Preparation method of vanadium-phosphorus-oxide catalyst, vanadium-phosphorus-oxide catalyst and application of vanadium-phosphorus-oxide catalyst

Abstract

The invention provides a preparation method of a vanadium-phosphorus-oxide catalyst, the vanadium-phosphorus-oxide catalyst and application of the vanadium-phosphorus-oxide catalyst, and relates to the technical field of preparation of maleic anhydride through butane oxidation. The preparation method of the vanadium phosphorus oxide catalyst comprises the following steps: mixing a pentavalent vanadium compound, a pentavalent phosphorus compound, a first cocatalyst and an organic alcohol solution, and reacting to obtain a first precursor; carrying out first-stage calcination on the first precursor in an inert atmosphere or a vacuum condition, and then carrying out second-stage calcination in an oxygen-containing atmosphere to obtain a second precursor; placing the second precursor in a solution containing a second cocatalyst, and carrying out dipping treatment to obtain a third precursor; and mixing the third precursor with a lubricant, carrying out molding treatment, and then carrying out activating treatment to obtain the vanadium phosphorus oxide catalyst. The vanadium phosphorus oxide catalyst prepared by the preparation method of the vanadium phosphorus oxide catalyst has high activity, high selectivity and good stability, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the technical field of butane oxidation to prepare maleic anhydride, and in particular to a method for preparing a vanadium phosphorus oxidase catalyst, the vanadium phosphorus oxidase catalyst and its application. Background Technology

[0002] Maleic anhydride (C4H2O3) is an important chemical intermediate among acid anhydrides, ranking third in global production after phthalic anhydride and acetic anhydride. It is a colorless crystal at room temperature with a pungent odor, readily soluble in organic solvents such as ethanol and ether, but sparingly soluble in petroleum ether and carbon tetrachloride. As a basic chemical raw material, maleic anhydride is widely used in the synthesis of... c Maleic anhydride is an important chemical containing butyrolactone (GBL), 1,4-butanediol (BDO), tetrahydrofuran (THF), and succinic acid. It is also a core raw material for the production of unsaturated polyester resins, alkyd resins, and other polymer materials, and is widely used in composite materials, coatings, and plastics industries. Furthermore, maleic anhydride has important applications in pharmaceuticals, pesticides, and food additives, and in recent years has expanded into emerging fields such as biodegradable materials, lithium battery solvents, and electronic chemicals, becoming an indispensable key raw material in the chemical industry chain.

[0003] The selective oxidation of n-butane to maleic anhydride is the only low-carbon alkane selective oxidation process to date that has achieved large-scale industrialization, with vanadium phosphorus oxide (VPO) catalyst widely recognized as the most effective catalyst in this reaction system. From a mechanistic perspective, the conversion of n-butane to maleic anhydride is a complex selective oxidation process involving the transfer of 14 electrons, including the breaking of 8 CH bonds and the insertion of 3 oxygen atoms. These steps all occur on the catalyst surface, requiring it to simultaneously possess multiple active sites, including alkane CH bond breaking, allyl CH bond breaking, and oxygen insertion, and to achieve synergistic effects among these active sites to complete the entire electron transfer process.

[0004] The final yield of maleic anhydride is highly dependent on three key catalyst performance indicators: n-butane conversion, maleic anhydride selectivity, and long-term operational stability. These properties are closely related to the synthesis method of the VPO catalyst precursor VOHPO4·0.5H2O and subsequent activation processes. It is particularly important to note that non-selective oxidation side reactions (mainly producing CO and CO2) release significantly more heat than the main reaction. If the catalyst selectivity is insufficient, it will lead to a sharp rise in local temperature within the reactor, thereby accelerating deep oxidation side reactions and creating a vicious cycle of "temperature increase - selectivity decrease." Therefore, improving catalyst selectivity is not only necessary for increasing efficiency but also a crucial prerequisite for ensuring the safe and stable operation of the reaction system.

[0005] To improve the performance of VPO catalysts, research institutions and companies at home and abroad have proposed a variety of technical solutions, but all of them have their own limitations.

[0006] CN1091998A discloses a method for increasing the specific surface area (BET>28 m²) of a catalyst by introducing co-catalysts such as bismuth, zirconium, nickel, and zinc. 2 While the method of ( / g) can enhance catalytic activity to some extent, there is no clear structure-activity relationship between the type and amount of doping elements, specific surface area and catalytic performance. As a result, catalyst design is still mainly based on experience, with insufficient predictability and controllability.

[0007] CN106622317A discloses a catalyst modification method that adjusts the vanadium valence state through organic solvent post-treatment. This method uses organic solvents with dielectric constants between 5 and 55 (such as methanol, ethanol, isobutanol, etc.) to treat VPO catalysts with specific valence states (4.10~4.40), reducing the average vanadium valence state to below 4.10. Although this method increases the maleic anhydride yield to approximately 59.4% at 85% n-butane conversion, it comes at the cost of reduced mechanical strength—the lateral compressive strength of the catalyst after organic solvent impregnation is only about 5 pounds, which is detrimental to resisting mechanical stress during industrial applications, affecting service life and operational stability.

[0008] CN111437849A discloses a method for preparing a molybdenum-modified VPO catalyst. Its key technical feature lies in strictly controlling the initial moisture content of the reaction system (≤0.2 wt%) and maintaining a closed system during the reduction process. Under these conditions, V5+ compounds are reduced to a vanadium hydroxide phosphate intermediate, which is then filtered, dried (≤350℃), and activated (>200℃) to finally obtain the catalyst. This method can achieve a selectivity of 59-66% at 85% conversion under laboratory conditions. However, its stringent requirements for moisture control make it difficult to guarantee process stability and catalyst performance reproducibility during industrial scale-up, posing a significant challenge for practical applications.

[0009] CN116020502A discloses a catalyst for selective oxidation of hydrocarbons, its preparation method, and its application. The vanadium-phosphorus oxide catalyst comprises vanadium-phosphorus oxide and optional auxiliary elements, and by weight, the catalyst comprises 5-10% carbon. This invention also discloses a method for preparing the catalyst and its application in the selective oxidation of hydrocarbons to produce acid anhydrides.

[0010] In summary, current methods for improving VPO catalysts generally suffer from problems such as limited modification techniques, unclear structure-performance correlations, or sacrificing other key properties in pursuit of a particular performance indicator. Especially in complex n-butane selective oxidation reaction systems, how to achieve improved selectivity and stability while maintaining high catalyst activity through systematic catalyst design remains an unsolved technical challenge in this field.

[0011] Therefore, addressing the aforementioned shortcomings of existing technologies, developing a novel method for preparing VPO catalysts that balances high activity, high selectivity, good stability, and suitability for industrial production has significant scientific research value and industrial application implications. An ideal solution should achieve synergistic optimization of the catalyst bulk phase and surface properties through rational structural design, thereby overcoming the performance bottlenecks of existing technologies.

[0012] In view of this, the present invention is hereby proposed. Summary of the Invention

[0013] The purpose of this invention is to provide a method for preparing a vanadium phosphorus oxycatalyst, the vanadium phosphorus oxycatalyst itself, and its applications. The method for preparing the vanadium phosphorus oxycatalyst of this invention solves the problems of functional conflict of the co-catalyst, imprecise control of the active phase structure, and difficulty in optimizing surface acidity in the preparation of traditional VPO catalysts. The resulting catalyst exhibits excellent comprehensive performance in the selective oxidation of n-butane to maleic anhydride.

[0014] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising: A pentavalent vanadium compound, a pentavalent phosphorus compound, a first co-catalyst, and an organic alcohol solution are mixed and reacted to obtain a first precursor. The first precursor is first calcined in an inert atmosphere or vacuum, and then calcined in an oxygen-containing atmosphere to obtain the second precursor. The second precursor is placed in a solution containing the second co-catalyst and impregnated to obtain the third precursor. The third precursor and lubricant are mixed, shaped, and then activated to obtain the vanadium-phosphorus-oxygen catalyst.

[0015] Furthermore, the molar ratio of P in the pentavalent phosphorus compound to V in the pentavalent vanadium compound is (1.00~1.15):1, preferably (1.05~1.10):1.

[0016] Furthermore, the pentavalent vanadium compound is selected from any one or a combination of at least two of vanadium pentoxide, ammonium metavanadate, sodium metavanadate, vanadium oxychloride, or vanadium trifluoride, preferably vanadium pentoxide.

[0017] Furthermore, the pentavalent phosphorus compound is selected from any one or a combination of at least two of orthophosphoric acid, polyphosphoric acid, ammonium orthophosphate, phosphorus pentoxide, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate, preferably orthophosphoric acid or polyphosphoric acid.

[0018] Furthermore, the orthophosphoric acid (H3PO4) is preferably anhydrous phosphoric acid or phosphoric acid with low water content, i.e., the mass fraction of phosphoric acid is 98~100%.

[0019] Furthermore, the first co-catalyst includes a first metal element M; wherein the first metal element M is selected from any one or a combination of at least two of Mo, Fe, Co, Ni, Zn, Nb or Zr, preferably Mo and / or Zn.

[0020] Furthermore, the first co-catalyst is selected from any one or a combination of at least two of the following: ammonium salt of the first metal element, nitrate of the first metal element, oxalate of the first metal element, chloride of the first metal element, or oxychloride of the first metal element.

[0021] Furthermore, the molar ratio of the first metal element M in the first co-catalyst to the V element in the pentavalent vanadium compound is (0.01~0.10):1, preferably (0.03~0.07):1.

[0022] Furthermore, the organic alcohol solution includes a reducing agent and a solvent; wherein the reducing agent is an aromatic alcohol capable of reducing pentavalent vanadium oxide to at least partially form vanadium hydroxide phosphate, preferably benzyl alcohol; and the solvent is a high-boiling-point aliphatic alcohol, preferably isobutanol.

[0023] Furthermore, in the organic alcohol solution, the molar ratio of the reducing agent to pentavalent vanadium oxide is (0.4~2.7):1, preferably (0.8~1.5):1.

[0024] Furthermore, in the organic alcohol solution, the volume of the solvent accounts for 25-90% of the total volume of the reaction system, preferably 65-85%.

[0025] Furthermore, the reaction temperature is 95~120℃, preferably 100~110℃; the reaction time is 5~18 h, preferably 8~12 h.

[0026] Furthermore, the reaction process further includes the following post-processing steps: The solid suspension obtained from the reaction was subjected to solid-liquid separation, and the separated solid was dried to obtain the first precursor.

[0027] Furthermore, the drying temperature is 80~120℃.

[0028] Furthermore, the chemical formula of the first precursor is VO(HPO4)·xH2O; where x is 0~1.

[0029] Furthermore, the average valence state of vanadium in the first precursor is +3.9 to +4.1.

[0030] Furthermore, the temperatures of the first and second calcination stages are each independently 150~350℃.

[0031] Furthermore, the inert atmosphere is selected from any one or a combination of at least two of nitrogen, argon, or helium, preferably nitrogen.

[0032] Furthermore, the calcination temperature in the first stage is 110~200℃, preferably 120~150℃; the calcination time in the first stage is 0.5~3 h.

[0033] Furthermore, in the oxygen-containing atmosphere, the volume content of oxygen accounts for 1 to 50% of the total volume content of the oxygen-containing atmosphere.

[0034] Furthermore, the calcination temperature in the second stage is 250~320℃, preferably 280~300℃; the calcination time in the first stage is 2~5 h.

[0035] Furthermore, the average valence state of vanadium in the second precursor is +3.9 to +4.0.

[0036] Furthermore, the second co-catalyst includes a second metal element M'; wherein the second metal element M' is selected from alkali metals or alkaline earth metals.

[0037] Furthermore, the second metallic element M' is selected from any one or a combination of at least two of Cs, K, Ce or La, preferably Cs and / or Ce.

[0038] Furthermore, the second co-catalyst is selected from the nitrate of a second metal element.

[0039] Furthermore, the molar ratio of the second metal element M' in the second co-catalyst and the V element in the second precursor is (0.008~0.03):1, preferably (0.01~0.02):1.

[0040] Furthermore, the impregnation treatment is either an over-impregnation method or an equal-volume impregnation method.

[0041] The concentration of the solution containing the second co-catalyst is determined based on the total pore volume of the support (equal volume impregnation) or the target M' loading (excessive impregnation).

[0042] When the excess impregnation method is used, the concentration of the solution containing the second co-catalyst is 0.01~0.10 g / mL, calculated as the second metal element M'.

[0043] When using the equal-volume impregnation method, the added volume (V) of the impregnation solution and the total pore volume (Vp) of the carrier satisfy the following: 0.9≤V / Vp≤1.1, preferably 0.95≤V / Vp≤1.05.

[0044] Furthermore, the total pore volume of the carrier is determined by water titration or low-temperature nitrogen adsorption.

[0045] Furthermore, in the impregnation process, the solvent used for impregnation is selected from water, any one or a combination of at least two of C1-C4 low-carbon alcohols, preferably deionized water or ethanol.

[0046] Furthermore, the impregnation process is an equal-volume impregnation.

[0047] Furthermore, the temperature of the impregnation treatment is 10~40℃, preferably 20~30℃; the time of the impregnation treatment is 1~24 h, preferably 2~8 h.

[0048] Furthermore, the following post-processing steps are included after the impregnation treatment is completed: The solid obtained from the impregnation process is dried to obtain the third precursor.

[0049] Furthermore, the drying temperature is 80~150℃.

[0050] Furthermore, the amount of lubricant added accounts for 2-6% of the total mass of the third precursor, preferably 3-5%.

[0051] Furthermore, the lubricant is selected from any one or a combination of at least two of starch, calcium stearate, stearic acid, or graphite, preferably graphite.

[0052] Furthermore, the molding process is a sheet forming process, and the shaped body after the molding process is a cored cylindrical shape; its outer diameter is 4~8 mm, preferably 5~6 mm; its inner diameter is 1.5~3 mm, preferably 2~2.5 mm; and its height is 3~8 mm, preferably 4~6 mm.

[0053] Furthermore, the lateral compressive strength of the molded body after molding treatment is 20 N or more, preferably 25 N or more.

[0054] Furthermore, the specific steps of the activation treatment include: The precursor after molding was subjected to a first-stage activation treatment in an inert atmosphere to obtain the first activated product. The first activated product is subjected to a second-stage activation treatment in an inert atmosphere, a mixture of air and water vapor, to obtain a second activated product. In an inert atmosphere, a mixed atmosphere of air and water vapor, first cool the second activation product to 150 - 250 °C, stop introducing water vapor and air, and continue to cool to below room temperature under the inert atmosphere to obtain the vanadium phosphorus oxygen catalyst.

[0055] Further, the heating rate of the first-stage activation treatment is 1 - 15 °C / min, preferably 2 - 10 °C / min; the temperature of the first-stage activation treatment is 200 - 330 °C, preferably 280 - 320 °C; the time of the first-stage activation treatment is 0.5 - 5 h, preferably 2 - 4 h.

[0056] Further, the heating rate of the second-stage activation treatment is 1 - 10 °C / min, preferably 3 - 6 °C / min; the temperature of the second-stage activation treatment is 380 - 450 °C, preferably 390 - 460 °C; the time of the second-stage activation treatment is 4 - 10 h, preferably 5 - 7 h.

[0057] Further, based on the total volume content of the mixed atmosphere being 100%, the mixed atmosphere includes 1 - 21% oxygen, 5 - 40% water vapor by volume percentage, and the balance is nitrogen.

[0058] Further, the temperature at which the introduction of water vapor and air is stopped is 180 - 220 °C, preferably 190 - 210 °C.

[0059] In a second aspect, the present invention provides a vanadium phosphorus oxygen catalyst, which is prepared by the preparation method of the vanadium phosphorus oxygen catalyst as described in the first aspect.

[0060] Further, the average valence state of vanadium in the vanadium phosphorus oxygen catalyst is +4.0 - +4.2.

[0061] Further, the bulk density of the vanadium phosphorus oxygen catalyst is 0.7 - 1.2 g / mL.

[0062] In a third aspect, the present invention provides an application of the vanadium phosphorus oxygen catalyst prepared by the preparation method as described in the first aspect, or the vanadium phosphorus oxygen catalyst as described in the second aspect, as a catalyst for the oxidation of butane to prepare maleic anhydride.

[0063] In a fourth aspect, the present invention provides a method for the selective oxidation of n-butane to prepare maleic anhydride, the method comprising: Reacting n-butane with an oxygen-containing gas in the presence of a catalyst to obtain maleic anhydride; wherein the catalyst comprises the vanadium phosphorus oxygen catalyst prepared by the preparation method as described in the first aspect, or the vanadium phosphorus oxygen catalyst as described in the second aspect.

[0064] Compared with the prior art, the present invention has the following beneficial effects: (1) Synergistic optimization and significant improvement of catalytic performance: The preparation method of the vanadium phosphorus oxygen catalyst of the present invention adopts a "step-by-step doping" strategy. First, a first co-catalyst is introduced in the catalyst precursor synthesis stage so that it can be embedded in the VOP lattice, effectively stabilizing the main active phase - vanadium pyrophosphate ((VO)2P2O7), optimizing the bulk structure and lattice oxygen activity of the catalyst, and laying the foundation for achieving high conversion rate. Subsequently, a second co-catalyst is introduced on the calcined support by impregnation method so that it is highly dispersed on the catalyst surface, accurately neutralizing harmful strong acid sites, effectively inhibiting the deep oxidation side reaction of maleic anhydride, thereby greatly improving the selectivity of the reaction.

[0065] (2) Fine control of catalyst microstructure and macroscopic properties: The preparation method of the vanadium phosphorus oxygen catalyst of the present invention adopts the "segmented calcination" process; first, it is treated at a low temperature (above the boiling point of the solvent) in an inert atmosphere to gently remove residual solvent and water and avoid collapse of the pore structure; then, the crystal phase transformation is completed at a higher temperature in an oxygen-containing atmosphere; this process helps to form a more developed and suitable pore structure and promotes the diffusion of reactants and products.

[0066] (3) The catalyst exhibits excellent stability and extends its service life: The preparation method of the vanadium-phosphorus-oxygen catalyst described in this invention employs a unique "ternary atmosphere (nitrogen, air, and water vapor) programmed temperature activation" method; this method ensures that the VPO precursor can be completely and stably converted into a state with ideal crystal form and valence (V) by strictly controlling the proportion and presence of the three atmospheres during the critical activation stage (>380℃) and setting specific heating / cooling programs and key water shut-off temperature points (150~250℃). 4+ The catalyst consists of an active phase (primarily composed of active phases) and surface-active phases. While achieving high activity, the catalyst also possesses excellent stability, extending its service life. Detailed Implementation

[0067] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0068] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] In a first aspect, the present invention provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising: (1) A pentavalent vanadium compound, a pentavalent phosphorus compound, a first co-catalyst and an organic alcohol solution are mixed and reacted to obtain a first precursor; (2) The first precursor is first calcined in an inert atmosphere or vacuum, and then calcined in an oxygen-containing atmosphere to obtain the second precursor. (3) The second precursor is placed in a solution containing the second co-catalyst and impregnated to obtain the third precursor; (4) The third precursor and lubricant are mixed, molded, and then activated to obtain the vanadium phosphorus oxygen catalyst.

[0070] This invention provides a design concept and preparation method for a high-performance vanadium pyrophosphate (VPO) catalyst for the selective oxidation of n-butane to maleic anhydride. The advancement of this invention lies in the fact that it is not a simple improvement on existing technologies, but rather a synergistic preparation technology that integrates "stepwise doping," "segmented calcination," and "programmed activation" based on a systematic approach to catalyst material design. This preparation technology separates the "bulk phase modification" and "surface modification" of the co-catalyst in terms of process time and space, solving the long-standing problem of functional synergy in VPO catalyst development. At the same time, through the precise design of the heat treatment path, it achieves cross-scale precise control of the catalyst from microscopic crystal structure to macroscopic channels and surface properties.

[0071] It should be noted that in the preparation method of the vanadium-phosphorus-oxygen catalyst of the present invention, the first and second metal source co-catalysts are added in a stepwise manner: Step 1 (lattice doping): During the synthesis of the VPO precursor, a metal source with a radius similar to V is introduced. 4+ The first co-catalyst, which is close to the VPO crystal lattice, allows it to enter the VPO crystal lattice; the first promoter (within the lattice): added during the synthesis of the active phase (VO)₂P₂O₇, due to its ionic radius being similar to that of VPO. 4+In close proximity, it can replace some vanadium sites, stabilizing the crystal structure of VPO. This effectively prevents phase transformation of the active phase (VO)₂P₂O₇ or excessive oxidation of vanadium species during the reaction, thus significantly improving the structural stability and lifetime of the catalyst. Subsequently, in the third step (surface modification): after the precursor is formed, a second co-catalyst is introduced by post-impregnation; the second aid (surface): added after calcination, after forming a stable framework, the main function of the second co-catalyst is to neutralize the strong acid sites on the catalyst surface. These strong acid sites lead to the deep oxidation of butane and maleic anhydride (generating CO). x The culprit is maleic anhydride; by loading it onto the catalyst surface through post-impregnation, these strong acid sites can be precisely poisoned without excessively affecting the desired weak acid sites and redox sites, thereby significantly improving the selectivity of maleic anhydride.

[0072] As an optional implementation, the molar ratio of phosphorus (P) in the pentavalent phosphorus compound to vanadium (V) in the pentavalent vanadium compound is (1.00~1.15):1, for example, it can be 1.00:1, 1.02:1, 1.04:1, 1.05:1, 1.06:1, 1.08:1, 1.10:1, 1.12:1, 1.14:1, 1.15:1, etc. (hereinafter referred to as phosphorus / vanadium atomic ratio or P / V atomic ratio).

[0073] In a preferred embodiment, the molar ratio of phosphorus (P) in the pentavalent phosphorus compound to vanadium (V) in the pentavalent vanadium compound is (1.05~1.10):1.

[0074] As an optional implementation, the pentavalent vanadium compound is selected from any one or a combination of at least two of vanadium pentoxide, ammonium metavanadate, sodium metavanadate, vanadium oxychloride, or vanadium trifluoride, preferably vanadium pentoxide.

[0075] In a preferred embodiment, the pentavalent vanadium compound is vanadium pentoxide.

[0076] As an optional implementation, the pentavalent phosphorus compound is selected from any one or a combination of at least two of orthophosphoric acid, polyphosphoric acid, ammonium orthophosphate, phosphorus pentoxide, ammonium dihydrogen phosphate or diammonium hydrogen phosphate, preferably orthophosphoric acid or polyphosphoric acid.

[0077] As an optional implementation, the orthophosphoric acid (H3PO4) is preferably anhydrous phosphoric acid or phosphoric acid with low water content, i.e., the mass fraction of phosphoric acid is 98~100%.

[0078] In a preferred embodiment, the pentavalent phosphorus compound is phosphoric acid.

[0079] As an optional implementation, the first co-catalyst includes a first metal element M; wherein the first metal element M is selected from any one or a combination of at least two of Mo, Fe, Co, Ni, Zn, Nb or Zr.

[0080] In a preferred embodiment, the first co-catalyst includes a first metal element M; wherein the first metal element M is Mo and / or Zn.

[0081] It should be noted that these first metallic elements are usually similar to vanadium in ionic radius or valence state, and can enter the VOP lattice to stabilize the active structure or change the electronic environment.

[0082] As an optional implementation, the first co-catalyst is selected from any one or a combination of at least two of the following: ammonium salt of the first metal element, nitrate of the first metal element, oxalate of the first metal element, chloride of the first metal element, or oxychloride of the first metal element.

[0083] As an optional implementation, the molar ratio of the first metal element M in the first co-catalyst to the V element in the pentavalent vanadium compound is (0.01~0.10):1, for example, it can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, etc. (hereinafter referred to as the first metal element / vanadium atomic ratio, or M / V atomic ratio).

[0084] In a preferred embodiment, the molar ratio of the first metal element M in the first co-catalyst to the V element in the pentavalent vanadium compound is (0.03~0.07):1.

[0085] As an optional embodiment, the organic alcohol solution includes a reducing agent and a solvent; wherein the reducing agent is an aromatic alcohol capable of reducing pentavalent vanadium oxide to at least partially form vanadium hydroxide phosphate; and the solvent is a high-boiling-point aliphatic alcohol.

[0086] In a preferred embodiment, the organic alcohol solution includes a reducing agent and a solvent; wherein the reducing agent is benzyl alcohol and the solvent is isobutanol.

[0087] As an optional implementation, in the organic alcohol solution, the molar ratio of the reducing agent to pentavalent vanadium oxide is (0.4~2.7):1, for example, it can be 0.4:1, 0.6:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.7:1, etc.

[0088] In a preferred embodiment, the molar ratio of the reducing agent to pentavalent vanadium oxide in the organic alcohol solution is (0.8~1.5):1.

[0089] As an optional implementation, in the organic alcohol solution, the volume of the solvent accounts for 25-90% of the total volume of the reaction system, for example, it can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0090] In a preferred embodiment, the volume of the solvent in the organic alcohol solution accounts for 65-85% of the total volume of the reaction system.

[0091] As an optional implementation, in step (1), the reaction is carried out under reflux conditions; that is, the pentavalent vanadium compound is reduced under reflux conditions to generate vanadium hydroxide hydrate containing the first co-catalyst, forming a blue solid suspension.

[0092] As an optional implementation, in step (1), the reaction temperature is 95~120℃, for example, it can be 95℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃; the reaction time is 5~18 h, for example, it can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, etc.

[0093] In a preferred embodiment, in step (1), the reaction temperature is 100~110℃ and the reaction time is 8~12 h.

[0094] As an optional implementation, step (1) further includes the following post-processing steps after the reaction is completed: The solid suspension obtained from the reaction was subjected to solid-liquid separation, and the separated solid was dried to obtain the first precursor.

[0095] As an optional implementation, in step (1), the drying temperature in the post-processing after the reaction is completed is 80~120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.

[0096] As an optional implementation, in step (1), the drying temperature in the post-processing after the reaction is completed is 2 to 10 degrees lower than the reaction temperature, for example, it can be 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, 10 degrees, etc.

[0097] As an optional implementation, the chemical formula of the first precursor is VO(HPO4)·xH2O; where x is 0~1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc.

[0098] As an optional implementation, the average valence state of vanadium in the first precursor is +3.9 to +4.1, for example, it can be +3.90, +3.92, +3.94, +3.96, +3.98, +4.00, +4.02, +4.04, +4.06, +4.08, or +4.10.

[0099] As an optional implementation, in step (2), the temperatures of the first stage calcination and the second stage calcination are each independently 150~350℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, etc.

[0100] As an optional implementation, step (2) specifically includes the following steps: Under inert atmosphere or vacuum conditions, the first precursor is heated to a first temperature and held for a first period of time for a first stage of calcination; wherein the first temperature is greater than the boiling point of the organic alcohol solution; subsequently, under an oxygen-containing atmosphere, the material is heated to a second temperature and held for a second period of time for a second stage of calcination, and the calcination is completed to obtain the second precursor.

[0101] As an optional implementation, in step (2), the inert atmosphere is selected from any one or a combination of at least two of nitrogen, argon or helium.

[0102] In a preferred embodiment, the inert atmosphere in step (2) is nitrogen.

[0103] As an optional implementation, in step (2), the calcination temperature of the first stage is 110~200℃, for example, it can be 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, etc.; the calcination time of the first stage is 0.5~3 h, for example, it can be 0.5 h, 0.6 h, 0.8 h, 1.0 h, 1.2 h, 1.4 h, 1.5 h, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h, 2.5 h, 2.6 h, 2.8 h, 3.0 h, etc.

[0104] In a preferred embodiment, in step (2), the calcination temperature of the first stage is 120~150℃.

[0105] As an optional implementation, in step (2), the volume content of oxygen in the oxygen-containing atmosphere is 1% to 50% of the total volume content of the oxygen-containing atmosphere, for example, it can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0106] As an optional implementation, in step (2), the oxygen-containing atmosphere is air.

[0107] As an optional implementation, in step (2), the oxygen-containing atmosphere is a mixture of oxygen and an inert atmosphere.

[0108] As an optional implementation, in step (2), the calcination temperature of the second stage is 250~320℃, for example, it can be 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, 290℃, 295℃, 300℃, 305℃, 310℃, 315℃, 320℃, etc.; the calcination time of the first stage is 2~5 h, for example, it can be 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5 h, etc.

[0109] In a preferred embodiment, in step (2), the calcination temperature of the second stage is 280~300℃.

[0110] As an optional implementation, the average valence state of vanadium in the second precursor is +3.9 to +4.0, for example, it can be +3.90, +3.91, +3.92, +3.93, +3.94, +3.95, +3.96, +3.97, +3.98, +3.99, +4.00, etc.

[0111] As an optional embodiment, the second co-catalyst includes a second metal element M'; wherein the second metal element M' is selected from alkali metals or alkaline earth metals.

[0112] As an optional implementation, the second metallic element M' is selected from any one or a combination of at least two of Cs, K, Ce or La.

[0113] In a preferred embodiment, the second metallic element M' is Cs and / or Ce.

[0114] It should be noted that the second co-catalyst includes a second metal element M', which is mainly used to adjust the acidity or alkalinity of the catalyst surface.

[0115] As an optional implementation, the second co-catalyst is selected from the nitrate of a second metal element.

[0116] As an optional implementation, the molar ratio of the second metal element M' in the second co-catalyst and the V element in the second precursor is (0.008~0.03):1, for example, it can be 0.008:1, 0.01:1, 0.012:1, 0.014:1, 0.016:1, 0.018:1, 0.02:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1, 0.03:1, etc. (hereinafter referred to as the atomic ratio of the second metal element M' / vanadium or the atomic ratio of M' / V).

[0117] In a preferred embodiment, the molar ratio of the second metal element M' in the second co-catalyst and the V element in the second precursor is (0.01~0.02):1.

[0118] As an optional implementation, in step (3), the impregnation treatment is either an over-impregnation method or an equal-volume impregnation method; wherein, the concentration of the solution containing the second co-catalyst is determined based on the total pore volume of the carrier (equal-volume impregnation) or the target M' loading (over-impregnation).

[0119] As an optional implementation, when the excess impregnation method is used, the concentration of the solution containing the second co-catalyst is 0.01~0.10 g / mL, calculated as the second metal element M'.

[0120] As an optional implementation, when using the equal volume impregnation method, the added volume (V) of the impregnation liquid and the total pore volume (Vp) of the carrier satisfy: 0.9≤V / Vp≤1.1, preferably 0.95≤V / Vp≤1.05.

[0121] As an optional implementation, the total pore volume of the carrier is determined by water titration or low-temperature nitrogen adsorption.

[0122] As an optional implementation, in the impregnation process, the solvent used for impregnation is selected from water, any one of C1 to C4 low alcohols, or a combination of at least two of them.

[0123] In a preferred embodiment, the solvent used in the impregnation process is water and / or ethanol.

[0124] In a preferred embodiment, in step (3), the impregnation process is an equal-volume impregnation.

[0125] As an optional implementation, in step (3), the temperature of the impregnation treatment is 10~40℃, for example, it can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, etc.; the time of the impregnation treatment is 1~24 h, for example, it can be 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, etc.

[0126] In a preferred embodiment, in step (3), the temperature of the immersion treatment is 20~30℃; and the time of the immersion treatment is 2~8 h.

[0127] As an optional implementation, step (3) further includes the following post-processing steps after the impregnation treatment is completed: The solid obtained from the impregnation process is dried to obtain the third precursor.

[0128] As an optional implementation, in step (3), the drying temperature in the post-treatment after the impregnation treatment is 80~150℃, for example, it can be 80℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc.

[0129] As an optional implementation, the amount of lubricant added accounts for 2 to 6% of the total mass of the third precursor, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0130] As an optional implementation, the amount of lubricant added accounts for 3 to 5% of the total mass of the third precursor.

[0131] As an optional implementation, the lubricant is selected from any one or a combination of at least two of starch, calcium stearate, stearic acid, or graphite.

[0132] In a preferred embodiment, the lubricant is graphite.

[0133] As an optional implementation, in step (4), the molding process is tableting.

[0134] As an optional implementation, in step (4), the shaped body after the molding process is a cored cylindrical shape.

[0135] As an optional implementation, in step (4), the outer diameter of the molded body after the molding process is 4~8 mm, for example, it can be 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, etc.; the inner diameter is 1.5~3 mm, for example, it can be 1.5 mm, 1.75 mm, 2 mm, 2.25 mm, 2.5 mm, 2.75 mm, 3 mm, etc.; the height is 3~8 mm, for example, it can be 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, etc.

[0136] In a preferred embodiment, in step (4), the outer diameter of the molded body after the molding process is 5~6 mm; the inner diameter is 2~2.5 mm; and the height is 4~6 mm.

[0137] As an optional implementation, in step (4), the lateral compressive strength of the molded body after molding treatment is 20 N or more, for example, it can be 20 N, 21 N, 22 N, 23 N, 24 N, 25 N, 26 N, 27 N, 28 N, 29 N, 30 N, etc.

[0138] As an optional implementation, in step (4), the lateral compressive strength of the molded body after molding treatment is 25N or more.

[0139] As an optional implementation, step (4) includes the following specific steps in the activation process: The precursor after molding was subjected to a first-stage activation treatment in an inert atmosphere to obtain the first activated product. The first activated product is subjected to a second-stage activation treatment in an inert atmosphere, a mixture of air and water vapor, to obtain a second activated product. In an inert atmosphere, a mixture of air and water vapor, the second activated product is first cooled to 150-250°C, the introduction of water vapor and air is stopped, and the temperature is further reduced to below room temperature under an inert atmosphere to obtain the vanadium-phosphorus-oxygen catalyst.

[0140] In a preferred embodiment, step (4) includes the following specific steps of the activation treatment: Under an inert atmosphere, the precursor after molding is heated from room temperature to the first activation temperature and then subjected to the first isothermal activation treatment. The atmosphere is switched to a mixed atmosphere containing inert atmosphere, air and water vapor, and the temperature is programmed to rise to a second activation treatment temperature of 380~450℃, and a second isothermal activation treatment is performed; wherein the second isothermal treatment time is 2~10h. After the second isothermal activation treatment is completed, when the temperature is cooled to 150~250℃, the introduction of water vapor and air is stopped, the inert atmosphere is switched back, and the temperature is further cooled to below room temperature to obtain the vanadium phosphorus oxygen catalyst.

[0141] As an optional implementation, in step (4), the heating rate of the first stage activation treatment is 1~15℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, etc.; the temperature of the first stage activation treatment is 200~330℃, for example, it can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, etc.; the time of the first stage activation treatment is 0.5~5 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc. h, 4.5 h, 5 h, etc.

[0142] In a preferred embodiment, in step (4), the heating rate of the first stage activation treatment is 2~10℃ / min; the temperature of the first stage activation treatment is 280~320℃; and the time of the first stage activation treatment is 2~4h.

[0143] As an optional implementation, in step (4), the heating rate of the second stage activation treatment is 1~10℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.; the temperature of the second stage activation treatment is 380~450℃, for example, it can be 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc.; the time of the second stage activation treatment is 4~10h, for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, etc.

[0144] In a preferred embodiment, in step (4), the heating rate of the second stage activation treatment is 1~10℃ / min, preferably 3~6℃ / min; the temperature of the second stage activation treatment is 380~450℃, preferably 390~460℃; and the time of the second stage activation treatment is 4~10 h, preferably 5~7 h.

[0145] As an optional implementation, in step (4), during the second stage activation treatment, the total volume content of the mixed atmosphere is 100%, and the mixed atmosphere includes, by volume percentage: oxygen 1~21% (for example, it can be 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, etc.), water vapor 5~40% (for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.), and the balance is nitrogen.

[0146] As a preferred embodiment, in step (4), in the second stage of activation treatment, the total volume content of the mixed atmosphere is 100%, and the mixed atmosphere includes, by volume percentage: 5-15% oxygen, 15-30% water vapor, and the remainder is nitrogen.

[0147] As an optional implementation, in step (4), the temperature at which the water vapor and air are stopped is 180~220℃, for example, it can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.

[0148] In a preferred embodiment, in step (4), the temperature at which the steam and air are stopped is 190~210°C.

[0149] In a second aspect, the present invention provides a vanadium-phosphorus-oxygen catalyst, which is prepared by the method for preparing vanadium-phosphorus-oxygen catalyst as described in the first aspect.

[0150] As an optional implementation, the average valence state of vanadium in the vanadium-phosphorus-oxygen catalyst is +4.0 to +4.2, for example, it can be +4.0, +4.02, +4.04, +4.06, +4.08, +4.1, +4.12, +4.14, +4.16, +4.18, +4.2, etc.

[0151] As an optional embodiment, the bulk density of the vanadium-phosphorus-oxygen catalyst is 0.7~1.2 g / mL, for example, it can be 0.7 g / mL, 0.75 g / mL, 0.8 g / mL, 0.85 g / mL, 0.9 g / mL, 0.95 g / mL, 1.0 g / mL, 1.05 g / mL, 1.1 g / mL, 1.15 g / mL, 1.2 g / mL, etc.

[0152] Thirdly, the present invention provides a vanadium-phosphorus-oxygen catalyst prepared according to the preparation method described in the first aspect, or the vanadium-phosphorus-oxygen catalyst described in the second aspect, used as a catalyst for the oxidation of butane to prepare maleic anhydride.

[0153] Fourthly, the present invention provides a method for the selective oxidation of n-butane to prepare maleic anhydride, the method comprising: In the presence of a catalyst, n-butane is reacted with an oxygen-containing gas to yield maleic anhydride. The catalyst includes a vanadium-phosphorus-oxygen catalyst prepared by the preparation method described in the first aspect, or a vanadium-phosphorus-oxygen catalyst as described in the second aspect.

[0154] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0155] Example 1 This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Mo-Cs system. The method specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g of vanadium pentoxide (V2O5, 0.2 mol) and 49.95 g of 85% phosphoric acid (H3PO4) to a three-necked flask equipped with a reflux condenser to make the P / V atomic ratio = 1.08; add a mixed solvent of 400 mL isobutanol and 100 mL benzyl alcohol as the reaction medium and reducing agent; then add 3.4 g of ammonium dimolybdate ((NH4)2Mo2O7) to make the Mo / V atomic ratio = 0.05 to obtain a mixture; (a-2) The mixture was heated to 105°C in an oil bath and stirred under reflux for 10 h to obtain a blue suspension of molybdenum-containing vanadium hydroxide phosphate hydrate. (a-3) After the reaction was completed, the solid was filtered while hot and washed three times with isobutanol. The filter cake was dried in an oven at 100℃ for 12 h to obtain the blue first precursor. The chemical formula of the first precursor is VO(HPO4)·xH2O, where x is 1 / 2. Chemical analysis showed that the average valence of vanadium was +4.02.

[0156] (b) Preparation of the second precursor: The first precursor obtained in step (a) was placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under a nitrogen atmosphere (100 mL / min), the temperature was increased to 130°C at 5°C / min and calcined at a constant temperature for 1 h; then, the temperature was switched to an air atmosphere (50 mL / min) and a nitrogen atmosphere (50 mL / min), and the temperature was increased to 290°C at 2°C / min and calcined at a constant temperature for 3 h to obtain a dark green second precursor with an average vanadium valence of +3.98.

[0157] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with an aqueous solution containing 1.17 g of cesium nitrate (CsNO3) using an equal-volume impregnation method, so that the Cs / V atomic ratio was 0.015. After standing at room temperature for 4 h, it was dried at 120 °C for 6 h to obtain the third precursor.

[0158] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is mixed evenly with 4 wt% graphite powder and compressed into a cored cylindrical tablet with an outer diameter of 5.5 mm, an inner diameter of 2.2 mm and a height of 5.0 mm on a tablet press under a pressure of 250 MPa. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (200 mL / min), the temperature is increased from room temperature to 300℃ at 3℃ / min and activated at a constant temperature for 3 h; then, the temperature is switched to a mixed gas (oxygen content ~10%, water vapor content ~25%) consisting of N2 (86 mL / min), air (150 mL / min, providing oxygen) and water vapor (approximately 25 vol%) introduced by a steam generator, and the temperature is increased to 400℃ at 4℃ / min and activated at a constant temperature for 6 h; finally, when the temperature is reduced to 200℃, the air and water vapor are stopped, and the temperature is switched to pure N2 for purging and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.12; bulk density 0.80 g / mL; lateral crushing strength 31 N.

[0159] Example 2 This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Zn-Ce system. The method for preparing the vanadium-phosphorus-oxygen catalyst based on the Zn-Ce system specifically includes the following steps: (a) Preparation of the first precursor: (a-1) A mixture of 36.5 g V2O5, 50.88 g 85% H3PO4 (P / V=1.10), 450 mL isobutanol and 50 mL benzyl alcohol was used as solvent; then, 7.16 g zinc nitrate (Zn(NO3)2·6H2O) was added to make the Zn / V atomic ratio = 0.06, and a mixture was obtained. (a-2) The reaction was refluxed and stirred at 103 °C for 9 h to obtain a molybdenum-containing vanadium hydroxide hydrate suspension; (a-3) After the reaction is complete, the solid is filtered and dried at 100°C to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence is +4.05.

[0160] (b) Preparation of the second precursor: The first precursor obtained in step (a) was placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under N2 atmosphere (120 mL / min), the temperature was increased to 140℃ at 5℃ / min and calcined at a constant temperature for 1.5 h; then, the temperature was switched to air atmosphere (120 mL / min) and increased to 285℃ at 5℃ / min and calcined at a constant temperature for 4 h to obtain the second precursor; its vanadium average valence state is +3.99.

[0161] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with an aqueous solution containing 2.09 g of cerium nitrate (Ce(NO3)3·6H2O) using the equal volume impregnation method, so that the Ce / V atomic ratio was 0.012. The impregnation was carried out at 25°C for 3 h and then dried at 120°C for 12 h to obtain the third precursor.

[0162] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is added to 3.5 wt% graphite, mixed evenly, and compressed into a cored cylindrical tablet with an outer diameter of 5.0 mm, an inner diameter of 2.0 mm, and a height of 4.5 mm on a tablet press under a pressure of 250 MPa. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (85 mL / min), the temperature is increased from room temperature to 310℃ at 5℃ / min and activated at a constant temperature for 3 h; then, the temperature is switched to a mixture of N2 (85 mL / min), air (88 mL / min, providing oxygen), and water vapor introduced by a steam generator (oxygen content ~8%, water vapor content ~25%), and the temperature is increased to 410℃ at 5℃ / min and activated at a constant temperature for 5 h; finally, when the temperature is cooled to 195℃, the air and water vapor are stopped, and the temperature is switched to pure N2 purging and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.15; bulk density 0.78 g / mL; lateral crushing strength 26 N.

[0163] Example 3 This embodiment provides a method for preparing a vanadium phosphorus oxygen catalyst based on a Zn / Mo-Cs system. The method for preparing the vanadium phosphorus oxygen catalyst based on a Zn / Mo-Cs system specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g V2O5, 50.42 g 85% H3PO4 (P / V atomic ratio of 1.09), and 500 mL isobutanol to the reactor; then add 2.05 g ammonium dimolybdate ((NH4)2Mo2O7) and 3.58 g zinc nitrate (Zn(NO3)2·6H2O) (Mo:Zn=1:1, total M / V atomic ratio of 0.06) to obtain a mixture; (a-2) The reaction was refluxed and stirred at 102 °C for 11 h to obtain a suspension of vanadium hydroxide hydrate containing molybdenum and zinc; (a-3) After the reaction is complete, the solid is filtered and dried at 95°C to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence state is +3.98.

[0164] (b) Preparation of the second precursor: The first precursor obtained in step (a) is placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under vacuum conditions, the temperature is increased to 125°C at 5°C / min and calcined at a constant temperature for 2 h; then, under diluted air with an oxygen content of 5%, the temperature is increased to 295°C at 5°C / min and calcined at a constant temperature for 2.5 h to obtain the second precursor; its vanadium average valence state is +3.99.

[0165] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with an aqueous solution containing 1.41 g of cesium nitrate (CsNO3) using an equal-volume impregnation method (to make the Cs / V atomic ratio = 0.018), impregnated at 25°C for 6 h, and dried at 120°C for 12 h to obtain the third precursor.

[0166] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is added to 4.5 wt% graphite, mixed evenly, and compressed into a cored cylindrical tablet with an outer diameter of 6.0 mm, an inner diameter of 2.5 mm, and a height of 5.5 mm on a tablet press at a pressure of 240 MPa; the lateral strength is 30 N. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (100 mL / min), the temperature is increased from room temperature to 290℃ at 3℃ / min and activated at a constant temperature for 3 h; then, the temperature is switched to a mixed gas consisting of N2 (50 mL / min), air (115 mL / min, providing oxygen), and water vapor introduced by a steam generator (oxygen content ~12%, water vapor content ~18%), and the temperature is increased to 390℃ at 4℃ / min and activated at a constant temperature for 7 h; finally, when the temperature is cooled to 205℃, the air and water vapor are stopped, and the temperature is switched to pure N2 purging and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.05; bulk density 1.00 g / mL; lateral crushing strength 35 N.

[0167] Example 4 This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Nb-K system. The method for preparing the vanadium-phosphorus-oxygen catalyst based on the Nb-K system specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g V2O5, 48.56 g 85% H3PO4 (P / V=1.05), and 500 mL isobutanol to the reactor; then add 1.12 g niobium oxalate (Nb2O5·xH2C2O4, calculated as Nb) to make the Nb / V atomic ratio = 0.03, and obtain a mixture; (a-2) The reaction was refluxed and stirred at 110℃ for 8 h to obtain a niobium-containing vanadium hydroxide hydrate suspension; (a-3) After the reaction is complete, the solid is filtered and dried at 105°C to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence is +4.02.

[0168] (b) Preparation of the second precursor: The first precursor obtained in step (a) was placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under N2 atmosphere (120 mL / min), the temperature was increased to 150°C at 3°C / min and calcined at a constant temperature for 0.5 h; then, the temperature was switched to diluted air with an oxygen content of 20% (120 mL / min), and the temperature was increased to 300°C at 3°C / min and calcined at a constant temperature for 5 h to obtain the second precursor; its vanadium average valence state is +3.97.

[0169] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with an aqueous solution containing 0.41 g of potassium nitrate (KNO3) using the equal volume impregnation method, so that the K / V atomic ratio was 0.01. The impregnation was carried out at 25°C for 2 h and then dried at 110°C for 12 h to obtain the third precursor.

[0170] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is added to 3 wt% calcium stearate, mixed evenly, and compressed into a cored cylindrical tablet with an outer diameter of 5.2 mm, an inner diameter of 2.3 mm, and a height of 4.0 mm on a tablet press at a pressure of 250 MPa. The lateral strength of the tablet is 27 N. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for activation by heating: the specific procedure for the activation by heating is as follows: First, the temperature was increased from room temperature to 320℃ at 10℃ / min under N2 (200 mL / min) and held at this temperature for 3 h. Then, the temperature was switched to a mixture of N2 (0 mL / min), air (200 mL / min, providing oxygen), and water vapor introduced from a steam generator (oxygen content ~14.7%, water vapor content ~30%), and the temperature was increased to 450℃ at 6℃ / min and held at this temperature for 5 h. Finally, when the temperature was cooled to 190℃, the air and water vapor were stopped, and the temperature was switched to pure N2 for purging. The temperature was then cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.20; bulk density 1.10 g / mL; lateral crushing strength 27 N.

[0171] Example 5 This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Fe-La system. The method specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g V2O5, 48.11 g 85% H3PO4 (P / V atomic ratio of 1.04), and 600 mL n-butanol to the reactor; then add 3.23 g ferric nitrate nonahydrate (Fe(NO3)3·9H3O) to make the Fe / V atomic ratio = 0.02, and obtain a mixture; (a-2) The reaction was refluxed and stirred at 118℃ for 15 h to obtain an iron-containing vanadium hydroxide hydrate suspension; (a-3) After the reaction is complete, the solid is filtered and dried at 90°C to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence is +3.92.

[0172] (b) Preparation of the second precursor: The first precursor obtained in step (a) was placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under N2 atmosphere (120 mL / min), the temperature was increased to 117°C at 3°C / min and calcined at a constant temperature for 2.5 h; then, the temperature was switched to air atmosphere (120 mL / min) and increased to 270°C at 4°C / min and calcined at a constant temperature for 4 h to obtain the second precursor; its vanadium average valence state is +3.93.

[0173] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with an aqueous solution containing 1.56 g of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) using the equal volume impregnation method, so that the La / V atomic ratio was 0.009. The impregnation was carried out at 20°C for 20 h and then dried at 105°C for 10 h to obtain the third precursor.

[0174] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is added to 2 wt% starch, mixed evenly, and compressed into a cored cylindrical tablet with an outer diameter of 5.9 mm, an inner diameter of 2.8 mm, and a height of 5.0 mm on a tablet press under a pressure of 250 MPa; the lateral strength of the tablet is 22 N. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (200 mL / min), the temperature is increased from room temperature to 250℃ at 1℃ / min and activated at a constant temperature for 4 h; then, the temperature is switched to a mixed gas consisting of N2 (100 mL / min), air (12 mL / min, providing oxygen), and water vapor introduced by a steam generator (oxygen content ~2%, water vapor content ~10%), and the temperature is increased to 395℃ at 2℃ / min and held at a constant temperature for 8 h; finally, when the temperature is cooled to 170℃, the air and water vapor are stopped, and pure N2 is used for purging. The temperature is then cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.00; bulk density 1.00 g / mL; lateral crushing strength 22 N.

[0175] Example 6 This embodiment provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Zr-K system. The specific method for preparing the vanadium-phosphorus-oxygen catalyst based on the Nb-K system includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g V2O5, 486.26 g 85% H3PO4 (P / V=1.00), 550 mL benzyl alcohol, and 55 mL n-butanol to the reactor; then add 1.29 g zirconium oxychloride (ZrOCl2·8H2O) to make the Zr / V atomic ratio = 0.01, and obtain a mixture; (a-2) The mixture was heated to 116°C in an oil bath and stirred under reflux for 18 h to obtain a zirconium-containing vanadium hydroxide hydrate suspension. (a-3) After the reaction is complete, filter while hot, wash with benzyl alcohol, and dry the filter cake in an oven at 110℃ for 12 h to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence state is +3.90.

[0176] (b) Preparation of the second precursor: The first precursor obtained in step (a) is placed in a tube furnace for segmented calcination. The specific procedure for segmented calcination is as follows: under vacuum conditions, the temperature is increased to 200°C at 5°C / min and calcined at a constant temperature for 3 h; then, the temperature is switched to 50% diluted air (a mixture of pure oxygen and pure nitrogen at a flow rate of 50 mL / min) and increased to 320°C at 5°C / min, and calcined at a constant temperature for 5 h to obtain the second precursor; its vanadium average valence state is +3.90.

[0177] (c) Preparation of the third precursor: Weigh 20.0 g of the second precursor obtained in step (b), and impregnate it with an aqueous solution containing 1.213 g of potassium nitrate (KNO3) using the equal volume impregnation method, so that the K / V atomic ratio is 0.03. Let it stand at room temperature for 24 h, and dry it at 120℃ for 6 h to obtain the third precursor.

[0178] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) The third precursor obtained in step (c) is added to 2.5% wt stearic acid, mixed evenly, and compressed into a cored cylindrical tablet with an outer diameter of 5.9 mm, an inner diameter of 2.8 mm, and a height of 5.0 mm on a tablet press at a pressure of 240 MPa. The lateral strength of the tablet is 20 N. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for activation by heating: the specific procedure for the activation by heating is as follows: First, the temperature was increased from room temperature to 330℃ at 12℃ / min under N2 (200 mL / min) and held at this temperature for 0.5 h. Then, the temperature was switched to a mixture of N2 (130 mL / min), pure oxygen (70 mL / min, to provide oxygen), and water vapor introduced from a steam generator (oxygen content ~21%, water vapor content ~40%), and the temperature was increased to 460℃ at 10℃ / min and held at this temperature for 10 h. Finally, when the temperature was cooled to 150℃, the air and water vapor were stopped, and the temperature was switched to pure N2 for purging. The temperature was then cooled to room temperature to obtain the final vanadium-phosphorus-oxygen catalyst. The physicochemical properties of the vanadium-phosphorus-oxygen catalyst in this embodiment are as follows: vanadium average valence state +4.20; bulk density 1.20 g / mL; lateral crushing strength 20 N.

[0179] Comparative Example 1 This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on the Cu-Na system. The method specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g V2O5, 45.8 g 85% H3PO4 (P / V=0.99), 400 mL ethanol, and 100 mL isobutanol to the reactor; add 14.54 g copper nitrate trihydrate (Cu(NO3)2·3H2O) to make the Cu / V atomic ratio = 0.15, and obtain a mixture; (a-2) The mixture was refluxed at 78°C for 4 h to obtain a copper-containing vanadium hydroxide hydrate suspension; (a-3) After the reaction is completed, the solid is filtered and dried at 75°C to obtain the first precursor; wherein the chemical formula of the first precursor is VO(HPO4)·xH2O; wherein x is 1 / 2; chemical analysis shows that the vanadium valence state is +3.80.

[0180] (b) Preparation of the second precursor: The first precursor obtained in step (a) is placed in a tube furnace for segmented calcination: the segmented calcination procedure is as follows: under an air atmosphere, the temperature is raised to 100°C and held for 0.2 h; under a pure oxygen atmosphere, the temperature is raised to 400°C and held for 1 h to obtain the second precursor; its vanadium average valence state is +4.20.

[0181] (c) Preparation of the third precursor: The second precursor obtained in step (b) was impregnated with a solution containing 0.171 g sodium nitrate (NaNO3) (Na / V=0.005) at room temperature for 0.5 h, and then dried to obtain the third precursor.

[0182] (d) Preparation of vanadium-phosphorus-oxygen catalyst: (d-1) Add 1% talc powder (wt. 1%) of the third precursor obtained in step (c) to the third precursor, mix evenly, and press into a cored cylindrical tablet. The tablet has an outer diameter of 5 mm, an inner diameter of 2.3 mm, a height of 5 mm, and a lateral strength of 18 N. (d-2) The tablets prepared in step (d-1) are loaded into a fixed-bed reactor for activation by heating: the specific procedure for the activation by heating is as follows: First, the temperature was raised to 150℃ at 25℃ / min and held for 0.1 hours under N2. Then, the temperature was raised to 500℃ at 15℃ / min and held for 5 hours under a mixed gas (O2~0.5%, H2O~2%). Finally, the temperature was switched to pure N2 at 100℃ and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. Physicochemical properties of the comparative vanadium-phosphorus-oxygen catalyst: average vanadium valence state +4.40; bulk density 0.7 g / mL; lateral crushing strength 20 N.

[0183] Comparative Example 2 This comparative example provides a method for preparing a vanadium phosphorus oxygen catalyst based on a Mo system. The method for preparing the vanadium phosphorus oxygen catalyst based on a Mo system specifically includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g of vanadium pentoxide (V2O5, 0.2 mol) and 49.95 g of 85% phosphoric acid (H3PO4) (P / V atomic ratio = 1.08) to a three-necked flask equipped with a reflux condenser; then add a mixed solvent of 400 mL isobutanol and 100 mL benzyl alcohol; subsequently, add 3.4 g of ammonium dimolybdate ((NH4)2Mo2O7) to make the Mo / V atomic ratio = 0.05, and obtain a mixture; (a-2) Heat to 105°C in an oil bath and reflux with stirring for 10 h to obtain a blue suspension; (a-3) After the reaction was completed, the mixture was filtered while hot, washed with isobutanol, and the filter cake was dried in an oven at 100°C for 12 h to obtain the blue first precursor; its vanadium average valence state was +4.02.

[0184] (b) Preparation of the second precursor: The first precursor obtained in step (a) is placed in a tube furnace for segmented calcination: the segmented calcination procedure is as follows: the temperature is raised to 130°C and held for 1 h in a N2 atmosphere; then, the temperature is switched to an air atmosphere and raised to 290°C and held for 3 h to obtain the second precursor; its vanadium average valence state is +3.98; the second precursor is used as the material for molding.

[0185] (c) Preparation of vanadium-phosphorus-oxygen catalyst: (c-1) The third precursor obtained in step (b) is dried at 120°C for 2 h. The dried material is mixed with 4 wt% graphite powder and pressed into a cored cylindrical tablet with an outer diameter of 5.5 mm, an inner diameter of 2.2 mm, and a height of 5.0 mm. (c-2) The tablets prepared in step (c-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (200 mL / min), the temperature is increased from room temperature to 300℃ at 3℃ / min and activated at a constant temperature for 3 h; then, the temperature is switched to a mixed gas (oxygen content ~10%, water vapor content ~25%) consisting of N2 (86 mL / min), air (150 mL / min, providing oxygen) and water vapor (approximately 25 vol%) introduced by a steam generator, and the temperature is increased to 400℃ at 4℃ / min and activated at a constant temperature for 6 h; finally, when the temperature is reduced to 200℃, the air and water vapor are stopped, and the temperature is switched to pure N2 for purging and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst. Physicochemical properties of the comparative vanadium-phosphorus-oxygen catalyst: average vanadium valence state +4.10; bulk density 0.85 g / mL; lateral crushing strength 29 N.

[0186] Comparative Example 3 This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst based on a Mo-Cs system. The specific method includes the following steps: (a) Preparation of the first precursor: (a-1) Add 36.5 g of vanadium pentoxide (V2O5, 0.2 mol) and 49.95 g of 85% phosphoric acid (H3PO4) to a three-necked flask equipped with a reflux condenser to make the P / V atomic ratio = 1.08; add a mixed solvent of 400 mL isobutanol and 100 mL benzyl alcohol; then add 3.4 g of ammonium dimolybdate ((NH4)2Mo2O7) and 1.17 g of cesium nitrate (CsNO3) to make the Mo / V atomic ratio = 0.05 and the Cs / V atomic ratio = 0.015 to obtain a mixture; (a-2) The mixture was heated to 105°C in an oil bath and stirred under reflux for 10 h to obtain a suspension of vanadium hydroxide phosphate containing molybdenum and cesium. (a-3) After the reaction was completed, the solid was filtered while hot, washed three times with isobutanol, and the filter cake was dried in an oven at 100°C for 12 h to obtain the blue first precursor.

[0187] (b) Preparation of the second precursor: The first precursor obtained in step (a) is placed in a tube furnace for segmented calcination: the segmented calcination procedure is as follows: under a nitrogen atmosphere (100 mL / min), the temperature is increased to 130°C at 5°C / min and calcined at a constant temperature for 1 h; then, the temperature is switched to an air atmosphere (100 mL / min), and the temperature is increased to 290°C at 2°C / min and calcined at a constant temperature for 3 h to obtain the second precursor.

[0188] (c) Preparation of vanadium-phosphorus-oxygen catalyst: (c-1) The second precursor obtained in step (b) is mixed evenly with 4 wt% graphite powder and compressed into a cored cylindrical tablet with an outer diameter of 5.5 mm, an inner diameter of 2.2 mm, and a height of 5.0 mm on a tablet press under a pressure of 250 MPa. (c-2) The tablets prepared in step (c-1) are loaded into a fixed-bed reactor for heating and activation. The specific heating and activation procedure is as follows: First, under N2 (200 mL / min), the temperature is increased from room temperature to 300℃ at 3℃ / min and activated at a constant temperature for 3 h; then, the temperature is switched to a mixed gas (oxygen content ~10%, water vapor content ~25%) consisting of N2 (86 mL / min), air (150 mL / min, providing oxygen) and water vapor introduced by a steam generator, and the temperature is increased to 400℃ at 4℃ / min and activated at a constant temperature for 6 h; finally, when the temperature is reduced to 200℃, the air and water vapor are stopped, and the temperature is switched to pure N2 purging and cooled to room temperature to obtain the final vanadium phosphorus oxygen catalyst.

[0189] Physicochemical properties of the comparative vanadium-phosphorus-oxygen catalyst: average vanadium valence state +4.08; bulk density 0.88 g / mL; lateral crushing strength 30 N.

[0190] Comparative Example 4 This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst. The only difference from Example 1 is that step (b) involves a one-step calcination. Specifically, the first precursor is placed in a tube furnace, and a mixture of nitrogen (100 mL / min) and air (20 mL / min) (oxygen content approximately 3.5%) is directly introduced. The temperature is programmed to rise from room temperature to 290°C at a rate of 2°C / min, and then calcined at 290°C for 3 h. A dark green second precursor is obtained; its average vanadium valence state is +4.08 according to chemical analysis; other settings are consistent with Example 1.

[0191] Catalyst performance and properties: Vanadium average valence state +4.27; bulk density 0.91 g / mL; lateral crushing strength 27 N.

[0192] Comparative Example 5 This comparative example provides a method for preparing a vanadium-phosphorus-oxygen catalyst. The only difference from Example 1 is that step (d) uses a one-step activation method. Specifically, the tablets are loaded into a fixed-bed reactor, and a mixed gas consisting of nitrogen (160 mL / min) and air (40 mL / min) (oxygen content approximately 4.2%) is directly introduced. Subsequently, the temperature is directly programmed to rise from room temperature to 400°C at a rate of 4°C / min, and activated at 400°C for 6 hours. After activation, the reactor is allowed to cool naturally to room temperature. No water vapor is introduced during the entire activation process; other settings are consistent with Example 1.

[0193] Catalyst physicochemical properties: Vanadium average valence: +4.41; bulk density: 0.95 g / mL; lateral crushing strength: 25 N.

[0194] Test case Test samples: vanadium phosphorus oxygen catalysts provided in Examples 1-6 and vanadium phosphorus oxygen catalysts provided in Comparative Examples 1-5.

[0195] Test method: The above-mentioned active vanadium-phosphorus-oxygen catalyst was applied to the n-butane oxidation reaction system, and the reaction temperature was set at 405℃ and the gas hourly space velocity was 1800 h⁻¹. -1 The reaction pressure was 0.1 MPa, and the reaction system was a mixture of n-butane, water vapor, and air; wherein the molar content of n-butane was 1.7%, and the molar content of water vapor was 2.8%. The gas phase composition of the tail gas was analyzed by gas chromatography.

[0196] The specific test results are shown in Table 1 below: Table 1

[0197] As shown in Table 1, this invention provides a specific method for preparing the above-mentioned high-performance VPO catalyst. The core of this method is to achieve precise control over the catalyst composition, structure, and activation process through an integrated and innovative process. The main steps include: First, in an organic alcohol solution, a pentavalent vanadium compound, a phosphorus source, and a first co-catalyst (such as Mo or Zn, selected based on ionic radius or valence state similar to vanadium, thus enabling embedding into the VOP lattice and stabilizing the active structure or regulating the electronic environment) undergo a reflux reaction to generate a blue vanadium oxyphosphate hydrate precursor, which, after separation and drying, yields the first precursor.

[0198] Subsequently, a key segmented calcination technique was employed: first, low-temperature dehydration was performed under an inert atmosphere, followed by high-temperature crystallization in an oxygen-containing atmosphere, transforming it into a second precursor. This process facilitates the formation of an ideal porous structure. Next, a second co-catalyst (such as Cs, Ce, or other alkali metals or rare earth metals typically used to adjust surface acidity / alkalinity) was loaded onto the second precursor using an equal-volume impregnation method. This approach effectively synergistically combined bulk phase modification and surface modification through a "stepwise doping" strategy. Finally, the shaped catalyst was placed in a carefully designed nitrogen-air-water vapor ternary mixed atmosphere for programmed temperature activation, ensuring the complete formation and structural stability of the active phase. The resulting catalyst exhibited a synergistic improvement in high activity, high selectivity, and excellent stability during the reaction.

[0199] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a vanadium-phosphorus-oxygen catalyst, characterized in that, The preparation method of the vanadium-phosphorus-oxygen catalyst includes: A pentavalent vanadium compound, a pentavalent phosphorus compound, a first co-catalyst, and an organic alcohol solution are mixed and reacted to obtain a first precursor. The first precursor is first calcined in an inert atmosphere or vacuum, and then calcined in an oxygen-containing atmosphere to obtain the second precursor. The second precursor is placed in a solution containing the second co-catalyst and impregnated to obtain the third precursor. The third precursor and lubricant are mixed, shaped, and then activated to obtain the vanadium-phosphorus-oxygen catalyst.

2. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The molar ratio of phosphorus (P) in the pentavalent phosphorus compound to vanadium (V) in the pentavalent vanadium compound is (1.00~1.15):1, preferably (1.05~1.10):1; Preferably, the pentavalent vanadium compound is selected from any one or a combination of at least two of vanadium pentoxide, ammonium metavanadate, sodium metavanadate, vanadium oxychloride, or vanadium trifluoride, and is preferably vanadium pentoxide; Preferably, the pentavalent phosphorus compound is selected from any one or a combination of at least two of orthophosphoric acid, polyphosphoric acid, ammonium orthophosphate, phosphorus pentoxide, ammonium dihydrogen phosphate or diammonium hydrogen phosphate, preferably orthophosphoric acid or polyphosphoric acid; Preferably, the first co-catalyst includes a first metal element M; wherein the first metal element M is selected from any one or a combination of at least two of Mo, Fe, Co, Ni, Zn, Nb or Zr, preferably Mo and / or Zn; Preferably, the first cocatalyst is selected from any one or a combination of at least two of the following: ammonium salt of the first metal element, nitrate of the first metal element, oxalate of the first metal element, chloride of the first metal element, or oxychloride of the first metal element. Preferably, the molar ratio of the first metal element M in the first co-catalyst to the V element in the pentavalent vanadium compound is (0.01~0.10):1, more preferably (0.03~0.07):1; Preferably, the organic alcohol solution comprises a reducing agent and a solvent; wherein the reducing agent is an aromatic alcohol capable of reducing pentavalent vanadium oxide to at least partially form vanadium hydroxide phosphate, preferably benzyl alcohol; and the solvent is a high-boiling-point aliphatic alcohol, preferably isobutanol. Preferably, in the organic alcohol solution, the molar ratio of the reducing agent to pentavalent vanadium oxide is (0.4~2.7):1, more preferably (0.8~1.5):1; Preferably, in the organic alcohol solution, the volume of the solvent accounts for 25-90% of the total volume of the reaction system, more preferably 65-85%.

3. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The reaction temperature is 95~120℃, preferably 100~110℃; the reaction time is 5~18 h, preferably 8~12 h. Preferably, the reaction further includes the following post-processing steps: The solid suspension obtained from the reaction was subjected to solid-liquid separation, and the separated solid was dried to obtain the first precursor; Preferably, the drying temperature is 80~120℃; Preferably, the chemical formula of the first precursor is VO(HPO4)·xH2O; where x is 0~1; Preferably, the average valence state of vanadium in the first precursor is +3.9 to +4.

1.

4. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The temperatures for the first and second stages of calcination are each independently 150~350℃; Preferably, the inert atmosphere is selected from any one or a combination of at least two of nitrogen, argon, or helium, with nitrogen being the most preferred. Preferably, the calcination temperature in the first stage is 110~200℃, more preferably 120~150℃; the calcination time in the first stage is 0.5~3 h. Preferably, in the oxygen-containing atmosphere, the volume content of oxygen accounts for 1% to 50% of the total volume content of the oxygen-containing atmosphere; Preferably, the calcination temperature in the second stage is 250~320℃, more preferably 280~300℃; the calcination time in the first stage is 2~5 h. Preferably, the average valence state of vanadium in the second precursor is +3.9 to +4.

0.

5. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The second co-catalyst includes a second metal element M'; wherein the second metal element M' is selected from alkali metals or alkaline earth metals; Preferably, the second metallic element M' is selected from any one or a combination of at least two of Cs, K, Ce or La, and is preferably Cs and / or Ce; Preferably, the second co-catalyst is selected from the nitrate of a second metal element; Preferably, the molar ratio of the second metal element M' in the second co-catalyst and the V element in the second precursor is (0.008~0.03):1, more preferably (0.01~0.02):1; Preferably, the impregnation treatment is an over-impregnation method or an equal-volume impregnation method; Preferably, the temperature of the impregnation treatment is 10~40℃, more preferably 20~30℃; the time of the impregnation treatment is 1~24h, more preferably 2~8h. Preferably, the following post-processing steps are further included after the impregnation treatment: The solid obtained by impregnation is dried to obtain the third precursor. Preferably, the drying temperature is 80~150℃.

6. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The amount of lubricant added accounts for 2-6% of the total mass of the third precursor, preferably 3-5%; Preferably, the lubricant is selected from any one or a combination of at least two of starch, calcium stearate, stearic acid, or graphite, with graphite being the most preferred. Preferably, the molding process is a tablet molding process, and the shaped body after the molding process is a cored cylindrical shape; its outer diameter is 4~8 mm, preferably 5~6 mm; its inner diameter is 1.5~3 mm, preferably 2~2.5 mm; and its height is 3~8 mm, preferably 4~6 mm. Preferably, the lateral compressive strength of the molded body after molding treatment is 20 N or more, and more preferably 25 N or more.

7. The method for preparing the vanadium-phosphorus-oxygen catalyst according to claim 1, characterized in that, The specific steps of the activation treatment include: The precursor after molding was subjected to a first-stage activation treatment in an inert atmosphere to obtain the first activated product. The first activated product is subjected to a second-stage activation treatment in an inert atmosphere, a mixture of air and water vapor, to obtain a second activated product. In an inert atmosphere, air and water vapor mixed atmosphere, the second activation product is first cooled to 150~250°C, the water vapor and air are stopped, and the temperature is further cooled to below room temperature under an inert atmosphere to obtain the vanadium phosphorus oxygen catalyst. Preferably, the heating rate of the first stage activation treatment is 1~15℃ / min, more preferably 2~10℃ / min; the temperature of the first stage activation treatment is 200~330℃, more preferably 280~320℃; and the time of the first stage activation treatment is 0.5~5 h, more preferably 2~4 h. Preferably, the heating rate of the second-stage activation treatment is 1~10℃ / min, more preferably 3~6℃ / min; the temperature of the second-stage activation treatment is 380~450℃, more preferably 390~460℃; and the time of the second-stage activation treatment is 4~10 h, more preferably 5~7 h. Preferably, the mixed atmosphere comprises, by volume percentage, 1-21% oxygen, 5-40% water vapor, and the remainder nitrogen, with the total volume content of the mixed atmosphere being 100%. Preferably, the temperature at which the introduction of water vapor and air is stopped is 180~220℃, and more preferably 190~210℃.

8. A vanadium-phosphorus-oxygen catalyst, characterized in that, The vanadium-phosphorus-oxygen catalyst is prepared by the method for preparing the vanadium-phosphorus-oxygen catalyst as described in any one of claims 1 to 7; And / or, the average valence state of vanadium in the vanadium-phosphorus-oxygen catalyst is +4.0 to +4.2; And / or, the bulk density of the vanadium-phosphorus-oxygen catalyst is 0.7~1.2 g / mL.

9. The use of a vanadium-phosphorus-oxygen catalyst prepared by any one of claims 1 to 7, or the vanadium-phosphorus-oxygen catalyst according to claim 8, as a catalyst for the oxidation of butane to prepare maleic anhydride.

10. A method for the selective oxidation of n-butane to prepare maleic anhydride, characterized in that, The method includes: In the presence of a catalyst, n-butane is reacted with an oxygen-containing gas to yield maleic anhydride. The catalyst includes the vanadium phosphorus oxygen catalyst prepared by the preparation method according to any one of claims 1 to 7, or the vanadium phosphorus oxygen catalyst according to claim 8.

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