursor described in step (2) were ball-milled and mixed for 9 hours at a mass ratio of 2:100, a material-to-ball ratio of 1.8:1 and a speed of 300 r / min. The mixture was then pressed into tablets, crushed and sieved to obtain a vanadium phosphoric oxygen catalyst precursor of 20-40 mesh. Subsequently, the precursor was calcined for 12 hours at 400°C in a mixed atmosphere of n-butane and air at a volume ratio of 1:99 to obtain the vanadium phosphoric oxygen catalyst.

[0099] The La(CoCrFeMnNi)O in this embodiment x The high-entropy oxide has a perovskite structure, and its SEM image is shown below. Figure 2 As shown, it can be seen that its distribution is uniform and there is almost no particle aggregation.

[0100] Example 6

[0101] This embodiment provides a method for preparing a vanadium phosphorus oxygen catalyst. Except for step (1) in which ethylene glycol is used as the hydrogen bond donor, the preparation method is the same as in Example 1.

[0102] Example 7

[0103] This embodiment provides a method for preparing a vanadium phosphorus oxygen catalyst. Except for step (1) in which urea is used as the hydrogen bond donor, the preparation method is the same as in Example 1.

[0104] Figure 3 The XRD patterns of the high-entropy oxides prepared by the preparation methods provided in Examples 1 and 6-7 are shown. The presence of characteristic peaks verifies the successful preparation of the high-entropy oxides. Furthermore, high-entropy oxides can be successfully prepared regardless of whether lactic acid, ethylene glycol, or urea is used as the hydrogen bond donor.

[0105] Example 8

[0106] This embodiment provides a method for preparing a vanadium phosphorus oxygen catalyst. The preparation method is the same as in Example 1, except that FeCl3·6H2O in step (1) is replaced with TiCl4.

[0107] Example 9

[0108] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst. Except for the first calcination temperature of 500°C in step (1), the preparation method is the same as in Example 1.

[0109] Example 10

[0110] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst. Except for the first calcination temperature of 1100°C in step (1), the preparation method is the same as in Example 1.

[0111] Example 11

[0112] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, wherein, except for step (3) where (CoCrFeMnNi)O is prepared, the method provides a method for preparing a vanadium-phosphorus-oxygen catalyst. x Except for the mass ratio of high-entropy oxide to the vanadium phosphate precursor being 0.1:100, everything else is the same as in Example 1.

[0113] Example 12

[0114] This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst, wherein, except for step (3) where (CoCrFeMnNi)O is prepared, the method provides a method for preparing a vanadium-phosphorus-oxygen catalyst. x Except for the mass ratio of high-entropy oxide to the vanadium phosphate precursor being 10:100, everything else is the same as in Example 1.

[0115] II. Comparative Example

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst. The preparation method does not include the preparation of high-entropy oxide in step (1), and step (3) is the same as in Example 1 except that the high-entropy oxide is not mixed. Instead, the vanadium-phosphorus-oxygen precursor is prepared according to step (2), followed by direct ball milling, tableting, crushing and sieving, and second calcination.

[0118] XPS results of the vanadium-phosphorus-oxygen catalyst obtained in this comparative example show that the ratio of lattice oxygen to surface oxygen is only 3.61, which is lower than that of Example 1. Its catalytic activity is far inferior to that of the (CoCrFeMnNi)O catalyst provided in Example 1. x Vanadium-phosphorus oxygen catalysts obtained from high-entropy oxides.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst. The method is the same as that in Example 1 except that step (1) is omitted in the preparation of the high-entropy oxide, and in step (2) five metal salts of the same amount as those in Example 1 are directly added to a mixture of V2O5, benzyl alcohol and isobutanol.

[0121] Comparative Example 3

[0122] This comparative example provides a method for preparing a vanadium phosphorus oxygen catalyst. The preparation method is the same as in Example 1 except that four metal salts are used as hydrogen bond donors, i.e., FeCl3·6H2O is not added, and the reduced molar amount of FeCl3·6H2O is evenly distributed to CoCl2·6H2O, CrCl3·6H2O, MnCl2·4H2O and NiCl2·6H2O.

[0123] The vanadium-phosphorus-oxygen catalyst obtained in this comparative example is doped with only metals, not high-entropy oxides.

[0124] III. Tests and Results

[0125] The vanadium-phosphorus-oxygen catalysts prepared by the methods described in the above examples and comparative examples were loaded into a fixed-bed reactor for catalytic performance evaluation. The specific test procedure is as follows: in an atmosphere containing butane / air (V / V = 1.8 / 98.2) and a space velocity of 2000 h⁻¹. -1 The reaction of n-butane oxidation to maleic anhydride was carried out at a temperature of 420℃, and the results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] As can be seen from the data in Table 1:

[0130] (1) As can be seen from Examples 1 to 5, the vanadium phosphorus oxygen catalyst obtained by combining high-entropy oxide and vanadium phosphorus oxygen precursor has high catalytic activity. When catalyzing the oxidation of n-butane to prepare maleic anhydride, the conversion rate of n-butane is improved to over 93.6%, while ensuring the selectivity and yield of maleic anhydride. The selectivity of maleic anhydride is over 62.6%, and the yield of maleic anhydride is over 61.0%.

[0131] (2) Based on the comprehensive results of Examples 1 and 6-7, it can be seen that: compared with Example 1, the hydrogen bond donor in Example 6 is ethylene glycol, and its n-butane conversion rate decreases to 92.8% and maleic anhydride yield decreases to 58.8%; the hydrogen bond donor in Example 7 is urea, and its n-butane conversion rate decreases to 93.3%. It can be seen that the present invention further preferably uses lactic acid as a hydrogen bond donor, which further improves the catalytic activity of the obtained vanadium phosphorus oxygen catalyst and improves the n-butane conversion rate.

[0132] (3) Based on the combined results of Example 1 and Example 8, it can be seen that compared with Example 1, in Example 8, FeCl3·6H2O was replaced with TiCl4, which resulted in a poor synergistic effect among the components of the high-entropy oxide, thereby reducing the catalytic activity of the obtained vanadium-phosphorus-oxygen catalyst and decreasing the conversion rate of n-butane to 95.4%.

[0133] (4) Based on the comprehensive results of Examples 1 and 9-10, it can be seen that: compared with Example 1, the first calcination temperature in step (1) of Example 9 is lower, resulting in a decrease in the conversion rate of n-butane to 94.8%; the first calcination temperature in step (1) of Example 10 is higher, resulting in a decrease in the conversion rate of n-butane to 96.1%. It can be seen that the present invention further preferably uses a first calcination temperature of 600-1000℃, which further improves the performance of the obtained high-entropy oxide, thereby further improving the catalytic activity of the obtained vanadium-phosphorus-oxygen catalyst, and ensuring low reaction energy consumption.

[0134] (5) As can be seen from the combined examples 1 and 11-12, compared with example 1, the (CoCrFeMnNi)O in step (3) of example 11 is different. x The mass ratio of the high-entropy oxide to the vanadium phosphate precursor is 0.1:100, meaning the high-entropy oxide doping amount is relatively small, resulting in a decrease in the n-butane conversion rate to 95.3%; the (CoCrFeMnNi)O in step (3) of Example 12 xThe mass ratio of high-entropy oxide to vanadium phosphate precursor is relatively high, but the improvement in catalytic performance is not significant. Therefore, the present invention further optimizes the mass ratio of high-entropy oxide to vanadium phosphate precursor to (1-3):100, which further improves the catalytic activity and selectivity of the obtained vanadium phosphate catalyst for catalyzing n-butane, and at a lower cost.

[0135] (6) Based on the comprehensive results of Example 1 and Comparative Examples 1-3, it can be seen that: since the vanadium phosphorus oxygen catalyst obtained in Comparative Example 1 was not doped with high-entropy oxides, its n-butane conversion rate was only 91.2%, maleic anhydride selectivity was only 59.4%, and maleic anhydride yield was only 54.2%; since the vanadium phosphorus oxygen catalyst obtained in Comparative Example 2 was prepared by metal salt doping of vanadium phosphorus oxygen precursor, that is, simple metal dispersion doping and not high-entropy oxide doping, its n-butane conversion rate was only 93.4%, maleic anhydride selectivity was only 59.8%, and maleic anhydride yield was only 55.9%; and in Comparative Example 3, only four metal salts were added, which resulted in the inability to form high-entropy oxides, thus causing a decrease in the catalytic performance of the obtained vanadium phosphorus oxygen catalyst. It can be seen that the present invention combines high-entropy oxides and vanadium phosphorus oxygen precursors, and the two work synergistically to improve the catalytic activity and selectivity of vanadium phosphorus oxygen catalyst.

[0136] 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 method for preparing a vanadium-phosphorus-oxygen catalyst, characterized in that, The preparation method includes the following steps: (1) At least five metal salt-based eutectic solvents are subjected to a first calcination in an oxidizing gas atmosphere to obtain high-entropy oxides; (2) The high-entropy oxide described in step (1) is mechanically mixed with the vanadium phosphorus oxygen precursor, and then subjected to a second calcination to obtain the vanadium phosphorus oxygen catalyst.

2. The preparation method according to claim 1, characterized in that, The hydrogen bond donor in the metal salt-based eutectic solvent in step (1) includes lactic acid, ethylene glycol, or uric acid, preferably lactic acid; Preferably, the hydrogen bond acceptors in the metal salt-based eutectic solvent of step (1) include at least five chloride salts of soluble metals and / or acetate salts of soluble metals; Preferably, the soluble metal includes Co, Ni, Fe, Mn, Cr, Zn, Bi, Cu, Li, Zr, U, Mg, Ce, Mo, In, Sb, Ti, La, Eu, Sm, Y, Yb or Gd, and more preferably Co, Ni, Fe, Mn, La, Cr, Zn, Bi, Cu, Zr, Mg, Ce or Eu; Preferably, the molar ratio of hydrogen bond donor to hydrogen bond acceptor in the metal salt-based eutectic solvent in step (1) is (1-3):1, more preferably (1.8-2.2):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The oxidizing gas in the oxidizing gas atmosphere of step (1) includes O2 and / or air; Preferably, the temperature of the first calcination in step (1) is 500-1000℃, more preferably 600-1000℃; Preferably, the heating rate of the first calcination in step (1) is 3-8 °C / min; Preferably, the roasting time in step (1) is 1 to 4 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The mass ratio of the high-entropy oxide to the vanadium-phosphorus-oxygen precursor in step (2) is (0.1-10):100, preferably (1-3):100; Preferably, the mechanical mixing method in step (2) includes ball milling; Preferably, the ball-to-material ratio in the ball mill is (0.5–2):1; Preferably, the rotational speed of the ball mill is 100–500 r / min; Preferably, the ball milling time is 0.2 to 20 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step (2), the second roasting temperature is 300-500℃, preferably 350-480℃; Preferably, the second roasting time in step (2) is 6 to 24 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The method for preparing the vanadium-phosphorus-oxygen precursor includes: mixing a vanadium source, benzyl alcohol, and a C3-C8 monohydric alcohol and sequentially subjecting them to a first heating and a first reflux to obtain a mixture; then mixing the mixture with a phosphorus source and sequentially subjecting them to a second heating and a second reflux to obtain a vanadium-phosphorus-oxygen precursor solution; and then obtaining the vanadium-phosphorus-oxygen precursor by solid-liquid separation and drying.

7. The preparation method according to claim 6, characterized in that, The molar ratio of vanadium in the vanadium source to phosphorus in the phosphorus source is 1:(0.8-1.5); Preferably, the volume ratio of benzyl alcohol to C3-C8 monohydric alcohol is 1:(1-25), more preferably 1:(3-9); Preferably, the C3-C8 monohydric alcohol includes any one or a combination of at least two of propanol, isobutanol, n-butanol, pentanol, hexanol, heptanol, or octanol, with isobutanol being the most preferred. Preferably, the endpoint temperature of the first heating is 120–140°C; Preferably, the first reflux time is 3 to 10 hours; Preferably, the endpoint temperature of the second heating is 120–140°C; Preferably, the second reflux time is 6 to 18 hours; Preferably, the drying temperature is 120–150°C; Preferably, the drying time is 10 to 20 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The preparation method of the vanadium-phosphorus-oxygen catalyst includes the following steps: (1) At least five metal salt-based eutectic solvents are heated to 500-1000°C for 1-4 hours in an O2 and / or air atmosphere at a heating rate of 3-8°C / min to obtain high-entropy oxides. The hydrogen bond donors in the metal salt-based eutectic solvent include lactic acid, ethylene glycol, or uric acid, and the hydrogen bond acceptors include chloride salts of at least five soluble metals and / or acetate salts of soluble metals; the soluble metals include Co, Ni, Fe, Mn, Cr, Zn, Bi, Cu, Li, Zr, U, Mg, Ce, Mo, In, Sb, Ti, La, Eu, Sm, Y, Yb, or Gd; the molar ratio of hydrogen bond donors to hydrogen bond acceptors in the metal salt-based eutectic solvent is (1–3):1; (2) The high-entropy oxide and vanadium-phosphorus-oxygen precursor described in step (1) are ball-milled at a mass ratio of (0.1-10):100 for 0.2-20 h at a ball-to-material ratio of (0.5-2):1 and a rotation speed of 100-500 r / min. The mixture is then calcined at 300-500 °C for 6-24 h to obtain the vanadium-phosphorus-oxygen catalyst. The method for preparing the high-entropy oxide includes: mixing a vanadium source, benzyl alcohol, and a C3-C8 monohydric alcohol, heating the mixture to 120-140°C, and then refluxing it for 3-10 hours to obtain a mixture; mixing the mixture with a phosphorus source, heating the mixture to 120-140°C, and then refluxing it for 6-18 hours to obtain a vanadium-phosphorus-oxygen precursor solution; performing solid-liquid separation; and then drying the solution at 120-150°C for 10-20 hours to obtain the vanadium-phosphorus-oxygen precursor; the molar ratio of vanadium in the vanadium source to phosphorus in the phosphorus source is 1:(0.8-1.5); and the volume ratio of benzyl alcohol to the C3-C8 monohydric alcohol is 1:(1-25).

9. A vanadium-phosphorus-oxygen catalyst, characterized in that, The vanadium phosphorus oxygen catalyst is prepared by the method according to any one of claims 1 to 8.

10. An application of the vanadium-phosphorus-oxygen catalyst according to claim 9, characterized in that, The vanadium-phosphorus-oxygen catalyst is used for the selective catalytic oxidation of n-butane to maleic anhydride.

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