A catalyst, its preparation and use

Abstract

The application provides a catalyst and a preparation method and application thereof, and the catalyst comprises a carrier and an active metal component loaded thereon; the carrier comprises ZSM-5 zeolite and a binder, and the molar ratio of SiO2 / Al2O3 in the ZSM-5 zeolite is 15-50; the amount of strong acid centers on the outer surface of the catalyst is less than or equal to 10 mu mol / g; and the ratio of the saturated adsorption amount of p-xylene to the saturated adsorption amount of o-xylene of the catalyst is 3-20 under the condition of 400 DEG C. The catalyst provided by the application can catalyze the generation of benzene from toluene dealkylation under a medium-temperature condition, and the selectivity of benzene is good and the yield is high.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically, to a catalyst for preparing benzene, a method for preparing the catalyst, and its application. Background Technology

[0002] Benzene is a basic organic raw material with huge consumption and a rich downstream industrial chain. The main downstream products include ethylbenzene (41.0%), phenol (16%), caprolactam (16%), and cyclohexane (12%). In recent years, the production capacity of downstream styrene and phenol-acetone has maintained an expansion trend.

[0003] Currently, the main chemical processes for directly producing benzene include catalytic reforming, ethylene cracking, and coal chemical coking. Among these, catalytic reforming and ethylene cracking processes, in addition to producing benzene, also generate many other alkylbenzenes, resulting in limited benzene yield. Furthermore, toluene disproportionation technology is currently the most widely used technology for benzene production; however, theoretically, toluene disproportionation technology can only produce 1 mole of benzene and 1 mole of xylene from 2 moles of toluene, failing to achieve a significant increase in benzene yield.

[0004] Chinese patent CN101121139A discloses a catalyst for the shape-selective disproportionation reaction of toluene to produce p-xylene. Under hydrogen-exposed conditions at 425°C, the main product is p-xylene, with a selectivity for p-xylene greater than 94% and a molar ratio of benzene to p-xylene less than 1.4. The catalyst targets p-xylene as the product, but has a low selectivity for benzene.

[0005] Chinese patent CN1107077A discloses a rare earth C9-C containing... 10 Aromatic hydrocarbon dealkylation catalyst and its preparation method are disclosed. This catalyst can also be used for the catalytic dealkylation of toluene to produce benzene. However, the reaction temperature of the catalytic dealkylation of toluene via hydrogenation is as high as 590-620℃, which requires the use of a cold-wall reactor, resulting in high investment and operating costs.

[0006] Therefore, there is a need to develop a medium-temperature dealkylation catalyst for the efficient production of benzene from toluene. Summary of the Invention

[0007] To address the above problems, this invention provides a catalyst, its preparation method, and its application. The catalyst can catalyze the dealkylation of toluene to produce benzene under intermediate temperature conditions, exhibiting good selectivity and high yield.

[0008] First, one of the objectives of this invention is to provide a catalyst.

[0009] Specifically, the catalyst comprises a support and an active metal component loaded thereon. The support comprises ZSM-5 zeolite and a binder. The molar ratio of SiO2 / Al2O3 in the ZSM-5 zeolite is 15–50, preferably 20–35. The amount of strong acid centers on the outer surface of the catalyst is less than or equal to 10 μmol / g, preferably less than or equal to 5 μmol / g, more preferably less than or equal to 2 μmol / g, further preferably less than or equal to 1.5 μmol / g, and most preferably less than or equal to 1 μmol / g. Under 400°C conditions, the ratio of the saturated adsorption capacity of p-xylene to the saturated adsorption capacity of o-xylene is 3–20, preferably 5–20, particularly preferably 8–20, and most preferably 10–20.

[0010] Furthermore, the adhesive is selected from one or a combination of silicon dioxide and γ-alumina.

[0011] Furthermore, the active metal component in the catalyst is selected from hydrogenated metal components; wherein the hydrogenated metal is selected from group VIB metals; preferably one or a combination of chromium metal and molybdenum metal.

[0012] Furthermore, based on 100 wt% of the total catalyst weight, the content of ZSM-5 zeolite is 60-95 wt%, preferably 65-90 wt%; the content of binder is 5-30 wt%, preferably 8-20 wt%; and the content of active metal component as metal oxide is 0.1-10 wt%, preferably 0.5-8.0%.

[0013] In addition to the main components described above, the catalyst of this invention may also include other catalyst additives commonly used in the art, such as diatomaceous earth and activated clay. The dosage can be the usual dosage.

[0014] Secondly, another objective of the present invention is to provide a method for preparing the catalyst according to one of the objectives of the present invention.

[0015] Specifically, the method includes the following steps:

[0016] ZSM-5 zeolite is mixed with a binder and shaped, dried at 90℃~150℃, and calcined at 530℃~600℃ to obtain the catalyst body (i.e., catalyst support). An active metal component is supported (loaded) onto the catalyst body to obtain a catalyst precursor. This precursor is then impregnated with a silicon-containing organic compound and calcined in air at 500℃~560℃. After multiple impregnation and calcination cycles, the catalyst is obtained. The calcination time for each of the above steps is preferably 1~6 hours.

[0017] The ZSM-5 zeolite and binder mixture described above can be molded using common methods for preparing catalyst supports, such as extrusion, ball rolling, or oil column molding. Similarly, the method for loading the active metal component onto the catalyst body can also employ conventional methods, such as impregnating the catalyst body with an aqueous solution of the active metal component. Specific impregnation conditions include impregnating the catalyst support with an aqueous solution of the active metal compound using an equal-volume impregnation method, drying at 60–150°C, and then calcining in air at 450–520°C for 1–4 hours to obtain the catalyst precursor.

[0018] Furthermore, the silicon-containing organic compound is selected from one or a combination of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, methyl silicone oil, ethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, phenyl silicone oil, amino silicone oil, and methyl hydroxy silicone oil.

[0019] It is worth mentioning that this invention modifies the catalyst containing ZSM-5 zeolite as a support by selecting specific silicon-containing organic materials, and controls the degree of modification of the catalyst by adjusting the silicon-containing organic materials and their combination, dosage, and number of impregnation and calcination cycles. The modified catalyst has a low content of strong acid centers on its outer surface, and the ratio of the saturated adsorption capacity of p-xylene to o-xylene of the catalyst can be maintained within an appropriate range at a certain temperature, which effectively improves the conversion rate of toluene and the selectivity of benzene.

[0020] Preferably, when modifying the catalyst precursor with silicon-containing organic matter each time, the amount of silicon-containing organic matter used is 5-25 wt% of the catalyst precursor mass, preferably 10-20 wt%. More preferably, the catalyst precursor is modified by impregnation with silicon-containing organic matter 2-4 times, preferably 2-3 times. It is worth mentioning that insufficient or excessive modification of the catalyst precursor will affect the strong acid content on the catalyst surface and the ratio of p-xylene saturated adsorption capacity to o-xylene saturated adsorption capacity. This invention avoids the use of organic solvents such as alkanes during the modification process, and avoids residual organic solvents after impregnation causing dealuminization of the molecular sieve and loss of activity in the catalyst during calcination. The use of silicon-containing organic matter and combinations of silicon-containing organic matter to modify the catalyst effectively improves the catalytic activity of toluene and increases the selectivity for benzene.

[0021] Finally, a third objective of the present invention is to provide the application of the catalyst for one of the objectives of the present invention.

[0022] Specifically, one of the objectives of this invention is to use a catalyst for the catalytic dealkylation of toluene to produce benzene.

[0023] Furthermore, the applicable conditions for the catalyst to catalyze the dealkylation of toluene to prepare benzene are as follows:

[0024] The catalytic temperature is 400–550℃, preferably 420–500℃.

[0025] The catalytic pressure is 1–5 MPa, preferably 1.5–4.0 MPa.

[0026] The molar ratio of hydrogen to toluene is 1 to 4, preferably 1 to 3.

[0027] Toluene weight hourly space velocity (WHSV) is 1–5 h⁻¹ -1 Preferably 1 to 4.5 hours -1 .

[0028] It is worth mentioning that when the catalyst provided by the present invention catalyzes the dealkylation of toluene to prepare benzene, the toluene conversion rate is greater than or equal to 35%, preferably greater than or equal to 40%, and more preferably greater than or equal to 45%.

[0029] More notably, when the catalyst provided by the present invention catalyzes the dealkylation of toluene to prepare benzene, the molar ratio of benzene / xylene in the product is greater than or equal to 1.4, preferably greater than or equal to 2.0, and more preferably greater than or equal to 2.5.

[0030] More notably, the catalyst provided by this invention exhibits a good shape selectivity range when catalyzing the dealkylation of toluene to prepare benzene, with the molar ratio of p-xylene / total xylene in the product ranging from 40% to 90%; preferably from 45% to 85%; and more preferably from 50% to 80%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The catalyst provided by this invention has good catalytic performance, with a high catalytic conversion rate for toluene and high selectivity for benzene. It also has lower reaction temperature requirements, making it more suitable for industrial applications and improving the production efficiency of benzene. Detailed Implementation

[0033] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0034] In the following examples and comparative examples, the raw materials were all commercially available products. Specifically, the hydrogen-form ZSM-5 zeolite was purchased from Sinopec Catalyst Co., Ltd.; the pseudo-boehmite was purchased from Aluminum Corporation of China Shandong Branch; and the silica sol was purchased from Nalco.

[0035] The analysis methods for the following examples and comparative examples are as follows:

[0036] Elemental analysis: Al, Si, and metal elemental analysis were performed using a US PS-6 vacuum inductively coupled plasma atomic emission spectrometer.

[0037] Acidity characterization: A Bruker IFS88 infrared spectrometer was used, with a scanning range of 4000–1300 cm⁻¹. -1 The resolution is set to 4.0cm. -1 Molecular sieve samples at 400℃ and 10 -4 After vacuum dehydration under Torr for 2 hours, the sample was cooled to room temperature and subjected to bulk scanning. After saturation adsorption of dimethylpyridine, the temperature was increased, and desorption was completed at 200℃, 300℃, and 400℃, respectively. Infrared scanning was then performed, and the amount of strong acid centers on the outer surface was calculated based on the spectra.

[0038] Adsorption characterization: A Thermofisher IS50 infrared spectrometer equipped with an MCT detector was used. At 400℃, a nitrogen gas stream containing 1% partial pressure of p-xylene and 1% o-xylene was used as the catalyst. The weight of the saturated adsorption amounts of p-xylene and o-xylene was measured, and their adsorption ratio was calculated.

[0039] Example 1

[0040] 1800g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 22.5), 290g of pseudoboehmite (Al2O3 dry basis content of 70%) and 60g of guar gum powder were mixed, and 1200g of 6% dilute nitric acid solution was added to knead and extrude the mixture. After curing for 24 hours, the mixture was dried at 110℃ for 12 hours and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0041] 50g of ammonium heptamolybdate was dissolved in water, and molybdenum was supported on the catalyst substrate using an equal-volume impregnation method. The substrate was dried at 90°C for 12 hours, and then calcined in air at 500°C for 4 hours to obtain the molybdenum-supported catalyst precursor.

[0042] The molybdenum-supported catalyst precursor was placed in a rotary kiln, and methyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles after the first calcination were then placed in the rotary kiln, and phenyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. Catalyst A was obtained.

[0043] Catalyst A was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0.12 μmol / g, and the p-xylene / o-xylene adsorption capacity was 17.52 μmol / g.

[0044] Catalyst A was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The conditions were controlled at 450°C, 2 MPa, and a toluene weight hourly space velocity of 4 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 2, samples were taken for analysis after 24 hours of stable reaction. The toluene conversion rate was 46.7%, and the benzene / xylene molar ratio in the product was 3.2, while the p-xylene / total xylene ratio was 76.2%.

[0045] Example 2

[0046] 1800g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 22.5), 820g of silica sol (SiO2 dry basis content of 40%), 450g of water and 80g of guar gum powder were mixed, kneaded and extruded into strips, cured for 24 hours, dried at 110℃ for 12 hours, and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0047] 50g of ammonium heptamolybdate was dissolved in water, and molybdenum was supported on the catalyst substrate using an equal-volume impregnation method. The substrate was dried at 90℃ for 12 hours, and then calcined in air at 500℃ for 4 hours to obtain the molybdenum-supported catalyst precursor.

[0048] The molybdenum-supported catalyst precursor was placed in a rotary kiln, and methyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles after the first calcination were then placed in the rotary kiln, and phenyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. Catalyst B was obtained.

[0049] Catalyst B was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0.06 μmol / g, and the p-xylene / o-xylene adsorption capacity was 18.23 μmol / g.

[0050] Catalyst B was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The conditions were controlled at 450°C, 2 MPa, and a toluene weight hourly space velocity of 4 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 2, samples were taken for analysis after 24 hours of stable reaction. The toluene conversion rate was 45.4%, and the benzene / xylene molar ratio in the product was 3.4, while the p-xylene / total xylene ratio was 79.6%.

[0051] Example 3

[0052] 1800g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 28.9), 290g of pseudoboehmite (Al2O3 dry basis content of 70%) and 60g of guar gum powder were mixed, and 1200g of 6% dilute nitric acid solution was added to knead and extrude the mixture. After curing for 24 hours, the mixture was dried at 110℃ for 12 hours and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0053] 50g of ammonium heptamolybdate was dissolved in water, and molybdenum was supported on the catalyst substrate using an equal-volume impregnation method. The substrate was dried at 90℃ for 12 hours, and then calcined in air at 500℃ for 4 hours to obtain the molybdenum-supported catalyst precursor.

[0054] The molybdenum-supported catalyst precursor was placed in a rotary kiln, and methyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles after the first calcination were then placed in the rotary kiln, and phenyl silicone oil (15 wt% of the precursor weight) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. Catalyst C was obtained.

[0055] Catalyst C was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0.09 μmol / g, and the p-xylene / o-xylene adsorption capacity was 13.61 μmol / g.

[0056] Catalyst C was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The temperature was controlled at 470°C, 1.8 MPa, and a toluene weight hourly space velocity (WHSV) of 3.5 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 3, after 24 hours of stable reaction, the toluene conversion rate was 48.9%, and the benzene / xylene molar ratio in the product was 2.9, and the p-xylene / total xylene ratio was 64.4%.

[0057] Example 4

[0058] 1700g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 28.9), 950g of silica sol (SiO2 dry basis content of 40%), 200g of water and 80g of guar gum powder were mixed, kneaded and extruded into strips, cured for 24 hours, dried at 110℃ for 12 hours, and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0059] 64g of chromium anhydride was dissolved in water, and molybdenum was supported on the catalyst substrate using an equal-volume impregnation method. The substrate was dried at 90°C for 12 hours, and then calcined in air at 500°C for 4 hours to obtain the chromium-supported catalyst precursor.

[0060] The chromium-supported catalyst precursor was placed in a rotary kiln, and 12 wt% amino silicone oil (by weight of the precursor) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles from the first calcination step were then placed in the rotary kiln, and 20 wt% methyl silicone oil (by weight of the precursor) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. Catalyst D was obtained.

[0061] Catalyst D was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0.08 μmol / g, and the p-xylene / o-xylene adsorption capacity was 14.89 μg.

[0062] Catalyst D was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The temperature was controlled at 470°C, 1.8 MPa, and a toluene weight hourly space velocity (WHSV) of 3.5 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 3, after 24 hours of stable reaction, the toluene conversion rate was 47.5%, and the product had a benzene / xylene molar ratio of 3.1 and a p-xylene / total xylene ratio of 70.2%.

[0063] Example 5

[0064] In this embodiment, the chromium-supported catalyst precursor used is prepared in the same way as the chromium-supported catalyst precursor provided in Example 4.

[0065] The chromium-supported catalyst precursor was placed in a rotary kiln, and 20 wt% tetraethyl orthosilicate (tetraethyl orthosilicate) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles from the first calcination step were then placed in the rotary kiln, and 15 wt% amino silicone oil (amino silicone oil) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. The catalyst particles from the second calcination step were then placed in the rotary kiln, and 7 wt% methyl silicone oil (methyl silicone oil) was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the third calcination process, yielding catalyst E.

[0066] Catalyst E was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0.02 μmol / g, and the p-xylene / o-xylene adsorption capacity was 19.85.

[0067] Catalyst D was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The temperature was controlled at 470°C, 1.8 MPa, and a toluene weight hourly space velocity (WHSV) of 3.5 h⁻¹. -1Under reaction conditions with a hydrogen / toluene molar ratio of 3, after 24 hours of stable reaction, the toluene conversion rate was 40.6%, and the benzene / xylene molar ratio in the product was 2.7, while the p-xylene / total xylene ratio was 84.5%.

[0068] Comparative Example 1

[0069] 1800g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 22.5), 290g of pseudoboehmite (Al2O3 dry basis content of 70%) and 60g of guar gum powder were mixed, and 1200g of 6% dilute nitric acid solution was added to knead and extrude the mixture. After curing for 24 hours, the mixture was dried at 110℃ for 12 hours and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0070] 50g of ammonium heptamolybdate was dissolved in water, and molybdenum was supported on the catalyst body using an equal-volume impregnation method. The catalyst was dried at 90℃ for 12 hours and then calcined in air at 500℃ for 4 hours to obtain molybdenum-supported catalyst F.

[0071] Catalyst F was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 17.25 μmol / g, and the p-xylene / o-xylene adsorption capacity was 1.7 μmol / g.

[0072] Catalyst F was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The conditions were controlled at 450°C, 2 MPa, and a toluene weight hourly space velocity of 4 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 2, samples were taken for analysis after 24 hours of stable reaction. The toluene conversion rate was 52.6%, and the molar ratio of benzene / xylene in the product was 1.3, and the molar ratio of p-xylene to total xylene was 23.9%.

[0073] Comparative Example 2

[0074] 1800g of hydrogen-type ZSM-5 (SiO2 / Al2O3 molar ratio of 22.5), 820g of silica sol (SiO2 dry basis content of 40%), 450g of water and 80g of guar gum powder were mixed, kneaded and extruded into strips, cured for 24 hours, dried at 110℃ for 12 hours, and then calcined in air at 550℃ for 4 hours to obtain the catalyst body.

[0075] 50g of ammonium heptamolybdate was dissolved in water, and molybdenum was supported on the catalyst substrate using an equal-volume impregnation method. The substrate was dried at 90℃ for 12 hours, and then calcined in air at 500℃ for 4 hours to obtain the molybdenum-supported catalyst precursor.

[0076] The molybdenum-supported catalyst precursor was placed in a rotary kiln, and 35 wt% (by weight) of methyl silicone oil was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the first calcination process. The catalyst particles calcined in the first step were then placed in the rotary kiln, and 30 wt% (by weight) of phenyl silicone oil was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the second calcination process. The catalyst particles calcined in the second step were then placed in the rotary kiln, and 27 wt% (by weight) of phenyl silicone oil was added. The kiln was rotated until uniform diffusion was achieved, and the mixture was kept at 530°C in air for 3 hours to complete the third calcination process. Catalyst G was obtained.

[0077] Catalyst G was used, and its acid content and p-xylene / o-xylene adsorption capacity were characterized according to the aforementioned characterization methods. The amount of strong acid centers on its outer surface was 0, and the p-xylene / o-xylene adsorption capacity was 26.5.

[0078] Catalyst G was loaded into the reactor and pretreated for 6 hours at 450°C in a hydrogen atmosphere. The conditions were controlled at 450°C, 2 MPa, and a toluene weight hourly space velocity of 4 h⁻¹. -1 Under reaction conditions with a hydrogen / toluene molar ratio of 2, samples were taken for analysis after 24 hours of stable reaction. The toluene conversion rate was 36.5%, and the molar ratio of benzene / xylene in the product was 2.4, while the ratio of p-xylene to total xylene was 94.5%.

[0079] The catalysts provided in Examples 1-5 of this invention exhibit good toluene conversion and excellent benzene selectivity, with a benzene / xylene molar ratio greater than 2.5 in all products, indicating that toluene is primarily converted to benzene. In contrast, the catalyst precursor in Comparative Example 1 was unmodified, resulting in a high content of strong acid centers on its external surface and low adsorption of p-xylene / o-xylene, leading to low selectivity for benzene. Furthermore, the catalyst precursor in Comparative Example 2, after excessive modification, had almost zero strong acid centers on its external surface, resulting in excessively high adsorption of p-xylene / o-xylene and consequently low toluene conversion efficiency. Therefore, this invention, by appropriately modifying the catalyst precursor with silicon-containing organic materials, can effectively improve the toluene conversion and benzene selectivity.

[0080] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalyst comprising a support and an active metal component loaded thereon; the support comprising ZSM-5 zeolite and a binder, wherein the molar ratio of SiO2 / Al2O3 in the ZSM-5 zeolite is 15–50; the amount of strong acid centers on the outer surface of the catalyst is less than or equal to 10 μmol / g; and at 400 °C, the ratio of the saturated adsorption capacity of p-xylene to the saturated adsorption capacity of o-xylene in the catalyst is 3–20.

2. The catalyst according to claim 1, characterized in that, At 400°C, the ratio of the saturated adsorption capacity of p-xylene to the saturated adsorption capacity of the catalyst is 5–20; preferably 8–20; and / or, The amount of strong acid centers on the outer surface of the catalyst is less than or equal to 5 μmol / g; preferably less than or equal to 2 μmol / g.

3. The catalyst according to claim 1, characterized in that, The molar ratio of SiO2 / Al2O3 in the ZSM-5 zeolite is 20–35; and / or, The adhesive is selected from one or a combination of silicon dioxide and γ-alumina; and / or, The active metal component is a hydrogenated metal component; preferably, the hydrogenated metal is selected from at least one of group VIB metals; more preferably, the hydrogenated metal is selected from one or a combination of chromium metal and molybdenum metal.

4. The catalyst according to any one of claims 1 to 3, characterized in that, Based on a total catalyst weight of 100 wt%, The ZSM-5 zeolite content is 60–95 wt%, preferably 65–90 wt%; and / or, The adhesive content is 5-30 wt%, preferably 8-20 wt%; and / or, The active metal component, calculated as metal oxide, has a content of 0.1 to 10 wt, preferably 0.5 to 8.0%.

5. A method for preparing the catalyst according to any one of claims 1 to 4, comprising the following steps: ZSM-5 zeolite was mixed with a binder and shaped, dried at 90℃~150℃, and calcined at 530℃~600℃ to obtain the catalyst body; an active metal component was supported on the catalyst body to obtain a catalyst precursor; then impregnated with a silicon-containing organic material, and then calcined at 500℃~560℃ in an air atmosphere. After multiple impregnation and calcination, the catalyst was obtained.

6. The method for preparing the catalyst according to claim 5, characterized in that, The silicon-containing organic compound is selected from one or a combination of methyl orthosilicate, ethyl orthosilicate, methyl silicone oil, ethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, phenyl silicone oil, amino silicone oil, and methyl hydroxy silicone oil; and / or, The amount of the silicon-containing organic material used in a single impregnation is 5-25 wt% of the mass of the catalyst precursor, preferably 10-20 wt%; and / or, The silicon-containing organic material is impregnated 2 to 4 times, preferably 2 to 3 times.

7. The application of the catalyst according to any one of claims 1 to 4, for catalytic dealkylation of toluene to prepare benzene.

8. The application of the catalyst according to claim 7, characterized in that, The reaction conditions for the catalytic dealkylation of toluene to prepare benzene are as follows: The reaction temperature is 400–550°C; preferably 420–500°C; and / or, The reaction pressure is 1–5 MPa; preferably 1.5–4.0 MPa; and / or, The molar ratio of hydrogen to toluene is 1–4; preferably 1–3; and / or, The weight hourly space velocity (WHSV) of toluene is 1–5 h⁻¹. -1 Preferably 1 to 4.5 hours -1 .

9. The application of the catalyst according to claim 7, characterized in that, The toluene conversion rate is greater than or equal to 35%; preferably greater than or equal to 40%; more preferably greater than or equal to 45%.

10. The application of the catalyst according to claim 7, characterized in that, The molar ratio of benzene to xylene in the product is greater than or equal to 1.4; preferably greater than or equal to 2.0; more preferably greater than or equal to 2.

5.

11. The application of the catalyst according to claim 7, characterized in that, The molar ratio of p-xylene to total xylene in the product ranges from 40% to 90%; preferably from 45% to 85%; more preferably from 50% to 80%.