Preparation method and application of transition metal phosphide catalyst

Abstract

The invention relates to the technical field of catalysis, and particularly discloses a preparation method and application of a transition metal phosphide catalyst. The invention relates to a preparation method of a transition metal phosphide catalyst. The preparation method comprises the following steps: (1) carrier pretreatment: taking a carrier and carrying out dipping treatment by using an alkali solution or an acid solution; (2) active metal loading: dipping the pretreated carrier obtained in the step (1) in a solution containing active metal, and adding 1-hydroxyethylidene-1, 1-diphosphonic acid at the same time; and (3) phosphating treatment: phosphating the carrier loaded with the active metal in the step (2) in an inert atmosphere to obtain the transition metal phosphide catalyst, in the step (2), a functional auxiliary agent accounting for 3-5% of the weight of the carrier is also added, the functional auxiliary agent is composed of titanium oxide, zirconium oxide and cerium oxide, and the weight ratio of titanium oxide to zirconium oxide to cerium oxide is (2-3): (1.4-1.6): 1. The transition metal phosphide catalyst prepared by the invention is improved in the aspects of low-temperature fluidity improvement and durability of biodiesel.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysis technology, more particularly, it relates to a preparation method and application of a transition metal phosphide catalyst. BACKGROUND

[0002] The transition metal phosphide catalyst is a complex catalyst material in which transition metal nanoparticles are dispersed on a molecular sieve carrier. This catalyst combines the high specific surface area, regular pore structure of the molecular sieve and the unique catalytic activity of the transition metal phosphide, and exhibits excellent performance in hydrogenation, dehydrogenation, desulfurization and other reactions, and is mainly used in biodiesel.

[0003] Currently, the transition metal phosphide catalyst is mainly a molecular sieve supported transition metal phosphide catalyst, which is a composite catalyst material in which transition metal phosphide nanoparticles are dispersed on a molecular sieve carrier. This catalyst combines the high specific surface area, regular pore structure of the molecular sieve and the unique catalytic activity of the transition metal phosphide, and exhibits excellent performance in hydrogenation, dehydrogenation, desulfurization and other reactions, and is mainly 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, the low-temperature flowability of biodiesel directly affects the starting and running performance of the engine under cold conditions. The low-temperature flowability of biodiesel refers to its ability to maintain a flowing state under low-temperature conditions. Currently, the low-temperature flowability of biodiesel depends on transition metal phosphide catalysts, which can reduce the freezing point and pour point by promoting the conversion of heavy components in the oil to light components. The freezing point refers to the highest temperature at which the biodiesel stops moving completely under standard test conditions, reflecting the critical point at which the oil loses its flowability. The pour point is the temperature at which the first wax crystal appears, causing turbidity, which affects the blockage of the fuel system.

[0005] Although traditional transition metal phosphide catalysts can reduce the freezing point and pour point of biodiesel to some extent, their performance still needs to be improved in practical applications, especially under extremely low temperature conditions. Existing technical improvement attempts usually focus on adjusting the properties of the carrier or changing the type of active metal. However, these methods either increase the complexity of the process or make it difficult to balance excellent stability and durability, resulting in poor activity retention rate and high specific surface area loss during long-term use. Therefore, there is an urgent need to propose a solution to solve the above technical problems. SUMMARY

[0006] In order to improve the improvement effect of the transition metal phosphide catalyst on the low-temperature flowability of biodiesel and maintain the excellent durability of the transition metal phosphide catalyst, the present application provides a preparation method and application of a transition metal phosphide catalyst.

[0007] In a first aspect, the application provides a preparation method of a transition metal phosphide catalyst, which adopts the following technical solution: The preparation method of the transition metal phosphide catalyst comprises the following steps: (1) carrier pretreatment: taking a carrier and immersing it in an alkali solution or an acid solution for treatment; (2) active metal loading: immersing the pretreated carrier obtained in step (1) in a solution containing active metal, while adding hydroxyethylidene diphosphonic acid; (3) phosphorization treatment: carrying out phosphorization on the carrier on which the active metal is loaded in step (2) under an inert atmosphere to obtain a transition metal phosphide catalyst.

[0008] By adopting the above technical solution, the carrier is immersed in an alkali solution or an acid solution for treatment, the acidity or alkalinity of the carrier is enhanced through ion exchange or surface modification, the interaction between the carrier and the active metal is improved, the metal particles are prevented from agglomerating, and the uniformity of subsequent loading is ensured; then the pretreated carrier is immersed in a solution containing active metal, and hydroxyethylidene diphosphonic acid is added, the hydroxyethylidene diphosphonic acid chelates metal ions through phosphonate groups, prevents the metal ions from agglomerating, and provides uniform active metal-phosphorus precursors for subsequent phosphorization reaction; finally, the active metal-phosphorus precursors are generated into high-activity transition metal phosphides through phosphorization treatment under an inert atmosphere, and a transition metal phosphide catalyst is obtained. In the above preparation process, not only is the high dispersion of active metal ions achieved through the chelation of hydroxyethylidene diphosphonic acid, the phosphides formed have more edge active sites, the pour point and the solidifying point of biodiesel are significantly reduced, and the improvement effect on the low-temperature fluidity of biodiesel is improved, but also a three-dimensional coordination network is formed between the phosphonate groups of hydroxyethylidene diphosphonic acid and metal ions, the migration and agglomeration of metal particles are inhibited during phosphorization, a phosphate protective layer is generated on the surface of the catalyst by using the decomposition products of hydroxyethylidene diphosphonic acid to reduce the poisoning of active sites by impurities such as sulfur and oxygen during the reaction process, and metal ions in biodiesel can be chelated to prevent the deposition and blockage of channels, thereby the application durability of the transition metal phosphide catalyst can be significantly improved; in this way, through the application of hydroxyethylidene diphosphonic acid, the improvement effect of the transition metal phosphide catalyst on the low-temperature fluidity of biodiesel can be improved, and the excellent durability of the transition metal phosphide catalyst itself can be maintained, so that the transition metal phosphide catalyst is improved in both the low-temperature fluidity and the durability of biodiesel.

[0009] Preferably, in step (2), the amount of hydroxyethylidene diphosphonic acid added is 3-7% of the weight of the carrier.

[0010] By adopting the technical scheme, the hydroxyethylidene diphosphonic acid in the above-mentioned addition amount range can ensure that it fully chelates active metal ions in the application process, forms a uniform metal-phosphonic acid coordination network, and inhibits the agglomeration of active metal particles during high-temperature phosphating; at the same time, the hydroxyethylidene diphosphonic acid in the above-mentioned proportion range can not only provide sufficient phosphorus atoms to participate in the formation of metal phosphides, but also avoid excessive phosphorus from causing excessive coverage of phosphates on the surface of the catalyst, thereby ensuring the exposure rate of active sites; in this way, the transition metal phosphide catalyst obtained finally can have excellent and stable quality.

[0011] Preferably, in step (2), the temperature of the impregnation treatment is 50-70℃, and the time is 1.5-3h.

[0012] By adopting the technical scheme, the temperature range can effectively promote the chelation reaction of the hydroxyethylidene diphosphonic acid and the active metal ions, form a stable active metal-phosphonic acid complex, and improve the metal loading rate, and can avoid the collapse of the carrier pore caused by high temperature; and the above-mentioned time can ensure that the metal ions fully diffuse into the carrier, and can ensure the balance between energy consumption and efficiency; in this way, the hydroxyethylidene diphosphonic acid can play an excellent corresponding role effect in the application process, and finally a transition metal phosphide catalyst with excellent and stable quality can be obtained.

[0013] Preferably, in step (2), a functional additive with a weight of 3-5% of the carrier is further 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.

[0014] By adopting the technical scheme, in the use process of the functional additive, the composite oxide of titanium oxide and zirconium oxide can promote the isomerization reaction of saturated fatty acid methyl ester in biodiesel to generate a branched structure, thereby reducing the freezing point; and the cerium oxide can accelerate the hydrogenation process of unsaturated ester and inhibit low-temperature crystallization, thereby reducing the pour point; when the titanium oxide, the zirconium oxide and the cerium oxide are used cooperatively, the cooperation among the three can bring a synergistic effect, thereby further improving the improvement effect of the transition metal phosphide catalyst on the low-temperature fluidity of biodiesel. At the same time, the high thermal stability of the zirconium oxide can inhibit the sintering of the carrier; the dynamic oxygen buffering capacity of the cerium oxide can repair the lattice defects generated in the phosphating process; part of the titanium oxide and the decomposition product of the hydroxyethylidene diphosphonic acid form a titanium phosphate protective layer to block the poisoning of impurities such as sulfur and calcium in biodiesel to the active sites; and the enhanced mechanism formed by the three can significantly improve the application durability of the transition metal phosphide catalyst. In this way, the functional additive can further improve the low-temperature fluidity and durability of the transition metal phosphide catalyst.

[0015] Preferably, the weight ratio of the titanium oxide, the zirconium oxide and the cerium oxide is 5:3:2.

[0016] By adopting the above technical scheme, the titanium oxide, zirconium oxide and cerium oxide in the above weight ratio have better corresponding effects when applied in the functional additive, and excellent synergy in promoting isomerization at strong acid sites, constructing a thermal stability support structure and dynamic balance of oxygen vacancies, thereby significantly improving the low-temperature flowability and durability of the transition metal phosphide catalyst for biodiesel.

[0017] Preferably, the particle size of the functional additive is 10-50 nm.

[0018] By adopting the above technical scheme, the titanium oxide, zirconium oxide and cerium oxide with a particle size of 10-50 nm have a specific surface area of 100-300 m 2 / g, which can significantly increase the contact sites with hydroxyethylidene diphosphonic acid, improve the metal loading efficiency, and the functional additive with the above particle size can subsequently form a stable space network structure, avoiding agglomeration and ensuring strong interaction with the carrier. Thus, the functional additive can bring better effect, and finally obtain a transition metal phosphide catalyst with excellent and stable application quality.

[0019] Preferably, in step (2), the active metal used is any one or a combination of several of Ni, Mo and W, and the loading amount of the active metal is 10-25% of the weight of the carrier.

[0020] By adopting the above technical scheme, the elemental Ni in the sulfided state exhibits excellent hydrogen dissociation capacity, which can promote the hydrogenation saturation of unsaturated fatty acids, and has good low-temperature activity; the sulfide layered structure of Mo can effectively inhibit the adsorption of coke precursors, and can achieve relatively high isomerization selectivity at a low loading amount, effectively improving the low-temperature flowability of biodiesel; the sulfided state of W provides a strong metal-sulfur bond, promoting the deep hydrogenation of unsaturated esters in biodiesel; the three active technologies have different focuses, and one or more can be selected for combined use according to the needs of the actual application scene. The loading amount range of the above active metals is selected to achieve excellent balance of the triple synergy of “active site density-metal synergy-thermal stability”, and finally obtain a transition metal phosphide catalyst with excellent and stable application quality. Preferably, in step (1), the alkali 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.

[0021] By adopting the above technical solutions, the specifications of the alkali solution and the acid solution are selected and the corresponding temperature and time are matched, so that excellent and stable modification effect can be achieved on the surface of the carrier under the premise of ensuring the integrity of the pore size structure of the carrier, and then after the pretreatment of the carrier is completed, the active metal can fully and uniformly interact with the carrier in subsequent operations, so as to facilitate the final production of the transition metal phosphide catalyst with excellent and stable quality.

[0022] Preferably, in step (3), phosphorization is carried out at 2-5℃ / min to 400-600℃ under an inert atmosphere for 2-4h.

[0023] By adopting the above technical solutions, the above heating rate can ensure controllable growth of the crystal structure, avoid grain agglomeration caused by rapid heating, and maintain thermal stress balance to reduce the probability of interface crack; and the temperature of 400-600℃ can significantly improve the exposure degree of active sites under the premise of ensuring structural stability, thereby significantly enhancing the catalytic activity; at the same time, controlling the phosphorization time to be 2-4h can maintain a better phosphorization effect and avoid grain coarsening caused by excessive phosphorization; thus, it is beneficial to finally obtain a transition metal phosphide catalyst with excellent and stable quality.

[0024] In a second aspect, the application provides an application of a transition metal phosphide catalyst, which adopts the following technical solution: An application of a transition metal phosphide catalyst, which is prepared by the above-mentioned method for preparing a transition metal phosphide catalyst, and is applied in the production of biodiesel.

[0025] In summary, the application has the following beneficial effects: 1. In the preparation process of the transition metal phosphide catalyst, the application of hydroxyethylidene diphosphonic acid not only realizes the high dispersion of active metal ions, forms phosphide with more edge active sites, significantly reduces the pour point and freezing point of biodiesel, but also improves the durability of the transition metal phosphide catalyst, and further improves the low-temperature flowability and durability of the transition metal phosphide catalyst in biodiesel; 2. In the preparation process of the transition metal phosphide catalyst, a functional additive composed of titanium oxide, zirconium oxide and cerium oxide is used, and through the synergistic compounding of titanium oxide, zirconium oxide and cerium oxide, the low-temperature flowability and durability of the transition metal phosphide catalyst in biodiesel are further improved. DETAILED DESCRIPTION

[0026] The application will be further described in detail below in combination with preparation examples, examples and comparative examples.

[0027] The raw materials used in the preparation examples, examples and comparative examples of the present application are commercially available, except for special instructions.

[0028] The carrier is a nano-sized ZSM-5 carrier class molecular sieve purchased from Mingguang Feizhou New Material Co., Ltd., spherical, and the model is XH-5.

[0029] The active metal-containing solution is a Ni(NO3)2 solution.

[0030] Example 1 A preparation method of a transition metal phosphide catalyst, comprising the following steps: (1) carrier pretreatment: taking the carrier and immersing it in an alkali solution for treatment; (2) active metal loading: immersing the pretreated carrier obtained in step (1) in an active metal-containing solution, while adding hydroxyethylidene diphosphonic acid; (3) phosphating treatment: carrying out phosphating on the carrier with loaded active metal in step (2) under an inert atmosphere to obtain a transition metal phosphide catalyst.

[0031] Note: In step (1), the alkali solution is a 0.55 mol / L NaOH solution, the treatment temperature is 75°C, and the treatment time is 2h. In step (2), the addition amount of hydroxyethylidene diphosphonic acid is 5% of the weight of the carrier; the temperature for immersion treatment is 60°C, and the time is 2.25h; the active metal used is Ni, and the loading amount of the active metal is 17.5% of the weight of the carrier. In step (3), phosphating is carried out under an inert atmosphere at a temperature of 3.5°C / min to 500°C for 3h.

[0032] Example 2 A preparation method of a transition metal phosphide catalyst, which is different from example 1 in that the alkali solution is a 0.3 mol / L NaOH solution, the treatment temperature is 90°C, and the treatment time is 1h.

[0033] Example 3 A preparation method of a transition metal phosphide catalyst, which is different from example 1 in that the alkali solution is a 0.8 mol / L NaOH solution, the treatment temperature is 60°C, and the treatment time is 3h.

[0034] Example 4 A preparation method of a transition metal phosphide catalyst, which is different from example 1 in that the alkali solution in step (1) is replaced by 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.

[0035] Example 5 A preparation method of a transition metal phosphide catalyst, different from example 1 is that the alkaline solution in step (1) is replaced by an acid solution, the acid solution is a hydrochloric acid solution with pH of 4, the treatment temperature is 90℃, and the treatment time is 1h.

[0036] Example 6 A preparation method of a transition metal phosphide catalyst, different from example 1 is that the alkaline solution in step (1) is replaced by an acid solution, the acid solution is a hydrochloric acid solution with pH of 2, the treatment temperature is 60℃, and the treatment time is 3h.

[0037] Example 7 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (2), the addition amount of hydroxyethylidene diphosphonic acid is 3% of the weight of the carrier.

[0038] Example 8 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (2), the addition amount of hydroxyethylidene diphosphonic acid is 7% of the weight of the carrier.

[0039] Example 9 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (2), the temperature of the impregnation treatment is 50℃, and the time is 3h.

[0040] Example 10 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (2), the temperature of the impregnation treatment is 70℃, and the time is 1.5h.

[0041] Example 11 A preparation method of a transition metal phosphide catalyst, different from example 1 is that the loading amount of active metal is 10% of the weight of the carrier.

[0042] Example 12 A preparation method of a transition metal phosphide catalyst, different from example 1 is that the loading amount of active metal is 25% of the weight of the carrier.

[0043] Example 13 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (3), phosphorization is carried out under an inert atmosphere at a temperature of 600℃ with a temperature increase of 2℃ / min for 2h.

[0044] Example 14 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (3), phosphorization is carried out under inert atmosphere at 5℃ / min to 400℃ for 4h.

[0045] Example 15 A preparation method of a transition metal phosphide catalyst, different from example 1 is that in step (2), a functional additive is further added, which is 4% 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 5:3:2, and the particle size of the functional additive is 30nm.

[0046] Example 16 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the addition amount of the functional additive is 3% of the weight of the carrier.

[0047] Example 17 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the addition amount of the functional additive is 5% of the weight of the carrier.

[0048] Example 18 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the functional additive is composed of titanium oxide, zirconium oxide and cerium oxide in a weight ratio of 2:1.4:1.

[0049] Example 19 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the functional additive is composed of titanium oxide, zirconium oxide and cerium oxide in a weight ratio of 3:1.6:1.

[0050] Example 20 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the particle size of the functional additive is 10nm.

[0051] Example 21 A preparation method of a transition metal phosphide catalyst, different from example 15 is that the particle size of the functional additive is 50nm.

[0052] Example 22 A preparation method of a transition metal phosphide catalyst, different from example 15 is that titanium oxide and cerium oxide in the functional additive are not added.

[0053] Example 23 A preparation method of a transition metal phosphide catalyst, different from example 15 is that zirconium oxide and cerium oxide in the functional additive are not added.

[0054] Example 24 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 15 in that titanium oxide and zirconium oxide in the functional additive are not added.

[0055] Example 25 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 15 in that titanium oxide in the functional additive is not added.

[0056] Example 26 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 15 in that zirconium oxide in the functional additive is not added.

[0057] Example 27 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 15 in that cerium oxide in the functional additive is not added.

[0058] Comparative Example 1 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 1 in that hydroxyethylidene diphosphonic acid is replaced by diammonium hydrogen phosphate.

[0059] Comparative Example 2 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 1 in that hydroxyethylidene diphosphonic acid is replaced by sodium hypophosphite.

[0060] Comparative Example 3 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 1 in that the carrier pretreatment is not performed.

[0061] Comparative Example 4 A preparation method of a transition metal phosphide catalyst, which is different from that of Example 15 in that hydroxyethylidene diphosphonic acid is replaced by diammonium hydrogen phosphate.

[0062] Performance detection test Test samples: The transition metal phosphide catalysts prepared by the preparation methods of the transition metal phosphide catalysts in Examples 1-27 were used as test samples 1-27, and the transition metal phosphide catalysts prepared by the preparation methods of the transition metal phosphide catalysts in Comparative Examples 1-4 were used as control samples 1-4.

[0063] Test method: The transition metal phosphide catalysts were tested for application, and the reaction conditions were adjusted as follows: Biodiesel refers to fatty acid methyl or ethyl ester formed by ester conversion of vegetable oil (such as rapeseed oil, soybean oil, peanut oil, corn oil, cottonseed oil, etc.), animal oil (such as fish oil, lard, tallow, mutton oil, etc.), waste oil or microbial oil with methanol or ethanol.

[0064] The raw material oil was waste cooking oil (acid value 5.6 mgKOH / g, water content 2000 ppm, oxygen content 8.5 wt%).

[0065] The mass ratio of catalyst to raw material oil was 1:120.

[0066] The reaction conditions were temperature 320℃, pressure 4.5 MPa, hydrogen to oil ratio 800:1, and space velocity 2 h⁻¹.

[0067] (1) Low-temperature flowability test (ASTM D97 / D5950): Take 30-40 mL of oil sample, filter to remove impurities using a 0.45 μm filter membrane, avoid interference of wax crystal heterogeneous nucleation; preheat the sample to 45℃ water bath for 10 min to eliminate thermal history; cool at a rate of 1℃ / min, tilt the test tube by 45° to observe the flowability every 2℃, and record the highest temperature when there is no flow for 3 consecutive times as the freezing point; under the same cooling conditions, tilt the test tube by 45° every 3℃, and record the temperature when the liquid surface stops moving as the pour point.

[0068] (2) Durability test (500h continuous operation): Take 5g of representative catalyst sample, crush to 20-40 mesh (particle size 0.5-1mm), and dry at 105℃ for 4h to remove moisture.

[0069] Use a specific surface area instrument (BET method) to determine the initial specific surface area.

[0070] Stage 1 (0-100h): run at 250℃ to evaluate the initial activity (conversion rate A0); Stage 2 (100-300h): gradually increase the temperature to 500℃, and sample every 50h to detect activity decay; Stage 3 (300-500h): maintain 500℃ high pressure (5MPa) to simulate extreme working conditions; After the above stages 1-3, test the activity retention rate (%) and specific surface area loss (%).

[0071] After testing the test samples 1-27 and the control sample 1-4, record the test results in Table 1.

[0072] Table 1 Test results of test samples 1-27 and control sample 1-4 Sample Pour point depression (°C) Pour point depression (°C) Activity retention (%) 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 It can be seen from the combination of Example 1 and Comparative Examples 1-3 and Table 1 that, in the preparation of the transition metal phosphide catalyst, the application of hydroxyethylidene diphosphonic acid can improve the performance of the transition metal phosphide catalyst in the reduction of the freezing point (℃), the reduction of the pour point (℃), the activity retention rate (%) and the specific surface area loss (%) compared with the application of traditional diammonium hydrogen phosphate and sodium hypophosphite, which can improve the low-temperature fluidity and durability of the transition metal phosphide catalyst. At the same time, if the carrier is not pretreated, it is found that the transition metal phosphide catalyst prepared by applying hydroxyethylidene diphosphonic acid will have the above performance loss.

[0073] It can be seen from the combination of Example 1 and Examples 15-21 and Table 1 that, in the preparation of the transition metal phosphide catalyst, the use of the functional additive composed of titanium oxide, zirconium oxide and cerium oxide can further improve the low-temperature fluidity and durability of the transition metal phosphide catalyst, and the freezing point reduction (℃), pour point reduction (℃), activity retention rate (%) and specific surface area loss (%) obtained by the above tests are all obviously improved. In combination with Examples 22-27 and Table 1, it can be seen that if only one or two of titanium oxide, zirconium oxide and cerium oxide are selected for addition, the corresponding improvement effect is limited, and the effect is only a simple superposition of each other. Only when the three are used in combination, can the significant synergistic effect of 1+1>2 be achieved. In combination with Comparative Examples 1 and 4 and Table 1, it can be seen that, in the preparation of the transition metal phosphide catalyst, if hydroxyethylidene diphosphonic acid is replaced by diammonium hydrogen phosphate, it is found that the corresponding effect of the functional additive will be significantly lost, which shows that the functional additive and hydroxyethylidene diphosphonic acid can exhibit a certain synergistic effect in application, so that the transition metal phosphide catalyst can perform better in the improvement of the low-temperature fluidity and durability of the biodiesel.

[0074] This specific embodiment is only an explanation of the application, and is not a limitation of the application. Those skilled in the art can make modifications to this embodiment without creative contribution after reading this specification, but as long as it is within the scope of the claims of the application, it is protected by the Patent Law.

Claims

1. A method for preparing a transition metal phosphide catalyst, characterized in that: The following steps are involved: (1) Carrier pretreatment: The carrier is immersed in an alkaline solution or an acid solution; (2) Active metal loading: the pretreated support obtained in step (1) is immersed in a solution containing active metals, and hydroxyethylene diphosphonic acid is added; (3) Phosphating treatment: Phosphating the carrier loaded with active metal in step (2) under an inert atmosphere to obtain a transition metal phosphide catalyst; In step (2), a functional auxiliary agent is added in an amount of 3-5% by weight of the carrier, wherein the functional auxiliary agent 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 a transition metal phosphide catalyst according to claim 1, wherein: In step (2), the amount of hydroxyethylene diphosphonic acid added is 3-7% of the weight of the carrier.

3. The method for preparing a transition metal phosphide catalyst according to claim 1, wherein: In step (2), the immersion temperature is 50-70°C and the time is 1.5-3 hours.

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

2.

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

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

7. The method for preparing a transition metal phosphide catalyst according to claim 1, wherein: 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°C, and the treatment time is 1-3 hours.

8. The method for preparing a transition metal phosphide catalyst according to claim 1, wherein: In step (3), the temperature is raised to 400-600°C at 2-5°C / min under an inert atmosphere for phosphating for 2-4 hours.

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