A preparation method for producing anhydrous formaldehyde catalyst

Abstract

The present invention belongs to the field of chemical technology innovation and relates to a preparation method for producing an anhydrous formaldehyde catalyst. The catalyst is composed of a transition metal and non-metal nitrogen-carbon doped molecular sieve. The nitrogen-carbon doping is used to regulate the acid sites and charge distribution of the molecular sieve. At the same time, the formed metal-N-C bonds are used to slow down the agglomeration of the metal during the reaction, thereby improving the stability and service life of the catalyst. The catalyst exhibits excellent catalytic activity for the oxygen-free dehydrogenation of methanol in the temperature range of 400-700°C, with a methanol conversion rate of 90-99% and a formaldehyde yield of 57-67%. The catalytic performance remains stable within 70 hours.

Description

Technical Field

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

[0002] Formaldehyde, an important commodity chemical raw material, is widely used in industries such as petrochemicals, pharmaceuticals, textiles, biochemicals, energy, and transportation. It is not only used as a disinfectant and preservative, but also in the preparation of a variety of products, including phenolic / urea-formaldehyde resins, melamine resins, hexamethylenetetramine, and pentaerythritol. Industrial production of formaldehyde often relies on the methanol oxidation process, which primarily utilizes silver- or iron-based catalysts to catalyze the oxidative dehydrogenation of methanol under high temperature to produce an aqueous solution containing 35-45% formaldehyde. Concentrated formaldehyde is then obtained through vacuum distillation or solvent azeotropy. The low vapor pressure of aqueous formaldehyde solutions and their tendency to form azeotropes with water make their separation and purification difficult and expensive. However, excessive water content in formaldehyde can affect the preparation of downstream products such as engineering plastics, electronic chemicals, and hexamethylenetetramine. Therefore, high-concentration or anhydrous formaldehyde offers greater economic value and a wider market demand.

[0003] The anaerobic dehydrogenation of methanol to anhydrous formaldehyde simplifies the process flow and avoids the high energy consumption, high costs, wastewater and exhaust gas pollution, and equipment corrosion caused by the traditional oxidation-dehydration method, such as the byproduct formic acid. Traditional anaerobic dehydrogenation of methanol to anhydrous formaldehyde primarily utilizes metal oxide or alkali metal carbonate catalysts in the gas or liquid phase. However, these processes suffer from high reaction temperatures (400-800°C), high energy consumption, and susceptibility to catalyst deactivation. Therefore, the development of an efficient and stable catalyst is crucial for achieving anaerobic dehydrogenation of methanol to anhydrous formaldehyde. Existing technologies primarily utilize metal catalysts, such as copper, zinc, and palladium. While these metal catalysts can catalyze the oxygen-free dehydrogenation of methanol, they suffer from low selectivity at high temperatures and catalyst deactivation due to metal reduction, volatilization, or sintering (CN1390639A, CN1544147A, CN102274722A, and CN105712857A). Alkali metal carbonate catalysts offer high selectivity, but they also experience high reaction temperatures (700–900°C) and are prone to melting and loss, requiring the addition of additives or supports to enhance their activity and stability (CN101147872A and CN1029411112A). Other studies have employed composite materials, such as metal-organic frameworks (MOFs) and carbon-based materials, as supports (CN104447242A), loading metal particles to prepare catalysts. However, these catalysts suffer from issues such as metal particle agglomeration and weak interactions between the support and the metal. Catalysts composed of molecular sieves and other metals or non-metals exhibit high activity or selectivity for the oxygen-free dehydrogenation of methanol at high temperatures. However, the strong acidity of the catalysts can lead to increased production of byproducts such as water and dimethyl ether (CN107162884A, CN105732350A, and CN1044447248A). Therefore, developing a new, efficient, and stable catalyst that improves its activity, selectivity, and stability, making it suitable for industrial application, is an urgent challenge in the field of anhydrous formaldehyde production. Summary of the Invention

[0004] In view of this, the present invention provides a preparation method for producing anhydrous formaldehyde catalysts, which aims to overcome the problems faced by existing methanol oxygen-free dehydrogenation molecular sieve catalysts, such as excessively strong carrier acidity, easy agglomeration of metal particles, and easy deactivation of the catalyst due to sintering and carbon deposition. This patent obtains a modified molecular sieve catalyst by doping the molecular sieve with nitrogen-carbon-transition metals. It not only adjusts the acidity and charge distribution on the molecular sieve surface, but also combines the strong interaction between the metal and the carrier to improve the stability of the catalyst, avoiding the rapid decline in catalyst activity and selectivity caused by the reduction, agglomeration, and carbon deposition of the metal components during the reaction process, thereby ensuring key performance indicators such as the activity, selectivity, and service life of the catalyst.

[0005] To achieve the above objectives, the present invention discloses a technical solution as follows: The modified molecular sieve catalyst is prepared using a combined hydrothermal and impregnation method. First, the molecular sieve and nitrogen-containing organic compound are dispersed evenly in a solution for 2-5 hours, then placed in a hydrothermal reactor for a hydrothermal reaction. After cooling, washing, and drying overnight, the mixture is calcined in a tube furnace at 350-700°C under an inert atmosphere for 3-12 hours to obtain a nitrogen-carbon-doped molecular sieve. Secondly, the obtained nitrogen-carbon-doped molecular sieve is impregnated in a transition metal soluble salt solution with stirring for 2-8 hours. After drying overnight, the mixture is calcined in a tube furnace at 300-600°C under an inert atmosphere for 3-6 hours to obtain a transition metal and nitrogen-carbon modified molecular sieve catalyst.

[0006] The modified molecular sieve is one of USY, ZSM-5, SAPO-34, NaY, HY, Beta molecular sieve and titanium silicon molecular sieve, preferably Beta and ZSM-5 molecular sieve.

[0007] The nitrogen and carbon sources are one or more of cyanamide, dicyandiamide, melamine, urea, diethylamine and triethylamine, preferably dicyandiamide and melamine.

[0008] The solvent in step (1) includes one or more of water, methanol, N,N-dimethylformamide (DMF), 1,2-bis(2-methoxyethoxy)ethane (DME), ethylenediamine and ammonia. The HgCl2 solution is adjusted to 9.5-11.5 in a hydrothermal environment.

[0009] Wherein, the transition metal salt comprises one or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Zr(NO3)2, Ce(NO3)2, Ga(NO3)2, Mg(NO3)2, and Al(NO3)3.

[0010] The modified molecular sieve catalyst was used as a raw material for oxygen-free dehydrogenation experiments in a fixed bed reactor in a N2 atmosphere. The reaction temperature was 400-700 °C, the methanol volume content was 5-40%, and the mass space velocity of the bed was 2-15 mL∙g cat. -1 ∙s -1 .

[0011] The nitrogen-carbon-transition metal doping developed by the present invention is used to prepare a modified molecular sieve catalyst, and a nitrogen-containing organic compound is used to carry out a hydrothermal reaction with a molecular sieve to obtain a modified molecular sieve to regulate its surface acid sites, while the charge distribution of the molecular sieve surface is regulated by the modified nitrogen-carbon doping; At the same time, the transition metal cation is anchored as an active component on the surface or pores of the modified molecular sieve by the strong interaction between the carrier and the metal. In addition, by carrying out high-temperature calcination on the modified molecular sieve carrier, the crystal structure is made more regular, thereby improving the thermal stability and chemical stability of the molecular sieve, and the acid sites of the molecular sieve can be increased, so that it shows better activity in the catalytic reaction. Compared to pure molecular sieve catalysts, nitrogen-carbon-doped molecular sieve catalysts can form metal-NC bonds, in which C is more likely to bond to the carrier, and the π orbital lone pair of electrons of the N atom is more likely to coordinate with the d orbital of the metal to form a metal-N configuration, and it is easy to transfer electrons during the catalytic process, thereby improving the catalytic activity and enhancing the stability of the metal active component, avoiding problems such as decreased activity due to self-sintering. Therefore, the nitrogen-carbon-transition metal-modified molecular sieve catalyst can achieve high methanol conversion and formaldehyde selectivity at relatively low temperatures (400-650°C). The advantages of this invention are that this modified molecular sieve catalyst not only exhibits excellent methanol conversion and anhydrous formaldehyde yield at relatively low temperatures, but also has improved catalyst stability, preventing deactivation over a relatively long operating time, significantly extending the catalyst's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is the single service life of Ag-NC(1) / Beta 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 Ag-NC(1) / APO-34 molecular sieve catalyst

[0015] 10 g of SAPO-34 molecular sieve with a silicon-aluminum ratio of 0.5 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.2. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was hydrothermally treated at 180 °C for 12 h. After cooling, it was centrifugally washed with deionized water and ethanol three times each. It was placed in an 80 °C oven to dry overnight and calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / SAPO-34 molecular sieve. NC(1) / SAPO-34 molecular sieve was placed in 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain Ag-NC(1) / SAPO-34 molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0016] Example 2: Preparation of Ag-NC(1) / USY molecular sieve catalyst

[0017] 10 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.3. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was hydrothermally treated at 180 °C for 12 h. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 °C oven overnight. It was calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / USY molecular sieve. The NC(1) / USY molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain the Ag-NC(1) / USY molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0018] Example 3: Preparation of Ag-NC(1) / Beta molecular sieve catalyst

[0019] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.1. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was treated at 180 °C for 12 h in a hydrothermal autoclave. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 °C oven overnight. It was calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / Beta molecular sieve. NC(1) / Beta molecular sieve was placed in 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain Ag-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0020] Example 4: Preparation of Ag-NC(1) / ZSM-5 molecular sieve catalyst

[0021] 10 g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 46 was weighed and dispersed in DMF, 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.5, 0.5 g of melamine was slowly added, and the mixture was stirred in a polytetrafluoroethylene liner for 4 h. Then, it was treated in a hydrothermal autoclave at 180 °C for 12 h. After cooling, it was centrifugally washed with deionized water and ethanol three times each, and then placed in an 80 °C oven to dry overnight. It was calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / ZSM-5 molecular sieve. The NC(1) / ZSM-5 molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain the Ag-NC(1) / ZSM-5 molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0022] Example 5: Preparation of Ag-NC(2) / Beta molecular sieve catalyst

[0023] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.8. 0.5 g of dicyandiamide was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. The mixture was then hydrothermally heated at 180 °C for 12 h. After cooling, the mixture was centrifugally washed three times with deionized water and ethanol, dried overnight in an 80 °C oven, and calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(2) / Beta molecular sieve. The NC(2) / Beta molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain the Ag-NC(2) / Beta molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0024] Example 6: Preparation of Zn-NC(1) / Beta molecular sieve catalyst

[0025] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.7. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. The mixture was then hydrothermally treated at 180 °C for 12 h. After cooling, the mixture was centrifugally washed three times with deionized water and ethanol, dried overnight in an 80 °C oven, and calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / Beta molecular sieve. The NC(1) / Beta molecular sieve was placed in a 0.1 M zinc nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain a Zn-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0026] Example 7: Preparation of Cu-NC(1) / Beta molecular sieve catalyst

[0027] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.6. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. The mixture was then hydrothermally treated at 180°C for 12 h. After cooling, the mixture was centrifugally washed three times with deionized water and ethanol, dried overnight in an 80°C oven, and calcined at 700°C for 4 h under a nitrogen atmosphere to obtain NC(1) / Beta molecular sieve. The NC(1) / Beta molecular sieve was placed in a 0.1 M copper nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500°C and calcined for 5 h under a nitrogen atmosphere to obtain a Cu-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0028] Example 8: Preparation of Ce-NC(1) / Beta molecular sieve catalyst

[0029] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.8. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. The mixture was then hydrothermally treated at 180°C for 12 h. After cooling, the mixture was centrifugally washed three times with deionized water and ethanol, dried overnight in an 80°C oven, and calcined at 700°C for 4 h under a nitrogen atmosphere to obtain NC(1) / Beta molecular sieve. The NC(1) / Beta molecular sieve was placed in a 0.1 M cerium nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500°C and calcined for 5 h under a nitrogen atmosphere. The calcined Ce-NC(1) / Beta molecular sieve catalyst was formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0030] Example 9: The catalyst in Example 3 was further subjected to methanol dehydrogenation at 500°C. This single life experiment showed that the catalyst had good stability and operating life (see Figure 1 ).

[0031] Comparative Example 1: Preparation of Ag / SAPO-34 molecular sieve catalyst

[0032] 10 g of SAPO-34 molecular sieve with a silicon-aluminum ratio of 0.5 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.5. The mixture was stirred for 4 hours in a polytetrafluoroethylene-lined container and then hydrothermally heated at 180°C for 12 hours. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation. The mixture was then dried in an 80°C oven overnight and calcined at 700°C under a nitrogen atmosphere for 4 hours to obtain the SAPO-34 molecular sieve. The prepared SAPO-34 molecular sieve was then placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 hours, filtered, dried, and then calcined at 500°C under a nitrogen atmosphere for 5 hours to obtain the Ag / SAPO-34 molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0033] Comparative Example 2: Preparation of Ag / USY molecular sieve catalyst

[0034] 10 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.6. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h and then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation. The mixture was then dried in an 80°C oven overnight and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the USY molecular sieve. The prepared USY molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Ag / USY molecular sieve catalyst. This catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as the carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0035] Comparative Example 3: Preparation of Ag / Beta Molecular Sieve Catalyst

[0036] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.4. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h, then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation, dried overnight in an 80°C oven, and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the Beta molecular sieve. The prepared Beta molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Ag / Beta molecular sieve catalyst. The catalyst was then formed and filled into a reaction tube, creating a 2 cm bed. Nitrogen was introduced as the carrier gas at atmospheric pressure, and methanol was introduced via a micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0037] Comparative Example 4: Preparation of Ag / ZSM-5 molecular sieve catalyst

[0038] 10 g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 46 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.5. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h, then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation, dried overnight in an 80°C oven, and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the ZSM-5 molecular sieve. The prepared ZSM-5 molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Ag / ZSM-5 molecular sieve catalyst. This catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as the carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0039] Comparative Example 5: Preparation of Zn / Beta Molecular Sieve Catalyst

[0040] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.4. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h, then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation, dried overnight in an 80°C oven, and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the Beta molecular sieve. The prepared Beta molecular sieve was placed in a 0.1 M zinc nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Zn / Beta molecular sieve catalyst. The resulting 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 by micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0041] Comparative Example 6: Preparation of Cu / Beta Molecular Sieve Catalyst

[0042] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.6. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h, then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation, dried overnight in an 80°C oven, and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the Beta molecular sieve. The prepared Beta molecular sieve was placed in a 0.1 M copper nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Cu / Beta molecular sieve catalyst. This catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as the carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0043] Comparative Example 7: Preparation of Ce / Beta Molecular Sieve Catalyst

[0044] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.4. The mixture was stirred in a polytetrafluoroethylene-lined reactor for 4 h, then hydrothermally heated at 180°C for 12 h. After cooling, the mixture was washed three times with deionized water and three times with ethanol by centrifugation, dried overnight in an 80°C oven, and calcined at 700°C under a nitrogen atmosphere for 4 h to obtain the Beta molecular sieve. The prepared Beta molecular sieve was placed in a 0.1 M cerium nitrate solution, stirred at room temperature for 6 h, filtered, and dried. The mixture was then heated to 500°C and calcined under a nitrogen atmosphere for 5 h to obtain the Ce / Beta molecular sieve catalyst. This catalyst was then formed and filled into a reaction tube to form a 2 cm bed. Nitrogen was introduced as the carrier gas at atmospheric pressure, and methanol was introduced by micropump at a volume fraction of 15%. The reaction was carried out at 500°C with a feed space velocity of 10 mL∙g. cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0045] Comparative Example 8: Preparation of NC(1) / Beta Molecular Sieve Catalyst

[0046] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.8. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was treated at 180 ° C for 12 h in a hydrothermal autoclave. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 ° C oven overnight. It was calcined at 700 ° C for 4 h under a nitrogen atmosphere to obtain NC (1) / Beta molecular sieve. After forming, it was filled into a reaction tube to fill a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micropump with a volume content of 15%. The reaction was carried out at 500 ° C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0047] Comparative Example 9: Preparation of NC(1) / USY molecular sieve catalyst

[0048] 10 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.6. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was treated at 180 °C for 12 h in a hydrothermal autoclave. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 °C oven overnight. It was calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain NC(1) / USY molecular sieve. After forming, it was filled into a reaction tube to fill a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micropump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0049] Comparative Example 10: Preparation of Ag-NC(1) / Beta-2 Molecular Sieve Catalyst

[0050] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L ethylenediamine solution was added to adjust the pH to 10.5. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was treated in a hydrothermal autoclave at 180 °C for 12 h. After cooling, it was centrifugally washed 3 times with deionized water and ethanol each and then dried in an 80 °C oven overnight. NC(1) / Beta molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C in a nitrogen atmosphere and calcined for 5 h to obtain Ag-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into a reaction tube to fill a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micropump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0051] Comparative Example 11: Preparation of Ag-NC(1) / Beta-3 molecular sieve catalyst

[0052] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in DMF. 0.1 mol / L acetic acid solution was added to adjust the pH to 4.4. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, the mixture was treated at 180 °C for 12 h in a hydrothermal autoclave. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 °C oven overnight. It was calcined at 700 °C for 4 h under a nitrogen atmosphere to obtain Ag-NC(1) / Beta-3 molecular sieve catalyst. NC(1) / Beta molecular sieve was placed in 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C and calcined for 5 h under a nitrogen atmosphere to obtain Ag-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into the reaction tube to fill a 2 cm bed. Nitrogen was introduced as the carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0053] Comparative Example 12: Preparation of Ag-NC(1) / Beta-4 Molecular Sieve Catalyst

[0054] 10 g of Beta molecular sieve with a silicon-aluminum ratio of 26 was weighed and dispersed in deionized water. 0.5 g of melamine was slowly added and stirred in a polytetrafluoroethylene liner for 4 h. Then, it was treated at 180 °C in a hydrothermal autoclave for 12 h. After cooling, it was centrifugally washed with deionized water and ethanol three times each and then dried in an 80 °C oven overnight. It was calcined at 700 °C under a nitrogen atmosphere for 4 h to obtain Ag-NC(1) / Beta molecular sieve catalyst. NC(1) / Beta molecular sieve was placed in a 0.1 M silver nitrate solution, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C under a nitrogen atmosphere and calcined for 5 h to obtain Ag-NC(1) / Beta molecular sieve catalyst. After forming, it was filled into a reaction tube to fill a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micropump with a volume content of 15%. The reaction was carried out at 500 °C with a feed space velocity of 10 mL∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0055] Table 1. Performance of a series of molecular sieve catalysts for catalytic dehydrogenation of methanol to anhydrous formaldehyde.

[0056]

[0057] The modified molecular sieve dehydrogenation catalyst of the present invention modulates the acidity and charge distribution of the molecular sieve by nitrogen-carbon doping molecular sieves with different silicon-aluminum ratios. The formed metal-NC bonds prevent grain growth and sintering, ensuring the catalyst's activity, stability, and operating life. The prepared Ag-NC(1) / Beta can achieve high methanol conversion and formaldehyde yield (55-70%) at relatively low temperatures (400-700°C) and is not easily deactivated within 70 hours.

[0058] 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 nitrogen-carbon doped transition metal molecular sieve catalyst in the anaerobic dehydrogenation of methanol to anhydrous formaldehyde, characterized in that: The preparation method of the nitrogen-carbon doped transition metal molecular sieve catalyst comprises the following steps: (1) Dispersing the molecular sieve and the nitrogen-containing organic compound in a solvent, adjusting the pH to 9.5-11.5 in a hydrothermal environment, cooling, washing, drying, and calcining under an inert atmosphere after hydrothermal treatment to obtain a nitrogen-carbon doped molecular sieve; (2) The nitrogen-carbon doped molecular sieve is dispersed in a transition metal soluble salt solution, dried and calcined in an inert atmosphere to obtain a molecular sieve catalyst modified with transition metal and nitrogen-carbon.

2. The use according to claim 1, characterized in that The prepared catalyst was formed and loaded into a fixed-bed reactor. Methanol dehydrogenation experiments were carried out at 400-800 °C under N2 atmosphere, with a methanol volume fraction of 5-40% and a bed mass space velocity of 2-15 mL·g cat. -1 ·s -1 .

3. The use according to claim 1, characterized in that The molecular sieve in step (1) includes one or more of USY, ZSM-5, SAPO-34, NaY, HY, Beta molecular sieve and titanium silicalite molecular sieve; the nitrogen-containing organic compound includes one or more of cyanamide, dicyandiamide, melamine, urea, diethylamine and triethylamine; The mass ratio of the carrier to the nitrogen-containing organic compound is 1:10~1:

50.

4. The use according to claim 1, characterized in that The solvent in step (1) includes one or more of water, methanol, N,N-dimethylformamide, 1,2-bis(2-methoxyethoxy)ethane, ethylenediamine and ammonia.

5. The use according to claim 1, characterized in that The temperature of the hydrothermal treatment in step (1) is 120-240°C; the hydrothermal time is 6-24 hours; In step (1), the calcination temperature is 400-800°C; and the calcination time is 4-12 h.

6. The use according to claim 5, characterized in that The temperature of the hydrothermal treatment in step (1) is 140-200°C; the hydrothermal time is 8-20 h; In step (1), the calcination temperature is 500-700°C; and the calcination time is 4-10 h.

7. The use according to claim 1, characterized in that In step (2), the transition metal salt comprises one or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Zr(NO3)2, and Ce(NO3)2; the mass ratio of the transition metal to the modified carrier is 1:20 to 1:

60.

8. The use according to claim 1, characterized in that The mass ratio of transition metal to modified support is 1:25~1:

40.

9. The use according to claim 1, wherein the calcination temperature in step (2) is 300-800°C; the calcination time is 3-8 hours, and the inert atmosphere during the calcination process is one or two of nitrogen, argon, and helium.

10. The use according to claim 9, wherein the calcination temperature in step (2) is 400-600°C and the calcination time is 3-6 hours.

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