Carbon nanotube supported cerium-doped calcium-based photothermal catalyst and application thereof in preparation of biodiesel

Abstract

This invention discloses a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes and its application in the preparation of biodiesel, belonging to the field of catalysis technology. The photothermal catalyst is prepared by the following method: a calcium source and a cerium source are mixed and dissolved in an aqueous ethanol solution, then multi-walled carbon nanotubes are added and stirred to load the calcium and cerium sources onto the surface of the multi-walled carbon nanotubes. The mixture is then dried to remove the solvent; calcined under nitrogen protection; and after calcination, naturally cooled to obtain the cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes. This invention utilizes the strong electronic interaction between cerium and calcium to regulate the structure of active sites, inhibiting the aggregation and loss of active components, while simultaneously enhancing the catalyst's broad-spectrum light absorption and photothermal conversion capabilities, thereby achieving efficient and green biodiesel production.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst and its application in the preparation of biodiesel. Background Technology

[0002] Biodiesel is a clean and renewable energy source that can effectively replace traditional fossil diesel. Biodiesel production is divided into two categories: physical methods and chemical methods. Physical methods include direct mixing and microemulsion methods, which have simple operating procedures. Chemical methods encompass high-temperature cracking, esterification, and transesterification. Among these, transesterification offers mild reaction conditions and stable product quality, making it the mainstream industrial route currently. The main oilseeds for biodiesel production include vegetable oils, waste cooking oils, and microalgae oils.

[0003] Oils obtained through physical methods are prone to stratification and have poor combustion performance, making them suitable only for small-scale trials and unsuitable for large-scale production. High-temperature pyrolysis requires harsh high-temperature and high-pressure conditions, resulting in high equipment investment and a complex product composition that is difficult to separate and purify. Esterification processes can only process high-acid-value oils, limiting the range of applicable raw materials. Industrially used homogeneous alkalis such as NaOH and KOH offer high catalytic efficiency, but the catalysts cannot be recovered. The washing process generates large amounts of saline wastewater, which corrodes equipment, and saponification reactions easily occur when oils contain water or free acids, reducing yield. Solid alkalis such as CaO tend to agglomerate during reactions, leading to significant calcium leaching and loss. They are also rapidly deactivated by water and free acids, resulting in poor recycling capacity. Furthermore, existing processes rely on external heat sources, resulting in high overall energy consumption and carbon emissions, making it difficult to meet the development requirements of green and low-carbon manufacturing. Summary of the Invention

[0004] This invention provides a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes, which is prepared by the following method: Cerium and calcium sources were mixed and dissolved in an aqueous ethanol solution. Multi-walled carbon nanotubes were then added and stirred to load the calcium and cerium sources onto the surface of the multi-walled carbon nanotubes. The mixture was then dried to remove the solvent. Under nitrogen protection, the mixture was calcined. After calcination, the mixture was allowed to cool naturally to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0005] In the above technical solution, the cerium source is at least one of cerium nitrate hexahydrate, anhydrous cerium acetate, cerium chloride, cerium carbonate, cerium oxalate, and cerium hydroxide.

[0006] In the above technical solution, the calcium source is at least one of calcium acetate monohydrate, anhydrous calcium acetate, calcium nitrate tetrahydrate, calcium chloride, calcium carbonate, and calcium hydroxide.

[0007] In the above technical solution, the cerium-calcium molar ratio of the cerium source and the calcium source is 0.05~0.25; preferably 0.2.

[0008] In the above technical solution, the mass ratio of the cerium source and calcium source mixture to the multi-walled carbon nanotubes is (1~10):(1~10); preferably 1:1.

[0009] In the above technical solution, the calcination conditions are: calcination at 750~850 ℃ for 1.5~2.5 h.

[0010] This invention provides the application of the above-mentioned carbon nanotube-supported cerium-doped calcium-based photothermal catalyst in the preparation of biodiesel.

[0011] This invention provides a method for preparing biodiesel, comprising the following steps: Oils, alcohols, and cerium-doped calcium-based photothermal catalysts supported on carbon nanotubes were mixed and reacted under light conditions; after the reaction was completed, the mixture was centrifuged to obtain biodiesel.

[0012] In the above-mentioned method for preparing biodiesel, the oil is at least one of soybean oil, rapeseed oil, peanut oil, palm oil, sunflower seed oil, cottonseed oil, corn oil, rice bran oil, coconut oil, palm kernel oil, olive oil, jatropha oil, Chinese pistache oil, tung oil, rubber seed oil, microalgae oil, chlorella oil, and waste cooking oil; the alcohol is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, and isoamyl alcohol.

[0013] In the above-mentioned method for preparing biodiesel, the molar ratio of alcohol to oil is (4~12):1; the amount of cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes is 2~10% of the oil mass; and the irradiance of the light is 0.5~2 kW m. -2 The reaction time is 1-2 hours.

[0014] In the above-mentioned method for preparing biodiesel, the light irradiation can be converted into heat by a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes, thereby meeting the temperature conditions required for the reaction; wherein, the light irradiation conditions should enable the temperature of the reaction system to reach 55~65℃.

[0015] The beneficial effects of this invention are as follows: This invention utilizes the strong electronic interaction between cerium and calcium to regulate the structure of active sites, inhibit the aggregation and loss of active components, and simultaneously enhance the broad-spectrum light absorption and photothermal conversion capabilities of the catalyst, thereby driving the transesterification reaction between oils and alcohols to achieve efficient and green biodiesel production. It has good application prospects in the field of catalysis technology.

[0016] The photothermal catalyst of this invention has a full-spectrum light absorption rate exceeding 99% at 1 kW m -2After 300 seconds of xenon lamp irradiation, the surface temperature can reach over 70°C, exhibiting excellent photothermal performance. It can generate heat in situ using solar energy, eliminating the need for an external heat source. It also boasts high catalytic activity, achieving a biodiesel conversion rate of over 97% under mild reaction conditions, with a short reaction cycle.

[0017] The photothermal catalyst of this invention exhibits strong cycle stability. Cerium doping effectively inhibits CaO aggregation and leaching, and the catalyst maintains a high conversion rate even after multiple reuses, allowing for repeated recycling and reducing industrial production costs. Furthermore, the photothermal catalyst demonstrates good resistance to water and acids, maintaining a high biodiesel conversion rate even when the feedstock system contains moisture and oleic acid.

[0018] This invention uses multi-walled carbon nanotubes as the catalyst support, which achieves full-spectrum light absorption due to its structural advantages. Calcium oxide is used as the main catalytically active component, combined with cerium dioxide for doping modification. This invention limits the molar ratio of cerium to calcium in the catalyst to the range of 0.15~0.25. This ratio allows the two metal elements to form stable electronic interactions, fundamentally inhibiting the aggregation and loss of calcium oxide particles. Attached Figure Description

[0019] Figure 1 The UV-Vis-NIR absorption spectra of each catalyst are shown.

[0020] Figure 2 The images show the infrared thermal images of each catalyst.

[0021] Figure 3 The X-ray diffraction patterns of each catalyst are shown.

[0022] Figure 4 The catalytic performance of each catalyst was tested.

[0023] Figure 5 For the optimization of catalytic conditions; where (a) is the amount of catalyst, (b) is the molar ratio of methanol to palm oil, (c) is the reaction temperature, and (d) is the reaction time.

[0024] Figure 6 The results are stability test results under optimal catalytic conditions; (a) is the reusability test, and (b) is the water and acid resistance test. Detailed Implementation

[0025] In this invention, multi-walled carbon nanotubes were purchased from Shenzhen Suiheng Technology Co., Ltd., with a diameter of 15 nm; calcium acetate monohydrate (Ca(C2H3O2)2·H2O) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and was an analytical grade reagent with a purity of 98%; cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and was an analytical grade reagent with a purity of 99.95%.

[0026] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0027] Example 1

[0028] The steps for preparing a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes are as follows: Dissolve 3 g of a mixture of calcium acetate monohydrate and cerium nitrate hexahydrate (cerium-calcium molar ratio of 0.05) in 200 mL of an aqueous ethanol solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0029] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The powder was then naturally cooled to room temperature to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0030] Example 2

[0031] The steps for preparing a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes are as follows: Dissolve 3 g of a mixture of calcium acetate monohydrate and cerium nitrate hexahydrate (cerium-calcium molar ratio of 0.1) in 200 mL of an aqueous ethanol solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0032] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The powder was then naturally cooled to room temperature to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0033] Example 3

[0034] The steps for preparing a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes are as follows: Dissolve 3 g of a mixture of calcium acetate monohydrate and cerium nitrate hexahydrate (cerium-calcium molar ratio of 0.15) in 200 mL of an aqueous ethanol solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0035] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The powder was then naturally cooled to room temperature to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0036] Example 4

[0037] The steps for preparing a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes are as follows: Dissolve 3 g of a mixture of calcium acetate monohydrate and cerium nitrate hexahydrate (cerium-calcium molar ratio of 0.2) in 200 mL of an aqueous ethanol solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0038] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The powder was then naturally cooled to room temperature to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0039] Example 5

[0040] The steps for preparing a cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes are as follows: Dissolve 3 g of a mixture of calcium acetate monohydrate and cerium nitrate hexahydrate (cerium-calcium molar ratio of 0.25) in 200 mL of an aqueous ethanol solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0041] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The powder was then naturally cooled to room temperature to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

[0042] Comparative Example 1 The steps for preparing calcium-based catalysts supported on carbon nanotubes are as follows: Dissolve 3 g of calcium acetate monohydrate in 200 mL of ethanol-water solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0043] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The furnace was then allowed to cool naturally to room temperature to obtain a calcium-based catalyst supported on carbon nanotubes.

[0044] Comparative Example 2 The steps for preparing carbon nanotube-supported cerium-based catalysts are as follows: Dissolve 3 g of cerium nitrate hexahydrate in 200 mL of ethanol-water solution (ethanol:water = 1:3), then add 3 g of multi-walled carbon nanotubes and stir for 2 h to uniformly load the active precursor onto the carrier surface; place the mixed suspension in a drying oven at 105 ℃ for 15 h to remove the solvent.

[0045] The dried solid powder was transferred into a tube furnace, and nitrogen gas was continuously introduced at a rate of 50 mL / min as a protective gas. The temperature was increased to 800 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. The furnace was then allowed to cool naturally to room temperature to obtain a carbon nanotube-supported cerium-based catalyst.

[0046] I. Physical Properties Figure 1 The light absorption performance curves of C2-CNT (Example 4), CeO2-CNT (Comparative Example 2), and CeO2 in the 300–2500 nm spectral range, characterized by a UV-Vis-NIR spectrophotometer, are presented. The test results show that the light absorption efficiency of CeO2 decreases in the UV, visible, and part of the near-infrared regions, with an average light absorption rate of only 29%. In contrast, the average light absorption rates of C2-CNT and CeO2-CNT are essentially equivalent across the entire spectral range, both exceeding 99%, demonstrating excellent light-harvesting capabilities.

[0047] To evaluate the photothermal conversion efficiency of the material, the surface temperature change at the center of the sample was monitored using an infrared thermal imager. The infrared thermal image spectrum is shown below. Figure 2 As shown. At 1 kW m -2After irradiation for 300 s at a certain irradiance, the core temperature of pure CeO2 was only 41.5 ℃, while the core temperatures of C2-CNT and CeO2-CNT rose to 73.1 ℃ and 73.7 ℃, respectively. Under the condition of irradiation for 300 s, the surface temperature of C2-CNT showed a linear increasing trend with the increase of irradiance, with corresponding temperatures of 62.6 ℃, 73.1 ℃, and 84.0 ℃, respectively. The C2-CNT catalyst exhibits excellent light absorption and photothermal conversion performance in the 300-2500 nm spectral range. The light energy it captures can be rapidly converted into heat energy and efficiently transferred to the CaO active sites, achieving precise and efficient heating of the reaction sites.

[0048] Figure 3 The X-ray diffraction patterns of each catalyst are shown below; where C0.5-CNT is Example 1, C1-CNT is Example 2, C1.5-CNT is Example 3, C2-CNT is Example 4, C2.5-CNT is Example 5, CaO-CNT is Comparative Example 1, and CeO2-CNT is Comparative Example 2.

[0049] Depend on Figure 3 It was found that characteristic diffraction peaks of CeO2 and CaO were clearly detected in all tested catalyst samples. The 2θ diffraction peaks at 28.55°, 33.08°, 47.48°, and 56.34° were completely consistent with the peak positions on the CeO2 standard PDF card (PDF#78-0694). The 2θ diffraction peaks at 32.20°, 37.36°, 53.86°, 64.16°, and 67.38° highly matched the standard peak positions on the CaO standard card (PDF#99-0070). This characterization result confirms that after high-temperature calcination, the precursor was successfully converted into the two target phases, CeO2 and CaO, and the conversion process was efficient and thorough. Furthermore, the Ce / Ca molar ratio has a significant impact on the intensity of the characteristic diffraction peaks of the two phases. As the Ce / Ca molar ratio increases, the intensity of the characteristic diffraction peak of CeO2 in the catalyst gradually increases, while the intensity of the characteristic diffraction peak of CaO decreases accordingly.

[0050] II. Preparation of Biodiesel Palm oil was selected as the feedstock to study a photothermal-driven catalytic transesterification reaction. A xenon lamp was used as a simulated solar light source, with the irradiance set at 1.5 kW m². -2 The emission spectrum closely matches the natural solar spectrum. The transesterification reaction requires a specific temperature to proceed; the amount of light energy input is controlled by adjusting the distance between the xenon lamp and the reaction flask, thus maintaining the steady-state temperature of the reaction system at the set temperature. The photothermal-driven experimental system is not equipped with external heating devices such as water baths or oil baths; the heat required for the reaction is entirely supplied by the photothermal conversion effect of the catalyst.

[0051] First, the irradiance of the light source was measured. Then, palm oil, methanol, and the catalyst were mixed in a flask and reacted for a predetermined time under simulated AM 1.5 standard sunlight irradiation with a xenon lamp and magnetic stirring. After the reaction, biodiesel, glycerol, and the catalyst were obtained by centrifugation. A water bath heating control group was also set up, using a constant-temperature water bath as the external heat source. The palm oil transesterification reaction was carried out under uniform experimental conditions.

[0052] Fixed experimental conditions: catalyst dosage (by mass of palm oil) 8 wt.%, methanol to palm oil molar ratio 10:1, reaction temperature 60 ℃, reaction time 1.5 h.

[0053] Biodiesel conversion rate was determined using Fourier transform attenuated total reflectance infrared spectroscopy. This method is based on the fact that fatty acid methyl esters at 1436 cm⁻¹... -1 The characteristic absorption peak at the location is used to complete quantitative detection in conjunction with Lambert-Beer's law.

[0054] The test results are as follows Figure 4 As shown: When the Ce / Ca molar ratio is 2, the conversion rate of the C2-CNT catalyst reaches its maximum of 96.45%. Its optimal catalytic performance comes from the appropriate doping synergistic effect formed by Ce and Ca. An appropriate amount of Ce can effectively inhibit CaO agglomeration and improve the dispersion of active components on the CNT support. The electronic interaction between Ce and CaO can also regulate the strength and distribution of alkaline sites and improve the utilization rate of active sites, thereby enhancing the catalytic activity.

[0055] When the Ce / Ca molar ratio is less than or greater than 2, the catalyst conversion rate declines. On the one hand, when the Ce / Ca molar ratio is too low, it is insufficient to effectively inhibit CaO agglomeration, thereby reducing the catalyst's catalytic activity. On the other hand, when the Ce / Ca molar ratio is too high, excessive Ce doping will occupy CaO active sites, reducing effective basic active sites and decreasing the contact efficiency between reactants and active sites, thus weakening the catalytic activity.

[0056] Repeated use stability tests showed that all cerium-calcium catalysts exhibited superior cycling performance compared to the CaO-CNT catalyst. Ce doping enhanced the catalyst's structural stability, inhibited CaO leaching and sintering, and reduced the loss of active sites. The high specific surface area and chemical stability of the CNT support also provided a stable loading environment for the active components. Catalyst stability gradually improved with increasing Ce / Ca molar ratio, but excessive Ce, while improving stability, reduced catalytic activity. Considering catalytic activity, cycling stability, and preparation cost, the optimal Ce / Ca molar ratio was 0.2.

[0057] III. Optimization of Catalytic Conditions Based on the experimental conditions in Part II above, using C2-CNT as the catalyst, the reaction conditions were optimized using a single-factor variable method. The catalyst dosage was set to 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.%, and 10 wt.% respectively; the molar ratio of methanol to palm oil was 4:1, 6:1, 8:1, 10:1, and 12:1; the reaction temperature was 50 ℃, 55 ℃, 60 ℃, and 65 ℃; and the reaction time was 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, and 120 min respectively.

[0058] The test results are as follows Figure 5 As shown: As shown in (a), when the catalyst dosage is 2–8 wt.%, the biodiesel conversion rate increases from 60.38% to 97.83%, with the increased number of active sites promoting the reaction. When the catalyst dosage is increased to 10 wt.%, the system viscosity increases, particles agglomerate, mass transfer is hindered, and the conversion rate drops to 86.74%. Therefore, the optimal catalyst dosage is 8 wt.%.

[0059] As shown in (b), the conversion rate increases from 63.16% to 97.83% when the alcohol-to-oil molar ratio is 4–10, with excess methanol driving the transesterification equilibrium to the positive side. When the alcohol-to-oil molar ratio increases to 12, the oil is diluted, effective collisions decrease, and separation energy consumption increases. Therefore, the optimal alcohol-to-oil molar ratio is 10:1.

[0060] As shown in (c), the conversion rate increases from 74.25% to 97.83% when the reaction temperature is 50-60 ℃. Increasing the reaction temperature to 65 ℃ only slightly increases the conversion rate by 1.39%, and higher temperatures also increase the energy consumption for photothermal regulation. Therefore, the optimal reaction temperature is selected as 60 ℃.

[0061] As shown in (d), the conversion rate rapidly reached 77.03% in the first 45 min of the reaction, and rose to 97.83% at 90 min. Further extending the time only slightly improved the conversion rate. In order to balance energy consumption and efficiency, the optimal reaction time was selected as 90 min.

[0062] The above experiments verified that the optimal reaction conditions are: catalyst dosage 8 wt.%, alcohol-oil molar ratio 10:1, reaction temperature 60 ℃, and reaction time 1.5 h.

[0063] IV. Performance Testing under Optimal Conditions Based on the above optimal reaction conditions, tests were conducted, and the experimental results are as follows: Figure 6 As shown.

[0064] Catalyst reusability test: After a single reaction, the reaction mixture is centrifuged. The resulting solid catalyst is not washed or regenerated and is directly used in the next transesterification reaction. Figure 6 As shown in (a), the biodiesel conversion rate can still reach 81.19% after the catalyst is continuously circulated 6 times.

[0065] Water resistance test: Different masses of deionized water (system water content of 1 wt.%, 3 wt.%, and 5 wt.%) were added to palm oil, and the mixture was thoroughly stirred to prepare a water-containing feedstock oil, while other reaction conditions remained unchanged. Figure 6 As shown in (b), when the moisture content of the system is 5 wt.%, the biodiesel conversion rate is 79.80%.

[0066] Acid resistance test: Different masses of oleic acid (oil content of 1 wt.%, 3 wt.%, and 5 wt.% respectively) were added to palm oil, and the mixture was thoroughly stirred to prepare an acid-containing feedstock oil, while other reaction conditions remained unchanged. Figure 6 As shown in (b), when the oleic acid content is 5 wt.%, the biodiesel conversion rate is 75.64%.

[0067] The above water and acid resistance test results show that the catalyst of the present invention has excellent resistance to water and free fatty acid interference. Water and oleic acid will consume the alkaline active sites on the catalyst surface through hydrolysis and neutralization, respectively. Therefore, as the water content and oleic acid content of the system increase, the biodiesel conversion rate gradually decreases. However, even under the condition of 5 wt.% high water and high oleic acid impurities, the system can still maintain a relatively high conversion rate of over 75%, indicating that the catalyst has outstanding resistance to impurity deactivation. It can be adapted to unrefined, high-acid, and high-water low-cost industrial raw materials such as kitchen waste oil and crude palm oil, which greatly broadens the actual raw material application scenarios of this catalytic system and has good industrial application potential.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. 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 scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A cerium-doped calcium-based photothermal catalyst supported on carbon nanotubes, characterized in that, It is prepared by the following method: Cerium and calcium sources were mixed and dissolved in an aqueous ethanol solution. Multi-walled carbon nanotubes were then added and stirred to load the calcium and cerium sources onto the surface of the multi-walled carbon nanotubes. The mixture was then dried to remove the solvent. Under nitrogen protection, the mixture was calcined. After calcination, the mixture was allowed to cool naturally to obtain a carbon nanotube-supported cerium-doped calcium-based photothermal catalyst.

2. The carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to claim 1, characterized in that, The cerium source is at least one of cerium nitrate hexahydrate, anhydrous cerium acetate, cerium chloride, cerium carbonate, cerium oxalate, and cerium hydroxide.

3. The carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to claim 1, characterized in that, The calcium source is at least one of calcium acetate monohydrate, anhydrous calcium acetate, calcium nitrate tetrahydrate, calcium chloride, calcium carbonate, and calcium hydroxide.

4. The carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to claim 1, characterized in that, The cerium-calcium molar ratio of the cerium source and the calcium source is 0.05~0.

25.

5. The carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to claim 1, characterized in that, The mass ratio of the cerium source and calcium source mixture to the multi-walled carbon nanotubes is 1:

1.

6. The carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to claim 1, characterized in that, The calcination conditions are: calcination at 750~850 ℃ for 1.5~2.5 h.

7. The application of the carbon nanotube-supported cerium-doped calcium-based photothermal catalyst according to any one of claims 1 to 6 in the preparation of biodiesel.

8. A method for preparing biodiesel, characterized in that, The steps are as follows: Oils, alcohols, and the carbon nanotube-supported cerium-doped calcium-based photothermal catalyst described in claim 1 are mixed and reacted under light irradiation; after the reaction is completed, the mixture is centrifuged to obtain biodiesel.

9. The biodiesel preparation method according to claim 8, characterized in that, The oil is at least one of soybean oil, rapeseed oil, peanut oil, palm oil, sunflower seed oil, cottonseed oil, corn oil, rice bran oil, coconut oil, palm kernel oil, olive oil, jatropha oil, Chinese pistache oil, tung oil, rubber seed oil, microalgae oil, chlorella oil, and waste cooking oil from kitchens; the alcohol is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, and isopentanol.

10. The biodiesel preparation method according to claim 8, characterized in that, The molar ratio of the alcohol to the oil is (4~12):1; the amount of the carbon nanotube-supported cerium-doped calcium-based photothermal catalyst added is 2~10% of the oil mass; the irradiance of the light is 0.5~2 kW m. -2 The reaction time is 1-2 hours.

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