A method for preparing a transition metal phosphide catalyst and applications thereof

Abstract

The application relates to the field of catalysis technology, and particularly discloses a preparation method and application of a transition metal phosphide catalyst. The preparation method of the transition metal phosphide catalyst comprises the following steps: (1) carrier pretreatment: taking a carrier and immersing the carrier in an alkali solution or an acid solution for treatment; (2) active metal loading: immersing the pretreated carrier obtained in the step (1) in a solution containing active metal, and adding hydroxyethylidene diphosphonic acid at the same time; (3) phosphorization treatment: carrying out phosphorization on the carrier on which the active metal is loaded in the step (2) under an inert atmosphere to obtain the transition metal phosphide catalyst; in the step (2), 3-5% of a functional additive of the carrier weight is additionally added, the functional additive is composed of titanium oxide, zirconium oxide and cerium oxide, and the weight ratio of the titanium oxide, the zirconium oxide and the cerium oxide is (2-3):(1.4-1.6):1. The transition metal phosphide catalyst prepared in the application is improved in both low-temperature flowability and durability of biodiesel.

Description

Technical Field

[0001] This application relates to the field of catalysis technology, and more specifically, to a method for preparing and applying a transition metal phosphide catalyst. Background Technology

[0002] Transition metal phosphide catalysts are based on transition metals and form complex systems with organic ligands. They are widely used in electrocatalytic water splitting, organic synthesis reactions, and olefin conversion. Their core catalytic mechanisms include coordination activation and electron transfer, achieving high-efficiency catalysis by regulating the electronic state of the metal center.

[0003] Currently, most transition metal phosphide catalysts are molecular sieve-supported transition metal phosphide catalysts, which are composite catalytic materials in which transition metal phosphide nanoparticles are dispersed on a molecular sieve support. These catalysts combine the high specific surface area and regular pore structure of molecular sieves with the unique catalytic activity of transition metal phosphides, exhibiting excellent performance in reactions such as hydrogenation, dehydrogenation, and desulfurization, and are widely used in biodiesel.

[0004] Biodiesel is considered a pseudo-binary mixture, composed of high-melting-point saturated fatty acid methyl esters and low-melting-point unsaturated fatty acid methyl esters. In application, its low-temperature fluidity directly affects the engine's starting and operating performance under cold conditions. The low-temperature fluidity of biodiesel refers to its ability to maintain a flowing state in low-temperature environments. Currently, improvements in the low-temperature fluidity of biodiesel rely on transition metal phosphide catalysts. These catalysts lower the pour point and cloud point by promoting the conversion of heavy components in the fuel into light components. The pour point refers to the highest temperature at which biodiesel, under standard test conditions, cools to the point where the liquid surface completely stops moving, reflecting the critical point at which the fuel loses its fluidity. The cloud point is the temperature at which wax crystals first appear, causing turbidity, reflecting its impact on the fuel system's clogging.

[0005] While traditional transition metal phosphide catalysts can lower the pour point and freeze point of biodiesel to some extent, their efficiency still needs improvement in practical applications, especially under extreme low-temperature conditions. Existing technical improvements have generally focused on adjusting the properties of the support or changing the type of active metal, but these methods either increase the complexity of the process or make it difficult to achieve excellent stability and durability, resulting in poor activity retention and high specific surface area loss during long-term use. Therefore, there is an urgent need to propose a solution to address the above technical problems. Summary of the Invention

[0006] To improve the low-temperature flowability of biodiesel by transition metal phosphide catalysts while maintaining their excellent durability, this application provides a method for preparing and applying a transition metal phosphide catalyst.

[0007] In a first aspect, this application provides a method for preparing a transition metal phosphide catalyst, employing the following technical solution:

[0008] A method for preparing a transition metal phosphide catalyst includes the following steps:

[0009] (1) Carrier pretreatment: The carrier is treated by immersion in an alkaline solution or an acid solution;

[0010] (2) Active metal loading: The pretreated carrier obtained in step (1) is immersed in a solution containing active metal, and hydroxyethylidene diphosphonic acid is added at the same time;

[0011] (3) Phosphating treatment: The support for active metal loading completed in step (2) is phosphated under an inert atmosphere to obtain a transition metal phosphide catalyst.

[0012] By adopting the above technical solution, the support is impregnated with an alkaline or acidic solution. The acidity or alkalinity of the support is enhanced by ion exchange or surface modification, which improves the interaction between the support and the active metal, prevents metal particle agglomeration, and ensures the uniformity of subsequent loading. Then, the pretreated support is impregnated in a solution containing the active metal, and hydroxyethylidene diphosphonic acid is added. The hydroxyethylidene diphosphonic acid chelates metal ions through phosphonate groups, preventing their agglomeration, and at the same time provides a uniform active metal-phosphorus precursor for the subsequent phosphating reaction. Finally, phosphating is carried out under an inert atmosphere to generate highly active transition metal phosphides from the active metal-phosphorus precursor, thus obtaining a transition metal phosphide catalyst. In the above preparation process, not only is the high dispersion of active metal ions achieved through the chelating effect of hydroxyethylidene diphosphonic acid, resulting in phosphides with more edge active sites, significantly reducing the pour point and freezing point of biodiesel and improving its low-temperature flowability, but the phosphonate groups of hydroxyethylidene diphosphonic acid also form a three-dimensional coordination network with metal ions, inhibiting the migration and aggregation of metal particles during phosphating. Furthermore, the decomposition products of hydroxyethylidene diphosphonic acid generate a phosphate protective layer on the catalyst surface, reducing the poisoning of active sites by impurities such as sulfur and oxygen during the reaction. This chelation of metal ions in biodiesel prevents deposition and pore blockage, thus significantly improving the application durability of transition metal phosphide catalysts. Therefore, the application of hydroxyethylidene diphosphonic acid enhances the improvement effect of transition metal phosphide catalysts on the low-temperature flowability of biodiesel while maintaining the excellent durability of the transition metal phosphide catalyst itself, achieving a balance between improving the low-temperature flowability and durability of transition metal phosphide catalysts for biodiesel.

[0013] Preferably, in step (2), the amount of hydroxyethylidene diphosphonic acid added is 3-7% of the weight of the carrier.

[0014] By adopting the above technical solution, the hydroxyethylidene diphosphonic acid in the above-mentioned addition range can ensure that it fully chelates active metal ions during application, forming a uniform metal-phosphonic acid coordination network and inhibiting the agglomeration of active metal particles during high-temperature phosphating. At the same time, the hydroxyethylidene diphosphonic acid in this ratio range can provide enough phosphorus atoms to participate in the formation of metal phosphides, while avoiding excessive phosphorus leading to excessive phosphate coverage on the catalyst surface, thus ensuring the exposure rate of active sites. In this way, the final transition metal phosphide catalyst can be guaranteed to have excellent and stable quality.

[0015] Preferably, in step (2), the immersion treatment temperature is 50-70℃ and the time is 1.5-3h.

[0016] By adopting the above technical solution, this temperature range can effectively promote the chelation reaction between hydroxyethylidene diphosphonic acid and active metal ions, forming a stable active metal-phosphonic acid complex, thereby increasing the metal loading rate and avoiding the collapse of the support pores caused by high temperature. The above time ensures that the metal ions can fully diffuse into the interior of the support and maintains a balance between energy consumption and efficiency. In this way, hydroxyethylidene diphosphonic acid can play an excellent role in the application process, ultimately resulting in a high-quality and stable transition metal phosphide catalyst.

[0017] Preferably, in step (2), a functional additive is added at 3-5% of the weight of the carrier. The functional additive is composed of titanium oxide, zirconium oxide and cerium oxide, and the weight ratio of titanium oxide, zirconium oxide and cerium oxide is (2-3):(1.4-1.6):1.

[0018] By adopting the above technical solution, during the use of functional additives, the composite oxides of titanium dioxide and zirconium oxide can promote the isomerization reaction of saturated fatty acid methyl esters in biodiesel, generating branched structures and lowering the pour point; while cerium oxide can accelerate the hydrogenation process of unsaturated esters, inhibit low-temperature crystallization, and lower the pour point. When titanium dioxide, zirconium oxide, and cerium oxide are used synergistically, the combination of the three can bring about a compound synergistic effect, further enhancing the improvement effect of transition metal phosphide catalysts on the low-temperature fluidity of biodiesel. At the same time, the high thermal stability of zirconium oxide can inhibit support sintering; the dynamic oxygen buffering capacity of cerium oxide can repair lattice defects generated during phosphating; some titanium dioxide and the decomposition products of hydroxyethylidene diphosphonic acid form a titanium phosphate protective layer, blocking the poisoning of active sites by impurities such as sulfur and calcium in biodiesel; the enhancement mechanism formed by the three can significantly improve the application durability of transition metal phosphide catalysts. In this way, functional additives can further improve the low-temperature fluidity and durability of transition metal phosphide catalysts in biodiesel.

[0019] Preferably, the weight ratio of titanium oxide, zirconium oxide and cerium oxide is 5:3:2.

[0020] By adopting the above technical solution, the titanium oxide, zirconium oxide and cerium oxide in the above weight ratio have better synergistic effects when used as functional additives. They show excellent synergy in promoting isomerization at strong acid sites, constructing thermally stable supporting structures and maintaining the dynamic balance of oxygen vacancies, thus significantly improving the low-temperature fluidity and durability of biodiesel produced by transition metal phosphide catalysts.

[0021] Preferably, the particle size of the functional additive is 10-50 nm.

[0022] By adopting the above technical solutions, the specific surface area of ​​titanium oxide, zirconium oxide, and cerium oxide with a particle size of 10-50 nm can reach 100-300 m². 2 / g can significantly increase the contact sites with hydroxyethylidene diphosphonic acid, thereby improving the metal loading efficiency. Furthermore, the functional additives at the above particle size can form a stable spatial network structure, which avoids agglomeration and ensures strong interaction with the support. This ensures that the functional additives bring better effects, and finally, a transition metal phosphide catalyst with excellent application quality and stability is obtained.

[0023] Preferably, in step (2), the active metal used is any one or a combination of Ni, Mo and W, and the loading of the active metal is 10-25% of the weight of the carrier.

[0024] By employing the above technical solutions, elemental Ni exhibits excellent hydrogen dissociation capability in its sulfide state, promoting the hydrogenation saturation of unsaturated fatty acids and demonstrating good low-temperature activity. The layered sulfide structure of Mo effectively inhibits the adsorption of coke precursors, achieving relatively high isomerization selectivity at low loading levels and effectively improving the low-temperature fluidity of biodiesel. The sulfide state of W provides strong metal-sulfur bonds, promoting deep hydrogenation of unsaturated esters in biodiesel. These three activation technologies have different focuses and can be used individually or in combination depending on the specific application scenario. Furthermore, the selection of the loading range of the aforementioned active metals achieves an excellent balance of "active site density - metal synergy - thermal stability," resulting in a transition metal phosphide catalyst with excellent and stable application quality.

[0025] Preferably, in step (1), the alkaline solution is a 0.3-0.8 mol / L NaOH solution, the acid solution is a hydrochloric acid solution with a pH of 2-4, the treatment temperature is 60-90℃, and the treatment time is 1-3h.

[0026] By adopting the above technical solution, the selection of the specifications of the alkaline solution and acid solution, as well as the corresponding temperature and time, can achieve excellent and stable modification effect on the surface of the support while ensuring the integrity of the pore structure of the support. In this way, after the support pretreatment is completed, it can fully and uniformly interact with the active metal in subsequent operations, which is conducive to finally obtaining a high-quality and stable transition metal phosphide catalyst.

[0027] Preferably, in step (3), phosphating is performed for 2-4 hours at a temperature of 2-5℃ / min to 400-600℃ under an inert atmosphere.

[0028] By adopting the above technical solution, the heating rate can ensure controllable growth of the crystal structure, avoid grain agglomeration caused by rapid heating, maintain thermal stress balance, and reduce the probability of interface crack formation. The temperature of 400-600℃ can significantly improve the exposure of active sites while ensuring structural stability, thereby significantly enhancing catalytic activity. At the same time, controlling the phosphating time to 2-4h can maintain a good phosphating effect and avoid grain coarsening caused by over-phosphating. This is conducive to obtaining a high-quality and stable transition metal phosphide catalyst.

[0029] Secondly, this application provides an application of a transition metal phosphide catalyst, employing the following technical solution:

[0030] An application of a transition metal phosphide catalyst, which is prepared by the above-described method for preparing transition metal phosphide catalysts, is used in the production of biodiesel.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. In the preparation process of transition metal phosphide catalyst, the application of hydroxyethylidene diphosphonic acid not only achieves high dispersion of active metal ions and forms phosphides with more edge active sites, significantly reducing the pour point and freezing point of biodiesel, but also improves the application durability of transition metal phosphide catalyst, thereby achieving a balance between improving the low-temperature fluidity and durability of transition metal phosphide catalyst in biodiesel.

[0033] 2. In the preparation process of transition metal phosphide catalyst, this application uses a functional additive composed of titanium oxide, zirconium oxide and cerium oxide. Through the synergistic compounding of titanium oxide, zirconium oxide and cerium oxide, the low-temperature flowability and durability of transition metal phosphide catalyst in biodiesel are further improved. Detailed Implementation

[0034] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0035] Unless otherwise specified, all raw materials used in the preparation examples, embodiments and comparative examples of this application are commercially available.

[0036] The carrier is a molecular sieve purchased from Mingguang Feizhou New Materials Co., Ltd. It is a nano-grade ZSM-5 carrier-type molecular sieve, spherical in shape, model XH-5.

[0037] The solution containing the active metal is a Ni(NO3)2 solution.

[0038] Example 1

[0039] A method for preparing a transition metal phosphide catalyst includes the following steps:

[0040] (1) Carrier pretreatment: The carrier is treated by immersion in an alkaline solution;

[0041] (2) Active metal loading: The pretreated carrier obtained in step (1) is immersed in a solution containing active metal, and hydroxyethylidene diphosphonic acid is added at the same time;

[0042] (3) Phosphating treatment: The support for active metal loading completed in step (2) is phosphated under an inert atmosphere to obtain a transition metal phosphide catalyst.

[0043] Note: In step (1), the alkaline solution is a 0.55 mol / L NaOH solution, the treatment temperature is 75℃, and the treatment time is 2 h. In step (2), the amount of hydroxyethylidene diphosphonic acid added is 5% of the carrier weight; the impregnation treatment temperature is 60℃, and the time is 2.25 h; the active metal used is Ni, and the loading of the active metal is 17.5% of the carrier weight. In step (3), phosphating is carried out for 3 h at 500℃ under an inert atmosphere with a heating rate of 3.5℃ / min.

[0044] Example 2

[0045] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that the alkaline solution is a 0.3 mol / L NaOH solution, the treatment temperature is 90°C, and the treatment time is 1 h.

[0046] Example 3

[0047] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that the alkaline solution is a 0.8 mol / L NaOH solution, the treatment temperature is 60°C, and the treatment time is 3 h.

[0048] Example 4

[0049] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that the alkaline solution in step (1) is replaced with an acid solution, the acid solution is a hydrochloric acid solution with a pH of 3, the treatment temperature is 75°C, and the treatment time is 2h.

[0050] Example 5

[0051] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that the alkaline solution in step (1) is replaced with an acid solution, the acid solution is a hydrochloric acid solution with a pH of 4, the treatment temperature is 90°C, and the treatment time is 1 h.

[0052] Example 6

[0053] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that the alkaline solution in step (1) is replaced with an acid solution, the acid solution is a hydrochloric acid solution with a pH of 2, the treatment temperature is 60°C, and the treatment time is 3h.

[0054] Example 7

[0055] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that, in step (2), the amount of hydroxyethylidene diphosphonic acid added is 3% of the weight of the support.

[0056] Example 8

[0057] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that, in step (2), the amount of hydroxyethylidene diphosphonic acid added is 7% of the weight of the support.

[0058] Example 9

[0059] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that, in step (2), the impregnation treatment temperature is 50°C and the time is 3 hours.

[0060] Example 10

[0061] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that, in step (2), the impregnation treatment temperature is 70°C and the time is 1.5h.

[0062] Example 11

[0063] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that the loading of the active metal is 10% of the weight of the support.

[0064] Example 12

[0065] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that the loading of the active metal is 25% of the weight of the support.

[0066] Example 13

[0067] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that, in step (3), phosphating is performed for 2 hours at 2°C / min to 600°C under an inert atmosphere.

[0068] Example 14

[0069] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that, in step (3), phosphating is performed at 400°C for 4 hours under an inert atmosphere by heating at 5°C / min.

[0070] Example 15

[0071] A method for preparing a transition metal phosphide catalyst differs from Example 1 in that, in step (2), a functional additive is added at 4% of the weight of the support. The functional additive is composed of titanium oxide, zirconium oxide and cerium oxide, and the weight ratio of titanium oxide, zirconium oxide and cerium oxide is 5:3:2. The particle size of the functional additive is 30 nm.

[0072] Example 16

[0073] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that the amount of functional additive added is 3% of the weight of the support.

[0074] Example 17

[0075] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that the amount of functional additive added is 5% of the weight of the support.

[0076] Example 18

[0077] A method for preparing a transition metal phosphide catalyst differs from that in Example 15 in that the functional additive is composed of titanium oxide, zirconium oxide and cerium oxide in a weight ratio of 2:1.4:1.

[0078] Example 19

[0079] A method for preparing a transition metal phosphide catalyst differs from Example 15 in that the functional additive is composed of titanium oxide, zirconium oxide and cerium oxide in a weight ratio of 3:1.6:1.

[0080] Example 20

[0081] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that the particle size of the functional additive is 10 nm.

[0082] Example 21

[0083] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that the particle size of the functional additive is 50 nm.

[0084] Example 22

[0085] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that titanium oxide and cerium oxide, which are used as functional additives, are not added.

[0086] Example 23

[0087] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that zirconium oxide and cerium oxide, which are used as functional additives, are not added.

[0088] Example 24

[0089] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that titanium oxide and zirconium oxide, which are used as functional additives, are not added.

[0090] Example 25

[0091] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that titanium oxide, a functional additive, is not added.

[0092] Example 26

[0093] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that zirconium oxide, a functional additive, is not added.

[0094] Example 27

[0095] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that cerium oxide, a functional additive, is not added.

[0096] Comparative Example 1

[0097] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that hydroxyethylidene diphosphonic acid is replaced with diammonium hydrogen phosphate.

[0098] Comparative Example 2

[0099] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that hydroxyethylidene diphosphonic acid is replaced with sodium hypophosphite.

[0100] Comparative Example 3

[0101] A method for preparing a transition metal phosphide catalyst, which differs from Example 1 in that no support pretreatment is performed.

[0102] Comparative Example 4

[0103] A method for preparing a transition metal phosphide catalyst, which differs from Example 15 in that hydroxyethylidene diphosphonic acid is replaced with diammonium hydrogen phosphate.

[0104] Performance testing

[0105] Test samples: The transition metal phosphide catalysts prepared by the method in Examples 1-27 were used as test samples 1-27, and the transition metal phosphide catalysts prepared by the method in Comparative Examples 1-4 were used as control samples 1-4.

[0106] Experimental methods: Application tests were conducted on the transition metal phosphide catalyst, and the reaction was adjusted as follows:

[0107] Biodiesel refers to fatty acid methyl esters or ethyl esters formed by esterification of vegetable oils (such as rapeseed oil, soybean oil, peanut oil, corn oil, cottonseed oil, etc.), animal oils (such as fish oil, lard, tallow, mutton fat, etc.), waste oils or microbial oils with methanol or ethanol.

[0108] The feedstock oil is waste cooking oil (acid value 5.6 mgKOH / g, water content 2000 ppm, oxygen content 8.5 wt%).

[0109] The mass ratio of catalyst to feedstock oil is 1:120.

[0110] The reaction conditions were: temperature 320℃, pressure 4.5MPa, hydrogen-to-oil ratio 800:1, and space velocity 2 h⁻¹.

[0111] (1) Low temperature fluidity test (ASTM D97 / D5950): Take 30-40 mL of oil sample, filter it with a 0.45 μm filter membrane to remove impurities and avoid interference from heterogeneous wax crystal nucleation; preheat the sample to 45℃ water bath and keep it at 10 min to eliminate thermal history; cool it down at a rate of 1℃ / min, tilt the test tube 45° every 2℃ drop to observe the fluidity, and record the highest temperature at which there is no flow for 3 consecutive times as the pour point; under the same cooling conditions, tilt the test tube 45° every 3℃ drop and record the temperature at which the liquid surface stops moving as the pour point.

[0112] (2) Durability test (500h continuous operation): Take 5g of representative catalyst sample, crush it to 20-40 mesh (particle size 0.5-1mm), and vacuum dry at 105℃ for 4h to remove moisture.

[0113] The initial specific surface area was determined using a specific surface area meter (BET method).

[0114] Phase 1 (0-100h): Run at 250℃ to evaluate initial activity (conversion rate A0);

[0115] Phase 2 (100-300h): Gradual heating to 500℃, with samples taken every 50h to detect activity decay;

[0116] Phase 3 (300-500h): Maintain 500℃ high pressure (5MPa) to simulate extreme working conditions;

[0117] After completing stages 1-3 above, the activity retention rate (%) and specific surface area loss (%) were tested.

[0118] After performing the above tests on test samples 1-27 and control samples 1-4, the test results are recorded in Table 1.

[0119] Table 1. Test results of test samples 1-27 and control samples 1-4

[0120] sample Pour point depression (°C) Pour point decrease (°C) Activity retention rate (%) Specific surface area loss (%) Test sample 1 28.6 33.3 93.9 4.77 Test sample 2 27.4 32.1 92.7 4.86 Test sample 3 27.9 32.6 93.2 4.82 Test sample 4 28.1 32.8 93.4 4.81 Test sample 5 27.6 32.3 92.9 4.84 Test sample 6 27.3 32.0 92.6 4.83 Test sample 7 27.5 32.2 92.8 4.89 Test sample 8 27.7 32.4 93.0 4.85 Test sample 9 27.0 31.7 92.0 4.87 Test sample 10 27.8 32.5 93.1 4.79 Test sample 11 28.0 32.7 93.3 4.80 Test sample 12 28.2 32.9 93.5 4.88 Test sample 13 27.1 31.8 92.4 4.91 Test sample 14 27.2 31.9 92.5 4.90 Test sample 15 32.9 37.6 98.2 2.63 Test sample 16 32.5 37.2 97.8 2.69 Test sample 17 32.6 37.3 97.9 2.67 Test sample 18 32.7 37.4 98.0 2.65 Test sample 19 32.3 37.0 97.6 2.66 Test sample 20 32.4 37.1 97.7 2.68 Test sample 21 32.2 36.9 97.5 2.70 Test sample 22 29.5 34.2 94.8 4.34 Test sample 23 29.9 34.6 95.2 4.06 Test sample 24 29.7 34.4 95.0 4.10 Test sample 25 30.6 35.3 95.9 3.67 Test sample 26 31.0 35.7 96.3 3.39 Test sample 27 30.8 35.5 96.1 3.63 Control sample 1 12.8 15.9 72.4 18.25 Control sample 2 11.9 14.3 65.9 19.56 Control sample 3 21.3 26.4 88.7 5.59 Control sample 4 16.4 19.6 76.1 17.76

[0121] As can be seen from Examples 1 and Comparative Examples 1-3, and Table 1, in the preparation process of transition metal phosphide catalysts, the application of hydroxyethylidene diphosphonic acid, compared with the traditional application of diammonium hydrogen phosphate and sodium hypophosphite, improves the performance in terms of pour point reduction (°C), activity retention rate (%), and specific surface area loss (%). This demonstrates that it can achieve a balance between improving the low-temperature flowability and durability of transition metal phosphide catalysts in biodiesel. Furthermore, without support pretreatment, the transition metal phosphide catalysts prepared using hydroxyethylidene diphosphonic acid all exhibit the aforementioned performance losses.

[0122] As can be seen from Examples 1 and 15-21, and in conjunction with Table 1, this application uses a functional additive composed of titanium dioxide, zirconium oxide, and cerium oxide in the preparation process of the transition metal phosphide catalyst. This further enhances both the low-temperature fluidity and durability of the transition metal phosphide catalyst in biodiesel. The reduction in pour point (°C), activity retention rate (%), and specific surface area loss (%) obtained from the above tests are all significantly improved. Furthermore, as can be seen from Examples 22-27 and in conjunction with Table 1, if only one or two of titanium dioxide, zirconium oxide, and cerium oxide are used, the corresponding improvement effects are limited, and the effects are merely a simple additive effect. Only when all three are used in combination can a significant combined improvement effect (1+1>2) be achieved. Combined with Comparative Examples 1 and 4 and Table 1, it can be seen that if hydroxyethylidene diphosphonic acid is replaced with diammonium hydrogen phosphate during the preparation of transition metal phosphide catalysts, the corresponding effects brought by the functional additives will be significantly lost. This shows that the functional additives and hydroxyethylidene diphosphonic acid can exhibit a certain synergistic effect in application, making the transition metal phosphide catalysts perform better in improving the low-temperature fluidity and durability of biodiesel.

[0123] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a transition metal phosphide catalyst, characterized in that, Includes the following steps: (1) Carrier pretreatment: The carrier is treated by immersion in an alkaline solution or an acid solution; (2) Active metal loading: The pretreated carrier obtained in step (1) is immersed in a solution containing active metal, and hydroxyethylidene diphosphonic acid is added at the same time; (3) Phosphating treatment: The support for which the active metal was loaded in step (2) is phosphated under an inert atmosphere to obtain a transition metal phosphide catalyst; In step (2), a functional additive is added at 3-5% of the weight of the carrier. The functional additive is composed of titanium oxide, zirconium oxide and cerium oxide, and the weight ratio of titanium oxide, zirconium oxide and cerium oxide is (2-3):(1.4-1.6):

1. The carrier is a molecular sieve carrier.

2. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: In step (2), the amount of hydroxyethylidene diphosphonic acid added is 3-7% of the weight of the carrier.

3. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: In step (2), the immersion treatment temperature is 50-70℃ and the time is 1.5-3h.

4. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: The weight ratio of titanium oxide, zirconium oxide and cerium oxide is 5:3:

2.

5. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: The particle size of the functional additive is 10-50 nm.

6. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: In step (2), the active metal used is Ni, and the loading of the active metal is 10-25% of the weight of the carrier.

7. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: In step (1), the alkaline solution is a 0.3-0.8 mol / L NaOH solution, the acid solution is a hydrochloric acid solution with a pH of 2-4, the treatment temperature is 60-90℃, and the treatment time is 1-3h.

8. The method for preparing the transition metal phosphide catalyst according to claim 1, characterized in that: In step (3), phosphating is carried out for 2-4 hours at 400-600℃ under an inert atmosphere by heating at 2-5℃ / min.

9. The application of a transition metal phosphide catalyst, characterized in that: The transition metal phosphide catalyst is prepared by the method described in any one of claims 1-8 and is used in the production of biodiesel.