Preparation method and application of Beta molecular sieve catalyst rich in outer surface B acid

Abstract

The invention discloses a preparation method and application of a Beta molecular sieve catalyst rich in outer surface B acid, and solves the technical problem that the existing efficient catalyst is unstable in structure. The preparation method comprises the following steps: synthesizing the H-Beta carrier rich in the outer surface B acid: drying Beta zeolite raw powder without removing a template agent, then carrying out ion exchange for 2 hours by using an NH4Cl aqueous solution, washing a solid with water, drying, repeating the ion exchange process, and roasting the obtained ion exchange solid at 550 DEG C for 4 hours to obtain the H-Beta carrier rich in the outer surface B acid; and preparing the supported bifunctional catalyst: loading the metal Ir onto the H-Beta carrier rich in the B acid on the outer surface by an equivalent impregnation method. The Beta molecular sieve disclosed by the invention is rich in outer surface B acid, is used for a catalytic reaction for synthesizing high-density endothermic aviation fuel by converting polycycloalkane, provides higher reaction active site density and promotes diffusion of macromolecular cycloalkane.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation and application, specifically to a method for preparing a Beta molecular sieve catalyst with rich outer surface area of ​​Brønsted acid and its application. Background Technology

[0002] With the rapid development of hypersonic aircraft, the demand for high-energy-density endothermic aviation fuels is becoming increasingly strong. Coal tar, a byproduct of coal dry distillation, is rich in polycyclic aromatic hydrocarbons. The content of phenanthrene and anthracene in medium- and low-temperature coal tar is about 1 wt%, and its carbon number is similar to that of aviation fuels, making it suitable for the preparation of high-performance fuels and realizing the deep development and utilization of coal tar. For example, the alkyl decahydronaphthalene product (SRO) prepared by selective ring-opening of the full hydrogenation product of phenanthrene in coal tar and the alkyl adamantane product (PSA) prepared by skeleton rearrangement have the characteristics of high density, high calorific value, low freezing point, and high thermal stability. Among them, the coke formed by the cracking of SRO products is greatly reduced, exhibiting a higher heat sink, making it an ideal component of high-density endothermic aerospace fuels with excellent low-temperature performance. At the same time, SRO and PSA have the same carbon number as full hydrogen phenanthrene, reducing resource waste.

[0003] Current research on selective ring-opening and isomerization reactions of polycyclic aromatic hydrocarbons (PAHs) mainly focuses on monocyclic and bicyclic alkanes; therefore, research on alkanes with ≥3 ring numbers is attractive and promising. Selective ring-opening and isomerization reactions of PAHs are typically catalyzed by bifunctional catalysts possessing both metal and acidic sites. Beta molecular sieves exhibit excellent performance in cycloalkane ring-opening reactions due to their large pore size and unique three-dimensional channels. However, their high aluminum content makes them prone to framework aluminum removal during high-temperature calcination to remove the organic template, leading to the collapse of the porous framework and loss of acidity. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing Beta molecular sieve catalysts with rich external surface area and their applications, so as to solve the technical problem of unstable structure of existing high-efficiency catalysts.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a Beta molecular sieve catalyst with a rich outer surface Brønsted acid, comprising the following steps:

[0007] S1. Synthesis of H-Beta carriers rich in external surface Brønsted acid

[0008] The original Beta zeolite powder without template agent removal was dried, and then ion exchanged with NH4Cl aqueous solution for 2 hours. The solid was washed with water, dried, and the ion exchange process was repeated. The resulting ion-exchanged solid was calcined at 550℃ for 4 hours to obtain H-Beta support with rich outer surface Brønsted acid.

[0009] S2. Preparation of supported bifunctional catalysts: Metal Ir is loaded onto a surface-rich Brønsted acid H-Beta support by an equal-volume impregnation method.

[0010] Furthermore, in step S1, the drying temperature of the unremoved template agent Beta zeolite powder is 140°C, and the drying time is 6 hours; the drying temperature after washing the solid with water is 120°C, and the drying time is 1 hour.

[0011] Furthermore, in step S1, the ion exchange is performed at a temperature of 80°C for 2 hours, and the ion exchange process is repeated twice to ensure that most of the Na in the Beta zeolite is preserved. + With NH4 + Ion exchange was performed.

[0012] Furthermore, step S2 specifically includes the following steps:

[0013] S21. Mix 2.0 g of H-Beta support rich in external surface Brønsted acid with 2.51 g of H2IrCl6 aqueous solution, sonicate the mixture at room temperature for 15 minutes, and then age it overnight;

[0014] S22. The aged sample was dried at 80°C for 4 hours, and then heated and reduced in 10% H2 / Ar to obtain the Ir-supported catalyst, which contained 1.5 WT% Ir loading.

[0015] Further, in step S22, at 10% H2 / Ar, the temperature is increased by 1°C / min. -1 The heating rate was reduced at 450℃ for 3.5 hours.

[0016] Secondly, the present invention provides a Beta molecular sieve catalyst with rich outer surface Brønsted acid prepared according to the preparation method described above.

[0017] Thirdly, the present invention provides the application of the aforementioned Beta molecular sieve catalyst with rich outer surface area in the catalytic reaction of polycyclic alkanes to synthesize high-density endothermic aviation fuel.

[0018] Based on the above technical solution, the embodiments of the present invention can produce at least the following technical effects:

[0019] This invention provides a method for preparing a Beta molecular sieve catalyst rich in external surface Brønsted acid. Employing an improved ion exchange strategy and loading Ir metal via an equal-volume impregnation method, a highly crystalline Ir / H-Beta bifunctional catalyst was successfully prepared. The improved ion exchange strategy reduces energy consumption during catalyst preparation. The Beta molecular sieve rich in external surface Brønsted acid, used in the catalytic reaction of polycyclic alkanes to synthesize high-density endothermic aviation fuels, provides a higher density of reactive sites, promoting the diffusion of large cycloalkanes. The synergistic effect of Ir metal and Brønsted acid sites further enhances catalytic performance. Compared to conventional Beta molecular sieves, the Beta molecular sieve catalyst rich in external surface Brønsted acid prepared in this invention significantly improves the yield of high-density endothermic aviation fuels. Compared to the conventional Beta molecular sieve catalyst Ir / NorB, the yields of SRO and PSA products of the Ir / ExB rich external surface acid Beta molecular sieve catalyst are increased by 33.55% and 39.15%, respectively. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is an X-ray crystal diffraction pattern according to an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0023] The objective of this invention is achieved through the following technical solution:

[0024] I. Implementation Examples

[0025] Example 1

[0026] A method for preparing a Beta molecular sieve catalyst with rich external surface area Brønsted acid includes the following steps:

[0027] S1. Synthesis of H-Beta carriers rich in external surface Brønsted acid

[0028] The unremoved template agent Beta zeolite powder was dried at 140°C for 6 hours, then subjected to ion exchange at 80°C with a 1M NH4Cl (50 mL / g solid) aqueous solution for 2 hours. The solid was washed with water and dried at 120°C for 1 hour. This ion exchange process was then repeated twice to ensure that most of the Na in the Beta zeolite was removed. + With NH4 + Ion exchange was performed, and the resulting ion-exchange solid was calcined in air at 550°C for 4 hours to obtain a surface-rich Brønsted acid H-Beta support, denoted as ExB support.

[0029] S2. Preparation of supported bifunctional catalyst: Metallic Ir was loaded onto a surface-rich Brønsted acid H-Beta support using an equal-volume impregnation method. 2.0 g of ExB zeolite was mixed with 2.51 g of H₂IrCl₆ aqueous solution (0.062 M), and the mixture was sonicated at room temperature for 15 min, followed by overnight aging. Subsequently, the sample was dried at 80 °C for 4 h, and then subjected to 1 °C / min H₂ / Ar. -1 The catalyst was reduced at 450°C for 3.5 hours to obtain an Ir-supported catalyst, denoted as Ir / ExB catalyst, which contained 1.5 WT% Ir loading.

[0030] Example 2

[0031] A method for preparing a NorB catalyst includes the following steps:

[0032] The unremoved template agent Beta zeolite powder was calcined at 550°C for 4 hours, then subjected to ion exchange at 80°C with a 1M NH4Cl (50 mL / g solid) aqueous solution for 2 hours. The solid was washed with water and dried at 120°C for 1 hour. This ion exchange process was then repeated twice to ensure that most of the Na in the Beta zeolite was removed. + With NH4 + Ion exchange was performed, and the resulting ion-exchanged solid was calcined in air at 550°C for 4 hours to obtain a common H-Beta catalyst, denoted as NorB catalyst.

[0033] Example 3

[0034] A method for preparing an Ir / NorB catalyst includes the following steps:

[0035] S1. The unremoved template agent Beta zeolite powder was calcined at 550℃ for 4 hours, then subjected to ion exchange at 80℃ with a 1M NH4Cl (50mL / g solid) aqueous solution for 2 hours. The solid was washed with water and dried at 120℃ for 1 hour. This ion exchange process was then repeated twice to ensure that most of the Na in the Beta zeolite was removed. + With NH4 + Ion exchange was performed, and the resulting ion-exchanged solid was calcined in air at 550°C for 4 hours to obtain a common H-Beta catalyst, denoted as NorB catalyst.

[0036] S2. Preparation of supported bifunctional catalyst: Metallic Ir was loaded onto NorB catalyst by an equal-volume impregnation method. NorB catalyst was mixed with H2IrCl6 aqueous solution (0.062M), and the mixture was sonicated at room temperature for 15 minutes, followed by aging overnight. Subsequently, the sample was dried at 80℃ for 4 hours, and then subjected to 1℃ / min H2 / Ar. -1 The heating rate was reduced at 450℃ for 3.5 hours to obtain the Ir-supported catalyst, denoted as the Ir / NorB catalyst.

[0037] II. Experimental Examples

[0038] The catalysts obtained in Examples 1-3 were subjected to selective ring-opening experiments of perhydrophenanthrene. The SRO reaction of perhydrophenanthrene was carried out in a 100 mL stainless steel batch reactor equipped with an electromagnetic stirrer.

[0039] 0.8 g of perhydrophenanthrene, 39.2 g of cyclohexane, and 0.4 g of the catalyst prepared in the previous section were charged into a reactor. The mixture was reacted at 230 °C and 5 MPa hydrogen atmosphere for 10 hours with stirring at 800 rpm. After the reaction, octadecane was added as an internal standard, and the products were qualitatively and quantitatively analyzed offline using GC×GC-FID / MS. The results of the catalyst-catalyzed conversion of perhydrophenanthrene are shown in Table 1 below.

[0040] Table 2 shows the results of evaluating the properties of different acid sites using pyridine-infrared spectroscopy (Py-IR) and di-tert-butylpyridine-infrared spectroscopy (dTBPy-IR). Pyridine (Py) can enter and probe the internal channels and surface acid sites of the zeolite framework, while 2,6-di-tert-butylpyridine (dTBPy), due to its larger kinetic diameter, is usually used to characterize the external surface acid sites of Beta zeolites. Analysis was performed on a VERTEX 70 infrared spectrometer (Brook), using approximately 20 mg of catalyst to prepare a self-supported sheet (13 mm in diameter). The background spectrum of the empty infrared cell was recorded before loading the catalyst. The cell containing the sample sheet was held at 400 °C under vacuum for 1 hour to remove impurities adsorbed from the sample. After pyridine was injected at 50 °C and stabilized for 30 minutes, the values ​​of 1000 to 1000 were measured at 200 °C. Infrared spectra within the wavenumber range. All [spectral data] are determined by recording the corresponding spectra. Acid. The determination of 2,6-di-tert-butylpyridine is similar to that of Py-IR. Because the saturated vapor pressure of dTBPy is lower than that of pyridine, the adsorption operation is carried out at 150 °C.

[0041] Figure 1 The X-ray diffraction patterns of the catalysts prepared in Examples 1-3 are shown. As can be seen from the figures, all samples exhibit clear diffraction peaks at 7.5°, 21.4°, and 22.4°. Comparing the relative crystallinity of the two samples reveals that the Ir / ExB catalyst synthesized using the modified strategy has a 17.5% higher relative crystallinity compared to the Ir / NorB catalyst prepared by the conventional ion exchange method. This indicates that the NH4+ reaction can be carried out while retaining the template agent. + Calcination after ion exchange effectively maintains the zeolite framework. No characteristic diffraction peaks corresponding to the Ir species were observed in the XRD pattern, which may be attributed to the low Ir loading and small particle size of the loaded Ir species, resulting in uniform dispersion of metallic Ir on the support.

[0042] Table 1 Catalysts for the conversion of all-hydrogen phenanthrene

[0043] catalyst Total hydrogen-phenanthrene conversion rate (%) Alkyl decahydronaphthalene yield (%) Alkyl adamantane yield (%) Ir / ExB 97.32 17.32 15.66 Ir / NorB 85.43 12.97 11.25 NorB 29.62 2.90 1.96

[0044] Table 2. Quantitative data of adsorption infrared spectra of pyridine and 2,6-di-tert-butylpyridine.

[0045]

[0046] Note: Pyridine infrared spectroscopy was performed at 200°C using a 1540 cm⁻¹ osmosis. -1 Spectral band calculation Total acid content.

[0047] 2,6-di-tert-butylpyridine infrared spectroscopy was used at 200℃ with a 3360 cm⁻¹. -1 Spectral band calculation The amount of acid on the outer surface of the acid.

[0048] The amount of acid used on the inner surface = the total amount of acid - the amount of acid used on the outer surface.

[0049] Among the prepared Ir-based catalysts, Ir / ExB exhibited higher BAS accessibility, total acidity (7.3% higher), and external surface acidity (24.0% higher) compared to Ir / NorB. This may be due to the migration of aluminum from outside the framework to the external surface and partial coverage during conventional ion exchange processes in the Ir / NorB catalyst. Acid sites. This result confirms that the improved ion exchange strategy can significantly enhance the external properties of Beta zeolite. Acid site density.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a Beta molecular sieve catalyst with rich external surface area β-acid, characterized in that, Includes the following steps: S1. Synthesis of H-Beta carriers rich in external surface Brønsted acid The original Beta zeolite powder without template agent removal was dried, and then ion exchanged with NH4Cl aqueous solution for 2 hours. The solid was washed with water, dried, and the ion exchange process was repeated. The resulting ion-exchanged solid was calcined at 550℃ for 4 hours to obtain H-Beta support with rich outer surface Brønsted acid. S2. Preparation of supported bifunctional catalysts: Metal Ir is loaded onto a surface-rich Brønsted acid H-Beta support by an equal-volume impregnation method.

2. The method for preparing the Beta-rich molecular sieve catalyst with rich external surface area according to claim 1, characterized in that, In step S1, the drying temperature of the Beta zeolite powder without template agent removal is 140°C and the drying time is 6 hours; the drying temperature of the solid after washing with water is 120°C and the drying time is 1 hour.

3. The method for preparing the Beta molecular sieve catalyst with rich external surface area according to claim 1, characterized in that, In step S1, the ion exchange is performed at a temperature of 80°C for 2 hours, and the process is repeated twice to ensure that most of the Na in the Beta zeolite is absorbed. + With NH4 + Ion exchange was performed.

4. The method for preparing the Beta molecular sieve catalyst with rich external surface area according to claim 1, characterized in that, Step S2 specifically includes the following steps: S21. Mix 2.0 g of H-Beta support rich in external surface Brønsted acid with 2.51 g of H2IrCl6 aqueous solution, sonicate the mixture at room temperature for 15 minutes, and then age it overnight; S22. The aged sample was dried at 80°C for 4 hours, and then heated and reduced in 10% H2 / Ar to obtain the Ir-supported catalyst, which contained 1.5 WT% Ir loading.

5. The method for preparing the Beta molecular sieve catalyst with rich external surface area according to claim 4, characterized in that, In step S22, at 10% H2 / Ar and 1℃ / min -1 The heating rate was reduced at 450℃ for 3.5 hours.

6. The Beta molecular sieve catalyst with rich outer surface Brønsted acid prepared by the preparation method according to any one of claims 1-5.

7. The application of the Beta molecular sieve catalyst with rich outer surface area according to claim 6 in the catalytic reaction of polycyclic alkanes to synthesize high-density endothermic aviation fuel.

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