Bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention discloses a bifunctional catalyst. Metal atoms of the bifunctional catalyst are anchored on a molecular sieve containing acidic sites through N atoms. The invention also discloses a preparation method of the bifunctional catalyst and application of the bifunctional catalyst in catalysis of a hydroisomerization reaction of long-chain n-alkanes.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a bifunctional catalyst, a preparation method and use thereof. Background Art

[0002] With the continuous growth of fossil fuel consumption such as gasoline, kerosene, and diesel, and the increasing demand for petroleum-based lubricant products in industries such as machinery and aerospace, the performance defects of oil products obtained by traditional process routes are becoming more and more obvious due to compositional limitations. For example, the high content of olefins and benzene in FCC gasoline products will cause high PM2.5 combustion emissions, and the excessively high content of normal alkanes in kerosene and diesel products limits the low-temperature performance of the products. Lubricants produced by the "old three sets" process are difficult to meet the high viscosity index requirements of API Class II and Class III. In order to achieve the purpose of upgrading oil quality, the hydroisomerization process is widely used in the new processes of the above products. The hydroisomerization reaction mainly depends on the performance of the hydroisomerization bifunctional catalyst, which generally contains a metal site with addition / dehydrogenation activity and an acid site with carbon skeleton isomerization activity. For metal sites, noble metals are widely used because of their stronger hydrogenation / dehydrogenation activity; for carriers, molecular sieve carriers not only have B acid sites and large specific surface area, but also their specific pore structure can select the molecules of reactants, intermediates and final products during the catalytic process, so they are used as carriers of bifunctional catalysts. In the hydrogen isomerization reaction of long-chain alkanes, the main side reaction is the cracking reaction. As the degree of molecular isomerization increases, the cracking rate also gradually increases. Therefore, how to effectively avoid cracking caused by excessive isomerization and improve the selectivity of isomerized products is a major challenge currently faced.

[0003] In the prior art, in order to improve the isomerization selectivity of bifunctional catalysts, Fuel 349 (2023) 128703 reported the preparation of a ZSM-48 molecular sieve and Al2O3 composite carrier, and achieved controllable regulation of the distance between the metal site and the acid site by regulating the metal placement (ZSM-48 molecular sieve / Al2O3); the study showed that when the metal and the acid site have nano-level intimacy, the catalyst has better isomerization yield and isomerization selectivity. Molecular Catalysis 559 (2024) 114108 reported that metal Pt was loaded on C3N4 by a low-temperature loading method, and then mixed and ground with SAPO-11 molecular sieve to prepare a Pt catalyst with lower electron density, thereby improving the selectivity of the catalyst. Fuel Processing Technology 256(2024)108076 reported that by adding a growth inhibitor to the initial gel of the SAPO-31 molecular sieve synthesis system, layered molecular sieve nanoparticles with rich intercrystalline mesopores were synthesized, which significantly improved the diffusion performance of the intermediates and increased the isomerization yield and selectivity of the catalyst.

[0004] The catalysts prepared by the above methods and technologies have improved the isomerization selectivity of the catalyst in the hydroisomerization reaction compared with the traditional catalyst preparation, but the preparation process of these methods is complicated. Based on this, we provide a method that is milder, simpler and more effective than the traditional molecular sieve preparation process to prepare a bifunctional catalyst, which achieves the improvement of isomerization selectivity at a high conversion rate of long-chain alkanes. For this reason, the present invention is proposed. Summary of the invention

[0005] The invention discloses a bifunctional catalyst. Metal atoms are anchored on a molecular sieve containing acidic sites through N atoms.

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

[0007] The first aspect of the present invention discloses a bifunctional catalyst, wherein the metal atom is anchored on a molecular sieve containing acidic sites via a N atom.

[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 the present invention discloses a method for preparing the bifunctional catalyst, comprising the following steps:

[0011] (1) impregnating the ammonia molecular sieve in a metal precursor solution and drying it naturally in air to obtain an impregnated molecular sieve;

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

[0013] Preferably, if the molecular sieve in step (1) is a sodium-type molecular sieve from which the template agent has not been removed, the template agent needs to be removed first, and then the sodium-type molecular sieve is converted into an ammonia-type molecular sieve, the steps being: (11) calcining the sodium-type molecular sieve from which the template agent has not been removed at 550-600° C. for 3-5 h to remove the template agent; (12) dispersing the sodium-type molecular sieve from which the template agent has been removed in an NH4Cl aqueous solution having a concentration of 0.8-1.2 mol / L, with a liquid-to-solid ratio of 1:(5-15); reflux at 40-90° C. for 2-6 h; and repeating this step at least three times.

[0014] Preferably, the metal precursor in step (1) 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 0.3-1 wt % of the metal in the molecular sieve.

[0015] Preferably, the calcination temperature in step (2) is 100 to 500° C. and the calcination time is 2 to 6 hours.

[0016] The third aspect of the present invention discloses the use of the bifunctional catalyst for catalyzing the hydroisomerization reaction of long-chain normal alkanes.

[0017] Beneficial effects of the present invention:

[0018] The bifunctional catalyst of the present invention has an unchanged pore structure, and the metal atoms are anchored on the SiO2 of the molecular sieve containing acidic sites through N atoms, thereby realizing in-situ construction of a metal-N coordination environment. The bifunctional catalyst of the present invention is used to catalyze the hydroisomerization reaction of long-chain normal alkanes, thereby improving the isomerization yield and isomerization selectivity of the hydroisomerization reaction of alkanes.

[0019] The preparation method of the bifunctional catalyst of the present invention uses the ammonia radical carried by the ammonia molecular sieve itself as a nitrogen source, combines calcination in a nitrogen atmosphere to protect the nitrogen source and the metal state, and anchors the metal on SiO2 through N; the preparation process is simple and does not introduce other substances, and the pore structure does not change. Currently, most commercial molecular sieves are sodium molecular sieves from which the template agent has not been removed. To prepare the bifunctional catalyst of the present invention, the template agent must be removed first, and then the sodium molecular sieve must be converted into an ammonia molecular sieve before use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XPS graphs of the catalysts obtained for the examples and comparative examples. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with specific implementation methods. It should be noted that the following examples 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 sieve; calcination at 300°C for 4h under N2 atmosphere.

[0023] (1) Dispersing commercially available Na-type molecular sieve ZSM-48 (without template agent) in 1 mol / L NH4Cl aqueous solution with a liquid-to-solid ratio of 1:10 to obtain molecular sieve powder; refluxing at 60°C for 4 h, and drying in an oven at 120°C;

[0024] The above process was repeated three times to ensure that NH4 + Completely Na + After exchange, wash with deionized water 2 to 3 times to obtain the ammonia type molecular sieve;

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

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

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

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

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

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

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

[0032] Figure 1 The XPS graphs of the catalysts obtained in Examples 1-3 and Comparative Examples 1-3 are shown in FIG. 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: Hydroisomerization 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 loaded into a micro fixed bed reactor and both ends were filled with silicon carbide. The conditions for the hydroisomerization reaction were: pressure 3 MPa, space velocity 2 h -1 , hydrogen to oil ratio 1000, temperature 310℃.

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

[0036] Table 1 Comparison of catalytic performance results of catalysts

[0037] catalyst Conversion rate / % ≤C15 / wt% Isomerized C16 / wt% Isomer selectivity / % 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] [Remarks] "≤C15 / wt%" in Table 1 indicates the total mass fraction of substances with carbon atoms less than or equal to 15 in the product; "Isomerized C16 / wt%" indicates the total mass fraction of n-hexadecane isomers in the product; "Isomer selectivity / %" indicates the percentage of n-hexadecane isomers selectively generated by the reactants.

[0039] As can be seen from Table 1, the catalyst conversion rates of Comparative Examples 1-3 and Examples 1-3 are all higher than 85%. At a higher conversion rate, the isomerization yield (i.e., "C16 / wt%) of Example 1 and Comparative Example 2 is increased by 42.60% [84.87%-42.27%=42.60%], the cracking rate (i.e., "≤C15 / wt%)" is reduced, and the maximum reduction can be 48.48% [55.74%-7.26%=48.48%], and the isomerization selectivity is increased by 48.98% [92.12%-43.14%=48.98%]. Compared with Comparative Examples 1-3, the N2 atmosphere in the catalyst preparation process of the embodiment and the NH4 + When both exist, the catalyst has a good isomerization yield and selectivity. Comparison between Example 3 and Examples 1 and 2 shows that the catalytic effect of the catalyst will be affected as the calcination temperature increases, which may be caused by metal agglomeration under high temperature. The results of Comparative Example 1 and Comparative Example 2 are similar, indicating that the calcination effects of Ar atmosphere and air atmosphere are basically the same, but Ar atmosphere is slightly better, but both are better than Comparative Example 3; indicating that NH4 + It plays a certain role in the preparation of this bifunctional catalyst, but calcination under N2 atmosphere is more important. Therefore, the preparation of bifunctional catalysts with higher isomerization yield and isomerization selectivity requires the presence of NH4 on the molecular sieve carrier. + The calcination is carried out in a N2 atmosphere, and the calcination temperature is controlled at 100-500°C.

[0040] The above description is only used to introduce the specific implementation methods of the present invention in detail, but the technical solution proposed by the present invention is not limited to the above method. Without departing from the basic principles of the present technology, equivalent modifications and changes made by those skilled in the art to the technology proposed by the present invention should be included in the scope of the claims of the present invention.

Claims

1. A bifunctional catalyst, characterized in that: Its metal atoms are anchored on the molecular sieve containing acidic sites through N atoms.

2. The bifunctional catalyst according to claim 1, characterized in that The metal atoms are anchored on the SiO2 of the molecular sieve through N atoms.

3. The bifunctional catalyst according to claim 1, characterized in that The metal atom is one of Pt, Au, Ru, Rh, Ir or Pd.

4. The method for preparing a bifunctional catalyst according to any one of claims 1 to 3, characterized in that: The steps include: (1) impregnating the ammonia molecular sieve in a metal precursor solution and drying it naturally in air to obtain an impregnated molecular sieve; (2) The impregnated molecular sieve obtained in step (1) is calcined at low temperature in a N2 atmosphere to obtain the bifunctional catalyst.

5. The preparation method according to claim 4, characterized in that If the molecular sieve in step (1) is a sodium-type molecular sieve from which the template agent has not been removed, the template agent needs to be removed first, and then the sodium-type molecular sieve is converted into an ammonia-type molecular sieve, the steps being: (11) calcining the sodium-type molecular sieve from which the template agent has not been removed at 550-600° C. for 3-5 h to remove the template agent; (12) dispersing the sodium-type molecular sieve from which the template agent has been removed in an NH4Cl aqueous solution having a concentration of 0.8-1.2 mol / L, with a liquid-to-solid ratio of 1:(5-15); reflux at 40-90° C. for 2-6 h; and repeating this step at least three times.

6. The preparation method according to claim 4, characterized in that The metal precursor in step (1) is one of Pt, Au, Ru, Rh, Ir or Pd salt solutions, and the metal loading is 0.3-1 wt% of the metal in the molecular sieve.

7. The preparation method according to claim 4, characterized in that The calcination temperature of step (2) is 100-500° C. and the calcination time is 2-6 hours.

8. Use of the bifunctional catalyst according to any one of claims 1 to 3 for catalyzing the hydroisomerization reaction of long-chain normal alkanes.

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