A Ni2P / SAPO-11 catalyst, its preparation method and application

Abstract

This invention belongs to the field of catalytic chemical technology and discloses a method for preparing a Ni2P / SAPO-11 catalyst and its application. Ni(NO3)2·6H2O and (NH4)2HPO4 are dissolved in deionized water to obtain a mixed solution A. Citric acid is dissolved in mixed solution A and ultrasonically treated until completely dissolved to obtain an impregnation solution B. Impregnation solution B is added dropwise to a SAPO-11 support, and after aging, drying, and calcination, a catalyst precursor is obtained. The precursor is reduced under a hydrogen atmosphere to prepare the active phase, thus obtaining a CA-modified CA(x)-Ni2P / SAPO-11 catalyst, where x is the CA / Ni molar ratio. This invention, by regulating the metal-acid active center balance with citric acid, promotes the synergistic effect of bifunctional active centers, significantly improving the catalyst's ability to simultaneously perform hydrodesulfurization and hydroxyl skeletal isomerization. This invention provides a new method for preparing bifunctional catalysts with deep desulfurization and olefin skeletal isomerization activities.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemical technology, and relates to a method for preparing Ni2P / SAPO-11 catalyst and its application. Background Technology

[0002] With increasing environmental pressure from fossil fuels, producing ultra-low sulfur clean gasoline has become a crucial task for the refining industry. Catalytic cracking gasoline contains a large amount of olefins and sulfides, which are prone to hydrogenation saturation during hydrodesulfurization, leading to a decrease in octane number. Therefore, developing bifunctional catalysts with deep desulfurization and olefin skeletal isomerization activity is of great significance for maintaining gasoline octane number while performing desulfurization.

[0003] Transition metal phosphides, such as nickel phosphide (Ni2P), are considered potential candidates for hydrogenation catalysts due to their noble metal-like electronic structure and excellent hydrodesulfurization activity. SAPO-11 molecular sieves, with their unique ten-membered ring one-dimensional channels and moderate acidity, are excellent supports for olefin skeletal isomerization, and the high specific surface area of ​​SAPO-11 facilitates the preparation of highly dispersed Ni2P active components. The Ni2P / SAPO-11 bifunctional catalyst shows promising application prospects in the coupled reaction of thiophene hydrodesulfurization and 1-hexene hydroisomerization.

[0004] However, Ni2P / SAPO-11 catalysts prepared by traditional methods suffer from difficulties in achieving efficient matching between acidity and metal active sites, resulting in weak metal-acid synergy and hindering the efficient and coordinated desulfurization and isomerization reactions. In this system, by adjusting the molar ratio of citric acid to nickel (CA / Ni), the interaction between nickel and phosphorus species in the precursor is enhanced while the acidity characteristics of the SAPO-11 molecular sieve are mildly modulated, optimizing the matching degree between the acid sites and metal active sites. This leads to overall optimization of the metal-acid balance of the supported bifunctional catalyst, thereby affecting the catalyst's hydrodesulfurization activity and olefin hydroisomerization selectivity. Currently, there are no reports on the application of citric acid in regulating the performance of Ni2P / SAPO-11 catalysts and their coupling reaction of thiophene hydrodesulfurization and 1-hexene hydroisomerization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a Ni2P / SAPO-11 catalyst. This invention improves the hydrodesulfurization activity and olefin hydroisomerization selectivity of the catalyst by leveraging the synergistic effect of citric acid in regulating the metal-acid balance and the bifunctional active center. By optimizing the molar ratio of citric acid to nickel, a high-performance catalyst exhibiting both excellent desulfurization activity and isomerization selectivity can be obtained.

[0006] The technical solution of the present invention: A Ni2P / SAPO-11 catalyst, using SAPO-11 molecular sieve as a support, with Ni2P dispersed on the support surface and a Ni2P loading of 5 wt.%.

[0007] A method for preparing a Ni2P / SAPO-11 catalyst, comprising the following steps: S1. Dissolve Ni(NO3)2·6H2O and (NH4)2HPO4 in deionized water to obtain mixed solution A; dissolve citric acid (CA) in mixed solution A and sonicate until completely dissolved to obtain impregnation solution B; add impregnation solution B dropwise onto SAPO-11 molecular sieve, and obtain catalyst precursor by aging, drying and calcination; S2. The active phase is prepared by reducing the catalyst precursor under a hydrogen atmosphere to obtain a CA-modified Ni2P / SAPO-11 catalyst, denoted as CA(x)-Ni2P / SAPO-11 catalyst, where x is the molar ratio of CA to Ni.

[0008] In step S1, the molar ratio of Ni(NO3)2·6H2O to (NH4)2HPO4 is 1:1.

[0009] In step S1, citric acid is added to disperse Ni2P on the support surface. The molar amount of citric acid is 0.1-0.5 times that of metallic Ni, that is, the molar ratio x of CA to Ni is 0.1-0.5.

[0010] In step S1, the aging conditions are: standing at room temperature for 12 hours.

[0011] In step S1, the drying conditions are: drying at 120 °C for 12 h.

[0012] In step S1, the calcination conditions are: calcination temperature 500 ℃, calcination time 3 h.

[0013] In step S2, the reduction conditions are: reduction temperature of 400-550 ℃ and reduction time of 2 h.

[0014] The application of a Ni2P / SAPO-11 catalyst in hydrodesulfurization and skeletal isomerization reaction is as follows: CA(x)-Ni2P / SAPO-11 catalyst is added to a heptane solution containing 10 wt.% 1-hexene and 0.1 wt.% thiophene, and the reaction is carried out at a temperature of 300-340 °C, a pressure of 1.5 MPa, and a hydrogen-to-oil ratio of 750.

[0015] The beneficial effects of this invention are: 1. Traditional Ni2P catalysts suffer from excessively large Ni2P particle size during preparation, which affects catalytic performance. This invention introduces citric acid as a complexing agent to enhance the interaction between nickel and phosphorus species in the precursor, which is beneficial for obtaining Ni2P active components with smaller particle size and more uniform dispersion.

[0016] 2. Existing research on citric acid-modified nickel phosphide catalysts mainly focuses on supports such as SBA-15 or unsupported systems, and has not yet addressed the regulation of metal-acid balance in SAPO-11 molecular sieve supported systems. This invention optimizes the surface properties of Ni2P and SAPO-11 by adjusting the molar ratio of citric acid to nickel, thereby modifying the ratio and synergistic efficiency of the metal active centers and SAPO-11 acidic centers. This allows the catalyst to significantly improve thiophene desulfurization activity and 1-hexene conversion activity while maintaining high skeletal isomer selectivity.

[0017] 3. The preparation method of this invention is simple, requiring only the introduction of CA and optimization of its dosage in the conventional impregnation step, without the need for additional equipment or complex operations, making it easy for industrial production. This invention provides a new modification strategy for optimizing the performance of bifunctional catalysts, which is of great significance to the development of clean gasoline production technology. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the CA(x)-Ni2P / SAPO-11 catalyst in Example 1 (n=0, 0.1, 0.2, 0.3, 0.4, 0.5).

[0019] Figure 2 The following are TEM images of the CA(0.3)-Ni2P / SAPO-11 catalyst in Example 1: (a) low-magnification TEM image; (b) high-resolution TEM (HRTEM) image.

[0020] Figure 3 The following are the NH3-TPD curves of the CA(x)-Ni2P / SAPO-11 catalyst in Example 1: (a) CA(0)-Ni2P / SAPO-11; (b) CA(0.1)-Ni2P / SAPO-11; (c) CA(0.2)-Ni2P / SAPO-11; (d) CA(0.3)-Ni2P / SAPO-11; (e) CA(0.4)-Ni2P / SAPO-11; (f) CA(0.5)-Ni2P / SAPO-11.

[0021] Figure 4 These are TEM images of the CA(0)-Ni2P / SAPO-11 catalyst in Example 2: (a) low-magnification TEM image; (b) high-resolution TEM (HRTEM) image. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0023] Example 1 Prepare CA(x)-Ni2P / SAPO-11 catalyst.

[0024] (1) Precursor preparation: 0.2105 g Ni(NO3)2·6H2O and 0.0937 g (NH4)2HPO4 were weighed according to a Ni / P molar ratio of 1:1, dissolved in a certain amount of deionized water and mixed. A certain amount of CA was added to the above mixture and sonicated until completely dissolved. The mixture was then uniformly added dropwise onto SAPO-11. The mixture was aged at room temperature for 12 h, dried at 120 ℃ in a drying oven for 12 h, and calcined at 500 ℃ in a muffle furnace for 3 h to obtain the CA(x)-Ni2P / SAPO-11 catalyst precursor, where x is the CA / Ni molar ratio.

[0025] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 100 mL / min, the catalyst was reduced from room temperature at a rate of 10 °C·min. -1 Raise to 400 °C, then increase by 1 °C·min -1 The temperature was raised to 550 °C and held for 2 h. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as CA(x)-Ni2P / SAPO-11 (x is the molar ratio of CA / Ni added).

[0026] The synthesized catalysts were CA(0.1)-Ni2P / SAPO-11, CA(0.2)-Ni2P / SAPO-11, CA(0.3)-Ni2P / SAPO-11, CA(0.4)-Ni2P / SAPO-11, and CA(0.5)-Ni2P / SAPO-11, respectively. XRD patterns are shown below. Figure 1 It can be observed that the characteristic diffraction peaks belonging to SAPO-11 remain unchanged, indicating that the addition of citric acid as an auxiliary agent during the preparation process does not affect the structure of SAPO-11. When the amount of CA added is CA / Ni ≤ 0.2, characteristic diffraction peaks of Ni2P appear, indicating that the Ni2P particles are larger or have higher crystallinity at this time; when the amount of CA added is CA / Ni>0.2, no characteristic diffraction peaks belonging to Ni2P are observed, which may be because the Ni2P formed at this time has a high degree of dispersion, exceeding the detection limit of the instrument. Combined with the TEM image of CA(0.3)-Ni2P / SAPO-11 ( Figure 2 The small size and uniform dispersion of Ni2P particles confirm the above inference. The observation of Ni2P lattice fringes proves that Ni2P was successfully synthesized.

[0027] Table 1 Texture parameters of CA(x)-Ni2P / SAPO-11 catalyst

[0028] As shown in Table 1, the introduction of citric acid effectively modulates the pore structure and specific surface area of ​​the catalyst. Compared with the unmodified catalyst, the CA(x)-Ni2P / SAPO-11 sample has a larger specific surface area and pore volume, providing favorable physical conditions for reactant diffusion and active site exposure. The NH3-TPD curves are shown in Table 1. Figure 3 Both exhibited two desorption peaks at 150-250℃ and 300-400℃, corresponding to the weak acid and moderately strong acid centers, respectively. With increasing CA / Ni ratio, the amounts of weak acid, moderately strong acid, and total acid increased, while the acidity of the weak acid and moderately strong acid decreased. The introduction of citric acid not only promoted the high dispersion of Ni₂P but also optimized the distribution of acidic sites on the catalyst surface by influencing the interaction between Ni species and the SAPO-11 support, thereby achieving a synergistic matching between metal sites and acid sites.

[0029] Application Example 1 The reaction performance of the CA(x)-Ni2P / SAPO-11 catalyst in Example 1 above was evaluated.

[0030] Reaction Procedure: The catalyst was loaded into the isothermal zone of a fixed-bed reactor, the apparatus was sealed and leak-tested, and the performance of the in-situ reduced catalyst was evaluated under the reaction conditions. The reactant conversion and product selectivity were investigated. The obtained products were analyzed in an Aglient 6890 N-type gas chromatograph using a commercially available HP-Innowax capillary column and a flame ionization detector.

[0031] Reaction conditions: catalyst loading mass 0.2 g, reaction temperature 300 ℃, reaction weight hourly space velocity 26 h⁻¹ -1 The reaction pressure was 1.5 MPa, the hydrogen-to-oil ratio was 750, and a solution of 10 wt.% 1-hexene and 0.1 wt.% thiophene in n-heptane was pumped in.

[0032] Table 2 Experimental results of CA(x)-Ni2P / SAPO-11 catalyst under different CA / Ni ratios.

[0033] As shown in Table 2, within the CA / Ni ratio range of 0.1-0.5, the selectivity of the skeletal isomers of the CA(x)-Ni2P / SAPO-11 catalyst is greater than 90%, maintaining high skeletal isomer activity. With increasing CA / Ni ratio, the conversion of thiophene gradually increases, reaching a maximum of 73.8% at a CA / Ni molar ratio of 0.3, and then gradually decreases with further increases in CA / Ni. The metal-to-medium-strong acid center ratio (M / A) results for each catalyst are shown in Table 3.

[0034] Table 3 shows that the ratio of metallic to moderately strong acid content in the catalyst changes with the CA / Ni molar ratio. When CA / Ni = 0, the M / A value is 7.00, indicating an imbalance between the ratio of active metal centers and acidic centers, making it difficult to achieve efficient synergy. When CA / Ni = 0.3, the M / A value is 4.88, achieving the optimal match between active metal centers and moderately strong acid centers. Under these conditions, the catalyst achieves a maximum thiophene desulfurization conversion rate of 73.8% while maintaining over 90% skeletal isomer selectivity. When CA / Ni continues to increase to 0.4-0.5, the M / A ratio recovers somewhat but deviates from the optimal range, disrupting the metal-acid balance and causing a decline in catalytic performance. These results fully demonstrate that CA / Ni = 0.3 is the optimal ratio for regulating the metal-acid balance of the catalyst and is also an important condition for achieving synergistic effects of desulfurization and isomerization.

[0035] Application Example 2 The reaction performance of the CA(0.3)-Ni2P / SAPO-11 catalyst in Example 1 above was evaluated at different temperatures.

[0036] Reaction conditions: catalyst loading mass 0.2 g, reaction temperature 280-340 ℃, reaction weight hourly space velocity 26 h⁻¹ -1 The reaction pressure was 1.5 MPa, the hydrogen-to-oil ratio was 750, and a solution of 10 wt.% 1-hexene and 0.1 wt.% thiophene in n-heptane was pumped in.

[0037] The reaction results are shown in Table 4.

[0038] Table 4. Experimental results of CA(0.3)-Ni2P / SAPO-11 at different reaction temperatures.

[0039] Table 4 shows that the reaction temperature (280-340 ℃) significantly affects the hydrodesulfurization of thiophene and the hydroisomerization properties of 1-hexene. As the reaction temperature increases from 280 ℃ to 340 ℃, the thiophene conversion rate increases from 50% to 100%, while the selectivity for isomers decreases from 95.5% to 85.1%. This is because excessively high reaction temperatures lead to over-hydrogenation of 1-hexene, generating byproducts such as n-hexane and cracking products.

[0040] Comparative Example 1 Prepare CA(0)-Ni2P / SAPO-11 catalyst.

[0041] (1) Precursor preparation: 0.2105 g Ni(NO3)2·6H2O and 0.0937 g (NH4)2HPO4 were weighed according to a Ni / P molar ratio of 1:1, dissolved in a certain amount of deionized water and mixed, and then uniformly added dropwise onto SAPO-11. The mixture was aged at room temperature for 12 h, dried at 120 ℃ in a drying oven for 12 h, and calcined at 500 ℃ in a muffle furnace for 3 h to obtain the CA(0)-Ni2P / SAPO-11 catalyst precursor.

[0042] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 100 mL / min, the catalyst was reduced from room temperature at a rate of 10 °C·min. -1 Raise to 400 °C, then increase by 1 °C·min -1 The temperature was raised to 550 °C and held for 2 h. After the process was completed, the temperature was lowered to room temperature. The resulting catalyst was designated Ni2P / SAPO-11.

[0043] The XRD pattern of the synthesized catalyst CA(0)-Ni2P / SAPO-11 is shown in the figure. Figure 1 Characteristic diffraction peaks attributable to SAPO-11 and Ni2P can be observed. See TEM image. Figure 4 The Ni₂P particles were large in size and unevenly distributed, with obvious agglomeration observed in some areas. The observation of Ni₂P lattice fringes confirms the successful synthesis of Ni₂P.

[0044] Comparative Application Example 1 The reaction performance of the CA(0)-Ni2P / SAPO-11 catalyst in Example 1 above was evaluated at different temperatures.

[0045] Reaction conditions: catalyst loading mass 0.2 g, reaction temperature 280-340 ℃, reaction weight hourly space velocity 26 h⁻¹ -1 The reaction pressure was 1.5 MPa, the hydrogen-to-oil ratio was 750, and a solution of 10 wt.% 1-hexene and 0.1 wt.% thiophene in n-heptane was pumped in.

[0046] The reaction results are shown in Table 5.

[0047] Table 5. Experimental results of CA(0)-Ni2P / SAPO-11 at different reaction temperatures.

[0048] As shown in Table 5, compared with the CA(0.3)-Ni2P / SAPO-11 in Example 1, the unmodified catalyst exhibited lower thiophene and 1-hexene conversion rates. Combined with TEM results, the Ni2P particles in the unmodified catalyst were larger, less dispersed, and had fewer exposed active sites, thus resulting in lower catalytic activity. Citric acid modification effectively improved the catalyst's hydrodesulfurization and olefin conversion activities.

[0049] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A Ni2P / SAPO-11 catalyst characterized in that, The Ni2P / SAPO-11 catalyst uses SAPO-11 molecular sieve as a support, with Ni2P dispersed on the support surface and a Ni2P loading of 5 wt.%.

2. A method for preparing a Ni2P / SAPO-11 catalyst, characterized in that, The steps are as follows: S1. Dissolve Ni(NO3)2·6H2O and (NH4)2HPO4 in deionized water to obtain mixed solution A; dissolve citric acid CA in mixed solution A and sonicate until completely dissolved to obtain impregnation solution B; add impregnation solution B dropwise onto SAPO-11 molecular sieve, and obtain catalyst precursor by aging, drying and calcination. S2. The catalyst precursor was reduced under a hydrogen atmosphere to prepare the active phase, and the CA-modified Ni2P / SAPO-11 catalyst was obtained, denoted as CA(x)-Ni2P / SAPO-11 catalyst, where x is the molar ratio of CA to Ni.

3. The preparation method according to claim 2, characterized in that, In step S1, the molar ratio of Ni(NO3)2·6H2O to (NH4)2HPO4 is 1:

1.

4. The preparation method according to claim 2, characterized in that, In step S1, citric acid is added to disperse Ni2P on the support surface. The molar amount of citric acid is 0.1-0.5 times that of metallic Ni, that is, the molar ratio x of CA to Ni is 0.1-0.

5.

5. The preparation method according to claim 2, characterized in that, In step S1, the aging conditions are: standing at room temperature for 12 hours.

6. The preparation method according to claim 2, characterized in that, In step S1, the drying conditions are: drying at 120 °C for 12 h.

7. The preparation method according to claim 2, characterized in that, In step S1, the calcination conditions are: calcination temperature 500 ℃, calcination time 3 h.

8. The preparation method according to claim 2, characterized in that, In step S2, the reduction conditions are: reduction temperature of 400-550 ℃ and reduction time of 2 h.

9. The application of a Ni2P / SAPO-11 catalyst in hydrodesulfurization and skeletal isomerization reactions, characterized in that, The steps are as follows: Add CA(x)-Ni2P / SAPO-11 catalyst to a heptane solution of 10 wt.% 1-hexene and 0.1 wt.% thiophene, and react at a temperature of 300-340 ℃, a pressure of 1.5 MPa, and a hydrogen-to-oil ratio of 750.

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