A bifunctional catalyst, its preparation method and use

Abstract

Disclosed is a bifunctional catalyst in which metal atoms are anchored to a molecular sieve containing acid sites via N atoms. Also disclosed are a method for preparing the bifunctional catalyst and the use of the bifunctional catalyst in catalyzing the hydroisomerization of long-chain n-alkanes.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to a bifunctional catalyst, its preparation method, and its uses. Background Technology

[0002] With the continuous growth in the consumption of fossil fuels such as gasoline, kerosene, and diesel, and the increasing demand for petroleum-based lubricating oils from industries such as machinery and aerospace, the performance defects of oils produced by traditional processes are becoming increasingly significant due to compositional limitations. For example, the high olefin and benzene content in FCC gasoline products leads to high PM2.5 combustion emissions; the excessively high n-alkanes content in kerosene and diesel products limits their low-temperature performance; and lubricating oils produced by the "old three-stage" processes struggle to meet the high viscosity index requirements of API Group II and III. To achieve oil quality upgrades, hydroisomerization processes have been widely applied in new processes for these products. Hydroisomerization reactions mainly rely on the performance of hydroisomerization bifunctional catalysts, which generally contain metal sites with addition / dehydrogenation activity and acidic sites with carbon skeleton isomerization activity. For metal sites, noble metals are widely used due to their stronger addition / dehydrogenation activity. For supports, molecular sieve supports not only possess Brønsted acid sites and a large specific surface area, but their specific pore structure also allows for molecular shape selection of reactants, intermediates, and final products during catalysis, thus serving as supports for bifunctional catalysts. In the hydroisomerization of long-chain alkanes, the main side reaction is cracking. As the degree of molecular isomerization increases, the cracking rate also gradually increases. Therefore, effectively avoiding cracking caused by excessive isomerization and improving the selectivity of isomer products is a major challenge currently faced.

[0003] In existing technologies, to improve the isomer selectivity of bifunctional catalysts, Fuel 349(2023)128703 reported the preparation of a ZSM-48 molecular sieve and Al2O3 composite support. By controlling the metal placement (ZSM-48 molecular sieve / Al2O3), the distance between the metal site and the acid site was controllably regulated. Studies have shown that when the metal and acid sites have nanoscale intimacy, the catalyst exhibits better isomer yield and isomer selectivity. Molecular Catalysis 559(2024)114108 reported the preparation of a Pt catalyst with lower electron density by loading metal Pt onto C3N4 using a low-temperature loading method, followed by mixing and grinding with SAPO-11 molecular sieve, thus improving the catalyst selectivity. Fuel Processing Technology 256(2024)108076 reported the synthesis of layered molecular sieve nanoparticles with abundant intercrystalline mesopores by adding growth inhibitors to the initial gel of the SAPO-31 molecular sieve synthesis system, which significantly improved the diffusion performance of the intermediate and increased the isomerization yield and selectivity of the catalyst.

[0004] The catalysts prepared by the above methods and techniques all exhibit improved isomer selectivity in hydroisomerization reactions compared to traditional catalyst preparation methods; however, these methods are complex. Therefore, we provide a milder, simpler, and more efficient method than traditional molecular sieve preparation to prepare a bifunctional catalyst, achieving improved isomer selectivity at high conversion rates of long-chain alkanes. This invention is proposed for this purpose. Summary of the Invention

[0005] This invention discloses a bifunctional catalyst. Metal atoms are anchored to a molecular sieve containing acidic sites via nitrogen atoms.

[0006] The technical solution of the present invention is as follows:

[0007] The first aspect of this invention discloses a bifunctional catalyst in which metal atoms are anchored to a molecular sieve containing acidic sites via N atoms.

[0008] Preferably, the metal atoms are anchored to the SiO2 of the molecular sieve via N atoms.

[0009] Preferably, the metal atom is one of Pt, Au, Ru, Rh, Ir, or Pd.

[0010] The second aspect of this invention discloses a method for preparing the bifunctional catalyst, comprising the following steps:

[0011] (1) The ammonia-type molecular sieve is immersed in a metal precursor solution and air-dried naturally to obtain the immersed molecular sieve.

[0012] (2) The molecular sieve obtained in step (1) is calcined at low temperature under N2 atmosphere to obtain the bifunctional catalyst.

[0013] Preferably, if the molecular sieve in step (1) is a sodium molecular sieve without template removal, the template needs to be removed first, and then the sodium molecular sieve is converted into an ammonia molecular sieve. The steps are as follows: (11) Calcine the sodium molecular sieve without template removal at 550-600℃ for 3-5 hours to remove the template; (12) Disperse the sodium molecular sieve with template removal in an aqueous solution of NH4Cl with a concentration of 0.8-1.2 mol / L and a liquid-to-solid ratio of 1:(5-15); reflux at 40-90℃ for 2-6 hours; repeat this step at least three times.

[0014] Preferably, in step (1), the metal precursor is one of Pt, Au, Ru, Rh, Ir or Pd salt solutions, and the amount of the metal precursor is such that the final metal loading is 0.3 to 1 wt% of the molecular sieve.

[0015] Preferably, the roasting temperature in step (2) is 100-500℃ and the time is 2-6h.

[0016] The third aspect of this invention discloses the use of the bifunctional catalyst in catalyzing the hydroisomerization reaction of long-chain n-alkanes.

[0017] The beneficial effects of this invention are:

[0018] The bifunctional catalyst of this invention maintains the same pore structure, with metal atoms anchored to SiO2 containing acidic sites via nitrogen atoms, thus achieving in-situ construction of a metal-N coordination environment. This bifunctional catalyst is used to catalyze the hydroisomerization reaction of long-chain n-alkanes, improving the isomerization yield and selectivity.

[0019] The preparation method of the bifunctional catalyst of this invention uses the ammonium ions carried by the ammonia-type molecular sieve itself as the nitrogen source, and combines calcination in a nitrogen atmosphere to protect the nitrogen source and the metal state, anchoring the metal to SiO2 through N; the preparation process is simple and does not introduce other substances, and the pore structure remains unchanged. Currently, most commercial molecular sieves are sodium-type molecular sieves without template removal. For the preparation of the bifunctional catalyst of this invention, the template must be removed first, and then the sodium-type molecular sieve must be converted into an ammonia-type molecular sieve before it can be used. Attached Figure Description

[0020] Figure 1 XPS plots of the catalysts obtained in the examples and comparative examples. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be noted that the examples described below are only used to illustrate and explain the present invention in detail, and the application scope of the present invention is not limited by the conditions in the examples.

[0022] Example 1: Preparation of bifunctional molecular sieves; calcination at 300°C for 4 hours under N2 atmosphere.

[0023] (1) Commercially available Na-type molecular sieve ZSM-48 (without template agent) was dispersed in a 1 mol / L NH4Cl aqueous solution with a liquid-to-solid ratio of 1:10 to obtain molecular sieve powder; after reflux at 60℃ for 4 h, it was dried in an oven at 120℃.

[0024] The above process is repeated three times to ensure NH4 + Completely convert Na + After the exchange process, the sample is washed 2-3 times with deionized water to obtain an ammonia-type molecular sieve.

[0025] (2) Using the equal volume impregnation method, the ammonia-type molecular sieve obtained in step (1) is impregnated in 0.5wt% Pt(NH3)4(NO3)2 solution and air-dried naturally to obtain the impregnated molecular sieve.

[0026] (3) The molecular sieve obtained in step (2) is calcined at 300°C for 4 hours under N2 atmosphere to obtain the bifunctional catalyst.

[0027] Example 2: Same as Example 1, except that step (3) is to calcine at 100°C for 4 hours under N2 atmosphere.

[0028] Example 3: Same as Example 1, except that step (3) is to calcine at 500°C for 4 hours under N2 atmosphere.

[0029] Comparative Example 1: Same as Example 1, except that step (3) is to calcine at 300°C for 4 hours under an Ar atmosphere.

[0030] Comparative Example 2: Same as Example 1, except that step (3) is to calcine at 300°C for 4 hours in an air atmosphere.

[0031] Comparative Example 3: Same as Comparative Example 1, except that: in step (1), the ammonia-type molecular sieve was calcined at 550°C for 4 hours to convert the molecular sieve into the hydrogen type; then in step (3), it was calcined at 300°C for 4 hours in an air atmosphere.

[0032] Figure 1 XPS plots of the catalysts obtained in Examples 1-3 and Comparative Examples 1-3. Figure 1 It can be seen that the catalysts obtained in Examples 1-3 have N-containing structures, including Pt-N and N-SiO2 structures; while the catalysts obtained in Comparative Examples 1-3 do not have N-containing structures.

[0033] Example 4: Hydrogenation isomerization of n-hexadecane.

[0034] The catalysts obtained in Examples 1-3 and Comparative Examples 1-3 were applied to the hydroisomerization reaction of n-hexadecane. The catalysts were packed in a micro-fixed-bed reactor, with both ends filled with silicon carbide. The hydroisomerization reaction conditions were: pressure 3 MPa, space velocity 2 h⁻¹. -1 The hydrogen-to-oil ratio is 1000, and the temperature is 310℃.

[0035] The conversion, isomerization yield, and isomerization selectivity of the catalysts in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0036] Table 1 Comparison of Catalytic Performance Results of Catalysts

[0037] Example 1 92.14 7.26 84.87 92.12 Example 2 86.19 5.38 80.81 93.76 Example 3 99.27 49.01 50.26 50.63 Comparative Example 1 98.62 55.08 43.54 44.15 Comparative Example 2 98.01 55.74 42.27 43.14 Comparative Example 3 99.65 82.69 16.76 16.82

[0038]

Note

[0039] As shown in Table 1, the catalyst conversion rates of Comparative Examples 1-3 and Examples 1-3 are all higher than 85%. At higher conversion rates, Examples 1 and Comparative Example 2 show a 42.60% increase in isomer yield (i.e., "C16 / wt%)" [84.87% - 42.27% = 42.60%], a decrease in cracking rate (i.e., "≤C15 / wt%)", with a maximum reduction of 48.48% [55.74% - 7.26% = 48.48%], and an increase in isomer selectivity of 48.98% [92.12% - 43.14% = 48.98%]. Compared to Comparative Examples 1-3, the N2 atmosphere and NH4 on the molecular sieve support during the catalyst preparation process of the Examples are different. + When both are present, the catalyst exhibits good isomerization yield and selectivity. A comparison of Example 3 with Examples 1 and 2 shows that increasing calcination temperature affects the catalyst's catalytic effect, possibly due to metal agglomeration at high temperatures. Comparative Example 1 and Comparative Example 2 show similar results, indicating that calcination effects under Ar and air atmospheres are essentially the same, but Ar atmosphere is slightly better, though both are superior to Comparative Example 3; this indicates that NH4... + While calcination under an N2 atmosphere plays a role in the preparation of such bifunctional catalysts, it is more crucial to ensure its effectiveness. Therefore, the presence of NH4 on the molecular sieve support is essential for the preparation of bifunctional catalysts with higher isomerization yields and selectivity. + Furthermore, it is calcined under a N2 atmosphere, with the calcination temperature controlled between 100 and 500°C.

[0040] The above description is only used to detail the specific embodiments of the present invention, but the technical solutions proposed by the present invention are not limited to the above methods. All equivalent modifications and variations made by those skilled in the art to the technology proposed by the present invention without departing from the basic principles of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A bifunctional catalyst for catalyzing the hydroisomerization reaction of long-chain n-alkanes, characterized in that, Its metal atoms are anchored to the molecular sieve containing acidic sites via N atoms; the metal atoms are anchored to the SiO2 of the molecular sieve via N atoms; The preparation method of the bifunctional catalyst includes the following steps: (1) using the equal volume impregnation method, the ammonia-type molecular sieve is impregnated in 0.5wt% Pt(NH3)4(NO3)2 solution and air-dried naturally to obtain the impregnated molecular sieve; (2) the impregnated molecular sieve is calcined at 300℃ for 4h under N2 atmosphere to obtain the bifunctional catalyst.

2. The bifunctional catalyst according to claim 1, characterized in that, If the molecular sieve in step (1) is a sodium molecular sieve without template removal, the template needs to be removed first, and then the sodium molecular sieve is converted into an ammonia molecular sieve. The steps are as follows: (11) Calcine the sodium molecular sieve without template removal at 550-600℃ for 3-5 h to remove the template; (12) Disperse the sodium molecular sieve with template removal in an aqueous solution of NH4Cl with a concentration of 1 mol / L and a liquid-to-solid ratio of 1:10; reflux at 60℃ for 4 h; repeat this step three times.

3. Use of the bifunctional catalyst according to any one of claims 1-2 in the catalytic hydroisomerization reaction of long-chain n-alkanes.

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