Low-temperature catalyst for preparing methyl formate through methanol dehydrogenation as well as preparation method and application of low-temperature catalyst

Abstract

The invention relates to the technical field of catalyst materials and discloses a low-temperature catalyst for preparing methyl formate through methanol dehydrogenation as well as a preparation method and application of the low-temperature catalyst. The low-temperature catalyst comprises Cu nano-particles and a composite metal oxide attached outside the Cu nano-particles, the composite metal oxide comprises CaO and CeO2. When the low-temperature catalyst disclosed by the invention is used for catalyzing methanol dehydrogenation to prepare methyl formate, the reaction can be realized at a relatively low temperature, and the low-temperature catalyst has relatively high methyl formate selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst materials, and in particular to a low-temperature catalyst for preparing methyl formate by dehydrogenating methanol, and a preparation method and application thereof. Background Art

[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 numerous applications in the pharmaceutical field, including the synthesis of drugs such as methylpyrimidine sulfonate, sulfamonomethoxysulfonamide, and the antitussive dextromethorphan. In addition to its chemical nature, methyl formate has recently been identified as a novel liquid hydrogen storage medium due to its high hydrogen storage density by mass (8.4 wt.%) and volume (1 L equivalent to 1200 bar of high-pressure H2).

[0003] Using methanol as a raw material, traditional methods for producing methyl formate include methanol carbonylation, methanol selective oxidation, and methanol dehydrogenation. Methanol carbonylation, currently the predominant method used industrially, uses sodium or potassium methoxide as catalysts to catalyze the carbonylation reaction of methanol with high-pressure CO to produce methyl formate. This method offers advantages such as high selectivity for methyl formate and scalable production. However, it suffers from disadvantages such as extreme sensitivity to H₂O, CO₂, O₂, and sulfides, low conversion rates, high reaction pressures, strong corrosiveness, and difficulty in separating homogeneous catalysts, leading to recycling difficulties. Compared to methanol carbonylation, methanol selective oxidation offers milder reaction conditions and higher conversion rates. However, the reaction is highly exothermic, making it difficult to control the reaction temperature and manage the heat generated during the reaction.

[0004] The methanol dehydrogenation method has a single reactant and a simple reaction. It can be carried out at normal pressure. In addition to methyl formate, hydrogen can also be directly separated and utilized. It is expected to develop into a green, economical and efficient method for preparing methyl formate. The reported methanol gas-phase oxygen-free dehydrogenation catalysts mostly use Cu-based catalysts. The reaction temperature of these catalysts is higher than 200 o C. Higher reaction temperature will not only increase the maintenance cost of the equipment, but also increase the selectivity of the main by-product CO and reduce the stability of the catalyst. For example, patent CN105597756A discloses a copper-based core-shell catalyst for methanol dehydrogenation to methyl formate, as well as its preparation method and application. The catalyst is composed of a mesoporous silica shell and nano-copper oxide particles wrapped therein. When the catalyst is used for the reaction of methanol dehydrogenation to methyl formate, the reaction temperature is 180 ° C. o C, even if the methanol mass space velocity is as low as 1 h -1 The methanol conversion rate can only reach 25%. When the reaction temperature is increased to 250 o C, the methanol conversion rate can be increased to 50% (methanol mass space velocity is 8 h-1 ), but the selectivity for methyl formate is only 70%. Designing a catalyst for low-temperature methanol dehydrogenation to 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 of the high reaction temperature required by existing Cu-based catalysts for catalyzing the dehydrogenation of methanol to methyl formate, the present invention provides a low-temperature catalyst for the dehydrogenation of methanol to methyl formate, as well as its preparation method and application. When used to catalyze the dehydrogenation of methanol to methyl formate, this low-temperature catalyst can achieve the reaction at relatively low temperatures and exhibits high methyl formate selectivity.

[0006] The specific technical solutions of the present invention are: 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 outside of the Cu nanoparticles; the composite metal oxide comprises CaO and CeO2.

[0007] Unlike traditional supported catalysts that load metal nanoparticles on metal oxide supports, the present invention attaches metal oxides to the outside of Cu nanoparticles, which can allow the catalyst to contain more Cu. A stronger interaction can be formed between the Cu nanoparticles and the metal oxide, inhibiting the aggregation of Cu. At the same time, more interface sites can be created between the Cu nanoparticles and the metal oxide, which is beneficial to improving the catalytic efficiency.

[0008] On this basis, the present invention adopts Cu nanoparticles in combination with two metal oxides, CaO and CeO2, so that when the catalyst is used for dehydrogenating methanol to produce methyl formate, the catalyst can catalyze the reaction at a relatively low temperature and achieve a high selectivity for methyl formate. Specifically, methanol is adsorbed and dehydrogenated on the surface of the Cu nanoparticles; CaO can promote β-elimination of methanol to form a formaldehyde intermediate; CeO2 can provide suitable acidic and basic sites to promote the dehydrogenation of methanol to the formaldehyde intermediate and the condensation of the formaldehyde intermediate to form methylal. At the same time, CeO2 can also strengthen the interaction between CaO and Cu, enrich the interface sites, and accelerate the conversion rate of methanol to methyl formate; the Cu nanoparticles further promote the dehydrogenation of hemiacetal to obtain the methyl formate product.

[0009] In addition, the use of CeO2 in the present invention to provide acidic and basic sites for the catalyst also has the following advantages: CeO2 will not catalyze the decomposition of formaldehyde intermediates to produce CO, causing a significant decrease in selectivity; and CeO2 and Cu are not easy to form alloys during the catalyst pretreatment (reduction and pre-activation of the catalyst before use), which will not cause a reduction in the interface sites between CaO and Cu, thereby adversely affecting the methanol conversion rate.

[0010] Preferably, the ratio of the total molar amount of Ca element and Ce element to the molar amount of Cu element is 1:0.6-2.5; the molar ratio of Ca element to Ce element is 1:0.1-0.3.

[0011] Among the three elements Cu, Ca, and Ce, when the Cu content is too low, the methanol adsorption and dehydrogenation rates slow, leading to a low methanol conversion rate. At the same time, excessive surface acid and base sites lead to an increase in the proportion of byproducts. When the Cu content is too high, the β-elimination after methanol dehydrogenation is hindered, slowing the formation of formaldehyde intermediates, which in turn leads to a low methanol conversion rate. Based on this, the present invention designs the ratio of the total molar amount of Ca and Ce elements to the molar amount of Cu to be 1:0.6-2.5. This can achieve a higher methanol conversion rate at low temperatures in the methanol dehydrogenation reaction to methyl formate, while ensuring a certain methyl formate selectivity.

[0012] When the Ca content is too low, the catalyst surface has a low proportion of basic sites, slowing the β-elimination process and the conversion of methanol to methyl formate. This reduces the methanol conversion rate. Therefore, the present invention designs a Ca to Ce molar ratio of 1:0.1 to 0.3, achieving a higher methanol conversion rate.

[0013] Furthermore, the molar ratio of Ca element to Ce element is 1:0.2~0.3.

[0014] Of the two elements, Ca and Ce, a low Ce content weakens the interaction between CaO and Cu, reducing interface sites and hindering the reaction. This also reduces surface acid sites, slowing the conversion of the formaldehyde intermediate to methylal and slowing the conversion of methanol to methyl formate. Based on this, the present invention designs a Ca to Ce molar ratio of 1:0.2 to 0.3, which can further improve methanol conversion.

[0015] Preferably, the particle size of the Cu nanoparticle substrate is 10-20 nm.

[0016] In a second aspect, the present invention provides a method for preparing the 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 for a co-precipitation reaction, separating a solid product, and calcining the solid product.

[0017] Preferably, the calcination temperature is 400-450 o C, the time is 1.5~2.5 h; the specific process of mixing with oxalic acid solution for coprecipitation reaction includes: dropping into the oxalic acid solution under stirring, and continuing to stir for 2~3 h after the dropwise addition is completed.

[0018] 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.

[0019] Preferably, the concentration of the oxalic acid solution is 0.005-0.015 g / mL; and the volume ratio of the reaction solvent to the oxalic acid solution is 1:0.5-2.

[0020] In a third aspect, the present invention provides an application of the low-temperature catalyst in catalyzing the dehydrogenation of methanol to produce methyl formate.

[0021] Preferably, the application includes the following steps: after pre-activating the low-temperature catalyst by reduction under the action of hydrogen, methanol gas is brought into contact with the low-temperature catalyst under an inert atmosphere to carry out a methanol dehydrogenation reaction to produce methyl formate.

[0022] Preferably, the temperature of the methanol dehydrogenation reaction to prepare methyl formate is 130-160 o C.

[0023] Preferably, the reduction pre-activation conditions are as follows: the temperature is 300-350 o C, the reaction time is 1.5-2.5 h; the reaction gas is a mixture of hydrogen and inert gas, in which the volume fraction of hydrogen is 10-20%, and the volume space velocity of the reaction gas is 15000-20000 mL·g -1 ·h -1 .

[0024] Preferably, during the methanol dehydrogenation reaction to produce methyl formate, the mass space velocity of methanol gas is 5.5-9.3 h -1 .

[0025] Compared with the prior art, the present invention has the following advantages: (1) In the catalyst of the present invention, by using Cu nanoparticles to cooperate with two metal oxides, CaO and CeO2, and attaching the metal oxides to the outside of the Cu nanoparticles, the catalyst can catalyze the reaction at a lower temperature when used for dehydrogenation of methanol to methyl formate, and achieve a higher selectivity for methyl formate.

[0026] (2) In the catalyst of the present invention, by controlling the ratio of the total molar amount of Ca element and Ce element to the molar amount of Cu element, as well as the molar ratio of Ca element to Ce element 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a microscope image of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the embodiments.

[0029] First, the present invention relates to a low-temperature catalyst for preparing methyl formate from methanol dehydrogenation, comprising Cu nanoparticles and a composite metal oxide attached to the outside of the Cu nanoparticles; the composite metal oxide comprises CaO and CeO2.

[0030] In some specific embodiments, in the low-temperature catalyst, the ratio of the total molar amount of Ca element and Ce element to the molar amount of Cu element is 1:0.6-2.5; and the molar ratio of Ca element to Ce element is 1:0.1-0.3.

[0031] In some specific embodiments, the Cu nanoparticle substrate has a particle size of 10-20 nm.

[0032] Second, the present invention relates to a method for preparing the low-temperature catalyst, comprising the following steps: dissolving a copper source, a calcium source and a cerium source in a reaction solvent, mixing with an oxalic acid solution for a co-precipitation reaction, separating a solid product, and calcining it.

[0033] In some specific embodiments, the specific process of mixing with the oxalic acid solution for co-precipitation reaction includes: dropping into the oxalic acid solution under stirring, and continuing to stir for 2 to 3 hours after the dropwise addition is completed.

[0034] 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.

[0035] In some specific embodiments, the concentration of the oxalic acid solution is 0.005-0.015 g / mL; and the volume ratio of the reaction solvent to the oxalic acid solution is 1:0.5-2.

[0036] In some embodiments, the calcination temperature is 400-450 o C, time is 1.5~2.5 h.

[0037] Third, the present invention relates to the use of the low-temperature catalyst in the catalytic dehydrogenation of methanol to methyl formate.

[0038] In some specific embodiments, the temperature of the methanol dehydrogenation reaction to produce methyl formate is 130-160 o C.

[0039] In some specific embodiments, the application includes the following steps: after pre-activating the low-temperature catalyst by reduction under the action of hydrogen, methanol gas is brought into contact with the low-temperature catalyst under an inert atmosphere to perform a methanol dehydrogenation reaction to produce methyl formate. Optionally or preferably, the following steps are performed: The conditions for the reduction pre-activation are as follows: the temperature is 300-350 o C, time is 1.5~2.5 h; the reaction gas is a mixture of hydrogen and inert gas, the volume fraction of hydrogen is 10~20%, and the volume space velocity of the reaction gas is 15000~20000 mL·g -1 ·h -1 ; The conditions for the methanol dehydrogenation reaction to produce methyl formate are as follows: the temperature is 130-160 o C, the mass space velocity of methanol gas is 5.5~9.3 h -1 . Specific embodiments The present invention is described below by way of specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, any changes and advantages that can be imagined by those skilled in the art 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.

[0041] Examples 1-3: Catalytic effects of catalysts at different temperatures The catalysts of Examples 1 to 3 were prepared by the following steps and used to catalyze the dehydrogenation of methanol to methyl formate: S1: Preparation of catalyst 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, weigh 1.89 g oxalic acid and dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, which is 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, stirring rapidly during the addition process. After the addition is completed, continue stirring for 2 hours, then filter and wash. The washed sample is heated at 60 o C vacuum oven overnight, and the obtained solid was o The catalyst was calcined for 2 hours and then tableted. The particles were sieved to obtain 40-60 mesh particles to obtain a catalyst (unactivated). The molar ratio of Ca, Ce, and Cu in the catalyst prepared in this example was 25:5:70.

[0042] The catalyst prepared in this embodiment is as follows Figure 1 As shown, it can be seen that the size of the Cu nanoparticles in the catalyst is small, mainly 10~20 nm, and most of the Cu nanoparticles are wrapped in the oxide shell formed by CaO and CeO2.

[0043] S2: Catalyst pretreatment and application 0.1 g of catalyst (unactivated) was loaded into a fixed bed at atmospheric pressure and reduced by programmed temperature in a 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 C atmospheric pressure, the volumetric space velocity of the H2 / Ar mixture is 18000 mL·g -1 ·h -1 , the reduction time is 2 h. After completing the above reduction process, the activated catalyst is obtained. Then, N2 is introduced to replace the temperature and cool it to a certain reaction temperature (the specific temperature settings of each embodiment are shown in Table 1). The methanol liquid is heated at 9.3 h. -1 The mass airspeed is 130 o After vaporization, the C was introduced into a fixed-bed reactor using nitrogen. A dehydrogenation reaction was carried out at a specific reaction temperature (see Table 1 for the specific temperature settings for each example) and atmospheric pressure. After one hour of reaction, the product was analyzed online by gas chromatography. The results were calculated and listed in Table 1.

[0044] Table 1 Catalytic effects at different temperatures

[0045] Analyzing the data in Table 1, we can see that: When the catalyst of the present invention is used, at 130o C, methanol dehydrogenation to methyl formate can be achieved, indicating that the catalyst has low-temperature catalytic activity.

[0046] Examples 4-5 and Comparative Examples 1-2: Effect of Cu Content on Catalytic Effect The catalysts of Examples 4 and 5 and Comparative Examples 1 and 2 were prepared by the following steps and used to catalyze the dehydrogenation of methanol to methyl formate: S1: Preparation of catalyst Accurately weigh a certain amount of Cu(NO3)2·3H2O, Ca(NO3)2·4H2O, and Ce(NO3)3·6H2O (see Table 2 for the specific amounts used in each example and comparative example) and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, weigh 1.89 g of oxalic acid and dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, which is transferred 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. Continue stirring for 2 hours after the addition is complete, filter, wash, and refrigerate the washed sample at 60°C. o C vacuum oven overnight, and the obtained solid was o The catalyst was calcined for 2 hours and then tableted. The particles were sieved to obtain 40-60 mesh particles to obtain a catalyst (unactivated). The molar ratios of Ca, Ce, and Cu in the catalysts prepared in the Examples and Comparative Examples are shown in Table 2.

[0047] S2: Catalyst pretreatment and application 0.1 g of catalyst (unactivated) was loaded into a fixed bed at atmospheric pressure and reduced by programmed temperature in a 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 C atmospheric pressure, the volumetric space velocity of the H2 / Ar mixture is 18000 mL·g -1 ·h -1 After the above reduction process, the activated catalyst was obtained. Then N2 was introduced to replace the catalyst and the temperature was lowered to 140 o C, methanol liquid at 9.3 h -1 The mass airspeed is 130 o C was vaporized and carried into the fixed bed reactor with N2 at 140 o The dehydrogenation reaction was carried out under conditions of C and normal pressure. After 1 hour of reaction, the product was analyzed by gas chromatography online, and the test results were calculated and listed in Table 3.

[0048] Table 2 Precursor dosage and element ratio in catalyst

[0049] Table 3 Effect of Cu content on catalytic effect

[0050] Analyzing the data in Table 3, we can see that: (1) From the comparative example 1 and the examples 2, 4 and 5, it can be seen that among the three elements Cu, Ca and Ce, when the proportion of Cu is too high, the methanol conversion rate will be low. The reason may be that the β-elimination process of methanol after dehydrogenation to form formaldehyde intermediates is hindered, and the rate of forming formaldehyde intermediates is slowed down, which leads to a lower overall reaction rate.

[0051] (2) From the comparative example 2 and the examples 2, 4 and 5, it can be seen that among the three elements Cu, Ca and Ce, when the proportion of Cu is too low, the methanol conversion rate and methyl formate selectivity will be low, and the CO2 selectivity will increase. The reason may be that the adsorption of methanol on the catalyst surface and the initial dehydrogenation process slow down, and at the same time, the surface oxide vacancies promote the oxidation of methanol to produce more CO2.

[0052] Examples 6-7 and Comparative Examples 3-4: Effect of the Ratio of Ca and Ce on Catalytic Effect The catalysts of Examples 6-7 and Comparative Examples 3-4 were prepared by the following steps and used to catalyze the dehydrogenation of methanol to methyl formate: S1: Preparation of catalyst Accurately weigh a certain amount of Cu(NO3)2·3H2O, Ca(NO3)2·6H2O, and Ce(NO3)3·6H2O (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, weigh 1.89 g of oxalic acid and dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, which is transferred 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. Continue stirring for 2 hours after the addition is complete, filter, wash, and refrigerate the washed sample at 60°C. o C vacuum oven overnight, and the obtained solid was o The catalyst was calcined for 2 hours and then tableted. The particles were sieved to obtain 40-60 mesh particles to obtain a catalyst (unactivated). The molar ratios of Ca, Ce, and Cu in the catalysts prepared in the Examples and Comparative Examples are shown in Table 4.

[0053] S2: Catalyst pretreatment and application 0.1 g of catalyst (unactivated) was loaded into a fixed bed at atmospheric pressure and reduced by programmed temperature in a H2 / Ar mixed atmosphere (where the volume fraction of H2 was 10%). The reduction conditions were as follows: the heating rate was 5o C / min, 300 o C atmospheric pressure, the volumetric space velocity of the H2 / Ar mixture is 18000 mL·g -1 ·h -1 After the above reduction process, the activated catalyst was obtained. Then N2 was introduced to replace the catalyst and the temperature was lowered to 140 o C, methanol liquid at 9.3 h -1 The mass airspeed is 130 o C was vaporized and carried into the fixed bed reactor with N2 at 140 o The dehydrogenation reaction was carried out under conditions of C and normal pressure. After 1 hour of reaction, the product was analyzed by gas chromatography online, and the test results were calculated and listed in Table 5.

[0054] Table 4 Precursor dosage and element ratio in catalyst

[0055] Table 5 Effect of the ratio of Ca and Ce elements on catalytic effect

[0056] Analyzing the data in Table 5, we can see that: (1) Compared with Comparative Example 3, the methanol conversion rates of Examples 2, 6, and 7 were significantly improved, while the methyl formate selectivity decreased slightly (but not significantly). This indicates that by introducing CeO2 into the catalyst system composed of Cu and CaO, the methanol conversion rate can be effectively improved without excessively affecting the methyl formate selectivity. The reason for this is that CeO2 can simultaneously provide suitable acidic and basic sites, promote the dehydrogenation of methanol to formaldehyde intermediates, and promote the condensation of formaldehyde intermediates to form acetal. At the same time, CeO2 can also strengthen the interaction between CaO and Cu, enrich the interface sites, and accelerate the conversion rate of methanol to methyl formate.

[0057] (2) From Examples 2, 6 and 7, it can be seen that among the two elements Ca and Ce, when the proportion of Ce is small (Example 6), the methanol conversion rate is relatively low. The reason for this is that the interaction between CaO and Cu is weakened, the interface sites are reduced, and it is not conducive to the reaction; at the same time, the surface acid sites are reduced, and the further conversion of formaldehyde intermediates to methylal is slowed down, which slows down the rate of methanol to methyl formate.

[0058] (3) From the comparative example 4 and the examples 2, 6 and 7, it can be seen that when the proportion of Ce element is too large, the methanol conversion rate will be low. The reason for this is that the reduction of CaO content leads to a decrease in the proportion of surface alkaline sites, slowing down the β-elimination process and slowing down the rate of methanol to methyl formate.

[0059] Comparative Examples 5-9: Effect of Metal Oxide Selection on Catalytic Effect The catalysts of Comparative Examples 5 to 9 were prepared by the following steps and used to catalyze the dehydrogenation of methanol to methyl formate: S1: Preparation of catalyst Accurately weigh 1.69 g of Cu(NO3)2·3H2O, 0.59 g of Ca(NO3)2·6H2O, and a certain amount of nitrate (the specific nitrate selection for each comparative example is shown in Table 6, and the amount of nitrate used is 0.0005 mol, calculated as the metal element), and dissolve them in 200 mL of anhydrous ethanol in a beaker to obtain a metal salt solution. Then, weigh 1.89 g of oxalic acid and dissolve it in 200 mL of ethanol to obtain an oxalic acid solution, which is 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, stirring rapidly during the addition process. After the addition is completed, continue stirring for 2 hours, then filter and wash. The washed sample is heated at 60 o C vacuum oven overnight, and the obtained solid was o C was calcined for 2 hours, and then tableted, and 40-60 mesh particles were sieved to obtain a catalyst (unactivated).

[0060] S2: Catalyst pretreatment and application 0.1 g of catalyst (unactivated) was loaded into a fixed bed at atmospheric pressure and reduced by programmed temperature in a 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 C atmospheric pressure, the volumetric space velocity of the H2 / Ar mixture is 18000 mL·g -1 ·h -1 After the above reduction process, the activated catalyst was obtained. Then N2 was introduced to replace the catalyst and the temperature was lowered to 140 o C, methanol liquid at 9.3 h -1 The mass airspeed is 130 o C was vaporized and carried into the fixed bed reactor with N2 at 140 o The dehydrogenation reaction was carried out under conditions of C and normal pressure. After 1 hour of reaction, the product was analyzed by gas chromatography online, and the test results were calculated and listed in Table 6.

[0061] Table 6 Effect of metal oxide selection on catalytic effect

[0062] Analyzing the data in Table 6, we can see that: (1) Compared with Comparative Example 3, the introduction of Cr oxide into the Cu and CaO catalyst system in Comparative Example 5 significantly improved the methanol conversion, but significantly decreased the methyl formate selectivity (significantly lower than in Example 2), and produced a larger amount of CO byproduct. This is attributed to the Cr oxide's ability to catalyze the decomposition of the formaldehyde intermediate to produce CO.

[0063] (2) Compared to Comparative Example 3, the methanol conversion rates of Comparative Examples 6 and 7, after introducing Zr oxide and Ga oxide into the catalyst system composed of Cu and CaO, respectively, increased slightly (compared to Example 2). This is likely due to the fact that Zr oxide and Ga oxide have weak acidity and alkalinity, and therefore have a weak effect on the catalytic process.

[0064] (3) Compared with Comparative Example 3, the methanol conversion rate in Comparative Example 8 was slightly reduced after the introduction of Al oxide into the catalyst system composed of Cu and CaO. The reason for this is that the interaction between Al oxide and CaO and Cu is weak, resulting in a decrease in interfacial sites and a decrease in the methanol conversion rate.

[0065] (4) Compared with Comparative Example 3, the methanol conversion rate in Comparative Example 9 was significantly reduced after the introduction of Zn oxide into the catalyst system composed of Cu and CaO. The reason for this is that Zn oxide and Cu easily form an alloy during the catalyst pretreatment (reduction preactivation), which reduces the interface sites between CaO and Cu and is not conducive to the reaction.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used herein are conventional in the art and can be obtained from conventional commercial sources. The methods used herein are conventional in the art, unless otherwise specified.

[0067] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A low-temperature catalyst for dehydrogenating methanol to methyl formate, characterized in that: The invention comprises Cu nanoparticles and composite metal oxides attached to the outside of the Cu nanoparticles; the composite metal oxides comprise CaO and CeO2.

2. The low-temperature catalyst according to claim 1, characterized in that The ratio of the total molar amount of Ca element and Ce element to the molar amount of Cu element is 1:0.6~2.5; the molar ratio of Ca element to Ce element is 1:0.1~0.

3.

3. The low-temperature catalyst according to claim 1, characterized in that The particle size of the Cu nanoparticle substrate is 10-20 nm.

4. A method for preparing a low-temperature catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: The copper source, the calcium source and the cerium source are dissolved in a reaction solvent, and then mixed with an oxalic acid solution to carry out a co-precipitation reaction; a solid product is separated and then roasted.

5. The preparation method according to claim 4, characterized in that The calcination temperature is 400-450 o C, the time is 1.5~2.5 h; the specific process of mixing with oxalic acid solution for coprecipitation reaction includes: dropping into the oxalic acid solution under stirring, and continuing to stir for 2~3 h after the dropwise addition is completed.

6. Use of the low-temperature catalyst according to any one of claims 1 to 3 in the catalytic dehydrogenation of methanol to methyl formate.

7. The use according to claim 6, characterized in that The following steps are involved: After the low-temperature catalyst is pre-activated by reduction under the action of hydrogen, methanol gas is brought into contact with the low-temperature catalyst under an inert atmosphere to carry out a methanol dehydrogenation reaction to prepare methyl formate.

8. The use according to claim 6, characterized in that The temperature of the methanol dehydrogenation reaction to prepare methyl formate is 130-160 o C.

9. The use according to claim 7, characterized in that The conditions for the reduction pre-activation are as follows: the temperature is 300-350 o C, the reaction time is 1.5-2.5 h; the reaction gas is a mixture of hydrogen and inert gas, in which the volume fraction of hydrogen is 10-20%, and the volume space velocity of the reaction gas is 15000-20000 mL·g -1 ·h -1 .

10. The use according to claim 7, characterized in that During the methanol dehydrogenation reaction to produce methyl formate, the mass space velocity of methanol gas is 5.5~9.3 h -1 .

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