Heterogeneous catalyst as well as preparation method and application thereof

Abstract

The invention discloses a heterogeneous catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) synthesizing a niobium oxide precursor from a niobium precursor, a surfactant and a solvent by adopting a hydrothermal method; (2) performing high-temperature treatment on the niobium oxide precursor to obtain a niobium oxide carrier; and (3) loading an active metal component on the niobium oxide carrier by adopting an adsorption-impregnation method, and carrying out adsorption, drying and segmented calcination to obtain the supported metal / niobium oxide catalyst, the mass ratio of the niobium precursor to the surfactant to the solvent is (1-50): (0.01-20): (5-1000). According to the method, olefin, alcohol and normal-pressure CO molecules directly react on the catalyst to generate ester under the condition that no additives such as acid, alkali and organic ligands are needed, the route is a reaction process with the atom economy being 100%, efficient utilization of CO is achieved, and a green and efficient route is provided for synthesis of ester.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst technology, and particularly relates to a heterogeneous catalyst, a preparation method and application thereof, and the catalyst for synthesizing ester compounds through direct combination reaction (alkoxycarbonylation reaction) of olefins and CO, alcohols. BACKGROUND

[0002] Ester compounds have wide application value in the fields of medicine, pharmaceuticals, perfumes, material science, etc. The alkoxycarbonylation reaction of olefins is an important reaction for synthesizing ester compounds. The alkoxycarbonylation reaction is a process for preparing ester products by using transition metals (such as palladium complexes) as catalysts, using olefins as raw materials, carbon monoxide (CO) as a carbonyl source, and alcohols as hydrogen sources and nucleophilic reagents, which has the advantages of high product value and good atom economy. Through the implementation of this route, millions of tons of esters and acids can be produced every year. One of the most important industrial examples is the synthesis of methyl propionate. Methyl propionate is a key intermediate for synthesizing polymer methacrylate, and has a large demand. At present, methyl propionate is mainly produced by using a palladium-ligand complex system as a catalyst, under the conditions of high-pressure CO (usually > 40 bar) and organic acid as a promoter, to catalyze the carbonylation reaction of ethylene and methanol to obtain methyl propionate.

[0003] The route of the alkoxycarbonylation reaction of olefins is a reaction process with an atomic economy of (nearly) 100%, and is a green and low-carbon reaction route. Since the alkoxycarbonylation reaction was discovered, research in the past 70 years has mainly focused on homogeneous catalytic systems, especially the fine synthesis of ligands and the control of regioselectivity of carbonyl insertion (i.e. Markovnikov or Anti-Markovnikov carbonyl insertion). However, high-pressure CO (higher than 40 bar) is often necessary in the homogeneous system, in order to prevent the decarbonylation of acyl metal intermediates, which leads to a large amount of CO being wasted, and the utilization rate is extremely low (<1%). In addition, an acid promoter needs to be added to the system to stabilize the palladium hydride species formed, so as to maintain the catalytic activity of the palladium complex, which causes problems such as easy corrosion of the reaction container and difficult separation of the product.

[0004] Compared with homogeneous catalysts, heterogeneous catalysts have many advantages, including the avoidance of the use of acid promoters, easy separation and recovery, thereby reducing costs and waste. Recently, heterogeneous catalysts have been used for carbonylation reactions, such as hydroformylation (Science 2022, 377, 1223-1227; Nature 2022, 609, 287-292) and aminocarbonylation (Angewandte Chemie International Edition 2018, 57, 12308-12312). For alkoxycarbonylation, ceria-supported Ru catalysts can work without acid promoters, but still use a higher CO pressure, resulting in lower CO utilization (Journal of the American Chemical Society 2018, 140, 4172-4181).

[0005] Therefore, it is crucial to develop a heterogeneous catalyst capable of achieving alkoxycarbonylation under normal (low) pressure for efficient and green synthesis of esters.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a heterogeneous catalyst and a preparation method and application thereof, in particular, a heterogeneous catalyst for the normal pressure carbonylation of olefins with alcohols to generate esters and a preparation method thereof. The present application develops a heterogeneous catalyst Ru / NbO x for the alkoxycarbonylation (esterification) of olefins. Under the conditions of normal or near-normal pressure CO without any acid or base additives, various types of olefins (multiple aromatic olefins, aliphatic olefins) are directly reacted with CO and alcohols to generate esters, with a yield of up to 71%. The development of the catalyst of the present application realizes the normal pressure, green, sustainable and efficient synthesis of ester compounds.

[0008] To solve the above technical problems, the basic idea of the technical solution of the present application is:

[0009] The first object of the present application is to provide a preparation method of a heterogeneous catalyst, comprising:

[0010] (1) synthesizing a niobium oxide precursor by hydrothermal method using a niobium precursor, a surfactant and a solvent;

[0011] (2) obtaining a niobium oxide carrier by high-temperature treatment of the niobium oxide precursor;

[0012] (3) loading active metal components on the niobium oxide carrier by adsorption-impregnation method, and obtaining a supported metal / niobium oxide catalyst through adsorption, drying and step-by-step calcination.

[0013] This invention has developed a heterogeneous catalyst for the alkoxycarbonylation (esterification) of olefins. Under atmospheric or near-atmospheric CO conditions, without any acid or base additives, various olefins (including various aromatic and aliphatic olefins) react directly with CO and alcohols to produce esters, with yields up to 71%. The development of this catalyst enables the efficient, environmentally friendly, sustainable synthesis of ester compounds at atmospheric pressure.

[0014] In a further embodiment, in step (1), the mass ratio of niobium precursor: surfactant: solvent is (1-50): (0.01-20): (5-1000); preferably, the mass ratio is (1-20): (0.01-5): (10-100).

[0015] In a further embodiment, the niobium precursor is selected from one or more of Nb2O5, NbCl5, Nb(OC2H5)5, Nb(OC2O4)5, Nb(NO3)5, NaNbO3, LiNbO3, and BiNbO4;

[0016] The surfactant is selected from one or more of sodium dodecyl sulfate SDS, cetyltrimethylammonium bromide CTAB, polyethylene glycol PEG, polyoxyethylene stearate SLES, polycarboxylate ether PAA and PMAA, 3-aminopropyl triethoxysilane APTES, polyethyleneimine PEI, cetyl phosphate OP-10, and sodium cetyl sulfate SLES; preferably, the polycarboxylate ether is selected from PAA and PMAA;

[0017] The solvent is selected from one or more of methanol, ethanol, propanol, butanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ionic liquid or water.

[0018] In a further solution, the ionic liquid is selected from 1-Ethyl-3-methylimidazolium, tetrafluoroborate([C2mim]BF4), 1-Butyl-3-methylimidazolium tetrafluoroborate([C4mim]BF4), 1-Hexyl-3-methylimidazolium tetrafluoroborate([C6mim]BF4),1-Butyl-2,3-dimethylimidazolium tetrafluoroborate([C4m2im]BF4),1-Butyl-3-methylimidazolium bromide([C4mim]Br),1-butyl-3-methylimidazolium chloride([C4mim]Cl),1-Butyl-3-methylimidazolium hexafluorophosphate([C4mim]PF6),1-butyl-3-methylimidazolium One or more of bis[(trifluoromethyl)sulfonyl]imide([C4mim]NTf2), and 1-Butyl-3-methylimidazolium tetrachloroaluminate([C4mim]AlCl4);

[0019] Preferably, the ionic liquid is selected from one or more of 1-Ethyl-3-methylimidazolium,tetrafluoroborate ([C2mim]BF4), 1-Butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4).

[0020] In a further embodiment, in step (1), the hydrothermal synthesis process comprises: mixing and stirring a niobium precursor, a surfactant, and a solvent, then loading the mixture into a hydrothermal reactor for hydrothermal reaction, and washing and drying the mixture after natural cooling to obtain a niobium oxide precursor;

[0021] The niobium precursor, surfactant and solvent are mixed and stirred for dissociation at a temperature of 20 to 100° C. for 5 to 180 minutes; the hydrothermal reaction is carried out at a temperature of 100 to 250° C. for 5 to 48 hours.

[0022] In a further embodiment, in step (2), the niobium oxide precursor is calcined at a temperature of 200 to 700° C. for 1 to 12 hours in an atmosphere of air, argon, pure hydrogen, or diluted hydrogen with a volume ratio of 0.1% to 10%.

[0023] In a further embodiment, in step (3), the mass ratio of the active metal component to the niobium oxide support is 0.001 to 10:1, preferably, the mass ratio is 0.1 to 5:1;

[0024] Preferably, the metal component supported on the niobium oxide carrier is selected from one or more of Pt, Ru, Pd, Rh, Ir, Au, Co, Fe, Ni, and Cu.

[0025] Preferably, the metal component supported on the niobium oxide carrier is Ru.

[0026] The Ru / NbOx catalyst of the present application has a high concentration of oxygen vacancies on the NbOx carrier, which makes the dissociation of CH3OH easy to proceed, generating *OCH3 and *H species, and can migrate to the Ru surface through a process with almost no (low) energy barrier; Ru nanoparticles have excellent multi-component co-adsorption ability, and simultaneously adsorb and activate CO, olefins, and the *H and *OCH3 species generated by adsorption and dissociation, which undergo CO and OCH3 methylation, olefin insertion, and hydrogenation removal processes on Ru to generate esters.

[0027] By preparing Nb2O5 supports with low (no) oxygen vacancies and corresponding Ru / Nb2O5 catalysts, the reaction data (Example 4 in Table 1), in situ infrared ( Figures 5-6 ) and DFT calculations ( Figure 7 ) shows that the synergy of carrier oxygen vacancies and Ru is the key to the direct formation of esters under normal or near-normal pressure conditions.

[0028] In the present invention, the synergy between Ru and the carrier oxygen vacancies produces a better effect. For metals that strongly adsorb CO, such as Pt or Pd, excessive CO adsorption coverage may prevent the adsorption of other substrate molecules, thereby poisoning the metal. For metals that weakly adsorb CO, such as Au or other non-precious metals such as Fe, Ni, and Cu, CO coverage on the metal surface may be too low, preventing the carbonylation reaction.

[0029] In a further embodiment, in step (3), the process of preparing the product by adsorption-impregnation method includes:

[0030] A soluble metal compound solution containing a mass concentration of 0.01% to 50% is uniformly mixed with a niobium oxide carrier, stirred at 20 to 100° C. for 1 to 48 hours, and then dried at 20 to 200° C. for 1 to 48 hours; calcination is carried out in two stages, the first stage calcination temperature is 100 to 800° C., and the calcination time is 1 to 24 hours; the second stage calcination temperature is 100 to 800° C., and the calcination time is 1 to 24 hours; the calcination atmosphere is air, argon, pure hydrogen or diluted hydrogen with a volume ratio of 0.1% to 10%.

[0031] In the present invention, calcination atmosphere and temperature are key conditions for obtaining a high-concentration oxygen vacancy catalyst.

[0032] A second object of the present invention is to provide a heterogeneous catalyst for catalyzing an alkoxycarbonylation reaction. The heterogeneous catalyst comprises a niobium oxide support and an active metal component supported on the niobium oxide support.

[0033] The mass ratio of the active metal component to the niobium oxide carrier is 0.001 to 10:1, preferably, the mass ratio is 0.1 to 5:1;

[0034] Preferably, the metal component supported on the niobium oxide carrier is selected from one or more of Pt, Ru, Pd, Rh, Ir, Au, Co, Fe, Ni, and Cu.

[0035] Preferably, the heterogeneous catalyst is prepared using the preparation method described above.

[0036] The third object of the present invention is to provide a use of the heterogeneous catalyst prepared by the preparation method described above in an alkoxycarbonylation reaction;

[0037] Preferably, the heterogeneous catalyst is used in the direct reaction of olefins with CO and alcohols to produce esters.

[0038] A fourth object of the present invention is to provide a method for preparing esters from olefins, comprising: mixing olefins, a heterogeneous catalyst, and an alcohol, introducing CO, and controlling the temperature and time to carry out an esterification reaction;

[0039] The mass ratio of the heterogeneous catalyst to the olefin is 0.001 to 100, and the pressure of CO is normal pressure or 0.1 to 6 MPa;

[0040] Preferably, the reaction temperature is controlled to be 100-300°C and the reaction time is 0.5-60h;

[0041] Preferably, the olefin is selected from aromatic olefins or aliphatic olefins; more preferably, the aromatic olefin is selected from one or more of styrene and its derivatives containing substituents, styrene propene and its derivatives containing substituents, styrene butene and its derivatives containing substituents; the aliphatic olefin is selected from one or more of ethylene, propylene, butene and butadiene;

[0042] The alcohol is selected from one or more of methanol, ethanol, propanol, butanol and isopropanol.

[0043] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0044] 1. Instead of the traditional synthesis route of homogeneous metal-complex catalytic system under acidic and high pressure, the present invention develops a heterogeneous catalyst that does not require any acid or base additives and ligands, achieving efficient synthesis of ester compounds.

[0045] 2. The metal / niobium oxide catalyst developed by the present invention has multiple active sites (metal sites for CO adsorption, oxygen vacancies for alcohol dissociation, and sites for olefin adsorption), which can alkoxycarbonylate olefins under normal pressure CO conditions, achieving the synthesis of ester compounds with an atom economy close to 100% in the reaction process.

[0046] 3. The method of the present invention has mild reaction conditions throughout the entire reaction route, is green, and the catalyst and product are easily separated.

[0047] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an undue limitation of the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventive effort. In the accompanying drawings:

[0049] Figure 1 2%Ru / NbO in Example 1 of the present invention x TEM image of the catalyst;

[0050] Figure 2 2%Ru / NbO in Example 1 of the present invention x , NbO x , oxygen vacancy concentration and EPR patterns of Nb2O5 and Nb(OH)5 catalysts;

[0051] Figure 3 2%Ru / NbO in Examples 1 and 2 of the present invention xand 0.1%Ru / NbO x CO-pulsechemisorption diagram of the catalyst;

[0052] Figure 4 This is a GC chart of Application Example 4 of the present invention, in which methyl propionate is directly synthesized using ethylene as a raw material.

[0053] Figure 5 This is an in-situ infrared image of the adsorption of substrate molecules styrene, CO and methanol on Nb2O5 in Example 1 of the present invention.

[0054] Figure 6 It is NbO in Example 1 of the present invention. x In situ infrared images of the adsorption of substrate molecules styrene, CO and methanol on the substrate.

[0055] Figure 7 These are the adsorption and dissociation energy barrier diagrams of methanol molecules on Nb2O5 and NbOx in Example 1 obtained by DFT simulation.

[0056] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0058] Example 1

[0059] First, niobium oxalate, hexadecyltrimethylammonium bromide and water were mixed and stirred at a mass ratio of 5:1:30 at 30°C, maintained in a hydrothermal autoclave at 180°C for 10 hours, naturally cooled and dried at 60°C for 16 hours; calcined at a rate of 10°C / min to 350°C in air and maintained for 4 hours; accurately weighed niobium oxide material, added with a certain amount of RuCl3 solution under stirring, then dried at 120°C for 2 hours; calcined at 350°C in air for 2 hours at a heating rate of 10°C / min; finally calcined at 350°C in air at a rate of 10°C / min for 4 hours to obtain Nb2O5 or NbO x The Ru weight fractions of the loaded Ru catalysts are 0.1 wt% and 2 wt%, respectively.

[0060] Example 2

[0061] The calcination atmosphere in the first stage was changed to argon, and the other conditions were the same as in Example 1.

[0062] Example 3

[0063] The calcination atmosphere in the second stage was changed to pure hydrogen, and the other conditions were the same as those in Example 1.

[0064] Example 4

[0065] The calcination atmosphere in the third stage was changed to 10% diluted hydrogen, and other conditions were the same as in Example 1.

[0066] Example 5

[0067] The calcination atmosphere in the first and second stages was changed to argon, and other conditions were the same as in Example 1.

[0068] Example 6

[0069] The calcination atmosphere in the first and second stages was changed to pure hydrogen, and the other conditions were the same as in Example 1.

[0070] Example 7

[0071] The calcination atmosphere in the first and second stages was changed to 10% diluted hydrogen, and other conditions were the same as in Example 1.

[0072] Example 8

[0073] The calcination atmosphere in the first and third stages was changed to argon, and the other conditions were the same as in Example 1.

[0074] Example 9

[0075] The calcination atmosphere in the first and third stages was changed to pure hydrogen, and other conditions were the same as in Example 1.

[0076] Example 10

[0077] The calcination atmosphere in the first and third stages was changed to 10% diluted hydrogen, and other conditions were the same as in Example 1.

[0078] Example 11

[0079] The calcination temperature in the first stage was changed to 550°C, and the other conditions were the same as in Example 10.

[0080] Example 12

[0081] The second stage calcination temperature was changed to 550°C, and other conditions were the same as in Example 11.

[0082] Example 13

[0083] The calcination temperature in the third stage was changed to 550°C, and the other conditions were the same as in Example 10.

[0084] Example 14

[0085] The second stage was 200°C and the third stage was 350°C, and other conditions were the same as in Example 11.

[0086] Example 15

[0087] The second stage was 550°C and the third stage was 200°C, and other conditions were the same as in Example 11.

[0088] Application Example 1

[0089] The reaction was carried out in a stainless steel reactor. The reactor was charged with one of the catalysts described in the examples or the catalysts listed in Table 1, 0.2 mmol of substrate, 20 μl of n-dodecane, and 2 mL of methanol solvent. The reactor was purged with CO and filled to the specified pressure at room temperature. The reactor was then placed in a furnace heated to 160°C and stirred at 600 rpm. After 10 hours of reaction, the reactor was cooled in cold water. The resulting mixture was transferred to a centrifuge tube and separated by centrifugation.

[0090] Quantitative analysis of the liquid products was performed using a gas chromatograph (Agilent 6820) equipped with a flame ionization detector (FID) and an HP-5 capillary column (0.25 mm in diameter and 30 m in length). The identification of the products and substrates was determined by gas chromatography-mass spectrometry (GC-MS) analysis and comparative analysis using standard reagents in the GC. The carbon balance was calculated based on the amount of benzene rings before and after the reaction.

[0091]

[0092] Table 1. Reaction performance of olefins with CO and methanol over different catalysts

[0093]

[0094] Reaction conditions: 20 mg of catalysts (catalysts 1-4, 5 wt.% metal loading), 20 mg of catalysts (catalysts 5-10, 2 wt.% Ru), 160°C, 10 h.

[0095] As can be seen from the results in Table 1, the Ru / NbO x Catalysts (Nos. 9-10) exhibited superior esterification performance compared to other catalysts, with ester selectivities reaching up to 90%. Furthermore, under near-ambient CO pressure conditions, conversion rates were significantly improved while maintaining carbonyl insertion selectivity. Catalyst (No. 8) in Example 4 also exhibited high carbonyl insertion selectivity, but conversion rates were lower.

[0096] Application Example 2

[0097] The CO pressure in Application Example 1 was adjusted to 1 bar, the reaction temperature was 170° C., and the reaction time was changed. Other conditions were the same as in Application Example 1.

[0098]

[0099] Table 2. Ru / NbOx Catalytic performance of styrene intercalation carbonylation

[0100]

[0101]

[0102] Reaction conditions: 30 mg catalyst, 170 °C.

[0103] The results in Table 2 show that as the reaction time increases, styrene is almost completely reacted at 16 h, at which time the esterification selectivity reaches 72%, and does not change with further extension of time.

[0104] Application Example 3

[0105] The substrate in Application Example 2 was adjusted to styrene containing various substituents, the reaction time was adjusted to more than 20 h, and the other conditions were the same as those in Application Example 2.

[0106]

[0107]

[0108] Application Example 4

[0109] The aromatic olefin substrate in Application Example 3 was converted into aliphatic ethylene, and the reaction time was shortened to 10 h, to obtain methyl propionate (MP) with a selectivity greater than 99%.

[0110] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present invention can make slight changes or modifications to equivalent embodiments using the above-mentioned technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A method for preparing a heterogeneous catalyst, characterized in that: include: (1) synthesizing a niobium oxide precursor by a hydrothermal method using a niobium precursor, a surfactant and a solvent; (2) subjecting a niobium oxide precursor to high-temperature treatment to obtain a niobium oxide support; (3) Active metal components are loaded on the niobium oxide carrier by the adsorption-impregnation method, and a loaded metal / niobium oxide catalyst is obtained after adsorption, drying and staged calcination.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of niobium precursor: surfactant: solvent is (1-50): (0.01-20): (5-1000); Preferably, the mass ratio is (1-20):(0.01-5):(10-100).

3. The preparation method according to claim 1, characterized in that In step (1), The niobium precursor is selected from one or more of Nb2O5, NbCl5, Nb(OC2H5)5, Nb(OC2O4)5, Nb(NO3)5, NaNbO3, LiNbO3, and BiNbO4; The surfactant is selected from one or more of sodium dodecyl sulfate SDS, cetyltrimethylammonium bromide CTAB, polyethylene glycol PEG, polyoxyethylene stearate SLES, polycarboxylate ether PAA and PMAA, 3-aminopropyl triethoxysilane APTES, polyethyleneimine PEI, cetyl phosphate OP-10, and sodium cetyl sulfate SLES; preferably, the polycarboxylate ether is selected from PAA and PMAA; The solvent is selected from one or more of methanol, ethanol, propanol, butanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ionic liquid or water.

4. The preparation method according to claim 1, characterized in that In step (1), the hydrothermal synthesis process includes: mixing and stirring a niobium precursor, a surfactant, and a solvent, then loading the mixture into a hydrothermal reactor for hydrothermal reaction, naturally cooling the mixture, washing the mixture, and drying the mixture to obtain a niobium oxide precursor; The niobium precursor, surfactant and solvent are mixed and stirred for dissociation at a temperature of 20 to 100° C. for 5 to 180 minutes; the hydrothermal reaction is carried out at a temperature of 100 to 250° C. for 5 to 48 hours.

5. The preparation method according to claim 1 or 3, characterized in that In step (2), the niobium oxide precursor is calcined at a temperature of 200 to 700° C. for 1 to 12 hours in an atmosphere of air, argon, pure hydrogen, or diluted hydrogen with a volume ratio of 0.1% to 10%.

6. The preparation method according to any one of claims 1 to 5, characterized in that In step (3), the mass ratio of the active metal component to the niobium oxide carrier is 0.001 to 10:1, preferably, the mass ratio is 0.1 to 5:1; Preferably, the metal component supported on the niobium oxide carrier is selected from one or more of Pt, Ru, Pd, Rh, Ir, Au, Co, Fe, Ni, and Cu.

7. The preparation method according to any one of claims 1 to 6, characterized in that In step (3), the process of preparing by adsorption-impregnation method includes: A soluble metal compound solution containing a mass concentration of 0.01% to 50% is uniformly mixed with a niobium oxide carrier, stirred at 20 to 100° C. for 1 to 48 hours, and then dried at 20 to 200° C. for 1 to 48 hours; calcination is carried out in two stages, the first stage calcination temperature is 100 to 800° C., and the calcination time is 1 to 24 hours; the second stage calcination temperature is 100 to 800° C., and the calcination time is 1 to 24 hours; the calcination atmosphere is air, argon, pure hydrogen or diluted hydrogen with a volume ratio of 0.1% to 10%.

8. A heterogeneous catalyst, characterized in that The heterogeneous catalyst comprises a niobium oxide carrier and an active metal component supported on the niobium oxide carrier; the mass ratio of the active metal component to the niobium oxide carrier is 0.001 to 10:1; Preferably, the mass ratio of the active metal component to the niobium oxide carrier is 0.1 to 5:1; Preferably, the metal component supported on the niobium oxide carrier is selected from one or more of Pt, Ru, Pd, Rh, Ir, Au, Co, Fe, Ni, and Cu; Preferably, the heterogeneous catalyst is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a heterogeneous catalyst prepared by the preparation method according to any one of claims 1 to 7 in an alkoxycarbonylation reaction; Preferably, the heterogeneous catalyst is used in the direct reaction of olefins with CO and alcohols to produce esters.

10. A method for preparing esters from olefins, characterized in that include: Mixing olefin, the heterogeneous catalyst prepared by the preparation method according to any one of claims 1 to 7 or the heterogeneous catalyst according to claim 8, and alcohol, introducing CO, and controlling the temperature and time to carry out esterification reaction; The mass ratio of the heterogeneous catalyst to the olefin is 0.001 to 100, and the pressure of CO is normal pressure or 0.1 to 6 MPa; Preferably, the reaction temperature is controlled to be 100-300°C and the reaction time is 0.5-60h; Preferably, the olefin is selected from aromatic olefins or aliphatic olefins; more preferably, the aromatic olefin is selected from one or more of styrene and its derivatives containing substituents, styrene propene and its derivatives containing substituents, styrene butene and its derivatives containing substituents; the aliphatic olefin is selected from one or more of ethylene, propylene, butene and butadiene; The alcohol is selected from one or more of methanol, ethanol, propanol, butanol and isopropanol.

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