Porous carbon-supported catalysts, their preparation methods and applications

Abstract

This invention discloses a porous carbon-supported catalyst, its preparation method, and its application. In the catalyst of this invention, the content of active metal components distributed within the pores of the porous carbon support, based on active metal oxides, exceeds 50% of the total content of active metal components in the catalyst. The catalyst of this invention exhibits stable properties in the system, and the active centers are not easily lost, solving the problems of easy loss of active components and short catalyst lifetime in heterogeneous catalysts in previous technologies. In addition, the catalyst of this invention exhibits excellent conversion rate and selectivity when used in the preparation of dialkyl carbonates.

Description

Catalyst Supported on Porous Carbon Carrier, Preparation Method Thereof and Application Thereof The present invention provides a supported catalyst, and more specifically relates to a catalyst in which an active metal component is mainly supported in the pores of a porous carbon carrier, a preparation method of the catalyst, and an application of the catalyst in the preparation of dialkyl carbonate. Dimethyl carbonate (DMC) has active chemical properties, excellent physical properties, is non-toxic and easily biodegradable. It is a new type of green basic chemical raw material with low pollution and environmental friendliness. It can be used as a solvent, gasoline additive, lithium ion battery electrolyte, and carbonylation, methylation and carbonyl methoxylation reagent, and is widely used in the chemical industry. Currently, various countries are actively researching green chemical processes based on this environmentally friendly chemical raw material DMC. Among them, the transesterification method is superior due to mild reaction conditions, high yield and co-production of ethylene glycol or propylene glycol, and has become a method with great industrial prospects. Generally speaking, transesterification reactions mostly use alkali metal hydroxides, alkali metal carbonates, alkali metal alcohols, etc. (US2011040117A1; WO2010063780A1) as catalysts. However, since they are homogeneous catalysts, they are not easy to separate from the products and are difficult to reuse. Commonly used heterogeneous catalysts include alkali metals or alkali metal salts supported on carriers, metal oxide catalysts, alkali (earth) metal-exchanged zeolites or clay materials, and ion exchange resins, etc. Alkali metals or alkali metal salts supported on carriers, such as KF / Al 2 O 3 、NaOH / chitosan and Cs 2 CO 3 / SiO 2 -Al 2 O 3 etc. (CN101249452A; CN101121147A; WO2001056971A1). Their disadvantages are that they are easily affected by water and CO in the air 2 and at the same time are easily lost during the reaction, resulting in a decrease in activity; metal oxide catalysts, such as Al 2 O 3, MgO, etc. (US2005080287A1; US6207850B1), and alkali (earth) metal-exchanged zeolites or clay materials, such as Cs-ZSM-5, Mg-smectite, etc. (WO2000073256A1). The disadvantages of these two types of catalysts are that their activity or selectivity is usually relatively low; ion exchange resins, such as quaternary ammonium type or tertiary amine type resins. These types of catalysts usually cannot withstand high temperatures and swelling, and their activity decreases relatively quickly over a long time. Therefore, there is still an urgent need in the art to find a catalyst for preparing dialkyl carbonate with high stability and high conversion rate. In view of the above situation, through in-depth research, the inventors of the present invention surprisingly found that by loading an active metal component on a modified resin carrier and then calcining the resin carrier, a catalyst can be obtained in which the active metal component is mainly distributed in the pores of the porous carbon carrier. This catalyst exhibits excellent stability and high catalytic activity, thus completing the present invention. Specifically, the first aspect of the present invention provides a catalyst supported on a porous carbon carrier, which is characterized in that it includes a porous carbon carrier, an active metal component, and at least one heteroatom selected from nitrogen, sulfur, and phosphorus. Among them, relative to the total mass of the catalyst, the content of the porous carbon carrier is 50% - 99%, the content of the active metal component calculated as the active metal oxide is 0.1% - 50%, and the content of the heteroatom calculated as an element is 0.1% - 5%; the active metal is at least one selected from magnesium, aluminum, and calcium. Calculated as the active metal oxide, the proportion of the active metal component distributed in the pores of the porous carbon carrier relative to the content of all active metal components in the catalyst exceeds 50%. The second aspect of the present invention provides a method for preparing a catalyst, which includes the following steps: (1) A modification step of contacting a haloalkylated resin with a modifier to perform modification to obtain a modified haloalkylated resin; (2) A contacting step of contacting the modified haloalkylated resin with a metal precursor of an active metal to obtain a contact product; and (3) A calcining step of optionally drying the contact product and then calcining it in a non-active gas atmosphere. The third aspect of the present invention provides a method for preparing dialkyl carbonate. Among them, in the presence of the catalyst of the present invention above or the catalyst prepared by the preparation method of the present invention, a carbonate ester and a lower alcohol are reacted to obtain dialkyl carbonate. Technical effects In the catalyst of the present invention, compared with the active metal components distributed on the surface of the porous carbon support, the content of the active metal components that enter the pores of the porous carbon support and are distributed in the pores is higher, and the proportion relative to the content of all the active metal components contained in the catalyst exceeds 50%. Therefore, the catalyst of the present invention exhibits excellent conversion rate and selectivity in the preparation of dialkyl carbonate, has a long catalyst life, and is suitable for industrial use. Moreover, when the carbon support catalyst is used in the preparation of dialkyl carbonate, the properties of the catalyst system are stable, and the active centers are not easily lost, solving the problems of easy loss of active components of heterogeneous catalysts and short catalyst life in the prior art. In the preparation method of the catalyst of the present invention, by using a spherical porous resin support, the utilization rate of the support and the density of active centers can be effectively improved, solving the problem of low activity of heterogeneous catalysts in the prior art; by modifying the resin, and then loading the precursor of the active metal, and then calcining, more active metal components can enter the interior of the pores of the carbon support. Thus, the catalyst of the present invention can be efficiently prepared. In the preparation method of the dialkyl carbonate of the present invention, the catalyst of the present invention or the catalyst prepared by the preparation method of the present invention is used, so as to prepare dialkyl carbonate from carbonate and lower alcohol with a high conversion rate of dialkyl carbonate and high selectivity. The present invention is described in detail below in conjunction with specific embodiments. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments and theoretical explanations, but is determined by the scope of the patent application. In the present invention, except for the content clearly described, any matters or items not mentioned are directly applicable to the content known in the art without any change. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are regarded as part of the original disclosure or record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider that the combination is obviously unreasonable. All the features disclosed in the present invention can be combined arbitrarily. These combinations should be understood as the content disclosed or recorded in the present invention. Unless those skilled in the art consider that the combination is obviously unreasonable, they should all be regarded as specifically disclosed and recorded by the present invention. The numerical points disclosed in this specification, unless otherwise specified, not only include the specific numerical points disclosed in the examples, but also include the endpoints of the numerical ranges in the specification. The ranges formed by any combination of these numerical points should be regarded as the ranges disclosed or recorded in the present invention. For the technical and scientific terms in the present invention, those with definitions shall be subject to their definitions, and those without definitions shall be understood according to the common meanings in the art. [Carbon support catalyst] The present invention provides a catalyst supported on a porous carbon support, which comprises a porous carbon support, an active metal component, and at least one heteroatom selected from nitrogen, sulfur, and phosphorus. Among them, relative to the total mass of the catalyst, the content of the porous carbon support is 50% to 99%, the content of the active metal component in terms of the active metal oxide is 0.1% to 50%, and the content of the heteroatom in terms of the element is 0.1% to 5%; the active metal is at least one selected from magnesium, aluminum, and calcium, and in terms of the active metal oxide, the content of the active metal component distributed in the pores of the porous carbon support accounts for more than 50% of the content of all the active metal components in the catalyst. In the catalyst of the present invention, the porous carbon support is obtained by calcining a porous resin material in an inert gas. In the catalyst of the present invention, there is no particular limitation on the particle size of the porous carbon support, and the particle size can be 0.1 mm to 3 mm, preferably 0.3 mm to 2 mm. There is no particular limitation on the pore diameter of the porous carbon support of the present invention, and for example, it can be 5 to 500 nm, preferably 50 to 300 nm. In one embodiment of the present invention, relative to the total mass of the catalyst, the content of the porous carbon support is 50% to 99%, preferably 55 to 90%, more preferably 60 to 85%. In the present invention, at least one heteroatom selected from nitrogen, sulfur, and phosphorus comes from the modifier used in the preparation of the catalyst. In the calcination step, the modifier is calcined to leave at least one heteroatom among nitrogen, sulfur, and phosphorus. In one embodiment of the present invention, relative to the total mass of the catalyst, the content of at least one heteroatom selected from nitrogen, sulfur, and phosphorus in terms of the element is 0.1% to 5%; preferably 0.3 to 4.5%, more preferably 0.5 to 4%. In the present invention, the catalyst also contains oxygen element. However, the present invention does not intend to limit the content of the oxygen element. Generally, the content of the oxygen element is calculated within the oxides of the present invention. In one embodiment of the present invention, the catalyst may also contain halogen elements, and the halogen elements come from halogenated alkyl resins. Generally, during calcination, the halogen elements are calcined and removed. However, there may still be residual halogen elements with impurity content, and the present invention does not intend to limit the content of the halogen elements. In the present invention, by means well known in the art such as elemental analysis, the content of the active metal component in terms of the oxide and the content of the heteroatom in terms of the element and the content of the halogen atoms in terms of the element optionally present in the catalyst can be measured. After excluding the content of the active metal oxide, the content of the heteroatom, and the content of the halogen atoms optionally present, the remaining content is recorded as the content of the porous carbon support of the present invention. In the present invention, the active metal oxide comes from the calcination product of the precursor of the active metal introduced during the preparation of the catalyst. In one embodiment of the present invention, the content of the active metal component in terms of the active metal oxide is 0.1% to 50% based on the total mass of the catalyst, preferably 5% to 45%, more preferably 10% to 40%. In one embodiment of the present invention, the active metal is at least one selected from magnesium, aluminum, and calcium, preferably at least one selected from magnesium and calcium. In the catalyst of the present invention, the active metal component in the catalyst of the present invention includes any valence state and any oxidation state of the active metal. Generally, in the catalyst of the present invention, the active metal component usually exists in the form of a metal oxide, which is the product after the precursor of the active metal is calcined. In the present invention, unless otherwise specified, the active metal component is usually measured in the form of the active metal oxide. In the catalyst of the present invention, compared with the active metal component distributed on the surface (sometimes also referred to as the outer surface or exterior in the present invention) of the porous carbon support, the content of the active metal component distributed in the pores (sometimes also referred to as the inner surface or interior in the present invention) of the porous carbon support is more. In one embodiment of the present invention, in terms of the active metal oxide, the proportion of the content of the active metal component distributed in the pores of the porous carbon support relative to the content of the active metal component contained in the catalyst exceeds 50%, preferably 55% or more, more preferably 60% or more, further preferably 65% or more, and most preferably 75% or more. There is no particular limitation on the upper limit of the proportion of the content of the active metal component distributed in the pores of the porous carbon support relative to the content of the active metal component contained in the catalyst, and it is preferably 100%, but from the perspective of actual production cost, the upper limit can be 99%, 98%, 96%, 96%, 95%. In one embodiment of the present invention, in terms of the active metal oxide, the content of the active metal component distributed on the surface (outer surface or exterior) of the porous carbon support is less than 50% relative to the content of the active metal component contained in the catalyst, preferably 45% or less, more preferably 40% or less, further preferably 35% or less, and most preferably 30% or less. The lower the lower limit of the content of the active metal component distributed on the surface (outer surface or exterior) of the porous carbon support relative to the content of the active metal component contained in the catalyst, the better, and it is preferably 0, but from the perspective of actual production cost, the lower limit can be 5%, 4%, 3%, 2%, 1%. In the present invention, for the content of the active metal component distributed on the surface (outer surface or exterior) of the porous carbon support, XPS can be used for measurement. That is, in the present invention, the content of the active metal of the porous carbon support measured by XPS is used as the content of the active metal on the surface (outer surface or exterior) of the porous carbon support. It should be noted that in the present invention, the content of the active metal component in the pores (inner surface or interior) of the porous carbon support can be obtained by subtracting the content of the active metal component distributed on the surface (outer surface or exterior) of the porous carbon support from the total content of the active metal component in the porous carbon support. Here, for the total content of the active metal component in the catalyst, the content of the active metal component contained in the catalyst can be determined by elemental analysis or the like; on the other hand, in the present invention, the content of the active metal component of the porous carbon support measured by XPS is taken as the content of the active metal component on the surface (outer surface or exterior) of the porous carbon support. Thus, based on these two values, the content of the active metal component distributed in the pores (inner surface or interior) of the porous carbon support can be calculated. The content of the active metal component in the pores (inner surface or interior) = the total content of the active metal component in the porous carbon support - the content of the active metal component distributed on the surface (outer surface or exterior) of the porous carbon support measured by XPS. In the present invention, by mainly (for example, more than 50%) distributing the active metal component in the pores of the porous carbon support, and more preferably distributing most of the active metal component (for example, 55% or more, preferably 60% or more, further preferably 65% or more, and most preferably 70% or more) in the pores of the porous carbon support, the catalyst exhibits excellent conversion rate, high selectivity, and the catalyst life is greatly extended. In one embodiment of the present invention, a catalyst for preparing dimethyl carbonate is provided, which includes a support and an active component. The characteristics are that the mass percentage contents of the support and the active component in the catalyst are respectively: support 50% - 99.9%, active component 0.1% - 50%; the support is carbon, and the active component is selected from at least one of magnesium, calcium, and aluminum; the carbon is obtained by carbonizing a modified chloromethyl resin; The active component is distributed on the surface of the support and in the pores of the support, and the content of the active component in the pores of the support is greater than the content of the active component on the surface of the support. Preparation method of the catalyst The second aspect of the present invention provides a preparation method of a catalyst, which includes the following steps: (1) A modification step of contacting a haloalkylated resin with a modifier for modification to obtain a modified haloalkylated resin; (2) A contacting step of contacting the modified haloalkylated resin with a metal precursor of an active metal to obtain a contact product; and (3) An optional drying step of the contact product and then a calcination step of calcining in an inert gas atmosphere, The modifier is at least one compound selected from nitrogen-containing compounds, sulfur-containing compounds, and phosphorus-containing compounds. The inventors of the present invention found that by modifying a halogenated alkylated resin with a modifier, allowing the modified resin to interact with an active metal precursor, and then calcining, a catalyst can be obtained in which the active metal component is mainly distributed in the pores of a porous carbon support. In the present invention, the halogen or halide may include fluorine, chlorine, bromine, and iodine, preferably chlorine or iodine, and more preferably chlorine. In the present invention, the alkyl group in the alkylation may include C1-C6 alkyl groups, preferably C1-C4 alkyl groups, and more preferably methyl, ethyl, propyl, and isopropyl. In one embodiment of the present invention, the halogenated alkylation is preferably halomethylation, and more preferably chloromethylation. In the present invention, the halogenated alkylated resin can be obtained by subjecting a general resin to halogenated alkylation modification (preferably halomethylation modification, more preferably chloromethylation modification), or a commercially available halogenated alkylated resin can be used as long as the resin has a porous structure. In the present invention, examples of the halogenated alkylated resin include halogenated alkylated styrene resins, such as chloromethyl resins, especially chloromethyl styrene resins. The halogenated alkylated styrene resin can be a commercially available product and can also be prepared by methods known in the art, including but not limited to the following methods: alkylating polystyrene with a halogenated olefin (C2-C6 halogenated olefin) to produce a halogenated alkyl polystyrene (CN1137788A). In addition, as the chloromethyl styrene resin, it can be a commercially available product and can also be prepared by methods known in the art, including but not limited to the following methods: preparing polystyrene microsphere resin by suspension polymerization and reacting it with chloromethyl ether to obtain chloromethyl styrene resin (CN103864973A). In addition, reference can also be made to the methods described in CN103709278A, CN104788592A, etc. to prepare halogenated alkylated styrene resins or chloromethyl styrene resins. In one embodiment of the present invention, the particle size of the halogenated alkylated resin is 0.1 mm to 3 mm, preferably 0.3 mm to 2 mm. In one embodiment of the present invention, the pore diameter of the halogenated alkylated resin is 5 to 500 nm, preferably 50 to 300 nm. In one embodiment of the present invention, the halogenated alkylated resin is spherical. In step (1) of the present invention, a modifier is contacted with a haloalkylated resin for modification to obtain a modified haloalkylated resin (hereinafter sometimes also referred to as a modification product or a modified resin). The present invention does not intend to restrictively explain the reaction occurring at this time. It is speculated that it may be due to the interaction between the heteroatoms of nitrogen, phosphorus, or sulfur contained in the modifier and the haloalkyl group. Moreover, the introduced heteroatoms can promote the dispersion of the subsequent active metal precursor inside the carrier, improve the dispersion degree of the metal active component, promote alkalinity, and prompt the active metal component to deposit in the pores of the porous carbon carrier after calcination. Therefore, in the present invention, the modifier is at least one compound selected from nitrogen-containing compounds, sulfur-containing compounds, and phosphorus-containing compounds. In one embodiment of the present invention, the nitrogen-containing compound is a nitrogen-containing organic compound. In one embodiment of the present invention, the nitrogen-containing organic compound only needs to be an organic compound containing a nitrogen atom, and there is no particular limitation. Alkylamines or 5- or 6-membered nitrogen-containing heteroaromatic compounds can be used. Examples of alkylamines include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, cyclohexylamine, octylamine, decylamine, dimethylamine, diethylamine, dibutylamine, trimethylamine, triethylamine, tributylamine, etc. Examples of 5- or 6-membered nitrogen-containing heteroaromatic compounds include at least one of 5- or 6-membered nitrogen-containing heteroaromatic compounds optionally substituted with a C1-C6 alkyl group. Examples of 5- or 6-membered nitrogen-containing heteroaromatic compounds include piperidine, pyridine, imidazole, 1-methylimidazole, quinoline, pyrrole, indole, oxazole, isoindole, thiazole, etc. These nitrogen-containing heteroaromatic compounds are optionally substituted with a C1-C6 alkyl group. In the present invention, the C1-C6 alkyl group is preferably a C1-C4 alkyl group, and more preferably methyl, ethyl, propyl, or isopropyl. In one embodiment of the present invention, the number of substituents of "substituted with a C1-C6 alkyl group" can be 1, 2, 3, 4, or 5, preferably 1, 2, or 3, and more preferably 1 or 2. In one embodiment of the present invention, the sulfur-containing compound is a sulfur-containing organic compound. In one embodiment of the present invention, the sulfur-containing organic compound may be any organic compound containing a sulfur atom, and there is no particular limitation. For example, sulfur ethers such as dimethyl sulfide, diethyl sulfide, dipropyl sulfide, dihexyl sulfide, dicyclohexyl sulfide, and diphenyl sulfide can be cited; dialkyl disulfide compounds such as dimethyl disulfide, diethyl disulfide, dipropyl disulfide, dibutyl disulfide, dihexyl disulfide, dicyclohexyl disulfide, and ethyl methyl disulfide; thiophenes optionally substituted with a C1-C6 alkyl group such as thiophene, 2-methylthiophene, 3-methylthiophene, 2,3-dimethylthiophene, 2-ethylthiophene, and benzothiophene; heterocyclic sulfur compounds such as tetrahydrothiophene and thiopyran; aromatic sulfur compounds such as diphenyl sulfide, diphenyl disulfide, methylphenyl disulfide, and methylphenyl sulfide: thiourea; and sulfides such as methyl sulfide, ethyl sulfide, and butyl sulfide, etc. In one embodiment of the present invention, the phosphorus-containing compound is a phosphorus-containing organic compound. In one embodiment of the present invention, the phosphorus-containing organic compound may be any organic compound containing a phosphorus atom, and there is no particular limitation. For example, phosphines such as triphenylphosphine, triethylphosphine, tributylphosphine, tripropylphosphine, trioctylphosphine, and tricyclohexylphosphine can be cited. In one embodiment of the present invention, the modifier is preferably at least one selected from imidazole optionally substituted with a C1-C6 alkyl group, pyridine optionally substituted with a C1-C6 alkyl group, thiophene optionally substituted with a C1-C6 alkyl group, thiazole optionally substituted with a C1-C6 alkyl group, piperidine optionally substituted with a C1-C6 alkyl group, and triphenylphosphine, and more preferably at least one selected from imidazole, 1-methylimidazole, pyridine, piperidine, and thiophene. In one embodiment of the present invention, the mass ratio of the haloalkylated resin to the modifier is 1:(0.1-1.2), preferably 1:(0.15-1), for example, 1:1, 1:0.8, 1:0.6. In one embodiment of the present invention, the modification step can be carried out in a solvent. As the solvent, it can be at least one selected from toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, tert-butanol, tetrahydrofuran, dichloromethane, chloroform, N,N-dimethylformamide, ether, and water. In one embodiment of the present invention, the mass ratio of the haloalkylated resin to the solvent is 1:(1-10), preferably 1:(2-8), for example, 1:3.792, 1:5.688. In one embodiment of the present invention, the modification step can be carried out at a temperature of 30°C to 150°C, preferably 40°C to 120°C, for example, 70°C, 80°C, 90°C. The temperature of the solution containing the resin raw material can be raised before the resin raw material contacts the modifier, and the temperature of the solution can also be raised during the contact process of the resin raw material and the modifier. In the present invention, there is no particular limitation on the modification time of the modification step. In one embodiment of the present invention, the modification time of the modification step is 1 h to 24 h, preferably 2 h to 18 h, such as 12 h or 15 h. In one embodiment of the present invention, during the modification process, the solution containing the resin raw material and the modifier can also be mixed and stirred. The rate of the mixing and stirring is 50 revolutions per minute to 1000 revolutions per minute, preferably 100 revolutions per minute to 800 revolutions per minute, such as 500 revolutions per minute or 800 revolutions per minute. The stirring time is not particularly limited and can be, for example, 2 h. In one embodiment of the present invention, in step (1), if necessary, the modified product can be washed and dried. At this time, the above solvent can be used for washing, and then drying is carried out. As the drying conditions, the drying temperature can be 80°C to 180°C, such as 100°C or 120°C; the drying time is 1 h to 48 h, such as 24 h. In step (2) of the present invention, the modified haloalkylated resin (modified product) is contacted with the metal precursor of the active metal to obtain a contact product. In the present invention, the metal precursor of the active metal is loaded on the modified haloalkylated resin through step (2). In the present invention, the active metal is at least one selected from magnesium, calcium, and aluminum, preferably at least one selected from magnesium and calcium. In one embodiment of the present invention, the metal precursor of the active metal is at least one of the nitrate form, chloride form, and sulfate form of the active metal. In one embodiment of the present invention, the mass ratio of the modified haloalkylated resin to the metal precursor of the active metal is 1:0.1 to 3, preferably 1:0.2 to 2. In one embodiment of the present invention, the metal precursor of the active metal exists in the form of a solution. At this time, the solvent can be selected from the above solvents, preferably water. In one embodiment of the present invention, the mass concentration of the metal precursor solution of the active metal is 5% to 50%, such as 6.5%, 7%, 8%, 8.8%, 17.6%, 26.4%, 35.2%. In one embodiment of the present invention, the mass ratio of the modified haloalkylated resin to the solution containing the metal precursor of the active metal is 1:(1 to 10), preferably 1:(2 to 6). In one embodiment of the present invention, the contacting step is carried out in the presence of a solvent, and the solvent may be at least one selected from toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, tert-butanol, tetrahydrofuran, dichloromethane, chloroform, N,N-dimethylformamide, ether, and water. In one embodiment of the present invention, a solution of a metal precursor containing a modified resin and an active metal is mixed and stirred. The conditions for the mixing and stirring are not particularly limited. For example, the rate of the mixing and stirring is 100 revolutions per minute to 800 revolutions per minute, preferably 200 revolutions per minute to 600 revolutions per minute; the temperature of the stirring is 30°C to 100°C, preferably 50°C to 80°C, such as 50°C and 80°C, and the stirring time is 1 h to 10 h, preferably 2 h to 8 h, such as 2 h, 6 h, and 8 h. In step (3) of the present invention, the product obtained in the contacting step is calcined in an inert gas atmosphere to obtain the catalyst of the present invention. In one embodiment of the present invention, in step (3) of the present invention, the product obtained in the contacting step is first dried and then calcined. The conditions for the drying are not particularly limited. For example, the temperature is 80°C to 180°C, preferably 90°C to 150°C, such as 100°C, and the time is 1 h to 48 h, preferably 2 h to 36 h, such as 14 h and 24 h. In the present invention, the modified resin particles loaded with the active metal precursor are calcined. During the calcination process, the resin particles are carbonized to be converted into a porous carbon support. This porous carbon support serves as the porous carbon support of the catalyst of the present invention, and on this porous carbon support, the active metal components are mainly enriched in the pores (inner surface or inside) of the porous carbon support. At the same time, the modifier is removed and at least one heteroatom selected from nitrogen, sulfur, and phosphorus remains in the carbon support. In the present invention, there is no limitation on the inert gas, as long as it is an inert gas known in the art. In one embodiment of the present invention, the inert gas may include nitrogen and rare gases such as argon. In one embodiment of the present invention, the calcination temperature is 200°C to 1000°C, preferably 250°C to 600°C, such as 400°C, 500°C, and 600°C, and the calcination time is 1 h to 48 h, preferably 2 h to 24 h, such as 4 h, 5 h, and 8 h. In one embodiment of the present invention, a method for preparing a catalyst for preparing dimethyl carbonate is provided. When modifying the chloromethyl resin, the chloromethyl resin is mixed with a solvent, and a modifier is added to obtain a modified chloromethyl resin by modification; preferably, the modifier is a nitrogen-containing five- or six-membered heterocyclic aromatic compound, the modified chloromethyl resin is a modified chloromethyl styrene resin, and the solvent is at least one of toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, tert-butanol, tetrahydrofuran, dichloromethane, trichloromethane, N,N-dimethylformamide, ether, and water; more preferably, the chloromethyl resin is styrene-based, and the modifier is at least one of piperidine, imidazole, and pyridine; still more preferably, the particle size of the chloromethyl resin is 0.1 mm to 3 mm, preferably 0.3 mm to 2 mm; the chloromethyl resin is spherical; And / or, the mass ratio of the chloromethyl resin to the solvent is 1:(1 to 10), preferably 1:(2 to 8); And / or, the mass ratio of the chloromethyl resin to the modifier is 1:(0.1 to 1.2), preferably 1:(0.15 to 1); And / or, before adding the modifier, a temperature-raising step is further included; the temperature after raising the temperature is 30°C to 150°C, preferably 40°C to 120°C; And / or, the mixing and stirring rate is 50 revolutions per minute to 1000 revolutions per minute, preferably 100 revolutions per minute to 800 revolutions per minute; the mixing and stirring time is 2 h; And / or, the modification time is 1 h to 24 h, preferably 2 h to 18 h; preferably, after modification, steps of cooling, separating and washing the product, and drying the product are further included; more preferably, the drying temperature is 80 to 180°C, and the drying time is 1 h to 48 h; And / or, the preparation method includes a step of loading an active component on a carrier. In one embodiment of the present invention, when loading the active component on the carrier, the carrier is mixed and stirred with a metal precursor solution containing the active component, then dried, and then calcined in an inert gas atmosphere to obtain the catalyst. In one embodiment of the present invention, the metal precursor solution containing the active component is at least one of nitrate solutions, chloride solutions, and sulfate solutions of magnesium, calcium, and aluminum, and the mass concentration of the metal precursor solution containing the active component is 5% to 50%. In one embodiment of the present invention, when loading the active component on the carrier, the mass ratio of the carrier to the metal precursor solution containing the active component is 1:(1 to 10), preferably 1:(2 to 6); And / or, the stirring rate is 100 revolutions per minute to 800 revolutions per minute, the stirring temperature is 50 °C to 80 °C, and the stirring time is 2 h to 8 h; And / or, the drying temperature is 80 °C to 180 °C, and the time is 1 h to 48 h; And / or, the inert gas is nitrogen or argon; And / or, the roasting temperature is 200 °C to 1000 °C, and the time is 1 h to 48 h. Preferably, the roasting temperature is 250 °C to 600 °C, and the time is 2 h to 24 h. [Method for preparing dialkyl carbonate] The third aspect of the present invention provides a method for preparing a dialkyl carbonate represented by the following general formula (I), which includes the step of reacting a carbonate represented by the following general formula (II) with a lower alcohol represented by the following general formula (III) under the action of a catalyst to obtain a dialkyl carbonate represented by the general formula (I); the catalyst is the catalyst of the present invention or the catalyst prepared by the catalyst preparation method of the present invention, R 1 -OCOO-R 1 (I) In formula (I), each R 1 independently selects from C1-C6 alkyl; R 2 -OCOO-R 2 (II) In formula (II), each R 2 independently selects from C1-C6 alkyl, and at least one R 2 is different from at least one R 1 ; or two Rs 2 bond to each other to form a C2-C6 alkylene group; R 1 -OH (III) In formula (III), R 1 selects from C1-C6 alkyl. In one embodiment of the present invention, the reaction temperature for the preparation of the dialkyl carbonate represented by the general formula (I) is 40 °C to 130 °C, preferably 50 °C to 120 °C. For example, 70 °C, 80 °C, 90 °C, 110 °C, 120 °C. In one embodiment of the present invention, the reaction time for the preparation of the dialkyl carbonate represented by the general formula (I) is 1 h to 15 h, preferably 2 h to 12 h, such as 4 h, 6 h, 8 h, 10 h. In one embodiment of the present invention, in the preparation of the dialkyl carbonate represented by the general formula (I), the molar ratio of the lower alcohol represented by the general formula (III) to the carbonate represented by the general formula (II) is (0.5 to 15):1, preferably (1 to 12):1, such as 4:1, 6:1, 8:1. In one embodiment of the present invention, in the preparation of the dialkyl carbonate represented by the general formula (I), the mass ratio of the catalyst to the carbonate represented by the general formula (II) is (0.001 to 0.5):1, preferably (0.05 to 0.5):1. For example, 0.2:1, 0.3:1, 0.4:1. In one embodiment of the present invention, in the dialkyl carbonate represented by the general formula (I), the two Rs 1 may be the same or different. When the two Rs 1 are the same, the dialkyl carbonate is a symmetric dialkyl carbonate. When the two Rs 1 are different, the dialkyl carbonate is an asymmetric dialkyl carbonate. In the present invention, R 1 may include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl. Therefore, in the present invention, the dialkyl carbonates represented by the general formula (I) may include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, dibutyl carbonate, etc. In one embodiment of the present invention, in the carbonate represented by the general formula (II), each R 2 is independently selected from C1-C6 alkyl, and at least one R 2 is different from at least one R 1 In the present invention, R 2 may include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl, pentyl, hexyl. In one embodiment of the present invention, in the carbonate represented by the general formula (II), the two Rs 2 are connected to each other to form a C2-C6 alkylene group. At this time, the carbonate represented by the general formula (II) is a cyclic carbonate, and may be, for example, ethylene carbonate, propylene carbonate. In the present invention, one or more than two lower alcohols represented by the general formula (III) can be used. Examples of the lower alcohol of the present invention include methanol, ethanol, propanol, isopropanol, butanol and their isomers. In the present invention, R in the lower alcohol represented by the general formula (III) 1 is the same as at least one of the two Rs in the dialkyl carbonate represented by the general formula (I) 1 In the present invention, R 2 and R 1 can be the same, however, at least one R 2 is different from at least one R 1 In other words, in the present invention, the transesterification reaction occurs between the carbonate represented by the general formula (II) and the lower alcohol represented by the general formula (III), so that R in the lower alcohol represented by the general formula (III) 1 becomes at least one end of the dialkyl carbonate represented by the general formula (I). In one embodiment of the present invention, there is provided a method for preparing dimethyl carbonate, which is characterized by including the step of reacting an alkylene carbonate with methanol under the action of a catalyst to obtain dimethyl carbonate; the catalyst is the catalyst of the present invention; and / or, the reaction temperature is 40°C to 130°C, preferably 50°C to 120°C; and / or, the reaction time is 1 h to 15 h, preferably 2 h to 12 h, and / or, the molar ratio of the methanol to the alkylene carbonate is (2 to 15):1, preferably (3 to 12):1; and / or, the mass ratio of the catalyst to the alkylene carbonate is (0.001 to 0.5):1, preferably (0.05 to 0.5):1; and / or, the alkylene carbonate is one or more of ethylene carbonate or propylene carbonate. The catalyst of the present invention or the catalyst prepared by the above catalyst preparation method of the present invention is used in the reaction for preparing dialkyl carbonate by the transesterification reaction of the carbonate represented by the general formula (II) and the lower alcohol represented by the general formula (III). Even when used repeatedly for many times (for example, more than 10 times), the activity decrease is less than 5%, and good technical effects are achieved. ​​As an example of the conditions for the reaction for preparing dialkyl carbonate, the following can be cited: The reaction is carried out for 10 h under the conditions that the reaction temperature is 80 °C, the molar ratio of the lower alcohol to the cyclic carbonate is 8:1, and the mass ratio of the catalyst to the cyclic carbonate is 0.3:1. At this time, the conversion rate of the cyclic carbonate is 80.4%, and the selectivity of the dialkyl carbonate is 99.9%. Example The present invention will be further described below in conjunction with examples. However, the present invention is not limited by these examples. In the present invention, the gas chromatograph is an Agilent 7890 chromatograph. The analysis conditions are as follows: chromatographic column HP-FFAP, injection port temperature 280 °C, FID detector, programmed temperature rise in the column oven. After maintaining at 50 °C for 3 minutes, it is raised to 230 °C at 10 °C / min and held for 10 minutes, split ratio 50:1, and the component content analysis is carried out by the corrected normalization method. The elemental analysis of the heteroatom content is carried out using a Therm2000 instrument. The XPS test is carried out on an X-ray photoelectron spectrometer (XPS, AXIS ULTRA DLD) of Kratos Company, Japan. The analysis and test of metal elements are carried out by ICP-OES, and the instrument used is Varian 725ES. SEM is carried out using a scanning electron microscope (SEM, Merlin) of ZEISS Company, Germany. TEM is obtained on a Tecnai 20 S-TWIN transmission electron microscope, and the operating voltage is 200 kV. The calculation method of the conversion rate of the raw material in the example is: (mass of the input raw material - mass of the product after the reaction * content of the raw material) / mass of the input raw material * 100%. The calculation method of the selectivity of the carbonate in the example is: yield of the carbonate product after the reaction / theoretical yield of the carbonate of the consumed raw material * 100%. The calculation method of the proportion of the content of the active metal component distributed in the pores of the porous carbon carrier is: (content of the active metal component in the catalyst calculated as the active metal oxide - content of the active metal component detected by XPS calculated as the active metal oxide) / content of the active metal component in the catalyst calculated as the active metal oxide. Example 1 This example provides a method for preparing dimethyl carbonate: Preparation of Catalyst for Preparing Dimethyl Carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 200 ml (189.6 g) of N,N-dimethylformamide, then stir at a rate of 500 revolutions per minute for 2 h. Heat up to 90 °C, add 50 g of imidazole, keep the temperature for reaction for 12 h, cool and separate the product, then wash with deionized water, and dry the product at 100 °C for 24 h to obtain the modified resin. Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 8.8 g of magnesium nitrate in 100 g of water to form a solution, stir at a rate of 500 revolutions per minute at 80 °C for 6 h, put it in an oven and dry at 100 °C for 14 h, then transfer it to a muffle furnace and calcine in a nitrogen atmosphere at 500 °C for 5 h to obtain catalyst C1. The mass percentage content of magnesium oxide in catalyst C1 is 10%. The scanning electron microscope image of catalyst C1 is shown in Figure 1, and the transmission electron microscope image of catalyst C1 is shown in Figure 3. The nitrogen content of the catalyst is 2.6%, the pore diameter is 150 nm, and the content ratio of magnesium oxide inside the pore channels is 86.7%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 0.5 mm. Preparation of Dimethyl Carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 4.4 g of catalyst C1 in a 100 mL autoclave, and react at 120 °C for 4 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C1 to ethylene carbonate is 0.2:1. After the reaction, cool the autoclave to room temperature and vent. Take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.4%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, put it in an oven and dry at 100 °C for 24 h for reuse. Under the same conditions as the above dimethyl carbonate preparation process, take the liquid-phase product after the reaction for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. In Figure 5, (a) shows the scanning electron microscope image of catalyst C1 prepared in Example 1 of the present invention at a scale of 100 microns; (b) shows the scanning electron microscope of the interior of the catalyst prepared in Example 1 of the present invention at a scale of 10 microns. It can be seen from this that the outer surface of the carbon carrier is smooth, and magnesium oxide is mainly distributed on the inner surface of the carbon carrier. In Figure 6, (a) shows a scanning electron microscope image of the interior of catalyst C1 prepared in Example 1 of the present invention at a scale of 200 nm; (b) shows a scanning electron microscope image of the interior of catalyst C1 prepared in Example 1 of the present invention at a scale of 100 nm. It can be seen that the pores are filled to a certain extent, indicating the deposition of magnesium oxide inside. Figure 7 shows the energy spectrum surface scan and EDX spectrum of catalyst C1 prepared in Example 1 of the present invention; (a) shows the selected area surface scan spectrum; (b) shows the carbon element distribution map; (c) shows the oxygen element distribution map; (d) shows the magnesium element distribution map; (e) shows the EDX energy spectrum. It can be seen that magnesium oxide is mainly distributed inside the carbon carrier, and the EDX relative abundance is high. Example 2 This example provides a method for preparing dimethyl carbonate: Preparation of the catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 200 ml (189.6 g) of N,N-dimethylformamide, and stir at a rate of 500 revolutions per minute for 2 h. Heat up to 90 °C, add 50 g of imidazole, keep the temperature for reaction for 12 h, cool and separate the product, then wash with deionized water, and dry the product at 100 °C for 24 h to obtain the modified resin; then in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 17.6 g of magnesium nitrate in 100 g of water to form a solution, stir at a rate of 600 revolutions per minute at 50 °C for 8 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace, and calcine it at 400 °C for 8 h under a nitrogen atmosphere to obtain catalyst C2. The mass percentage content of magnesium oxide in catalyst C2 is 20%. The nitrogen content of the catalyst is 2.2%, the pore diameter is 200 nm, and the content ratio of magnesium oxide inside the pores is 71.1%. During the above catalyst preparation process, the chloromethylstyrene resin is spherical with a particle diameter of 0.9 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 48.0 g (1.5 mol) of methanol and 4.4 g of catalyst C2 in a 100 mL autoclave, and react at 110 °C for 6 h. Among them, the molar ratio of methanol to ethylene carbonate is 6:1, and the mass ratio of catalyst C2 to ethylene carbonate is 0.2:1. After the reaction, cool the autoclave to room temperature and vent; take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 74.5%, and the selectivity of dimethyl carbonate is 99.9%. Further, after the reaction is completed, the granular catalyst in the reaction solution is filtered and recovered, washed with deionized water, and then placed in an oven and dried at 100 °C for 24 h for reuse. The conditions are the same as those in the above dimethyl carbonate preparation process. After the reaction, the liquid-phase product is taken for gas chromatography analysis, and then the conversion rate of ethylene carbonate is calculated. The catalyst was recycled 10 times, and the conversion rate of ethylene carbonate was greater than 74%, and the selectivity of dimethyl carbonate remained at 99.9%. Example 3 This example provides a method for preparing dimethyl carbonate: Preparation of the catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide were added, and the mixture was stirred at a rate of 800 revolutions per minute for 2 h. Then the temperature was raised to 80 °C, 40 g of imidazole was added, and the mixture was kept at this temperature for reaction for 12 h. After cooling, the product was separated, washed with deionized water, and then dried at 120 °C for 24 h to obtain a modified resin. Then, in another 500 ml three-necked flask, 20 g of the modified resin was added, and 26.4 g of magnesium nitrate was dissolved in 100 g of water to form a solution. The mixture was stirred at a rate of 300 revolutions per minute at 50 °C for 8 h, then placed in an oven and dried at 100 °C for 24 h, and then transferred to a muffle furnace. Under a nitrogen atmosphere, it was calcined at 500 °C for 4 h to obtain catalyst C3. The content of magnesium oxide in catalyst C3 was 30%. The nitrogen content of the catalyst was 1.7%, the pore diameter was 250 nm, and the proportion of the magnesium oxide content inside the pore channels was 63.3%. In the above catalyst preparation process, the chloromethylstyrene resin was spherical with a particle diameter of 0.7 mm. Preparation of dimethyl carbonate: 22.0 g (0.25 mol) of ethylene carbonate, 32.0 g (1.0 mol) of methanol and 4.4 g of catalyst C3 were placed in a 100 mL autoclave and reacted at 110 °C for 10 h. Among them, the molar ratio of methanol to ethylene carbonate was 4:1, and the mass ratio of catalyst C3 to ethylene carbonate was 0.2:1. After the reaction was completed, the autoclave was cooled to room temperature and the gas was vented. The liquid-phase product was taken for gas chromatography analysis and calculation, and the conversion rate of ethylene carbonate was 61.4%, and the selectivity of dimethyl carbonate was 99.9%. Further, after the reaction is completed, the granular catalyst in the reaction solution is filtered and recovered, washed with deionized water, and then placed in an oven and dried at 100 °C for 24 h for reuse. The conditions are the same as those in the above dimethyl carbonate preparation process. After the reaction, the liquid-phase product is taken for gas chromatography analysis, and then the conversion rate of ethylene carbonate is calculated. The catalyst was recycled 10 times, and the conversion rate of ethylene carbonate was greater than 60%, and the selectivity of dimethyl carbonate was maintained at 99.9%. Example 4 This example provides a method for preparing dimethyl carbonate: Preparation of the catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of imidazole, keep the temperature for reaction for 15 h, then cool and separate the product. After washing with deionized water, dry the product at 120 °C for 24 h to obtain a modified resin; then in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 35.2 g of magnesium nitrate in 100 g of water to form a solution, stir at a rate of 400 revolutions per minute at 50 °C for 2 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace and calcine it at 500 °C for 4 h in a nitrogen atmosphere to obtain catalyst C4. The magnesium oxide content in catalyst C4 is 40%. The nitrogen content of the catalyst is 1.8%, the pore diameter is 300 nm, and the proportion of magnesium oxide content inside the pore channels is 63.3%. During the above catalyst preparation process, the chloromethylstyrene resin is spherical with a particle diameter of 1.0 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 8.8 g of catalyst C4 in a 100 ml autoclave, and react at 90 °C for 8 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C4 to ethylene carbonate is 0.4:1. After the reaction, cool the autoclave to room temperature and vent; take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.9%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, and then dry it in an oven at 100 °C for 24 h for reuse. Under the same conditions as the above dimethyl carbonate preparation process, take the liquid-phase product after the reaction for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst was recycled 10 times, and the conversion rate of ethylene carbonate was greater than 80%, and the selectivity of dimethyl carbonate was maintained at 99.9%. Example 5 This example provides a method for preparing dimethyl carbonate: Preparation of a catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of imidazole, keep the temperature for reaction for 15 h, then cool and separate the product. After washing with deionized water, dry the product at 120 °C for 24 h to obtain a modified resin. Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 26.4 g of magnesium nitrate in 100 g of water to form a solution, stir at a rate of 400 revolutions per minute at 50 °C for 2 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace and calcine it in a nitrogen atmosphere at 500 °C for 4 h to obtain catalyst C5. The content of magnesium oxide in catalyst C5 is 30%. The nitrogen content of the catalyst is 1.8%, the pore diameter is 180 nm, and the content ratio of magnesium oxide inside the pore channels is 64.4%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 1.0 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol, and 6.6 g of catalyst C5 in a 100 ml autoclave, and react at 80 °C for 10 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C5 to ethylene carbonate is 0.3:1. After the reaction, cool the autoclave to room temperature and vent it. Take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.5%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, place it in an oven and dry it at 100 °C for 24 h for reuse. The conditions are the same as those in the above dimethyl carbonate preparation process. After the reaction, take the liquid-phase product for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 6 This example provides a method for preparing dimethyl carbonate: Preparation of a catalyst for the preparation of dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of thiophene, keep the temperature for reaction for 15 h, cool and separate the product, then wash with deionized water, and dry the product at 120 °C for 24 h to obtain a modified resin; Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 26.4 g of magnesium nitrate in water to make 100 g of solution, stir at a rate of 400 revolutions per minute at 50 °C for 2 h, put it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace, and calcine it at 500 °C for 4 h under a nitrogen atmosphere to obtain catalyst C6. The magnesium oxide content in catalyst C6 is 30%. The sulfur content of the catalyst is 2.7%, the pore diameter is 100 nm, and the proportion of magnesium oxide content inside the pore channels is 66.4%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 1 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 8.8 g of catalyst C6 in a 100 ml autoclave, and react at 70 °C for 8 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C6 to ethylene carbonate is 0.4:1. After the reaction, cool the autoclave to room temperature and vent; Take the liquid-phase product for gas chromatography analysis and then calculate. The conversion rate of ethylene carbonate is 80.2%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, put it in an oven and dry it at 100 °C for 24 h for reuse. The conditions are the same as those in the above dimethyl carbonate preparation process. After the reaction, take the liquid-phase product for gas chromatography analysis and then calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 7 This example provides a method for the preparation of dimethyl carbonate: Preparation of Catalyst for Preparing Dimethyl Carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of imidazole, keep the temperature for reaction for 15 h, then cool and separate the product. After washing with deionized water, dry the product at 120 °C for 24 h to obtain the modified resin. Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 8 g of calcium nitrate in water to make 100 g of solution, stir at a rate of 300 revolutions per minute at 50 °C for 2 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace and calcine it at 500 °C for 4 h in a nitrogen atmosphere to obtain catalyst C7. The calcium oxide content in catalyst C7 is 20%. The nitrogen content of the catalyst is 2.2%, the pore diameter is 120 nm, and the proportion of calcium oxide content inside the pore channels is 68.8%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 1.0 mm. Preparation of Dimethyl Carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol, and 8.8 g of catalyst C7 in a 100 ml autoclave, and react at 70 °C for 8 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C7 to ethylene carbonate is 0.4:1. After the reaction, cool the autoclave to room temperature and vent it. Take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.4%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, place it in an oven and dry it at 100 °C for 24 h for reuse. Under the same conditions as the above dimethyl carbonate preparation process, take the liquid-phase product after the reaction for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 8 This example provides a method for preparing dimethyl carbonate: Preparation of a catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of triphenylphosphine, keep the temperature for reaction for 15 h, cool and separate the product. After washing with deionized water, dry the product at 120 °C for 24 h to obtain a modified resin. Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 17.6 g of magnesium nitrate in 80 g of water to form a solution, stir at a rate of 500 revolutions per minute at 50 °C for 2 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace and calcine it under a nitrogen atmosphere at 500 °C for 4 h to obtain catalyst C8. The magnesium oxide content in catalyst C8 is 20%. The phosphorus content of the catalyst is 2.2%, the pore diameter is 150 nm, and the proportion of magnesium oxide content inside the pore channels is 71.6%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 1.0 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 8.8 g of catalyst C8 in a 100 ml autoclave, and react at 90 °C for 8 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C8 to ethylene carbonate is 0.4:1. After the reaction is completed, cool the autoclave to room temperature and vent it. Take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.3%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction is completed, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, place it in an oven and dry it at 100 °C for 24 h for reuse. The conditions are the same as those in the above dimethyl carbonate preparation process. After the reaction, take the liquid-phase product for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 9 This example provides a method for preparing dimethyl carbonate: Preparation of a catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, and stir at a rate of 800 revolutions per minute for 2 h. Heat up to 70 °C, add 30 g of piperidine, keep the temperature for reaction for 15 h, cool and separate the product. After washing with deionized water, dry the product at 120 °C for 24 h to obtain a modified resin. Then, in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 11.4 g of aluminum nitrate in water to make 100 g of solution, stir at a rate of 500 revolutions per minute at 50 °C for 2 h, place it in an oven and dry at 100 °C for 24 h, then transfer it to a muffle furnace and calcine in a nitrogen atmosphere at 600 °C for 4 h to obtain catalyst C9. The alumina content in catalyst C9 is 20%. The nitrogen content of the catalyst is 0.8%, the pore diameter is 100 nm, and the proportion of alumina content inside the pore channels is 67.6%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle diameter of 1.2 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 8.8 g of catalyst C9 in a 100 ml autoclave, and react at 90 °C for 8 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C9 to ethylene carbonate is 0.4:1. After the reaction, cool the autoclave to room temperature and vent it. Take the liquid-phase product for gas chromatography analysis and calculate. The conversion rate of ethylene carbonate is 80.6%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash it with deionized water, place it in an oven and dry it at 100 °C for 24 h for reuse. Under the same conditions as the above dimethyl carbonate preparation process, take the liquid-phase product for gas chromatography analysis after the reaction and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 10 This example provides a method for preparing dimethyl carbonate: Preparation of Catalyst for Preparing Dimethyl Carbonate: In a 500 ml three-necked flask, add 50 g of chloromethylstyrene resin and 300 ml (284.4 g) of N,N-dimethylformamide, stir at a rate of 800 revolutions per minute for 2 h, heat up to 70 °C, add 30 g of 1-methylimidazole, keep the temperature for reaction for 15 h, cool and separate the product, then wash with deionized water, and dry the product at 120 °C for 24 h to obtain the modified resin; then in another 500 ml three-necked flask, add 20 g of the modified resin, dissolve 26.4 g of magnesium nitrate in 100 g of water to prepare a solution, stir at a rate of 500 revolutions per minute at 50 °C for 2 h, place in an oven and dry at 100 °C for 24 h, then transfer to a muffle furnace, and calcine in a nitrogen atmosphere at 500 °C for 4 h to obtain catalyst C10. The content of magnesium oxide in catalyst C10 is 30%. The nitrogen content of the catalyst is 1.6%, the pore diameter is 150 nm, and the content ratio of magnesium oxide inside the pore channels is 66.5%. During the preparation process of the above catalyst, the chloromethylstyrene resin is spherical with a particle size of 1.0 mm. Preparation of Dimethyl Carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol, and 6.6 g of catalyst C10 in a 100 ml autoclave, react at 80 °C for 10 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst C10 to ethylene carbonate is 0.3:1. After the reaction, cool the autoclave to room temperature and vent; take the liquid-phase product for gas chromatography analysis and calculation, and the conversion rate of ethylene carbonate is 80.5%, and the selectivity of dimethyl carbonate is 99.9%. Furthermore, after the reaction, filter and recover the particulate catalyst in the reaction solution, wash with deionized water, place in an oven and dry at 100 °C for 24 h for reuse. Under the same conditions as the above dimethyl carbonate preparation process, take the liquid-phase product after the reaction for gas chromatography analysis and calculate the conversion rate of ethylene carbonate. The catalyst is recycled 10 times, and the conversion rate of ethylene carbonate is greater than 80%, and the selectivity of dimethyl carbonate remains 99.9%. Example 11 This example provides a method for preparing ethyl methyl carbonate: Preparation of Ethyl Methyl Carbonate: 22.5 g (0.25 mol) of dimethyl carbonate, 46.0 g (1 mol) of ethanol and 6.75 g of catalyst C10 were placed in a 100 ml autoclave and reacted at 100 °C for 10 h. Among them, the molar ratio of ethanol to dimethyl carbonate was 4:1, and the mass ratio of catalyst C10 to dimethyl carbonate was 0.3:1. After the reaction, the autoclave was cooled to room temperature and vented. The liquid-phase product was taken for gas chromatography analysis and calculation. The conversion rate of dimethyl carbonate was 91.6%, and the selectivity of ethyl methyl carbonate was 92.4%. Example 12 This example provides a method for preparing ethyl methyl carbonate: Preparation of Ethyl Methyl Carbonate: 22.5 g (0.25 mol) of dimethyl carbonate, 11.5 g (0.25 mol) of ethanol and 4.5 g of catalyst C10 were placed in a 100 ml autoclave and reacted at 100 °C for 10 h. Among them, the molar ratio of ethanol to dimethyl carbonate was 1:1, and the mass ratio of catalyst C10 to dimethyl carbonate was 0.2:1. After the reaction, the autoclave was cooled to room temperature and vented. The liquid-phase product was taken for gas chromatography analysis and calculation. The conversion rate of dimethyl carbonate was 64.5%, and the selectivity of ethyl methyl carbonate was 73.1%. Comparative Example 1 This comparative example provides a method for preparing dimethyl carbonate: Preparation of the catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, 20 g of chloromethylstyrene resin was added. After 8.8 g of magnesium nitrate was dissolved in 100 g of water to form solution, it was stirred at 80 °C for 6 h, then dried in an oven at 100 °C for 14 h, and then transferred to a muffle furnace. Under a nitrogen atmosphere, it was calcined at 500 °C for 5 h to obtain catalyst S1. The mass percentage content of magnesium oxide in catalyst S1 was 10%. The scanning electron microscope image of catalyst S1 is shown in Figure 2, and the transmission electron microscope image of catalyst S1 is shown in Figure 4. After measurement and calculation, there was almost no active metal component in the pores. During the above catalyst preparation process, the chloromethylstyrene resin was spherical with a particle size of 0.5 mm. Preparation of dimethyl carbonate: 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 4.4 g of catalyst S1 were placed in a 100 ml autoclave and reacted at 120 °C for 4 h. Among them, the molar ratio of methanol to ethylene carbonate was 8:1, and the mass ratio of catalyst S1 to ethylene carbonate was 0.2:1. After the reaction, the autoclave was cooled to room temperature and vented. The liquid-phase product was taken for gas chromatography analysis and calculation, and the conversion rate of ethylene carbonate was 59.6%, and the selectivity of dimethyl carbonate was 99.8%. In Fig. 8, (a) shows a scanning electron microscope image of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 100 μm; (b) shows a scanning electron microscope image of the inside of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 20 μm. It can be seen that the outer surface of the carbon support is rough and magnesium oxide adheres thereto, while almost no magnesium oxide is seen on the inner surface of the carbon support. In Fig. 9, (a) shows a scanning electron microscope image of the inside of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 200 nm; (b) shows a scanning electron microscope image of the inside of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 100 nm. It can be seen that the inside of the carbon support maintains its pore structure and no magnesium oxide enters. Fig. 10 shows the energy spectrum surface scan and EDX spectrum of catalyst S1 prepared in Comparative Example 1 of the present invention; (a) shows the selected area surface scan spectrum; (b) shows the carbon element distribution map; (c) shows the EDX energy spectrum. It can be seen that there is basically no magnesium oxide distribution in the internal pores of the carbon support, and magnesium cannot be detected by the EDX result basically. Comparative Example 2 This comparative example provides a method for preparing dimethyl carbonate: Preparation of the catalyst for preparing dimethyl carbonate: 20 g of magnesium nitrate was transferred to a muffle furnace and calcined at 500 °C for 5 h under a nitrogen atmosphere to obtain a powdered catalyst S2. Preparation of dimethyl carbonate: 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol and 4.4 g of catalyst S2 were placed in a 100 ml autoclave and reacted at 120 °C for 4 hours. Among them, the molar ratio of methanol to ethylene carbonate was 8:1, and the mass ratio of catalyst S2 to ethylene carbonate was 0.2:1. After the reaction, the autoclave was cooled to room temperature and vented. The liquid-phase product was taken for gas chromatography analysis and calculation, and the conversion rate of ethylene carbonate was 32.7%, and the selectivity of dimethyl carbonate was 99.9%. Comparative Example 3 The present invention provides a method for preparing dimethyl carbonate as follows: Preparation of the catalyst for preparing dimethyl carbonate: In a 500 ml three-necked flask, add 20 g of styrene resin. After dissolving 8.8 g of magnesium nitrate in 100 g of water to form a solution, stir at 80 °C for 6 h, place it in an oven and dry at 100 °C for 14 h, then transfer it to a muffle furnace and calcine in a nitrogen atmosphere at 500 °C for 5 h to obtain catalyst S3. The mass percentage of magnesium oxide in catalyst S3 is 6.5%. After measurement and calculation, there is almost no active metal component in the pores. During the above catalyst preparation process, the chloromethylstyrene resin is spherical with a particle size of 0.5 mm. Preparation of dimethyl carbonate: Place 22.0 g (0.25 mol) of ethylene carbonate, 64.0 g (2 mol) of methanol, and 4.4 g of catalyst S3 in a 100 ml autoclave, and react at 120 °C for 4 h. Among them, the molar ratio of methanol to ethylene carbonate is 8:1, and the mass ratio of catalyst S3 to ethylene carbonate is 0.2:1. After the reaction, cool the autoclave to room temperature and vent; take the liquid-phase product for gas chromatography analysis and calculation, and obtain the conversion rate of ethylene carbonate as 39.4% and the selectivity of dimethyl carbonate as 99.9%. It should be noted that the above embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the patent application of the present invention as stipulated, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions. Figure 1 is a scanning electron microscope image of catalyst C1 prepared in Example 1 of the present invention; Figure 2 is a scanning electron microscope image of catalyst S1 prepared in Comparative Example 1 of the present invention; Figure 3 is a transmission electron microscope image of catalyst C1 prepared in Example 1 of the present invention; Figure 4 is a transmission electron microscope image of catalyst S1 prepared in Comparative Example 1 of the present invention. Figure 5 (a) is a scanning electron microscope image of catalyst C1 prepared in Example 1 of the present invention at a scale of 100 microns; (b) is a scanning electron microscope image of the interior of the catalyst prepared in Example 1 of the present invention at a scale of 10 microns. Figure 6 (a) is a scanning electron microscope image of the interior of catalyst C1 prepared in Example 1 of the present invention at a scale of 200 nanometers; (b) is a scanning electron microscope image of the interior of catalyst C1 prepared in Example 1 of the present invention at a scale of 100 nanometers. Figure 7 is the energy spectrum surface scan and EDX spectrum of catalyst C1 prepared in Example 1 of the present invention; (a) selected area surface scan spectrum; (b) carbon element distribution map; (c) oxygen element distribution map; (d) magnesium element distribution map; (e) EDX energy spectrum. Figure 8 (a) is a scanning electron microscope image of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 100 microns; (b) is a scanning electron microscope image of the interior of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 20 microns. Figure 9 (a) is a scanning electron microscope image of the interior of catalyst S prepared in Comparative Example 1 of the present invention at a scale of 200 nanometers; (b) is a scanning electron microscope image of the interior of catalyst S1 prepared in Comparative Example 1 of the present invention at a scale of 100 nanometers. Figure 10 is the energy spectrum surface scan and EDX spectrum of catalyst S1 prepared in Comparative Example 1 of the present invention; (a) selected area surface scan spectrum; (b) carbon element distribution map; (c) EDX energy spectrum.

Claims

1. A porous carbon-supported catalyst, characterized in that it comprises a porous carbon support, an active metal component, and at least one heteroatom selected from nitrogen, sulfur, and phosphorus, wherein, The porous carbon support contains 50% to 99% of the total mass of the catalyst, the active metal component content (calculated as active metal oxide) is 0.1% to 50%, and the heteroatom content (calculated as element) is 0.1% to 5%. The active metal is selected from at least one of magnesium, aluminum, and calcium. The active metal component distributed in the pores of the porous carbon support, calculated as active metal oxide, accounts for more than 50% of the total active metal component content in the catalyst.

2. The catalyst as claimed in claim 1, wherein the porous carbon support has a particle size of 0.1 mm to 3 mm; and the porous carbon support has a pore size of 5 to 500 nm.

3. The catalyst as claimed in claim 1 or 2, wherein the content of the active metal component distributed in the pores of the porous carbon support, based on the active metal oxide, is 55% or more relative to the content of all active metal components in the catalyst; the content of the porous carbon support is 55-90% relative to the total mass of the catalyst, the content of the active metal component based on the active metal oxide is 5-45%; and the content of heteroatoms based on elements is 0.3-4.5%.

4. The catalyst as claimed in claim 1 or 2, wherein the content of active metal components distributed on the outer surface of the porous carbon support, as determined by XPS, based on active metal oxides, is less than 50% relative to the total content of active metal components in the catalyst.

5. The catalyst as claimed in claim 1 or 2, wherein the porous carbon support has a particle size of 0.3 mm to 2 mm and a pore size of 50 to 300 nm; the content of active metal components distributed in the channels of the porous carbon support, based on active metal oxides, is 70% or more relative to the content of all active metal components in the catalyst; the content of the porous carbon support is 60% to 85% relative to the total mass of the catalyst, and the content of active metal components, based on active metal oxides, is 10% to 40%; the content of heteroatoms, based on elements, is 0.5% to 4%; and the content of active metal components distributed on the outer surface of the porous carbon support, based on active metal oxides and determined by XPS, is 30% or less relative to the content of all active metal components in the catalyst.

6. A method for preparing a porous carbon-supported catalyst, comprising the following steps: (1) a modification step of contacting a haloalkylated resin with a modifier to modify it and obtain a modified haloalkylated resin; (2) a contact step of contacting the modified haloalkylated resin with a metal precursor of an active metal to obtain a contact product; and (3) a calcination step of optionally drying the contact product and then calcining it in an inactive gas atmosphere, wherein the modifier is at least one compound selected from nitrogen-containing compounds, sulfur-containing compounds and phosphorus-containing compounds, and the active metal is at least one selected from magnesium, aluminum and calcium.

7. The method for preparing the catalyst as described in claim 6, wherein, Step (1) satisfies at least one of the following conditions: the halogenated alkylating resin is a halogenated methylating resin; the modifier is a nitrogen-containing organic compound, a sulfur-containing organic compound, or a phosphorus-containing organic compound; the mass ratio of the halogenated alkylating resin to the modifier is 1:(0.1-1.2); the modification step is carried out in a solvent, which is selected from at least one of toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, terbutanol, tetrahydrofuran, dichloromethane, chloroform, N,N-dimethylformamide, ether, and water, and the mass ratio of the halogenated alkylating resin to the solvent is 1:(1-10); the temperature of the modification step is 30℃~150℃; the modification time of the modification step is 1 h~24 h; the modification step is carried out under mixing and stirring, and the mixing and stirring rate is 50 rpm~1000 rpm. In the modification step, the obtained modified halogenated alkyl resin is washed and dried. The drying conditions are: drying temperature 80℃~180℃ and drying time 1 h~48 h.

8. A method for preparing the catalyst as described in claim 6 or 7, wherein, Step (2) satisfies at least one of the following conditions: the metal precursor of the active metal is at least one of the nitrate, chloride, or sulfate forms of the active metal; the mass ratio of the modified haloalkylated resin to the metal precursor of the active metal is 1:0.1 to 3; the metal precursor of the active metal is contacted in solution with the modified haloalkylated resin obtained in step (1), and the solvent is at least one selected from toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, terbutanol, tetrahydrofuran, dichloromethane, chloroform, N,N-dimethylformamide, ether, and water; step (2) is carried out under mixing and stirring conditions, the mixing and stirring rate is 100 rpm to 800 rpm; the mixing and stirring temperature is 30°C to 100°C; and the mixing and stirring time is 1 h to 10 h.

9. A method for preparing the catalyst as described in claim 6 or 7, wherein, Step (3) satisfies at least one of the following conditions: The contact product obtained in step (2) is dried, and the drying conditions are: temperature 80℃~180℃, time 1 h~48 h; The inactive gas is at least one of nitrogen and rare gas; The calcination temperature is 200℃~1000℃, and the calcination time is 1 h~48 h.

10. A method for preparing the catalyst as described in claim 6, wherein, It satisfies at least one of the following conditions: In step (1), the halogenated alkylating resin is chloromethylated styrene resin; In step (1), the modifier is at least one of methylamine, ethylamine, hexylamine, propylamine, dimethylamine, diethylamine, piperazine optionally substituted with C1-C6 alkyl, pyridine optionally substituted with C1-C6 alkyl, imidazole optionally substituted with C1-C6 alkyl, quinoline optionally substituted with C1-C6 alkyl, pyrrole optionally substituted with C1-C6 alkyl, indole optionally substituted with C1-C6 alkyl, thiozolium optionally substituted with C1-C6 alkyl, isoindole optionally substituted with C1-C6 alkyl, thiazole optionally substituted with C1-C6 alkyl, thiophene optionally substituted with C1-C6 alkyl, and triphenylphosphine; In step (1), the mass ratio of the halogenated alkylating resin to the modifier is 1:(0.15-1); In step (1), the modification step is carried out in a solvent, which is selected from at least one of toluene, methanol, ethanol, n-propanol, n-butanol, isobutanol, tributanol, tetrahydrofuran, dichloromethane, chloroform, N,N-dimethylformamide, ether, and water, and the mass ratio of the haloalkylated resin to the solvent is 1:(2-8); In step (1), the temperature of the modification step is 40℃~120℃; In step (1), the modification time of the modification step is 2 h~18 h; In step (1), the modification step is carried out under mixing and stirring, and the mixing and stirring rate is 100 rpm~800 rpm; In step (2), the mass ratio of the modified haloalkylated resin to the metal precursor of the active metal is 1:0.2~2; Step (2) is carried out under mixing and stirring conditions, wherein the mixing and stirring rate is 200 rpm to 600 rpm; the mixing and stirring temperature is 50℃ to 80℃; and the mixing and stirring time is 2 h to 8 h. In step (3), the contact product obtained in step (2) is dried, wherein the drying conditions are: temperature 90℃ to 150℃; and time 2 h to 36 h. In step (3), the calcination temperature is 250℃ to 900℃; and the calcination time is 2 h to 24 h.

11. A method for preparing a dialkyl carbonate of the following general formula (I), characterized in that, under the action of a catalyst as described in any one of claims 1-5 or a catalyst prepared by any one of claims 6-10, the carbonate of the following general formula (II) and the lower alcohol of the following general formula (III) are reacted to obtain the dialkyl carbonate of the following general formula (I); R1-OCOO-R1 (I) In formula (I), each R1 is independently selected from C1-C6 alkyl; R2-OCOO-R2 (II) In formula (II), each R2 is independently selected from C1-C6 alkyl, and at least one R2 is different from at least one R1; or two R2s are bonded to each other to form a C2-C6 alkylene; R1-OH (III) In formula (III), R1 is selected from C1-C6 alkyl.

12. The preparation method as described in claim 11, wherein at least one of the following conditions is met: the reaction temperature is 40°C to 130°C; and the reaction time is 1 h to 15 h.

13. The preparation method as claimed in claim 11 or 12, wherein at least one of the following conditions is satisfied: the molar ratio of the lower alcohol represented by general formula (III) to the carbonate represented by general formula (II) is (0.5-15):1; the mass ratio of the catalyst to the carbonate represented by general formula (II) is (0.001-0.5):1; in formula (I), the two R1s are identical to each other; and in formula (II), the two R2s are bonded to each other to form a C2-C6 alkylene group.

14. The preparation method as claimed in claim 11 or 12, wherein the following condition is satisfied: the carbonate represented by general formula (II) is at least one selected from ethylene carbonate and propylene carbonate, and the lower alcohol is at least one selected from methanol, ethanol, propanol, isopropanol, and butanol; the dialkyl carbonate represented by general formula (I) is at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, and dibutyl carbonate.

15. The preparation method as claimed in claim 11, wherein at least one of the following conditions is satisfied: the reaction temperature is 50°C to 120°C; the reaction time is 2 h to 12 h; the molar ratio of the lower alcohol represented by general formula (III) to the carbonate represented by general formula (II) is (1-12):1; and the mass ratio of the catalyst to the carbonate represented by general formula (II) is (0.05-0.5):1.

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