Preparation method and application of a catalyst for producing anhydrous formaldehyde by oxygen-free dehydrogenation of methanol

Abstract

The present invention belongs to the field of chemical technology innovation and relates to a preparation method and application of a catalyst for the oxygen-free dehydrogenation of methanol to anhydrous formaldehyde. The dehydrogenation catalyst is prepared by modifying a molecular sieve with alkali metal ions and transition metal ions. By combining the low-temperature catalytic performance of transition metals Ag, Cu, and Zn, the strong adsorption of methanol methoxy groups by oxygen-rich vacancies on the surface of reducible metal oxides, and the high-temperature catalytic activity of Li-doped acidic adjustable molecular sieves, the AgCeLi-USY modified molecular sieve catalyst achieves excellent catalytic activity over a wide temperature range of 350-700°C, with a methanol conversion rate of 80-99% and a formaldehyde yield of 54-65%. It can also be recycled and reused more than six times.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a preparation method and application of a catalyst for producing anhydrous formaldehyde through anaerobic dehydrogenation of methanol. Background Art

[0002] Formaldehyde is an important organic chemical raw material, mainly used to produce chemical products such as urea-formaldehyde resin, phenol-formaldehyde resin, melamine-formaldehyde resin, urotropine, polyols, polyoxymethylene, nylon-4 and vinylon. It is also widely used in medicine, pesticides, dyes, disinfectants, fungicides, preservatives, wood processing and chemical fiber. In recent years, the increasing demand for high-performance engineering plastics, electronic chemicals and urotropine has led to an increasing demand for high-concentration formaldehyde. At present, the industry mainly adopts a two-step method to prepare high-concentration formaldehyde: (1) Ag or Cu catalyst oxidative dehydrogenation at 597~697 °C or iron molybdate catalyst at 297~397 °C with excess air oxidation to prepare an aqueous solution containing 35~45% formaldehyde; (2) the formaldehyde aqueous solution is concentrated by vacuum distillation or solvent azeotropy. However, the vapor pressure of formaldehyde aqueous solution is very low and formaldehyde and water easily form azeotropes, so the separation and purification of formaldehyde aqueous solution is very difficult and expensive.

[0003] The oxygen-free dehydrogenation of methanol to produce anhydrous formaldehyde is a new process with potential industrial prospects. It can avoid the shortcomings of high energy consumption, high cost and environmental pollution caused by the traditional oxidation-dehydration method. Directly converting methanol into anhydrous formaldehyde simplifies the process flow, reduces energy consumption and cost, reduces the emission of wastewater and exhaust gas, and avoids problems such as the oxidation of methanol to formic acid and corrosion of equipment. However, this process needs to be carried out at high temperatures of 400~800 ℃, and faces problems such as the generation of thermodynamically favorable by-products at high temperatures, the decomposition of formaldehyde at high temperatures, and self-polymerization and oxidation at low temperatures. Therefore, the difficulty of this technology lies in developing a catalyst with high activity, high selectivity and high stability at high temperatures. Commonly used catalysts for the oxygen-free dehydrogenation of methanol include alkali metal carbonates, metals and metal oxides, and molecular sieve catalysts. Among them, alkali metal carbonates such as sodium bicarbonate have high selectivity, but have low activity and high reaction temperature (700~900 ℃), easy to melt and lose and form methyl carbonate or formate with the catalyst, and need to add additives or carriers to improve their activity and stability (CN101147872A, CN102941112A); metals and metal oxides mainly include metals such as Cu, Ag, Zn, Zr, V and their oxides. Such catalysts have high activity, but have problems such as low high temperature selectivity and catalyst deactivation due to metal reduction, volatilization or sintering (CN1390639A, CN1537673A, CN1544 147A, CN102274722A, CN101961650A, CN105712857A); molecular sieve catalysts and their composite catalysts with other metals or non-metals have high stability at high temperatures, but they also suffer from poor low-temperature activity, low high-temperature selectivity, excessive catalyst acidity leading to side reactions such as dehydration and polycondensation, and small pores that can easily cause diffusion resistance and blockage (CN107162884A, CN105732350A, CN104447248A). Therefore, developing a dehydrogenation catalyst with significant and stable formaldehyde yields over a wide reaction temperature range is of great significance, laying the foundation for the industrialization of methanol anaerobic dehydrogenation technology. Summary of the Invention

[0004] In view of this, the present invention provides a preparation method and application of a catalyst for the oxygen-free dehydrogenation of methanol to anhydrous formaldehyde, aiming to overcome the problems faced by existing methanol oxygen-free dehydrogenation catalysts, such as a narrow reaction temperature range and low formaldehyde yield. This patent modifies the molecular sieve to obtain a modified molecular sieve catalyst doped with alkali metals and transition metals. This not only adjusts the acidity of the molecular sieve surface, but also combines the reactivity of the molecular sieve in the high-temperature reaction range (600-900°C) and the transition metal in the low-temperature reaction range (350-650°C) defined in this case, as well as the adsorption of methanol by oxygen vacancies on the surface of the reducible metal oxide, thereby achieving excellent catalytic activity and formaldehyde yield over a wide reaction window of 350-700°C.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: The modified molecular sieve catalyst is prepared using an ion exchange-electrostatic adsorption method. First, the molecular sieve is placed in an alkali metal salt solution for ion exchange for 2-5 hours, followed by centrifugation. After repeated exchange 2-4 times, the ion exchange is placed in an oven to dry overnight, and then calcined at 350-700°C for 3-12 hours to obtain an alkali metal-modified molecular sieve catalyst. Secondly, the obtained alkali metal-modified molecular sieve catalyst is placed in a transition metal salt solution and stirred for 2-8 hours for electrostatic adsorption. The catalyst is then centrifuged, washed, dried overnight, and calcined in a muffle furnace at 300-600°C for 3-6 hours to obtain a transition metal and alkali metal-modified molecular sieve catalyst.

[0006] The modified molecular sieve is one of USY, ZSM-5, Beta and HY molecular sieves, preferably USY and Beta molecular sieves.

[0007] The alkali metal salt is selected from any one or more of water-soluble lithium salts, potassium salts, and sodium salts; and the anion of the alkali metal salt is selected from any one of carbonates, nitrates, acetates, and oxalates.

[0008] In some embodiments, the alkali metal salt is one or more of Li2CO3, LiNO3, CH3COOLi, Li2C2O4, K2CO3, CH3COOK, K2C2O4, KNO3, Na2CO3, CH3COONa, and Na2C2O4, wherein the alkali metal ion concentration is 0.02~1.0 mol / L.

[0009] The transition metal salt comprises one or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Ce(NO3)2, and Al(NO3)3, and the transition metal concentration is 0.02~5.0 mol / L.

[0010] The modified molecular sieve catalyst uses methanol as raw material and undergoes an oxygen-free dehydrogenation reaction in a fixed-bed quartz tube reactor in a N2 atmosphere. The reaction temperature is 400-800°C, the methanol volume content is 5-40%, and the bed mass space velocity is 1.5-10 ml∙g cat. -1 ∙s -1 .

[0011] The ion exchange-electrostatic adsorption method developed in this study prepares modified molecular sieve catalysts. Alkali metal salts, particularly alkali metal carbonates, are used to exchange ions with molecular sieves to produce modified molecular sieves with adjustable surface acidity. The modified alkali metal ions also regulate the charge distribution on the molecular sieve surface, allowing transition metal cations to be evenly dispersed on the surface or within the pores of the molecular sieve through electrostatic adsorption. Compared to pure molecular sieve catalysts, alkali metal-modified molecular sieves promote the desorption of hydrogen produced from the reaction and inhibit carbon deposit formation. However, the reaction still requires a temperature of 600-800°C to achieve a reasonable formaldehyde yield. Transition metal catalysts such as Cu and Ag, and their oxides, can achieve high methanol conversion and formaldehyde selectivity at relatively low temperatures (350-650°C), but they face challenges such as reduced activity due to reduction of the metal oxides by the product hydrogen and sintering. Therefore, active components such as Cu and Ag are anchored to the surface or pores of the modified molecular sieve through electrostatic adsorption. Simultaneously, during the anaerobic dehydrogenation of methanol, intermediates formed by the metals and methoxy groups migrate to and stabilize within the silanol nests within the molecular sieve, effectively avoiding rapid metal sintering. The advantages of this invention are that this modified molecular sieve catalyst not only exhibits excellent methanol conversion and formaldehyde yield over a wide reaction temperature range, but also extends the catalyst's service life through chemical recycling and regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the cyclic regeneration activity of AgLi-USY molecular sieve catalyst. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below through examples.

[0014] Example 1: Preparation of AgCeLi-USY molecular sieve catalyst.

[0015] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion exchanged three times in a 0.1 M lithium carbonate solution. The product was then centrifuged and washed three times and then dried in an oven at 80 °C overnight. The product was calcined at 650 °C for 4 h in an air atmosphere to obtain Li-USY molecular sieve.

[0016] The prepared Li-USY molecular sieve was further placed in a 0.1M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 hours, filtered, dried, and then calcined at 500°C in an air atmosphere for 3 hours. The calcined AgCeLi-USY molecular sieve catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0017] Example 2: Preparation of AgCeNa-USY molecular sieve catalyst.

[0018] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M sodium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Na-USY molecular sieve was then calcined at 650°C for 4 h in air to obtain the Na-USY molecular sieve. The prepared Na-USY molecular sieve was then placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined AgCeNa-USY molecular sieve catalyst was formed and filled into a reaction tube to create a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was carried out at 350–700°C with a feed space velocity of 3–10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0019] Example 3: Preparation of AgCeK-USY molecular sieve catalyst.

[0020] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M potassium carbonate solution. The product was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting K-USY molecular sieve was then calcined at 650°C for 4 h in air. The resulting K-USY molecular sieve was then placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined AgCeK-USY molecular sieve catalyst was then formed and filled into a reaction tube to create a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was carried out at 350–700°C with a feed space velocity of 3–10 ml∙g.cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0021] Example 4: Preparation of CuCeLi-USY molecular sieve catalyst.

[0022] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The Li-USY molecular sieve was calcined at 650°C for 4 h in air to obtain the Li-USY molecular sieve. The prepared Li-USY molecular sieve was further placed in a 0.1 M mixed solution of copper nitrate and cerium nitrate. The mixture was stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined CuCeLi-USY molecular sieve catalyst was formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0023] Example 5: Preparation of ZnCeLi-USY molecular sieve catalyst.

[0024] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Li-USY molecular sieve was then calcined at 650°C for 4 h in air to obtain the Li-USY molecular sieve. The prepared Li-USY molecular sieve was then placed in a 0.1 M mixed solution of zinc nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined ZnCeK-USY molecular sieve catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0025] Example 6: Preparation of AgCeLi-ZSM-5 molecular sieve catalyst.

[0026] 50 g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 60 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Li-ZSM-5 molecular sieve was then placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined AgCeLi-ZSM-5 molecular sieve catalyst was formed and filled into a reaction tube to create a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was conducted at 350–700°C with a feed space velocity of 3–10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0027] Example 7: Preparation of AgCeLi-Beta molecular sieve catalyst.

[0028] 50 g of Beta molecular sieve with a silicon-aluminum ratio of 25 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Li-Beta molecular sieve was then placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 hours, filtered, dried, and then calcined at 500°C for 3 hours in air. The calcined AgCeLi-Beta molecular sieve catalyst was formed and filled into a reaction tube to create a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was carried out at 350–700°C with a feed space velocity of 3–10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0029] Example 8: Preparation of AgCeLi-HY molecular sieve catalyst.

[0030] 50 g of HY molecular sieve with a silicon-aluminum ratio of 40 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Li-HY molecular sieve was then calcined at 650°C for 4 h in an air atmosphere. The prepared Li-HY molecular sieve was placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in an air atmosphere. The calcined AgCeLi-HY molecular sieve catalyst was formed and filled into a reaction tube, creating a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was carried out at 350–700°C with a feed space velocity of 3–10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0031] Example 9: The catalyst after the reaction in Example 1 was purged with N2 for 30 minutes, then calcined in situ at 500°C for 1 hour, and then purged under N2 for another 30 minutes before conducting a methanol dehydrogenation experiment. The cyclic oxidation regeneration experiment showed that the catalyst had good stability and recyclability (see Figure 1 ).

[0032] Comparative Example 1: USY, Beta, TS-1, and MCM-22 molecular sieves were formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure. Methanol was introduced by a micropump with a volume content of 5-20%. The reaction was carried out at 600-800°C and a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0033] Comparative Example 2: Preparation of Li-USY, Na-USY, K-USY, and Cs-USY molecular sieve catalysts.

[0034] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in 0.1 M solutions of lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate, respectively. The mixture was then centrifugally washed three times and dried overnight at 80°C in an oven. The calcined Li-USY, Na-USY, and K-USY molecular sieve catalysts were then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 600-800°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s-1 The product was detected online by gas chromatography dual-channel TCD.

[0035] Comparative Example 3: Preparation of Li-MCM-22, Li-Beta, and Li-TS-1 catalysts.

[0036] 50 g of MCM-22 (a Si / Al ratio of 28), 50 g of Beta (a Si / Al ratio of 25), and 50 g of TS-1 (a Ti / Si ratio of 30) molecular sieves were weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. After centrifugal washing three times, the mixture was dried overnight at 80°C in an oven and calcined at 650°C in air for 4 h. The calcined Li-SAPO-11, Li-Beta, and Li-TS-1 molecular sieve catalysts were then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 600-800°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0037] Comparative Example 4: Preparation of AgCe-USY catalyst.

[0038] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate. The mixture was stirred at room temperature for 6 hours, filtered, and dried. The mixture was then heated to 500°C and calcined for 3 hours in an air atmosphere. The calcined AgCe-USY molecular sieve catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0039] Comparative Example 5: Preparation of ZrCeLi-USY molecular sieve catalyst.

[0040] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The Li-USY molecular sieve was then calcined at 650°C for 4 h in air to obtain the Li-USY molecular sieve. The prepared Li-USY molecular sieve was then placed in a 0.1 M mixed solution of zirconyl nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined ZrCeLi-USY molecular sieve catalyst was formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0041] Comparative Example 6: Preparation of AgMgLi-USY molecular sieve catalyst.

[0042] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The Li-USY molecular sieve was calcined at 650°C for 4 h in air to obtain the Li-USY molecular sieve. The prepared Li-USY molecular sieve was further placed in a 0.1 M mixed solution of magnesium nitrate and silver nitrate, stirred at room temperature for 6 h, filtered, dried, and then calcined at 500°C for 3 h in air. The calcined AgMgLi-USY molecular sieve catalyst was formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume content of 5-20%. The reaction was carried out at 350-700°C with a feed space velocity of 3-10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0043] Comparative Example 7: Preparation of AgCeLi-TS-1 molecular sieve catalyst.

[0044] 50 g of TS-1 molecular sieve with a titanium-silicon ratio of 30 was weighed and ion-exchanged three times in a 0.1 M lithium carbonate solution. The mixture was then centrifugally washed three times and dried in an oven at 80°C overnight. The resulting Li-TS-1 molecular sieve was then placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 hours, filtered, dried, and then calcined at 500°C for 3 hours in air. The calcined AgCeLi-TS-1 molecular sieve catalyst was formed and filled into a reaction tube to create a 2 cm bed. Nitrogen was introduced as a carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume content of 5–20%. The reaction was carried out at 350–700°C with a feed space velocity of 3–10 ml∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0045] Table 1. Performance of a series of molecular sieve catalysts for catalytic dehydrogenation of methanol to anhydrous formaldehyde.

[0046]

[0047] The above experiments show that the modified zeolite catalysts based on TS-1 and MCM-22 exhibit poor formaldehyde yields, while the modified USY, Beta and HY zeolite catalysts have better catalytic activity. Among them, compared with the catalysts modified with Zr and Mg metals, the AgCeLi-USY modified zeolite has outstanding methanol conversion rate and formaldehyde yield in a wider temperature range (350~700 ℃), which is mainly due to the synergistic effect of low-temperature high-activity Ag, reducible CeO2 with rich oxygen vacancies and acidity-adjustable Li-doped high-temperature active USY zeolite.

[0048] The above-described embodiments are merely preferred embodiments of the present invention, but the present invention is not limited to the specific details of the above-described embodiments. Within the technical concept of the present invention, various modifications and improvements may be made to the technical solution of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the appended claims.

Claims

1. Application of modified molecular sieve catalyst in the anaerobic dehydrogenation of methanol to anhydrous formaldehyde, characterized in that: The prepared catalyst was formed and loaded into a fixed-bed quartz tube reactor. Methanol dehydrogenation experiments were carried out at 400-800 °C under N2 atmosphere, with a methanol volume content of 5-40% and a bed mass space velocity of 1.5-10 mL·g cat. -1 ·s -1 ; The modified molecular sieve catalyst is prepared by the ion exchange-electrostatic adsorption method, that is, the molecular sieve is modified in sequence by alkali metal ions and transition metal ions, and then calcined and formed. The modified molecular sieve is one or more of USY, Beta, ZSM-5 and HY molecular sieves, and the transition metal salt contains two or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Ce(NO3)2, and Al(NO3)3.

2. The use according to claim 1, characterized in that (1) The molecular sieve is placed in an alkali metal salt solution for exchange for 2 to 5 hours, then centrifuged, and the exchange is repeated 2 to 4 times, and then dried in an oven, and then calcined to obtain an alkali metal-modified molecular sieve catalyst; (2) The alkali metal modified molecular sieve catalyst obtained in step 1 is placed in a transition metal salt solution and stirred for 2 to 8 hours, and the negative charge enriched on the surface of the alkali metal modified molecular sieve is used to realize electrostatic adsorption of transition metal cations. Then, after centrifugation, washing, drying and calcination, a transition metal and alkali metal modified molecular sieve is obtained.

3. The use according to claim 2, characterized in that The alkali metal salt in step (1) is selected from any one or more of water-soluble lithium salts, potassium salts, and sodium salts; the anion of the alkali metal salt is selected from any one of carbonates, nitrates, acetates, and oxalates.

4. The use according to claim 2, characterized in that The concentration of alkali metal ions is 0.02~1.0 mol / L.

5. The use according to claim 2, characterized in that The calcination temperature of the molecular sieve after ion exchange in step (1) is 350-700°C, and the calcination time is 3-12 h.

6. The use according to claim 2, characterized in that The transition metal concentration in step (2) is 0.02-5.0 mol / L.

7. The use according to claim 2, characterized in that In the step (2), the modified molecular sieve after electrostatic adsorption of the transition metal is calcined at a temperature of 300-600° C. and for a time of 3-6 h.

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