Low-temperature catalysts for the dehydrogenation of methanol to methyl formate, their preparation methods and applications

Abstract

This invention relates to the field of catalyst materials technology, and discloses a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, its preparation method, and its application. The low-temperature catalyst comprises Cu nanoparticles and a composite metal oxide attached to the Cu nanoparticles; the composite metal oxide includes CaO and CeO2. When used to catalyze the dehydrogenation of methanol to methyl formate, the low-temperature catalyst of this invention enables the reaction to proceed at a relatively low temperature and exhibits high selectivity for methyl formate.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, and in particular to a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, its preparation method and application. Background Technology

[0002] Methyl formate is one of the most important industrial chemicals, widely used in the production of over 50 chemicals, including formic acid, N,N-dimethylformamide, formamide, and dimethyl carbonate. Furthermore, methyl formate itself has various applications in the pharmaceutical field, being used to synthesize drugs such as sulfonated methylpyrimidine, sulfamethoxy, and the antitussive dextromethorphan. In addition to its chemical uses, methyl formate has been recognized in recent years as a potential novel liquid hydrogen storage medium due to its high mass hydrogen storage density (8.4 wt.%) and volumetric hydrogen storage density (1 L is equivalent to 1200 bar of high-pressure H2).

[0003] Traditional methods for producing methyl formate using methanol as a raw material mainly include: methanol carbonylation, methanol selective oxidation, and methanol dehydrogenation. Methanol carbonylation is currently the main industrially used method. Using sodium methoxide or potassium methoxide as a catalyst, methanol and high-pressure CO undergo a carbonylation reaction to obtain methyl formate. The advantages of this method are high selectivity for methyl formate and scalable production. However, it suffers from disadvantages such as extreme sensitivity of the system to H₂O, CO₂, O₂, and sulfides, low conversion rate, high reaction pressure, strong corrosiveness, and difficulty in separating the homogeneous catalyst, leading to recycling difficulties. Compared to methanol carbonylation, methanol selective oxidation offers milder reaction conditions and higher conversion rates. However, this reaction is strongly exothermic, making it difficult to control the reaction temperature and manage the heat generated during the reaction in industrial applications.

[0004] Methanol dehydrogenation is a simple process with a single reactant, can be carried out at atmospheric pressure, and produces methyl formate. Hydrogen gas can also be directly separated and utilized, making it a promising green, economical, and efficient method for the preparation of methyl formate. Most reported gas-phase oxygen-free methanol dehydrogenation catalysts are Cu-based, and these catalysts are suitable for reaction temperatures above 200°C. o C. Higher reaction temperatures not only increase equipment maintenance costs but also improve the selectivity of the main byproduct CO, leading to decreased catalyst stability. For example, patent CN105597756A discloses a copper-based core-shell catalyst for the dehydrogenation of methanol to methyl formate, its preparation method, and its application. This catalyst consists of a mesoporous silica shell and nano-copper oxide particles encapsulated within it. When using this catalyst for the dehydrogenation of methanol to methyl formate, at 180°C... o At C, even if the methanol mass hourly space velocity is as low as 1 h⁻¹ -1 The methanol conversion rate can only reach 25%, and when the reaction temperature is increased to 250°C... o At temperature C, the methanol conversion rate can be increased to 50% (methanol mass hourly space velocity is 8 h⁻¹).-1 However, the selectivity of methyl formate is only 70%. Designing a catalyst for the low-temperature dehydrogenation of methanol to prepare methyl formate will help save industrial production costs and improve the selectivity and stability of methyl formate. Summary of the Invention

[0005] To address the aforementioned technical problem—namely, the high reaction temperatures required by existing Cu-based catalysts for the catalytic dehydrogenation of methanol to methyl formate—this invention provides a low-temperature catalyst for the catalytic dehydrogenation of methanol to methyl formate, its preparation method, and its applications. This low-temperature catalyst enables the reaction to proceed at relatively low temperatures and exhibits high methyl formate selectivity when used for the catalytic dehydrogenation of methanol to methyl formate.

[0006] The specific technical solution of this invention is as follows:

[0007] In a first aspect, the present invention provides a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, comprising Cu nanoparticles and a composite metal oxide attached to the Cu nanoparticles; the composite metal oxide comprising CaO and CeO2.

[0008] Unlike traditional supported catalysts that load metal nanoparticles onto metal oxide supports, this invention attaches metal oxides to the outside of Cu nanoparticles, which allows the catalyst to contain more Cu and enables strong interactions between Cu nanoparticles and metal oxides, inhibiting Cu aggregation. At the same time, it also creates more interfacial sites between Cu nanoparticles and metal oxides, which is beneficial to improving catalytic efficiency.

[0009] Based on this, the present invention utilizes Cu nanoparticles in combination with two metal oxides, CaO and CeO2, to enable the catalyst to catalyze the reaction at a lower temperature and achieve high selectivity for methyl formate during methanol dehydrogenation. Specifically: methanol adsorption and dehydrogenation occur on the surface of Cu nanoparticles; CaO promotes β-elimination of methanol to form a formaldehyde intermediate; CeO2 provides suitable acidic and basic sites, promoting methanol dehydrogenation to the formaldehyde intermediate and the condensation of the formaldehyde intermediate to form methyl acetal. At the same time, CeO2 can also enhance the interaction between CaO and Cu, enriching the interfacial sites and accelerating the conversion rate of methanol to methyl formate; Cu nanoparticles further promote the dehydrogenation of hemiacetal to obtain methyl formate product.

[0010] Furthermore, the use of CeO2 as a catalyst in this invention to provide acidic and basic sites has the following advantages: CeO2 will not catalyze the decomposition of formaldehyde intermediates to generate CO, thus avoiding a significant decrease in selectivity; and CeO2 and Cu are less likely to form alloys during catalyst pretreatment (reduction and pre-activation of the catalyst before use), thus avoiding a reduction in the interface sites between CaO and Cu, which would have an adverse effect on methanol conversion.

[0011] Preferably, the ratio of the total molar amount of Ca and Ce to the molar amount of Cu is 1:0.6~2.5; the molar ratio of Ca to Ce is 1:0.1~0.3.

[0012] Among the three elements Cu, Ca, and Ce, a low Cu content slows down methanol adsorption and dehydrogenation rates, leading to low methanol conversion and an increased proportion of byproducts due to excessive surface acid and base sites. Conversely, a high Cu content hinders β-elimination after methanol dehydrogenation, slowing the formation of formaldehyde intermediates and resulting in low methanol conversion. Therefore, this invention designs the molar ratio of total Ca and Ce to Cu to be 1:0.6~2.5, enabling higher methanol conversion at low temperatures in the methanol dehydrogenation to methyl formate reaction while ensuring a certain selectivity for methyl formate.

[0013] When the proportion of Ca is too low, the proportion of basic sites on the catalyst surface is low, the β-elimination process slows down, and the rate of methanol to methyl formate is reduced, thus causing a decrease in methanol conversion rate. Therefore, this invention designs the molar ratio of Ca to Ce to be 1:0.1~0.3, which can achieve a higher methanol conversion rate.

[0014] Furthermore, the molar ratio of Ca to Ce is 1:0.2~0.3.

[0015] When the proportion of Ce in the Ca and Ce elements is low, the interaction between CaO and Cu weakens, reducing interfacial sites and hindering the reaction. Simultaneously, the reduction in surface acidic sites slows the further conversion of formaldehyde intermediates into methyl acetal, thus decreasing the rate of methanol to methyl formate conversion. Therefore, this invention designs the molar ratio of Ca to Ce to be 1:0.2~0.3, which can further improve the methanol conversion rate.

[0016] Preferably, the Cu nanoparticle substrate has a particle size of 10~20 nm.

[0017] Secondly, the present invention provides a method for preparing the aforementioned low-temperature catalyst, comprising the following steps: dissolving a copper source, a calcium source, and a cerium source in a reaction solvent, mixing them with an oxalic acid solution to carry out a co-precipitation reaction, separating the solid product, and calcining it.

[0018] Preferably, the calcination temperature is 400~450°C. o C, the time is 1.5~2.5 h; the specific process of the co-precipitation reaction with oxalic acid solution includes: adding oxalic acid solution dropwise under stirring, and continuing to stir for 2~3 h after the addition is completed.

[0019] Preferably, the copper source is copper nitrate and / or copper nitrate hydrate; the calcium source is calcium nitrate and / or calcium nitrate hydrate; the cerium source is cerium nitrate and / or cerium nitrate hydrate; the reaction solvent is an organic alcohol and / or water; and the solvent in the oxalic acid solution is an organic alcohol and / or water.

[0020] Preferably, the concentration of the oxalic acid solution is 0.005~0.015 g / mL; the volume ratio of the reaction solvent to the oxalic acid solution is 1:0.5~2.

[0021] Thirdly, the present invention provides the application of the aforementioned low-temperature catalyst in the catalytic dehydrogenation of methanol to produce methyl formate.

[0022] Preferably, the application includes the following steps: after reducing and pre-activating the low-temperature catalyst under the action of hydrogen, methanol gas is brought into contact with the low-temperature catalyst under an inert atmosphere to carry out the methanol dehydrogenation to methyl formate reaction.

[0023] Preferably, the temperature of the methanol dehydrogenation to methyl formate reaction is 130~160°C. o C.

[0024] Preferably, the reduction pre-activation conditions are as follows: temperature 300~350℃. o C, time is 1.5~2.5 h; the reaction gas is a mixture of hydrogen and inert gas, wherein the volume fraction of hydrogen is 10~20%, and the volume hourly space velocity of the reaction gas is 15000~20000 mL·g -1 ·h -1 .

[0025] Preferably, during the methanol dehydrogenation to methyl formate reaction, the mass hourly space velocity (MSV) of methanol gas is 5.5–9.3 h⁻¹. -1 .

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) In the catalyst of the present invention, by using Cu nanoparticles in combination with two metal oxides, CaO and CeO2, and attaching the metal oxides to the outside of Cu nanoparticles, the catalyst can catalyze the reaction at a lower temperature when used for methanol dehydrogenation to methyl formate, and achieve a higher selectivity for methyl formate.

[0028] (2) In the catalyst of the present invention, by controlling the ratio of the total molar amount of Ca and Ce to the molar amount of Cu, and the molar ratio of Ca to Ce within a specific range, a higher methanol conversion rate and methyl formate selectivity can be achieved in the reaction of methanol dehydrogenation to methyl formate. Attached Figure Description

[0029] Figure 1 This is a microscope image of the catalyst prepared in Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments.

[0031] First, the present invention relates to a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, comprising Cu nanoparticles and a composite metal oxide attached to the Cu nanoparticles; the composite metal oxide comprises CaO and CeO2.

[0032] In some specific embodiments, in the low-temperature catalyst, the total molar amount of Ca and Ce elements to the molar amount of Cu elements is 1:0.6~2.5; the molar ratio of Ca elements to Ce elements is 1:0.1~0.3.

[0033] In some specific embodiments, the particle size of the Cu nanoparticle substrate is 10~20 nm.

[0034] Second, the present invention relates to a method for preparing the aforementioned low-temperature catalyst, comprising the following steps: dissolving a copper source, a calcium source, and a cerium source in a reaction solvent, mixing them with an oxalic acid solution to carry out a co-precipitation reaction, separating the solid product, and calcining it.

[0035] In some specific embodiments, the specific process of coprecipitation reaction with oxalic acid solution includes: adding oxalic acid solution dropwise while stirring, and continuing stirring for 2-3 hours after the addition is completed.

[0036] In some specific embodiments, the copper source is copper nitrate and / or copper nitrate hydrate; the calcium source is calcium nitrate and / or calcium nitrate hydrate; the cerium source is cerium nitrate and / or cerium nitrate hydrate; the reaction solvent is an organic alcohol and / or water; and the solvent in the oxalic acid solution is an organic alcohol and / or water.

[0037] In some specific embodiments, the concentration of the oxalic acid solution is 0.005~0.015 g / mL; the volume ratio of the reaction solvent to the oxalic acid solution is 1:0.5~2.

[0038] In some specific embodiments, the calcination temperature is 400~450°C. o C, time is 1.5~2.5 h.

[0039] Third, the present invention relates to the application of the low-temperature catalyst in the catalytic dehydrogenation of methanol to methyl formate.

[0040] In some specific embodiments, the temperature of the methanol dehydrogenation to methyl formate reaction is 130~160°C. o C.

[0041] In some specific embodiments, the application includes the following steps: after reducing and pre-activating the low-temperature catalyst under the action of hydrogen, methanol gas is contacted with the low-temperature catalyst under an inert atmosphere to carry out the methanol dehydrogenation to methyl formate reaction. Optionally or preferably:

[0042] The conditions for the reduction pre-activation are as follows: temperature 300~350℃. o C, time is 1.5~2.5 h; the reaction gas is a mixture of hydrogen and inert gas, wherein the volume fraction of hydrogen is 10~20%, and the volume hourly space velocity of the reaction gas is 15000~20000 mL·g -1 ·h -1 ;

[0043] The conditions for the methanol dehydrogenation to methyl formate reaction are as follows: temperature 130~160℃. o C, the mass hourly space velocity (MSV) of methanol gas is 5.5–9.3 h⁻¹. -1 . Specific Implementation

[0045] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0046] Examples 1-3: Catalytic effect of catalyst at different temperatures

[0047] The catalysts of Examples 1-3 were prepared by following these steps and used to catalyze the dehydrogenation of methanol to methyl formate:

[0048] S1: Catalyst Preparation

[0049] Accurately weigh 1.69 g Cu(NO3)2·3H2O, 0.59 g Ca(NO3)2·6H2O, and 0.22 g Ce(NO3)3·6H2O, and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, separately weigh 1.89 g oxalic acid, dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, and transfer it to a 1000 mL round-bottom flask. Subsequently, slowly add the metal salt solution dropwise to the round-bottom flask containing the oxalic acid solution, stirring rapidly during the addition. After the addition is complete, continue stirring for 2 hours, then filter, wash, and sterilize the sample at 60°C. o Dry overnight in a vacuum oven at C, then heat the resulting solid at 400°C. o The catalyst was calcined at C for 2 hours, then pressed into tablets, and sieved to obtain particles of 40-60 mesh to obtain an unactivated catalyst. The molar ratio of Ca, Ce, and Cu in the catalyst prepared in this example was determined to be 25:5:70.

[0050] The catalyst prepared in this embodiment is as follows: Figure 1 As shown, the size of Cu nanoparticles in the catalyst is relatively small, mainly 10~20 nm, and most of the Cu nanoparticles are encapsulated in an oxide shell formed by CaO and CeO2.

[0051] S2: Catalyst Pretreatment and Application

[0052] 0.1 g of catalyst (unactivated) was packed into a fixed bed at atmospheric pressure and reduced under programmed temperature rise in an H2 / Ar mixed atmosphere (where the volume fraction of H2 was 10%). The reduction conditions were as follows: the heating rate was 5... o C / min, 300 o At atmospheric pressure, the volumetric hourly space velocity (VHSV) of the H2 / Ar mixture is 18000 mL·g⁻¹. -1 ·h -1 The reduction time was 2 hours. After completing the above reduction process, an activated catalyst was obtained. Then, N2 was introduced to replace and cool the catalyst to a certain reaction temperature (the specific temperature settings for each embodiment are shown in Table 1), and methanol liquid was reacted at a rate of 9.3 hours. -1 Mass airspeed at 130 o After C vaporization, it was carried into a fixed-bed reactor by N2, and a dehydrogenation reaction was carried out under certain reaction temperatures (specific temperature settings for each embodiment are shown in Table 1) and atmospheric pressure. After 1 h of reaction, the products were analyzed online by gas chromatography, and the test results are listed in Table 1 after calculation.

[0053] Table 1 Catalytic effect at different temperatures

[0054]

[0055] Analyzing the data in Table 1, we can see that:

[0056] When the catalyst of the present invention is used, at 130 o The reaction of methanol dehydrogenation to methyl formate can be achieved at C, indicating that the catalyst has low-temperature catalytic activity.

[0057] Examples 4-5 and Comparative Examples 1-2: Effect of Cu Proportion on Catalytic Efficiency

[0058] The catalysts of Examples 4-5 and Comparative Examples 1-2 were prepared by following the steps below, and then used to catalyze the dehydrogenation of methanol to methyl formate:

[0059] S1: Catalyst Preparation

[0060] Accurately weigh a certain amount of Cu(NO3)2·3H2O, Ca(NO3)2·4H2O, and Ce(NO3)3·6H2O (the specific amounts for each example and comparative example are shown in Table 2), and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, separately weigh 1.89 g of oxalic acid, dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, and transfer it to a 1000 mL round-bottom flask. Subsequently, slowly add the metal salt solution dropwise to the round-bottom flask containing the oxalic acid solution, stirring rapidly during the addition. After the addition is complete, continue stirring for 2 hours, then filter, wash, and the washed sample is heated to 60°C. o Dry overnight in a vacuum oven at C, then heat the resulting solid at 400°C. o The catalyst was calcined at C for 2 hours, then pressed into tablets, and sieved to obtain particles of 40-60 mesh to obtain an unactivated catalyst. The molar ratios of Ca, Ce, and Cu in the catalysts prepared in each example and comparative example are shown in Table 2.

[0061] S2: Catalyst Pretreatment and Application

[0062] 0.1 g of catalyst (unactivated) was packed into a fixed bed at atmospheric pressure and reduced under programmed temperature rise in an H2 / Ar mixed atmosphere (where the volume fraction of H2 was 10%). The reduction conditions were as follows: the heating rate was 5... o C / min, 300 o At atmospheric pressure, the volumetric hourly space velocity (VHSV) of the H2 / Ar mixture is 18000 mL·g⁻¹. -1 ·h -1 The reduction time was 2 hours. After completing the above reduction process, the activated catalyst was obtained. Then, N2 was introduced to replace the catalyst and the temperature was lowered to 140°C. o C, methanol liquid at 9.3 h -1 Mass airspeed at 130 o After C is vaporized, it is carried into the fixed-bed reactor by N2 and heated at 140°C. oThe dehydrogenation reaction was carried out under C and atmospheric pressure conditions. After 1 h of reaction, the products were analyzed online by gas chromatography, and the results are listed in Table 3 after calculation.

[0063] Table 2. Precursor dosage and elemental ratio in catalyst

[0064]

[0065] Table 3 Effect of Cu percentage on catalytic effect

[0066]

[0067] Analyzing the data in Table 3, we can see that:

[0068] (1) From Comparative Example 1 and Examples 2, 4 and 5, when the proportion of Cu is too high among the three elements Cu, Ca and Ce, the methanol conversion rate will be low. The reason may be that the process of β-elimination to form formaldehyde intermediate after methanol dehydrogenation is blocked, the rate of formaldehyde intermediate formation slows down, and thus the overall reaction rate is low.

[0069] (2) From Comparative Example 2 and Examples 2, 4 and 5, when the proportion of Cu is too low among the three elements Cu, Ca and Ce, the methanol conversion rate and methyl formate selectivity will be low, and the CO2 selectivity will be high. The reason may be that the adsorption of methanol on the catalyst surface and the initial dehydrogenation process are slowed down, while the surface oxide holes promote the oxidation of methanol to produce more CO2.

[0070] Examples 6-7 and Comparative Examples 3-4: Effect of the ratio of Ca to Ce elements on catalytic effect

[0071] The catalysts of Examples 6-7 and Comparative Examples 3-4 were prepared by following the steps below, and then used to catalyze the dehydrogenation of methanol to methyl formate:

[0072] S1: Catalyst Preparation

[0073] Accurately weigh a certain amount of Cu(NO3)2·3H2O, Ca(NO3)2·6H2O, and Ce(NO3)3·6H2O (the specific amounts for each example and comparative example are shown in Table 4), and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, separately weigh 1.89 g of oxalic acid, dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, and transfer it to a 1000 mL round-bottom flask. Subsequently, slowly add the metal salt solution dropwise to the round-bottom flask containing the oxalic acid solution, stirring rapidly during the addition. After the addition is complete, continue stirring for 2 hours, then filter, wash, and the washed sample is heated to 60°C. o Dry overnight in a vacuum oven at C, then heat the resulting solid at 400°C. oThe catalyst was calcined at C for 2 hours, then pressed into tablets, and sieved to obtain particles of 40-60 mesh to obtain an unactivated catalyst. The molar ratios of Ca, Ce, and Cu in the catalysts prepared in each example and comparative example are shown in Table 4.

[0074] S2: Catalyst Pretreatment and Application

[0075] 0.1 g of catalyst (unactivated) was packed into a fixed bed at atmospheric pressure and reduced under programmed temperature rise in an H2 / Ar mixed atmosphere (where the volume fraction of H2 was 10%). The reduction conditions were as follows: the heating rate was 5... o C / min, 300 o At atmospheric pressure, the volumetric hourly space velocity (VHSV) of the H2 / Ar mixture is 18000 mL·g⁻¹. -1 ·h -1 The reduction time was 2 hours. After completing the above reduction process, the activated catalyst was obtained. Then, N2 was introduced to replace the catalyst and the temperature was lowered to 140°C. o C, methanol liquid at 9.3 h -1 Mass airspeed at 130 o After C is vaporized, it is carried into the fixed-bed reactor by N2 and heated at 140°C. o The dehydrogenation reaction was carried out under C and atmospheric pressure conditions. After 1 h of reaction, the products were analyzed online by gas chromatography, and the results are listed in Table 5 after calculation.

[0076] Table 4. Precursor dosage and elemental ratio in catalyst

[0077]

[0078] Table 5 Effect of the ratio of Ca to Ce elements on catalytic effect

[0079]

[0080] Analyzing the data in Table 5, we can see that:

[0081] (1) Compared with Comparative Example 3, the methanol conversion rate of Examples 2, 6 and 7 was significantly improved, while the selectivity of methyl formate decreased slightly (but not by much). This indicates that introducing CeO2 into the catalyst system composed of Cu and CaO can effectively improve the methanol conversion rate without excessively affecting the selectivity of methyl formate. The reason for this is that CeO2 can provide suitable acidic and basic sites at the same time, promote the dehydrogenation of methanol to formaldehyde intermediate, and promote the condensation of formaldehyde intermediate to form methyl acetal. At the same time, CeO2 can also strengthen the interaction between CaO and Cu, enrich the interfacial sites, and accelerate the conversion rate of methanol to methyl formate.

[0082] (2) From Examples 2, 6 and 7, when the proportion of Ce is relatively small (Example 6), the methanol conversion rate is relatively low. The reason is that the interaction between CaO and Cu is weakened, the interfacial sites are reduced, which is not conducive to the reaction. At the same time, the surface acid sites are reduced, the formaldehyde intermediate is further converted into methyl acetal more slowly, and the rate of methanol to methyl formate is slowed down.

[0083] (3) From Comparative Example 4 and Examples 2, 6 and 7, when the proportion of Ce is too large, the methanol conversion rate will be low. The reason is that the reduction of CaO content leads to a decrease in the proportion of surface alkaline sites, which slows down the β-elimination process and slows down the rate of methanol to methyl formate.

[0084] Comparative Examples 5-9: The Effect of Metal Oxide Selection on Catalytic Efficiency

[0085] The catalysts for comparative examples 5-9 were prepared through the following steps and used to catalyze the dehydrogenation of methanol to methyl formate:

[0086] S1: Catalyst Preparation

[0087] Accurately weigh 1.69 g Cu(NO3)2·3H2O, 0.59 g Ca(NO3)2·6H2O, and a certain amount of nitrate (the specific nitrate selection for each comparative example is shown in Table 6; the amount of nitrate used is 0.0005 mol based on the metal element) and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, separately weigh 1.89 g oxalic acid and dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, which is then transferred to a 1000 mL round-bottom flask. Subsequently, the metal salt solution is slowly added dropwise to the round-bottom flask containing the oxalic acid solution, with rapid stirring during the addition. After the addition is complete, stirring is continued for 2 hours. The sample is then filtered, washed, and heated at 60°C. o Dry overnight in a vacuum oven at C, then heat the resulting solid at 400°C. o C calcination for 2 hours, followed by tableting and sieving to obtain 40-60 mesh particles to obtain the catalyst (unactivated).

[0088] S2: Catalyst Pretreatment and Application

[0089] 0.1 g of catalyst (unactivated) was packed into a fixed bed at atmospheric pressure and reduced under programmed temperature rise in an H2 / Ar mixed atmosphere (where the volume fraction of H2 was 10%). The reduction conditions were as follows: the heating rate was 5... o C / min, 300 o At atmospheric pressure, the volumetric hourly space velocity (VHSV) of the H2 / Ar mixture is 18000 mL·g⁻¹. -1 ·h -1The reduction time was 2 hours. After completing the above reduction process, the activated catalyst was obtained. Then, N2 was introduced to replace the catalyst and the temperature was lowered to 140°C. o C, methanol liquid at 9.3 h -1 Mass airspeed at 130 o After C is vaporized, it is carried into the fixed-bed reactor by N2 and heated at 140°C. o The dehydrogenation reaction was carried out under C and atmospheric pressure conditions. After 1 h of reaction, the products were analyzed online by gas chromatography, and the results are listed in Table 6 after calculation.

[0090] Table 6. Effect of metal oxide selection on catalytic performance

[0091]

[0092] Analyzing the data in Table 6, we can see that:

[0093] (1) Compared with Comparative Example 3, Comparative Example 5 showed a significant increase in methanol conversion rate after introducing Cr oxide into the catalyst system composed of Cu and CaO, but the selectivity of methyl formate was significantly reduced (significantly lower than that of Example 2), resulting in more CO byproducts. The reason for this is that Cr oxide has the effect of catalyzing the decomposition of formaldehyde intermediates to generate CO.

[0094] (2) Compared with Comparative Example 3, the methanol conversion rate of Comparative Examples 6 and 7 increased only slightly after introducing Zr oxide and Ga oxide into the catalyst systems composed of Cu and CaO, respectively (compared to Example 2). The reason for this is that the acidity and basicity of Zr oxide and Ga oxide are not strong, and their influence on the catalytic process is relatively weak.

[0095] (3) Compared with Comparative Example 3, the methanol conversion rate of Comparative Example 8 decreased slightly after introducing Al oxides into the catalyst system composed of Cu and CaO. The reason for this is that the interaction between Al oxides and CaO and Cu is weak, resulting in fewer interfacial sites and thus a decrease in the methanol conversion rate.

[0096] (4) Compared with Comparative Example 3, the methanol conversion rate of Comparative Example 9 was significantly reduced after introducing Zn oxide into the catalyst system composed of Cu and CaO. The reason for this is that Zn oxide and Cu are prone to forming an alloy during catalyst pretreatment (reduction preactivation), which reduces the interfacial sites between CaO and Cu, which is not conducive to the reaction.

[0097] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, characterized in that, Includes the following steps: After dissolving copper, calcium, and cerium sources in a reaction solvent, they are mixed with oxalic acid solution for co-precipitation reaction. The solid product is separated and calcined to obtain a low-temperature catalyst consisting of Cu nanoparticles and composite metal oxides attached to the Cu nanoparticles. The composite metal oxides include CaO and CeO2. The molar ratio of the total molar amount of Ca and Ce to the molar amount of Cu is 1:0.6~2.5, and the molar ratio of Ca to Ce is 1:0.1~0.

3.

2. The preparation method according to claim 1, characterized in that, The Cu nanoparticle substrate has a particle size of 10~20 nm.

3. The preparation method according to claim 1, characterized in that, The roasting temperature is 400~450℃. o C, the time is 1.5~2.5 h.

4. The preparation method according to claim 1, characterized in that, The specific process of the co-precipitation reaction with oxalic acid solution includes: adding oxalic acid solution dropwise while stirring, and continuing to stir for 2-3 hours after the addition is complete.

5. The application of the low-temperature catalyst prepared by the method according to any one of claims 1 to 4 in the catalytic dehydrogenation of methanol to methyl formate.

6. The application according to claim 5, characterized in that, Includes the following steps: After the low-temperature catalyst is reduced and pre-activated by hydrogen, methanol gas is brought into contact with the low-temperature catalyst under an inert atmosphere to carry out the methanol dehydrogenation to methyl formate reaction.

7. The application according to claim 5, characterized in that, The temperature for the methanol dehydrogenation to methyl formate reaction is 130-160°C. o C.

8. The application according to claim 6, characterized in that, The conditions for the reduction pre-activation are as follows: temperature 300~350℃. o C, time is 1.5~2.5 h; the reaction gas is a mixture of hydrogen and inert gas, wherein the volume fraction of hydrogen is 10~20%, and the volume hourly space velocity of the reaction gas is 15000~20000 mL·g -1 ·h -1 .

9. The application according to claim 6, characterized in that, In the methanol dehydrogenation to methyl formate reaction, the mass hourly space velocity (MSV) of methanol gas is 5.5–9.3 h⁻¹. -1 .

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