Vanadium-phosphorus-oxygen catalyst, its preparation method and application

Abstract

The present application provides a kind of vanadium phosphorus oxygen catalyst, it has the following weight composition components: vanadyl pyrophosphate 66-94%, vanadyl phosphate 0.5-6%, attapulgite 0.8-25%, graphite 1-6%.Prepared by the following method: organic solvent, vanadium pentoxide and phosphoric acid are mixed to react, obtain blue slurry reaction liquid containing vanadium phosphorus oxygen catalyst precursor, wherein attapulgite carrier is added, then after filtration, drying, shaping, calcination, activation and other steps, the catalyst is obtained.The catalyst of the present application is applied to n-butane oxidation reaction for maleic anhydride, in the reaction temperature interval of 380-420 DEG C, n-butane conversion and maleic anhydride yield are higher than that of catalyst without adding attapulgite.

Description

Technical Field

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

[0002] Maleic anhydride, also known as maleic acid anhydride, is an important organic chemical raw material. It is the world's third largest organic acid anhydride after phthalic anhydride and acetic anhydride. Maleic anhydride contains a conjugated maleyl group, with one vinyl group linked to two carboxyl groups. It is chemically very reactive and can be used to derive numerous downstream products through addition reactions, esterification reactions, sulfonation reactions, and other processes. It is widely used in petrochemical, food processing, pharmaceutical, and building materials industries. Specific applications include the manufacture of unsaturated polyester resins, alkyd resins, maleic acid (maleic acid), fumaric acid (fumaric acid), as well as pesticides, coatings, fiberglass, lubricant additives, paper chemical additives, surfactants, and more.

[0003] Benzene oxidation and n-butane oxidation are the two main production methods for maleic anhydride. Benzene oxidation was the earliest applied process, and its reactor and catalyst technologies are mature. However, due to the relatively high price of benzene and the relatively serious environmental pollution it generates, its shortcomings have become increasingly apparent. Since Monsanto's n-butane oxidation process for producing maleic anhydride was first industrialized in 1974, it has become the main route for maleic anhydride production worldwide due to its advantages of low raw material cost, low environmental pollution, and low maleic anhydride production cost. The selective oxidation of n-butane to maleic anhydride can be divided into fixed-bed, fluidized-bed, and moving-bed production processes. However, all of the above processes require vanadium phosphorus oxide (VPO) catalysts as the catalyst for the reaction. Since the successful commercialization of VPO catalysts, extensive and in-depth research has been conducted on their preparation methods, resulting in numerous papers and patent applications. See CATAL.REV.-SCI.ENG.27(1985):373.

[0004] The selective oxidation of n-butane using vanadium-phosphorus-oxygen catalysts is a typical example of a large class of selective oxidation reactions of hydrocarbons that proceed via a redox mechanism. The chemical reaction involves the transfer of 14 electrons, including the loss of electrons from 8 hydrogen atoms and the insertion of electrons from 3 oxygen atoms. The exploration of its reaction mechanism has always been a hot topic in the research of vanadium-phosphorus-oxygen catalysts. Vanadium-phosphorus-oxygen catalysts are a complex catalyst system, and their physical properties and structure are closely related to the preparation method. The preparation process has a significant impact on the catalytic performance.

[0005] Jiang Haoxi et al. Study on the active phase of catalyst for butane oxidation to maleic anhydride [J]. Chemical Industry and Engineering, 2004, 21(1): 29. The study pointed out that the process of butane oxidation to maleic anhydride can only be carried out in the VOPO4 phase (V5+ ) and (VO)2P2O7 (V 4+ Only with the synergistic effect of the (VO)2P2O7 phase can butane molecules be properly activated, allowing the butane dehydrogenation reaction control step to proceed smoothly. All surface adsorption and atomic migration occur on the (020) crystal plane. However, in the presence of only the (VO)2P2O7 phase, the conversion and yield of butane are not high enough, far less than those with a suitable amount of β-VOPO4 phase (V 5+ The presence of this phenomenon indicates that the β-VOPO4 phase must influence the butane dehydrogenation process in some way. Since the dehydrogenation reaction is the rate-controlling step in the entire butane oxidation to maleic anhydride reaction, its presence has a significant impact on catalyst performance. The reason for this phenomenon may be that butane molecules are saturated aliphatic hydrocarbons, chemically inactive, and dehydrogenation is relatively difficult, requiring strong Lewis acid sites to activate butane. The β-VOPO4 phase on the (020) facet... 4+ The acid strength of (VO)₂P₂O₇ is not ideal, resulting in low activity for catalysts containing only (VO)₂P₂O₇. However, the situation is completely different when the β-VOPO₄ phase, with V oxidation state of +5 and strong acid strength, is present. The β-VOPO₄ phase, embedded in the (VO)₂P₂O₇ crystal lattice, utilizes its strong acid strength to interact with the V on the (020) surface of the (VO)₂P₂O₇ phase. 4+ The combined effect activates the CH atoms of butane, enabling the (VO)₂P₂O₇ (020) phase facet to effectively catalyze butane dehydrogenation. However, when the β-VOPO₄ phase content exceeds a certain limit, it will interact with the V atoms on the (VO)₂P₂O₇ (020) crystal facet. 4+ Competitive adsorption occurs, resulting in a significant amount of butane in V 5+ Deep oxidation at the butane site results in CO and CO2, leading to an increase in butane conversion and a significant decrease in maleic anhydride yield.

[0006] Early preparations of vanadium-phosphorus-oxygen catalysts used water as a solvent and hydrochloric acid (including hydrogen chloride gas) and oxalic acid as reducing agents; the resulting catalysts had relatively small specific surface areas (<10 m²). 2 / g). Later methods involved preparing catalysts in organic phases, using reducing agents such as alcohols, aldehydes, and esters. Catalysts prepared in organic phases have a larger specific surface area (>20m²). 2 Moreover, catalysts prepared in organic phases generally exhibit better catalytic performance than those prepared using water as a solvent.

[0007] USP 4,632,915 discloses a method for preparing and activating a vanadium-phosphorus-oxygen catalyst. In a stirred reactor equipped with a reflux cooler, isobutanol, phosphoric acid (100%), vanadium pentoxide, lithium chloride, and iron powder are added under cooling. Hydrogen chloride gas is then introduced, and the mixture is refluxed at 102°C for more than 2.5 hours to obtain a catalyst precursor. After drying, calcination, and shaping, the catalyst is activated first by heating at a rate of 3°C / min in an air atmosphere containing 1.8% water using butane and air reaction atmosphere. The catalyst performance evaluation results of this method are: butane conversion of 78.1% and maleic anhydride molar yield of 54.5%.

[0008] CN 101157048A proposes a method for preparing a nanostructured vanadium-phosphorus-oxygen catalyst. This method improves upon conventional organic solvent methods by introducing bismuth salts and other promoters, dimethyl sulfoxide, and polyethylene glycol during the preparation of the vanadium-phosphorus-oxygen catalyst precursor. The method also provides an activation method for the catalyst: the pressed catalyst precursor is activated at 400℃ for 72 hours in a mixture of 1.5% and 98.5% air by volume to obtain the activated catalyst. Performance evaluation results show a conversion rate of 68-81% and a maleic anhydride selectivity of 41-71%.

[0009] USP4,855,459 proposes a method for preparing maleic anhydride by oxidizing n-butane. This method involves diluting and packing inert silica-alumina spheres with a catalyst. By diluting and packing the catalyst at the hot spot in the reaction tube, the hot spot temperature is reduced, the selectivity of maleic anhydride is improved, and the yield of maleic anhydride is increased. At the same time, the stability period of the catalyst is extended. However, the disadvantage is that the addition of inert materials reduces the effective volume of the reactor and also reduces the production efficiency. Summary of the Invention

[0010] During the research and development process, the inventors of this case made a surprising discovery: the two-component vanadium-phosphorus oxygen catalyst, formulated with attapulgite powder, exhibits superior physicochemical properties and catalytic performance due to the colloidal, adsorption, reinforcing, support, and high-temperature thermal stability properties of attapulgite, as well as the synergistic acid-base effect of attapulgite's Lewis acidification and alkalization centers. This method and result are novel and unexpected; those skilled in the art would not have anticipated that attapulgite could be used as both a support and active component in the preparation of vanadium-phosphorus oxygen catalysts. Because attapulgite possesses carbocation activity in organic reactions and also exhibits synergistic acid-base effects, the vanadium-phosphorus oxygen catalyst-attapulgite composite catalyst prepared using this method demonstrates improved selective oxidation capacity. When used in the catalytic reaction of n-butane oxidation to maleic anhydride, this catalyst exhibits high n-butane conversion, good maleic anhydride selectivity, and high maleic anhydride yield.

[0011] The first aspect of the present invention aims to provide a vanadium-phosphorus-oxygen catalyst having the following components by weight:

[0012] Vanadium pyrophosphate 66-94%

[0013] Vanadium oxyphosphate 0.5-6%

[0014] Attapulgite 0.8-25%

[0015] Graphite 1-6%.

[0016] Further preferred options are:

[0017] Vanadium pyrophosphate 70-92%

[0018] Vanadium oxyphosphate 0.75-5%

[0019] Attapulgite 3-20%

[0020] Graphite 1-5%

[0021] The best option is:

[0022] Vanadium oxypyrophosphate 72-92%

[0023] Vanadium oxyphosphate 1-5%

[0024] Attapulgite 5-18%

[0025] Graphite 1-5%

[0026] Furthermore, the catalyst also includes an auxiliary agent selected from at least one of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr, and Ce, wherein the auxiliary agent, in terms of molar amount, is 0.001 to 0.2 times the amount of V atoms in terms of metal element.

[0027] The technical objective of the second aspect of this invention is to provide a method for preparing a vanadium-phosphorus-oxygen catalyst, comprising: mixing and reacting an organic solvent, vanadium pentoxide, and phosphoric acid to obtain a blue slurry containing a vanadium-phosphorus-oxygen catalyst precursor; adding attapulgite to the slurry to obtain a composite catalyst precursor; filtering; drying; and obtaining the vanadium-phosphorus-oxygen catalyst after molding and calcination.

[0028] The mass percentages of each component, based on the total weight of the prepared catalyst, are as follows:

[0029] Vanadium pyrophosphate 66-94%

[0030] Vanadium oxyphosphate 0.5-5%

[0031] Attapulgite 0.8-25%

[0032] Graphite 1-6%.

[0033] Furthermore, the attapulgite has a particle size of 80-800 mesh, preferably 100-400 mesh.

[0034] Furthermore, the attapulgite is refined attapulgite, which is made by refining raw attapulgite powder by treating it with hydrochloric acid. Specifically, the raw attapulgite powder is mixed with 1-5 mol / L, preferably 2-3 mol / L, hydrochloric acid, stirred for 5-10 hours, filtered, washed until no chloride ions are present, and dried.

[0035] Furthermore, the organic solvent, vanadium pentoxide, and phosphoric acid are reacted in a reactor equipped with a stirrer and a reflux condenser. First, the organic solvent and vanadium pentoxide are mixed and reacted for 2-4 hours. Then, phosphoric acid is added and reacted for 4-8 hours. The reaction temperature range is 95-120℃.

[0036] Furthermore, the organic solvent is a solvent suitable for preparing vanadium-phosphorus-oxygen catalyst systems, which is well known to those skilled in the art. It can be a single solvent or a mixture of two or more solvents. As one more specific embodiment, the organic solvent is selected from at least one of isobutanol, benzyl alcohol, ethylene glycol, 1,3-propanediol, and 1,4-butanediol; preferably a mixture of isobutanol and benzyl alcohol, with a volume ratio of 5:1 to 100:1, and most preferably 10:1 to 25:1.

[0037] Furthermore, the weight ratio of the organic solvent to vanadium pentoxide is 5:1-25:1, preferably 10:1-20:1.

[0038] Furthermore, the concentrated phosphoric acid has a weight percentage concentration of 85%-100%.

[0039] Furthermore, the amount of phosphoric acid added makes the molar ratio of phosphorus to vanadium 0.85-1.35, preferably 0.95-1.20.

[0040] Furthermore, the drying is carried out at a temperature of 95-170°C, preferably 120-150°C, for 8-12 hours.

[0041] Furthermore, the molding process is a conventional molding method in the art, such as extrusion, sheeting, or spheroidization, and the catalyst is generally in the form of a solid cylinder, a hollow cylinder, a Raschig ring, or a clover shape.

[0042] Furthermore, the roasting temperature is 250-350℃, preferably 270-300℃; the roasting time is 3-10 hours, preferably 4-6 hours.

[0043] Furthermore, the above preparation method also includes a step of introducing an additive. The additive is selected from one or more of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr, and Ce; the additive is calculated as 0.001 to 0.2 times the number of V atoms in terms of metal elements. The additive is introduced into the catalyst in one of the following ways: (1) introduced into the reaction solution during the preparation of the vanadium phosphorus oxygen precursor; (2) introduced before or during the catalyst forming process.

[0044] Furthermore, the above preparation method also includes a catalyst activation step, wherein the activation is carried out in an atmosphere of one or more combinations of air / inert gas, air / butane, air / water vapor, and butane / inert gas mixture, preferably in a butane / air mixture, wherein the butane volume content in the butane / air mixture is 0.8-1.5%, more preferably 1.0-1.2%. The activation temperature is generally 260-450℃, preferably 370-430℃, and most preferably 400-420℃; the activation time is 10-40 hours, preferably 15-25 hours. The heating rate during activation is 1-10℃ / min, preferably 3-5℃ / min.

[0045] The technical objective of the second aspect of this invention is to provide a method for the oxidation of n-butane to maleic anhydride, using a vanadium-phosphorus-oxygen catalyst prepared by the above method.

[0046] Furthermore, the reaction of n-butane oxidation to maleic anhydride can be carried out in a fixed-bed reaction mode, a fluidized-bed reaction mode, or a moving-bed reaction mode.

[0047] Furthermore, the reaction conditions for the oxidation of n-butane to maleic anhydride are: reaction temperature 380-450℃, pressure atmospheric pressure -0.5MPa, and n-butane gas hourly space velocity 1000-3500 h⁻¹. -1 The concentration of n-butane in the gas mixture is 1.0%-1.85% (volume percentage).

[0048] When the vanadium-phosphorus-oxygen catalyst of the present invention is applied to the reaction of n-butane oxidation to maleic anhydride, the n-butane conversion rate is high, the maleic anhydride selectivity is good, and the byproducts of acetic acid and acrylic acid are low.

[0049] Compared with the prior art, the technical solution provided by the present invention has the following advantages:

[0050] (1) The process of butane oxidation to maleic anhydride requires the butane molecule to be dehydrogenated and activated first in order for the reaction to proceed smoothly. In other words, butane dehydrogenation is the control step of this reaction. In the catalytic process of vanadium phosphorus oxygen catalyst-attapulgite composite catalyst, attapulgite, as the active component, has a strong Lewis acidification center, which can accelerate the control step of butane dehydrogenation reaction and synergistically interact with the oxidation active components VOPO4 phase and (VO)2P2O7 of vanadium phosphorus oxygen catalyst, thereby obtaining excellent catalytic performance of butane oxidation to maleic anhydride.

[0051] (2) The vanadium-phosphorus-oxygen catalyst-attapulgite composite catalyst has a high specific surface area and a large pore volume, and the catalyst has high activity. The thermal stability of attapulgite can disperse the heat of oxidation reaction as a catalyst support, which is conducive to heat transfer and removal of the heat of reaction, effectively reducing the hot spot of reaction and improving the selectivity of maleic anhydride. The adhesiveness of attapulgite makes the strength control range of the catalyst large. Attapulgite is inexpensive and readily available, which can effectively reduce the manufacturing cost of the catalyst.

[0052] (3) The catalyst of the present invention is used in the reaction of n-butane oxidation to maleic anhydride, with high butane conversion rate, high maleic anhydride selectivity and high catalytic activity. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are not intended to limit the scope of protection of the present invention. Those skilled in the art can make appropriate extensions in conjunction with the present invention specification and the full text, and these extensions should all be within the scope of protection of the present invention.

[0054] In this embodiment, the catalyst strength tester used was a DLⅡ type intelligent particle strength tester from Dalian Chemical Research and Design Institute, and the specific surface area was measured using an AUTOSORB3B fully automatic specific surface area and pore size distribution analyzer from Quantachrome, USA. Catalyst evaluation results were analyzed using an HP7890A gas chromatograph from Agilent Technologies.

[0055] The contents of vanadium pyrophosphate and vanadium phosphate in the catalyst prepared by this invention were determined by potassium permanganate oxidation-ferrous ammonium sulfate titration method (YB-T5328-2009), as follows: In sulfuric acid medium, tetravalent vanadium was oxidized to pentavalent vanadium with potassium permanganate. Excess potassium permanganate was decomposed with sodium nitrite in the presence of urea. The total vanadium content of the catalyst was determined by titration with ferrous ammonium sulfate standard solution using N-phenyl-o-aminobenzoic acid as an indicator. In parallel, the pentavalent vanadium in the catalyst was determined by titration with ferrous ammonium sulfate standard solution using N-phenyl-o-aminobenzoic acid as an indicator. The vanadium phosphate content was obtained. The content of tetravalent vanadium pyrophosphate was calculated based on the total vanadium content of the catalyst.

[0056] Example 1

[0057] Add 649 mL of a mixture of isobutanol and benzyl alcohol (isobutanol / benzyl alcohol volume ratio 10:1), 29.53 g of vanadium pentoxide, 0.3 g of nickel nitrate hexahydrate and 0.5 g of zirconium nitrate to a reactor equipped with a stirrer and a reflux condenser. Start stirring, raise the reaction temperature and maintain it at 100±2℃, and reflux for 4 hours. Then add 34.98 g of 100% phosphoric acid (phosphorus / vanadium molar ratio 1.1) and continue reflux for 4 hours. Then add 0.5 g of 100-mesh refined attapulgite and continue stirring for 5 hours. After the reaction solution is cooled to room temperature, vacuum filter it. Wash the filter cake three times with a small amount of isobutanol, place the filter cake in an enamel dish and air dry it at room temperature. Then dry it in an oven at 100℃ for 8 hours to obtain a lake-blue catalyst precursor.

[0058] The catalyst precursor prepared above was added to 1.8g of graphite powder, and after being thoroughly mixed, it was extruded into Raschig ring catalyst product using a rotary tablet press with appropriate adjustment of the impact force.

[0059] The aforementioned Raschig ring catalyst particles were calcined in a muffle furnace at 300°C for 4 hours. The calcined catalyst was then placed in a tubular reactor and subjected to a butane / air mixture containing 1.2% butane by volume, with a gas hourly space velocity (VHSV) of 1000 h⁻¹. -1 The heating rate is 3℃ / min, and the activation temperature is raised to 400℃ for activation. The temperature is maintained at 400℃ for 20 hours. The activation process is then completed, and the vanadium phosphorus oxygen catalyst of the present invention is obtained.

[0060] The contents of vanadium pyrophosphate and vanadium phosphate were determined by titration, and the contents of attapulgite, graphite and additives (calculated as metal elements) were calculated based on the feed ratio.

[0061] The side pressure strength, specific surface area and pore volume of the obtained catalyst were measured, and the results are shown in Table 1.

[0062] Example 2

[0063] Except for replacing 0.5g of attapulgite with 2.6g of 200-mesh refined attapulgite, everything else is the same as in Example 1.

[0064] Example 3

[0065] Except for replacing 0.5g of attapulgite with 5.2g of 300-mesh refined attapulgite, everything else is the same as in Example 1.

[0066] Example 4

[0067] Except for replacing 0.5g of attapulgite with 7.8g of 200-mesh refined attapulgite, everything else is the same as in Example 1.

[0068] Example 5

[0069] Except for replacing 0.5g of attapulgite with 13.0g of 100-mesh refined attapulgite, everything else is the same as in Example 1.

[0070] Comparative Example 1

[0071] To a reactor equipped with a stirrer and a reflux condenser, add 649 mL of a mixture of isobutanol and benzyl alcohol (isobutanol / benzyl alcohol volume ratio 10:1), 29.53 g of vanadium pentoxide, 0.3 g of ferric nitrate hexahydrate, and 0.5 g of zirconium nitrate. Start stirring, raise the reaction temperature to 100±2℃, and reflux for 4 hours. Then add 34.98 g of 100% phosphoric acid (phosphorus / vanadium molar ratio 1.1) and continue reflux for another 4 hours. The reaction is then complete. After cooling to room temperature, the mixture is vacuum filtered. The filter cake is washed three times with a small amount of isobutanol, placed in an enamel dish, and air-dried at room temperature. Finally, it is dried in a 100℃ oven for 8 hours to obtain a blue catalyst precursor.

[0072] The catalyst precursor prepared above was added to 1.8g of graphite powder, and after thorough mixing, it was extruded into Raschig ring catalyst product using a rotary tablet press with appropriate adjustment of the impact force.

[0073] Take 50g of the above-mentioned Raschig ring catalyst particles and calcine them in a muffle furnace at 300℃ for 4 hours. After calcine, place the catalyst in a tubular reactor and calcine it in an atmosphere of butane / air mixture with a butane volume content of 1.2% at a gas hourly space velocity of 1000 h⁻¹. -1 The heating rate is 3℃ / min, and the activation temperature is raised to 400℃ for activation. The temperature is maintained at 400℃ for 20 hours. The activation process is then completed, and the vanadium phosphorus oxygen catalyst of the present invention is obtained.

[0074] Lateral compressive strength, specific surface area, and pore volume are shown in Table 1.

[0075] Table 1

[0076] serial number Lateral compressive strength, N / piece <![CDATA[Pore volume, cm 3 / g]]> <![CDATA[Specific surface area, m 2 / g]]> Acid distribution, B / L Example 1 25 0.080 22 1 / 1.75 Example 2 29 0.102 28 1 / 2.35 Example 3 35 0.113 32 1 / 3.87 Example 4 46 0.136 39 1 / 4.26 Example 5 67 0.127 43 1 / 5.35 Comparative Example 1 23 0.076 19 1 / 1.40

[0077] The catalysts obtained in the above examples and comparative examples were crushed and sieved. 5 mL of catalyst particles (10-20 mesh) were diluted 1:1 with quartz sand of the same mesh size and packed into a stainless steel reaction tube with an inner diameter of 10 mm. The reactor wall temperature was controlled at 400°C, the inlet reaction pressure at 0.25 MPa, and the reactant was a butane / air mixture with a butane volume concentration of 1.5% and a gas hourly space velocity of 1600 h⁻¹. -1 Catalytic performance was evaluated under the specified reaction conditions. The product composition was analyzed by gas chromatography, and the performance evaluation results are shown in Table 2.

[0078] Table 2

[0079] serial number salinity, °C Hot spot temperature, °C Butane conversion rate, % (mol) Maleic anhydride selectivity, % (mol) Maleic anhydride yield, % (mol) Example 1 400 418.8 81.57 66.25 54.04 Example 2 400 420.3 84.13 69.81 58.73 Example 3 400 421.6 87.42 71.74 62.71 Example 4 400 422.0 89.06 70.13 62.45 Example 5 400 417.2 85.62 67.54 57.82 Comparative Example 1 400 430.1 80.26 60.65 48.67

Claims

1. A method for preparing a vanadium-phosphorus-oxygen catalyst, comprising: An organic solvent, vanadium pentoxide, and phosphoric acid are mixed and reacted to obtain a blue slurry containing a vanadium-phosphorus-oxygen catalyst precursor. Attapulgite is added to the mixture to obtain a composite catalyst precursor. The precursor is filtered, dried, shaped, and calcined to obtain the vanadium-phosphorus-oxygen catalyst. The attapulgite has a particle size of 40-800 mesh, and the attapulgite is refined attapulgite, which is refined by treating raw attapulgite powder with hydrochloric acid. The mass percentages of each component, based on the total weight of the prepared catalyst, are as follows: Vanadium pyrophosphate 66-94% Vanadium oxyphosphate 0.5-5% Attapulgite 0.8-25% Graphite 1-6%; The preparation method further includes the step of introducing an auxiliary agent, which is selected from one or more of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr and Ce; wherein the auxiliary agent is added at a ratio of 0.5-4% of the total weight of the catalyst for each of the above elements.

2. The preparation method according to claim 1, characterized in that, The mass percentage of vanadium pyrophosphate is 70-92%, the mass percentage of vanadium phosphate is 0.75-5%, the mass percentage of attapulgite is 3-20%, and the mass percentage of graphite is 1-5%.

3. The preparation method according to claim 1, characterized in that, Organic solvent, vanadium pentoxide, and phosphoric acid are reacted in a reactor equipped with a stirrer and a reflux condenser. First, the organic solvent and vanadium pentoxide are mixed and reacted for 2-4 hours. Then, phosphoric acid is added and reacted for 4-8 hours. The reaction temperature range is 95-120℃.

4. The preparation method according to claim 1, characterized in that, The organic solvent is selected from at least one of isobutanol, benzyl alcohol, ethylene glycol, 1,3-propanediol and 1,4-butanediol.

5. The preparation method according to claim 1, characterized in that, The weight ratio of the organic solvent to vanadium pentoxide is 5:1 to 25:

1.

6. The preparation method according to claim 1, characterized in that, The phosphoric acid has a weight percentage concentration of 85%-100%, and the amount of phosphoric acid added makes the molar ratio of phosphorus to vanadium 0.85-1.

35.

7. The preparation method according to claim 1, characterized in that, The additive is introduced into the catalyst in one of the following ways: (1) in the reaction solution during the preparation of the vanadium phosphorus oxygen precursor; (2) before or during the catalyst forming process.

8. The preparation method according to claim 1, characterized in that, It also includes a step of activating the catalyst, wherein the activation is carried out in an atmosphere of one or more combinations of air / inert gas, air / butane, air / water vapor, and butane / inert gas mixture; the activation temperature is 260-450℃, the activation time is 10-40 hours, and the heating rate during activation is 1-10℃ / min.

9. A method for oxidizing n-butane to maleic anhydride, wherein the vanadium phosphorus oxygen catalyst prepared by the method described in claim 1 is used for catalytic reaction.

10. The method according to claim 9, characterized in that, The reaction can be carried out in a fixed bed, fluidized bed, or moving bed manner.

11. The method according to claim 9, characterized in that, The reaction conditions for the oxidation of n-butane to maleic anhydride are: reaction temperature 380-450℃, pressure atmospheric pressure -0.5MPa, and n-butane gas hourly space velocity 1000-3500 h⁻¹. -1 The volume concentration of n-butane in the gas mixture is 1.0%-1.8%.