Methanol-to-formaldehyde catalyst, preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of C1 chemical industry, and relates to a methanol-to-formaldehyde catalyst, a preparation method therefor and a use thereof. The methanol-to-formaldehyde catalyst comprises the following components in percentage by weight based on the total dry basis: MoO3: 75-85 wt%, Fe2O3: 10-20 wt%, Cr2O3: 0.1-3 wt%, CeO2: 0.1-5 wt%, P2O5: 0.1-1 wt%, and Al2O3: 0.5-2.5 wt%. When the catalyst provided by the present invention is applied in the process of oxidation of methanol to formaldehyde, the catalyst has the characteristics of excellent catalytic conversion reaction performance, high activity and high selectivity, particularly has the characteristics of good mechanical strength, excellent stable conversion performance, high formaldehyde yield and the like under harsh reaction conditions, and has wide practical application value.

Description

A methanol-to-formaldehyde catalyst and its preparation method and application Technical Field

[0001] The present invention relates to the field of carbon-chemical technology, and in particular to a methanol-to-formaldehyde catalyst, a preparation method, and applications thereof. More specifically, the present invention relates to an iron-molybdenum catalyst for producing formaldehyde by oxidizing methanol, a preparation method thereof, and specific applications of the catalyst in a process for producing formaldehyde by oxidizing methanol. Background Art

[0002] The oxidation of methanol to formaldehyde is an important chemical process. The product, formaldehyde, is a widely used organic chemical raw material with active properties that can react with almost all organic or inorganic compounds. It is a bulk chemical product with a simple production process and sufficient raw material supply, and is also the backbone product in the methanol downstream product chain.

[0003] Since industrial production began in Germany in 1888, global formaldehyde production capacity currently exceeds 80 million tons, with annual output exceeding 50 million tons, primarily produced using methanol. Production capacity is primarily concentrated in China, the United States, and Europe. China is the largest producer and consumer, accounting for approximately half of global formaldehyde production capacity.

[0004] There are two industrial methods for producing formaldehyde through direct oxidation of methanol: the silver-catalyst method (silver contact method) and the iron-molybdenum catalyst method (Formox method). The silver-catalyst method offers simpler processes and greater adjustability. Methanol is flammable and explosive. To avoid explosion limits, the methanol content in the raw material must be above 37%. This high methanol concentration in the reaction mixture and the high equipment load result in lower investment. However, the methanol conversion rate is low, unit consumption is high, and the raw material purity requirement is high. Consequently, the methanol content in the finished formaldehyde product is high, resulting in only low-concentration formaldehyde.

[0005] The silver process operates at a high temperature of around 600°C, which makes it easy for electrolytic silver grains to grow under these conditions. Furthermore, the silver catalyst is extremely sensitive to poisons in the raw materials, resulting in a short catalyst lifespan, as described in patents USP 3956184, USP 3959383, USP 4045369, USP 4167527, and CN 99113969.0. 70% of existing formaldehyde production facilities abroad still use the silver process.

[0006] The iron-molybdenum catalyst method is an important formaldehyde production process. The methanol content in the raw material mixture must be less than 7%. This process has the advantages of a low reaction temperature (~280°C), high catalyst activity, good selectivity, long life, insensitivity to poisons, high methanol conversion, low unit cost, high formaldehyde yield, and the absence of a distillation unit. It can produce high-concentration formaldehyde, and the finished formaldehyde product has a low alcohol content, which can be directly used to produce high-value-added formaldehyde downstream products. The production capacity of the equipment is also large, as described in documents such as GB-B1080508, DE-A1144252, CN1898013A, and CN113666815A. However, this method requires high investment, high power consumption, significant heat waste, and difficult tail gas treatment. The preparation of iron-molybdenum formaldehyde catalysts is also difficult, with high technical barriers. This is particularly true for high-space-velocity catalyst preparation, which is monopolized by foreign companies, as described in CN113200838A.

[0007] Development of formaldehyde production technology using iron-molybdenum catalysts began in the early 1930s, achieving industrialization in 1952 and rapidly expanding with the rise of polyoxymethylene engineering plastics in 1959. Because the iron-molybdenum catalyst method can directly produce low-alcohol, high-concentration formaldehyde, the raw material for polyoxymethylene, the iron-molybdenum catalyst process was widely used in formaldehyde plants at the time. Considering operating conditions, product quality, and environmental protection, the iron-molybdenum process was superior to the silver process. Therefore, the iron-molybdenum process became the trend of development in formaldehyde production technology. Since the 1980s, most new large-scale production facilities built abroad have adopted the iron-molybdenum catalyst production process.

[0008] In 1968, the United States disclosed an iron-molybdenum two-component catalyst in USP 3408309. Subsequently, to improve activity, stability, and mechanical strength, other metal oxides were added as additives to the iron-molybdenum two-component catalyst, leading to the development of a series of iron-molybdenum catalysts. In 1974, USP 3846341 disclosed an iron-molybdenum catalyst prepared by a gel method, in which small amounts of tungsten and cobalt were added to improve catalytic performance. In 1976, USP 3978136 disclosed a catalyst prepared by a coprecipitation method using ferric chloride hexahydrate and ammonium paramolybdate as raw materials. The addition of TiO2 resulted in a more ideal catalyst.

[0009] The main active components of the iron-molybdenum catalyst for the production of formaldehyde by oxidation of methanol are iron molybdate and molybdenum trioxide. Studies have shown that adding different additives can improve catalyst performance, as described in CN109806881A. The process using the iron-molybdenum catalyst does not require high-temperature reaction, which reduces side reactions, improves selectivity, and has high catalyst efficiency and long life. There are a large number of documents that disclose the technology of preparing iron-molybdenum catalysts by coprecipitation, such as those reported in patents such as USP4829042, USP4420421, CN1546232A, CN100413584C, CN1100667A, CN103933998A, CN103933998A and CN105457648A.

[0010] In order to improve the performance of the catalyst, the preparation also focuses on the modification of the precursor. CN108816241A obtains a precursor with uniform particle size and relatively large grain size through a hydrothermal synthesis reaction at a higher temperature and pressure. The prepared catalyst has higher activity and selectivity. In the preparation method disclosed in CN107537577A, the particle size distribution of the catalyst precursor is uniform and concentrated, which improves the activity, selectivity and stability of the catalyst.

[0011] In addition to the coprecipitation method, the sol-gel method, also used in GB1282949 and USP3846341, is also used to prepare iron-molybdenum catalysts. Molybdenum and iron salts are dissolved in an organic acid to form a sol, which is then evaporated to form a gel. However, for both coprecipitation and sol-gel methods, the resulting iron-molybdenum compound requires further shaping for ease of use. This is done by mixing with additives such as a binder and then extruding or pressing it into a shape. The size and shape are determined by the requirements of the industrial process.

[0012] In order to reduce the large amount of industrial wastewater in the preparation process, CN106582673A adopts a solid-phase reaction preparation method, mixing ammonium molybdate with iron salts and grinding them to generate iron molybdate to prepare an iron molybdate catalyst; compared with the traditional reaction of ammonium molybdate with a dilute aqueous solution of iron salts such as ferric nitrate or ferric chloride, it can greatly reduce the amount of water used and the amount of wastewater, simplify sewage treatment and reduce production costs. Similarly, CN108435192A adopts a mechanochemical synthesis method to prepare an iron-molybdenum catalyst, mixing molybdate and iron salts evenly, and then ball milling them to prepare an iron molybdate catalyst. The steps are simple and greatly reduce water consumption and industrial wastewater discharge, but the disadvantage of solid-phase reaction is that it is easy to cause insufficient reaction during mixing, which will deteriorate the performance of the catalyst.

[0013] CN113019385A uses industrial molybdenum oxide and iron oxide as raw materials, solid-state grinding and ammonia soaking treatment; then inorganic acid is added for acid precipitation to produce an iron-molybdenum catalyst; CN113019387A uses mechanically crushed and roasted molybdenum concentrate as raw material, adds iron salt for solid-state grinding and ammonia soaking treatment, and inorganic acid precipitation to produce the required catalyst; CN113019386A uses mechanically crushed and roasted iron ore as raw material, adds ammonium molybdate and solid-state grinding, and adds deionized water and inorganic acid for acidification to produce the iron-molybdenum catalyst.

[0014] CN11089338944A also uses an organic acid to react with iron to generate the corresponding organic acid iron, which is then reacted with molybdic acid to generate iron molybdate and the corresponding organic acid. While obtaining the desired catalyst, the organic acid can also be recycled; CN115487818A adds an organic amine during the coprecipitation process to adjust the physical structure of the catalyst, thereby improving the activity, stability and service life of the catalyst.

[0015] To improve mixing uniformity, CN115007165A employs emulsification technology in coprecipitation preparation; CN114618507A even employs mixing technology used in inkjet printing. While these disclosed coprecipitation preparation techniques can produce catalysts with good activity and strength that generally meet the requirements, they still suffer from high preparation costs and easy catalyst deactivation, causing inconvenience in further applications.

[0016] To improve catalyst performance, CN1044339C coprecipitates the active component molybdenum with a structural additive metal oxide to create a two-, three-, or four-component catalyst. This eliminates the need for acid solution washing, simplifying the process and reducing pollution and equipment corrosion. CN109012682A utilizes a mechanochemical method to prepare a metal-modified iron-molybdenum catalyst. Solid-phase ball milling eliminates the need for solvents such as water and other precipitants, simplifying the process and significantly reducing wastewater emissions and manufacturing costs. The addition of metal salts significantly improves conversion and selectivity.

[0017] Adding rare earth elements such as cerium has always been a key focus in improving catalyst performance. CN1792444A uses cerium modification to increase stability and lifespan, and uses an oxidant to oxidize the iron powder during the reaction with molybdenum trioxide. CN1792443A addresses the degradation of catalyst performance by molybdenum loss, using cerium to reduce the hotspot temperature of the catalyst bed, thereby increasing stability and lifespan. CN111229242A discloses the preparation of a cerium-doped catalyst by precisely controlling the spatial relationship and ratio of the active components CeO2, Fe2(MoO4)3, and MoO3, modulating the number and distribution of oxygen vacancies in MoO3 and effectively preventing the formation of the inactive phase Fe2O3. CN109806881A uses a mixed rare earth oxide additive modified with lanthanum and cerium as the primary catalyst, and adds an activator to promote metal dispersion, thereby improving catalyst performance.

[0018] In addition to rare earth elements, chromium and vanadium are also used in the modification of iron-molybdenum catalysts. In CN100413584C, chromium and vanadium oxides are added as additives to form a four-component catalyst, which exhibits high conversion and yield, good thermal stability, and a long service life. In CN113457690A, chromium and vanadium oxides are introduced to form a four-component catalyst. CN106693981A uses vanadium for modification, reducing calcination and reaction temperatures, resulting in low cost and long service life.

[0019] CN103933998 modified the catalyst with alkali metal elements to improve the yield and stability of the target product, lower the reaction temperature, and reduce molybdenum loss and by-products. CN111097461A modified the catalyst with tin, zirconium, manganese, and hydroxyapatite, giving it better stability and activity.

[0020] In addition to improving catalytic performance through elemental modification, these existing technologies also utilize improved catalyst pore distribution to enhance reactivity. For example, CN105457648A, while modifying with the additive nickel, controls the coprecipitation reaction rate to improve the catalyst pore distribution, facilitating mass and heat transfer and enhancing the catalyst's reactivity. CN107262105A utilizes an auxiliary pore-forming agent, resulting in a high catalyst surface area, large pore diameter and pore volume, further facilitating mass and heat transfer, and exhibiting excellent low-temperature catalytic activity and stability, thereby increasing conversion and yield.

[0021] Changing the catalyst's shape and physical structure can also improve mass and heat transfer. For example, CN2286649Y discloses a special-shaped columnar catalyst with a large surface area, high porosity, excellent mass and heat transfer performance and activity, low pulverization resistance, and low resistance. CN114618506A also uses 3D printing technology to aid catalyst molding and enhance mechanical strength.

[0022] Inhibiting the loss of active components has always been a key concern in the improvement of iron-molybdenum catalysts. CN112916019A uses a core-shell structure in which iron molybdate is coated with molybdenum trioxide particles, which effectively inhibits the volatilization and loss of molybdenum trioxide, ensures the stability of the catalyst element composition, physical structure, and physical and chemical properties, exhibits excellent catalytic performance, and does not produce wastewater during preparation. CN113368863A allows silicon dioxide to wrap around micron-sized active particles, forming an eggshell-shaped structure with small particles of active components as the core and silicon oxide as the shell, and then pressing into tablets after roasting. CN111097429A loads iron molybdate particles that meet size requirements on molybdenum oxide nanobelts, which can maintain a high molybdenum-iron ratio to improve service life. CN108097259B is also prepared using a nano self-assembly method to adjust the size and morphology of the iron-molybdenum ordered nanostructure, and regulate the spacing, proportion, and distribution of active centers.

[0023] Shell-type structures, coatings, and support preparation technologies also utilize support technology, resulting in lower bed hotspot temperatures than unsupported catalysts and reduced molybdenum sublimation rates. For example, CN101340975B employs a shell-type catalyst structure, comprising molybdenum and iron oxides or precursor compounds, an organic binder, and a silica-alumina sol, coated onto an inert, non-porous support. This reduces bed overheating and extends catalyst life. CN112657504A also utilizes coating technology to prepare active component-structured catalysts. Using ultrasound and a complexing agent for dispersion, the active components are roll-coated onto the surface of a spherical inert support, increasing the effective utilization of the active metal and extending its service life. CN106552658A sprays a prepared Fe-Mo sol onto a spherical SiC support under hot ammonia to produce a spherical coated catalyst. CN108114744B and CN114618579A utilize titanium silicalite (TS-1) as a support, controlling the distribution of the iron and molybdenum active components within the pores of the TS-1, creating a synergistic effect. The monolithic catalysts of CN112619657A and CN114618508A use honeycomb ceramics as a skeleton matrix, load molybdenum oxide nanorod support coating and iron molybdate active components, and improve the activity, selectivity, pressure drop and wear of the catalyst.

[0024] In summary, there are many existing technologies for preparing iron-molybdenum catalysts for the oxidation of methanol to formaldehyde. Although they can all produce highly active catalysts, none of them effectively address the problems of catalyst deactivation and short service life caused by the loss of the active component molybdenum due to high surface temperatures during use. Although CN114931955A specifically prepares high-temperature resistant catalysts, including high-temperature resistant composite oxide materials of magnesium oxide and aluminum oxide or aluminum oxide and silicon oxide, iron-molybdenum catalysts for the oxidation of methanol to formaldehyde are among the most difficult to prepare. Domestic iron-molybdenum processes still rely heavily on imported catalysts, which has caused inconvenience and restrictions on the further application of iron-molybdenum formaldehyde processes in China.

[0025] The oxidation of methanol to formaldehyde is a highly exothermic reaction, making the control of reaction heat crucial. High reaction heat will cause the sublimation of molybdenum oxide in the catalyst under feed gas conditions. With the continued precipitation and loss of molybdenum oxide, the ferric molybdate in the catalyst gradually decomposes into ferrous molybdate and ferric oxide. This not only deactivates the catalyst but also significantly reduces its strength, gradually breaking down and pulverizing, clogging the bed, increasing the bed pressure drop and preventing the reaction from continuing. Maintaining the catalyst's strength and activity stability under the harsh hydrothermal and high-temperature conditions of the reaction is crucial, addressing the current short service life of industrial catalysts and ensuring that the catalyst maintains high strength and catalytic activity even after long periods of operation under high-temperature conditions.

[0026] Summary of the Invention

[0027] To address the above-mentioned issues, the present invention provides a methanol-to-formaldehyde catalyst, its preparation method, and its application. The present invention aims to meet the needs of the actual methanol-to-formaldehyde oxidation reaction process, overcome some of the shortcomings of the prior art, and further improve the performance of methanol-to-formaldehyde catalysts. Specifically, it provides an improved iron-molybdenum catalyst, its preparation method, and its application.

[0028] In a first aspect, the present invention provides a methanol-to-formaldehyde catalyst, which comprises the following components in weight percentage, calculated on a dry basis: MoO3 75wt% to 85wt%, Fe2O3 10wt% to 20wt%, Cr2O3 0.1wt% to 3wt%, CeO2 0.1wt% to 5wt%, P2O5 0.1wt% to 1wt% and Al2O3 0.5wt% to 2.5wt%.

[0029] Furthermore, the methanol-to-formaldehyde catalyst has a MoO3 active phase and a Fe2(MoO4)3 active phase, and contains at least the diffraction peaks shown in Table 1 in the X-ray diffraction data;

[0030] Table 1

[0031] 2q(o)I / Io2q(o)I / Io12.5-13.5M23.5-24.5W13.5-14.5W24.5-25.5M15.0-16.0M25.5-26.5VS19.0-20.0W2 7.0-28.0S20.0-21.0S27.5-28.5W21.5-22.5M28.0-29.0W22.5-23.5VS30.0-31.0M23.0-24.0M31.0-32.0W

[0032] In Table 1, W, M, S, and VS represent the relative ratios of the diffraction peak intensity I to the strongest diffraction peak I, respectively, with W being 0% to 20%, M being 20% ​​to 60%, S being 60% to 80%, and VS being 80% to 100%.

[0033] Furthermore, the parameters of the methanol to formaldehyde catalyst include: specific surface area 5-15 square meters / gram, pore radius 100-250 nanometers, porosity 0.3-0.5 milliliters / gram and bulk density 0.75-1.2 grams / milliliters.

[0034] In a second aspect, the present invention provides a method for preparing the methanol-to-formaldehyde catalyst according to any one of the first aspects, the preparation method comprising the following steps:

[0035] Molybdate and iron salt are added to water, mixed and ground, and then chromium compound is added and ground again to obtain a mixture;

[0036] The mixed material is washed with deionized water and then dried to obtain a first solid;

[0037] The first solid object, a molding aid, and a binder are mixed, formed, and then calcined to obtain a second solid object;

[0038] The second solid material is immersed in a solution containing a cerium compound and a phosphorus compound, and then calcined to obtain the methanol to formaldehyde catalyst.

[0039] Furthermore, the weight ratio of the molybdate, the iron salt and the chromium compound is (75-85): (10-20): (0.1-3).

[0040] Furthermore, the molybdate includes at least one of ammonium heptamolybdate, ammonium tetramolybdate and ammonium dimolybdate; the iron salt includes at least one of ferric nitrate, ferric sulfate and basic ferric acetate; and the chromium compound includes at least one of chromium nitrate, chromium sulfate, chromium acetate, chromium oxalate, chromium carbonate, chromium hydroxide and chromium trioxide.

[0041] Furthermore, the weight ratio of the first solid object, the molding aid and the binder is (85-95): (0.1-3): (5-15).

[0042] Furthermore, the weight ratio of the second solid, the cerium compound and the phosphorus compound is (95-99): (0.1-5): (0.1-1).

[0043] Furthermore, the cerium compound includes at least one of cerium nitrate, cerium sulfate, cerium acetate, cerium oxalate, cerium carbonate, cerium hydroxide and cerium dioxide.

[0044] Furthermore, the phosphorus compound includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and aluminum phosphate.

[0045] Furthermore, the grinding working parameters include: grinding temperature of 40 to 90° C., and grinding time of 10 to 250 minutes.

[0046] Furthermore, the drying working parameters include: drying temperature of 100-150° C., and drying time of 1-15 hours.

[0047] Furthermore, the preparation and molding method includes at least one of extrusion molding and compression molding, and the prepared molding shape includes at least one of spherical, sheet-like, cylindrical, ring-like, hollow cylindrical, hollow chrysanthemum-shaped and special-shaped columnar, and the crushing strength is 80 to 170 Newtons.

[0048] Furthermore, the preparation and molding method is compression molding, and the prepared molding has an outer dimension of a hollow cylinder with a size of (3 to 8) × (1 to 5) × (2 to 5) mm and a crushing strength of 100 to 160 Newtons.

[0049] Furthermore, the roasting working parameters include: a roasting temperature of 250-450° C. and a roasting time of 0.5-2 hours.

[0050] Furthermore, the calcination working parameters include: calcination temperature of 400-700° C., and calcination time of 1-10 hours.

[0051] In a third aspect, the present invention provides a methanol-to-formaldehyde catalyst as described in any one of the first aspects, and / or a methanol-to-formaldehyde catalyst prepared by the preparation method as described in any one of the second aspects, in a methanol-to-formaldehyde process. The reaction conditions of the methanol-to-formaldehyde catalyst in the methanol oxidation to formaldehyde conversion process include: 270-380°C, pressure 0.1-0.3 MPa, contact reaction time between the material and the catalyst for 2-5 minutes, and a volume fraction of methanol in the feed of 1-10%.

[0052] The above technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0053] 1) The present invention provides a methanol-to-formaldehyde catalyst, specifically an iron-molybdenum-type methanol oxidation-to-formaldehyde catalyst. The catalyst active unit has better dispersibility, solves the problem of easy agglomeration of active phases, and realizes efficient utilization of active metals. At the same time, it effectively inhibits the migration and loss of molybdenum elements and the generation of inactive phases in a complex hydrothermal environment during the use of the catalyst, so that the active components of the catalyst are more evenly distributed during long-term reactions and the molybdenum active components are not easily lost. The catalyst has good diffusion and conductivity properties and excellent mechanical properties, overcoming the problems of existing catalysts such as insufficient effective utilization of active metals, easy deactivation of catalysts, and short service life.

[0054] 2) When used in the process of producing formaldehyde by oxidizing methanol, the methanol-to-formaldehyde catalyst provided by the present invention has very good catalytic conversion reaction performance, higher activity and selectivity, especially good mechanical strength under harsh reaction conditions, excellent stable conversion performance, high yield of product formaldehyde, and can save reaction raw materials, reduce reaction by-products, and reduce the cost of the conversion process. It is particularly suitable for producing formaldehyde by oxidizing methanol in industrial processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0057] FIG1 is a schematic flow diagram of a method for preparing a methanol-to-formaldehyde catalyst provided in an embodiment of the present invention.

[0058] FIG2 is an XRD diffraction characterization diagram of the methanol-to-formaldehyde catalyst provided in an embodiment of the present invention.

[0059] FIG3 is a physical diagram of the appearance of the methanol-to-formaldehyde catalyst after molding provided by an embodiment of the present invention.

[0060] DETAILED DESCRIPTION

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0062] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0063] While improvements have been made to existing iron-molybdenum catalysts for methanol oxidation to formaldehyde, enhancing some aspects of their performance, deficiencies remain. These improvements have made it difficult to comprehensively address existing issues with existing catalysts, such as the tendency for active phases to agglomerate, insufficient utilization of active metals, the tendency for molybdenum to sublime and lose during use, the gradual formation of inactive substances within the catalyst, which leads to catalyst deactivation, and insufficient mechanical strength and wear resistance, which shortens the catalyst's service life. Continuous research and improvement are needed to further improve the performance of iron-molybdenum catalysts, their preparation methods, and their application in methanol oxidation to formaldehyde, in terms of catalyst activity, selectivity, and, in particular, stability.

[0064] The purpose of the present invention is to meet the needs of the above-mentioned actual reaction process, overcome some deficiencies still existing in the prior art, further improve the performance of methanol oxidation to formaldehyde catalyst, and provide an improved iron-molybdenum catalyst and its preparation method and application. The present invention is specifically achieved through the following technical solutions:

[0065] In a first aspect, the present invention provides a methanol-to-formaldehyde catalyst, which comprises the following components in weight percentage, calculated on a dry basis: MoO3 75wt% to 85wt%, Fe2O3 10wt% to 20wt%, Cr2O3 0.1wt% to 3wt%, CeO2 0.1wt% to 5wt%, P2O5 0.1wt% to 1wt% and Al2O3 0.5wt% to 2.5wt%.

[0066] In some specific embodiments, the methanol to formaldehyde catalyst has a MoO3 active phase and a Fe2(MoO4)3 active phase, and contains at least the diffraction peaks shown in Table 1 in the X-ray diffraction data;

[0067] Table 1

[0068] 2q(o)I / Io2q(o)I / Io12.5-13.5M23.5-24.5W13.5-14.5W24.5-25.5M15.0-16.0M25.5-26.5VS19.0-20.0W2 7.0-28.0S20.0-21.0S27.5-28.5W21.5-22.5M28.0-29.0W22.5-23.5VS30.0-31.0M23.0-24.0M31.0-32.0W

[0069] In Table 1, W, M, S, and VS represent the relative ratios of the diffraction peak intensity I to the strongest diffraction peak I, respectively, with W being 0% to 20%, M being 20% ​​to 60%, S being 60% to 80%, and VS being 80% to 100%.

[0070] In some specific embodiments, the parameters of the methanol to formaldehyde catalyst include: specific surface area 5-15 m2 / g, pore radius 100-250 nm, porosity 0.3-0.5 ml / g and bulk density 0.75-1.2 g / ml.

[0071] In the actual methanol oxidation process to formaldehyde, it is crucial for the catalyst to maintain activity, selectivity, and stability. The deactivation and deterioration of selectivity in iron-molybdenum catalysts are primarily due to the loss of molybdenum during use. The accumulated iron exacerbates side reactions, ultimately necessitating catalyst replacement. To maintain long-term selectivity, industrial catalysts typically incorporate additional molybdenum oxide. This means that the molybdenum-to-iron molar ratio in the catalyst system must be greater than the 1.5:1 stoichiometric ratio based on the iron molybdate formula. Some industrial iron-molybdenum catalysts have molybdenum-to-iron ratios of 2:1 or even higher, which indeed improves their lifespan.

[0072] However, an excessively high molybdenum-to-iron ratio often results in relatively low catalyst activity, and it is difficult to maintain sufficiently high catalytic activity at high molybdenum-to-iron ratios. To balance these two factors, the present invention aims to control the composition of active components during the grinding process, improving the size and distribution of active component particles. This adjustment and control of size and distribution is crucial to ensuring catalyst performance.

[0073] In a second aspect, based on a general inventive concept, the present invention provides a method for preparing the methanol-to-formaldehyde catalyst according to any one of the first aspects, as shown in FIG1 , the preparation method comprising the following steps:

[0074] Molybdate and iron salt are added to water, mixed and ground, and then chromium compound is added and ground again to obtain a mixture;

[0075] The mixed material is washed with deionized water and then dried to obtain a first solid;

[0076] The first solid object, a molding aid, and a binder are mixed, formed, and then calcined to obtain a second solid object;

[0077] The second solid material is immersed in a solution containing a cerium compound and a phosphorus compound, and then calcined to obtain the methanol to formaldehyde catalyst.

[0078] In the preparation of catalysts, it is not easy to obtain catalysts with very low sodium content. When the catalyst contains insoluble sodium salts, it will cause accelerated over-oxidation to form CO2 and H2O, thereby reducing the yield of formaldehyde. Therefore, during the preparation process, the present invention seeks to reduce the alkali metal sodium content, which will have a positive impact on the performance of the catalyst. At the same time, how to effectively improve the mixing uniformity of molybdenum oxide and iron molybdate on a microscopic scale is one of the key factors for improving activity stability. In industry, methanol to formaldehyde mostly uses fixed bed reactors. Considering the bed pressure drop factor, the size of the molded catalyst is generally larger. For large particle catalysts, during use, the active components inside the particles are often not effectively utilized due to diffusion factors. Compared with the original powder of the active components before molding, the catalytic efficiency and stability of the molded catalyst will be significantly reduced.

[0079] Since the oxidation of methanol to formaldehyde is a highly exothermic reaction, a large amount of inert gas needs to be mixed in order to avoid the risk of explosion. The fixed-bed reactor of the iron-molybdenum method generally requires the use of multiple tubes, and the process of loading catalyst particles is very cumbersome. Moreover, under high space velocity and thermal shock, the catalyst particles are very easy to collide and wear each other. In the later stage of the reaction, the bed is blocked by fine powder, which is a common phenomenon in production. Therefore, the present invention uses powder engineering technology in the above-mentioned preparation steps and subsequent molding to prepare high-strength, impact-resistant catalyst particles, while taking into account both diffusion and protective layer factors, which is very important for maintaining the stability of the reaction process and the stability of the catalyst performance.

[0080] This invention utilizes the principle of an ultra-thin eggshell structure to produce an iron-molybdenum catalyst for methanol oxidation to formaldehyde. The active components are actually encapsulated by nanoscale modified sol compound particles formed after calcination, forming a thin shell-core structure. This enhances the catalyst's activity, mechanical strength, and service life, particularly in harsh hydrothermal reaction environments. The ultra-thin shell-core structure encapsulates the active components while maintaining their dispersion, increasing mechanical strength and enhancing selectivity. It effectively prevents localized overheating caused by combustion and explosion on the catalyst surface, thereby mitigating molybdenum loss and improving the catalyst's activity, stability, and service life.

[0081] The catalyst prepared and the preparation method of the present invention can effectively disperse and stabilize the active centers of the catalyst, and provide easier diffusion conditions for reactants to be adsorbed and desorbed on the catalyst in terms of structure and shape, thereby improving the activity and stability of the catalyst, effectively dispersing the heat on the catalyst surface, and reducing the loss of molybdenum due to local high temperature; the addition of an appropriate amount of oxide binder greatly improves the mechanical strength of the catalyst; the prepared catalyst has a high conversion rate, few by-products, good mechanical strength, and a long service life.

[0082] In some specific embodiments, the weight ratio of the molybdate, the iron salt, and the chromium compound is (75-85):(10-20):(0.1-3).

[0083] In some specific embodiments, the molybdate includes at least one of ammonium heptamolybdate, ammonium tetramolybdate and ammonium dimolybdate; the iron salt includes at least one of ferric nitrate, ferric sulfate and basic ferric acetate; and the chromium compound includes at least one of chromium nitrate, chromium sulfate, chromium acetate, chromium oxalate, chromium carbonate, chromium hydroxide and chromium trioxide.

[0084] In some specific embodiments, the weight ratio of the first solid object, the molding aid, and the binder is (85-95): (0.1-3): (5-15).

[0085] In some specific embodiments, the weight ratio of the second solid, the cerium compound, and the phosphorus compound is (95-99):(0.1-5):(0.1-1).

[0086] In some specific embodiments, the cerium compound comprises at least one of cerium nitrate, cerium sulfate, cerium acetate, cerium oxalate, cerium carbonate, cerium hydroxide, and cerium dioxide. During the preparation and reaction process of the present invention, cerium molybdate, which is trivalent or tetravalent cerium, can further enhance the performance of the catalyst. Cerium molybdate significantly reduces hotspot temperatures in the catalyst bed, increasing the stability of the catalyst bed under reaction conditions and thereby extending its service life.

[0087] In some specific embodiments, the phosphorus compound includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and aluminum phosphate.

[0088] In some specific embodiments, the grinding operating parameters include: a grinding temperature of 40 to 90°C and a grinding time of 10 to 250 minutes. Specifically, after the molybdate and the iron salt are added to water and mixed and then ground: the molybdate and the iron salt are mixed according to the composition ratio, 0 to 30% of water is added to the total weight, and then zirconium beads are added at a weight ratio of 1:1 to 1:5, and the mixture is ground in a stirred mill at 40 to 90°C for 60 to 250 minutes. When the chromium compound is added and the grinding is continued: after the chromium compound modification component is added according to the composition ratio, the grinding is continued for 10 to 30 minutes.

[0089] In some specific embodiments, the drying working parameters include: a drying temperature of 100-150° C., and a drying time of 1-15 hours.

[0090] In some specific embodiments, the preparation and molding method includes at least one of extrusion molding and compression molding, and the shape of the prepared molding includes at least one of spherical, sheet-like, cylindrical, annular, hollow cylindrical, hollow chrysanthemum-shaped, and special-shaped columns, with a crushing strength of 80 to 170 Newtons. The molding method involved in the present invention is well known to those skilled in the art, and the molding device can be easily obtained by commercial means; preferably, during the molding preparation process, the dried powder is first sieved through 40 to 200 mesh; the screening method is well known to those skilled in the art, and the screening device can be easily obtained by commercial means; the molding aids and binders are alumina sol, hydrated alumina, polyaluminum oxalate, and acidic aluminum sol, and the general addition amount is 5 to 30 wt% of the total dry mass of the catalyst composition calculated as alumina. Preferably, alumina sol is added according to the composition restrictions of the catalyst. It is a commonly used construction binder and can be purchased commercially.

[0091] The preparation method of the methanol-to-formaldehyde catalyst provided by the present invention is simple, does not require additional specialized equipment, and is suitable for industrial production. Furthermore, this preparation method is based on the methanol-to-formaldehyde catalyst described in any one of the first aspects, and thus exhibits at least the beneficial effects of the methanol-to-formaldehyde catalyst described in any one of the first aspects, which will not be further elaborated herein.

[0092] In a third aspect, based on a general inventive concept, the present invention provides the use of the methanol-to-formaldehyde catalyst described in any one of the first aspects, and / or the methanol-to-formaldehyde catalyst prepared by the preparation method described in any one of the second aspects in a methanol-to-formaldehyde process, wherein the reaction conditions of the methanol-to-formaldehyde catalyst in the methanol oxidation to formaldehyde conversion process include: 270-380°C, pressure 0.1-0.3 MPa, contact reaction time of the material and the catalyst for 2-5 minutes, and a volume fraction of methanol in the feed of 1-10%.

[0093] The methanol-to-formaldehyde catalyst provided by the present invention has very good catalytic conversion reaction performance, higher activity and selectivity when used in the process of producing formaldehyde by oxidizing methanol. In particular, it has good mechanical strength under harsh reaction conditions, excellent stable conversion performance, and a high yield of product formaldehyde. It can save reaction raw materials, reduce reaction by-products, and lower the cost of the conversion process. It is particularly suitable for producing formaldehyde by oxidizing methanol in industrial processes and has wide practical application value.

[0094] In some specific embodiments, preferably, the reaction conditions of the catalyst in the methanol oxidation to formaldehyde conversion process are: 278-282°C under normal pressure, 2.5-3.5 minutes of contact reaction time between the material and the catalyst, and 5.5-6.5% by volume of methanol in the feed.

[0095] In summary, the technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0096] 1) The present invention provides a methanol-to-formaldehyde catalyst, specifically an iron-molybdenum-type methanol oxidation-to-formaldehyde catalyst. The catalyst active unit has better dispersibility, solves the problem of easy agglomeration of active phases, and realizes efficient utilization of active metals. At the same time, it effectively inhibits the migration and loss of molybdenum elements and the generation of inactive phases in a complex hydrothermal environment during the use of the catalyst, so that the active components of the catalyst are more evenly distributed during long-term reactions and the molybdenum active components are not easily lost. The catalyst has good diffusion and conductivity properties and excellent mechanical properties, overcoming the problems of existing catalysts such as insufficient effective utilization of active metals, easy deactivation of catalysts, and short service life.

[0097] 2) When used in the process of producing formaldehyde by oxidizing methanol, the methanol-to-formaldehyde catalyst provided by the present invention has very good catalytic conversion reaction performance, higher activity and selectivity, especially good mechanical strength under harsh reaction conditions, excellent stable conversion performance, high yield of product formaldehyde, and can save reaction raw materials, reduce reaction by-products, and reduce the cost of the conversion process. It is particularly suitable for producing formaldehyde by oxidizing methanol in industrial processes.

[0098] It should be noted that the raw material components involved in the methanol-to-formaldehyde catalyst, preparation method, and application provided by the present invention, unless otherwise specified or detailed, can be purchased directly from commercial products or prepared in-house using existing preparation processes. Furthermore, the process steps involved, unless otherwise specified or detailed, can be carried out according to actual needs and existing processes, and will not be detailed in this application document.

[0099] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0100] The methanol-to-formaldehyde catalyst provided by the present invention is specifically an iron-molybdenum catalyst suitable for use in the production process of methanol oxidation to formaldehyde. In the following examples, comparative examples, and test examples, the element content in the catalyst was determined by X-ray fluorescence; the specific surface area, pore volume, and pore distribution of the catalyst were determined by a combination of nitrogen adsorption and mercury porosimetry; and the mechanical strength of the catalyst was determined using a pressure gauge. Formaldehyde and methanol solutions were analyzed and measured in accordance with the national standard GB / T 9009-2011, "Industrial Formaldehyde Solutions." For other analytical tests, please refer to the relevant analytical methods in the "National Standard for Testing Methods for Petroleum and Petroleum Products," published by China Standards Press in 1989, and the "Analytical Methods for Petrochemical Industry (RIPP Test Method)," published by Science Press in 1990.

[0101] Example 1

[0102] This example provides a methanol-to-formaldehyde catalyst, the preparation method of which comprises the following steps:

[0103] According to the calculated amount of the catalyst composition, 880 g of ammonium molybdate tetrahydrate (industrial product, 98%) and 576 g of ferric nitrate nonahydrate (industrial product, 99%) were weighed, mixed with zirconium balls, and placed in a stirred mill. At this time, the ball-to-material mass ratio was 3. For the convenience of grinding, an appropriate amount of deionized water not exceeding 30% of the total amount of the material was added during the grinding. The grinding time was 90 minutes and the material temperature was 70°C. 11 g of chromium nitrate (chemically pure reagent, 90%) was weighed and added to the material, and the grinding was continued for 30 minutes. After the grinding was completed, the material was taken out, washed three times with deionized water, filtered, and the filter cake was placed in an oven and dried at 90°C for 4 hours to obtain a catalyst precursor sample. Then, 100 g of alumina sol (industrial product, Al2O3 20%), and then pressed into a hollow cylindrical shape using a tablet press; after drying, the mixture was calcined in a muffle furnace at 400°C for 1 hour. 13 g of cerium nitrate hexahydrate (chemically pure reagent, 99%) and 5 g of diammonium hydrogen phosphate (chemically pure reagent, 99%) were weighed to prepare an impregnation solution for impregnation; the mixture was dried at 110°C for 1 hour, and then calcined in a muffle furnace at 560°C for 4 hours to obtain the catalyst sample of Example 1.

[0104] The catalyst obtained in this example has a specific surface area of ​​9.1 m2 / g, a pore radius of 100-250 nm, a porosity of 0.39 ml / g, a bulk density of 0.82 g / ml, and a crushing strength of 152 Newtons. Its XRD diffraction pattern is shown in FIG2 . The catalyst strength is shown in FIG2 . When the diffraction angle is 20-30, the stronger the strength. The catalyst appearance is shown in FIG3 , and the external dimensions are 5 mm × 2.5 mm × 3 mm.

[0105] Example 2

[0106] This example provides a methanol-to-formaldehyde catalyst, the preparation method of which comprises the following steps:

[0107] Weigh ammonium heptamolybdate and ferric sulfate according to the calculated amount, mix them with zirconium balls, and place them in a stirred mill. At this time, the ball-to-material mass ratio is 5. For the convenience of grinding, add an appropriate amount of deionized water not exceeding 30% of the total amount of the material during grinding. The grinding time is 70 minutes and the material temperature is 80°C. Weigh the calculated amount of chromium oxalate and add it to the material, and continue grinding for 40 minutes. After the grinding is completed, take out the material, put it into an oven and dry it at 100°C for 2 hours to obtain a catalyst precursor sample. Add the calculated amount of alumina sol and mix it, and then press it into a hollow cylinder with a tablet press. Then, place the sample in a muffle furnace and roast it at 380°C for 4 hours. Weigh cerium oxalate and ammonium phosphate according to the calculated amount to prepare an impregnation solution for impregnation; dry it at 110°C for 1 hour, place it in a muffle furnace and roast it at 550°C for 6 hours to obtain the catalyst sample of Example 2.

[0108] The composition, specific surface area, porosity, bulk density, crushing strength, pore radius distribution, and external dimensions of the catalyst obtained in this example are similar to those in Example 1. The XRD diffraction pattern is similar to that in FIG2 , and the catalyst appearance is the same as that in FIG3 .

[0109] Example 3

[0110] This example provides a methanol-to-formaldehyde catalyst, the preparation method of which comprises the following steps:

[0111] Weigh ammonium dimolybdate and basic ferric acetate according to the calculated ratio, mix them with zirconium balls, and place them in a stirred mill. At this time, the ball-to-material mass ratio is 4. For the convenience of grinding, add an appropriate amount of deionized water not exceeding 30% of the total amount of the material during grinding. The grinding time is 120 minutes and the material temperature is 85°C. Weigh the calculated amount of chromium carbonate and add it to the material, and continue grinding for 20 minutes. After the grinding is completed, take out the material, put it into an oven and dry it at 95°C for 2 hours to obtain a catalyst precursor sample. Add the calculated amount of nano-alumina sol and mix it, and then press it into a hollow cylinder with a tablet press. Then, place the sample in a muffle furnace and roast it at 350°C for 5 hours. Weigh cerium carbonate and ammonium dihydrogen phosphate according to the calculated amount to prepare an impregnation solution for impregnation; dry it at 100°C for 2 hours, place it in a muffle furnace and roast it at 600°C for 2 hours to obtain the catalyst sample of Example 3.

[0112] The composition, specific surface area, porosity, bulk density, crushing strength, pore radius distribution, and external dimensions of the catalyst obtained in this example are similar to those in Example 1. The XRD diffraction pattern is similar to that in FIG2 , and the catalyst appearance is the same as that in FIG3 .

[0113] Comparative Example 1

[0114] This example provides a methanol-to-formaldehyde catalyst. A catalyst having a molar ratio of iron and molybdenum as the main active component similar to that of Example 1 was prepared according to the methods and steps disclosed in USP 3408309, USP 3846341, USP 3978136, USP 4420421, and USP 4829042, serving as the sample for Comparative Example 1. The preparation method comprises the following steps:

[0115] 880 g of ammonium molybdate tetrahydrate (technical, 98%) and 576 g of ferric nitrate nonahydrate (technical, 99%) were weighed and dissolved in water, with the stirrer running for the first hour. A colloid was obtained. The pale yellow suspension at 8-10°C was slowly reheated with moderate stirring (300 rpm) and hardened at 14°C approximately 20 minutes after the introduction of the reactants. Aging at 30°C for 2 hours yielded a dark green, homogeneous, transparent, crystalline, amorphous gel. This gel was dried in a 70°C oven for 48 hours, converting to a new reddish-brown gel containing 60.44% ammonium nitrate and 1-2% water by weight. This gel was also transparent and crystallographically amorphous. The gel was then dried in an oven heated to 170-180°C for 36 hours, converting to a new sandy-yellow product with a weight loss of 18-22%. This product was removed and crushed to a particle size of less than 250 μm. 1200 g of the resulting powder were gradually moistened with 120 ml of water to form a homogeneous paste, which was aged for 2 hours at 20° C. The resulting plastic material was extruded in an Andor apparatus to obtain cylinders of average length with a diameter of 3-5 mm.

[0116] Comparative Example 2

[0117] This example provides a methanol-to-formaldehyde catalyst. A catalyst having a similar molar ratio of iron and molybdenum as the main active component was prepared according to the method and steps of Comparative Example 1, and a metal promoter Cr compound was added in the same proportion as in Example 1 to prepare the sample of Comparative Example 2. The preparation method includes the following steps:

[0118] 880 g of ammonium molybdate tetrahydrate (technical product, 98%) and 576 g of ferric nitrate nonahydrate (technical product, 99%) were weighed and dissolved in water, mixed, and stirred. 11 g of chromium nitrate (chemically pure reagent, 90%) was added to the mixture. During the first hour, with the stirrer running, a colloid was obtained. The pale yellow suspension at 8-10°C was slowly reheated with moderate stirring (300 rpm) and hardened at 14°C approximately 20 minutes after the introduction of the reactants. Aging at 30°C for 2 hours yielded a dark green, homogeneous, transparent, crystalline, amorphous gel. Drying in a 70°C oven for 48 hours converted the gel into a new, reddish-brown gel containing 60.44% ammonium nitrate and 1-2% water by weight. This gel was also transparent and crystallographically amorphous. The gel was then dried in an oven heated to 170-180°C for 36 hours, converting it to a new, sandy-yellow gel with a weight loss of 18-22%. The product was removed and pulverized to a particle size of less than 250 μm. 1200 g of the resulting powder was gradually moistened with 120 ml of water to form a homogeneous paste, which was aged at 20° C. for 2 hours. The resulting plastic material was extruded in an Andor-type apparatus to obtain cylinders with an average length of 3-5 mm in diameter.

[0119] Comparative Example 3

[0120] This example provides a methanol-to-formaldehyde catalyst. A catalyst having a similar molar ratio of iron and molybdenum as the main active components was prepared according to the method and steps of Comparative Example 1, and a metal promoter Ce compound was added in the same proportion as in Example 1 to prepare the sample of Comparative Example 3. The preparation method includes the following steps:

[0121] 880 g of ammonium molybdate tetrahydrate (technical product, 98%) and 576 g of ferric nitrate nonahydrate (technical product, 99%) were weighed and dissolved in water, and 13 g of cerium nitrate hexahydrate (chemically pure reagent, 99%) was weighed and stirred. During the first hour, the stirrer was running, resulting in a colloid. The pale yellow suspension at 8-10°C was slowly reheated with moderate stirring (300 rpm) and hardened at 14°C approximately 20 minutes after the introduction of the reactants. Aging at 30°C for 2 hours yielded a dark green, homogeneous, transparent, crystalline, amorphous gel. Drying in an oven at 70°C for 48 hours transformed the gel into a new, reddish-brown gel containing 60.44% ammonium nitrate and 1-2% water by weight. This gel was also transparent and crystallographically amorphous. The gel was then dried in an oven heated to 170-180°C for 36 hours, transforming it into a new, sandy-yellow gel with a weight loss of 18-22%. The product was removed and pulverized to a particle size of less than 250 μm. 1200 g of the resulting powder was gradually moistened with 120 ml of water to form a homogeneous paste, which was aged at 20° C. for 2 hours. The resulting plastic material was extruded in an Andor-type apparatus to obtain cylinders with an average length of 3-5 mm in diameter.

[0122] Comparative Example 4

[0123] This example provides a methanol-to-formaldehyde catalyst. A catalyst having a similar molar ratio of iron and molybdenum as the main active components was prepared according to the method and steps of Comparative Example 1, and an alumina binder was added in the same proportion as in Example 1 to prepare the sample of Comparative Example 4. The preparation method includes the following steps:

[0124] 880 g of ammonium molybdate tetrahydrate (technical, 98%) and 576 g of ferric nitrate nonahydrate (technical, 99%) were weighed and dissolved in water, mixed, and then 100 g of alumina sol (technical, 20% Al2O3) was added and kneaded. The stirrer was running for the first hour to produce a colloid. The pale yellow suspension at 8-10°C was slowly reheated with moderate stirring (300 rpm) and hardened at 14°C approximately 20 minutes after the introduction of the reactants. Aging at 30°C for 2 hours yielded a dark green, homogeneous, transparent, crystalline, amorphous gel. Drying in an oven at 70°C for 48 hours converted the gel into a new reddish-brown gel containing 60.44% ammonium nitrate and 1-2% water by weight. This gel was also transparent and crystallographically amorphous. The gel is then dried in an oven heated to 170-180°C for 36 hours, transforming into a new sandy-yellow product with a weight loss of 18-22%. This product is removed and crushed to a particle size of less than 250 microns. 1200 grams of the resulting powder is gradually moistened with 120 milliliters of water to form a homogeneous paste, which is then aged at 20°C for 2 hours. The resulting plastic material is extruded in an Andor-type apparatus to produce cylinders with an average length of 3-5 mm in diameter.

[0125] Test Case

[0126] The performance of the methanol-to-formaldehyde catalysts obtained in Examples 1-2 and Comparative Examples 1-4 was tested.

[0127] Testing Method: The stable activity and selectivity of the catalysts of various examples and comparative examples of the present invention were tested using a small laboratory reactor evaluation device. Data after 600 hours of reaction were compared, and catalyst damage was also detected. The reaction conditions were: reaction temperature of 283°C at atmospheric pressure, methanol volume fraction of 6.2%, and contact reaction time between methanol and catalyst of 3 minutes. The reaction results are shown in Table 2.

[0128] Table 2 Results of 600-hour long-cycle reaction of methanol oxidation to formaldehyde

[0129] Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Methanol conversion rate / % 99.1 99.2 98.8 85.2 89.7 89.4 84.8 Formaldehyde yield / % 90.2 89.7 89.9 84.1 82.9 83.2 83.7

[0130] The comparative data in Table 2 demonstrates that, even without process optimization, the stable reaction activity and formaldehyde yield of Examples 1-3 using the methanol-to-formaldehyde catalysts (i.e., iron-molybdenum catalysts) provided by the present invention were higher than those of the catalyst samples in Comparative Examples 1-4. After long-term operation, the catalysts in Examples 1-3 maintained their integrity, maintained their strength, and significantly outperformed the catalysts in Comparative Examples 1-4 in terms of breakage, pulverization, and overall integrity. This demonstrates that the iron-molybdenum catalysts of the present invention possess higher stability, activity, and usability than the catalysts in the Comparative Examples. In Table 2, the catalyst selectivity of Examples 1-3 is also slightly higher than that of the catalysts in Comparative Examples 1-4. Therefore, the methanol-to-formaldehyde catalysts (i.e., iron-molybdenum catalysts) of the present invention exhibit superior catalytic reaction performance and usability.

[0131] Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in a range format is only for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention; therefore, the range description should be considered to have specifically disclosed all possible subranges and single numerical values ​​within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is intended to include any cited numeral (fractional or integer) within the indicated range.

[0132] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A methanol to formaldehyde catalyst, characterized in that Calculated on a dry basis, the methanol-to-formaldehyde catalyst includes the following components in weight percentage: MoO3 75wt% to 85wt%, Fe2O3 10wt% to 20wt%, Cr2O3 0.1wt% to 3wt%, CeO2 0.1wt% to 5wt%, P2O5 0.1wt% to 1wt% and Al2O3 0.5wt% to 2.5wt%.

2. The methanol to formaldehyde catalyst according to claim 1, characterized in that The methanol-to-formaldehyde catalyst has a MoO3 active phase and a Fe2(MoO4)3 active phase, and contains at least the diffraction peaks shown in Table 1 in the X-ray diffraction data; Table 1 2q(o)I / Io2q(o)I / Io12.5-13.5M23.5-24.5W13.5-14.5W24.5-25.5M15.0-16.0M25.5-26.5VS19.0-20.0W2 7.0-28.0S20.0-21.0S27.5-28.5W21.5-22.5M28.0-29.0W22.5-23.5VS30.0-31.0M23.0-24.0M31.0-32.0W In Table 1, W, M, S, and VS represent the relative ratio of the diffraction peak intensity I to the strongest diffraction peak I, respectively, with W being 0% to 20%, M being 20% ​​to 60%, S being 60% to 80%, and VS being 80% to 100%.

3. The methanol to formaldehyde catalyst according to claim 1 or 2, characterized in that: The parameters of the methanol-to-formaldehyde catalyst include: a specific surface area of ​​5 to 15 square meters / gram, a pore radius of 100 to 250 nanometers, a porosity of 0.3 to 0.5 milliliters / gram, and a bulk density of 0.75 to 1.2 grams / milliliters.

4. A method for preparing a methanol-to-formaldehyde catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: Adding molybdate and iron salt into water, mixing and grinding, then adding chromium compound and continuing grinding to obtain a mixture; The mixed material is washed with deionized water and then dried to obtain a first solid; The first solid object, a molding aid and a binder are mixed, formed and then calcined to obtain a second solid object; The second solid material is immersed in a solution containing a cerium compound and a phosphorus compound, and then calcined to obtain the methanol to formaldehyde catalyst.

5. The method for preparing a methanol-to-formaldehyde catalyst according to claim 4, characterized in that: The weight ratio of the molybdate, the iron salt and the chromium compound is (75-85): (10-20): (0.1-3).

6. The method for preparing a methanol-to-formaldehyde catalyst according to claim 4, characterized in that: The molybdate includes at least one of ammonium heptamolybdate, ammonium tetramolybdate and ammonium dimolybdate; the iron salt includes at least one of ferric nitrate, ferric sulfate and basic ferric acetate; the chromium compound includes at least one of chromium nitrate, chromium sulfate, chromium acetate, chromium oxalate, chromium carbonate, chromium hydroxide and chromium trioxide.

7. The method for preparing a methanol-to-formaldehyde catalyst according to claim 4, characterized in that: The weight ratio of the first solid object, the molding aid and the binder is (85-95): (0.1-3): (5-15); the weight ratio of the second solid object, the cerium compound and the phosphorus compound is (95-99): (0.1-5): (0.1-1).

8. The method for preparing a methanol-to-formaldehyde catalyst according to claim 4, characterized in that: The cerium compound includes at least one of cerium nitrate, cerium sulfate, cerium acetate, cerium oxalate, cerium carbonate, cerium hydroxide and cerium dioxide; the phosphorus compound includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid and aluminum phosphate.

9. The method for preparing a methanol-to-formaldehyde catalyst according to claim 4, characterized in that: The working parameters of the roasting include: a roasting temperature of 250-450° C. and a roasting time of 0.5-2 hours; the working parameters of the calcination include: a calcination temperature of 400-700° C. and a calcination time of 1-10 hours.

10. The methanol-to-formaldehyde catalyst according to any one of claims 1 to 3, and / or the use of the methanol-to-formaldehyde catalyst prepared by the preparation method according to any one of claims 6 to 9 in a methanol-to-formaldehyde process, characterized in that: The reaction conditions of the methanol-to-formaldehyde catalyst in the methanol oxidation-to-formaldehyde conversion process include: 270-380° C., pressure 0.1-0.3 MPa, contact reaction time between the material and the catalyst 2-5 minutes, and a volume fraction of methanol in the feed of 1-10%.

Images