A mesoporous composite metal oxide catalyst for ethanol-to-olefins and its preparation method

Abstract

This invention belongs to the field of catalyst materials technology, disclosing a mesoporous composite metal oxide catalyst for ethanol-to-olefins conversion, its preparation method, and its application. The catalyst is a Mg-Al-X composite metal oxide with a mesoporous structure and spinel crystal phase, where X is at least one of Sc, Sn, and Ce. It is prepared through template-free hydrothermal synthesis and in-situ isomorphous substitution, exhibiting a uniform distribution of active sites and synergistic acid-base dual-function. This invention does not use expensive template agents, has a simple preparation process, low cost, and low waste emissions, showing good industrialization prospects. The obtained catalyst possesses both high activity and high selectivity, with an ethanol conversion rate of up to 82.91% and an olefin selectivity of up to 99.21% under optimized conditions, and excellent thermal stability at 375℃ for 2.37 h. ‑1 No significant deactivation was observed after 150 hours of continuous reaction; the catalyst is suitable for reaction at 275–400℃ for 0.95–4.73 hours. ‑1 With a wide operating range and operating at normal pressure, it meets the green chemical needs of biomass ethanol to produce low-carbon olefins, and has significant economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, specifically relating to a mesoporous composite metal oxide catalyst for ethanol-to-olefins and its preparation method, particularly to a template-free hydrothermal synthesis of a magnesium-aluminum based composite oxide catalyst controlled by isomorphous substitution, and its application in the catalytic conversion of biomass ethanol to produce low-carbon olefins. Background Technology

[0002] Low-carbon olefins are key raw materials and intermediates in modern chemical industry for the production of synthetic fibers, plastics, electronic devices, and fine chemicals such as high-carbon olefins. Currently, the mainstream production route for low-carbon olefins in industry is still the petroleum route, namely the naphtha cracking process. This technical route is highly dependent on non-renewable petroleum resources and suffers from problems such as high energy consumption, low carbon resource utilization, and high production costs, which contradicts the industrial orientation of green, low-carbon, and sustainable development.

[0003] Therefore, developing new technological routes for producing important organic chemical products using renewable resources instead of petroleum feedstocks has become an important research direction in the chemical industry.

[0004] Ethanol, as a core product of biomass resource conversion and utilization, boasts significant advantages such as wide availability, abundant reserves, and a carbon cycle-friendly lifecycle. Its efficient catalytic conversion into high-value-added, low-carbon olefins offers both economic and environmental benefits. The key technology for ethanol-to-olefins (ETO) lies in developing highly active, selective, stable, and cost-effective catalysts. The properties of the catalyst's active sites, pore structure, and surface acidity / basicity directly determine the adsorption and activation mode and reaction pathway of ethanol, thus affecting product distribution and olefin yield. Rational design of catalyst composition and structure, and targeted regulation of the ethanol conversion pathway to suppress side reactions are crucial for improving process economics and promoting industrial application.

[0005] Currently, supported molecular sieve catalysts are the main type used in research and patent reports related to ethanol-to-olefins conversion. For example, Chinese patent CN106563497B discloses a SAPO-5 / MCM-41 composite molecular sieve catalyst, prepared using TEA and CTMAB dual template agents. It exhibits high ethanol conversion and olefin selectivity in the ethanol-to-olefins reaction, but the template agent is expensive, hindering large-scale industrial application. CN120733777B discloses a composite catalyst using MFI or SBA-16 molecular sieve as a support and introducing a metal promoter in one step, achieving high efficiency at 380℃ and an ethanol space velocity of 0.3 h⁻¹. -1 Under these conditions, the ethanol conversion rate was 87.2%, but the olefin selectivity was only 56.7%, and the product distribution was unsatisfactory. CN109833904B discloses a catalyst composed of tin-doped β-molecular sieve and magnesium oxide, prepared by a deposition-precipitation method at 425℃ and a space velocity of 1.6 h⁻¹.-1 Under these conditions, the ethanol conversion rate is 77% and the olefin selectivity is 84%, but the preparation process is complex and its large-scale application is limited.

[0006] Utilizing the synergistic effect of acid-base sites on the surface of metal oxides to regulate the ETO reaction performance is another feasible approach. CN111302885B discloses a catalyst composed of acid-base oxides such as MgO, ZnO, ZrO2, and Ta2O5, which reacts at 300℃ and a space velocity of 2h. -1 Under certain conditions, the olefin selectivity reached 98.8%, but the ethanol conversion rate was only 35%, resulting in low overall catalytic efficiency. In summary, existing ethanol-to-olefin catalysts generally suffer from the following problems: molecular sieve systems are costly and complex to prepare; metal oxide systems struggle to balance activity and selectivity, and suffer from insufficient stability. Therefore, developing an ethanol-to-olefin catalyst with a simple preparation process, low raw material cost, and simultaneously high activity, high selectivity, and high stability has significant theoretical value and promising industrial application prospects. Summary of the Invention

[0007] To address the problems existing in the catalysts used in the ethanol-to-olefins reaction, this invention aims to develop a mesoporous composite catalyst that is simple to prepare, inexpensive, and exhibits excellent activity in the ethanol-to-olefins reaction. A catalyst precursor is prepared via a template-free hydrothermal synthesis method. A spinel catalyst with a mesoporous structure is obtained under controlled calcination temperatures. Further, the surface properties of the catalyst are modulated through isomorphic substitution to obtain a mesoporous composite metal oxide catalyst. This catalyst possesses advantages such as uniform distribution of active sites and high thermal stability. The synergistic effect between acid and base sites can effectively regulate the catalyst's performance in the ethanol-to-olefins reaction, enabling it to simultaneously achieve high reactivity, high selectivity, and high stability under high-temperature conditions.

[0008] The technical solution adopted in this invention is: a mesoporous composite metal oxide catalyst for ethanol-to-olefins production, wherein the catalyst is a Mg-Al-X composite metal oxide with a mesoporous structure and a spinel crystal phase; wherein X is at least one metal element selected from Sc, Sn, and Ce; the catalyst is prepared by template-free hydrothermal synthesis and in-situ isomorphic substitution, and the active sites are uniformly distributed and have synergistic effects of acid-base bifunctional sites.

[0009] Furthermore, the amount of tin nitrate, scandium nitrate, or cerium nitrate introduced into the catalyst is 25-75 mol.

[0010] Furthermore, the molar ratio of aluminum nitrate to tin nitrate, scandium nitrate, or cerium nitrate is 1:(0.3~3).

[0011] Furthermore, the XRD pattern of the catalyst corresponds to the characteristic peaks of the spinel structure, and the N2 adsorption-desorption curve exhibits the adsorption hysteresis loop of a type IV mesoporous material.

[0012] Furthermore, the catalyst is subjected to conditions at 275–400 °C, atmospheric pressure, and a mass hourly space velocity (HHSV) of 0.95–4.73 h⁻¹. -1 Under the conditions used in the ethanol-to-olefins reaction, the ethanol conversion rate is ≥73.89% and the olefin selectivity is ≥95.97%.

[0013] A method for preparing a mesoporous composite metal oxide catalyst for ethanol-to-olefins production includes the following steps: (1) Prepare an aqueous solution containing magnesium salt, aluminum salt and metal salt X, and mix them to obtain a precursor solution; (2) Crystallize the catalyst precursor by template-free hydrothermal synthesis method; (3) The precursor was calcined at high temperature in air atmosphere to obtain a mesoporous composite metal oxide catalyst.

[0014] Further, in step (1), the magnesium salt is magnesium nitrate, the aluminum salt is aluminum nitrate, and the metal salt X is scandium nitrate, tin chloride, or cerium nitrate; the molar ratio of magnesium nitrate to aluminum nitrate is 3:1.

[0015] Further, in step (2), the hydrothermal crystallization conditions are 120~180℃ for 8~16h; the crystallized product is washed until neutral and dried at 60~100℃ for 12~24h to obtain the precursor.

[0016] Furthermore, in step (3), the calcination temperature is 400~1000℃, the calcination time is 3~5h, and the heating rate is 2~10℃ / min.

[0017] A method for the direct preparation of olefins from ethanol includes passing ethanol into a reactor containing the catalyst according to any one of claims 1 to 5, and maintaining the reactor at 275 to 400°C, atmospheric pressure, and a mass hourly space velocity (HHSV) of 0.95 to 4.73 h⁻¹. -1 The reaction yields low-carbon olefins.

[0018] The main advantages of this invention are as follows: This invention uses a template-free hydrothermal synthesis method to prepare catalyst precursors without using organic template agents, thus eliminating the cost of expensive template agents and the high-temperature treatment process for template removal. The preparation process is simple, the raw material cost is low, and the emissions of waste are minimal, making it more suitable for industrial mass production and significantly superior to traditional molecular sieve catalyst routes.

[0019] This invention introduces Sn, Sc, and Ce into magnesium-aluminum composite oxides through in-situ isomorphous substitution, resulting in a catalyst with a spinel crystal phase structure, uniformly distributed active sites, and synergistic effects of both acid-base bifunctional sites. This allows for precise control of ethanol activation and reaction pathways, significantly improving catalytic efficiency.

[0020] The catalyst prepared by this invention has a typical mesoporous structure and low diffusion resistance between reactants and products. In the ethanol-to-olefins reaction, it can simultaneously achieve high ethanol conversion and high olefin selectivity. Under optimized conditions, the ethanol conversion can reach up to 82.91% and the olefin selectivity can reach up to 99.21%, which is far superior to conventional metal oxide catalysts.

[0021] The catalyst of this invention exhibits excellent thermal and structural stability at 375°C and a mass hourly space velocity (HWV) of 2.37 h⁻¹. -1 Under the conditions of continuous reaction for 150 hours, it still maintains high conversion rate and high selectivity, with no obvious deactivation, thus solving the problems of easy deactivation and short life of existing catalysts.

[0022] This invention uses inexpensive metal salts such as magnesium, aluminum, tin, scandium, and cerium as raw materials, without using precious metals, resulting in low overall production costs. It also uses renewable bioethanol as a raw material to prepare low-carbon olefins, thus eliminating dependence on petroleum resources and meeting the requirements of carbon cycle and green chemical development, resulting in significant economic and social benefits.

[0023] The catalyst of this invention is applicable to a wide range of reaction temperatures (275–400 °C) and a wide range of mass hourly space velocities (0.95–4.73 h⁻¹). -1 It can operate efficiently under normal pressure, with mild reaction conditions, low equipment requirements, and simple operation, making it easy to apply directly to existing ethanol conversion devices. Attached Figure Description

[0024] Figure 1 The XRD patterns of the Mg-Al-T (T=400, 600, 800, 1000℃) catalysts prepared in this invention are shown below. Figure 2 The XRD pattern of the Mg-Al-X (X=Sc, Sn, Ce) mesoporous composite catalyst prepared in this invention; Figure 3 This is the N2 adsorption-desorption curve of the Mg-Al-Sn catalyst of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Non-substantial improvements and adjustments made by those skilled in the art based on the disclosure of this invention are all within the scope of protection of this invention.

[0026] A mesoporous composite catalyst for the direct production of olefins from ethanol is prepared by a template-free hydrothermal synthesis method to obtain a spinel catalyst with a mesoporous structure. A metal cation with specific catalytic activity is anchored to Al³⁺ through isomorphous substitution. + To construct mesoporous composite catalysts that combine acid-base synergy with redox activity, we explored specific sites.

[0027] A method for preparing a mesoporous composite catalyst for the direct production of olefins from ethanol includes the following steps: (1) Mix magnesium and aluminum nitrates with deionized water to obtain solution A; mix urea, oleic acid, ethanol and deionized water to obtain solution B; the molar ratio of magnesium nitrate, aluminum nitrate and urea is 3:1:4; tin nitrate, scandium nitrate and cerium nitrate are introduced into the magnesium and aluminum salt solution in this step by in-situ isomorphic substitution to prepare Mg-Al-X (X=Sc, Sn, Ce) catalyst, wherein the molar ratio of aluminum nitrate to tin nitrate, scandium nitrate and cerium nitrate is 1:(0.3-3); (2) Mix solution A obtained in step (1) with solution B and stir continuously for 30-120 min. Place the resulting mixed solution in a reaction vessel and heat at 120-180°C. o Crystallize at C for 8-12 hours; (3) Wash the solid product obtained in step (2) until the pH is neutral, between 60 and 100. o Drying at C for 12-24 h yields the Mg-Al precursor; (4) The Mg-Al precursor obtained in step (3) is placed in an air atmosphere at 400~1000 °C. o Mesoporous magnesium-aluminum metal oxide catalyst (Mg-Al) was obtained by calcination at C for 3-5 h, with a calcination heating rate of 2-10 h. o C / min; A method for the direct preparation of olefins from ethanol includes the following steps: (1) A certain amount of the catalyst described in claim 1 is compressed into tablets and granulated, and 40-60 mesh particles are sieved out. Then, the tablets are placed in a quartz reaction tube on a fixed bed under normal pressure. (2) The raw material ethanol is introduced into a fixed bed by a high-pressure pump and then into a quartz reaction tube under the purging of the carrier. The product is obtained after the reaction; the mass hourly space velocity is 0.95~4.73 h⁻¹. -1 The reaction temperature is 275~400℃. o C, the carrier gas is argon, and the flow rate is 60~100 mL / min; (3) After condensation, the liquid phase product is analyzed offline by gas chromatography, and the gas phase product is analyzed online by gas chromatography.

[0028] The following will provide a detailed description with reference to the accompanying drawings, through specific embodiments and application examples, such as... Figure 1As shown, Mg-Al catalysts obtained at different calcination temperatures all exhibit spinel-structure characteristic diffraction peaks. With increasing calcination temperature, the diffraction peak intensity gradually increases, indicating improved crystallinity. When the temperature reaches 1000℃, the diffraction peaks broaden slightly, suggesting that 800℃ is a more optimal calcination temperature, yielding moderately crystallized and structurally stable mesoporous spinel oxides. Figure 2 As shown, the Mg-Al-X catalyst, after isomorphous substitution by Sc, Sn, and Ce, still retains the spinel crystal phase and has no obvious impurity peaks, indicating that the introduced metal components are highly dispersed and have not damaged the matrix crystal structure, successfully forming a homogeneous composite metal oxide. Figure 2 As shown, the N2 adsorption-desorption curves of the Mg-Al-Sn catalyst exhibit typical type IV isotherms and type H1 hysteresis loops, proving that the catalyst has a typical mesoporous structure with uniform pore size distribution, which is conducive to the diffusion of reactants and products and enhances catalytic activity and stability.

[0029] Example 1 At room temperature, 20 mL of deionized water was added to 15.38 g of magnesium nitrate hexahydrate and 7.50 g of aluminum nitrate nonahydrate, and the mixture was stirred continuously for 30 min to obtain solution A. 4.8 g of urea, 4 mL of oleic acid, 15 mL of ethanol, and 10 mL of deionized water were mixed and stirred continuously for 30 min to obtain solution B. Solution A and solution B were mixed and stirred continuously for 60 min. The resulting mixture was placed in a reaction vessel and incubated at 160 °C. o Crystallize at C for 12 hours, then further wash the solid product until the pH is neutral, and then at 60°C. o The Mg-Al precursor was obtained by drying at C for 24 h. The Mg-Al precursor was then subjected to 400 °C in air atmosphere. o Calcination at C for 4 hours, with a heating rate of 5. o The Mg-Al-400 catalyst was obtained by adjusting the concentration of carbon dioxide (C / min).

[0030] Example 2 The same catalyst preparation and reaction steps were followed as in Example 1, except that the calcination temperature of the Mg-Al precursor was 600 °C. o C. The remaining steps remain unchanged to obtain the Mg-Al-600 catalyst.

[0031] Example 3 The same catalyst preparation and reaction steps were followed as in Example 1, except that the calcination temperature of the Mg-Al precursor was 800 °C. o C. The remaining steps remain unchanged to obtain the Mg-Al-800 catalyst.

[0032] Example 4 The same catalyst preparation and reaction steps were followed as in Example 1, except that the calcination temperature of the Mg-Al precursor was 1000 °C. oC. With the remaining steps unchanged, the Mg-Al-1000 catalyst is obtained.

[0033] Example 5 At room temperature, 20 mL of deionized water was added to 15.38 g of magnesium nitrate hexahydrate, 3.75 g of aluminum nitrate nonahydrate, and 3.39 g of scandium nitrate hexahydrate, and the mixture was stirred continuously for 30 min to obtain solution A. 4.8 g of urea, 4 mL of oleic acid, 15 mL of ethanol, and 10 mL of deionized water were mixed and stirred continuously for 30 min to obtain solution B. Solution A and solution B were then mixed and stirred continuously for 60 min. The resulting mixture was placed in a reaction vessel and incubated at 160 °C. o Crystallize at C for 12 hours, then further wash the solid product until the pH is neutral, and then at 60°C. o Drying at C for 24 h yields the Mg-Al-Sc precursor. The Mg-Al-Sc precursor is then subjected to 800 °C in air atmosphere. o Calcination at C for 4 hours, with a heating rate of 5. o The Mg-Al-Sc catalyst was obtained by measuring the temperature at C / min.

[0034] Example 6 At room temperature, 20 mL of deionized water was added to 15.38 g of magnesium nitrate hexahydrate, 3.75 g of aluminum nitrate nonahydrate, and 3.51 g of tin chloride pentahydrate, and the mixture was stirred continuously for 30 min to obtain solution A. 4.8 g of urea, 4 mL of oleic acid, 15 mL of ethanol, and 10 mL of deionized water were mixed and stirred continuously for 30 min to obtain solution B. Solution A and solution B were then mixed and stirred continuously for 60 min. The resulting mixture was placed in a reaction vessel and incubated at 160 °C. o Crystallize at C for 12 hours, then further wash the solid product until the pH is neutral, and then at 60°C. o The Mg-Al-Sn precursor was obtained by drying at C for 24 h. The Mg-Al-Sn precursor was then subjected to 800 °C in air atmosphere. o Calcination at C for 4 hours, with a heating rate of 5. o The Mg-Al-Sn catalyst was obtained by measuring the temperature at C / min.

[0035] Example 7 At room temperature, 20 mL of deionized water was added to 15.38 g of magnesium nitrate hexahydrate, 3.75 g of aluminum nitrate nonahydrate, and 4.34 g of cerium nitrate hydrate, and the mixture was stirred continuously for 30 min to obtain solution A. 4.8 g of urea, 4 mL of oleic acid, 15 mL of ethanol, and 10 mL of deionized water were mixed and stirred continuously for 30 min to obtain solution B. Solution A and solution B were mixed and stirred continuously for 60 min. The resulting mixture was placed in a reaction vessel and incubated at 160 °C. o Crystallize at C for 12 hours, then further wash the solid product until the pH is neutral, and then at 60°C. oThe Mg-Al-Ce precursor was obtained by drying at C for 24 h. The Mg-Al-Ce precursor was then subjected to 800 °C in air atmosphere. o Calcination at C for 4 hours, with a heating rate of 5. o C / min, Mg-Al-Ce catalyst was obtained.

[0036] Application Example 1 The catalysts obtained in Examples 1-4 were tableted and granulated, and solid particles of 40-60 mesh were screened out. The catalyst was loaded into a fixed bed at atmospheric pressure, and both ends were sealed with quartz sand. Ethanol was injected into the fixed bed using a high-pressure pump, and then introduced into a quartz reaction tube containing the solid composite catalyst for ethanol-to-olefins under argon purging (90 mL / min). The reaction temperature was controlled at 375°C. o C, WHSV is 2.37h -1 The reaction started and stabilized for 1 hour; the reaction products were then subjected to 0... o The cold trap of C collects the condensate for analysis by gas chromatography, and the gaseous products are analyzed online using a gas chromatograph.

[0037] Table 1: Effect of Mg-Al catalysts obtained at different calcination temperatures on the ethanol-to-olefins reaction. Table 1 above compares the catalysts in Examples 1-4 at 375°C. o The catalytic activity and olefin selectivity at C were observed from the reaction data. All catalysts exhibited some catalytic activity and high olefin selectivity, with the highest selectivity observed at 800 °C. o The Mg-Al catalyst obtained by calcination at C exhibits the highest ethanol conversion rate.

[0038] Application Example 2 The same reaction steps as in Application Example 1 are followed, except that the catalyst used is the catalyst prepared in Examples 5-7, and the rest of the steps remain the same.

[0039] Table 2: Effect of Mg-Al-X (X=Sc, Sn, Ce) catalyst on ethanol-to-olefins reaction Table 2 above compares the catalysts in Examples 5-6 at 375°C. o The catalytic activity and olefin selectivity under C were investigated. The experimental results showed that the conversion rate of ethanol was improved after introducing Sc, Sn and Ce into the Mg-Al catalyst. This indicates that the introduction of catalyst promoters through isomorphous substitution can effectively regulate the catalytic performance of Mg-Al catalysts and is beneficial to improving the catalyst's reaction activity.

[0040] Application Example 3 The catalyst prepared in Example 6 was tableted and granulated, and solid particles of 40-60 mesh were screened out. The catalyst was loaded into a fixed bed at atmospheric pressure, and both ends were sealed with quartz sand. Ethanol was injected into the fixed bed using a high-pressure pump, and then introduced into a quartz reaction tube containing the solid composite catalyst for ethanol-to-olefins under argon purging (90 mL / min). The reaction temperature was controlled at 275°C. o C, 300 o C, 325 o C, 350 o C, 375 o C, 400 o C, WHSV is 2.37h -1 The reaction started and stabilized for 1 hour; the reaction products were then subjected to 0... o The cold trap of C collects the condensate for analysis by gas chromatography, and the gaseous products are analyzed online using a gas chromatograph.

[0041] Table 3: Effect of Mg-Al-Sn catalyst on ethanol-to-olefins reaction Table 3 above compares the catalytic activity and olefin selectivity of the catalyst in Example 6 at different reaction temperatures. The experimental results show that the Mg-Al-Sn catalyst can be used at 275~375℃. o Under the reaction conditions of C, the target product olefin is produced, and the ethanol conversion rate increases with increasing reaction temperature, reaching a maximum at 400°C. o At C, the ethanol conversion rate and olefin selectivity can reach 82.91% and 95.97%, respectively.

[0042] Application Example 4 The catalyst prepared in Example 6 was tableted and granulated, and solid particles of 40-60 mesh were screened out. The catalyst was loaded into a fixed bed at atmospheric pressure, and both ends were sealed with quartz sand. Ethanol was injected into the fixed bed using a high-pressure pump, and then introduced into a quartz reaction tube containing the solid composite catalyst for ethanol-to-olefins under argon purging (90 mL / min). The reaction temperature was controlled at 375°C. o C, WHSV is 0.95h -1 2.37h -1 3.79h -1 4.73h -1 The reaction started and stabilized for 1 hour; the reaction products were then subjected to 0... o The cold trap of C collects the condensate for analysis by gas chromatography, and the gaseous products are analyzed online using a gas chromatograph.

[0043] Table 4: Effect of Mg-Al-Sn catalyst on ethanol-to-olefins reaction Table 4 above compares the catalytic activity and olefin selectivity of the catalysts in Example 6 under different WHSVs. The reaction data show that the Mg-Al-Sn catalyst can achieve catalytic activity in the range of 0.95–4.73 h⁻¹. -1 Under the reaction conditions, the target product olefin is produced, and it has a high ethanol conversion rate and olefin selectivity.

[0044] Application Example 5 The catalyst prepared in Example 6 was tableted and granulated, and solid particles of 40-60 mesh were screened out. The catalyst was loaded into a fixed bed at atmospheric pressure, and both ends were sealed with quartz sand. Ethanol was injected into the fixed bed using a high-pressure pump, and then introduced into a quartz reaction tube containing the solid composite catalyst for ethanol-to-olefins under argon purging (90 mL / min). The reaction temperature was controlled at 375°C. o C, WHSV is 2.37h -1 The reaction started and stabilized for 150 hours; the reaction products were subjected to 0 o The cold trap of C collects the condensate for analysis by gas chromatography, and the gaseous products are analyzed online using a gas chromatograph.

[0045] Table 5: Effect of Mg-Al-Sn catalyst on ethanol-to-olefins reaction Table 5 above compares the catalyst in Example 6 at 375°C. o The catalytic activity and olefin selectivity of the Mg-Al-Sn catalyst after 150 h of reaction at C were analyzed. The results showed that the Mg-Al-Sn catalyst still had high ethanol conversion and olefin selectivity after 150 h of reaction, which indicates that the catalyst has excellent stability.

[0046] In summary, the series of Mg-Al-X catalysts prepared by this invention can be used for the ethanol-to-olefin reaction. They also have advantages such as high conversion rate, good olefin selectivity, simple preparation process, low cost, and are easy to industrialize.

Claims

1. A mesoporous composite metal oxide catalyst for ethanol-to-olefins production, characterized in that, The catalyst is a Mg-Al-X composite metal oxide with a mesoporous structure and spinel crystal phase; wherein X is at least one metal element selected from Sc, Sn, and Ce; the catalyst is prepared by template-free hydrothermal synthesis and in-situ isomorphic substitution, and has a uniform distribution of active sites and synergistic effects of acid-base bifunctional sites.

2. The mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 1, characterized in that, The catalyst contains 25-75 mol of tin nitrate, scandium nitrate, or cerium nitrate.

3. The mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 1, characterized in that, The molar ratio of aluminum nitrate to tin nitrate, scandium nitrate, or cerium nitrate is 1:(0.3~3).

4. The mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 1, characterized in that, The XRD pattern of the catalyst corresponds to the characteristic peaks of the spinel structure, and the N2 adsorption-desorption curve exhibits the adsorption hysteresis loop of a type IV mesoporous material.

5. The mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 1, characterized in that, The catalyst is subjected to conditions of 275–400 °C, atmospheric pressure, and a mass hourly space velocity (HHSV) of 0.95–4.73 h⁻¹. -1 Under the conditions used in the ethanol-to-olefins reaction, the ethanol conversion rate is ≥73.89% and the olefin selectivity is ≥95.97%.

6. A method for preparing a mesoporous composite metal oxide catalyst for ethanol-to-olefins production, characterized in that, Includes the following steps: (1) Prepare an aqueous solution containing magnesium salt, aluminum salt and metal salt X, and mix them to obtain a precursor solution; (2) The catalyst precursor was obtained by crystallization using a template-free hydrothermal synthesis method; (3) The precursor was calcined at high temperature in air atmosphere to obtain a mesoporous composite metal oxide catalyst.

7. The method for preparing a mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 6, characterized in that, In step (1), the magnesium salt is magnesium nitrate, the aluminum salt is aluminum nitrate, and the metal salt X is scandium nitrate, tin chloride, or cerium nitrate; the molar ratio of magnesium nitrate to aluminum nitrate is 3:

1.

8. The method for preparing a mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 6, characterized in that, In step (2), the hydrothermal crystallization conditions are 120~180℃ for 8~16h; the crystallized product is washed until neutral and dried at 60~100℃ for 12~24h to obtain the precursor.

9. The method for preparing a mesoporous composite metal oxide catalyst for ethanol-to-olefins according to claim 6, characterized in that, In step (3), the calcination temperature is 400~1000℃, the calcination time is 3~5h, and the heating rate is 2~10℃ / min.

10. A method for the direct preparation of olefins from ethanol, characterized in that, Ethanol is passed into a reactor containing the catalyst according to any one of claims 1 to 5, and the reaction is carried out at 275 to 400°C, atmospheric pressure, and a mass hourly space velocity of 0.95 to 4.73 h⁻¹. -1 The reaction yields low-carbon olefins.

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