Preparation method and application of acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst
The acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst prepared by the co-precipitation-hydrothermal coupling method solves the problem of low deoxygenation and aromatization efficiency of existing catalysts in the biomass catalytic reforming process, and realizes the efficient conversion of biomass pyrolysis volatiles into high-value-added aromatics.
Patent Information
- Application Number
- CN202511484546.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-17
- Publication Date
- 2026-03-06
AI Technical Summary
Existing acidic and basic catalysts each have their limitations in the biomass catalytic reforming process. Acidic catalysts have insufficient deoxygenation capacity and are prone to carbon deposition and deactivation, while basic catalysts lack acidic sites, resulting in low aromatization efficiency and making it difficult to achieve efficient conversion of biomass into high-value-added aromatics.
A co-precipitation-hydrothermal coupling method was used to prepare a bifunctional magnesium-aluminum bimetallic oxide catalyst. A magnesium-aluminum hydrotalcite precursor was formed by co-precipitation, followed by hydrothermal treatment and calcination to obtain a magnesium-aluminum composite metal oxide with strong acid and strong basic sites, which was used for catalytic reforming of volatiles from biomass pyrolysis.
This method achieves efficient deoxygenation and aromatization of oxygen-containing compounds in the volatiles of biomass pyrolysis, significantly improving the selectivity of monocyclic aromatic hydrocarbons. The catalyst has a high specific surface area and uniform pore size distribution, which enhances its catalytic activity and stability.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of biomass catalytic conversion and heterogeneous catalytic materials technology, and particularly to a method for preparing and applying an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst. Background Technology
[0002] Biomass pyrolysis oil is a renewable resource with broad application prospects but also significant challenges. Its high water content, high oxygen content, low calorific value, low pH, complex composition, and unstable properties limit its direct and efficient utilization. In-depth research and development of corresponding treatment, upgrading, and utilization technologies are necessary to fully realize its potential. Biomass pyrolysis-catalytic reforming technology is an important pathway for converting biomass resources into high-value-added chemicals and fuels. This technology involves the biomass pyrolysis process and the catalytic reforming process of its pyrolysis volatiles. Biomass is pyrolyzed into pyrolysis volatiles, which are then further catalytically reformed in the catalyst region to adjust the product distribution and improve the selectivity of target products (such as monocyclic aromatic hydrocarbons). In this process, the design and performance of the catalyst are particularly critical; an ideal catalyst should possess suitable acid-base sites, high specific surface area, good thermal stability, and high selectivity.
[0003] In existing technologies, acidic catalysts are widely used in the catalytic cracking and aromatization processes of biomass. Their acidic sites facilitate cracking, decarbonylation, dehydration, and aromatization, significantly promoting the formation of monocyclic aromatic hydrocarbons such as benzene, toluene, and xylene. However, acidic catalysts are insufficient in deoxygenation capacity, easily leading to carbon deposition and deactivation, thus reducing catalyst lifetime. Basic catalysts possess cracking and deoxygenation capabilities, enabling the cracking and deoxygenation of large oxygen-containing molecules, significantly improving the quality of biomass pyrolysis products. In particular, alkali metal oxides can effectively inhibit coking and deactivation and have been studied for deoxygenation modification of bio-oils. However, it is worth noting that basic catalysts lack acidic sites, making effective hydrocracking and aromatization impossible, resulting in lower yields of high-value-added aromatic hydrocarbons.
[0004] To overcome the limitations of single-acid-base functional catalysts and achieve synergistic catalysis between deoxygenation and aromatization, this invention aims to construct a composite metal oxide catalyst with high specific surface area, uniform pore size distribution, and tunable acid-base sites via a co-precipitation-hydrothermal coupling method. This catalyst will enable highly efficient catalytic reforming of volatiles from biomass pyrolysis, significantly reducing the content of oxygen-containing compounds and improving the selectivity for monocyclic aromatic hydrocarbons. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention discloses an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst, its preparation method, and its application. The specific surface area of this acid-base bifunctional catalyst is 110-250 m² / g, and it is applied to the catalytic reforming of volatiles from biomass pyrolysis to significantly reduce the content of oxygen-containing compounds and improve the selectivity of monocyclic aromatic hydrocarbons.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst includes the following steps: (1) Weigh a certain amount of magnesium nitrate and aluminum nitrate, dissolve them together in a certain volume of ultrapure water, stir thoroughly to obtain a mixed solution of metal salts; (2) Prepare a sodium hydroxide aqueous solution of a certain concentration and volume, pour it into a dropping funnel, and add it drop by drop to the metal salt mixed solution obtained in step (1), while stirring thoroughly to obtain a turbid liquid; (3) The turbid liquid from step (2) is heated in a water bath to crystallize, and then transferred to a reaction vessel lined with polytetrafluoroethylene; (4) The reaction vessel was then placed in an oven for hydrothermal crystallization, and then cooled to room temperature. The crystallized sample was washed, centrifuged, and dried to obtain a hydrotalcite-like precursor. (5) The hydrotalcite-like precursor obtained in step (4) can be calcined to obtain the magnesium aluminum bimetallic oxide catalyst.
[0007] Further, in step (1), the molar ratio of magnesium nitrate to aluminum nitrate is 2:1, 3:1, 4:1, or 5:1.
[0008] Furthermore, in step (2), the concentration of the sodium hydroxide aqueous solution is the same as that of NO3 in the metal salt mixed solution in step (1). - The concentration is the same, and the volume is the same as that of the metal salt mixed solution in step (1).
[0009] Furthermore, in step (3), the water bath heating temperature is 60 ℃ and the crystallization time is 0.5-1h.
[0010] Furthermore, in step (4), the hydrothermal crystallization temperature is 180℃ and the crystallization time is 6-18h; the drying temperature is 80℃ and the drying time is 8-12h.
[0011] Furthermore, in step (5), the roasting temperature is 500℃ and the roasting time is 2-5h.
[0012] Furthermore, in the prepared magnesium-aluminum bimetallic oxide catalyst, Mg and Al exist in the form of a composite oxide, possessing both strong acidic and strong basic sites. Its specific surface area is 110-250 m² / g, its pore size distribution is 2-50 nm, and its average pore size is 8-22 nm.
[0013] Secondly, the present invention also discloses an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst prepared by the above method.
[0014] Thirdly, this invention also discloses the application of this acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst in the biomass pyrolysis-catalytic reforming process. The pyrolysis-catalytic reforming feedstock can be expanded to include various heavy carbon resources, including one or a blend of biomass, coal, and plastics, such as coal-biomass, coal-plastic, biomass-plastic, and coal-biomass-plastic. Specifically, biomass feedstock and catalyst are layered in a pyrolysis cup, with a biomass feedstock to catalyst mass ratio of 1:1. The feedstock is laid flat at the bottom of the pyrolysis cup, and the catalyst is placed on top of the feedstock, with quartz wool placed between the feedstock and catalyst for isolation. The pyrolysis temperature and catalytic reforming temperature of the biomass feedstock are 400-500℃, and the reaction pressure is atmospheric pressure. After the pyrolysis unit reaches the preset temperature, the pyrolysis cup is pushed into the pyrolysis unit to achieve rapid pyrolysis-catalytic reforming. Online gas chromatography-mass spectrometry is used to analyze the composition and relative content of the catalytic reforming products.
[0015] The beneficial effects of this invention are that, in the acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst prepared by the coprecipitation-hydrothermal coupling method, Mg and Al exist in the form of composite metal oxides, which realizes the atomic-level dispersion of active components, effectively inhibits the phase separation of metal oxides, and has a stable crystal structure. This bifunctional magnesium-aluminum bimetallic oxide catalyst possesses both strong acidic and strong basic sites, exhibiting bifunctionality. It boasts a high specific surface area of 110-250 m² / g, with a pore size distribution primarily concentrated in the 2-50 nm range and an average pore size of 8-22 nm, allowing for more complete contact and reaction with biomass pyrolysis volatiles. Based on these characteristics, this bifunctional composite metal oxide catalyst exhibits high catalytic activity, facilitating the deoxygenation, cracking, and aromatization of oxygen-containing macromolecular components in the initial pyrolysis volatiles of biomass. Attached Figure Description
[0016] Figure 1 This is a flowchart illustrating the synthesis process of an embodiment of the present invention; Figure 2 The XRD patterns of the magnesium-aluminum hydrotalcite precursor and the acid-base bifunctional magnesium-aluminum composite metal oxide in the embodiments of the present invention are shown. Figure 3 The N2 adsorption-desorption isotherm of the acid-base bifunctional magnesium-aluminum composite metal oxide in this embodiment of the invention; Figure 4 The attached diagrams are for the carbon dioxide temperature-programmed desorption (CO2-TPD) and ammonia temperature-programmed desorption (NH3-TPD) of the acid-base bifunctional magnesium-aluminum composite metal oxide in the embodiments of the present invention. Figure 5 This is a diagram showing the composition and distribution of lignin pyrolysis-catalytic reforming products in an embodiment of the present invention. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0018] Example 1 This invention discloses a method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst, such as... Figure 1 As shown, the specific steps are as follows: Weigh out 7.683g of magnesium nitrate hexahydrate and 3.752g of aluminum nitrate nonahydrate according to the ratio of n(Mg²⁺):n(Al³⁺) = 3:1, and dissolve them together in 50ml of ultrapure water; Weigh 3.632g NaOH and dissolve it in 50ml of ultrapure water. Stir with a glass rod, and then slowly add the NaOH aqueous solution to the metal salt mixture using a dropping funnel. Place the mixture in a magnetic stirrer and stir at 60°C for 30min. The stirred turbid liquid was transferred to a reaction vessel lined with polytetrafluoroethylene and placed in an oven for constant temperature crystallization at 180°C for 18 hours. The reaction vessel was removed and cooled to room temperature. It was then centrifuged with ultrapure water until neutral and dried at 80°C for 8 hours to obtain the hydrotalcite-like precursor Mg3Al1-LDH. The hydrotalcite-like precursor Mg3Al1-LDH was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and held at that temperature for 2 hours to obtain a magnesium-aluminum composite metal oxide catalyst, denoted as Mg3Al1-LDO.
[0019] Example 2 This invention discloses a method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst, the specific steps of which are as follows: Weigh out 5.133g of magnesium nitrate hexahydrate and 3.757g of aluminum nitrate nonahydrate according to the ratio of n(Mg²⁺):n(Al³⁺) = 2:1, and dissolve them together in 50ml of ultrapure water; Weigh 3.671g NaOH and dissolve it in 50ml of ultrapure water. Stir with a glass rod, and then slowly add the NaOH aqueous solution to the metal salt mixture using a dropping funnel. Place the mixture in a magnetic stirrer and stir at 60°C for 30min. The stirred turbid liquid was transferred to a reaction vessel lined with polytetrafluoroethylene, placed in an oven, and crystallized at 180°C for 18 hours. The reaction vessel was removed and cooled to room temperature. It was washed with ultrapure water, centrifuged until neutral, and dried at 80°C for 8 hours to obtain the hydrotalcite-like precursor Mg2Al1-LDH. The hydrotalcite-like material was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and held at that temperature for 2 hours to obtain a magnesium-aluminum composite metal oxide catalyst, denoted as Mg2Al1-LDO.
[0020] Example 3 This invention discloses a method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst, the specific steps of which are as follows: Weigh out 10.261g of magnesium nitrate hexahydrate and 3.753g of aluminum nitrate nonahydrate according to the ratio of n(Mg²⁺):n(Al³⁺) = 4:1, and dissolve them together in 50ml of ultrapure water; Weigh 3.682g of NaOH and dissolve it in 50ml of ultrapure water. Stir with a glass rod, and then slowly add the NaOH aqueous solution to the metal salt mixture using a dropping funnel. Place the mixture in a magnetic stirrer and stir at 60°C for 30min. The stirred turbid liquid was transferred to a reaction vessel lined with polytetrafluoroethylene, placed in an oven, and crystallized at 180°C for 18 hours. The reaction vessel was removed and cooled to room temperature. It was then centrifuged with ultrapure water until neutral and dried at 80°C for 8 hours to obtain the hydrotalcite-like precursor Mg4Al1-LDH. The hydrotalcite-like material was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and held at that temperature for 2 hours to obtain a magnesium-aluminum composite metal oxide catalyst, denoted as Mg4Al1-LDO.
[0021] Example 4 This invention discloses a method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst, the specific steps of which are as follows: Weigh out 12.282g of magnesium nitrate hexahydrate and 3.751g of aluminum nitrate nonahydrate according to the ratio of n(Mg²⁺):n(Al³⁺) = 5:1, and dissolve them together in 50ml of ultrapure water; Weigh 3.632g NaOH and dissolve it in 50ml of ultrapure water. Stir with a glass rod, then slowly add the NaOH aqueous solution to the metal salt mixture using a dropping funnel. Place the mixture in a magnetic stirrer and stir at 60°C for 30min. The stirred turbid liquid was transferred to a reaction vessel lined with polytetrafluoroethylene, placed in an oven, and crystallized at 180°C for 18 hours. The reaction vessel was removed and cooled to room temperature. It was then centrifuged with ultrapure water until neutral and dried at 80°C for 8 hours to obtain the hydrotalcite-like precursor Mg5Al1-LDH. The hydrotalcite-like material was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and held at that temperature for 2 hours to obtain a magnesium-aluminum composite metal oxide catalyst, denoted as Mg5Al1-LDO.
[0022] The magnesium-aluminum composite metal oxide catalysts prepared in Examples 1-4 are characterized below.
[0023] Figure 2 The XRD patterns of the hydrotalcite-like precursors and their corresponding magnesium-aluminum composite metal oxides are shown. All hydrotalcite-like precursors exhibited good layered double hydroxide characteristic diffraction peaks at 11°, 23°, 34°, 39°, 45°, 61°, and 65°, corresponding to the (002), (004), (101), (015), (106), (110), and (113) crystal planes, respectively, and the peaks were sharp, indicating that magnesium-aluminum hydrotalcite with good crystallinity and a typical rhombic structure was successfully synthesized. In the XRD patterns of Mg2Al1-LDH and Mg3Al1-LDH, in addition to the typical hydrotalcite-like diffraction peaks, characteristic peaks belonging to Mg(NO3)2 (PDF#00-019-0765) were also observed. After calcination at 500°C, the characteristic peaks of magnesium-aluminum hydrotalcite disappeared completely. All magnesium-aluminum composite metal oxide samples showed two obvious diffraction peaks near 43.3° and 62.8°, which perfectly matched the (303) and (413) crystal planes (PDF#00-033-0853) of magnesium-aluminum composite metal oxide MgAl2O4, indicating that magnesium-aluminum hydrotalcite had been completely transformed into magnesium-aluminum composite metal oxide.
[0024] The N2 adsorption-desorption isotherms of the four prepared magnesium-aluminum composite metal oxide catalysts are as follows: Figure 3 As shown in Table 1, the specific surface area, pore volume, and pore diameter are as follows.
[0025] Table 1 shows the specific surface area, pore volume, and pore size distribution of acid-base bifunctional magnesium-aluminum composite metal oxides. Among them, S total S represents the total specific surface area. mic S represents the specific surface area of the micropores. mes V represents the specific surface area of the mesoporous structures. total V represents the total pore volume; mic V represents the pore volume of the micropores. mes Mesopore volume Depend on Figure 3 It can be seen that all four catalysts exhibit type IV isotherms, and H3-type hysteresis loops exist between relative pressures P / P0 and 0.4–1.0, indicating mesoporous characteristics mainly composed of slits formed by nanosheet aggregation. Table 1 shows that Mg2Al1-LDO and Mg4Al1-LDO catalysts have similar pore volumes, while Mg3Al1-LDO and Mg5Al1-LDO have similar average pore diameters, pore volumes, and specific surface areas. Furthermore, the mesoporous surface areas (Si) of the four magnesium-aluminum composite metal oxides are similar. mes ) accounts for the total surface area (S total The fact that 60.3%–100% of the samples exhibited mesoporous surface area confirms the dominant role of mesoporous structures. Secondly, H3-type hysteresis loops are generally associated with pore structures with a wide pore size distribution, consistent with the results in Table 1 showing that the average pore size distribution of each sample ranges from 9.29 to 21.44 nm. In particular, Mg3Al1-LDO is dominated by mesoporous surface area, thus exposing more active sites and exhibiting better catalytic performance.
[0026] Figure 4 The figures show the CO2-TPD and NH3-TPD curves of Mg3Al1-LDO. The CO2-TPD curve exhibits multiple desorption peaks in the low-to-high temperature range, indicating the presence of basic sites ranging from weak to strong in Mg3Al1-LDO. The significant desorption signal, especially at high temperatures (>500°C), suggests the presence of strongly basic sites. Conversely, the NH3-TPD curve shows the presence of a small number of weakly acidic sites (<100°C) and strongly acidic sites (>500°C) in Mg3Al1-LDO. This coexistence of acidic and basic sites indicates that the material possesses bifunctional acid-base properties.
[0027] Application examples Rapid biomass pyrolysis-catalytic reforming experiments and product analysis were conducted using Py-GCMS. The specific procedures are as follows: 1 mg of lignin was weighed and placed at the bottom of a pyrolysis vessel. The upper layer was loaded with 1 mg of the magnesium-aluminum composite metal oxide catalyst prepared in Example 1. The two layers were separated by quartz wool. After the pyrolysis unit reached the preset temperature of 500°C, the pyrolysis vessel containing the sample was pushed into the pyrolysis unit (Frontier Lab). Pyrolysis and catalytic reforming were performed under a helium atmosphere. The volatiles were split (split ratio 50:1) and entered the GC-MS separation system (DB-5 column, 30 m × 0.25 mm × 0.25 μm) using an electron impact ionization (EI) source. The scanning range was [missing information]. m / z 20-450. The product was qualitatively identified by comparison with the NIST spectral library, and the peak areas of its chromatographic peaks were normalized and semi-quantitatively analyzed.
[0028] The pyrolysis experiment of 1 mg lignin without the addition of a magnesium-aluminum composite metal oxide catalyst served as a blank control group. Figure 5 As shown in the blank experiment, the main pyrolysis products of lignin include aromatic hydrocarbons, phenols (H-type phenols), methoxyphenols (G-type phenols and S-type phenols), ketones, ethers, alkanes, alkenes, esters and nitrogen-containing compounds, among which the relative content of methoxyphenols is about 32%.
[0029] Compared with the blank experiment, the acid-base bifunctional magnesium-aluminum composite metal oxide catalyst has a significant effect on the composition and relative content of volatiles from lignin pyrolysis. The main effects are as follows: (1) The relative contents of phenols, methoxyphenols, ethers and esters are significantly reduced. In particular, under the action of Mg2Al1-LDO, no obvious signal of methoxyphenols was detected, indicating that the catalyst has a high-efficiency deoxygenation performance, which is conducive to the breaking of CO bonds, promoting the conversion of methoxyphenols to small molecule phenols and further deoxygenation.
[0030] In addition, the catalyst promotes the deoxygenation of esters to ketones, thereby increasing the relative content of ketones. Among them, Mg3Al1-LDO has a higher selectivity for ketones. (2) The relative content of aromatics increased significantly, indicating that the catalyst has excellent aromatization performance. In particular, under the action of Mg2Al1-LDO catalyst, the relative content of monocyclic aromatics increased from 4% in the blank experiment to 21%, which proves that the catalyst has a significant aromatization ability and can convert oxygen-containing intermediates such as phenols into stable monocyclic aromatics through deoxygenation, cyclization, and dealkylation. The relative content of alkanes and alkenes also increased, mainly from cracking and hydrogenation reactions. Among them, Mg5Al1-LDO catalyst has a high selectivity for alkenes.
[0031] Overall, by adjusting the Mg / Al ratio, the distribution and selectivity of lignin catalytic conversion products can be effectively regulated, providing the possibility for the targeted preparation of target products.
[0032] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.
Claims
1. A method for preparing an acid-base bifunctional magnesium-aluminum double metal oxide catalyst, characterized by, The method comprises the following steps: (1) a certain amount of magnesium nitrate and aluminum nitrate are weighed and dissolved in a certain volume of ultrapure water, and stirred to obtain a mixed metal salt solution; (2) a sodium hydroxide solution with a certain concentration and volume is prepared and added dropwise into the mixed metal salt solution obtained in step (1) while stirring to obtain a turbid solution; (3) the turbid solution obtained in step (2) is heated in a water bath to crystallize, and then transferred to a reaction kettle lined with polytetrafluoroethylene; (4) the reaction kettle is placed in an oven for hydrothermal crystallization, and then cooled to room temperature; the crystallized sample is washed, centrifuged and dried to obtain a hydrotalcite-like precursor; (5) the hydrotalcite-like precursor obtained in step (4) is calcined to obtain a magnesium-aluminum bimetallic oxide catalyst.
2. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 1, characterized in that, In step (1), the molar ratio of magnesium nitrate to aluminum nitrate is 2:1, 3:1, 4:1 or 5:
1.
3. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 2, characterized in that, In step (2), the concentration of the aqueous sodium hydroxide solution is the same as the concentration of NO3 - in the metal salt mixed solution in step (1), and the volume of the aqueous sodium hydroxide solution is the same as the volume of the metal salt mixed solution.
4. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 3, characterized in that, In step (3), the water bath heating temperature is 60°C, and the crystallization time is 0.5-1h.
5. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 4, characterized in that, In step (4), the hydrothermal crystallization temperature is 180°C, and the crystallization time is 6-18h; the drying temperature is 80°C, and the drying time is 8-12h.
6. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 5, characterized in that, In step (5), the calcination temperature is 500°C, and the calcination time is 2-5h.
7. The method for preparing an acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst according to claim 6, characterized in that, The magnesium-aluminum bimetallic oxide catalyst prepared has Mg and Al in the form of a composite oxide, and has strong acid sites and strong basic sites; the specific surface area is 110-250 m² / g, the pore size distribution is 2-50 nm, and the average pore size is 8-22 nm.
8. An acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst prepared by the method of claim 7.
9. Use of the acid-base bifunctional magnesium-aluminum bimetallic oxide catalyst of claim 8 in a biomass pyrolysis-catalytic reforming process.